Abstract
These studies were conducted to compare the local cellular proliferation patterns in the rat tibia during distraction osteogenesis with those during nondistracted fracture healing. Bone specimens from distraction osteogenesis and nondistracted fracture groups were analyzed 2, 10, and 20 days after surgery. Proliferation was determined by metabolic labeling with [^3^H]thymidine and by immunocytochemistry with an antibody to proliferating cell nuclear antigen. Videomicroscopy was used to count the cells staining positively within specified regions. The number of cells incorporating [^3^H]thymidine was positively correlated (r^2^ = 0.78) with the number of proliferating cell nuclear antigen positive cells on alternating serial slides. At day 2, the latter cells were largely confined to the bone marrow and periosteum in both groups, and the cell numbers per mm^2^ were also equivalent. At days 10 and 20, the proliferating cell nuclear antigen positive cells predominated in both the proximal and distal primary matrix front zones in the distraction osteogenesis group. In contrast, the proliferating cell nuclear antigen positive cells in the nondistracted fracture group were scattered throughout the healing area. Significantly more of these cells were in the primary matrix front zones than in any location within the nondistracted fractureβhealing area. The number of these cells in the bone marrow adjacent to the surgical area declined from day 2 to day 10 in both groups. The results suggest that (a) proliferating cell nuclear antigen immunostaining is a reliable indicator of cycling cells; (b) by day 10, distraction osteogenesis is characterized by a zoneβspecific pattern of proliferating cells; and (c) distraction osteogenesis prolongs the stimulation of proliferation within the gap after fracture.