TNFSF11 and osteopetrosis: Growth plate hypertrophic chondrocytes express RANKL, which stimulates osteoclastogenesis.65,67Rankl deletion in hypertrophic chondrocytes causes osteopetrosis due to reduced cartilage resorption.68 Thus, hypertrophic chondrocyte-mediated RANKL secretion facilitates chondrocyte-to-osteoblast transformation by removal of nascent cartilage, allowing new bone formation.