Inflammation of Hoffa's fat pad in the setting of HIV: magnetic resonance imaging findings in six patients.

OBJECTIVE: To describe MR imaging findings of inflammation of Hoffa's fat pad as a cause of nonspecific knee pain in the HIV-infected population.
DESIGN: Retrospective review. PATIENTS: A retrospective review of 400 consecutive MR imaging studies of the knee performed at two institutions over a six-month period was conducted. Inclusion criteria included HIV infection in conjunction with diffuse high signal intensity throughout Hoffa's fat pad on fluid sensitive sequences. Medical histories and images were reviewed by two musculoskeletal radiologists. Exclusion criteria included post-surgical changes, internal derangement, and/or changes consistent with an active synovial inflammatory process.
RESULTS: Seven HIV-infected subjects with non-specific knee pain were identified, six of whom met imaging inclusion criteria. Findings in Hoffa's fat pad were present in nine MR studies (bilateral in three, and unilateral in three subjects). Other findings include bilateral enlargement of Hoffa's fat pad in one subject, global increase in signal intensity of the suprapatellar fat pad on fluid sensitive sequences in three subjects and of the prefemoral fat pad in four subjects, avascular necrosis in one subject, and a diffuse pattern of patchy bone marrow edema in one subject. Subjects were diagnosed with HIV from 1993-1999, with imaging performed in 2005. Subjects were on HAART medication for an indeterminate, extended duration of time prior to imaging. CD4 levels of subjects ranged from 448-1262 cells/muL (X=727.33 cells/muL).
CONCLUSIONS: While the MR imaging findings of diffuse inflammation of Hoffa's fat pad are nonspecific and unclear in etiology, an association with HIV may exist.