Superolateral Hoffa's fat pad (SHFP) oedema and patellar cartilage volume loss: quantitative analysis using longitudinal data from the Foundation for the National Institute of Health (FNIH) Osteoarthritis Biomarkers Consortium.

OBJECTIVES: To determine the association of superolateral Hoffa's fat pad (SHFP) oedema and patellofemoral joint structural damage in participants of Foundation for the National Institute of Health Osteoarthritis Biomarkers Consortium study.

METHODS: Baseline and 24-month MRIs of 600 subjects were assessed. The presence of SHFP oedema (using 0-3 grading scale) and patellar morphology metrics were determined using baseline MRI. Quantitative patellar cartilage volume and semi-quantitative MRI osteoarthritis knee score (MOAKS) variables were extracted. The associations between SHFP oedema and patellar cartilage damage, bone marrow lesion (BML), osteophyte and morphology were evaluated in cross-sectional model. In longitudinal analysis, the associations between oedema and cartilage volume loss (defined using reliable change index) and MOAKS worsening were evaluated.

RESULTS: In cross-sectional evaluations, the presence of SHFP oedema was associated with simultaneous lateral patellar cartilage/BML defects and inferior-medial patellar osteophyte size. A significant positive correlation between the degree of patella alta and SHFP oedema was detected (r = 0.259, p < 0.001). The presence of oedema was associated with 24-month cartilage volume loss (odds ratio (OR) 2.11, 95% confidence interval 1.46-3.06) and medial patellar BML size (OR 1.92 (1.15-3.21)) and number (OR 2.50 (1.29-4.88)) worsening. The optimal cut-off value for the grade of baseline SHFP oedema regarding both presence and worsening of patellar structural damage was ≥ 1 (presence of any SHFP hyperintensity).

CONCLUSIONS: The presence of SHFP oedema could be considered as a predictor of future patellar cartilage loss and BML worsening, and an indicator of simultaneous cartilage, BML and osteophyte defects.

KEY POINTS: • SHFP oedema was associated with simultaneous lateral patellar OA-related structural damage. • SHFP oedema was associated with longitudinal patellar cartilage loss over 24 months. • SHFP oedema could be considered as indicator and predictor of patellar OA.