Range of motion simulated with patient-specific three-dimensional simulation analysis for evaluating anterior dislocation after total hip arthroplasty.

BACKGROUND: Dislocation is a common complication following total hip arthroplasty (THA). In our previous study, we investigated range of motion (ROM) before impingement using computed tomography-based three-dimensional simulation analysis (simulated ROM). We found significant differences between patients with and without posterior dislocation. However, it is unclear whether the simulated ROM was related to anterior dislocation after THA.

METHODS: In this study, we compared simulated ROM in patients with and without anterior dislocation (n = 12 and 36, respectively). Risk factors were also compared including preoperative hip bone morphology, implant position, change of femoral offset, change of leg length, ischiofemoral length, ischial angle, and spinopelvic parameters.

RESULTS: Mean external rotation at neutral (ER) angle, extension angle, cup anteversion, and ischiofemoral length were significantly different between the groups (p = <0.001, <0.001, 0.018, 0.026, respectively). Receiver-operating characteristic curve analysis identified cutoff points for ER angle, extension angle, cup anteversion, and ischiofemoral length of 36.5°, 31.5°, 19.9°, and 18.4 mm, respectively.

CONCLUSIONS: Our findings suggest that preoperative planning to achieve a larger simulated ROM, ER angle, and extension angle may reduce the risk of anterior dislocation. Furthermore, fine-tuning of cup anteversion during preoperative planning may reduce the risk of anterior dislocation.