3D-Printed Patient Specific Instrumentation in Orthopaedic Oncology: Cut Slot Depth`s Impact on Accuracy

Introduction: Clear operative oncological margins are the main target in malignant bone tumour resections. Novel techniques like patient specific instruments (PSIs) are becoming more popular in orthopaedic oncology surgeries. By improving accuracy of surgical cuts, would facilitate highly delicate surgeries such as Joint Preserving Surgery (JPS). There are no universal guidelines on PSI designs and there are no studies showing how specific design of PSIs would affect accuracy of the surgical cuts.

We hypothesised if an increased depth of the cutting slot guide for sawblades on the PSI would improve accuracy of cuts.

Methods: A pilot drybone experiment was set up, testing 3 different designs of a PSI with changing cutting slot depth, simulating removal of a tumour on the proximal tibia.

A handheld 3D scanner (Artec Spider, Luxembourg) was used to scan tibia drybones and Computer Aided Design (CAD) software was used to simulate osteosarcoma position and plan intentioned cuts. PSI were designed accordingly to allow sufficient tumour. 7 orthopaedic surgeons were recruited to participate and perform JPS on the drybones. Fragments were then scanned with the 3D scanner and then matched onto the reference tibia with customized software to calculate how each cut) deviated from planned cut in millimetres and degrees:

Results: Comparing actual cuts to planned cuts, changing the height of the cutting slot guide on the designed PSI did not deviate accuracy enough to interfere with a tumour resection margin set to maximum 10mm.

Discussion: Simulating a cut to resect an osteosarcoma, none of the proposed designs introduced error that would interfere with the tumour margin set. We concluded that 10mm cutting slot would be sufficient for the accuracy needed for this specific surgical intervention.