The vascularized pig fibula bone flap model: Effects of multiple segmentalosteotomies on growth and viability

Previous work by this laboratory introduced the pig fibula bone flap as a m odel for the study of the pathophysiology of vascularized bone flaps. Anato mic and hemodynamic studies demonstrated a significant (p < 0.05) decrease in vascular perfusion after a series of segmental osteotomies and rigid fix ation (lag screws and miniplates) in the distal end of the flap, suggesting that blood flow to the distal osteotomized segment of the flap may be impa ired. Killing the animals after blood flow studies precluded assessment of the effect of these hemodynamic changes on bone healing. Therefore, the aim of this study was to assess the pig fibula bone flap model with respect to viability, healing, and subsequent growth after multiple segmental osteoto mies and rigid fixation to contribute to the understanding of vascularized bone flap pathophysiology. Yorkshire pigs (20 to 25 kg) were used for all experiments. Eight pigs unde rwent unilateral elevation of a vascularized fibula bone flap, which was os teotomized into three segments and orthotopically rigidly fixed using a 2.4 -mm mandibular reconstruction plate. The left fibula remained as the contro l. Fluorochrome labels were injected to assess bone viability and turnover, and both fibulae were assessed for growth radiologically. The fibulae were harvested 21 days postoperatively (when the animals were killed), and bone healing was assessed, histologically and clinically. There were no significant differences in preoperative and postoperative len gths of the osteotomized fibulae compared with the controls, suggesting tha t there was no impairment of growth potential after multiple segmental oste otomies and rigid fixation. Significant (p < 0.05) bony hypertrophy of the osteotomized fibulae was noted when compared with controls. Mobility was ob served in 3 of the 32 osteotomies (9 percent), occurring across one proxima l and two distal osteotomies in association with failure of fixation. Howev er, histologic and fluorochrome assessment confirmed the liability of all b one segments, as supported by the presence of tetracycline given 2 days pos toperatively. The pig fibula bone flap model is well tolerated by the pig, Multiple segme ntal osteotomies and rigid fixation, previously associated dth a significan t decrease in blood flow in the distal segment, did not impair either growt h potential, viability, or healing ability. It is suggested that the pig fi bula is a suitable model fur the study of bone nap pathophysiology.