Goeran Fiedler

Assessment of Internal and External Prosthesis Kinematics during Strenuous Activities Using Dynamic Roentgen Stereophotogrammetric Analysis

Optimal performance of artificial limbs is still largely dependent on the accurate evaluation of their biomechanical behavior. The accumulated expertise of the prosthetist and indirect measurements of socket and joint kinematics are currently used in a trial and error format for prosthesis-socket performance maximization. The accurate direct unobtrusive assessment of residual limb-skin slippage within the socket during dynamic high-speed activities remains an unresolved challenge till date. This assessment is further complicated in the case of transtibial amputees who have previously undergone joint arthroplasty surgery. This study uses a new method of assessment of the combination of three-dimensional (3D) total knee prosthesis kinematics and socket-residual limb kinematics/slippage during high-speed strenuous activities using Biplane Dynamic Roentgen Stereogrammetric Analysis (DRSA) instrumentation. Marker-based assessment of dynamic socket-residual limb and residual bone telescoping motion with as much as 0.03-mm translational and 1.3 degrees rotational accuracy was demonstrated. The in-vivo dynamic accuracy for the model-based (markerless) tracking (MBT) method to track the joint prosthesis was further improved from that reported previously. Quantitatively, measurement bias between DRSA and the MBT methods ranged from −0.012 to −0.11 mm (depending on coordinate axis) for the femoral prosthesis and from 0.004 to 0.048 mm for the socket. The results from this transtibial case study indicated that maximum 3D slippage for some socket-skin-marker pairs reached values of up to 16 mm for the fast-stop task and up to 8 mm for the step-down task. Maximum “deformation” of up to 12.5% is observed for the fast-stop trials and step-down trials between skin-to-skin marker pairs. The respective deformation between skin-to-socket marker pairs reached maximum values of almost 22%. The deformation between femur/tibia edges and skin/socket marker pairs reached maximum values of almost 100%. Relative skin strain calculated from skin-marker pairs reached values that range between 0.01 and 0.1 for step-down and fast-stop trials, respectively. The relative engineering shear (γ) between selected skin-marker clusters that form orthonormal meshes ranged between 81.5 and 129 degrees. This in-vivo, patient-specific, unobtrusive dynamic information is highly accurate and allows socket-residual limb interactions to be presented using 3D visualization tools that were until recently unavailable to the clinician prosthetist. These methods can significantly impact the iterative cycle of socket fitting and evaluation.

Rehabilitation of People with Lower-Limb Amputations

Rehabilitation of persons with lower-limb amputation is a complex endeavor that requires the consideration of a multitude of factors. This article provides an overview of the current practice of prosthesis prescription, mobility training, and the utilization of wheeled mobility options in the clinical care for this population. Recent technological advancements have helped fit persons with lower-limb amputation with more functional, better fitting, and less activity-limiting artificial limbs and wheelchairs. This is exemplified in modern computer-controlled prosthetic components and biomechanically optimized socket-fitting methods, as well as light weight and versatile wheelchairs to supplement or replace prosthetic devices. In the research setting, technology has enabled new approaches to the kinematic and kinetic assessment of prosthetic interventions, and the development of more accurate fitting and evaluation methods. Despite the noted progress in the field, there is still a considerable gap between the functionality of a sound leg and even the most advanced prosthesis. It can be predicted that continued research efforts will be undertaken to further close this gap.

Effects of physical exertion on trans-tibial prosthesis users' ability to accommodate alignment perturbations

Background: It has long been reported that a range of prosthesis alignments is acceptable in trans-tibial prosthetics. This range was shown to be smaller when walking on uneven surfaces. It has also been argued that findings on gait with prostheses that were obtained under laboratory conditions are limited in their applicability to real-life environments. Objectives: This study investigated the hypothesis that efforts to compensate for suboptimal alignments by active users of trans-tibial prostheses become less effective when levels of physical exertion increase. Study design: A 2 × 2 repeated-measures analysis of variance was conducted to compare the effects of physical exertion and subtle alignment perturbations on gait with trans-tibial prostheses. Methods: The gait of eight subjects with trans-tibial amputation was analyzed when walking with two different prosthesis alignments and two different physical exertion levels. The main and interaction effects were statistically evaluated. Results: Bilateral step length symmetry and measures of step variability within the same leg were found to be affected by the intervention. There was no significant effect on index variables that combined kinematic or kinetic measures. Conclusion: Findings showed that persons with trans-tibial prostheses responded heterogeneously to the interventions. For most variables, the research hypothesis could not be confirmed. Clinical relevance Findings support the practice of allotting several sessions to the alignment of trans-tibial prostheses, as users’ gait responds differently to perturbations when external factors (e.g. exertion) change. Furthermore, the found inhomogeneity in the population of persons with trans-tibial amputation supports the use of technical gait assessment methods in clinical practice.

