Histologic and Ultrastructural Soft Tissue Changes Following Immediate and Delayed Midface Distraction Osteogenesis
Shawkat Sati, MD1, Kip Panter, PhD2, Joyce C. Chen, MD1, Qian Wu, MD1, Jeffrey Weinzweig, MD1.
1Lahey Clinic, Burlington, MA, USA, 2USDA, Logan, UT, USA.
BACKGROUND: Midface distraction offers the advantages of advancement without bone grafting, greater potential advancement, and lower relapse rates. Previous work of ours demonstrated adverse effects of immediate (intra-operative) distraction on the facial artery, zygomaticus muscle, and infraorbital nerve. The purpose of the present study was to determine if distraction affects these tissues when performed in delayed or conventional post-operative fashion The impact of distraction tensile forces on these tissues is poorly understood. Several studies have evaluated the impact of mandibular and long-bone lengthening on soft tissues; the present work is the first to evaluate all three soft tissue parameters following conventional midface distraction.
METHODS:Using our congenital cleft palate model, midface distraction was performed on adult goats who had previously undergone cleft palate repair at 6 weeks of age. Unilateral harvesting of pre-distracted muscle, nerve and arteries was performed. Five days after surgery, distraction was initiated bilaterally (1mm/day) for 15 days. After 12 weeks of consolidation, contralateral soft tissue elements were harvested and studied.
RESULTS: : Light microscopy of distracted muscle demonstrated intermesial fibrosis, myotrophic atrophy, and intramuscular inflammation. Distracted arteries demonstrated hemosiderin deposition and tunical hemorrhage. Distracted nerves demonstrated myelin beading and staining heterogenecity with perineurial inflammatory infiltration. Electron microscopy corroborated these findings including vaso vasorum, nerve, and Schwann cell interruption.
CONCLUSIONS: The present work is the first to evaluate all three soft tissue elements following conventional midface distraction. Longitudinal distraction vector forces produced endoneurial and perineurial Wallerian degenerative nerve changes. Although nerve fibers are considered more vulnerable, reactive fibrous metaplasia and a paucity of elastin content and organization concentrated in the tunical media and intima represented demonstrative vascular susceptibility. Our findings support the adaptation cycle of muscle fibers to tensile forces beginning with hypertrophic, inflammatory and regenerative response pathways. Although bone receives the direct distractional force, soft tissue elements undergo significant stretching. The effect of these mechanical forces varies depending on the tissue's elastic, compensatory, and reparative properties.