Graphpad prism 8 number at risk
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Previous studies focused on the effect of abductor muscles on hip dislocation however, the association of muscles around the hip joint (including the psoas, iliac, and gluteus maximus (Gmax) and medius (Gmed)) with the FR angle or hip dislocation remains unclear.
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Hence, muscle atrophy due to surgical damage or disuse may have a greater effect on the postoperative femoral position in revision THA patients than in primary THA patients. The muscles may also affect the FR alignment. The muscles around the hip joint affect its stability, which is an important factor in preventing postoperative hip dislocation in THA patients. An external femoral rotation (FR) in revision THA patients may increase the functional angle of SA or risk of prosthetic or bony impingement and risk of hip dislocation in leg extension position, but this relationship has not yet been investigated. In revision cases, excessive external rotation of the femur is often observed at an early stage after surgery, although several studies demonstrated that internal changes occur in the femoral position of primary THA patients. Recurrent dislocation is among the major complications of THA, and the incidence rate of dislocation is higher in revision THA patients than in primary THA patients. Recent studies demonstrated the important effects of pelvic and femoral positions on anatomical and functional changes in the cup and SA angles, revealing the importance of tailored planning for the cup and SA that depends on the posture of THA patients. Using the combined anteversion technique for the cup and stem anteversion (SA) angle can minimize the risk of hip impingement during daily hip motions in total hip arthroplasty (THA) or revision THA patients. Patients who have undergone revision THA and have an excessive external FR may require careful monitoring for possible hip dislocation due to hip joint instability and impingement. Revision THA frequently causes an external FR that functionally increases the SA and impingement risk, particularly in hips with 2-stage revision with psoas and gluteus medius muscle atrophy. The odds ratio of FR and impingement distance for hip dislocation was identified as 1.061(95% confidence interval (CI): 1.011–1.114) and 0.901 (95% CI 0.820–0.991), respectively. FR, functional SA, impingement distance, CT density of psoas and gluteus medius muscle, body mass index, number of past operation, and ratio of 2-stage revision THA were significantly different between cases with dislocation and non-dislocation. During follow-up period, eight cases of revision THA showed hip dislocation. The independent factors associated with external FR in multivariate analysis were the anatomical SA, CT densities of the psoas, gluteus medius and maximus muscles, and 2-stage revision ( R 2 = 0.559). External FR was significantly correlated with anatomical SA ( r = − 0.54) and increase in functional SA ( r = 0.36), which was significantly correlated with impingement distance ( r = 0.46). Resultsįorty-five hip cases (81.8%) showed external FR (mean 13.0°). The patient background, angle of anatomical and functional SA, FR angle, sizes and densities of muscles around the hip joint, impingement distance, and consequence of postoperative hip dislocation were assessed by reviewing their medical history and imaging data that includes computed tomography (CT) scans before and after surgery. We enrolled 51 revision THA patients (55 hip cases). This study was conducted to investigate the prevalence of external FR, identify the factors associated with external FR, and determine the association of FR and other factors with hip dislocation in revision THA. Excessive external femoral rotation (FR) can functionally increase stem anteversion (SA) and is often observed at an early stage after surgery in revision total hip arthroplasty (THA).