Strength profiles in patients with knee osteoarthritis with and without unilateral transfemoral amputation

Abstract

Background: Individuals with lower limb amputation have increased risk of developing knee osteoarthritis (KOA) in the intact limb, however there is little information regarding strength profiles in individuals with KOA with and without amputation. Objective: To compare lower extremity strength in individuals with KOA with and without unilateral transfemoral (TF) amputation. Study Design: Descriptive laboratory study. Methods: Seven participants with unilateral TF amputation (3F/4M, 58.0 ± 11.0 years, 172.7 ± 12.8 cm, 90.8 ± 19.1 kg, 38.8 ± 14.4 years after amputation) and symptomatic KOA in the intact limb and 9 participants with unilateral KOA (control (CON)) without leg amputation (4F/5M, 66.0 ± 9.9 years, 170.5 ± 10.7 cm, 86.8 ± 18.1 kg) participated in this study. Both groups completed strength testing on the involved limb with KOA and the Knee Injury and Osteoarthritis Outcome Score (KOOS) questionnaire to meaure subjective function. Strength variables were mass-normalized. Results: There were no significant differences between groups in age, mass, or height. The CON group reported significantly reduced subjective function on the KOOS total score (P = 0.049; d = 1.03) and KOOS symptoms scores (P = 0.047, d = 0.95) compared with the TF amputation group. A lower subjective function score indicates worse function. There were no other significant differences between groups on KOOS subcategories. The TF amputation group had significantly greater average isokinetic quadriceps torque (P = 0.05; d = 1.10), peak isokinetic quadriceps torque (P = 0.02; d = 1.36), and average isokinetic quadriceps power (P = 0.02; d = 1.38) compared with the CON group. There were no differences between groups in isometric knee extensor strength or any differences in knee flexor isokinetic or isometric strength. Conclusions: The TF amputation group demonstrated greater isokinetic knee extensor strength in their intact limb with KOA compared with the CON group osteoarthritic limb; however, there were no differences in isometric strength. Furthermore, the differences in isokinetic strength may suggest that those with a history of leg amputation may require more strength and power in the intact limb to maintain daily activity and, therefore, may require greater thresholds of strength to protect the knee joint from cartilage degradation.