Joint Reaction Forces Decrease Following Total Knee Arthroplasty up to 12-Months Post-Surgery

Changes in mechanical loading following total knee arthroplasty (TKA) are a critical factor that is important to understand with respect to component fixation. The aims of this study were to estimate medial, lateral, and total knee joint contact forces preoperatively, and then at 3-, 6-, and 12-months postoperatively. Joint reaction forces (JRFs) were estimated using an electromyography (EMG) informed musculoskeletal modeling workflow with models scaled using computed tomography (CT) scans and weightbearing X-rays, for lower limb alignment. Joint loading peak values and impulses were estimated in 22 participants awaiting primary TKA for osteoarthritis (OA) (median age, range: 69, 49-80 years; median BMI, range: 33, 25-40 kg/m²) during level gait and sit-to-stand at each timepoint. Medial, lateral, and total JRF peak values and impulses reduced significantly postoperatively at 3-months and did not return to preoperative values at 12-months for either activity. During level gait, mean total JRF peak values reduced by 0.72 BW (p < 0.001) (medial mean difference: 0.39 BW, p < 0.001; lateral mean difference: 0.23 BW, p < 0.001) at 3-months post-surgery. A similar trend was observed in the sit-to-stand activity with a mean decrease of 0.44 BW in the peak total JRF at 3-months (p < 0.001). Impulse values followed a similar trend to the peak values. Clinical relevance: People do not return to preoperative JRFs even at 12-months post-TKA, and this may be a contributing factor for previously reported decreases in BMD around femoral and tibial components.