**Emergy-Based Regional Socio-Economic Metabolism Analysis: An Application of Data Envelopment Analysis and Decomposition Analysis**

#### **Zilong Zhang, Xingpeng Chen and Peter Heck**

**Abstract:** Integrated analysis on socio-economic metabolism could provide a basis for understanding and optimizing regional sustainability. The paper conducted socio-economic metabolism analysis by means of the emergy accounting method coupled with data envelopment analysis and decomposition analysis techniques to assess the sustainability of Qingyang city and its eight sub-region system, as well as to identify the major driving factors of performance change during 2000–2007, to serve as the basis for future policy scenarios. The results indicate that Qingyang greatly depended on non-renewable emergy flows and feedback (purchased) emergy flows, except the two sub-regions, named Huanxian and Huachi, which highly depended on renewable emergy flow. Zhenyuan, Huanxian and Qingcheng were identified as being relatively emergy efficient, and the other five sub-regions have potential to reduce natural resource inputs and waste output to achieve the goal of efficiency. The results of decomposition analysis show that the economic growth, as well as the increased emergy yield ratio and population not accompanied by a sufficient increase of resource utilization efficiency are the main drivers of the unsustainable economic model in Qingyang and call for polices to promote the efficiency of resource utilization and to optimize natural resource use.

Reprinted from *Sustainability*. Cite as: Zhang, Z.; Chen, X.; Heck, P. Emergy-Based Regional Socio-Economic Metabolism Analysis: An Application of Data Envelopment Analysis and Decomposition Analysis. *Sustainability* **2014**, *6*, 8618-8638.

#### **1. Introduction**

The process of economic development driven by industrialization can be seen as a transition from an agrarian to an industrial socio-metabolic regime [1]. The transition makes human society experience spectacular wealth accumulation, but it also causes large-scale ecological and social transformations [2]. Thus, the social-environmental relationship can be characterized as socio-economic metabolism [3,4]. The concept of socio-economic metabolism is applied to investigate the scale and composition of the socio-economic metabolic system [1,5–7] and to discuss its relationship with both economic growth [8], urbanization [5,9], industrialization [10,11] and environmental impacts [12]. The socio-economic metabolism perspective provides a useful framework for studying the interaction between human and natural systems [13] through quantifying the regional input-output amount and the structures of material and energy flows, the value of local resources and sustainability performance.

Nowadays, the term socio-economic metabolism has been widely applied in different fields, and related studies have been conducted at different levels, such as the household [14,15], industrial [10,16], urban [17–20] and regional level [21]. As for the regional level, related studies refer to quantifying material and the energy metabolic amount and the efficiency of different countries and regions, thus comparing the sustainability performance for different regional systems [22] by applying material flow analysis (MFA) [23], emergy analysis [20] and other integrated approaches (e.g., the multi-scale integrated analysis of socio-economic metabolism approach, MuSIASEM [21]).

As an instrument for aggregating various material flows into a few strategy indicators, MFA is applied to measure the weights of material inflows and outflows of socio-economic metabolism and can be broken into substance flow analyses (SFA), which deal with chemically-defined substances (such as phosphorus, copper, sulfur, *etc.*) in practical research [3]. However, the MFA-based socio-economic metabolism research has placed emphasis on the weight (quantities) of resource flows and ignored the varied qualities of material flows. Besides, the MFA-based metabolism studies provide strong and consistent evidence of the increasing consumption of resources in most economies, even in those economies that have focused their policies on dematerializing economic growth [24]. Emergy analysis, developed by Odum [25], is a technique of quantitative analysis that determines the values of resources, services and commodities in a common unit of solar energy, which allows all resources to be compared on a fair basis [26]. Therefore, emergy-based metabolism analysis, rather than the mass content of differing resources in the MFA, can overcome the limits of MFA that we mentioned above [3]. Moreover, emergy analysis provides an ecocentric bridge that connects economic and ecological systems and is a more holistic alternative to many existing methods for environmentally conscious decision making [27]. However, the emergy analysis has the problems of quantification, uncertainty and sensitivity, which also exist in all methods (such as MAF, LCA, exergy, *etc.*) that focus on a holistic view of industrial activity. In order to reduce the bias induced by the problems mentioned above, the paper integrated the emergy into data envelopment analysis, which is a nonparametric production frontier analysis approach and has been widely applied in micro- and macro-economic studies [24], to revise the results of emergy analysis and to provide decision makers with useful information regarding how to improve ecological efficiency. The paper also investigated the underlying determinant effects that influence the change of total emergy use by combining the methods of emergy and decomposition analysis. The present paper, taking Qiyang city and its eight sub-regions (Gansu Province, northwestern China) as the study case, investigates the features and findings of socio-economic metabolism.

#### **2. Research Area**

Qingyang city is located in the east part of Gansu province in northwestern China and ranges in latitude from 35°15ƍN to 37°10ƍN and in longitude from 106°20ƍE to 108°45ƍE, with a total administrative area of 27,119 km2 , consisting of one district, including Xifeng (XF), and seven counties, including Qingcheng (QC), Ningxian (NX), Zhengning (ZN), Huanxian (HX), Heshui (HS), Huachi (HC) and Zhenyuan (ZY) (Figure 1). Qingyang is one of the cradles of traditional Chinese farming culture and also is rich in crude oil and raw coal, with 3.25 billion tons of crude oil, 12 billion tons of raw coal and 1358.8 billion cubic-meters of coal-bed methane.

**Figure 1.** Qingyang city in China and the eight sub-regions.

In 2007, the GDP of Qingyang was \$264 million, and GDP per capita was \$1005, which was much lower than the average level of GDP per capita in China (\$2640). Qingyang is in the fast transition period from traditional agriculture to rapid industrialization [28], particularly after the discovery of abundant energy resources and the implementation of China's Western Development Program in 2000. With the large amount of exploitation and processing of energy resources, environmental pressure has increased rapidly. Thus, in the transition period, searching for a sustainable development model is a major task faced by local officials.

Specifically, the eight sub-regions in Qingyang all have their own distinctive features in the aspects of geography, environment and economy. For instance, XF is the political center of Qingyang region and is largely dependent on the inputs of energy, materials and products from outside. QC, with a relatively longer history of oil exploitation, is the main oilfield. NX and ZN, in the southeastern part of Qingyang, have certain similar features, such as rich coal resources and relatively developed agriculture. HX, in northern Qingyang, has a very high rate (99.8%) of soil erosion and water loss, as well as an underdeveloped economy. HS and HC have a relatively sound ecological environment and mid-level economic development. Economic development in ZY largely depends on the processing of agriculture products, especially apricot. Thus, to achieve sustainable development of Qingyang as a whole, differentiated policies regarding sustainable development, targeting each sub-region are crucial, as the each sub-region has special characteristics.

#### **3. Research Methods**

#### *3.1. Emergy and Emergy Based Indicators*

Emergy analysis is an environmental accounting method, which considers the energy system for the thermodynamics of an open system, aims to evaluate the contributory value of different material flows to the ecological economic system [29,30]. Emergy is measured in solar embodied joules, abbreviated sej. Emergy analysis characterizes all materials, energy, capital and services in equivalents of solar energy, *i.e.*, how much emergy would be required to do a particular task if the

solar radiation were the only input [27,31–33]. Thus, the key part of emergy analysis is to transform the various materials and capital in human activities to a unified unit, sej [25], in which the key parameter is the emergy transformity (Trf.). The transformity of solar radiation is assumed equal to one by definition (1.0 sej/J), while the transformities of all of the other materials, energy and services are calculated based on their convergence patterns through the biosphere hierarchy [34]. Regarding emergy flows, renewable, nonrenewable and feedback emergy are three streams at the input side of the system. Additionally, output product emergy and waste emergy are two steams at the output side (Figure 2). The major steps of emergy analysis include identifying the system boundary, collecting eco-economic data, establishing emergy flow accounting, calculating a set of indices and ratios and using them to conduct the socio-economic metabolism analysis. Theoretically, all of the material, information and capital flows through the target studied region should be diagramed and then calculated. However, that is usually difficult, due to the lack of databases, especially for a city located in an undeveloped area in China. Therefore, the paper carried out a black box study without probing into the socio-economic metabolic structure thoroughly.

**Figure 2.** Emergy flows of a regional system.

Based on standard transformation, the emergy flow accounting was based on Qingyang and 8 sub-regions' raw data, which were from the QY Statistic Year Book (2001–2008), the XF, HX, HC, HS, ZN, ZY, NX, QC Statistic Year Books (2001–2008) [35–42] and investigations conducted on two planning programs: Qingyang Eco-City Development Program (investigation time period: 11–19 August 2008) and Qingyang Circular Economy Development Program (investigation time period: 20–29 April 2009); the corresponding indicators are given in Table 1. Additionally, the emergy transformity (Trf.) we used in this work relies on the transformities calculated by Odum and co-workers [33,43] (The averaged transformities of natural resources, products and processes used in this paper may lead to estimation bias to some extent, which was also shared by other approaches and is inevitable).

**Table 1.** The geographic and economic features of eight sub-regions and the whole (data of 2007).

Notes: The abbreviations QY, XF, QC, ZN, NX, ZY, HX, HS and HC in the table represent Qingyang city, Xifeng district, Qingcheng, Zhengning, Ningxian, Zhenyuan, Huanxian, Heshui and Huachi, respectively.

## *3.2. Data Envelopment Analysis*

Data envelopment analysis (DEA), which is a non-parametric frontier approach to evaluate the relative efficiency of a set of homogeneous decision-making units (DMUs) featuring multiple inputs and outputs, has recently been widely applied to analyze energy, environmental and ecological efficiency [44,45]. In recent empirical studies in the macroeconomic literature, GDP is commonly used as the output, and capital, labor and natural resources (water, energy, land and other mineral resources) are used as the input. The DEA efficiency model considering pollutants can be divided into three types. The first model takes pollutants as investment costs and, thus, is used to as the input. The second model is the data transfer function method, which considers the pollutants as ordinary output after transferring the-smaller-the-better undesirable output into the-bigger-the-better desirable output. The third model is the distance function method first proposed by Färe *et al.* (1994) [46] and then further extended by Chung (1997) [47], Tone (2001) [48] and other scholars. Because it can redeem the defect of the first two methods, such as no reflection on the real production process, strong convexity constraints, *etc.* [45], the distance function method has been widely applied to analyze ecological (or environmental) efficiency and environmental performance.

