Interpretation of causal relationship between quadriceps tendon Young’s modulus and gait speed by structural equation modeling in patients with severe knee osteoarthritis

Abstract

Purpose: To clarify the causal relationship between quadriceps tendon stiffness and gait speed in patients with severe knee osteoarthritis (OA) using structural equation modeling. Methods: Participants were 36 patients with knee OA (median age, 75.0 [interquartile range, 67.3–76.0] years; Kellgren-Lawrence grade 3 or 4). We measured quadriceps tendon stiffness using Young’s modulus by ShearWave Elastography. Gait speed and kinematics parameters were measured using a motion analysis system. Additional data collected for each patient included age, sex, height, body weight, body mass index, femorotibial angle, knee range of motion, knee extension torque, and pain. We performed structural equation modeling for interpretation of the causal relationship. Results: The comparative fit index of the structural equation modeling was 0.990. Quadriceps tendon Young’s modulus was a predictor of maximum knee flexion angle during the swing phase (standardized partial regression coefficients [β] = –0.67, P < 0.001). Maximum knee flexion angle during the swing phase was a predictor of cadence and step length (β values 0.35 and 0.55, P = 0.035 and <0.001, respectively). Cadence and step length were predictors of gait speed (β values 0.50 and 0.63, P < 0.001 and <0.001, respectively). Conclusion: Our results showed a causal relationship between quadriceps tendon stiffness and gait speed in patients with severe knee OA. Quadriceps tendon Young’s modulus can affect gait speed through the maximum knee flexion angle during the swing phase, cadence, and step length. Adding therapeutic intervention to decrease the quadriceps tendon Young’s modulus may lead to increased gait speed.