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Results Figure 3: a. 3D Reconstruction of the control group with critical size defect; b. 3D Reconstruction of the treatment group with the device in situ Cranial Bone Transport Distraction Osteogenesis Using a Novel Worm-Gear Device Mikell Yuhasz BA 1 , Felix Koch MD 2 , Rob Travieso BS 3 , Kenneth Wong BS 1 , James Clune MD 3 , Zhen Zuang MD 4 , Derek Steinbacher MD, DMD 3 1. Yale University School of Medicine, 2. Department of Neurological Surgery, 3. Department of Surgery, Section of Plastic and Reconstructive Surgery; Yale University School of Medicine, 4. Bioimaging Science, Yale University Abstract Background: Reconstruction of calvarial defects is challenging. Bone transport distraction osteogenesis (DO) has been described and carries the advantage of maintaining the osseous blood-supply and promoting slow soft tissue accommodation. The purpose of this study is to reconstruct a critically-sized rabbit calvarial defect using transport distraction via a novel, three-footplate device. We postulate that this targeted device allows for improved transport control and requisite creation of contour. Methods: Four male New Zealand white rabbits (3 months; 3.5kg), 3 experimental, 1 control, were used. A cranial defect (16x16mm) in all animals and an anteriorly-abutting transport segment (10x16mm) in treatment animals were created leaving dura intact. Distraction took place for 13-15 days at 1.5mm/day (total of 20.5-21.5mm) and consolidated for 4-5.5 weeks. Animals were sacrificed and analyzed grossly, anatomically using microCT, and histologically. Results: The distraction protocol was well-tolerated. Gross inspection demonstrated regenerate bone in each treatment animal. MicroCT demonstrated interposed mineralized regenerate bone between the distracted segments. The control animal failed to show significant ossification within the defect. Histology revealed near uniform ossification and trabeculae between the distracted segments. Conclusions: Cranial bone transport distraction can be effectively implemented using a novel 3-footplate distraction device. In addition to incumbent benefits of DO, the middle footplate and conforming track of this device directs the transport segment trajectory, establishing a controlled 3-dimensional autologous reconstruction. Both the defect and transport gap exhibit osseous fill, and reestablish normal cranial contours. This represents a novel, autologous method for cranial reconstruction. Acknowledgements This work was supported by a grant provided through Synthes. Background Calvarial defects occur following a variety of insults, including trauma and tumor extirpation 1 . Goals of reconstruction entail wound healing, protection, and contour restitution. Methods of reconstruction include autologous bone grafts, prosthetic implants, vascularized free bone flaps. Bone transport distraction osteogenesis can be used to correct cranial defects 2 . The technique projects a vascularized bone segment across space to a target destination, maintaining blood-supply. Devices used for DO have traditionally been linear and use 2 footplates 2-3 . The purpose of this study is to prove effective cranial transport DO using a novel, three-footplate distractor with a defect-spanning track to guide trajectory and contour. We hypothesize that this device modification provides enhanced control of planned contour and segment targeting. Methods This study was approved by IACUC Yale. (Protocol number 11-11393). Surgical procedure Three New Zealand rabbits (2 treatment and 1 control) were used. A subperiosteal scalp flap was raised and critical sized defect created (16x16mm) using a piezo saw (Synthes). Dura was left intact. In treatment animals, a transport segment was created contiguous to the defect and device attached (Fig. 1 and 2) Distraction protocol After one-day of latency, animals were distracted at 1.5mm/day for13-15 days. Animals were sacrificed at 5 weeks consolidation. Micro CT Specimens were scanned by micro CT (in vivo CT-120, GE Healthcare Inc). (50um slice thickness, 32mA, 80kV) and analyzed with Osirix. New bone volume and bone density were measured. Histology Heads were prepared following device removal. Specimens were fixed by buffered formalin, washed (PBS), then decalcified by 4% EDTA (4 weeks) and embedded in Paraffin. Coronal (anteriorly) and sagittal (posteriorly) sections were stained with Hematoxilin and Eosin (HE). Results All rabbits tolerated the surgical procedure and post surgical distraction period without complication. Gross inspection. Device fixation and ossified regenerate were seen in all treatment animals. In R1 and 2, the transport segment was obliquely inclined and distracted 2/3 of the track distance. Rabbits R3 and 4, showed a level transport piece with full distraction. Micro CT: Bone density measured >10.5% (range 7.8-12.4%) in the distracted group versus 1% in the control (range 0.5-1.2%) (Fig. 3). Histology Trabeculae of new bone were seen in all treatment samples, in the region of the critical defect. Trabeculae were largely immature with large marrow spaces and covered with a highly vascularized, thick dura. Control samples showed no significant bone formation. Conclusions With a third footplate attached to a track, we provide target destination and exact trajectory for the transport segment. The bendable track conformation promotes 3D distraction. We demonstrate effective reconstruction of critical-sized rabbit calvarial defects using a novel transport distraction device. This represents a novel, autologous method for cranial reconstruction resulting in bone formation and recreation of desired three-dimensional contour, implementing an enhanced, targeted segment control. References 1. Sirola, K. Regeneration of defects in the calvaria: An experimental study. Ann Med Exp Biol Fenn. 1960;38(Suppl 2):1-87. 2. Ilizarov, G. A. The tension-stress effect on the genesis and growth of tissues. Part I. The influence of stability of fixation and soft-tissue preservation. Clin Orthop Relat Res. 1989;(283): 249-281. 3. Bouletreau, P. J., Warren, S. M., Paccione, M. F., et al. Transport distraction osteogenesis: a new method to heal adult calvarial defects. Plast Reconstr Surg. 2002;109:1074-1084. Figure 1. Distraction device consisting of three components: 1 & 2) anterior and posterior footplates, and 3) a movable plate attached to the transport segment Figure 2 2a: Control animal with critical- sized defect 2b: Treatment group with device in situ Figure 4 a. Midline coronal section of distracted section in a treatment animal showing thick trabeculae b. Midline coronal section of a control animal showing no new bone formation
