Choosing the Right Knee Implant for Joint ReplacementThere are many different kinds of implants available for knee joint replacement. Some allow greater motion than others. Some rotate. Others swivel. When the joint is unstable, an implant with "constraint" may be used. Constraint limits motion and improves stability. In this article orthopedic surgeons at the University of Washington in Seattle review four constraint designs available.
These include (from least to most constraint):
Constraint implants are needed when the soft tissues and ligaments around the knee can't handle the stress and load. The soft tissues may be lax or loose leading to joint instability. Constraint isn't always a good idea. Sometimes constraint implants increase the stress where the implant interfaces with the bone. Early implant loosening and failure may result.
The authors outline how each of these implants works and when they are used. The good and the bad of each one are reviewed. Some implants wear better than others. Some correct alignment problems while others are good at balancing the ligaments. Problems include implant loosening or fracture. The more constraint present, the less rotation is possible.
Surgeons try to use the implant with the least constraint but the most stability. Each case must be decided carefully. Amount of instability present, type of knee deformity, and other patient factors are considered.
Hannah Morgan, MD, et al. Constraint in Primary Total Knee Arthroplasty. In Journal of the American Academy of Orthopaedic Surgeons. December 2005. Vol. 13. No. 8. Pp. 515-524.
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