Abstract
Aims
Our study aimed to 1) determine if there was a difference for the HOOS-PS score between patients with stiff/normal/hypermobile spinopelvic mobility and 2) to investigate if functional sagittal cup orientation affected patient reported outcome 1 year post-THA.
Methods
This prospective diagnostic cohort study followed 100 consecutive patients having received unilateral THA for end-stage hip osteoarthritis. Pre- and 1-year postoperatively, patients underwent a standardized clinical examination, completed the HOOS-PS score and sagittal low-dose radiographs were acquired in the standing and relaxed-seated position. Radiographic measurements were performed for the lumbar-lordosis-angle, pelvic tilt (PT), pelvic-femoral-angle and cup ante-inclination. The HOOS-PS was compared between patients with stiff (ΔPT<±10°), normal (10°≤ΔPT≤30°) and hypermobile spinopelvic mobility (ΔPT>±30°).
Results
Preoperatively, 16 patients demonstrated stiff, 70 normal and 14 hypermobile spinopelvic mobility without a difference in the HOOS-PS score (66±14/67±17/65±19;p=0.905).
One year postoperatively, 43 patients demonstrated stiff, 51 normal and 6 hypermobile spinopelvic mobility. All postoperative hypermobile patients had normal spinopelvic mobility preoperatively and showed significantly worse HOOS-PS scores compared to patients with stiff or normal spinopelvic mobility (21±17/21±22/35±16;p=0.043).
Postoperatively, patients with hypermobile spinopelvic mobility demonstrated no significant difference for the pelvic tilt in the standing position compared to the other two groups (19±8°/16±8°/19±4°;p=0.221), but a significantly lower sagittal cup ante-inclination (36±10°/36±9°/29±8°;p=0.046).
Conclusion
The present study demonstrated that patients with normal preoperative and postoperative spinopelvic hypermobility show worse HOOS-PS scores than patients with stiff or normal spinopelvic mobility. The lower postoperative cup ante-inclination seems to force the pelvis to tilt more posteriorly when moving from the standing to seated position (spinopelvic hypermobility) in order to avoid anterior impingement. Thus, functional cup orientation in the sagittal plane seems to affect postoperative patient reported outcome.
