Metal artefact reduction (MAR) MRI is now widely
considered to be the standard for imaging metal-on-metal (MoM) hip
implants. The Medicines and Healthcare Products Regulatory Agency
(MHRA) has recommended cross-sectional imaging for all patients
with symptomatic MoM bearings. This paper describes the natural
history of MoM disease in a 28 mm MoM total hip replacement (THR)
using MAR MRI. Inclusion criteria were patients with MoM THRs who had
not been revised and had at least two serial MAR MRI scans. All
examinations were reported by an experienced observer and classified
as A (normal), B (infection) or C1–C3 (mild, moderate, severe MoM-related
abnormalities). Between 2002 and 2011 a total of 239 MRIs were performed
on 80 patients (two to four scans per THR); 63 initial MRIs (61%)
were normal. On subsequent MRIs, six initially normal scans (9.5%)
showed progression to a disease state; 15 (15%) of 103 THRs with
sequential scans demonstrated worsening disease on subsequent imaging. Most patients with a MoM THR who do not undergo early revision
have normal MRI scans. Late progression (from normal to abnormal,
or from mild to more severe MoM disease) is not common and takes
place over several years. Cite this article:
Metal-on-metal total hip replacement has been targeted at younger patients with anticipated long-term survival, but the effect of the production of metal ions is a concern because of their possible toxicity to cells. We have reviewed the results of the use of the Ultima hybrid metal-on-metal total hip replacement, with a cemented polished tapered femoral component with a 28 mm diameter and a cobalt-chrome (CoCr) modular head, articulating with a 28 mm CoCr acetabular bearing surface secured in a titanium alloy uncemented shell. Between 1997 and 2004, 545 patients with 652 affected hips underwent replacement using this system. Up to 31 January 2008, 90 (13.8%) hips in 82 patients had been revised. Pain was the sole reason for revision in 44 hips (48.9%) of which 35 had normal plain radiographs. Peri-prosthetic fractures occurred in 17 hips (18.9%) with early dislocation in three (3.3%) and late dislocation in 16 (17.8%). Infection was found in nine hips (10.0%). At operation, a range of changes was noted including cavities containing cloudy fluid under pressure, necrotic soft tissues with avulsed tendons and denuded osteonecrotic upper femora. Corrosion was frequently observed on the retrieved cemented part of the femoral component. Typically, the peri-operative findings confirmed those found on pre-operative metal artefact reduction sequence MRI and histological examination showed severe necrosis. Metal artefact reduction sequence MRI proved to be useful when investigating these patients with pain in the absence of adverse plain radiological features.
