The association between infrapatellar fat pad volume and knee pain in non-obese postmenopausal women.

BACKGROUND: The infrapatellar fat pad (IPFP) is a significant source of pro-inflammatory cytokines and may be related to knee pain. The study aim was to determine the association between knee symptoms and each of IPFP size from knee MRI and density from peripheral (p) QCT knee images in non-obese postmenopausal women. METHODS: Postmenopausal women 50-85 yrs old with a body mass index (BMI) < 30 kg/m2 and variable knee pain completed proton-density-weighted MRI and pQCT scans of the knee (one slice at the level of each compartment), where the IPFP was contoured to yield volumes (for MRI), areas and density (for pQCT). Knee symptoms were evaluated using the Intermittent and Constant Osteoarthritis Pain (ICOAP) and Knee Osteoarthritis Outcomes Score (KOOS) questionnaires, and OARSI physical function tests. Multivariable linear regression examined how IPFP metrics relate to these outcomes, accounting for age, BMI, use of pain medications, and Kellgren Lawrence (KL) score (≥2 vs <2). RESULTS: Among 47 women (mean age: 61.2(8.82) yrs, BMI:22.5(3.2) kg/m2, KL score ≥2: 27.6%), a 1 cm2 smaller IPFP area from pQCT slices of the medial femoral compartment was associated with a 2.3% lower KOOS activities of daily living (ADL) score, a 4.7% higher ICOAP constant pain score, and a 3.9% higher ICOAP total pain score. A 1 mg/cm3 higher IPFP density from the pQCT slice of the lateral tibial compartment was associated with a 4.27% lower KOOS ADL score. Meanwhile, a 1 cm3 larger overall IPFP volume from MRI was associated with a 2% higher ICOAP intermittent pain score. CONCLUSIONS: A denser and thinner IPFP cross-sectional area but with larger overall volume - suggesting a long, dense, and skinny phenotype - may be a correlate of having more knee pain in postmenopausal women.