Abstract
Introduction:
To date, there have been few reports of the results of revisions for failed metal-on-metal hip arthroplasties (MoM HA's). These series have included relatively modest numbers, and classification of the severity of adverse local tissue reaction (ALTR) has been under-reported. In this study, early outcomes and complications are analyzed as a function of pre-operative MRI grade and intra-operative ALTR severity to determine their prognostic value.
Methods:
This is a retrospective review of revisions of 121 failed MoM HA's performed between 2008 and 2012. Indications for revision include ALTR (n = 97), loose cup (n = 13), and combined loose cup and ALTR (n = 11). When pre-operative MRI's were available, these were graded according to Anderson's system by 2 radiologists who were blinded to the clinical results. Intra-operative findings were graded for severity according to an ALTR classification. Post-operative complications were recorded. Correlations between pre-operative MRI grade, intra-operative ALTR classification and post-operative complications were analyzed using Spearman's rank correlation.
ALTR Classification:
Type 0: No abnormal fluid or pseudotumor. Peri-articular structures intact.
Type 1: Abnormal fluid and/or pseudotumor. Peri-articular structures disrupted but repairable.
Type 2: Abnormal fluid and/or pseudotumor. Peri-articular structures disrupted and no meaningful repair possible.
Type 3: Abnormal fluid and/or pseudotumor. Peri-articular structrues disrupted, no meaningful repair possible, AND significant necrosis involving abductor muscles.
Results:
The average time to revision was 47 months (range: 7–198 months). In cases where the cup required revision, the average increase in outer diameter was 4.1 mm (range: 2–10 mm). Average revision head size was 38 mm (range: 32–48 mm). 19 patients (16%) experienced at least one complication which included dislocation (n = 12/10%), infection (n = 6/5%), recurrent pseudotumor requiring surgery (n = 2/1.7%), and VTE (n = 1/0.9%). The pre-operative MRI grade correlated significantly with the intra-operative ALTR classification (p = 0.03), and both the MRI grade and ALTR classification correlated significantly with post-operative complications (p < 0.01). Among the 23 patients with the most severe ALTR's (Type 2 and 3), 11 patients (48%) experienced complications.
Conclusion:
Revisions for failed MoM HA's can be heterogenous with varying degrees of soft tissue compromise. Despite the use of large femoral head sizes in the current series, the overall dislocation rate was 10%. The pre-operative MRI grade and intra-operative ALTR classification have good prognostic significance and may alert the surgeon and patient to an increased potential for complications after surgery.
