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Knee News

A Robot's View of ACL Function in Partial Knee Replacement

Engineers at Massachusetts General Hospital are using robots to get some answers about knee joint replacements. The role of the anterior cruciate ligament (ACL) is the focus of this study. How important is the ACL after unicompartmental knee arthroplasty (UKA)?

UKA replaces just half of the knee joint. UKA is becoming a popular solution because arthritis wears down a joint unevenly. UKA leaves the normal side of the joint intact. The patient doesn't need a total knee joint replacement. Usually the inside edge (the medial side) of the joint is replaced. This is called a medial UKA.

The ACL keeps the tibia (lower leg bone) from sliding too far forward during knee flexion. This ligament is often torn before the joint replacement. Sometimes it's cut during knee replacement. In this study, engineers measured the effect of UKA on the stability of the knee with and without the ACL.

Researchers used seven human knees saved for study after death. A robotic testing system measured knee motion before and after a UKA was implanted. The same system applied repeated loads to the knee before and after the ACL was cut. A computer recorded the forces transmitted through the knee.

As the engineers suspected, the tibia moved forward more when the ACL was cut than in either the normal knee or the knee with an UKA and intact ACL. The motion was like an ACL-deficient knee with or without UKA.

The authors don't think a medial UKA changes the forward stability of the knee. The results of this study show the importance of the ACL after UKA. A normal, working ACL is needed for the success of the UKA. In general the knee with an UKA does best when the soft tissues are left in place.


Jeremy F. Suggs, MS, et al. Function of the Anterior Cruciate Ligament after Unicompartmental Knee Arthroplasty: An In Vitro Robotic Study. In The Journal of Arthroplasty. February 2004. Vol. 19. No. 2. Pp. 224-229.

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