the advent of minimally invasive surgery has provided surgeons new techniques for treating clinical disease . within the field of spinal surgery ,
techniques in lumbar interbody arthrodesis have shown a continued evolution of procedural approach and instrumentation .
minimally invasive spine surgery aims to reduce approach related morbidity , while producing clinical outcomes comparable to its open predecessors .
one important example of this is the development of minimally invasive techniques for lumbar interbody fusion , including transforaminal lumbar interbody fusion ( tlif )
.   the mi - tlif technique , has displayed comparable outcomes to open tlif , while adding the benefits of less approach - related morbidity , decreased intraoperative blood loss , and shorter hospital stays .
however , critics of the technique have noted that the mi - tlif has longer operative times and exposes patients to increased fluoroscopic radiation . over the past decade
mi - tlif has been shown to have a number of benefits , especially with regard to peri - operative outcomes .
ultimately , comparing the known literature of a traditional , open tlif approach to published reports on mi - tlif will identify the unique risks and benefits associated with each .
this understanding may help guide improved clinical decision making for patients presenting with lumbar degenerative disk disease .   in this paper
, we evaluate the literature to examine the efficacy of mi - tlif compared to its open counterpart .
in addition , key studies discussing the risks and benefits of mi - tlif were included to more thoroughly explore the nature of the technique and its application .
in this paper , the authors have used the pubmed / medline search engines to search for relevant reports addressing the topic of transforaminal lumbar interbody fusion .
, a few historical reports have been added for completeness . included in this search was the following key phrases :  minimally invasive ,  
further , although articles were first identified by abstract , only full text manuscripts were used to compile this review of the topic .
further , inclusion criteria were based on the study 's contribution in terms of original data , technical variations , and contrasts between open and minimally invasive versions of the procedure ideally completed at the same institution . in total , 14 articles were selected on the aforementioned basis . all contributed to the established body of the literature pertaining to lumbar arthrodesis techniques , particularly different variants of tlif .
six of the 14 articles were prospective studies , while the remaining 8 were retrospective ( table 1 ) .
after failed conservative management for a minimum of 6 months , surgery becomes the next therapeutic option for patients presenting with degenerative disc disease ( ddd ) , radiculopathy with spinal instability , and/or grade 1 spondylolisthesis .
initially patients are assessed through radiological investigations including x - ray ( ap , lateral , flexion , and extention ) , and noncontrast lumbosacral mri . length of hospitalization
is determined by postoperative pain control and functional dependence , with patients of advanced age or medical comorbidities often requiring longer postoperative recovery . however , a majority of patients are admitted the day of surgery and discharged within 2472 hours after operation . under general anesthesia ,
the patient is prepped and draped in standard fashion , and a fluoroscopic c - arm is positioned in the sterile field . under fluoroscopic guidance
the appropriate level is marked and a 3  cm incision is made 4.5  cm of off midline .
a k - wire is targeted to the bony complex at the surgical level and serial dilators are consecutively passed to split the muscle fibers .
a working channel is placed , the dilators are removed , and the channel is secured appropriately for adequate visualization of the medial portion of the facet and inferior lamina .
a curette is used to detach the ligamentum flavum from the inferior edge of the lamina , and a kerrison is used to perform the hemilaminectomy .
the unilateral facet can be removed using an osteotome or high - speed drill . following adequate exposure of the disc space
curved and angled curettes and a disc scraper are then used to prepare the end plate .
an appropriately sized interbody spacer is inserted into the disc space , and a half sponge of bmp is packed into the disc space .
after removal of the working channel , a jamshidi needle is localized to the unilateral pedicle either above or below the discectomy level , and positioning is checked using fluoroscopic imaging .
a k - wire driver is used to insert a guide wire into the superficial portion of the pedicle . a sextant percutaneous screw system ( medtronic inc ; memphis , tn )
is used to pass a cannulated pedicle screw over the k - wire and into the pedicle under fluoroscopic guidance .
this is repeated at all desired pedicles on either side . the sextant holding sleeves are mated , the percutaneous rod holder and guide are attached , and a small skin incision is made to pass the rod percutaneously through the screw head .
after correct positioning of the rod is confirmed with fluoroscopy , the screw head is tightened , the rod holder is released , and the holding sleeve is removed .
skin closure is accomplished in the standard fashion . for a full detailed description see lawton et al . , see figures 1 and 2 for illustrative cases from patients treated with the mi - tlif procedure .
as noted , our review included 14 articles . follow - up times ranged across all articles from 6 months to 42 months .
