Introduction: The infrapatellar fat pad (IPFP) is commonly resected during knee joint arthroplasty, but the ramifications of doing so are unclear. This longitudinal study determined whether the size of the IPFP (maximum cross-sectional area (CSA)) was associated with knee cartilage loss and the development of knee pain in adults without knee osteoarthritis (OA).
Methods: A total of 297 adults without American College of Rheumatology clinical criteria for a diagnosis of knee OA were recruited. Knee MRI was performed at baseline and an average of 2.3 years later. IPFP maximal CSA and tibial cartilage volume were measured from MRI. A large and small IPFP were defined by the median split, with a large IPFP defined by being in the highest 50%. Body composition was performed at baseline using bio-impedance. Knee pain was assessed at follow-up using the Western Ontario and McMaster University Osteoarthritis Index (WOMAC).
Results: A larger IPFP at baseline was associated with reduced knee pain at follow-up (OR 0.5, 95% CI: 0.3 to 0.9, p = 0.02) and lateral tibial cartilage volume loss (β: -0.9% (95% CI: -1.6, -0.1%) per annum, p = 0.03). The maximal CSA of the IPFP was predominantly located in the lateral (54.2%), rather than the medial tibiofemoral compartment (1.7%). Male gender (OR 12.0, 95% CI: 6.5 to 22.0, p < 0.001) and fat free mass (OR 1.15, 95% CI 1.04 to 1.28, p = 0.007) were both associated with a large IPFP.
Conclusion: A larger IPFP predicts reduced lateral tibial cartilage volume loss and development of knee pain and mechanistically might function as a local shock-absorber. The lack of association between measures of adiposity and the size of the IPFP might suggest that the IPFP size is not simply a marker of systemic obesity.