Leg Laterality Differences in Persons with Bilateral Transtibial Amputation: A Pilot Study Using Prosthesis-Integrated Load Cells

ABSTRACTRehabilitation of persons with bilateral transtibial amputation is challenged by the unavailability of a sound leg to provide stability in standing and gait. Absence of a sound limb complicates both prosthetic fitting and gait training. Little evidence related to prosthetic fitting and gait training of persons with bilateral amputation is available to guide these clinical procedures. This work addresses questions that are frequently encountered by prosthetists, including is there a disparity in leg strength or controllability between limbs and, if so, which is the favored or dominant leg? A disparity or leg laterality may have implications in the selection and adjustment of prosthetic components, prescription of rehabilitation therapies, or recommendations for the use of assistive devices. In this study, the gait of two persons with bilateral transtibial amputation was assessed using prosthesis-integrated load cells installed in both legs. The load cells provided continuous measurement of kinetic and temporal outcomes (forces and moments) measured during gait on different surfaces and on stairs. Pairwise comparisons of gait variables measured by each load cell were used to quantify leg laterality. The results of this study suggest that integrated load cells have the potential to assess leg laterality in persons with bilateral amputation and that these may be useful tools for enhancing the clinical decision-making process.

Effect of observation on lower limb prosthesis gait biomechanics: Preliminary results.

Background: The Hawthorne effect, a subcategory of reactivity, causes human behavior to change when under observation. Such an effect may apply to gait variation of persons with prosthetics or orthotics devices. Objectives: This study investigated whether the presence of observers directly affects the gait pattern of users of lower limb prostheses. Study design: Within-subject intervention study. Methods: Primary outcome measures were gait parameters of initial double support time and upper body lateral tilt angle, which were collected with a mobile sensor attached to the subjects’ back. To make subjects feel unwatched, a certain amount of deception was necessary, and two different conditions were created and statistically compared against each other: one in which the subjects were initially unaware of the attention of observers and another one in which the same subjects were aware of a group of observers. Results: Data from two subjects using trans-femoral prosthesis are reported. Findings included a change in step initial double support percentage by up to 14.2% (p = 0.019). Considerable changes were also noted in secondary outcome measures including speed, stride length, and stride symmetry. Conclusions: A reactivity effect of observation exists in prosthetics gait analysis. More comprehensive studies may be motivated by these preliminary findings. Clinical relevance Results of this study suggest that users of lower limb prostheses walk differently when their gait is being assessed (e.g. in the prosthetist’s office) than in situations without observers. This may in part explain the clinical experience that modifications of prosthetic fit or alignment provide only short-term betterment.

Self-efficacy in Prosthetics & Orthotics students who did and did not participate in short term study abroad programs – preliminary results

It is conventional knowledge that travel is educational and that a study stay in a foreign country contributes to a students personality formation and well-roundedness. The benefit of such experiences on attitudes that shape professional aptitude and career success may, however, be debated. It could be argued that exposure to experiences that are irrelevant to a students chosen profession may have no sizeable impact - thus not justifying the invested time and money - or, in an extreme case, may even be detrimental to career success if the wrong conclusions are drawn. Examples for such occurrences may include the adoption of inappropriate belief systems, educational priorities, or work habits. In this study, it was investigated how a short-term study stay abroad was reflected in the self-efficacy of students and graduates of a professional Master of Science program. A cohort of U.S. American students of Prosthetics and Orthotics who had participated in non-compulsory study excursions to Germany and a comparable cohort of their peers who had not participated in such trips were asked to state their confidence in mastering specific hypothetical situations of daily work life. About one half of the subjects of each group had already graduated and were in residence at the time of the survey, whereas the remaining half was still in their first year of the study program. Answers were compared using descriptive statistics and qualitative analysis to investigate main and interaction effects of professional experience and short-term stay abroad. The results seem to support the hypothesis that the experience was beneficial, making the inclusion of respective course offerings recommendable.