DOI: 10.1097/PRS.0b013e31827c724e

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PMID: 23446610

Issn Print: 0032-1052

Publication Date: 2013/03/01


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Targeted Cranial Bone Transport Distraction Is Enhanced Using a Novel Device

Felix P. Koch; Mikell M. Yuhasz; Rob Travieso; Kenneth Wong; James Clune; Zhen W. Zuang; Derek M. Steinbacher

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Excerpt

Calvarial defects occur following a variety of insults, including trauma and tumor extirpation.1 The goals of reconstruction include wound healing, protection, and contour restoration. Bone transport distraction osteogenesis allows for adequate soft-tissue expansion and maintains vascularity by projecting a vascularized bone segment across space to a target destination. This has been described experimentally for cranial defect application with devices utilizing two linearly opening footplates.2,3 Although effective in small, one-dimensional reconstructions, this design results in haphazard transport segment trajectory without the ability to control contour or end position. The purpose of this study was to reconstruct critically sized rabbit calvarial defects using transport distraction osteogenesis via a novel, three-footplate, worm gear device. We postulate that this device allows for targeted, exact transport segment trajectory and requisite restoration of cranial contour (Figs. 1 and 2).
This study was approved by the Yale University Institutional Animal Care and Use Committee (11393). Four male New Zealand White rabbits (3 months old, weighing 3.5 kg), three experimental and one control, were used. A cranial defect (16 × 16 mm) was created in all animals, along with an anteriorly abutting transport segment (10 × 16 mm) in treatment animals. Distraction occurred for 13 to 15 days at 1.5 mm/day (total of 20.5 to 21.5 mm), and bone consolidated for 4 to 5.5 weeks. The animals were euthanized and analyzed anatomically, using micro–computed tomography, as well as histologically.
The procedure was well tolerated. Gross inspection demonstrated regenerate bone in each treatment animal. Natural and planned cranial contour was achieved, with histologic analysis demonstrating nearly uniform osteoid and trabeculae between segments in the distraction group. The control animal showed no significant ossification. Micro–computed tomography demonstrated interposed mineralized regenerate bone between the distracted segments in the treatment group. Bone density measured more than 10.5 percent (range, 7.8 to 12.4 percent) in the distracted group compared with 1 percent in the control group (range, 0.5 to 1.2 percent) (Fig. 3).
Conventional devices entail distraction of two footplates attached to a mechanism. Through conservation of Newton's law, equal/opposite forces are applied, resulting in motion of the more mobile transport segment. Soft-tissue variables, in addition to the alignment/orientation of the device, dictate segment trajectory, often without adequate control or three-dimensional capabilities.
With a third footplate attached to a track, we provide a target destination and an exact trajectory for the transport segment. The bendable track promotes three-dimensional distraction, providing vertical and horizontal projection, in addition to anteroposterior movement, to reconstruct the desired cranial curvature.
In two animals, the mobile footplate pivoted the transport segment 45 degrees during distraction. This orientation prevented the entirety of distraction trajectory. However, the once critical-sized defect was still reduced to 33 percent of its original size. Complete bony regeneration behind the transport segment was seen, and the smaller persistent defect ossified from the innate dural and periosteal influence. In all subsequent animals, the screws were placed more posteriorly, with the footplate aligned with the leading edge to prevent undesired pivoting, thereby resulting in complete distraction.
Future investigations for cranial transport distraction osteogensis will include modulation of paracrine factors as well as an investigation of its applicability in the setting of irradiated bone and contamination. Human applications can be considered following refinement in the animal model.
We demonstrate effective reconstruction of critical-sized rabbit calvarial defects using a novel transport distraction device, which enhanced targeted segment control and restoration of three-dimensional contour.
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