A 34-year-old man with chronic anterior knee pain underwent MRI after a radiograph of the left knee demonstrated no acute or significant degenerative findings. Sagittal and axial short TI inversion recovery (STIR) images (A and B, respectively) demonstrated increased signal at the superolateral aspect of the infrapatellar fat pad (solid arrows), and the Insall-Salvati ratio (C, dashed line/solid line) was 1.4.
Patellar tendon-lateral femoral condyle friction syndrome (Hoffa fat pad impingement) is thought to be an overuse injury characterized by direct contact of the patellar tendon against the lateral femoral condyle, causing compression of the superolateral aspect of the infrapatellar fat pad.1,2 The etiology of this syndrome is likely due to altered biomechanics and may be associated with patellar maltracking and a weakened vastus medialis muscle. This syndrome typically affects younger adults but can affect those aged 13 to 56 years. It is more common in individuals who do not participate in routine athletic activities.2
The diagnosis is classically made with MRI and usually occult on radiography and CT. MRI findings include increased focal T2-signal at the superolateral aspect of the infrapatellar fat pad. Other associated findings include lateral patellar subluxation/maltracking and increased Insall-Salvati ratio of > 1.2 (patella alta). Conservative treatment is usually successful, although full recovery may take time. Over the counter anti-inflammatory medications and taping/bandaging of the superior pole of the patella to relieve pressure of the infrapatellar fat pad have proven to result in high treatment success rates.1