Effects of Mobility Grade, Age, and Etiology on Functional Benefit and Safety of Subjects Evaluated in More Than 1200 C-Leg Trial Fittings in Germany

Introduction: Mobility grade (MG) rating is often used to indicate or contraindicate the use of a microprocessor-controlled prosthetic knee component for individuals with transfemoral (TF) limb loss. Methods: A retrospective cross-sectional analysis of a cohort that underwent a C-Leg or C-Leg compact trial fitting was conducted. Data were retrieved on standardized questionnaires from 445 prosthetic fitting centers. Utilization of functional benefits as assessed by both subjects and their practitioners was obtained on either 5-point Likert scales or corresponding measures. Correlations of functional benefits with age, MG, and amputation etiology were tested. Responders were defined as subjects receiving ratings within the top 40% of the respective scale. A logistic multiple regression model was used to calculate effect sizes. Results: Data on 1223 subjects (mean age, 55.6 years; predominantly male [83%]) were investigated. Eighty-eight percent of the trial fittings were conducted in a single day. The cohort was stratified based on age (21–40 years, 13.7%; 41–60 years, 44.1%; >60 years, 38.2%), MG (MOBIS: MG2, 38.4%; MG3, 39.2%; MG4, 6.5%), and amputation etiology (vascular disease including diabetes [24%] and other [76%]). Subjects showed a high potential to change MG after having been fitted with a C-Leg (MG2–MG3, 50%; MG3–MG4, 22%). The number of reported falls was high; 82% reported at least one fall in the past 12 months, 49% reported multiple falling in this period. The utilization of functional benefit (responsiveness) was related to safety (83%), relief of sound limb (95%), capability to divide attention (94%), gait pattern harmonization (95%), variation of gait speed (93%), overall reduction in walking effort (88%), and reduction in walking aids (23%). Kendall τ detected either none or weak correlations of functional benefit with age, MG, or amputation etiology. The multiple regression model calculated predictive power of the stratifiers to range between 0.7% and 9%. Conclusions: Responders are not limited to specific age groups, MGs, or amputation etiologies. The utilization of functional benefits is not correlated with age, MG, or etiology of the amputation nor do any of these factors possess any relevant predictive power. Rather, the responsiveness is highly independent of age, MG, and amputation etiology. Furthermore, it seems that technology itself substantially influences MG rating. Therefore, we find it important that the potential benefits of an microprocessor-controlled knee (MPK) are assessed on an individual basis. The present study suggests that a prediction of an individual’s capability to utilize the functional benefits of C-Leg solely on grounds of the aforementioned factors or their interdependencies is hard to argue.