In Vivo analysis of spinopelvic kinematics and peak head-cup contact in total hip arthroplasty patients with lumbar degenerative disc disease.

Anterior instability after total hip arthroplasty (THA) has been described in patients with thoracolumbar kyphotic deformity. Although compensatory posterior pelvic tilt with subsequent increased functional anteversion has been described as the mechanism, there is a paucity of in vivo data. The purpose of our study was to compare pelvic tilt, anteversion, inclination, and position of head-cup contact points in patients with lumbar degenerative disc disease (DDD) and a matched patient cohort without DDD. A total of 50 THA, 18 hips with lumbar DDD and 32 hips without DDD, underwent CT imaging for 3D hip reconstruction. Component orientations and in vivo hip gait kinematics was quantified using a validated dual fluoroscopic imaging system. Hip kinematics and head-cup contact points were compared. Patients with lumbar DDD demonstrated decreased maximum (5.9° ± 4.2° vs. 9.3° ± 5.4°, p = 0.02) and minimum (2.4° ± 4.1° vs. 6.2° ± 5.6°, p = 0.01) anterior pelvic tilt, and increased maximum cup anteversion (29.3° ± 8.7° vs. 25.1° ± 8.1°, p = 0.05). The peak head-cup contact points were shifted closer to the anterior edge of the polyethylene (7.8 ± 1.7 mm vs. 9.6 ± 2.2 mm, p = 0.02). Patients with lumbar degenerative disc disease demonstrated increased posterior pelvic tilt, functional acetabular anteversion, inclination as well as shifting of the peak head-cup contact pattern significantly closer to an anterior edge, suggesting sagittal spinopelvic deformity may predispose to anterior instability in THA patients during upright activities.