What Is Normal About a Unilateral Knee Replacement?Sometimes knee arthritis only affects one side of the joint. In such cases, a unicompartmental knee replacement (UKR) is done. This implant only replaces the affected side of the knee joint. This study looks at knee motion after a UKR and compares it to motion after a total knee replacement (TKR).
Six knees from cadavers were used. The knees chosen were free from defects or deformities. Only left knees were used. The soft tissues around the joint were tested for strength and found to be healthy before the operation. Knee motion and strength were tested before and after the UKR. Then the UKR was taken out and a TKR was inserted and tested in the same way.
Researchers weren't just looking at how much motion occurred. They were also measuring something called kinematics. Kinematics includes the small rotations, sliding movements, and sideways gliding that occurs during normal flexion and extension of the knee joint.
Since no ligaments are cut with the UKR, it's thought that the kinematics stay the same as in a normal knee. This study was able to confirm this idea. Knee kinematics didn't change with the UKR. When a TKR was implanted, the rotation of the tibia (lower leg bone) was altered during knee flexion.
The authors conclude that near normal function can be expected after UKR. Healthy ligaments aren't as important as the surface geometry of the knee. TKR changes the way the joint matches up and moves. Even the muscles work differently with the TKR compared to the UKR. Young, active adults who have arthritis on one side of the joint but need normal motion to join in sports may be the best candidates for a UKR.
Shantanu Patil, MD, et al. Can Normal Knee Kinematics Be Restored with Unicompartmental Knee Replacement? In Journal of Bone and Joint Surgery. February 2005. Vol. 87-A.
No. 2. Pp. 332-338.
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