The Impact of Spinopelvic and Hip Mobility on Passive Hip Flexion Range of Motion Assessment

Measuring passive hip flexion range of motion (ROM) is challenging due to compensatory movements. Despite the interest in using functional lateral radiographs for assessing hip mobility, the relationship with passive hip flexion ROM remains unclear. This study aims to elucidate this relationship and clarify spinopelvic parameters and mobility factors influencing variations in passive and radiographic hip flexion ROM.

A retrospective cross-sectional study was conducted on 154 preoperative patients undergoing primary total hip arthroplasty. Passive and radiographic hip flexion ROM were assessed to clarify these relationships, and these differences were classified into 3 groups (O, A and U). Spinopelvic and hip parameters were assessed in standing, relaxed-seated and flexed-seated positions, as well as lumbar, pelvis, and hip mobility between each position to identify factors influencing differences.

There was a moderate correlation between passive and radiographic hip flexion ROM (R² = 0.48, P < .01). A significant difference was found in pelvic and hip alignment in the flexed-seated position between all groups. In postural changes, the O group, which had more patients with relatively low hip mobility, showed greater lumbar spine and pelvic movement, while the U group, which had more patients with relatively high hip mobility, showed less lumbar spine and pelvic movement.

This study confirmed that passive hip flexion ROM and radiographic hip flexion ROM correlate and that spinopelvic and hip alignment and mobility influence these differences. This result suggests that clinicians should consider lumbar and pelvic alignment and mobility in clinical practice to improve the accuracy of passive hip flexion ROM measurements.