Musculoskeletal Differences Between Amputated and Non-Amputated Lower Limbs

Purpose: People with lower limb amputations frequently experience greater risks of musculoskeletal injury. Forces active during walking help to develop and maintain the shape, volume, and strength of musculoskeletal tissues. Conversely, altered walking patterns following limb loss may lead to atrophy of muscle and bone tissues. Reductions in joint spaces are indicative of excess stress placed on the limb, which may lead to osteoarthritis. Bone loss in high stress regions like the femoral neck can reduce the bone's ability to resist compressive or rotational movements, making the bone more susceptible to fracture. The aim of this study was to measure musculoskeletal differences between an individual's residual (amputated) limb and intact (non-amputated) limb to identify structures vulnerable to injury. We hypothesized that the residual limb, compared to the intact limb, would show: 1) less muscle mass and more fat as indicators of muscle atrophy, 2) wider hip and knee joint spaces as indicators of osteoarthritis in the intact limb, and 3) decreased femoral neck width as an indicator of fracture risk. Methods: CT scans of 10 males (42-79 years) were obtained from the New Mexico Decedent Image Database. 3D Slicer software was used to measure gross skeletal properties, hip and knee joint dimensions, and cross-sectional muscle and fat tissue areas at the midshaft. A Wilcoxon Signed-Rank test was used to assess the differences between residual and intact limbs. The significance level was set at α ≤ 0.10 due to a small sample size. Results: Compared to the intact limb, the residual limb had significantly less muscle tissue area (p=0.010) and a significantly narrower femoral neck width (p=0.077). No significant differences were found in hip or knee joint spaces between limbs. Conclusions: In agreement with hypotheses 1 and 3, these results suggest residual limbs are at increased risk of muscle atrophy and femoral neck fracture compared to intact limbs. Loading inequalities between the residual and intact limb likely contribute to these results. A better understanding of the structural properties associated with musculoskeletal atrophy could inform targeted therapies to reduce the likelihood of injury in this population. Future studies will assess biomechanical properties, such as moment of inertia, to better understand the residual limb's ability to withstand torsional forces and fracture. Additional data on how musculoskeletal tissues respond to unloading at multiple structural levels can improve clinical interventions for lower limb strength and function in amputees.