Fracture repair in the Snell dwarf mouse.

Snell dwarf mice are deficient in the somatomedin peptides which are mediators of growth hormone action on the skeleton. Tibial fractures in dwarf mice united within 6 weeks, however chondroid differentiation and osteogenesis at the fracture site were retarded in the first few weeks after fracture compared with normal mice. Administration of bovine growth hormone (5 micrograms daily) accelerated the repair process and 2 micrograms thyroxine daily resulted in rapid callus formation and ossification indistinguishable from normal controls. Normal somatomedin levels are not therefore essential for adequate fracture healing in Snell dwarf mice. The acceleration resulting from growth hormone and thyroxine administration may be due to an increased production of somatomedins locally or systemically or by direct action on connective tissue.