To comprehensively capture the physical flow (including inputs and outputs) of social and economic activities and to measure the ecological efficiency precisely, the inputs should include all kinds of inputs coming from the natural system and waste discharged into the environment. Usually, these inputs and outputs are measured in different measurement units. The emergy-based accounting system can solve the unit problem. In this paper, we combined the emergy-based accounting system and the undesirable output DEA model (slack-based undesirable output model) proposed by Tone (2001) to evaluate the ecological efficiency (EE) of the socio-economic metabolic system in Qingyang. A more detailed explanation of the model and its underlying mathematical procedures can be found in [48,49].

The paper uses the emergy content of natural resource inputs, production and waste emissions instead of mass content to construct aggregate input and output factors. The input factors include the nonrenewable input emergy (N) and feedback emergy (F), and the output factors include both the output product emergy (P), which is taken as a desirable output indicator, and waste emergy (W), which is taken as an undesirable output indicator. The score of ecological efficiency obtained by the slack-based undesirable output model is bounded by zero and one. If the score is upper-bounded to one, this means that it represents the best performance. Moreover, the lower the score, the worse the level of ecological efficiency [24,50].

#### *3.3. Decomposition Analysis*

Decomposition analysis is widely applied to investigate the underlying determinant factors that influence the change of energy consumption, CO2 emissions, material usage, *etc.* [51–54]. Decomposition analysis covers two kinds of specific methods. The first one is structural decomposition analysis (SDA), which handles the input-output model. The second one is index decomposition analysis (IDA), which uses sector- or regional- level data. Because of requiring less data, the IDA has been applied to environmental and resource issues more extensively than SDA [55]. The decomposition analysis carried out in this paper is IDA based on the advanced sustainability analysis (ASA) approach, which was developed by the Finland Futures Research Center [56–58].

Since the decomposition analysis is capable of assessing the efficiency in the use of a given input in affecting a final result, it can be considered a fundamental tool to ease the monitoring and evaluation of the sustainability of economies and productive sectors/processes [59]. The knowledge of the major factors that affect a process' performance is essential for the design of new policy instruments and the evaluation of the implemented measures over a desired pattern of sustainability [60,61]. Moreover, decomposition analysis is necessarily dealing with complex indicators to avoid the loss of information [62,63].

ASA is designed to investigate the relationship between changes in environmental, economic and social variables that are measured by any preferred indicator or index. An equation describing the relationship between the factors (e.g., intensive factor V/X1 and extensive factor X1) contributing to variable V can be expressed in its simplest form as follows:

$$V = \frac{V}{X\_1} \times X\_1 \tag{1}$$

The procedure can be applied to multiple actors, as well. The two-factor decomposition presented above can be continued by taking a result from the first decomposition as a starting point for further decompositions, and the new results can then be decomposed again. The equation that identifies the contributing variables can be formulated in a general form as follows:

$$V = \frac{V}{X\_2} \times \frac{X\_2}{X\_3} \times \dots \times \frac{X\_{n-1}}{X\_n} \times X\_n \tag{2}$$

A more detailed explanation of the ASA approach and its underlying mathematical procedures can be found in [64] and the DECOIN (2008) [65] and SMILE (2011) [66] websites.

#### **4. Results**

#### *4.1. Overview of the Emergy Results of Qingyang and the Eight Sub-Regions*

To characterize the metabolic structure and efficiency of the socio-economic system in Qingyang and its eight sub-regions, we calculated the emergy indices (Table 2). We found that the socio-economic system in Qingyang depended heavily on nonrenewable emergy, which occupied 61.13% of the total emergy input in 2007. Renewable emergy was the second largest input (23.54), followed by the feedback emergy input (15.32). The high value of the environment loading ratio (ELR = 3.25) and the low value of the emergy investment ratio (EIR = 0.18) refer to economic growth being greatly devoted to local non-renewable resources, which leads to high environmental pressure. An ESI (2.51) between one and ten means that Qingyang developed a "producer"-oriented economy that highly relied on non-renewable resources (Table 3).

XF, as the regional political center, mostly relied on feedback emergy, where the social-economic activity is supported by import emergy (96.76%). ZY also mainly relied on imported emergy (feedback emergy/total emergy input (F/U) is 54.99%). QC and ZN greatly depended on local non-renewable resources (U/nonrenewable input emergy (N) in the two sub-regions is greater than 50%). However, for HX and HC, the economic development highly relied on local renewable resources. The economic activities in NX and HS mainly depended on local renewable and non-renewable resources, respectively, but the dependence degree is less than HX and QC (Table 3).

The net emergy yield ratio (NEYR) is the ratio of the output emergy of the economic system to the feedback emergy from outside the region, which reflects the capability of local resources to support economic activities. Meanwhile, it shows the competitiveness of the economic system in supplying primary energy and resources [33]. The higher NEYR is, the higher the contribution of the regional economic system to the other regions is. In general, a value of NEYR of QY higher than five indicates that QY is an energy output region [67]. The NEYR of QC is the highest among the eight sub-regions, indicating the importance of QC in providing energy to the Qingyang economy. Additionally, this high value is due to the exploitation of non-renewable resources in QC. Conversely, the NEYR of XF is the lowest, which is caused by having the highest feedback emergy, as well as a higher EIR, emergy money ratio (EMR), emergy per capita (EPC) and emergy density (ED) compared to the average of QY, reflecting that XF has the strongest economic intensity and highest residential living conditions and ranks as the highest level of the economic system in QY city (Table 3).

**Table 3.** The emergy analysis results of socio-economic metabolism in Qiyang (2007). sej, solar embodied joules.

Notes: The abbreviations QY, XF, QC, ZN, NX, ZY, HX, HS and HC in the table represent Qingyang city, Xifeng district, Qingcheng, Zhengning, Ningxian, Zhenyuan, Huanxian, Heshui and Huachi, respectively.

The environment loading ratio (ELR) is the ratio of the sum of feedback and nonrenewable emergy to renewable emergy, which reflects the pressure of the social-economic process on the local ecosystem. The ELR of XF is highest (ELR = 35.68), reflecting high environmental pressure as a result of social economic activity. The ELR of QC (5.2) is the second highest and above the Qingyang average, due to its larger consumption of non-renewable resources (such as crude oil exploitation). On the other hand, the ELRs of the other five sub-regions are below Qingyang average. These regions can be considered as the areas with lower environmental pressure in terms of resources extraction and use (Table 3).

The emergy investment ratio (EIR) is the ratio of feedback (purchased) inputs to local resources (F/N + renewable input emergy (R)). The EIRs of XF and ZY are greater than one, indicating that the two regions relied more on purchased inputs than locally-available resources. However, the EIRs of the other six regions are less than one, indicating the need for local resources in these regions (Table 3).

The emergy sustainability index (ESI) is the ratio of NEYR to ELR. When ESI < 1, it is a consumption system; when 1 < ESI < 10, it is an energetic system with the potential of further development; and when ESI > 10, the system is economically lagging behind [72]. In general, the ESI of QY is between one and 10, which reflects that QY is an energetic regional system and has the potential for future development. Regarding the eight sub-regions, the ESI of XF is less than one, which reveals that XF is a consumption system. The ESIs of HX and HC are higher than 10, which shows that both regions are economically behind and economic development needs to be accelerated and strengthened. The ESIs of NX, QC, ZY, HS and ZN are between one and 10, where the economic development is energetic and robust (Table 3).

#### *4.2. Emergy-Based Data Envelopment Analysis*

Based on the emergy accounting database, the paper applied the undesirable-output DEA model to estimate the production frontier and calculate the ecological efficiency (EE) score of eight sub-regions in Qingyang using the input-oriented GRS (generalized returns-to-scale) framework. It is arguable to assume that there exists a production frontier for the eight sub-regions, because of the significant differences in the characteristics of the economic structures of those sub-regions.

The average EE score of eight sub-regions increased from 0.669 in the year 2000 to 0.766 in 2002, then decreased to 0.701 in 2006 and, finally, achieved an EE score of 0.728 in 2007. The EE scores of ZY and HX equal one during 2000–2007, which means that the two regions were identified as being relatively efficient. QC could be identified as an efficient region after 2002. The EE scores of NX, HS and HC decreased from 1.000, 0.309 and 0.805 to 0.802, 0.252 and 0.766. As for ZN, the EE score increased from 0.697 to 0.805. The emergy efficiency of XF was lowest among the eight sub-regions during the whole period (the EE score was below 0.2 in most years). In 2007, only three regions (QC, ZN and HX) were identified as efficient regions (Table 4).

#### *4.3. Decomposition Analysis of Total Emergy Use*

In order to understand the main drivers of the changes of total emergy flow (U), a decomposition equation was developed according to Equations (1) and (2). The time change of total emergy use (U) during 2000–2007 was decomposed as follows:

$$U = \frac{U}{F} \times \frac{F}{R+N} \times \frac{R+N}{GDP} \times \frac{GDP}{POP} \times POP \tag{l}$$

where F indicates feedback emergy flow, R is the value of all locally-available renewable emergy flows, N refers to the locally-available nonrenewable emergy flow, GDP is the value of gross domestic production and POP is the amount of population. According to Equation (3), changes of U are affected by five factors: U/F is the emergy yield ratio (EYR), which reflects the ability of a certain system to exploit available new emergy resources by investing local resources (local *versus* imported) [73]; F/(R + N) is the emergy investment ratio (EIR); (R + N)/GDP is the natural resource use per capital, which refers to the resource utilization rate; GDP/POP refers to the economic growth level; and POP refers to the population scale. The decomposition results of Qingyang and eight sub-regions are shown in Figures 3–11 with reference to the year 2000.

