SUSTAINED PROLIFERATION ACCOMPANIES DISTRACTION OSTEOGENESIS IN THE RAT

These studies were conducted to compare the local cellular proliferati on patterns in the rat tibia during distraction osteogenesis with thos e during nondistracted fracture healing. Bone specimens from distracti on osteogenesis and nondistracted fracture groups were analyzed 2, 10, and 20 days after surgery. Proliferation was determined by metabolic labeling with [H-3]thymidine and by immunocytochemistry with an antibo dy to proliferating cell nuclear antigen. Videomicroscopy was used to count the cells staining positively within specified regions. The numb er of cells incorporating [H-3]thymidine was positively correlated (r( 2)=0.78) with the number of proliferating cell nuclear antigen positiv e 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, t he proliferating cell nuclear antigen positive cells predominated in b oth the proximal and distal primary matrix front zones in the distract ion osteogenesis group. Tn contrast, the proliferating cell nuclear an tigen positive cells in the nondistracted fracture group were scattere d throughout the healing area. Significantly more of these cells were in the primary matrix front zones than in any location within the nond istracted fracture-healing 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) b y day 10, distraction osteogenesis is characterized by a zone specific pattern of proliferating cells; and (c) distraction osteogenesis prol ongs the stimulation of proliferation within the gap after fracture.