Radiology of orthopaedic implants
Cobalt levels painful vs well functioning MOM hips (Larger version)
Principal Investigator: Alister Hart
Co-Investigators: Adam Mitchell, Keshthra Satchithananda, Donald Mcrobbie
Also see the London Implant Retrieval Centre
1 million metal-on-metal (MOM) hip replacements have been implanted worldwide. 3 types have been withdrawn from use due to high early failure rates. The commonest reason for redo surgery of metal-on-metal (MOM) hip replacements is unexplained.
Our research involves the assessment of clinically useful advances in imaging (MRI and CT) to diagnose and quantify biocompatibility of hip replacements.
Using Metal Artefact Reduction Sequence (MARS) MRI we have shown that 62% (16/26) patients with painful MOM hips had soft tissue masses (Hart AJ, Sabah S, Henckel J, Lewis A, Cobb J, Sampson B, Mitchell A, Skinner JA. The painful metal-on-metal hip resurfacing. J Bone Joint Surg Br 2009;91-B-6:738-44.)
We have devised a standardised protocol for reporting MARS MRI of hips: Sabah SA, Mitchell AW, Henckel J, Sandison A, Skinner JA, Hart AJ. Magnetic Resonance Imaging Findings in Painful Metal-On-Metal Hips A Prospective Study. Epub April 2010: J Arthroplasty 2010.
LIRC MARS MRI protocol for hips 
See our Radiological Society of North America (RSNA) 2009 talk:What to see on MRI of MOM hips 
Examples of these are shown below
MARS MRI intrapelvic mass
Hip bursa fluid level
CT vs plain radiograph measurement
In trying to understand whether component position is involved with the mechanism of the formation of inflammatory masses on MARS MRI we have also carried out metal artefact reduction CT with 3D component position measurement. This is a challenging field because the measurement of cup angles of large diameter MOM hips on xray is difficult because the femoral head obscures the cup face.
Download 3D CT protocol from the London Implant Retrieval Centre
See www.jointanalysis.com, an Imperial College spinout
CT more accurate than xray (larger version)
Bland Altman Plot Xr vs CT
A Bland-Altman plot of the difference between 2 methods of measurement (plain radiographic and 3D CT) for the version angle of the cup of MOM hips. (In press).
Bland Altman Plot Xr vs CT (larger version)