**Table 4.** Summary of emergy efficiency evaluation.

Notes: The abbreviations QY, XF, QC, ZN, NX, ZY, HX, HS and HC in the table represent Qingyang city, Xifeng district, Qingcheng, Zhengning, Ningxian, Zhenyuan, Huanxian, Heshui and Huachi respectively.

For Qingyang as a whole, the decomposition analysis (Figure 3) indicates that the factors, U/F, GDP/POP and POP, have increased the total emergy use and economic growth; GDP/POP was the main diver of the increasing emergy use. The factors (R + N)/GDP and F/(R + N) have decreased the emergy use. The negative contribution of the resource utilization rate, (R + N)/GDP, suggests policies to promote the efficiency of resource utilization.

**Figure 3.** Advanced sustainability analysis (ASA) decomposition of the total emergy use (U) in Qingyang during 2000–2007; the contributions of five factors to the percentage of the 2000 total emergy use (U) level. POP, population.

**Figure 4.** ASA decomposition of the total emergy use (U) in Xifeng during 2000–2007; the contributions of five factors to the percentage of the 2000 total emergy use (U) level.

In Xifeng (Figure 4), the considerable increase in the total emergy use can be seen in the decomposition results as an increase in the GDP/POP, F/(R + N) and POP components, and the economic growth was the main driving force. Since EIR = F/(R + N) indicates the efficiency of external investment in exploiting a unit of local resource, the EIR's contribution to the growth of emergy use means that the social economic system of Xifeng is fragile due to the fact that the local resource basis (R + N) cannot easily be increased and the non-renewable input emergy (N) is mainly contributing to the climate change. The factor (R + N)/GDP contributed to the decrease of emergy use considerably. The U/F factor slightly decreased in the investigated period.

In Qingcheng (Figure 5), the factors GDP/POP and U/F were the main contributors to the increase in total emergy use; while the factor F/(R + N) has decreased the emergy use. However, the factor (R + N)/GDP, unlike Qingyang and Xifeng, was fluctuating to a large extent, while finally decreasing.

**Figure 5.** ASA decomposition of the total emergy use (U) in Qingcheng during 2000– 2007, contributions of five factors to the percentage of the 2000 total emergy use (U) level.

For Zhengning (Figure 6), the decomposition result indicates that GDP/POP was the main driver of the emergy use increase, but (R + N)/GDP contributed to the decrease in emergy use. The U/F factor slightly decreased, except in the second period. Inversely, the F/(R + N) factor slightly increased, except in the third period.

In Ningxian (Figure 7), the factors F/(R + N) and GDP/POP were the main driving forces of the increase in total emergy use, and the contribution of F/(R + N) was more stable. The considerable and steady contribution of F/(R + N) to the U growth refers to the fact that the social economic system of Ningxian is more fragile than Xifeng, and an appropriate policy would be to optimize natural resource use (e.g., convert solar radiation into photovoltaic electricity to replace fossil fuels, recycling waste material resources to replace new raw imports, recycling water after appropriate treatment, *etc.*). The EIR (U/F) and resource utilization rate ((R + N)/GDP) have been the major factors decreasing emergy use. The effect of population scale is smaller than other factors.

**Figure 6.** ASA decomposition of the total emergy use (U) in Zhengning during 2000– 2007; the contributions of five factors to the percentage of the 2000 total emergy use (U) level.

In Zhenyuan (Figure 8), the fast economic growth (GDP/POP) was the most important factor contributing to the emergy use increase, due to its energetic economic development (Table 3). The factor F/(R + N) also has increased emergy use, which suggests policies to optimize natural resource use, but the effect is less than the economic growth. The factor (R + N)/GDP has decreased the emergy use, except in the third period, and the U/F also had negative effects on the emergy use increase, except in the first period.

**Figure 7.** ASA decomposition of the total emergy use (U) in Ningxian during 2000– 2007; the contributions of five factors to the percentage of the 2000 total emergy use (U) level.

**Figure 8.** ASA decomposition of the total emergy use (U) in Zhenyuan during 2000– 2007; contributions of five factors to the percentage of the 2000 total emergy use (U) level.

The economic growth in Huanxian (Figure 9) has increased the emergy use. However, the improvement of resource utilization efficiency has decreased the emergy use. The behavior of U/F and F/(R + N) was a bit more complex. For the factor U/F, from 2000 to 2003, the emergy yield ratio (EYR) increased, and after 2003, the parameter shows instead a decline, except in the last year. The factor F/(R + N) shows an inverse behavior.

**Figure 9.** ASA decomposition of the total emergy use (U) in Huanxian during 2000– 2007; contributions of five factors to the percentage of the 2000 total emergy use (U) level.

In Heshui (Figure 10), economic growth was the main driving factor of the emergy use increase, and the increase of F/(R + N) contributed to the increase of the total emergy use, although to a lesser extent than GDP/POP. However, the factor (R + N)/GDP showed a steady decline (less natural emergy input per unit of GDP), which strongly contributed to the decrease of the emergy use in the investigated period. The decreasing of U/F contributed to the decease of the total emergy use, but to a lesser extent than (R + N)/GDP.

**Figure 10.** ASA decomposition of the total emergy use (U) in Heshui during 2000– 2007; the contributions of five factors to the percentage of the 2000 total emergy use (U) level.

In Huachi (Figure 11), the factors GDP/POP and (R + N)/GDP, respectively, contributed to increasing and decreasing total emergy use. The factors U/F and F/(R + N) slightly changed in the investigated period. The factor U/F increased before 2003, but after 2003, the parameter showed instead a decline. Inversely, the factor F/(R + N) decreased before 2003, but after 2003, the parameter showed instead an ascent.

**Figure 11.** ASA decomposition of the total emergy use (U) in Huachi during 2000– 2007; the contributions of five factors to the percentage of the 2000 total emergy use (U) level.

#### **5. Summary and Conclusions**

The main purpose of this study is to investigate metabolic structure and efficiency and, further to identify driving factors, so that we can employ an emergy-based analysis of the socio-economic metabolism of Qingyang city over 2000–2007 by combining data envelopment analysis (DEA) and decomposition analysis. By integrating emergy accounting into the DEA framework, the paper quantified the ecological efficiency of the socio-economic metabolic system, which can be applied to express the potential efficiency improvement and to make comparisons across different regions. The use of a multi-method analysis helps to avoid misleading interpretations based only on emergy-based indicators.

The investigated regional socio-economic metabolism greatly relied on non-renewable emergy flows and feedback (purchased) emergy flows, except Huanxian and Huachi, which highly depended on renewable emergy flow. Analysis of emerge indicators for sub-regions in Qingyang shows that Qingcheng, with the highest NEYR (35.9), is the main energy supplier in Qingyang, followed by Zhengning (14.24), Ningxian (12.66) and Huanxian (11.37). However, the ELR value of Qingcheng (5.2), which was above the Qingyang average (3.25), indicates that the current economic activities are not sustainable, as they relied mainly on local non-renewable emergy inputs. The highest EIR (29.87) and ELR (35.68) of Xifeng refer to the fact that the region relied more on purchased inputs than locally-available resources, and the region's current economic model has led to great environmental pressure. The ELRs of the other five regions indicate that these regions achieved a balance between the emergy use of renewable and non-renewable resources. The ESI results indicate that Xifeng developed a "consumer"-oriented economy; Ningxian, Qingcheng,

Zhenyuan, Heshui and Zhengning developed "producer"-oriented economies; and Huanxian and Huachi were economically behind, and their economic development needs to be accelerated and strengthened.

The emergy-based data envelopment analysis showed that the eight sub-regions, on average, had an EE level of 0.728 in 2007, which implies that Qingyang as a whole has the potential to reduce natural resource inputs and waste output. The EE scores (1.00) of Zhenyuan, Huanxian and Qingcheng indicate that the three regions can be considered as relatively emergy-efficient areas. The EE scores of Xifeng and Heshui are the lowest in Qingyang, and the scores in 2007 were 0.198 and 0.252, which suggest that the two regions could reduce natural resource consumption and waste emission to a great extent without scarifying any desirable output. The ecological efficiency of Zhengning, Ningxian and Huachi is higher than the average level of the whole of Qingyang. During the investigated period, the economic growth was the main driving factor of the increase in the total emergy use in Qingyang and its sub-regions. The contribution of the population scale factor is very small. The factor (R + N)/GDP contributed to the decrease of emergy use considerably (except Qingcheng), which suggests policies to promote the efficiency of resource utilization and, thus, to decrease emergy use further. The positive contribution of the environmental investment ratio to the growth of total emergy use in Xifeng, Zhengning, Ningxian, Zhenyuan, Huanxian, Heshui and Huachi demonstrates that the social economic system of the above seven regions is fragile, especially for Ningxian, Zhenyuan and Heshui.

The integrated approach used in this study is suggested as a tool to design future scenarios of resource use and ecological efficiency in the near future. The results of socio-economic metabolism analysis in Qingyang suggest policies to promote the efficiency of resource utilization, especially for Xifeng and Qingcheng. The fragile social economic systems of Xifeng, Ningxian, Zhenyuan, Heshui and Huachi suggest that series appropriate policies should be adopted to optimize natural resource use (e.g., convert solar radiation into photovoltaic electricity to replace fossil fuels, recycling waste material resources to replace new raw imports, recycling water after appropriate treatment, *etc.*).

It is worth noting that we cannot probe the structures of socio-economic metabolism that are regarded as crucial for policy makers to coordinate the system and improve regional eco-efficiency, because of insufficient statistical data in this economically lagging area. In addition, we employed the uniformed transformity of natural resources, products and processes, which may lead to estimation bias of the regional features to a certain extent. Nevertheless, we believe our findings provide solid and meaningful results that can provide useful implications for policy makers.

