Hip Joint Muscle Forces during Stair Ascent Following Total Knee Replacement

Abstract

The number of total knee replacement (TKR) surgeries have increased steadily in recent years. Research has shown that TKR patients have to compensate during stair walking following surgery, especially at the hip joint. Muscle modeling techniques have been utilized to simulate muscle force during specific movements. An understanding of the hip muscle forces during stair ascent following TKR would provide a greater understanding of the compensation necessary by TKR patients. Thus helping direct physical therapy interventions both prior to and after a TKR. PURPOSE: To compare hip joint muscle forces between health and TKR patients during stair ascent. METHODS: Five TKR (age: 63.6) and five healthy (age: 57.8) participants performed stair ascent using a 5-step staircase with 3 instrumented steps at a self-selected pace. A generic model of 12 segments, 19-degrees of freedom and 92 muscle (Gait 2392 Model, OpenSim 3.0.1, SimTK, Stanford, CA, USA) was used to simulate muscle forces of the major muscles surrounding the hip joint during the stance phase of the second step during stair ascent. RESULTS: During the loading phase, TKR patients had greater peak muscle force of the sartorius (0.68 N/kg vs. 0.34 N/kg), tensor fascia latte (0.88 N/kg vs. 0.54 N/kg), illiacus (5.49 N/kg vs. 1.77 N/kg), and psoas major (5.91 N/kg vs. 2.95 N/kg) when compared with healthy individuals (p < 0.05). During the push-off phase, the peak sartorius (0.68 N/kg vs. 0.42 N/kg) and adductor magnus (1.12 N/kg vs. 0.63 N/kg) muscle forces were greater in TKR patients compared to controls, while the adductor longus muscle force was greater in controls (1.09 N/kg vs. 0.65 N/kg). CONCLUSION: TKR patients in this study showed greater force in muscles responsible for hip flexion, abduction and lateral rotation during the loading phase of gait. During push-off the results were not as consistent. The adductor magnus force was greater, while the adductor longus force was reduced in TKR participants compared to controls. This study suggests that there are muscle force compensations at the hip joint during stair ascent following a TKR. The findings of this study suggest a number of muscles that have greater force demands during stair ascent following a TKR. Strengthening these muscles in post-TKR therapy may be one way to improve the recovery following surgery.