the mean follow - up was 20 months , with a mean patient cohort of 52 patients . within seven of the articles that directly compared outcomes of open tlif with mi - tlif ,
mean duration of mi - tlif surgery was 220 minutes , compared to 218 minutes for its open counterpart .
furthermore , blood loss was found to be on average 282  ml in mi - tlif cases , while open tlif resulted in 693  ml of blood loss .
the length of stay for mi - tlif was found to be 5.6 days , while open tlif had patients in the hospital for an average of 8.1 days ( see table 2 ) .  
though the literature displayed possible benefit of mi - tlif relative to its open counterpart , both procedures are associated with possible complications .
major sources of complications shared by mi - tlif and open tlif are allograft malposition , pedicle screw malposition , and infection . some minor complications found in both open and mi studies were hematoma , anemia , and cerebrospinal fluid leakage . in both lumbar arthrodesis techniques , placement of a k - wire is necessary , and this k - wire is held in place to formally place the expandable retractor moving the k - wire could result in entrance to the vertebral canal and possible damage to the nerve roots or cauda equina , which had the potential to occur in either tlif technique .  
complications more likely to be found in the open tlif approach include infections and muscular trauma as a result of the increased exposure and soft tissue dissection .
in addition , increased exposure has been shown to be potentially associated with 23.5% of reported complications being infectious in nature , within the open tlif studies .
open tlif may have a slightly lower rate of neurological complications , for neurological deficits were a considerably lower proportion of total complications , 11.8% , when compared to mi - tlif 's 20.7% .
however , there were a greater variety of unique complications to open tlif , as shown by 23.4% of complications coming in the form of dural tears , ileus , and atelectasis among others .
please refer to table 3 for further analysis .   in the mi - tlif literature reviewed , many authors discussed the challenging learning curve associated with mi - tlif , which makes certain complications , particularly those related to instrumentation more likely .
endoscopic visualization of the spinal structure limits the field of view for the surgeon , making identification of already unfamiliar landmarks even more difficult .
though visualization techniques have improved over time , percutaneous fixation systems do not have the ability to reposition three dimensionally .
tubular dilator retractors can result in poor decompression while resulting in higher rates of neurological injuries .
of all complications presented in the mi - tlif comparative literature , approximately 1 in 5 were related to neurological complications ( table 4 ) .
. wrote of possible inexperience leading to inappropriate placement of transpedicular screws , and inadequate preparation of intervertebral cage and fusion site which can lead to further instrumentation related complications .  
the operative surgeon additionally must be familiar with 3d lumbar anatomy and be able to carefully interpret 2d radiographic images to make a mental reconstruction .
this is a unique skill and one that is not as critical with a traditional , open approach .
the surgeon must be able to read anterior - posterior and lateral imaging in order to accurately insert percutaneous pedicle screws , thereby allowing for possible misinterpretation leading to complications .
screw misplacement and cage migration or subsidence accounted for 44.8% of complications reported in mi - tlif comparative studies .  
mi - tlif itself presents with increased risk to the surgeon related to increased radiation exposure due to lengthened intraoperative fluoroscopy times .
though many may claim that a surgeon 's experience level with minimally invasive procedures will dictate their fluoroscopy times , some studies found no significant difference as experience increased .
very few studies reported the duration and radiation exposure resulting from x - ray and fluoroscopy .
authors who did report this data found that mi - tlif had greater duration of radiation exposure for patients undergoing the procedure [ 3 , 5 , 7 ] . due to the relative recent adoption of mi - tlif use , the long - term effects of increased radiation exposure have not been evaluated .
the development of 2d computer assisted fluoroscopy systems as well as the o - arm is a modern means to decrease this exposure risk .
following data collection and the literature review , it is clear that there is a paucity of data comparing mi - tlif and open tlif . to our knowledge , there remains no high - class studies that directly compare these two techniques .
however , smaller studies , both prospective and retrospective in nature , have shown promise in regards to novel mi techniques for tlif .   scheufler et al . compared percutaneous transforaminal lumbar interbody fixation ( ptlif ) with mini - open transforaminal lumbar interbody fixation ( otlif ) while utilizing the wiltse method .
they found at 8 month and 16 month follow - up , overall clinical outcome did not differ between the two techniques .
however , in terms of pain following the operation , ptlif resulted in significantly lower levels of pain ( p < 0.01 ) .
though the study showed no decreased advantages due to the percutaneous approach , a longer prospective study would be needed to further discern the success and functionality of each multilevel fusion .   in a study examining 42 patients with mean follow - up time of 29 months , dhall et al .
