By: 25 October 2011

Cobb J et al.
The Journal of Bone and Joint Surgery (Br). 2006; 88-B: 188-97

This randomized controlled trial of unicompartmental knee arthroplasty (UKA) compared the performance of the Acrobot robotic system with conventional surgery.

Conventional UKA has a considerable revision rate possibly attributed to malpositioning of components, resulting in poor function. Computer-assistance devices have been developed to improve the accuracy of implantation using navigational techniques. The robotic device actively prevents the surgeon from removing bone outside the defined area in the pre-operative plan.

A total of 27 patients (28 knees) took part in the study, subject to inclusion and exclusion criteria. The primary outcome measurement was the angle of tibiofemoral alignment in the coronal plane, measured by CT (detecting a change in alignment of 1°).

In all of the Acrobot group, the tibiofemoral alignment in the coronal plane was within 2 degrees of the planned position, whereas 40% of the conventional group achieved this accuracy. These results were significant thus confirming that the use of an active constraint robotic assistant improved the positioning of the prosthesis in the coronal plane, in UKA. There was a trend towards improved performance with increasing accuracy based on the Western Ontario and McMaster Universities Osteoarthritis index and American knee society (AKS) scores at 6 weeks and 3 months, which may have clinical advantages. The difference in the mean operating time between the two groups was not significant. Despite the robot-assisted operations taking longer, the clinical outcome at 6 and 18 weeks did not reveal any detrimental effect.

This short term clinical outcome may be due to surgeon bias but the correlation between accuracy and function implies that there is a real association. Some shortcomings are that the AKS score has substantial inter- and intra-observer errors and no long-term follow up is available. In the future it may help to reduce the training time for acquiring a new skill and reduce error in joint replacement whether in angular positioning, translation, sizing of component or a combination of these.