The dysfunction of SSCs can also lead to skeletal diseases like delayed fracture healing or nonunion, bone tumors, etc. Deletion of Osx in Ctsk+ P-SSCs of Ctsk-Cre; Osxflox/flox mice lead to markedly impaired fracture healing with a significant decrease of callus formation showing that SSCs are indispensable for bone repair [6]. Here, CTSK is linked to bone disorder.