Contribution Of Achilles Tendon Mechanical Properties To Torque Steadiness In Persons With Transfemoral Amputation

Background:How Achilles tendon mechanics and plantar flexion strength and torque steadiness are altered in the intact leg of persons with trauma-related amputation is unknown. Understanding Achilles tendon mechanics following amputation will further inform rehabilitation approaches to enhance posture, balance, and force control.Objective:Conduct a pilot study to quantify plantar flexion maximal voluntary contraction torque, torque steadiness, and Achilles tendon mechanics in persons with unilateral trauma-related transfemoral amputation and controls without amputation.Study design:Cross-sectional study.Methods:Isometric plantar flexion maximal voluntary contractions were performed with the intact leg of ten males with transfemoral amputation (48 +/- 14 years) and the dominant leg of age-matched male controls without amputation. Torque steadiness was calculated as the coefficient of variation in torque over 6 s during submaximal tracking tasks (5%, 10%, 25%, 50%, and 75% maximal voluntary contraction). Achilles tendon elongation and cross-sectional area were recorded with ultrasound to calculate strain, stress, and stiffness.Results:Maximal voluntary contraction and torque steadiness did not differ between persons with amputation (90.6 +/- 31.6 N m, 3.7 +/- 2.0%) and controls (95.8 +/- 26.8 N m, 2.9 +/- 1.2%; p > 0.05). Tendon stiffness (21.1 +/- 18.2 N/mm) and strain (5.2 +/- 1.3%) did not differ between groups (p > 0.05). Tendon cross-sectional area was 10% greater in persons with amputation leading to 29% lower stress (p = 0.021). Maximal voluntary contraction was a predictor of a lower coefficient of variation in torque (R-2 = 0.11, p < 0.05).Conclusion:Persons with trauma-related transfemoral amputation do not differ in plantar flexion maximal voluntary contraction and torque steadiness of the intact leg compared with controls without amputation. Larger tendon cross-sectional area reduces stress and enables distribution of force across a greater area.