Synonym: liposynovitis prepatellaris
Risk factors:
(1) runners
(2) other causes of acute and/or repetitive trauma to the fat pad
(3) any cause of joint space narrowing
Clinical findings:
(1) anterior knee pain with or without discomfort behind the patella
(2) joint weakness
(3) extension of the bent knee is often painful
(4) variable knee swelling
Initially there is an acute phase which may be followed by chronic inflammation with scarring.
Findings on MRI:
(1) areas of increased signal intensity of T2-weighted MRI (due to edema and hemorrhage) in the infrapatellar fat pad
(2) bowing of the patellar tendon
(3) small joint effusion
(4) fibrotic trabeculae
Differential diagnosis includes:
(1) intra-articular synovial lipoma
(2) villous lipomatous proliferation of the synovial membrane (lipoma arborescens)
(3) knee ligament injury
