Nicola Jane Lyle MBBS, Presenter: Nothing to Disclose

Toby Briant-Evans, Abstract Co-Author: Institutional Research Grant, Biomet, Inc

Jennifer Teresa Hauptfleisch MBChB, FRCR, Abstract Co-Author: Nothing to Disclose

Andrea Pearce, Abstract Co-Author: Nothing to Disclose

Richard Harker, Abstract Co-Author: Nothing to Disclose

Kevin Conn, Abstract Co-Author: Nothing to Disclose

John Britton, Abstract Co-Author: Nothing to Disclose

Geoff Stranks, Abstract Co-Author: Nothing to Disclose

MRI is the gold standard imaging modality to assess soft tissue complications which occur around metal on metal (MoM) hip prostheses due to adverse reaction to metal debris (ARMD). The MR features of these ‘pseudotumours’ are well established but relatively little is known about the natural history of ARMD. This knowledge would be invaluable for appropriate patient management. The aim of this study was to investigate MRI changes over time in longitudinal follow up of our MoM total hip arthroplasties (THAs).

155 large head MoM THAs underwent at least two separate MRI scans. The images were reviewed retrospectively by two musculoskeletal radiologists and 1 orthopedic surgeon. They were classified as 1. Normal 2. Trochanteric fluid only 3. Effusion 4. ARMD (extra-articular fluid/ solid collections) The latter group was further classified according to the Oxford classification into Type I (thin-walled cystic), Type II (thick-walled cystic) and Type III (predominantly solid). Lesion volumes were also measured.  

The mean time from primary surgery to first scan was 48 months. The median interval between scans was 15 months. 54 (35%) were classified as normal and 30% of these hips developed an abnormality by the time of the second scan. 19 (12%) had isolated trochanteric fluid of which 9 (47%) got larger or developed into Type I ARMD lesions. 12 (8%) had effusions and 6 (58%) progressed in volume with one becoming a Type I ARMD lesion. 70 (46%) had ARMD, 49 type I, 16 type II and 5 type III. There was a significant increase in size of the pseudotumours in type I and II categories (77% progression rate). New osteolysis was seen in 4 cases in the type II group (25%). Lesions most likely to progress had an irregular pseudocapsule and progression was associated with high cobalt levels.  

Little has been published on the natural history of pseudotumours. In our series there was a high rate of ARMD (46%) and the majority (77%) showed a significant increase in size on serial MR. Pseudotumours with an irregular lining were more likely to progress. This progression rate is higher than in recently published smaller longitudinal series.

In MR follow-up of patients with MoM THAs there was a 46% rate of ARMD and 77% progressed. The decision to revise is clinical but this high rate of progression may lower the threshold for revision.

Lyle, N, Briant-Evans, T, Hauptfleisch, J, Pearce, A, Harker, R, Conn, K, Britton, J, Stranks, G, Longitudinal MRI Follow-up of Patients with Large Head Metal on Metal Total Hip Arthroplasties.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14003412.html