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Fat is not just used by the body as bulk tissue. In addition to its role in storing energy and regulating hormone action, fat is used in some parts of the body for its mechanical properties. The anatomy of anterior knee fat is more complex than it appears at first sight and is capable of withstanding considerable compressive and shear stress. Specific lesions occur when such mechanical stress exceeds the physiological limits and are yet little known. Superficial fat can be the site of either acute injury by closed degloving called the Morel-Lavallee lesion or chronic injury, when subject to repeat excessive shear forces, due to more complex and less well-defined disruptions that result in pseudo-bursitis. There are three main anterior, intracapsular and extrasynovial fat pads in the knee joint, which are the infrapatellar fat pad (IFP) or Hoffa's fat pad, the quadriceps fat pad and the prefemoral fat pad. The IFP plays an important role as a mechanical shock absorber and guides the patella tendon and even the patella itself during flexion-extension movements. In response to repeated excessive stress, an inflammatory reaction and swelling of the IFP is first observed, followed by a fibrotic reaction with metaplastic transformation into fibrous, cartilaginous or bone tissue. More rarely, the two other deep fat pads (quadriceps and prefemoral) can, if subject to repeated stress, undergo similar restructuring inflammatory reactions with metaplasia resulting in tissue hardening, anterior pain and partial loss of function.

Hoffa’s fat pad syndrome is a clinical condition, which develops as a result of impingement of the infrapatellar fat pad between the femorotibial and femoropatellar spaces after inflammation and edema . [1] Here we Report a case of Hoffa’s Disease involving left knee treated with complete excision of the involved tissue

Background Liposynovitis prepatellaris (Hoffa’s syndrome) is a rare condition in children and rarely discussed in the literature. Hoffa’s syndrome can lead to an obscure anterior knee pain resulting from impingement and inflammation of the infrapatellar fat pad. Aim of the work The aim of this case report is to increase awareness among rheumatologists about this condition among children to avoid erroneous diagnosis of juvenile idiopathic arthritis (JIA) and unnecessary treatment with disease-modifying antirheumatic drugs (DMARDs). Case report In this report we presented a 12 year-old child with this condition who presented with chronic pain and intermittent swelling involving his right knee. The patient was wrongly diagnosed as a case of JIA and wrongly treated with DMARDs for three years duration. The report will shed light on the characteristic MRI features of this condition and the value to order MRI in such atypical presentation. Conclusion Hoffa’s syndrome can present with chronic arthropathy in children that can mimic mono-articular JIA presentation and eventually unnecessary treatment with DMARDs. MRI is generally very helpful from the diagnostic point of view, it clearly depicts Hoffa’s infrapatellar fat pad entrapment and its findings may suggest Hoffa’s syndrome.

A 37-year-old male patient, who is an athletic runner, developed anterior knee pain of acute onset after prolonged running and swelling of his right knee. The patient experiences more pain when he flexes the knee and a sense of catching together with grade 1 effusion. The patient was clinically suspected to have internal derangement and MRI study of his right knee was ordered to exclude such possible diagnosis. The MRI study revealed the following: a hypointense lesion in the infrapatellar pad of fat in T2-weighted images (WI), postcontrast T1 WI with fat saturation demonstrated no enhancement, and STIR sequence showed slightly hyperintense lesion with minimal knee effusion. The MRI findings supported the diagnosis of Hoffa's syndrome, and arthroscopic resection of the fat pad was performed. There was a significant improvement in the symptoms and function after the surgery.