Background: This study of patients with hip primary osteoarthritis and a matched, asymptomatic, volunteers (controls) group aimed to determine spinopelvic differences between the two groups and their consequences for total hip arthroplasty.
Methods: 104 patients (52 in each group) had their sagittal spinopelvic parameters (lumbar lordosis angle, sacral slope, pelvic tilt, pelvic incidence, and the pelvic-femoral angle) measured in the standing, relaxed-seated, and deep-flexed seated positions. Spinopelvic movement was calculated as the change between the different positions, and individual spinopelvic mobility was classified in accordance with the change in pelvic tilt as previously described (ΔPT: stiff (<10°), normal (10-30°), and hypermobile (>30°)).
Results: Transitioning from the standing to relaxed-seated position, patients demonstrated 13˚ less hip flexion (P < .001), 12˚ more posterior pelvic tilt (P = .006), and 6˚ more lumbar flexion (P = .038) compared with controls. Transitioning from the standing to deep-flexed seated position, patients demonstrated 18˚ less hip flexion (P < .001), accompanied by a posterior and not an anterior pelvic tilt as in the controls (7˚ ± 14 vs -6˚ ± 17; P < .001). Patients showed a higher percentage of spinopelvic hypermobility (19% vs 2%; P = .008).
Conclusion: The reduced ability of flexion in the arthritic hip, leads to posterior pelvic tilt in the relaxed-seated position. This is associated with a likely compensatory increased lumbar flexion to keep an upright position. Therefore, spinopelvic hypermobility has to be defined as pathologic. When moving to the deep-flexed seated position, decreased flexion of the arthritic hip prevents the pelvis from tilting anteriorly while the lumbar spine performs a compensatory flexion by approximately the same amount compared with controls.
Level of evidence: Level II, diagnostic study.
Keywords: arthroplasty; hip; mobility; spine; spinopelvic; tilt.
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