Mandibular Abnormalities in Apert, Crouzon, and Pfeiffer Syndromes (original) (raw)

2005, Plastic and Reconstructive Surgery

INTRODUCTION: Objective criteria assessing bone healing in mandibular distraction osteogenesis (DO) do not currently exist.We are still utilizing general parameters from over fifty years ago to determine healing time as twice that of the distraction period. Our goal was to define more objective measures to quantify bone healing in the distraction regenerate.This would allow us to guide clinical decision-making as well as provide evidence-based approach to judge outcomes. Bone healing can be quantified using non-destructive measures, like imaging studies, and destructive measures, such as mechanical testing and histology. In this study, we chose to begin with quantitative imaging measures.While Dual Energy X-Ray Absorptiometry (DXA or DEXA) is used clinically, its use has not been extended to assess DO and fracture healing of the mandible. Our specific aim was to evaluate the efficacy of DXA when compared to micro-Radiography (µX-Ray) and micro-CT (CT), the current non-clinical "gold standard" of non-destructive bone density evaluations.To our knowledge this is the first reported use of DXA to assess DO and fracture healing the mandible. METHODS: A modified Ilizarov-type; bilateral external fixator was placed in the mandible of 400g male Sprague-Dawley rats.A unilateral vertical osteotomy was created in the body, posterior to the 3rd molar (Fig. 1). Pre-operative antibiotics and post-operative analgesia was provided. DO group:A latency period of 4 days was followed by 12 days of distraction at a rate and rhythm of 0.3mm Q12hr for a total DO gap of 5.1mm, then 28 days of consolidation. Fracture (Fx) group: 2mm fractures were matched for latency and consolidation. Control group: Paired hemi-mandibles for each DO and fracture were included.After euthanasia with IP pentobarbital, mandibles were harvested en-block for imaging studies. IMAGING: µCT (GE Healthcare Biosciences) images were obtained by scanning at a 45 micron voxel size, then reconstructed, reoriented , cropped and separated into surgical and control hemi-mandibles. DXA (Norland Sabre) images were obtained using a scan rate of 3mm/s with 0.2 x 0.2mm resolution. µX-Ray radiographs (MX-20, Faxitron X-Ray corp.) were obtained at 3x magnification with an exposure of 13s at a 25kV potential, and calibrated using an aluminum step-wedge. Regions of interest (Fig. 2) were selected using anatomical and surgical landmarks, directly behind the 3rd molar, and centered to encompass most of the gap (for DO and Fx) and matched for the contra-lateral side (control). Measurements were established so ROIs were directly comparable between the imaging modalities. Groups consisted of n = 11 for DO and n =7 for Fx, with paired controls.Values were listed as mean +/-SD. Student's paired t-tests were used to compare the surgery site with control mandibles for each imaging modality, and independent t-tests were used to compare the non-paired DO and Fx data.The results were considered to be significant if p < 0.05. RESULTS: The BMD was significantly lower in both the DO gap and fracture sites when compared to their respective controls (p<0.01).Although the initial appearance of BMD seemed to be less in DO than FX, no significant differences were found when comparing the Fx and DO sites independently in all three imaging studies (Graph 1). Finally, no differences were found when comparing DXA versus µX-Ray, DXA versus µCT, or µX-Ray versus µCT for either the fracture group, or the DO group (Graph 2).Thus, all imaging modalities provided no significant difference in measuring BMD. CONCLUSIONS: While µCT remains the gold standard of non-destructive, quantitative measurements of bone healing, our data supports the use of DXA and µX-Ray as equivalent two-dimensional measures of BMD, one such bone healing measure.We conclude that µX-Ray and DXA provide a cost-effective, time efficient, and potentially non-invasive quantitative imaging modality to objectively assess bone healing for both fracture repair and distraction regenerates in the mandible.