Seiza Sitting After Total Hip Arthroplasty: Patient-Reported Outcomes and Three-Dimensional Kinematic Analysis.

BACKGROUND: In Japan and other East Asian countries, Seiza sitting is essential for daily activities. However, it is often restricted after total hip arthroplasty (THA) due to dislocation concerns. This study aimed to (1) clarify the prevalence and factors limiting Seiza sitting post-THA and (2) evaluate its kinematic characteristics using 3-dimensional (3D) kinematic analysis.

METHODS: A questionnaire was conducted among 725 patients who underwent primary THA; 431 responded (response rate: 60%). We assessed the status of Seiza sitting and reasons for avoidance. Multivariable logistic analyses were performed to identify factors associated with postoperative Seiza ability. Subsequently, 52 patients (74 hips) who were able to perform Seiza underwent kinematic analysis using the 3D-to-2D model-image registration technique. Hip and pelvic kinematics, liner-to-neck or bone-to-bone contact, and clearance were evaluated.

RESULTS: Postoperatively, 49% could perform Seiza sitting easily, and 58% regained overall Seiza ability, with 68% doing so within six months. The most common reason for not performing Seiza was anxiety about dislocation. Multivariable analyses identified younger age, men, and lower body mass index as independent factors associated with Seiza ability. The mean maximum hip flexion angle was 74.9 ± 9.7° during the rising phase. Hip abduction and external rotation remained stable throughout the motion, 3.6 ± 1.0° and 1.4 ± 0.9°, respectively. The mean pelvic tilt excursion was limited to 8°. There was no liner-to-neck or bone-to-bone contact observed in any case. The mean anterior and posterior clearances were 45.0 ± 12.0° and 41.2 ± 17.7°, respectively.

CONCLUSION: Seiza sitting involves moderate hip flexion and stable pelvic kinematics with sufficient liner-to-neck clearance, suggesting that Seiza sitting may be kinematically feasible in selected patients after THA. Despite these findings, many patients refrain from Seiza due to anxiety about dislocation. Addressing dislocation anxiety through evidence-based information may help restore this culturally important activity.