the authors found that mean estimated blood loss for mini - open ( 194  ml ) was significantly lower ( p < 0.01 ) than the open - group ( 505  ml ) .
the length of stay was decreased for mini - open patients by on average , 2.5 days ( p < 0.01 ) . however , there were complications of neurologic nature in 2 patients , while 2 other patients required further revision .
all 42 patients displayed fusion , and the authors felt that the mini - open technique was a possible substitute to open tlif .
performed one of the earlier studies ( 2001 - 2002 ) on 49 patients who had mi - tlif
. majority of patients in the study either had degenerative disc disease with herniated nucleus pulposus ( hnp ) or spondylolisthesis .
mean operative times were approximately 240 minutes , approximate blood loss was 140  ml , and hospital stays averaged 1.9 days .
complications were limited to four patients , two of which required screw repositioning while two others developed radiculopathy following the procedure .
vaps changed on average from 7.2 to 2.1 while odi changed from 46 to 14 from preoperative assessment to final follow - up . ultimately , all patients in the study had fusion on follow - up imaging .
the author believed that mi - tlif is at least equivalent if not a marked improvement over its open counterpart .
a variation of the accepted microendoscopic discectomy was completed by isaacs and colleagues , which was termed metlif .
metlif resulted in less blood loss , shorter hospital stays , and decreased postoperative narcotic administration .
there were no associated procedural complications associated with the multicenter study . ultimately , this new variation showed promise .  
schizas et al . examined their institutional experience executing both mitlif and open midline transforaminal lumbar interbody fusion .
the study found that length of surgery , postoperative pain , analgesia requirements , and vas / odi scores were not significantly different between the mi and open procedures .
however , they did find that the mi - tlif did result in significantly less blood loss and a shorter hospital stay .
complications found in the mi - tlif group , three pseudorthrosis , may have likely been due to the surgeon 's gradual adjustment to the novel instrumentation and visualization techniques associated ( table 5 ) .
lumbar arthrodesis is an effective method for treating spinal pathology such as spondylolisthesis , ddd , and spinal instability .
as minimally invasive spine procedures have emerged , variants such as minimally invasive discectomy and minimally invasive cervical foraminotomies have allowed for reduced complications related to tissue trauma , while reducing blood loss and shortening recovery time [ 4 , 8 , 19 , 20 ] .
however , no procedure comes without inherent risks . due to mi - tlif being a novel procedure for some surgeons , it takes increasingly longer for them to become effective in carrying it out .
compared safety and effectiveness of mi - tlif and open tlif , showing similar long - term outcomes over the course of the 37.5-month follow - up period . assigning 63 patients to the open arm and 76 patients to the minimally invasive arm of the study , the authors matched by prior lumbar surgery , diagnosis , and levels at
they found significant improvement in mean estimated blood loss ( p < .0001 ) for mi ( 163.0  ml ) versus the open tlif ( 366.8  ml ) .
the study found improvements ( p = 0.02 ) in mean duration of hospitalization in mi - tlif ( 3 days ) relative to their open counterparts ( 4.2 days ) .
in addition , rates of neurological deficit were significantly higher ( p = 0.02 ) in the minimally invasive arm of the study ( 10.2% ) compared to the open cohort ( 1.6% ) .
operative times , mean change in vas scores , patient satisfaction , all significantly favored the open tlif procedure .
the authors hypothesized that the neurological deficits and other factors in favor of open tlif could have occurred as a result of the surgical learning curve .  
once the procedure is mastered , its application can positively impact patient care in numerous ways .
but , the fundamental advantage of mi - tlif comes from its decrease in tissue trauma and overall exposure of the patient .
a prospective cohort study was carried out by shunwu et al . with 62 patients that had undergone single level tlif by a single surgeon in a single hospital .
one cohort of 32 patients underwent mi - tlif with the tubular retractor system , while the remaining patients underwent open tlif .
serum creatine kinase levels , a measure of soft - tissue trauma , was measured on the third postoperative day .
also , time to ambulation and number of transfusions were also measured in the study .
shunwu and colleagues found that mi - tlif resulted in significantly lower serum creatine kinase levels were found , while patients needed less transfusions and were able to walk earlier than their open counterparts .
when comparing the two approaches , this study displayed that mi - tlif still proposes significant quantifiable benefit in terms of decreased soft tissue trauma .  
as a minimally invasive procedure , mi - tlif can be utilized to treat particular pathologies , while maintaining the same high levels of clinical success as the open tlif , even with over two years of follow - up .