#### **Acknowledgments**

The authors would like to thank Wenting Jiao and the other two anonymous reviewers for their helpful comments on this paper and would like to acknowledge the financial support from the Natural Science Foundation of China (41301652, 41101126 and 41261112), the Specialized Research Fund for the Doctoral Program of Higher Education<PHONE_NUMBER>0026) and the Fundamental Research Funds for the Central Universities (lzujbky-2013-132). Special thanks go to the Green Talent Program of BMBF Germany and the Alexander von Humboldt Foundation of Germany.

#### **Author Contributions**

Zilong Zhang and Xingpeng Chen conceived and designed the study; Zilong Zhang contributed to data collection, data processing and draft paper as well as paper revised; Peter Heck contributed to data analysis and paper revised.

#### **Conflicts of Interest**

The authors declare no conflict of interest.

#### **References**


**6.1 Carbon-MoS2 composite electrode materials**

MoS2/MWCNT nanocomposite synthesized by a hydrothermal method exhibited a large surface area and fast ionic transport properties and showed a high specific capacitance of 452.7 F g−1 with good cycling stability (95.8% retention after 1000 cycles), which is almost three times larger than the bare MoS2 (149.6 to 452.7 F g−1) [71]. Ali *et al.* fabricated MoS2/graphene composite from bulk MoS2 and graphite rod through facile electrochemical exfoliation method and exhibited high specific capacitance of 227 F g−1 as compared with the exfoliated MoS2 (70 F g−1) and exfoliated graphene (85 F g−1) at a current density of 0.1 A g−1 [72]. The high specific capacitance of MoS2/graphene composite is due to the synergistic effect between MoS2 and graphene. Ali *et al.* demonstrated the electrochemical performance of MoS2/CNT/GNF composite and compared the performance with MoS2/CNTs, MoS2/graphene nanoflakes [73]. It has been noticed that the electrochemical charge storage performance has been improved by incorporation of the carbon materials into the composite and the composite showed a maximum specific capacitance of 104 F g−1 at a current density of 0.5 A g−1 with capacitance retention of 75% after the 1000 cycle at a scan rate of 10 mV/s. Another interesting MoS2 rGO/MWCNT fiber electrode was fabricated by incorporating rGO nanosheets and MoS2 into aligned MWCNT, which operated at a stable potential window of 1.4 V and exhibited high coulombic efficiency of 100% over 7000 cycles in the bending state (**Figure 7(b-f )**) [74]. Zhang *et al.* reported an agarose induced technique to synthesize MoS2/carbon composite aerogel, which showed a high specific capacitance of 712.6 F g−1 at a current density of 1 A g−1 with cyclic stability of 97.3% over 13000 charge-discharge cycles (**Figure 7(g-j)**) [75]. The high specific capacitance of MoS2/carbon composite aerogel is because of 3D intercalated network with hierarchal porous and interlayer MoS2 expanded structures, which were beneficial for easy ion transportation. 3D graphene/MoS2 composite electrode material has been synthesized by Sun et al and co-workers through a simple and facile one-step hydrothermal process [76]. The as-synthesized composite electrode exhibited

**131**

*Carbon-Based Nanocomposite Materials for High-Performance Supercapacitors*

gravimetric capacitance of 410 F g−1 at a current density of 1 A g−1 and an excellent cycling stability of 80.3% over 10,000 continuous charge-discharge cycles at 2 A g−1 current density. The outstanding electrochemical performance of 3D graphene/ MoS2 composite electrode is due to the 3D architecture of conducting network graphene and flower-like structure of MoS2, which enhances the electrolyte ions

WS2 nanoplates supported on carbon fiber cloth (WS2/CFC) have been synthesized by a facile solvothermal process and used as electrode material for SC [77]. The 3D network of CFC not only prevent the agglomeration of WS2 nanoplates but also enhances the ion transport efficiency due to low charge transfer resistance (Rct) of 0.1 Ω. The as fabricated WS2/CFC electrode exhibited a high specific capacitance of 399 F g−1 at 1 A g−1 current density with cyclic retention of 99% over charge-discharge 500 cycles, which is higher than compared with bare WS2. In addition, developing such composite of WS2 with the carbon fibre helps for fabricating wearable SCs which are in demand for wearable electronics. Yang *et al.* fabricated WS2@CNT hybrid film electrode by incorporating conducting CNTs into WS2. The WS2@CNT hybrid film with a unique skeleton structure showed a maximum specific area capacitance of 752.53 mF cm−2 at a scan rate 20 mV s−1 with very good cyclic stability by only loss of 1.28% capacitance after 10,000 cycles. In addition, a quasi-solid-state flexible SC made by WS2@CNT hybrid film exhibited excellent bendability under bending to 135 10, 000 times with the loss of 23.12% at scan rate of 100 mV s−1 [53]. Tu *et al.* have been synthesized WS2/RGO hybrid material by using a simple molten salt process, which showed a high specific capacitance of 2508.07 F g−1 at 1 mV s−1 scan rate with excellent capacitance retention of 98.6% over 5000 cycles, due to synergic effect of highly conducting RGO and large charge-accumulating sites of WS2 networks. Likewise, Xu *et al.* demonstrated 3D composite of WS2 nanoflakes and quantum dots on N and S co-doped reduced graphene oxide (WS2/N,S-rGO) crumpled nanosheets through a rapid solution combustion synthesis of the precursor and subsequent gas-solid phase sulfurization process, which presented a significant specific capacitance of 1562.5 F g−1 at 1 A g−1 current density, and a rate capability of 780 F g−1 at 40 A g−1 (**Figure 8(a-c)**) [78]. The high specific capacitance of WS2/N,S-rGO hybrids is because of synergistic effect between WS2 and N,S-rGO, where N,S-rGO provides larger contact surface area, excellent charge transport, and shorter ion diffusion path. Hierarchical MoSe2/C hybrid was successfully fabricated by facile one-step hydrothermal strategy, which composed of few-layered MoSe2 nanosheets and amorphous carbon obtained from the decomposition of the triethylene glycol. As fabricated hierarchical MoSe2/C electrode exhibited high specific capacitance of 878.6 F g−1 in comparison with the bare MoSe2 at current density of 1 A g−1 and maintained 98% of initial capacitance over 2000 cycles without obvious decrease. The superior electrochemical performances of MoSe2/C hybrid can be ascribed to hierarchical structure of MoSe2 and conducting nature of carbon, which help for providing large surface area for electrochemical reactions and enhancing charge carriers transfer at the electrolyte/electrode interface [79]. Liu *et al.* fabricated VACNTF@MoSe2/NF composite electrode through a combined chemical vapor deposition method and solvothermal methods by growing MoSe2 nanoflakes on the vertically aligned carbon nanotube array film (VACNTF) with binder-free nickel foam as current collector [80]. The as fabricated VACNTF@MoSe2/NF composite electrode exhibited high specific capacitance of 435 F g−1 at a current density of 1 A g−1 with outstanding cycling stability

*DOI: http://dx.doi.org/10.5772/intechopen.95460*

**6.2 Carbon-WS2 composite electrode materials**

diffusion process.

#### *Carbon-Based Nanocomposite Materials for High-Performance Supercapacitors DOI: http://dx.doi.org/10.5772/intechopen.95460*

gravimetric capacitance of 410 F g−1 at a current density of 1 A g−1 and an excellent cycling stability of 80.3% over 10,000 continuous charge-discharge cycles at 2 A g−1 current density. The outstanding electrochemical performance of 3D graphene/ MoS2 composite electrode is due to the 3D architecture of conducting network graphene and flower-like structure of MoS2, which enhances the electrolyte ions diffusion process.


**10. Conclusion**

*Cytogenetics - Classical and Molecular Strategies for Analysing Heredity Material*

appropriate in light of consideration [40].

eukaryotic cells as well as mammalian cells [41].

**9. Mechanism of formation of chromosome aberration**

DNA breaks (especially dsDNA) is a serious threat for cell when unrepaired or misrepaired, as they can result in genomic instability or later on may lead to chromosomal alterations and even cell death. The chromosomal aberrations formation is one of the major alteration formed during dsDNA breaks. Moreover, it has been reported that during each cell division approximately 5000 ssDNA breaks were generated per nucleus and approximately 1% of total ssDNA breaks converted in dsDNA breaks. There were two theories forwarded for explanation of how chromosomal aberrations and its formation take place i.e. breakage and reunion theory and exchange theory. The breakage and reunion theory explains that breaks in chromosome may rejoin and form the original structure through restitution and the exchange theory might lead to exchange the aberration by rejoining another type of breaks. dsDNA breaks could be repaired by possibly three pathways i.e. homologous recombination repairing (HRR) which restores the original sequences, non-homologous DNA end joining (NHEJ) which usually generates and repairs small alterations such as base pair substitution, insertions, deletions at break sites etc., and single strand annealing (SSA) which may lead to the formation of interstitial deletions. HRR (requires one break) and NHEJ (requires two breaks) and SSA are important pathways for repairing of dsDNA breaks with one or two breaks in

Chromosomal aberrations may be caused by various physical and chemical factors such as ionizing radiations, chemicals and spontaneous dsDNA breaks e.g. endogenous reactive oxygen species, topoisomerases and replication errors.

material missing or for incomplete interstitial deletions, third, observe for presence of any minutes and fourth, if any extra additional distal segment is present but not related to short arm with abnormal band sequences, it may be regarded as incomplete complex changes and look for the origin of additional segment, (iv) fragment simple but non terminal; perhaps represents incomplete acentric ring or large interstitial deletion]. Chromatid type structural aberrations could be detected and identified in the form of interchanges (involve the interchanges of chromatids), interarm intra changes (requires two breaks and causes pericentric inversions, double duplications-deletions, dicentric and centric rings), intra arm intra changes (two breaks involved and caused the formation of isochromatid deletion, duplication-deletion, chromatid minutes and paracentric inversions), and breaks [{causes chromatid terminal deletions and may be of various types; (i) a tandem duplication may be present in the complete chromatid, (ii) a tandem duplication may be present either in centric or acentric portion of the incomplete chromatid, (iii) the origin of acentric fragment may be of intercalary type and the sister chromatid has a normal pattern but it may show a bending opposite to the site of deletion, (iv) a paracentric inversion could be possible adjacent to the break in the acentric fragment but other sister chromatid may be normal, (v) a paracentric inversion could be possible adjacent to the break in the centric region or portion but other sister chromatid may be normal}].Additional chromatid type structural aberrations could be possible in the form of as isochromatid (isochromatid exchanges), insertions and additional dark bands in one of the chromatid at the exchange point. It is important to locate the position of aberration or break points at some stage in the production of breakage and rejoining of chromatid threads as this is the event that causes disruption and could be observed using different techniques. A detectable point of breakage is generally referred to as 'break point' but 'presumptive break point' would be more

**56**

At present, most of the studies are surrounded towards the human health and disease caused by the interaction of genetic and environmental factors. Sometimes it is difficult to understand the genetic constitution or mechanism of chronic diseases. Therefore, it is very important to understand the mechanism behind the abnormal cells either genetic or environmental or both to solve the problems completely. The identification of a particular abnormality at the initial stage is crucial and banding techniques conventional or molecular provide such an opportunity. Banding and chromosome aberrations are played an important key role in the assessment of various risks faced by the genetic constitution of eukaryotic cells. Therefore, it may continue further to assess the risk of various kinds of ailments, diseases, and geno-toxicity induced by the radiations, pharmaceuticals, environmental and synthetic chemicals.


