Background Recent studies consider infrapatellar fat pad (IPFP) as an active joint tissue in the initiation and progression of knee OA, as inflammatory cells from IPFP can produce inflammatory mediators . As a result, partial resection or total excision of IPFP is usually occurred in the process of knee surgery (e.g., knee replacement, arthroscopy) without consideration of any side effects. However, as an intraarticular tissue, IPFP locates so closely to cartilage and bone surface that it may reduce the impact loading and absorb forces generated through the knee joint. So far, there have been no clinical or epidemiological studies reporting the association between IPFP and knee OA measures so the role of IPFP in knee OA is largely unknown.
Objectives To investigate cross-sectional and longitudinal associations between IPFP maximum area and knee osteoarthritic abnormalities in older adults
Methods A cross-sectional sample of 970 randomly selected subjects (mean 63 years, 48% female) was studied at baseline and 407 followed up 2.7 years later. Radiographic knee osteophyte and joint space narrowing (JSN) were assessed using OARSI atlas. T1- or T2-weighted fat suppressed magnetic resonance imaging (MRI) was utilized to infrapatellar fat pad maximum area, cartilage volume, cartilage defect and bone marrow lesions (BMLs). Knee pain was assessed by self-administered Western Ontario McMaster Osteoarthritis Index (WOMAC) questionnaire.
Results Infrapatellar fat pad maximum area was positively associated with age, height, weight, and negatively with female sex (all p<0.01 in multivariable analyses). After adjustments of age, sex, height, weight, disease status and/or knee radiographic features, infrapatellar fat pad maximum area was significantly associated with decreased joint space narrowing (OR: 0.74 [medial], 0.78 [lateral], all p<0.05) and medial osteophytes (OR: 0.52, p=0.001), increased knee tibial and patellar cartilage volume (β: 58.9 to 165.0 mm3/cm2, all P<0.001), decreased tibial cartilage defects (OR: 0.58 [medial], 0.54 [lateral], all p<0.01), decreased BMLs (OR: 0.77, p=0.01), and decreased knee pain (pain on flat surface, OR: 0.79, P<0.05).
Longitudinally, infrapatellar fat pad maximum area was significantly associated with less loss of cartilage volume (medial tibial, beta: 0.8% per cm2, p=0.01; lateral tibial, beta: 0.7% per cm2, p=0.019), and less increase in cartilage defects (medial tibiofemoral, OR: 0.65, p=0.003).
Conclusions Infrapatellar fat pad maximum area is associated with decreased knee pain, radiographic OA, BMLs, and less cartilage loss and defect progression/development, suggesting that infrapatellar fat pad may be protective against knee OA in older adults. Consequently, we must pay special attention to infrapatellar fat pad in the clinical settings, avoiding removal of normal IPFP in knee surgery.
Clockaerts S, Bastiaansen-Jenniskens YM, Runhaar J, et al. The infrapatellar fat pad should be considered as an active osteoarthritis joint tissue: a narrative review. Osteoarthritis Cartilage. 2012;18:876-882
Acknowledgements We especially thank the participants who made this study possible, and we gratefully acknowledge the role of the staff and volunteers in collecting the data, particularly research nurses Boon C and Boon P. Warren R assessed MR images and Dr Zhai G scored bone marrow lesions. Dr Srikanth V and Dr Cooley H assessed radiographs.
Disclosure of Interest None Declared