Coronal suture response to distraction osteogenesis in rabbits with delayed-onset craniosynostosis

Recent studies have identified a subpopulation of persons with craniosynost osis who exhibit progressive or delayed-onset synostosis and mild cranial v ault deformities. These persons may be good candidates for nonextirpation d istraction osteogenesis. The present studies were designed to determine for ce-displacement parameters and assess the effects of distraction osteogenes is on coronal suture growth and morphologic characteristics in a rabbit mod el with congenital, delayed-onset craniosynostosis. Data were collected fro m a total of 178 rabbits: 71 normal controls; 16 normal controls with distr action; 72 with delayed-onset coronal suture synostosis; and 19 with delaye d-onset coronal suture synostosis and distraction. At 10 days of age, all r abbits had amalgam markers placed on both sides of the coronal suture. In t he force-displacement study, force-displacement distracters were placed acr oss the coronal suture and distracted acutely for 1.0 mm at 42 days of age. Force-displacement curves for the coronal suture were best described by a third-order polynomial regression equation for both normal and synostosed g roups. Significant differences (P < 0.05) were found in the mean force nece ssary to distract a normal suture 1 mm in distance (13.72 kg) compared with a suture with delayed-onset synostosis (48.39 kg). A significant (P < 0.05 ) relationship was also found between the extent of synostosis and the dist ractive force in rabbits with delayed-onset synostosis. In the distraction study, internal distracters were fixed across the coronal suture at 25 days of age and percutaneously and intermittently activated at an average of 0. 11 mm/day for 42 days (4.54 mm total). Serial radiographs were taken at 10, 25, 42, and 84 days of age. Results revealed that rabbits with delayed-ons et synostosis and distraction had significantly (P < 0.01) more coronal sut ure growth rates compared with rabbits with delayed-onset synostosis and no distraction. Coronal sutures were harvested at 84 days of age for qualitat ive histologic examination. Normal, distracted coronal sutures showed widen ed sutural ligaments and thin, active osteogenic fronts. In contrast, distr acted coronal sutures from rabbits with delayed-onset synostosis showed nar rowed sutural ligaments, thickened and blunt osteogenic fronts, and increas ed collagen and bony matrix deposition compared with controls. Results sugg est that distraction osteogenesis without corticotomy may be a treatment al ternative in persons with progressive, delayed-onset synostosis. However, t hese preliminary data also suggest that distractive forces may accelerate o r stimulate osteogenesis differentially in persons with craniosynostosis, p ossibly through an underlying genetic disorder of bone and cytokine regulat ion. These differential osteogenic responses to distraction, if validated c linically, will need to be taken into account when planning distraction rat e and rhythm protocols for patients with craniosynostosis.