OBJECTIVE There has been a recent renewed interest in the use and potential applications of 3D printing in the assistance of surgical planning and the development of personalized prostheses. There have been few reports on the use of 3D printing for implants designed to be used in complex spinal surgery. METHODS The authors report 2 cases in which 3D printing was used for surgical planning as a preoperative mold, and for a custom-designed titanium prosthesis: one patient with a C-1/C-2 chordoma who underwent tumor resection and vertebral reconstruction, and another patient with a custom-designed titanium anterior fusion cage for an unusual congenital spinal deformity. RESULTS In both presented cases, the custom-designed and custom-built implants were easily slotted into position, which facilitated the surgery and shortened the procedure time, avoiding further complex reconstruction such as harvesting rib or fibular grafts and fashioning these grafts intraoperatively to fit the defect. Radiological follow-up for both cases demonstrated successful fusion at 9 and 12 months, respectively. CONCLUSIONS These cases demonstrate the feasibility of the use of 3D modeling and printing to develop personalized prostheses and can ease the difficulty of complex spinal surgery. Possible future directions of research include the combination of 3D-printed implants and biologics, as well as the development of bioceramic composites and custom implants for load-bearing purposes.

1. At necropsy the arterial distribution within the head and neck of the femur was investigated by arteriographic injection in fifty-seven uninjured hips of mostly elderly subjects. 2. Before injection all vessels to the head except for one or more particular groups were divided. 3. The superior retinacular arteries were found to be the most important arterial supply to the head. Through the widely distributed branches of their lateral epiphysial vessels (superior capital) they supplied the superior, medial, central and usually the lateral parts of the head: through anastomoses they could also supply the anterior and posterior segments, the subfovea and the inferior sector, which receive separate contributions. Sometimes the inferior or the lateral connections were defective. 4. The arteries in the ligamentum teres were either absent or unimportant for the head in most subjects. Either the vessels in the ligament never reached the head or they supplied only a limited subfoveal zone. In only one out of sixteen specimens was the whole head injected through the vessels of the ligamentum teres. 5. The inferior retinacular arteries were found to be of subsidiary importance and generally supplied a variable infero-lateral part of the head, particularly posteriorly. In a small number there was an anastomotic supply to other parts of the head, but only in two out of sixteen specimens was nearly all the head injected through these vessels. 6. The regular anastomotic supply from the superior retinacular arteries to the subfovea and to the inferior part of the head was in curious contrast to the infrequent anastomotic filling of the lateral epiphysial arteries from the inferior retinacular or ligamentum teres arteries. 7. Vessels within the femoral neck sometimes supplied the lateral part of the head but never the medial three-quarters. 8. The neck of the femur received important branches from the superior retinacular arteries but only in a small number (15 per cent) was part of it entirely dependent on this supply.

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Prior studies have suggested that biomodels enhance patient education, preoperative planning and intra-operative stereotaxy; however, the usefulness of biomodels compared to regular imaging modalities such as X-ray, CT and MR has not been quantified. Our objective was to quantify the surgeon's perceptions on the usefulness of biomodels compared to standard visualisation modalities for preoperative planning and intra-operative anatomical reference. Physical biomodels were manufactured for a series of 26 consecutive patients with complex spinal pathologies using a stereolithographic technique based on CT data. The biomodels were used preoperatively for surgical planning and customising implants, and intraoperatively for anatomical reference. Following surgery, a detailed biomodel utility survey was completed by the surgeons, and informal telephone interviews were conducted with patients. Using biomodels, 21 deformity and 5 tumour cases were performed. Surgeons stated that the anatomical details were better visible on the biomodel than on other imaging modalities in 65% of cases, and exclusively visible on the biomodel in 11% of cases. Preoperative use of the biomodel led to a different decision regarding the choice of osteosynthetic materials used in 52% of cases, and the implantation site of osteosynthetic material in 74% of cases. Surgeons reported that the use of biomodels reduced operating time by a mean of 8% in tumour patients and 22% in deformity procedures. This study supports biomodelling as a useful, and sometimes essential tool in the armamentarium of imaging techniques used for complex spinal surgery.