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uncovered in the remaining 53 hips.Results: At the minimum 5-year follow-up, 119 patients were still alive and had not beenrevised at a mean of 7.2 years (5-8.9 years), 4 hips were revised for dislocation between thefemoral head and the mobile insert (intra-prosthetic dislocation) at a mean of 5.9 years, 22patients were deceased, and 23 patients were lost to follow-up. Intra-prosthetic dislocationoccurred in 4 of the 53 hips (7.5%) with an incompletely covered Morse taper, whereas nodislocation were reported in the remaining 115 hips (p = 0.009).Discussion and Conclusion: A current cementless DM socket was highly effective in theprevention of dislocation following primary THA. However, fatigue damage and wear of themobile insert at the capturing area can lead to intra-prosthetic dislocation requiring revision.Surgeons should be aware of this specific complication and efforts should be made to avoidaggressive contact at the femoral neck to mobile insert articulation (“3 rd articulation”).Friday, October 8, 2010, 15:00-16:00Session A15: Alternate Bearings 2IntroductionAn MRI Classification of Lesions Around Metal-on-Metal HipReplacements*Alister Hart - Imperial College - London, UKKeshthra Satchithananda - Imperial College - London, UKJohann Henckel - Imperial College - London, UKJustin Cobb - Imperial College - London, UKShiraz Sabah - Imperial College - London, UKJohn Skinner - Royal National Orthopaedic Hospital Trust - Stanmore, UKAdam Mitchell - Imperial College - London, UK*Email: a.hart@imperial.ac.ukMetal Artefact Reduction Sequence (MARS) MRI is being increasingly used to detect softtissue inflammatory reactions surrounding metal-on-metal hip replacements. The UK MHRAsafety alert announced in April 2010 recommended cross-sectional imaging such as MRI for allpatients with painful MOM hips. The terms used to describe the findings include bursae, cysticlesions and solid masses. A recently used term, pseudotumour, incorporates all of these lesions.We aimed to correlate the pattern of abnormalities on MRI with clinical symptoms.Method:Following our experience with over 160 MARS MRI scans of patients with MOM hips werecognized patterns of lesions according to their: wall thickness, T1 / T2 signal, shape, andlocation. We categorised the 79 lesions from 159 MARS MRI scans of into our novelclassification scheme of 1, 2a, 2b and 3. There were two groups of patients: well functioningand painful.file:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]