park and foley contributed an article to the literature that described mi - tlif in 40 consecutive patients who were diagnosed with spondylolisthesis .
their percutaneous approach resulted in reduction of spondylolisthesis in all cases , with an average follow - up time of 35 months .
the average odi decreased from 55 to 16 , while the vas scores decreased from 65 to 8 in leg and 52 to 15 in back .
this was yet another proof of mi - tlif being a possible replacement to open tlif in patients with degenerative or isthmic spondylolisthesis . in a prospective study that contrasted clinical and imaging outcomes for mi - tlif and open tlif procedures , peng et al
. found that mi - tlif had equivalent long - term outcomes with open tlif .
the patient cohort had 29 patients in each arm of the study , and 48 of 58 patients were women .
the study examined , fluoroscopic times and found that mi - tlif had significantly ( p < 0.05 ) longer ( 105.5 seconds ) compared to open ( 35.2 seconds ) .
thus , it is clear that the mi - tlif cases ran significantly longer overall .
then , the authors discussed the significantly less blood loss , less morphine , and short hospitalization utilized for patients in the mi - tlif cohort . yet , open tlif and mi - tlif both were very similar in providing significant benefit to patients when rated by odi , nass , and vas , all at follow - ups of six months and two years .
in addition , there was no significant difference between open and mi - tlif in terms of fusion rates , both which were approximately 80% .
peng and colleagues presented data that was supportive of mi - tlif in terms of pain , hospitalization , and recovery , while at the same time retaining the high - fusion rate associated with open tlif at two year follow - up .   aside from particular pathologies that would benefit from mi - tlif , there are certain populations that could benefit from the decreased tissue disruption and decreased blood loss . in elderly patients , lee et al . completed a retrospective review of 27 consecutive cases and found a low complication rate and beneficial outcomes for patients over the age of 65 .
the average age of patients in the study was approximately 70 years , and each underwent a mini - open tlif .
they were then followed up for three years , displaying fusion rates of nearly 80% , similar to that seen in other studies .
however , 44% of patients displayed adjacent segment degeneration , which was statistically significant in terms of its relation to sacral tilt following the procedure ( p = 0.006 ) .
two patients experienced minor complications in the perioperative period , one being a drug eruption and the other a urinary tract infection .
overall , the authors strongly felt that mini - open tlif is a low - risk , beneficial option for the elderly .
though the studies presented displayed heterogeneous patient populations with different indications for lumbar arthrodesis , there were many patterns seen across studies . aside from possible complications such as screw displacement and neurological deficit , which were often related to a steep learning curve
, mi - tlif displayed no significant disadvantages when compared to open tlif or other standard lumbar fusion techniques .
the risks of blood loss , narcotic administration , pseudorthrosis , and infection all are equivalent if not decreased when utilizing mi - tlif as a possible technique . various postoperative recovery and
mi - tlif and open tlif are quite similar in absolute indications and often present with similar complications , thus a randomized clinical trial would be beneficial in further elucidating the risks and benefits associated with each .
as other variations emerge for mi - tlif , such as metlif , there is still need for an overall meta - analysis of all available data , comparing minimally invasive technique to traditional , open procedures .
 this paper reviews the current published data regarding open transforaminal lumbar interbody fusion ( tlif ) in relation to minimally invasive transforaminal lumbar interbody fusion ( mi - tlif ) . 
 introduction . 
 mi - tlif , a modern method for lumbar interbody arthrodesis , has allowed for a minimally invasive method to treat degenerative spinal pathologies . 
 currently , there is limited literature that compares tlif directly to mi - tlif . 
 thus , we seek to discuss the current literature on these techniques . methods . using a pubmed search , we reviewed recent publications of open and mi - tlif , dating from 2002 to 2012 . 
 we discussed these studies and their findings in this paper , focusing on patient - reported outcomes as well as complications . 
 results . 
 data found in 14 articles of the literature was analyzed . using these reports , we found mean follow - up was 20 months . 
 the mean patient study size was 52 . 
 seven of the articles directly compared outcomes of open tlif with mi - tlif , such as mean duration of surgery , length of post - operative stay , blood loss , and complications . conclusion . 
 although high - class data comparing these two techniques is lacking , the current evidence supports mi - tlif with outcomes comparable to that of the traditional , open technique . 
 further prospective , randomized studies will help to further our understanding of this minimally invasive technique . 
1. Introduction
2. Materials and Methods
3. MI-TLIF Technique
4. Review of the Literature
5. Discussion
6. Conclusion