Computer assisted surgery (CAS) and patient specific instrument (PSI) have been reported to increase accuracy and predictability of tumor resections. The challenging joint-preserving surgery that retains the native joint with an optimal function may benefit from these assistances. Literature has shown that the pelvic surgery can be improved by these assistances, but to date, there is no clear statement around the knee. This cadaver study aims at investigating the surgical accuracy of CAS and PSI in joint-preserving surgery of knee joint.

CT-scans of four cadavers (8 legs) were acquired. Eight metaphyseal bone sarcomas were simulated on distal femur and proximal tibia. Joint-preserving multiplanar resections were planned. Four techniques (freehand, CAS, PSI and CAS+PSI) were used to perform the resections. Total resection time was measured for each. Postoperative CT-scans were acquired and analysed to measure the location accuracy (maximum deviation of distance between the planned and achieved resections).

Both CAS+PSI and PSI techniques could reproduce the planned resections with mean location accuracy below 2mm, compared to 3.6mm for CAS and 9.2mm for the freehand technique. No statistical difference has been found between the CAS+PSI and PSI techniques (P=0.92). CAS and CAS+PSI were found significantly more accurate than CAS (respectively P=0.042 and P=0.034). Finally, freehand technique was found significantly less accurate than any other technique (P<0.05). PSI was significantly fastest (mean 4.8min) when compared to CAS+PSI technique (mean 12.8min, P<0.001) and CAS technique (mean 17.0min, P=<0.001). No difference was found between PSI and freehand technique (mean 6.8min).

This cadaveric study of simulated joint-preserving tumor surgery around the knee joint suggests that CAS, PSI or CAS+PSI techniques permitted to reproduce the multiplanar resections as planned. PSI technique could achieve the most accurate bone resections.

The accuracy obtained by using PSI, CAS or PSI+CAS is clinically sufficient to ensure a safe margin. However, the PSI accuracy depends on its stability on the bone surface. This is directly relative to the PSI design and the communication between surgeon and engineering team to define surgical approach and available bone surface.