Abstract
Background:
Higher than expected revision rates have been observed in large bearing metal-on-metal total hip replacements. We have introduced a metal on metal hip screening clinic at our unit and report the results.
Methods:
All patients who had a metal-on-metal total hip replacement implanted at our unit were recalled to clinic. Screening consisted of clinical examination, Oxford hip score, radiographs, MARS MRI and serum cobalt/chromium ion levels. MRI scans were graded (Norwich Classification) by a single consultant radiologist who was blinded to the history, examination, and metal levels. Patients were sub-classified into 6 groups, which determined further follow up and were either entered into a regular screening programme or referred to a revision arthroplasty surgeon for a decision on whether revision was required
Results:
A total of 278 patients were identified. Four patients had moved away, 2 refused follow-up and 1 patient had died. This left 271 patients in our cohort, having 299 metal-on-metal hip replacements with a M:F ratio of 1.5:1 and a mean age of 61.9 years (29–87).
59 (21.8%) patients complained of a recent deterioration in symptoms. Sixty seven (24.7%) patients had an abnormal xray appearance of their hip replacement (inclination >50 degrees, loosening, or migration of prosthesis).
Of the 232 hips which underwent MARS MRI, 118 (50.9%) were group A (normal appearance), 66 (28.4%) C1 (mild MOM disease), 31 (13.4%) C2 (moderate MOM disease), and 17 (7.3%) C3 (severe MOM disease). One hundred and seventeen (38.9%) had a substantial fluid collection around the hip.
Serum cobalt/chromium metal ions were raised in 135 patients (49.5%), 46 of which had one (8.8%) or both (8%) above 7 ppb (chromium >134 nmol/L, cobalt > 119 nmol/L).
One hundred and forty nine patients (55%) remained under review in the MOM clinic and 122 (45%, 148 hip replacements) were referred to a revision surgeon for specialist opinion. Of these 21 hips (14.2%) have been revised and a further 14 hips (9.5%) are awaiting revision.
In total 64 hips (21.3% of all large head metal on metal hips implanted in our unit) have been revised with a further 22 (7.3%) listed for revision. Of these, 13 were histologically proven to be an ALVAL reaction, 19 had the classic clinical findings of ALVAL (but not histologically confirmed), and 1 was a non-specific reaction to metal wear. 53 patients (19.4%, 56 hips) were completely asymptomatic but had evidence of ALVAL soft tissue reaction on MRI and/or rising metal ion levels – 9 of these hips have already been revised for ALVAL and 6 more listed for revision.
Conclusions
Our screening programme has identified 53 (19.6%) asymptomatic patients who have evidence of a suspicious reaction to their metal-on-metal hip replacements. 16 (3%) of these have gone on to revision. We would recommend all patients with a metal-on-metal total hip replacement in situ are fully screened for ARMD regardless of symptoms and metal ion levels.
