Background
Some patients undergoing total hip arthroplasty (THA) show postoperative changes in hip rotation. We investigated changes in the hip rotation angles of patients in the standing position before and after THA and the factors associated with such changes.
Methods
Participants included 77 patients (82 joints) who underwent primary THA for hip osteoarthritis. There were 17 joints in men and 65 joints in women, and the mean age at the time of surgery was 65.7 years. Standing hip rotation angles and hip internal/external rotation ranges of motion (ROM) were measured before and 2 weeks after THA to compare preoperative and postoperative measurements. For radiographic measurements, acetabular and cup anteversion, neck and stem anteversion, combined anteversion (CA), and leg length discrepancy were measured before and after THA to investigate the factors associated with changes in standing hip rotation angles.
Results
Regarding standing hip rotation angles, external rotation was 6.9° ± 4.1° before THA and 2.0° ± 2.4° after THA, showing a shift in the internal rotation direction (P = < .0001). The degree of change in standing hip rotation angles before and after THA was found to be negatively correlated with the degree of change in cup anteversion (- 0.429, P = < .0001) and CA (- 0.3012, P = .0063).
Conclusion
Postoperative changes in standing hip rotation following THA were considered associated with extra-articular position sense, rather than intra-articular position sense, to maintain the balance between the pelvis and proximal femur affected by the angles of the placed implant components.