Purpose of the study: The process of bone lengthening involves three phases: a latence period, distraction, then healing. The healing phase required stability maintained by an external fixator (EF) for 1.16 months/cm lengthening. This time exposes the patient to serious complications. The objective is to accelerate the healing phase in order to shorten the time the patient has to wear the EF. The effect of BMP on osteogenesis in distraction remains a controversial issue. This work was conducted to evaluate the benefit provided by rhBMP-2 for healing the regenerate bone after distraction.
Material and methods: Thirty-nine subadult male rabbits were selected at random. On day 0, a tibial osteotomy was performed followed by installation of a M101 EF. After the latency period of seven days, the distraction began at the rate of 0.5mm/12 h for 21 days. At day 28, at the end of distraction, a new operation was performed and three groups of 13 individuals were created at random. The first group received no material, the second a collagen type 1 sponge, and the third group a collagen type 1 sponge soaked in 100 μg/kg rhBMP-2. The animals were monitored with x-rays, absorptiometry and ultrasound for the qualitative and quantitative analysis. Histological and biomechanical analyses were performed at two months.
Results: Our complication rate was 41%. Qualitative analysis of the x-rays showed, in group 3, the development of more or less voluminous and dense, sometimes hypertrophic calluses. The progression curves of the bone mineral content showed higher values in group 3. The bone mineral content curves remained nevertheless parallel for the three groups. The calluses were thus denser in group 3 but with an early peak density. Groups 1 and 2 had equivalent radiographic and absorptiometric results. The statistical analysis of the imaging findings is ongoing. The histology and biomechanical exams are being performed.
Discussion: The preliminary results show that rhBMP-2 used early in the healing phase enables formation of more dense and hypertrophic calluses. rhBMP-2 does not acceleration the rate of callus formation but stimulates its mineralization. Use of a collagen sponge alone had no effect on healing. Analysis of the histological and mechanic properties observed in the three groups will provide a more precise description of the hypertrophic and strongly mineralized calluses.
Conclusion: Our early results show superior bone mineralization in the treated group.
