Correlation between sagittal plane deformities of the hip and spinopelvic alignment in advanced hip arthritis...

This study evaluated the relationship between fixed flexion deformity (FFD), hip range of motion (ROM), and dynamic spinopelvic parameters, and explored factors associated with early postoperative sacral slope (SS) mobility in patients with advanced hip arthritis undergoing total hip arthroplasty (THA).

In this prospective study, 45 patients with unilateral hip arthritis and FFD undergoing primary THA were evaluated preoperatively and at three months postoperatively. Clinical assessments included the Thomas test, hip ROM, Harris Hip Score (HHS), and Visual Analogue Scale (VAS) for pain. Radiographic measurements in standing and sitting positions included pelvic incidence, sacral slope, pelvic tilt, ante-inclination (AI), and pelvic-femoral angle. Spinopelvic mobility was defined by the change in sacral slope (ΔSS) between standing and sitting positions.

The mean age was 56.2 years. Mean FFD improved from 16.4° preoperatively to 0° postoperatively, while hip flexion increased from 72.5° to 114.1°. Preoperatively, 11% of patients exhibited a stiff spinopelvic pattern, 63% had normal mobility, and 26% were hypermobile. Following THA, spinopelvic mobility shifted toward a more physiological distribution. Preoperative FFD correlated positively with ΔSS (r = 0.45, p = 0.002). Exploratory multivariable regression analysis identified preoperative hip ROM (β = - 0.35, p = 0.012) and preoperative dynamic change in AI (β = 0.31, p = 0.026) as significant independent factors associated with postoperative ΔSS.

Correction of FFD through THA improves spinopelvic mobility and promotes pelvic realignment. Preoperative hip ROM and dynamic AI were independently associated with early postoperative SS mobility in this exploratory analysis; larger studies are required to validate these associations and determine their clinical significance.