Which of the following statement(s) is/are true concerning the biologic mechanisms of fracture repair?

a. The mechanisms involved depend primarily on the stability of the fracture

b. The first material formed by osteoblasts at the fracture site is woven bone

After initial inflammation and neovascularization of an area fracture, the repair continues by a combination of mechanisms: endochondral ossification, direct bone apposition, and primary healing involving an acceleration of the normal remodeling process directed across a stable, securely reduced fracture line. The occurrence and distribution of these mechanisms depends primarily on the stability of the fracture during the treatment and secondarily on the fracture location. The more unstable the fracture, the more endochondral the repair process and the greater the cross-sectional area of the callus. The biologic processes are driven by the need to establish mechanical integrity as quickly as possible. The first material formed by osteoblast at the fracture site is woven bone. Although woven bone has inferior mechanical properties when compared to lamellar bone, it can be laid down rapidly and at high density. The laws of mechanics dictate that an increase in the crosssectional area as produced by surrounding callus, greatly increases the resistance of the structure to bending or torsional loads. An increase in unit diameter of the cross-section raises the strength of the structure by the fourth power of the diameter change. Therefore, even if callus is made of an inferior material, the cross-sectional attributes more than compensate for the inferior substance. Once the fracture is stabilized by the initial woven bone proliferation, secondary remodeling occurs.