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Wednesday, April 4, 2012
Interesting finding on the occurance of pseudotumors in well funtioning MOM hips
Department of Orthopaedic Surgery, Charing Cross Hospital (Imperial College Healthcare NHS Trust and Imperial College London), Fulham Palace Road, London W6 8RF, United Kingdom. email@example.com
Many papers have been published recently on the subject of pseudotumors surrounding metal-on-metalhip resurfacing and replacement prostheses. These pseudotumors are sterile, inflammatory lesions within the periprosthetic tissues and have been variously termed masses, cysts, bursae, collections, or aseptic lymphocyte-dominated vasculitis-associated lesions (ALVAL). The prevalence of pseudotumors in patients with a well-functioningmetal-on-metalhip prosthesis is not well known. The purpose of this study was to quantify the prevalence of pseudotumors adjacent to well-functioning and painful metal-on-metalhip prostheses, to characterize these lesions with use of magnetic resonance imaging, and to assess the relationship between their presence and acetabular cup position with use of three-dimensionalcomputed tomography.
We performed a case-control study to compare the magnetic resonance imaging findings of patients with a well-functioning unilateral metal-on-metalhip prosthesis and patients with a painful prosthesis (defined by either revision arthroplasty performed because of unexplained pain or an Oxford hip score of <30 of 48 possible points). Thirty patients with a painful hip prosthesis and twenty-eight controls with a well-functioningprosthesis were recruited consecutively. All patients also underwent computed tomography to assess the position of the acetabular component.
Thirty-four patients were diagnosed with a pseudotumor. However, the prevalence of pseudotumors in patients with a painful hip (seventeen of thirty, 57%) was not significantly different from the prevalence in the control group (seventeen of twenty-eight, 61%). No objective differences in pseudotumor characteristics between the groups were identified. No clear association between the presence of a pseudotumor and acetabular component position was identified. The Oxford hip score in the group with a painful hip (mean, 20.2; 95% confidence interval [CI], 12.7 to 45.8) was poorer than that in the control group (mean, 41.2; 95% CI, 18.5 to 45.8; p ≤ 0.0001).
A periprosthetic cystic pseudotumor was diagnosed commonly (in thirty-four [59%] of the entire study cohort) with use of metal artifact reduction sequence (MARS) magnetic resonance imaging in this series of patients with a metal-on-metalhip prosthesis. The prevalence of pseudotumors was similar in patients with a well-functioninghip prosthesis and patients with a painful hip. Pseudotumors were also diagnosed commonly in patients with a well-positioned acetabular component. Although magnetic resonance imaging is useful for surgical planning, the presence of a cystic pseudotumor may not necessarily indicate the need for revision arthroplasty. Further correlation of clinical and imaging data is needed to determine the natural history of pseudotumors to guide clinical practice.