OBJECTIVE: Bone marrow adipose tissue (BMAT) is emerging as an important regulator of bone formation and energy metabolism. Lipolysis of BMAT releases glycerol and fatty acid substrates that are catabolized by osteoblasts. Here, we investigated whether BMAT lipolysis is involved in subchondral bone formation in hand osteoarthritis (OA). METHODS: Subchondral BMAT lipolysis and bone marrow adipocyte (BMAd) morphology were studied in clinical specimens of carpometacarpal (CMC-1) and distal interphalangeal joint OA. BMAd size, osteoblast numbers and expression of lipolysis enzymes (ATGL, phospho-HSL, MGLL) were compared between regions of low and high bone formation. Free fatty acids, glycerol and bone biomarkers were measured in osteochondral explants. RESULTS: Subchondral BMAd size was positively correlated with BMI (r = 0.60, [0.082,0.87]) and reduced in regions of high bone formation (-1149 µm CONCLUSION: Our findings reveal a previously unrecognized role of BMAT lipolysis in regulating bone formation in hand OA, which may be modulated by BMI.