Abstract
Introduction
The mechanisms of how spinal arthrodesis (SA) affects patient function after total hip replacement (THA) remain unclear. The objectives of this study were to a) Determine how outcome post-THA compares between patients with- and without-SA, b) Characterize sagittal pelvic changes that occur when moving between different functional positions, and test for differences between patients with- and without-SA, and c) Assess whether differences in sagittal pelvic dynamics are associated with outcome post-THA.
Patients/Materials & Methods
Forty-two patients with THA-SA (60 hips) were case-control matched for age, gender, BMI with 42 THA-only patients (60 hips). All presented for review where outcome, PROMs [including Oxford-Hip-Score(OHS)] and 4 radiographs of the pelvis and spino-pelvic complex in 3 positions (supine, standing, deep-seated) were obtained. Cup orientation and various spino-pelvic parameters [including pelvic tilt (PT) and Pelvic-Femoral-Angle (PFA)] were measured. The difference in PT between standing and seated allowed for patient classification based on spino-pelvic mobility into normal (±10–30°), stiff (<±10°) or hypermobile (>±30°).
Results
The THA-SA group had inferior PROMs (OHS: 33vs.43; P<0.001) and more complications (12vs.3; p=0.01), especially dislocation (5vs.0) than the THA-only group. No difference in change of PT between supine and standing positions was detected between groups. When standing, THA-SA patients had greater PT (24°vs.17°; p=0.01) and the hip was more extended (194°vs.185°; P<0.001). THA-SA patients were 4 times more likely to have spino-pelvic hypermobility with anterior tilting of their pelvis. Of all biomechanical parameters, only spino-pelvic hypermobility was associated with significant inferior PROMs (OHS:35; p=0.04) and was also present in dislocating hips that required revision despite optimum cup orientation.
Discussion
In patients with SA who have undergone a THA, the presence of spino-pelvic hypermobility is associated with an inferior outcome and leads to hip instability secondary to anterior impingement when deep seated (anterior tilt functionally retroverting cup). For those patients, current implant positioning may not be sufficient to avoid dislocation.
Conclusion
THA in the presence of a SA is associated with inferior outcomes and higher complication rates. We recommend that assessing spino-pelvic mobility should form an integral part of pre-operative assessment in patients with SA due for a THA.
