The accuracy of prosthesis implantation is closely related to their function and longevity; we report the development of an active constraint robot for minimally invasive unicompartmental knee arthroplasty (UKA) using CT and knee scoring.

Method: Pre and postoperative CT scans are performed. Pre-op scan CT scans were used to plan the precise position of implants on the bones. The femoral and tibial bone cuts were then generated, together with the software boundaries that constrain the surgeon. This plan was then used to define the cutting planes of the ‘Acrobot’ active constraint device that we have developed.

The Postoperative CT scan was compared with the preoperative plan. The distance of the joint line from the hip and ankle joint, and its angulation and rotation were compared to the preoperative plan. In addition, the position of the implants relative to their planned position has been computed.

Results: No significant complications have been encountered. Using the postoperative CT scans, in no case is the implant more than 2mm or 2 degrees from the planned position.

Conclusions: The Acrobot system for UKA has completed its preliminary trial satisfactorily. It provides a hands-on operation but with robotic levels of accuracy, through a minimally invasive approach. By abolishing outliers, it improves outcomes in UKA replacement.