Abstract
Aims
Metal-on-metal total hip replacements (MoM THRs) are frequently revised. However, there is a paucity of data on clinical outcomes following revision surgery in this cohort. We report on outcomes from the largest consecutive series of revisions from MoM THRs and consider pre-revision factors which were prognostic for functional outcome.
Materials and Methods
A single-centre consecutive series of revisions from MoM THRs performed during 2006–2015 was identified through a prospectively maintained, purpose-built joint registry. The cohort was subsequently divided by the presence or absence of symptoms prior to revision. The primary outcome was functional outcome (Oxford Hip Score (OHS)). Secondary outcomes were complication data, pre- and post-revision serum metal ions and modified Oxford classification of pre-revision magnetic resonance imaging (MRI). In addition, the study data along with demographic data was interrogated for prognostic factors informing on post-revision functional outcome.
Results
180 revisions in 163 patients were identified at a median follow-up of 5.48 (2–11.7) years. There were 152 (84.4%) in the symptomatic subgroup and 28 (15.6%) in the asymptomatic group. Overall median OHS improved from 29 to 37 with revision (P<0.001). Symptomatic patients experienced greater functional benefit (DOHS 6.5 vs. 1.4, p=0.012) compared to asymptomatic patients, though they continued to report inferior outcomes (OHS 36.5 vs 43, p=0.004). The functional outcome of asymptomatic patients was unaffected by revision surgery (pre-revision OHS 41, post-revision OHS 43, p=0.4). Linear regression analysis confirmed use of a cobalt-chrome (CoCr)-containing bearing surface (MoM or metal-on- polyethylene) at revision and increasing BMI were predictive of poor functional outcome (R2 0.032, p=0.0224 and R2 0.039, p=0.015 respectively). Pre- and post-revision serum metal ions and pre-revision MRI findings were not predictive of outcome. The overall complication rate was 36% (n=65) with a re-revision rate of 6.7%. The most common complication was ongoing adverse reaction to metal debris (ARMD, defined as positive post-revision MRI) in 21.1%. The incidence of ongoing ARMD was not significantly different between those with CoCr reimplanted and those without (p=0.12).
Conclusions
To our knowledge, our study represents the largest single-centre consecutive series of revision THRs from MoM bearings in the literature. Symptomatic patients experience the greatest functional benefit from revision surgery but do not regain the same level of function as patients who were asymptomatic prior to revision. The re-implantation of CoCr as a primary bearing surface and increasing BMI was associated with poorer functional outcome.
