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Normal Values for Joint Laxity for Surgeons to Use with Total Knee Replacements

Getting a good result after a total knee replacement (TKR) depends quite a bit on the surgeon's skill. The right size and type of implant must be selected. Putting the implant in so it's not too tight or too loose is important. In this study cadavers are used to find out how much joint laxity or looseness is normal. The surgeon can use these values to restore the natural anatomy as much as possible.

A new fluoroscopy-based computerized navigational system was used in this study to measure joint laxity. Fluoroscopy is a type of X-ray that allows the surgeon to see inside the joint during testing. The amount of joint movement was measured in three planes of motion. Two different positions of the knee were used to test ligament laxity. Joint laxity or gap was measured with the knee in full extension and again in 30 degrees of flexion.

The measures were repeated after a TKR was done. The authors report the measurements for anterior-posterior, medial-lateral, and rotational laxity before and after the TKR. They found the laxity values weren't much different from before to after. There was slightly less laxity along the lateral side of the joint after TKR. They suggest surgeons can use this information when doing TKRs on patients.

This is the first study to use a computerized navigational system to compare joint laxity before and after TKR. More studies like this are needed to give surgeons accurate values for knee laxity. Implanting a joint replacement with as close to normal biomechanics is the goal.

References: Geert Van Damme, MD, et al. What Should the Surgeon Aim for with Performing Computer-Assisted Total Knee Arthroplasty? In The Journal of Bone and Joint Surgery. December 2005. Vol. 87-A. Supplement 2. Pp. 52-58.

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