Tumor like swellings arising from Hoffa's fat pad: A report of three patients.

Sir,

I read with great interest the article by Ghate et al.1 The authors must be complimented for bringing out some rare pathology of the knee in the limelight. They have tried to establish a relationship of Hoffa's Fat Pad (HFP) to these conditions.

The infrapatellar fat pad (IFP), also known as Hoffa's fat pad (HFP), is an intracapsular, extrasynovial structure that fills the anterior knee compartment, and is richly vascularized and innervated. Though the precise function of the IFP is unknown, studies have shown that it may play a role in the biomechanics of the knee or act as a store for reparative cells after injury.1 It is intriguing to assume that HFP has some distinguished characteristics by which a variety of pathology like ganglionic cyst, hemangioma, villonodular synovitis, chondroma, etc., can develop from this fat pad, inside the knee joint. This is perhaps due to the presence of multipotent stem cells, which have the ability to differentiate into other cells like osteoblasts, chondrocytes, etc., under appropriate culture conditions.2

We have recent experience of dealing with two patients of similar lesions, with the tissue diagnosis of Localized Pigmented Villonodular Synovitis (LPVNS) and intraarticular hemangioma. The lesion in patient with LPVNS had continuity with the HFP, but the patient with hemangioma did not have any direct connection with HFP. Both of these lesions were excised in toto, arthroscopically.

I feel that Hoffa's syndrome is a distinct entity, as described by Albert Hoffa in 1904,3 which is characterized by infrapatellar anterior knee pain secondary to inflammation and impingement of the HFP. This entity should not be mixed up with the other lesions like ganglionic cyst, PVNS, hemangioma, etc., unless we can establish a direct proof of involvement of HFP in the pathogenesis of these conditions. These lesions may originate in the vicinity of the IFP, but not necessarily be associated with HFP.