**6.1 Sensor fusion**

The use of higher quality inertial/magnetic sensor modules will improve positioning accuracy but the cost of such a solution is often much higher. An alternative solution is to use various positioning data from multiple sources such as radio navigation aids and additional sensors onboard. Through the control applied to the drift error, a positioning system using multiple data sources "fused" together is able to outperform a system using a single data source. Complementary filtering techniques were used to integrate data from different positioning aids in the past. Nowadays, Kalman filtering is popular in combination of two estimates of a variable. For example, IPS data can be integrated with GPS data to provide enforced positioning ability in both indoor and outdoor environment.


**4. Principle of SDDS**

Presently, the conventional treatments exhibit escalation in dose and systemic toxicity upon administration of drug. Most anti-inflammatory therapeutic drugs are equitoxic to both the normal cells and inflamed cells. SDDS has been well recognized in the past few decades owing to its potential for site-specific and targeted delivery [66]. Encapsulation of anti-inflammatory drugs in nanoparticles can enhance the site-specificity, reduce the dose, curtail the systemic toxicity and improve the biodistribution to targeted disease site [67]. To overcome the disadvantage of conventional delivery of drugs, selective delivery whether passive or active can be used for targeting drug to the site of action as SDDS in RA therapy.

#### **4.1 Passive targeting**

Passive targeting can be accomplished by targeting the physiological and anatomical changes in inflamed tissues, that occurred due to RA. For passive targeting, NPs do not require any surface modification, either by conjugation or by attaching a surface ligand. Various studies have shown the enhanced permeability and retention (EPR) mechanism for passive accumulation in inflamed tissues [68]. In the inflammatory RA milieu, there is evidence of angiogenesis but no evidence of displaying an abnormal lymphatic drainage [69]. The long-circulating delivery vehicles have been evidenced to specifically accumulate within the pannus of the inflamed synovium [70]. The hyperplasia in pannus exhibits a leaky vasculature due to high vascular permeability comparable to solid tumors. Consequently, taking advantage of leaky vasculature may for passive targeting is a promising option [71]. EPR allows NPs in size range from 20 to 200 nm to selectively accumulate in pannus and display on the surface of inflamed tissue. In addition to the EPR effect, hypoxic and acidic environment of inflamed joint also favors passive targeting [70]. Arthritic inflamed joint has poor oxygen delivery and increased metabolic rate due to meager perfusion into the diseased synovial joint. Therefore, the two conditions can easily be used as method of passive drug targeting in less oxygen and acidic microenvironment of RA affected inflamed tissue. NPs administrated in blood stream with hydrophobic surface are easily recognized by reticuloendothelial system (RES) such as spleen and liver, and engulfed by macrophages, consequently quickly eliminated from systemic circulation.

## **4.2 Active targeting**

Targeted delivery involves active targeting to specific cells in the microenvironment of arthritic joints. Overexpressed receptors on particular immune cells can be targeted with its complimentary ligand that is decorated on nanoparticle surface. Several receptors are expressed by different cells, we shall be discussing a few including CD44, folate and beta-3 integrins. Targeting angiogenic vascular endothelial cells are also under investigation, with E-selectin as a promising target molecule [72]. Receptor mediated endocytosis is responsible for efficient uptake of the ligand decorated carrier molecule (ligand-receptor interaction) (**Figure 3**).

#### **Figure 3.**

*Outline of the targeting strategies for nanoparticulate drug delivery systems used in RA.*


**Author details**

Sunita Mishra\*, Gunjan Gupta and M.A. Firdaus Department of Food and Nutrition, School of Home Science, Babasaheb Bhimrao Ambedkar (A Central University), Lucknow, India

\*Address all correspondence to<EMAIL_ADDRESS>
© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Therapeutic Potential of Chocolate Coated Chinese Chestnut (A Nut Cum Fruit) DOI: http://dx.doi.org/10.5772/intechopen.108976*


*5.3. Effect of Ground Resistor*

A different ground resistor has an effect on the magnitude of transient signals, which will affect the accuracy of the protection actions. Here, the performance of the proposed method in dealing with PPF, PGF, LF, and AG-AC is discussed. Figure 17 shows the influence of the ground resistor on the action accuracy. As demonstrated by Figure 17, when the ground resistor is smaller than 50 Ω, the proposed method is immune to the change in ground resistor. However, with the increase in ground resistor, the fluctuation of high-frequency components of the transient currents becomes less obvious, which mean less disorder in high-frequency bands, and decreases. For internal faults, the values of W4 and W3 will decrease, and misoperations of protection will be found. However, for external faults, such as AG-AC, the criterion W5 = 0 is not affected. The judgment of external faults is still effective.

**Figure 17.** The influence of ground resistor on the action accuracy.


**7. Conclusions**

A direct power model developed from Park's reference frame for the SCES systems has been presented in this study. The direct power model controls instantaneous active and reactive powers regardless of the SCES system without employing typical phase-Locked-Loop. A PI-PBC approach was used to control the SCES system because it takes advantage of the pH structure of the SCES system to propose a control law that guarantees the stability of the system and exploits proportional-integral actions. The proposed controller demonstrates better performance in relieving the active and reactive power oscillations generated by wind generation considering imbalance when compared to the IDA-PBC approach.

**Author Contributions:** Conceptualization and writing—review and editing, W.G.-G. and O.D.M.; and supervision, writing—review and editing, F.M.S., C.A.R. and C.O.-H. All authors have read and agreed to the published version of the manuscript.

**Acknowledgments:** This work was partially supported by the National Scholarship Program Doctorates of the Administrative Department of Science, Technology and Innovation of Colombia (COLCIENCIAS), by calling contest 727-2015.

**Conflicts of Interest:** The authors declare no conflict of interest.


**Contents**

## **About the Editors**

#### **Anna Mazzi**

Anna Mazzi is an Associate Professor of Environment Health & Safety Management Systems at the Department of Industrial Engineering, University of Padova, Padova, Italy. She is the head of the research group SAM.lab, dedicated to supporting organizations in sustainability assessment and management. She is a member of the Italian Network of Life Cycle Assessment and coordinates one of its working groups. During her research activity at University of Padova, she has collaborated in several European research projects, in the funding lines LIFE Environment, Interreg, Intelligent Energy Europe, EQUAL and CIP Innovation. She has also collaborated in numerous research projects at national and regional levels on the implementation of environmental assessment and management tools and standards at industrial and territorial levels. Her current research activity, documented by about 170 publications (h-index: 22), is focused on environmental impact evaluation and minimization, through life cycle sustainability assessments, to support process optimization and product innovation in reuse and recycling.

#### **Jingzheng Ren**

Dr. Jingzheng Ren is currently an Assistant Professor at The Hong Kong Polytechnic University. He is also an Honorary Associate Professor of Energy System Engineering at University of Southern Denmark (Denmark) and an Associated Senior Research Fellow at Institute for Security & Development Policy (Sweden). He serves as the Co-Editor-in-Chief of *Environment, Development and Sustainability* (Springer) and Editor of *Sustainable Production and Consumption* (Elsevier), and was previously an Associate Editor of *Journal of Renewable and Sustainable Energy* (AIP), Associate Editor of *Renewable Energy & Sustainable Development*, and a Guest Editor of several leading SCI indexed international journals with impact factors. He has more than 200 publications to his name, including 170 journal papers, 17 authored/edited books, and more than 50 book chapters. Eleven of his papers have been selected as the ESI top 1% highly cited papers and four have been highlighted as Key Scientific Articles contributing to excellence in energy research. One paper was recognized as one of the three top papers published in Sustainable Production and Consumption in 2018 and won the Best Paper Award (with a second award for contributions to a leading journal on sustainability).


**Carlos Martin 1,2,3,\*, Nacho Aguilo 1,2, Dessislava Marinova 1,2 and Jesus Gonzalo-Asensio 1,2**

Received: 10 March 2020; Accepted: 31 March 2020; Published: 10 April 2020

**Abstract:** In addition to antibiotics, vaccination is considered among the most efficacious methods in the control and the potential eradication of infectious diseases. New safe and effective vaccines against tuberculosis (TB) could be a very important tool and are called to play a significant role in the fight against TB resistant to antimicrobials. Despite the extended use of the current TB vaccine Bacillus Calmette-Guérin (BCG), TB continues to be transmitted actively and continues to be one of the 10 most important causes of death in the world. In the last 20 years, different TB vaccines have entered clinical trials. In this paper, we review the current use of BCG and the diversity of vaccines in clinical trials and their possible indications. New TB vaccines capable of protecting against respiratory forms of the disease caused by sensitive or resistant *Mycobacterium tuberculosis* strains would be extremely useful tools helping to prevent the emergence of multi-drug resistance.

