Guidelines to Design Custom 3D Printed Jig for Orthopaedic Surgery

Abstract

In osteosarcoma (bone cancer), one of the major challenges for the surgeon is to resect the bone tumour with a margin that is oncologically safe and then reconstruct the defect gap to original anatomical shape and size necessary for proper function. It is very difficult to carry out resections in complex anatomical regions such as pelvis or joints. To ensure good alignment and fixation of patient-customized prosthesis, the bone cut must be accurate and match the geometry of such prosthesis. Proper resection and implant fixation can be achieved by using patient-customized surgical jigs, which guides the surgical tool. This work deals with the design, fabrication and application of orthopaedic surgery jigs. The starting point is the CT scan image set of the patient, which is converted to a 3D CAD model using a medical modelling software. The customized jigs are designed over the 3D model of patient’s anatomy. There are, however, no well-established design guidelines and standards for creating and verifying such jigs. This makes the task challenging to someone inexperienced in medicine and manufacturing. This was addressed by evolving a systematic process for patient-customized surgical jigs. Depending upon the function, the customized jigs are classified as drilling jigs, osteotomy jigs and implant location jigs. For each type, essential element or module that need be provided have been identified. For example, osteotomy guide includes the surface that is conformal to bone, k-wire or other fixation and the overhanging handle or the curved-shaped beam that connects the two parts. Relevant design guidelines were developed. A standard CAD model was developed for each key element. Their shape and dimensions were fixed considering the strength and ease of use. For example, the minimum thickness of the cutting guides was 5 mm to take care of bending. The jig surface that is in contact with the bone was set at 3 mm. The k-wire size was 1.6 mm. Special care was taken to eliminate sharp edges. The full jig is developed by incorporating these elements, making the process faster and reducing random customization that can increase manufacturing cost. The proposed methodology and design guidelines are illustrated with cases of pelvis and tibia surgery jigs, which were validated by the surgeon and proved to be beneficial.