Discussion
shoulder abduction, Mean shoulder abduction, wrist flexion improves gesture efficiency, pain, upper limb amputees, absence of sensory feedback, injuries
SAID
The main purpose of this study was to compare kinematic compensatory shoulder movement and dexterity in transradial amputees successively equipped with a Greifer and an Axon-hook during a BBT session.Mean shoulder abduction obtained during the BBT sessions was significantly greater with the Greifer compared to the Axon-Hook and with the Greifer compared to the NA side. The difference of percentage of time with shoulder abduction > 60° was more than 30% higher between the Greifer and the two other sides (Axon-Hook and NA side), but were not statistically significant. For these shoulder abduction variables, the difference between the Axon-Hook and the NA side was less than 1 degree (amplitude) and less than 1% (% of time with shoulder abduction > 60°) suggesting that the second hook could be more appropriate for limiting compensatory shoulder abduction. Although the differences were not statistically significant for percentage of time with shoulder abduction > 60° (probably due to the small number of participants and the presence of the atypical subject) these values were nonetheless of clinical relevance. This finding needs to be confirmed with a larger cohort performing the BBT.Although it is recommended that the BBT be performed in the sitting position, as was the case in this study, the literature only contains shoulder data with the BBT being performed in the standing position. In 19 standing, able-bodied subjects, shoulder abduction ranged between 15 and 20° when they were not restricted, and up to 35° when wrist and [An absence of sensory feedback and limited DOF with prostheses could be the first explanation of the compensatory movements that open the way for MSD. Secondly, the type of DOF (i.e., the rotation axis around which the movements are possible) allowed by the two hooks could explain the shoulder abduction differences. The Greifer allows wrist radial/ulnar deviation, whereas the Axon-Hook allows wrist flexion/extension, which is more suitable for a prehensive movement such as that used for the BBT. It is already known that with prosthetic hands, wrist flexion improves gesture efficiency and limits compensations [Conversely, with the Greifer, the ulnar or radial inclination of the wrist does not seem to influence shoulder abduction. The type of grip may also affect compensation: the Greifer has two movable fingertips while the Axon Hook has one movable and one stationary fingertip that may serve as a fixed support point to grab the block.The significant greater shoulder abduction observed with the Greifer may be explained by the strategy used by the participants to compensate with their shoulder when using the prosthetic limb.The question may be raised whether the wrist setting of the Greifer (ulnar or radial deviation) affects trunk compensation. The only participant (#2) having selected ulnar inclination showed predominant trunk compensation.Most participants (except #2) chose radial deviation, which indeed seems more appropriate since this hook orientation makes it easier to approach the blocks and corresponds to the movement imposed by the BBT (moving of blocks from the P side to the NA side).Irrespective of the side, the percentage of time spent with shoulder abduction > 60° during the BBT was above the threshold of 10% beyond which there is a risk of MSD [Significant greater shoulder abduction could be a source of major shoulder strain that could, in the long-term, cause pain in this joint [The study was carried out over a short period, but the repercussions of compensatory movements (MSD, pain, injuries, etc.…) only become visible after long periods of cyclic, repetitive movements. It would be interesting to follow the evolution of strategies over time on both sides (P side and NA side) and to check for the onset of MSD. Shoulder compensation is a risk on both sides. On the prosthetic side, it seems that compensatory movements are unavoidable regardless of the device used (based on currently available devices). The major concern of rehabilitation care is to help patients use the most effective and least harmful unavoidable compensatory strategy and to abandon avoidable ones. In order to do this, we need to improve our understanding of compensatory movement mechanisms and their causes. During rehabilitation, it seems essential to detect and correct avoidable shoulder compensatory strategies on the NA side that increase the risk of MSD.This study included an atypical participant (#2) who had a specific compensatory strategy. This case well illustrates the multi-articular/segmental complexity of compensatory strategies and emphasizes the importance of evaluating global compensatory strategies when carrying out a motor task. As pointed out by Metzger [Functional capacity or manual dexterity, reflected by the number of blocks moved during the BBT, was not significantly different with the Greifer and the Axon-Hook, either from a statistical or a clinical point of view, as the difference of 1.50±1.54 blocks was below the Minimum Detectable Change (MDC90 is set at 6.49 blocks for upper limb amputees [In the literature, the standard BBT had already been used to assess manual dexterity in upper limb amputees. Only one study evaluated the Greifer during a BBT session in three transradial amputees and reported a mean score of 25.6 blocks, in line with our results (25.4 blocks) [Kontson et al., in turn, used a wrist brace and finger straps in able-bodied subjects (limiting wrist radial/ulnar deviation, wrist flexion/extension, finger flexion, and restricting finger use to index and middle-finger) to simulate prosthesis DOF restrictions during BBT sessions in the standing position. In these conditions, the mean BBT score was 45 blocks, Beyond the fact that in this study there were statistical differences in compensatory movements (shoulder abduction significantly higher with Greifer than with Axon Hook), 75% of the study participants said they preferred the Axon-Hook. The notion of preference was based on multiple factors that contributed to the efficiency of the patient-prosthesis unit in the patient’s overall life project. A more detailed analysis of the reasons justifying hook preference should be carried out and factored into the prosthetic project.The rehabilitation program focusing on compensatory movements of prosthetic users should be personalized and should take into account this notion. A better understanding of compensatory strategies that would help discriminate between useful/unavoidable and harmful/avoidable ones, would allow more efficient rehabilitation care in upper limb amputees and improve their autonomy with respect to prosthetic settings. It is important that compensatory movements on the non-amputated side also be prevented.This search for more efficient compensatory strategies followed by their automation is delicate since compensatory strategies are multifactorial and depend on the patient (medical history, experience, esthetic choices…), on the prosthesis (components, settings…), on the patient-prosthesis interaction, on rehabilitation, but also on the type and complexity of the motor task needing to be performed.