**Keywords:** BCG; tuberculosis vaccines; TBVI; EDCTP; IAVI; CTVD


**5.1 Experimental protocol**

564 Sintering of Ceramics – New Emerging Techniques

electric field as well as by a maximum amount of net trapped charge in the sample, Qst,

state and then the practical choice of the injection time tinj is determined by the achievement of this state. The evolution of the net trapped charges Qt during injection, which can be

Fig. 6. Evolution with time, at 473 K, of the net charge, Qt, during the first pulse injection in polycrystalline alumina sample (d = 4.5 µm). The quantity Qt is derived from the currents of Fig. 5 via Eq. 7. The solid line represents the exponential fit of the data, as

t Q (t) Q 1 exp = −− τ

where τc is the charging time constant (found equal to 2.07x10-3 s), which characterizes the

The method described above gives the opportunity to evaluate the quantity of trapped charges during irradiation. If the probed zone is initially uncharged, Qt(t) characterizes the quantity of charges that accumulates after an irradiation time t. Depending on the insulator conduction properties, the accumulated charges can either remain localized or partially (or even totally) spread out of the irradiated volume (discharge phenomenon). Hence, the measurement of the ability of the material to spread charges is of technological interest. In this paragraph, we give details of the experimental procedure developed for the measurement of this ability and we define a recovery parameter allowing the quantitative

c

(11)

The best fit of data represented in Fig. 6, leads to an exponential time evolution:

t st

charging kinetic of the material in the used experimental conditions.

**5. Measurement of the ability to spread charges**

evaluation of the extent of discharge.

ind 0 − I (t) dt . The steady state is interesting because it will be taken as a reference

equal to inj t

given by Eq. 11.

deduced from Eq. 7, is shown in Fig. 6.

**net trapped charges Qt(pC)**

To characterize the degree of spreading (of discharge), we set up a protocol allowing its evaluation. The procedure consists in analysing the states of charging deduced from two pulse electron injections over the same area, separated by some lapse of time as explained in the three following stages.


**1. Introduction**

The cytochromes P450 (CYP) constitute the largest superfamily of hemoproteins, which have been studied since the late 1940s (see [1,2] for an historical survey). With the emergence of genomic data and the quickly growing number of P450 sequences, the superfamily has been phylogenetically classified in families, subfamilies and individuals, respectively, denoted by the first identification number, the letter following it and the second identification number (e.g., in human 1A2, 3A4, etc.). More than 18,000 P450s sequences in all living kingdoms were recognized in 2013 [3], but, since then, the number of known sequences keeps growing and can be estimated to be higher than 300,000 taking into account the current plant genomic projects [4]. CYPs are found in many bacteria, plants and animals. It is estimated that, in human or mammal metabolism, 75% of drug transformation reactions involve catalysis by P450s [5,6]. The secondary and tertiary structures of the CYPs have largely been

conserved throughout evolution [7]. The crystal structures of a large number of CYPs, in both the free and the substrate-bound forms, have been solved. The core is highly conserved within the structural fold, and the heminic active site of the CYP is buried inside the enzyme [7].

The human genome encodes 57 CYP isoforms, that play a major role in the biotransformation of drugs, pesticides or many other chemicals, and in the metabolism of endogenous compounds such as steroids and vitamins [8,9]. The detoxification reaction mediated by these CYPs can yield reactive intermediates which can damage DNA, as well as lipids and proteins [10], while the alteration of their activity often leads to serious diseases [11]. Tables of substrates of human isoforms are available [6,12–14]. Despite several attempts to predict substrates of CYPs [15–19], no clear prediction rule is known. It is known that lipophilicity can play a crucial role [20] and a summary of substrates/selectivity rules is proposed [21]. However, there is an urgent need to improve the accuracy, interpretability and confidence of the computation models used in drug discovery process (see [19] and references therein).

In this paper, we consider the human isoform 3A4. It lies in the human liver and is estimated to contribute to the phase I metabolism of roughly half of the drugs on the market [22,23]. The other isoforms accounting for more than 90% of the oxidation of drugs are 1A2, 2A6, 2C9, and 2D6 [24]. Although most of the CYPs have a binding allosteric site for their substrates which reversibly accommodates one molecule of substrate at a time, 3A4 isoform can accommodate more than one molecule in its binding site at the same time [25]. Recent advances about CYP3A4 show limited information on the pathways to the heminic site [26,27].

P450s catalyze an oxidation where the substrate binds in the active site on the distal side of the heme. Although the oxidation step has been investigated for a long [28–31], the ingress and egress of the compounds to and from the active site remain unclear. Structural flexibility is essential to allow chemical compounds to get in and out the active site, and it was shown that it correlates with substrate preferences for several CYPs, including for 3A4 [32].

Few biophysical and biochemical approaches have been proposed by wet biology teams to experimentally address the role of ligand access channels, as reviewed in [33], but never for CYP3A4. To our knowledge, only one article presents clear-cut results suggesting that a ligand diffuses through a given channel and not another one [34]. The authors mutated selected residues in one of the channels (double mutant Y309C/S360C) to introduce cross-linking by disulfide bond that resulted in one channel closure. They could then measure the kinetics of metabolism of two different substrates (benzphetamine and 7-EFC, i.e., 7-ethoxy-trifluoro-coumarine), and show that the double mutant exhibited unchanged activity for benzphetamine (98% of wild type activity), while it dropped to 19% compared to wild-type activity for 7-EFC, indicating that the two substrates do not cross the same channel to access the active site. This experiment necessitates choosing carefully the two residues to mutate, and obtaining an active form of the recombinant enzyme, which is never obvious.

Molecular dynamics based studies of the channels of several CYPs were performed [32,35–55]. Some of them were applied to 3A4 [32,42–45,48,51,53,55]. However, these studies do not lead to a consensus on the number and type of channels for a given isoform. Due to the prohibitively long time scale required to observe opening or closing of channels, we preferred to use a rapid geometric method to identify through which paths are travelling the compounds. Identifying and characterizing the access channels and their lining amino acids is not a trivial task because the channels can dynamically open/close in response to water or ligand passage and enzyme breathing motions [56].

In this context, we computed cavities and channels with CCCPP, which takes in account both the size and the shape of the ligands through a cylindrical model of the ligands, proved to be more realistic than the spherical model used almost everywhere in the literature [57]. The effect of the ligands conformational flexibility on their shape was taken in account in preliminary studies [58,59]. Then, we found that the 3A4 isoform has three major conformations while only two conformations are considered in the literature [60].

For the present study, we built version 2 of CCCPP to perform a refined analysis of the channels. Unless otherwise stated, further mentions of CCCPP refer to its enhanced version. The secondary structure of the members of the P450 family is described by a nomenclature defined by Poulos et al. [61] (see also Figure 1 in [62] and Figure 2 in [63]), which is widely used in the P450 scientific community and that we use throughout this paper. The major description of the channels [64] is based on a geometric method in terms of the secondary structures at which there is an egress of the computed channels. These channels were computed with the software CAVER [65], and gave rise to a channel nomenclature which is still in use [64]. However, there are dozens of other cavities and channels calculation softwares (see [57] for a review). They give a variety of results due to the diversity of output data structures. Thus, it is rather difficult to compare these results. For example, the CAVER based nomenclature established in [64] from all CYP crystal structures available in the Protein Data Bank (PDB) in March 2006 (total: 143 PDB files, 192 chains, 26 CYPs) indicates 14 channels, while CYP3A4 alone (PDB code 1TQN, 1 chain, included in the 2006 study) gave rise in 2012 to 21 channels with MOLEonline 2.0 [66], one of the successors of CAVER. In fact, only three channels were attributed to 3A4 in the 2006 study. Such discrepancies are not unusual. They appeared also between the P450*cam* (CYP101) channels calculated with CAVER and MOLEonline and the ones computed in [67], and the situation remains unclear despite the help of several molecular dynamics simulations [35,37]. The experimentalists are left with dozens of published software packages and they have to face to a huge of potentially contradictory results about the channels they are looking for: Which channels should be retained? Easy and rapid comparisons are needed. Giving the name of the secondary structure at which there is a channel egress does not suffice to describe the channels. For a given CYP chain, most of the channels have common parts. Thus, in our opinion, the network of channels should be described with the help of graph theory tools, in terms of paths along nodes and edges, as done in the present study. To compare these networks for different input CYPs, it is better to give a full description of the channels in terms of protein heavy atoms and residues, not only at the egress locations of the channels, but also all along the channels. These functionalities were unavailable in the original version of CCCPP described in [57]. Thus, no more visual examination of the secondary structures is needed to locate the egress of the channels, as it was needed with CAVER. Moreover, the lists of atoms and residues are returned by CCCPP, plus the data structure defining the boundary of each channel. This latter functionality was also available in the version 1 of CCCPP. Throughout this paper, channels named 1, 2a, 2b, etc., refer to the nomenclature of Cojocaru et al. [64] based on the secondary structures elements at the protein surface where the channels emerge.

#### **2. Methods**


*Article* **Lower-Limb Amputation in Children and Adolescents—A Rare Encounter with Unique and Special Challenges**

**Axel Horsch \* , Svenja Gleichauf, Burkhard Lehner, Maher Ghandour , Julian Koch, Merkur Alimusaj, Tobias Renkawitz and Cornelia Putz**

> Department of Orthopaedics, Heidelberg University Hospital, 69118 Heidelberg, Germany<EMAIL_ADDRESS>(S.G<EMAIL_ADDRESS>(B.L<EMAIL_ADDRESS>(M.G<EMAIL_ADDRESS>(J.K<EMAIL_ADDRESS>(M.A<EMAIL_ADDRESS>(T.R<EMAIL_ADDRESS>(C.P.)

