Bone Strength Loss and Muscle Atrophy in Residual Limbs of Unilateral Lower Limb Amputees

Abstract

With amputation, there is prolonged unloading of the bone(s) in the residual limb and a change in the muscle attachment points, leading to possible decreases in muscle size and bone strength. PURPOSE: The purpose of this study was to examine the effect of amputation on bone strength, muscle cross-sectional area (MSCA), body composition, and areal bone mineral density (aBMD) by comparing the intact and residual limbs in unilateral above-knee (AKA) (n=7) and below-knee (BKA) (n=7) amputees. METHODS: AKA and BKA subjects (23-63 years of age) who had been ambulatory with a prosthesis for at least 6 months gave informed consent to participate in this study. Polar strength strain index (SSI), a measure of torsional bone strength and MCSA were assessed at the distal end of the residual limb (femur for AKA and tibia for BKA) and a comparable cross-sectional slice on the same bone(s) of the intact limb using pQCT (Stratec XCT 3000). aBMD and body composition of the total body was assessed using DXA (GE Lunar Prodigy, enCORE version 10.50.086). RESULTS: MCSA and polar SSI in the residual limb were significantly less (p<0.05) than in the intact limb for both above- and below-knee amputees (Table 1). Leg % fat did not significantly differ between limbs (p>0.05). Percent differences (BKA 71-146%; AKA 38-150%) in MCSA and SSI values between legs did not significantly differ between groups (p>0.05).Table 1: Muscle Cross-Sectional Area (MCSA) and Polar Strength Strain Index (SSI)CONCLUSIONS: The end of the residual limb shows significant bone strength loss and muscle atrophy after amputation compared to the intact limb. Level of amputation did not affect the differences in SSI and MCSA between the limbs.