Not all total knee replacements (TKRs) are alike. Studies to compare them are ongoing. Tests done in the lab measure the effect of muscles, tendons, and ligaments on joint implants. This gives scientists information about joint laxity (looseness) and stability. Tests to measure the wear and tear on joint implantss are also done this way.

In this report, the authors look at how and why testing implants in the lab is not the same as testing them in human knees. Even so, they say that there is value in knowing what the joint can and can't do before putting it in a human knee. This report also reviews many of the studies on TKRs done by others. Included are comparisons of different machines used in the lab to move the joint implant.

Researchers have only begun to scratch the surface in studying TKRs. There are many factors to measure and compare. Besides comparing one implant to another, scientists also look at many other issues. For example, the joint can be tested at extreme motions or with different muscle forces. Changing the tightness of ligaments and testing during activity rather than at rest are just a few of the other conditions tested.

The authors conclude by saying that the way a joint moves depends on several factors. These include the shape of the joint surfaces, how much friction is created, and the overall design of the TKR.

Reference:

Peter S. Walker, PhD, and Hani Haider, PhD. Characterizing the Motion of Total Knee Replacements in Laboratory Tests. In Clinical Orthopaedics and Related Research. May 2003. Vol. 410. Pp. 54-68.'