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

We have updated our previous randomised controlled trial comparing release of chromium (Cr) and cobalt (Co) ions and included levels of titanium (Ti) ions. We have compared the findings from 28 mm metal-on-metal total hip replacement, performed using titanium CLS/Spotorno femoral components and titanium AlloFit acetabular components with Metasul bearings, with Durom hip resurfacing using a Metasul articulation or bearing and a titanium plasma-sprayed coating for fixation of the acetabular component.

Although significantly higher blood ion levels of Cr and Co were observed at three months in the resurfaced group than in total hip replacement, no significant difference was found at two years post-operatively for Cr, 1.58 μg/L and 1.62 μg/L respectively (p = 0.819) and for Co, 0.67 μg/L and 0.94 μg/L respectively (p = 0.207). A steady state was reached at one year in the resurfaced group and after three months in the total hip replacement group. Interestingly, Ti, which is not part of the bearing surfaces with its release resulting from metal corrosion, had significantly elevated ion levels after implantation in both groups. The hip resurfacing group had significantly higher Ti levels than the total hip replacement group for all periods of follow-up. At two years the mean blood levels of Ti ions were 1.87 μg/L in hip resurfacing and and 1.30 μg/L in total hip replacement (p = 0.001).

The study confirms even with different bearing diameters and clearances, hip replacement and 28 mm metal-on-metal total hip replacement produced similar Cr and Co metal ion levels in this randomised controlled trial study design, but apart from wear on bearing surfaces, passive corrosion of exposed metallic surfaces is a factor which influences ion concentrations. Ti plasma spray coating the acetabular components for hip resurfacing produces significantly higher release of Ti than Ti grit-blasted surfaces in total hip replacement.