**\*** Correspondence<EMAIL_ADDRESS>
**Abstract:** Background/Aim: The pattern of lower-limb amputation, indications, complications, and revision in pediatric cases differs globally. Therefore, we conducted this study to describe the patterns of lower-limb amputation at our institution. Methods: During a set period between 2010 and 2020, adolescent patients undergoing lower-limb amputation within the orthopedic department of Heidelberg University Hospital were retrospectively collected and analyzed. The retrieved dataset included two parts: data on lower-limb amputations and data on subsequent complications and revision surgeries at the same time. Besides patients' general information (age, gender), the dataset included data regarding amputation patterns (number, indications, and level of amputation, complications, and revision surgeries and their indications). Results: Twenty-two patients undergoing lower-limb amputation were examined, of which the majority were males (63.6%) with a mean age of 12 (5.1) years. Tumor was the most common indication for amputation (72.7%), and transfemoral amputation was the most frequent level (68.2%). Complications occurred in 10 patients, mostly due to stump impalement or bony overgrowth. Of all recorded patients requiring revision, nine were regarding bone and one case regarding soft tissue. Conclusions: Lower-limb amputation in adolescents is a rare encounter and it is commonly indicated due to bone tumors. The thigh is the most common level of amputation. Postoperative complications are frequent, mainly secondary to bony overgrowth, and often require revision surgery.

**Keywords:** amputation; lower extremity; complications; children; adolescents

#### **1. Introduction**

Amputations of major limbs, especially in pediatric populations, are a rare encounter. In patients where amputation is necessary, the subsequent emotional and psychological impact is often detrimental to both the family and the affected child [1]. These major amputations of either the lower extremity or upper extremity lead to a substantial disfigurement of the amputated limb, carrying with it a fairly increased risk for postoperative morbidity and mortality, and especially children who suffer from limb amputation often perceive themselves as being incomplete [2]. In this context, creating a stump that is considered fit for a function-restoring prosthesis is essential for orthopedic surgeons.

The decision to amputate a limb follows at least one of several indications, including severe trauma, infection, tumors, congenital anomalies, and vascular abnormalities [1]. Evidence suggests that the reasons for amputations and their frequencies differ widely between countries. For instance, peripheral vascular affection is perceived as the leading cause of amputation in developed countries, while trauma, infection, and malignant tumors are reported as leading causes for major limb amputation in developing countries [3,4].

**Citation:** Horsch, A.; Gleichauf, S.; Lehner, B.; Ghandour, M.; Koch, J.; Alimusaj, M.; Renkawitz, T.; Putz, C. Lower-Limb Amputation in Children and Adolescents—A Rare Encounter with Unique and Special Challenges. *Children* **2022**, *9*, 1004. https:// doi.org/10.3390/children9071004

Academic Editor: Vito Pavone

Received: 18 May 2022 Accepted: 1 July 2022 Published: 4 July 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Although lower-limb amputations in pediatrics is rare, they are often associated with several complications, mostly being bone overgrowth regarding the amputated end of the limb and leading to permanent internal penetration of soft tissue under load, making prosthetic use impossible [5]. Another observed complication is the formation of a sharpended spur that potentially penetrates overlying soft tissue due to continuous growth, particularly in transfemoral (TF) and transtibial (TT) amputation. Addressing this, revision surgery may be considered, particularly to correct frequent growth abnormalities [6]. Although lower-limb amputations in pediatrics is rare, they are often associated with several complications, mostly being bone overgrowth regarding the amputated end of the limb and leading to permanent internal penetration of soft tissue under load, making prosthetic use impossible [5]. Another observed complication is the formation of a sharpended spur that potentially penetrates overlying soft tissue due to continuous growth, particularly in transfemoral (TF) and transtibial (TT) amputation. Addressing this, revision surgery may be considered, particularly to correct frequent growth abnormalities [6].

tumors are reported as leading causes for major limb amputation in developing countries

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Due to the wide discrepancy in characteristics and outcome of pediatric patients undergoing major limb amputation within different countries, we conducted this research to study the pattern of lower-limb amputation in children and adolescents (<18 years of age), their indications, amputation levels, complications, and subsequent revision surgeries following amputation at our institution. Due to the wide discrepancy in characteristics and outcome of pediatric patients undergoing major limb amputation within different countries, we conducted this research to study the pattern of lower-limb amputation in children and adolescents (<18 years of age), their indications, amputation levels, complications, and subsequent revision surgeries following amputation at our institution.

#### **2. Materials and Methods 2. Materials and Methods**

[3,4].

#### *2.1. Study Population and Design 2.1. Study Population and Design*

This research is based on a retrospective analysis of patient records containing lowerextremity amputations at the Orthopedic University Hospital Heidelberg (Figure 1). This retrospective analysis was based on two main datasets: (1) data of patients who underwent a lower-extremity amputation during the period from 2010 to February 2020 and (2) data on complications and revisions performed after amputation during the same period. This research is based on a retrospective analysis of patient records containing lowerextremity amputations at the Orthopedic University Hospital Heidelberg (Figure 1). This retrospective analysis was based on two main datasets: (1) data of patients who underwent a lower-extremity amputation during the period from 2010 to February 2020 and (2) data on complications and revisions performed after amputation during the same period.

**Figure 1.** X-ray image of a patient included in our dataset. **Figure 1.** X-ray image of a patient included in our dataset.

To create the dataset, all surgical procedures with a corresponding code were selected from the internal procedure list. Then, a review of the collected data using the ICD-10 and the coding of the surgical procedures to determine complications and performed revisions was conducted. Retrieved data contained baseline characteristics of patients (age, gender) as well as clinical information (level and indication of amputation, complications, and revisions).

#### *2.2. Inclusion and Exclusion Criteria for Amputations*

Inclusion criteria were set to patients containing following variables: lower-extremity amputations, any sex, and less than 18 years of age, at time of amputation surgery. For dually listed patients, we considered whether the amputation was performed on the same extremity, thus changing only the level of amputation or whether amputations were performed on different extremities. In case of two separately conducted amputations of the same limb, scoring took place as one patient; otherwise, this patient counted as two cases.

Patients that underwent an amputation other than lower extremity, as well as patients undergoing nonprimary amputation surgery, were excluded from this study. Therefore, the patient collective contained 23 patients. Reviewing inclusion criteria, 22 patients were thereafter relevant for further analysis.

#### *2.3. Inclusion and Exclusion Criteria for Complications*

To determine whether complications occurred because of initially conducted amputations or independently, an examination was performed within the patient cohort undergoing amputation of the lower extremity. If this was not the case, the patient would be excluded. If multiple listing of patients was detected, it was checked whether complications were co- or independent. If a continuing complication was detected, it counted as one patient and was therefore flagged with "multiple necessary revisions". Independent complications were counted individually.

The patient population included a total of 10 patients, all of whom met the inclusion criteria and were therefore relevant for analysis.

#### *2.4. Study Variables*

Age, sex, cause of amputation, level of amputation, complications, and revisions performed were used as observation characteristics. A differentiated analysis of the abovementioned characteristics was then considered.

The causes of amputation were divided into tumor, infection, dysmelia, and circulatory disorders. The amputation level was divided into TT amputation, TF amputation, hemipelvectomy (HP), and hip-disarticulation (HX). With regard to complications, only residual limb complications occurred in children and adolescents. Revisions were subdivided into soft-tissue and bony.

#### *2.5. Statistical Analysis*

Statistical analysis of the collected data was performed using Microsoft Excel 365 (Microsoft 2022, Redmond, Washington, DC, USA), and i.s.h.med (SAP Walldorf, Germany) to add missing information. Descriptive data were presented as means and standard deviations (SD) for continuous variables, while categorical and dichotomous variables were presented as numbers and frequencies.

#### **3. Results**

#### *3.1. Demographic and Clinical Characteristics*

The baseline characteristics of the retrieved records are summarized in Table 1. A total of 22 children/adolescents undergoing lower-extremity amputation were included in this analysis. The mean age was 12 (SD = 5.1) years, and 63.6% (14/22) of patients were males. The mean follow-up was 4.3 years (SD = 3.4).

Amputation was conducted in all 22 patients with tumor being the most common reason for amputation, accounting for 16 patients (72.7%), followed by dysmelia (13.6%) and circulation (9.1%), respectively. Of patients with tumor as indication for ampu-

tation, osteosarcoma was the most commonly reported cause (15/16 patients; 93.8%), while Ewing's sarcoma was reported in one case. TF amputation was most common accounting for 68.2% of patients, followed by HX (13.6%), TT amputation (9.1%), and HP (9.1%), respectively.

**Table 1.** Demographic and clinical characteristics of included children/adolescents with lowerextremity amputation (*n* = 22).

*n*: Number; SD: Standard Deviation.

### *3.2. Complications following Amputations*

Complications occurred in 10 (45.45%) out of 22 amputated patients, all of which were residual limb complications. Based on an intact growth plate, which is present in transmetaphyseal amputations (at femoral and tibial levels) (Figure 2), impaling of the residual limb occurred. This happens mainly due to continuous longitudinal growth of the bone leading to excessive stress on soft tissue. As a result, 9 of 17 patients (52.9%) experienced stump impalement (Figure 3).

In four of the nine recorded patients with limb impalement as a complication, a shorting of the bone and a remolding of the distal end of the stump (deperiosteostomy) was performed during amputation. This procedure was not used in the remaining five patients.

**Figure 2.** Postoperative X-ray of transtibial amputation*.* **Figure 2.** Postoperative X-ray of transtibial amputation.

**Figure 3.** X-ray image of stump spike*.* **Figure 3.** X-ray image of stump spike.

*3.3. Revisions Secondary to Complications 3.3. Revisions Secondary to Complications*

Revision surgeries following amputation were performed in 10 patients that experienced postoperative complications, 9 of which received bony revisions accounting for 90% of all revisions, while 1 case had soft tissue revision. A summary of bony revision procedures that were carried out is provided in Table 2. Stump shortening and stump revision was most common in our population, accounting for 33.3% of revisions. Revision surgeries following amputation were performed in 10 patients that experienced postoperative complications, 9 of which received bony revisions accounting for 90% of all revisions, while 1 case had soft tissue revision. A summary of bony revision procedures that were carried out is provided in Table 2. Stump shortening and stump revision was most common in our population, accounting for 33.3% of revisions.

