Abstract
ObjectiveFemoral offset (FO) restoration is significantly correlated with functional recovery following total hip arthroplasty (THA). Accurately assessing the effects of FO changes on hip muscles following THA would help improve function and optimize functional outcomes. The present study aimed to (1) identify the impact of FO side difference on the hip muscle moment arms following unilateral THA during gait and (2) propose the optimal FO for a physiological hip muscle function.MethodsIn vivo hip kinematics from eighteen unilateral THA patients during gait were measured with a dual-fluoroscopic imaging system. The moment arms of thirteen hip muscles were calculated using CT-based 3D musculoskeletal models with the hip muscles’ lines of actions. The correlation coefficient (R) between FO and hip muscle moment arm changes compared with the non-implanted hip was calculated. We considered that the FO reconstruction was satisfactory when the abductor moment arms increased, while the extensor, adductor, and flexor moment arms decreased less than 5%.ResultsA decreased FO following THA was significantly correlated with a decrease of the abductor and external rotator moment arms during the whole gait (R > 0.5) and a decrease of extensor moment arms during the stance phase (R > 0.4). An increased FO following THA was significantly associated with shorter flexor moment arms throughout the gait (R < −0.5) and shorter adductor moment arms in the stance phase (R < −0.4). An increase in FO of 2.3–2.9 mm resulted in increased abductor moment arms while maintaining the maximum decrease of the hip muscles at less than 5.0%.ConclusionAn increase of 2–3 mm in FO could improve the abductor and external rotator function following a THA. Accurate surgical planning with optimal FO reconstruction is essential to restoring normal hip muscle function in THA patients.
Highlights
Total hip arthroplasty (THA) is an effective method for treating end-stage hip diseases (Schmalzried et al, 2000; Michaelsson, 2014; Yi et al, 2019)
To optimize the range of femoral offset (FO) difference, we considered that the FO reconstruction was satisfactory when the abductor moment arm increased, while other muscle moment arm decreased less than 5% (Arnold et al, 2000)
When FO difference is less than the recommended range (2.3–2.9 mm), focus on the training extensor, abductor, and external rotator, while when FO is larger than the range, focus on the training adductor and flexor
Summary
Total hip arthroplasty (THA) is an effective method for treating end-stage hip diseases (Schmalzried et al, 2000; Michaelsson, 2014; Yi et al, 2019). Accurate biomechanical reconstruction of the hip anatomy following THA allows for physiological muscle activities and restoration of hip function with fewer complications (Girard et al, 2006; Rudiger et al, 2017). A prospective cohort study of 222 patients demonstrated that a decrease in FO of more than 5 mm compared to the nonimplanted side was associated with poor functional recovery, weak hip abductor muscle, and more use of the walking aids (Mahmood et al, 2016). Bjordal and Bjorgul (2015) found that intraoperative FO repair could promote the recovery of the abductor moment arms, rebuilding the balance of the peri-hip muscle group, which is conducive to the rehabilitation of joint function following THA. Optimizing the FO for restoring physiological hip muscle function in patients with THA is crucial. Previous studies primarily measured FO and abductor moment arms using plain radiographs and compared these measurements in static positions (Pierchon et al, 1994; Mahmood et al, 2016)
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