SP7 and cyst: Chen et al. (2015) examined cellular composition of human OA subchondral bone cysts and showed that the number of osteoclasts, osteoprogenitors (osterix+), osteoblasts (osteocalcin+, OCN+), and SOX9+ cells were higher in bone cyst sites than those in peri-cyst sites, suggesting enhanced bone turnover and abnormal bone remodeling.