Morphological characteristics of the infrapatellar fat pad

The purpose of this study was to clarify the morphological characteristics of the infrapatellar fat pad (IFP) in Japanese cadavers and to elucidate the relationship between morphological characteristics of the IFP and degeneration of the patellofemoral joint. This investigation examined 41 legs from 25 Japanese cadavers. Morphological measurement was performed by one examiner, and the proximal IFP, IFP body length, width, and IFP volume were measured. The morphological characteristics of IFP proximal were used to categorize three types of IFP: Type I, IFP proximal located on medial and lateral sides of the patella; Type II, IFP proximal only located medially; and Type III, absence of IFP proximal medially and laterally. Articular surfaces were graded as macroscopically intact or mildly altered (Grade I), moderately altered (if fissuring or fibrillation was observed; Grade II), or severely altered (if eburnation was present; Grade III). Type I was identified in 36.6%, Type II in 48.8%, and Type III in 14.6%. IFP medial proximal was seen in 85%, IFP lateral proximal in 36.6%, and loop type was 2.4%. Grade II was significantly more frequent than Grades I or III in Type II, and Grade III was significantly more frequent than Grades I or II in Type III. In addition, IFP volume was significantly larger in Type I than in Types II or III. Causal relationships remain unclear, but the deformation of patellofemoral joint may be related to decreased IFP volume (atrophy).