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Increase of tibial slope reduces wear in medial UKA, study finds

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Patrick Weber

COPENHAGEN, Denmark — The wear rate in a mobile bearing unicompartmental knee arthroplasty implant decreases as tibial slope increases, according to German researchers.

Dr. Med. Patrick Weber, of Munich, presented his team’s findings at the 12th EFORT Congress, here.

According to Weber and his group, while the findings indicate a higher tibial slope should be recommended for mobile bearing unicompartmental knee arthroplasty (UKA) it should also be noted the higher tibial slope increases strain on the ACL.

Weber and colleagues used a custom servohydraulic knee wear simulator to carry out in vitro wear simulation of a medial mobile bearing UKA prosthesis with a spherical femoral surface.

They used tibial trays with two different medial tibial slopes — three each of 0° and 8°. Lateral tibial slope of the space-holder for each group was 0°, and was not changed. In all, the researchers measured 5 million cycles for each different slope tested and determine gravimetric wear rates through an analytical balance used every 500,000 cycles.

Weber reported wear rates of 3.46 ± 0.59 mg/million cycles in the 0° slope group and of 0.99 ± 0.42 mg/million cycles in the 8° slope group. “If we have a tibial slope of 4° or 8°, force is acting against the tibial slope and so there is less or even no more movement between the tibia and the femur,” he said.

The difference between the 0° tibial slope group and the 8° tibial slope group was labeled “highly significant” in the study abstract.

“In our study with a mobile bearing design, a higher slope stabilized the knee in a simulation during the heel strike,” Weber concluded. “Therefore, there was less movement between the tibial tray and the inlay, probably leading to less backside wear.”

Weber cautioned that while the results are promising, further studies are needed.

“Before we can give a general recommendation for the tibial slope in unicompartmental knee arthroplasty, several figures need to be considered such as ligament laxity, the lateral compartment, inlay motions and the bone-implant interface,” he said.

Reference:

• Weber P, Schroder C, Utzschneider S, et al. Increase of tibial slope reduces wear in medial unicompartmental knee arthroplasty. Paper #2690. Presented at the 12th EFORT Congress 2011. June 1-4. Copenhagen, Denmark.

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