The John Charnley Award: Diagnostic Accuracy of MRI Versus Ultrasound for Detecting Pseudotumors in Asymptomatic Metal-on-Metal THA
- 791 Downloads
The prevalence of pseudotumors in patients with large-head metal-on-metal (MOM) THA has been the subject of implant recalls and warnings from various regulatory agencies. To date, there is no consensus on whether ultrasound or MRI is superior for the detection of pseudotumors.
We prospectively compared ultrasound to MRI for pseudotumor detection in an asymptomatic cohort of patients with MOM THAs. We also compared ultrasound to MRI for assessment of pseudotumor growth and progressive soft tissue involvement at a 6-month interval.
We enrolled 40 patients with large-head MOM THAs in the study. The mean age was 54 years (range, 34–76 years). The mean time from surgery was 54 months (range, 40–81 months). There were 28 men and 12 women. All patients underwent ultrasound and MRI using slice encoding for metal artifact correction. The gold standard was defined as follows: if both ultrasound and MRI agreed, this was interpreted as concordant and the result was considered accurate.
Ultrasound and MRI agreed in 37 of 40 patients (93%). The prevalence of pseudotumors was 31% (12 of 39) in our cohort. Twenty-three of 39 patients (59%) had completely normal tests and four (10%) had simple fluid collections. Ultrasound had a sensitivity of 100% and specificity of 96% while MRI had a sensitivity of 92% and specificity of 100%.
A negative ultrasound rules out pseudotumor in asymptomatic patients as this test is 100% sensitive. Given its lower cost, we recommend ultrasound as the initial screening tool for pseudotumors.
Level of Evidence
Level I, diagnostic study. See the Instructions for Authors for a complete description of levels of evidence.
KeywordsPositive Predictive Value Negative Predictive Value Metal Artifact Artifact Reduction Negative Ultrasound
We thank Nelson V. Greidanus MD, MPH for contributing patients to the study; Diana Korlaet CRGS, PDDipAppSci (Medical Ultrasound) for performing the ultrasound scans; Hugue A. Ouellette MD, FRCPC, Gordon Andrews MD, FRCPC, and Borys Flak MD, FRCPC for reading the ultrasounds and MR images; Torsten O. Nielsen MD, PhD for his advice pertaining to musculoskeletal pathology; Eric C. Sayre PhD for his help with the statistical analysis; Lorna McLean BA for patient recruitment and data collection; and Daphné Savoy BA for her assistance in the preparation of this manuscript.
- 2.Bellamy N, Buchanan W, Goldsmith CH, Campbell J, Stitt LW. Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or the knee. J Rheumatol. 1988;15:1833–1840.PubMedGoogle Scholar
- 6.Canadian Hip Resurfacing Study Group. A survey on the prevalence of pseudotumors with metal-on-metal hip resurfacing in Canadian academic centers. J Bone Joint Surg Am. 2011;93(suppl 2):118–121.Google Scholar
- 15.Hart AJ, Satchithananda K, Liddle AD, Sabah SA, McRobbie D, Henckel J, Cobb JP, Skinner JA, Mitchell AW. Pseudotumors in association with well-functioning metal-on-metal hip prostheses: a case-control study using three-dimensional computed tomography and magnetic resonance imaging. J Bone Joint Surg Am. 2012;94:317–325.PubMedGoogle Scholar
- 17.Hennekins CH, Buring JE. Epidemiology in Medicine. Boston, MA: Little, Brown and Co; 1987.Google Scholar
- 23.Medicines and Healthcare products Regulatory Agency. MDA/2010/033 Medical Device Alert: all metal-on-metal (MoM) hip replacements. Available at: http://www.mhra.gov.uk/Publications/Safetywarnings/MedicalDeviceAlerts/CON079157. Accessed February 13, 2012.