**Table 2.** Summary of the bony revision procedures that were performed in complicated amputated patients. **Table 2.** Summary of the bony revision procedures that were performed in complicated amputated patients.

Total 9 (100%)

**Table 2.** *Cont.*

#### **4. Discussion**

Major limb amputation has been perceived as a frequent surgical procedure attempted in many orthopedic, general, vascular, and trauma settings, mainly for life-saving purposes. That being said, amputation is commonly associated with a substantial impact on the affected individual's social and psychological status [7,8]. The patterns of amputation indications, frequency, and levels, as well as subsequent complications and need for revision surgeries, are widely variable based on the age of patients, settings, and country in which they are carried out [1,6]. Therefore, we conducted this retrospective analysis of children and adolescent patients who underwent lower-limb amputation at our institution over a 10-year period to report patterns of amputation indications, complications, and revision surgery.

A total of 22 patients were included for descriptive analysis, following the exclusion of 1 case that did not match our eligibility criteria. All of them were children or adolescents with a mean age of 12 years. We observed a male predominance accounting for 63.6% of amputated patients. This observation stands in line with the recent literature [9–13]. Although, most of the available evidence provides data in adult patients, and it therefore seems that male predominance in amputation is a common observation across all age groups. However, this still warrants further investigation to determine the reasons behind this predominance, as the presented sample size is too small for a principal generalization.

Indications for limb amputation, particularly within pediatric population, vary greatly in different settings and countries. For instance, some reports indicate almost 80 to 90% of limb amputations in adults occur as a result of vascular abnormality in developed countries [14–16] while in developing countries, trauma and infections are perceived as the most prevalent indications for limb amputations [3,4]. It is assumed that in developed countries, pediatric amputations are mainly performed to treat tumors, while in developing countries, trauma and infections are the most common indications. In this study, tumors were the leading cause of amputation in children/adolescents, followed by dysmelia. This is somewhat consistent with the study by Chalya et al. [6], where vascular abnormalities were ranked third as a cause of lower-limb amputation; however, diabetic foot and trauma were ranked first and second, respectively. Of note, the authors included individuals of all age groups, while most of them had an age ranging between 41 and 50 years. Similar to the previous study, Jahmani et al. [5] reported diabetic foot (41.9%) and trauma (38.4%) as leading indications for amputation. The authors studied indications for lower-limb amputation in patients with (0-10) and (11-20) years of age, of which primary bone cancer and trauma were reported as the common indication for amputation within each of these age groups, respectively. The differences in indication for amputation between this study and recent literature could be related to this unique and young age group within the analyzed cohort.

Of note, in our population, the decision of which type of amputation was to be carried out was solely dependent on the findings of tumor extension, while putting into consideration an appropriate safety margin. In our study, TF amputation was the most frequent level of lower-limb amputation among children and adolescents. This is consistent with current literature, where above-knee amputation was reported as the most common level of amputation, both in the adult and pediatric population [10,17,18].

We observed many complications in our patients undergoing lower-limb amputation, accounting for 45.5% of the studied population. All observed complications were residual limb complications, with stump impalement or bony overgrowth being most frequent

(nine patients). In four of nine patients, deperiosteostomy was performed to tackle this complication. Preservation of the length of limb in this population is of great importance, mainly because the lost distal growth plate accounts for approximately 75% of vertical femoral growth. In these patients, TF amputations lead to a very short stump leading to a complex biomechanical situation regarding prosthetic fitting. On the other hand, TT amputation, although preserving the proximal growth plate, often leads to bony overgrowth at the distal end, which subsequently may continue growing until growth is stationary within amputated individuals [1]. Consistent with our findings, bony overgrowth is reported as the most prevalent complication following lower-limb amputation in adolescents, with rates ranging from 4 to 50% [19–24]. Importantly, age, location, indication for amputation, and level of amputations are perceived as attributable factors for such prevalence, whereas younger individuals are more likely to experience this complication [19,20,25]. This could be the reason for this complication being so frequent in our population, secondary to the young age of included individuals.

It is important to highlight an unfamiliar observation in one of our cases, where the fibula outgrew the tibia following amputation (Figure 4). Although the surgery was performed correctly and no epiphysiodesis was performed, this observation remains unclear.

More so, all amputated individuals in our study who experienced postoperative complications had undergone revision surgery (10 out of 10 patients). Little is reported regarding the value of revision surgery on lower-limb amputation, particularly in the pediatric population due to the scarcity of evidence in this particular field. In a recent analysis of 71 revision surgeries in patients who underwent lower-limb amputation, it was reported that soft-tissue pathology (31.0%) was the most common indication for revision surgery followed by infections (31.0%) and bone pathology (18.3%), respectively [26]. This differs from our observation, since in our series, nine patients underwent bony revision, whilst only one case underwent soft tissue revision surgery. This discrepancy could be related to indication for amputation in the first place, as in our study, tumor (mainly osteosarcoma) was the main indication for amputation, whereas trauma was most common for amputation in the previous study [26]. This highlights an important observation relating to the association between the primary indication for amputation and subsequent complications and revision surgeries. Nevertheless, larger and prospective studies are needed to further investigate this observation. That being said, it is of great importance to mention that this problem of bony impalement begins early in these patients, and due to the bone overgrowth, there is a significant stress on the surrounding soft tissues, leading to unequivocal growth and eventually penetration. This in turn results in a significant impact of affected patients' life in terms of pain and activities of daily living which can also negatively impact the affected child's mental health. In these circumstances, revision surgery is considered a necessary function-improving intervention.

Surgical options for revision surgery in children and adolescents include stump shortening with the option of temporary epiphysiodesis of the proximal growth plates. However, the resulting reduced bone growth can complicate restoration in very short residual limbs and lead to instability in the overlying joint, making length preservation/gain advantageous for prosthetic restoration. Even an operation according to Ertl does not solve the problem of the bone growing further. The orthopedic technical restoration with traction liners and the prosthetic restoration with stretching/tensioning of the soft tissues (i.e., pin system) should be optimized accordingly to reduce revision interventions during growth.

Of note, infantile amputation is a rare occurrence and our study is the first to provide valuable insights into lower-limb amputation patterns and complications in children and adolescents in Germany over a 10-year period. Despite the high revision rate due to bony impalement, there is no alternative to amputation in terms of providing good functional outcome. That being said, our study has several limitations, the biggest of which being the limited sample size; however, because lower-limb amputation in pediatric populations is rare, we could analyze this population's characteristics in a larger dataset, even though a retrospective design limits the conclusions that could be drawn from it, given the lack of

important data outlining a better perspective on this patient population. Therefore, future research should include a larger, more widely representative dataset to further investigate, describe and analyze lower-limb amputation patterns in pediatric patients. population, secondary to the young age of included individuals. It is important to highlight an unfamiliar observation in one of our cases, where the fibula outgrew the tibia following amputation (Figure 4). Although the surgery was performed correctly and no epiphysiodesis was performed, this observation remains unclear.

stationary within amputated individuals [1]. Consistent with our findings, bony overgrowth is reported as the most prevalent complication following lower-limb amputation in adolescents, with rates ranging from 4 to 50% [19–24]. Importantly, age, location, indication for amputation, and level of amputations are perceived as attributable factors for such prevalence, whereas younger individuals are more likely to experience this complication [19,20,25]. This could be the reason for this complication being so frequent in our

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**Figure 4***.* A clinical image showing an unfamiliar observation of the fibula outgrowing the tibia in an amputated case*.* **Figure 4.** A clinical image showing an unfamiliar observation of the fibula outgrowing the tibia in an amputated case.

#### **5. Conclusions**

Lower-limb amputation in children and adolescents is a rare encounter, which is more predominant in males and is commonly indicated due to bone tumors. TF amputation is the most common level of amputation. Postoperative complications are reported in nearly half the amputated population, besides bony overgrowth. Most of these complications indicate and result in revision surgery to correct for the occurring abnormality, of which stump growth is most common. Despite the high revision rate, it must be noted that amputation is without alternative in these cases. In addition, modern prosthesis fitting usually enables patients to have very good everyday function.

**Author Contributions:** Conceptualization: A.H.; methodology: A.H.; software: A.H. and S.G.; validation: A.H. and S.G.; formal analysis: A.H. and S.G.; investigation: A.H. and S.G.; resources: A.H.; data curation: S.G. and A.H.; writing—original draft preparation: A.H. and M.G.; writing review and editing: A.H., C.P., J.K., B.L., M.A., and T.R.; visualization: S.G.; supervision: A.H.; project administration: A.H. All authors have read and agreed to the published version of the manuscript.

**Funding:** The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors. For the publication fee we acknowledge financial support by Deutsche Forschungsgemeinschaft within the funding programme "Open Access Publikationskosten" as well as by Heidelberg University.

**Institutional Review Board Statement:** This research study was conducted in accordance with the Declaration of Helsinki, and was approved on 23 September 2019 by the ethics committee, Medical Faculty of Heidelberg (protocol registration number: S-649/2019).

**Informed Consent Statement:** Patient consent was waived due to minimal risk.

**Data Availability Statement:** All the Data analyzed in this manuscript can be provided upon request by contacting the corresponding author.

**Acknowledgments:** Statistical advice was provided by Thomas Bruckner, Institute for Medical Biometry and Informatics in Heidelberg.

**Conflicts of Interest:** The authors declare no conflict of interest. Regardless, Tobias Renkawitz has received research support and personal fees from Arbeitsgemeinschaft Endoprothetik (AE), DGOU, DGOOC; BVOU, DePuy International, Otto Bock Foundation, Deutsche Arthrose Hilfe, Aesculap, Zimmer, Stiftung Oskar Helene Heim Berlin, Vielberth Foundation Regensburg, the German Ministry of Education and Research as well as the German Federal Ministry of Economic Cooperation and Development. Axel Horsch received research support from Arthrose Hilfe and Ipsen.

#### **References**