Application of full-scale three-dimensional models in patients with rheumatoid cervical spine

Abstract

Full-scale three-dimensional (3D) models offer a useful tool in preoperative planning, allowing full-scale stereoscopic recognition from any direction and distance with tactile feedback. Although skills and implants have progressed with various innovations, rheumatoid cervical spine surgery remains challenging. No previous studies have documented the usefulness of full-scale 3D models in this complicated situation. The present study assessed the utility of full-scale 3D models in rheumatoid cervical spine surgery. Polyurethane or plaster 3D models of 15 full-sized occipitocervical or upper cervical spines were fabricated using rapid prototyping (stereolithography) techniques from 1-mm slices of individual CT data. A comfortable alignment for patients was reproduced from CT data obtained with the patient in a comfortable occipitocervical position. Usefulness of these models was analyzed. Using models as a template, appropriate shape of the plate-rod construct could be created in advance. No troublesome Halo-vests were needed for preoperative adjustment of occipitocervical angle. No patients complained of dysphasia following surgery. Screw entry points and trajectories were simultaneously determined with full-scale dimensions and perspective, proving particularly valuable in cases involving high-riding vertebral artery. Full-scale stereoscopic recognition has never been achieved with any existing imaging modalities. Full-scale 3D models thus appear useful and applicable to all complicated spinal surgeries. The combination of computer-assisted navigation systems and full-scale 3D models appears likely to provide much better surgical results.

Fig. 1

Preoperative planning and virtual surgery for occipitocervical fixation. Adequate occipitocervical angle of the plate can be determined in advance. If images from computed tomography (CT) are obtained in a position in which the patient does not feel discomfort while swallowing, the templating plate/rod is bent and fitted to produce the appropriate angle on the full-scale three-dimensional (3D) model. After bringing the sterilized templating plate/rod into the operating room, the true implanting plate/rod construct was bent as the same shape of the templating plate/rod during surgery

Fig. 2

Postoperative plain radiography. Appropriate plate-rod construct and occipitocervical angle are achieved

Fig. 3

Left: full-scale 3D model of vertical subluxation. Basilar impaction of the odontoid peg is clearly apparent in true dimensions. Right: transverse foramen and pedicle are readily surveyed in true perspective

Fig. 4

Virtual surgery for atlantoaxial fixation. Surgeons can see that insertion of C1 screws is not destroying the posterior arch and that C2 screws are inserted safely, without perforation of the transverse foramen