Histology and histomorphometry of bone regeneration after experimental injuries

Reparative callus formation upon tubular bone was studied after surgical injuries of different degrees. Thirty-seven young rats were divided into three groups. In the periosteum group the bone was scraped, in the fissure group we made a slit reaching the medulla, and in the defect group a standard defect was sawn. Rats were killed at 6, 12 and 18 days. The formed callus was studied histologically and histomorphometrically. The results suggest than even the primary osteochondrogenic callus formation is dependent on the mode of injury. At six days the three groups differed both qualitatively and quantitatively in regard to callus formation. At 12 and 18 days the total area of woven bone was proportional to the degree of trauma according to the linear regression line Y = 0.883 x X + 0.226 (r = 0.876, P less than 0.001). In the fissure and defect groups reparative bone filled the hole proportionally to the same extent. Periosteal and endosteal woven bone formed round the bone. Medullary bone formation was limited mainly to the area immediately adjacent to the trauma, the result being a cylinder-shaped callus. Cartilage formation was most abundant at six days and was related to the amount of woven bone in the external callus (r = 0.854, P less than 0.001) and to the trauma area (r = 0.707, P less than 0.05).