[Hoffa's disease of the adipose pad: magnetic resonance versus surgical findings]. / Malattie del corpo adiposo di Hoffa: Risonanza Magnetica e chirurgia a confronto.

INTRODUCTION: Hoffa's fat pad disease is characterized by chronic knee pain mostly under the patella. Acute cases are generally post-traumatic; the clinical picture consists of especially anterior pain and functional impairment mimicking a ligament injury, often in the presence of a bulky effusion even with blood from mucous ligament arteriole rupture. In chronic cases, recurrent episodes of hydrarthrosis are reported, together with joint weakening and subpatellar discomfort. At clinical examination, Hoffa's sign is difficult to observe but can be highly specific. Extending a bent knee putting pressure on the patellar tendon margins elicits a strong pain, an antalgic block and a defensive behavior of the patient. MRI clearly depicts Hoffa's infrapatellar fat pad and its findings may suggest the frequently ignored diagnosis of Hoffa's syndrome, alone or associated with other local or systemic conditions. This is really important for a complete and correct surgical planning, since the classic anterolateral arthroscopy and arthrotomy never visualize the pad itself and, at any rate, give no information on the possible changes. MATERIAL AND METHODS: June 30, 1995, to June 30, 1997, one hundred and ninety-three arthroscopies were performed at the Service of Orthopedics of Argenta Hospital. The present retrospective study excluded 107 patients (65.45%) who had not undergone MRI. In the remaining 86 patients (44.55%) who underwent MRI, the surgical, arthroscopic and nonarthroscopic patterns of Hoffa's pad were studied and 17 patients selected for surgical curettage of Hoffa's pad which was the site of isolated or associated conditions. All 17 MR examinations were reviewed to assess the patterns of the various pad abnormalities in the light of the surgical picture and of the latest indications from the international literature. RESULTS: T1-weighted sequences showed the fibrotic trabeculae of the pad thanks to the contrast offered by hyperintense fat and T2-weighted sequences demonstrated liquid infiltration in the pad and various synovial recesses. Despite the limitations of a retrospective study, MRI had high sensitivity in Hoffa's fat pad studies in our 17 patients; its specificity depended on the condition. MRI was particularly reliable in acute (Hoffa's pad rupture-detachment) and chronic conditions with aspecific hypertrophy (chondromatosis, pigmented villonodular synovitis), as well as in systemic disorders (rheumatoid arthritis). CONCLUSIONS: Accurate studies of Hoffa's fat pad are mandatory because different pad injuries may require a different arthroscopic approach from the classic ones. MRI was a useful tool in the study of Hoffa's fat pad, whose local and systematic involvement is an often ignored cause of anterior knee pain.