Figure 1.

Fracture healing in two different mechanical strain environments. Fracture sites are indicated by arrows. The radius (a) fixed with a rigid plate, and experiencing minimal mechanical strain, is healing by direct osteonal repair. The ulna (b), which is in a more flexible mechanical environment, and is experiencing motion and strain, is healing by endochondral bone formation. For both the radius and the ulna, the ECM and gene expression of the repair are being regulated by the biophysical environments. Reproduced with permission from Aaron RK, Bolander ME (eds). Physical Regulation of Skeletal Repair. Rosemont, IL: American Academy of Orthopaedic Surgeons; 2005.