Efficacy of rhBMP-2 during distraction osteogenesis.

BACKGROUND: Osteoinductive ability of bone morphogenetic protein-2 (BMP-2) has been studied in recent reports. In this study, we evaluated the efficacy of BMP-2 during distraction osteogenesis.

METHODS: A group of 24 Japanese white rabbits were divided into four groups randomly and underwent lengthening of the right femur. Distraction was performed for 2 weeks (1.0 mm/day). Group A began distraction following a 7-day waiting period after surgery. For all other groups (B-D), distraction was started immediately after surgery. Groups A and B did not undergo any surgical intervention at the osteotomy site, as a control. The delivery system for rhBMP-2 used a polymer-coated gelatin sponge (PGS). Buffer/PGS was implanted into the osteotomy site in group C, and group D received rhBMP-2/PGS. Callus was evaluated radiographically at 1, 2, 4, and 6 weeks after the surgery, and all rabbits were killed at 6 weeks. One rabbit from each group was examined histologically; the remaining five rabbits underwent biomechanical testing.

RESULTS: A significant increase in callus formation was evident in group D compared with that in other groups. In group D, regenerative changes were evident during the earlier phase. Formation of bone cortex and bone marrow cavity was almost complete in group D, and the cortex was thicker than that in the other groups. Torsional strength values (10(-2) Nm) of each group were as follows: A, 118.7 +/- 52.4; B, 160.0 +/- 40.7; C, 106.8 +/- 8.1; D, 266.1 +/- 93.1. Stiffness values (10(-3) Nm/degree) were as follows: A, 390.2 +/- 137.2; B, 391.8 +/- 158.4; C, 183.1 +/- 78.5; D, 624.4 +/- 214.2. Group D exhibited the highest values for both torsional strength and stiffness.

CONCLUSIONS: Acceleration of the regenerative changes during the early phase occurred in the BMP-2-treated group. The efficacy of BMP-2 in distraction osteogenesis was recognized radiographically, histologically, and by biomechanical testing (torsional strength and stiffness).