Precision freehand sculpting for unicondylar knee replacement: design and experimental validation

Precision freehand sculpting (PFS), is a hand-held semi-active robotic technology for bone shaping that works within the surgical navigation framework. PFS can alternate between two control modes - one based on control of exposure of the cutting bur and another based on the control of the speed of the cutting bur. In this study we evaluate the performance of PFS in preparing the femoral bone surface for unicondylar knee replacement (UKR). The experiment is designed to prepare a synthetic bone for UKR. The implant was a modified commercial design that allows accurate measurement of the implant position after it is placed on the prepared bone surface. The distal and anterior-distal facets were cut with a 5 mm cylindrical bur using exposure control. The posterior facet and the post holes were cut using a 6-mm spherical bur using speed control. Three users cut five specimens each. The performance was evaluated in terms of the implant fit and the performance time. The average cut times for the first two cuts combined were 4:35 min, and for the posterior cut 3:26 min. The average distance from the planned implant position was 0.54 mm (SD 0.23 mm) and the average angular difference was 1.08 degrees (SD 0.53 degrees).