Editorial Comment

Total knee arthroplasty is widely recognized as a cost-effective intervention for end-stage osteoarthritis of the knee. The number of total knee arthroplasties done in the United States continues to increase annually and it is expected it will do so during the next decade. In the population of patients who receive Medicare, which accounts for approximately 55% to 60% of the total knee arthroplasties done in the United States annually, the number of knee arthroplasties per thousand Medicare enrollees increased from approximately four per thousand in 1993 to five per thousand in 1997. In 2000, there were approximately 156,000 total knee arthroplasties done in patients who receive Medicare for a cost of more than 1.5 billion dollars. In addition to the increasing numbers of total knee replacements done annually, the operation is being done more commonly in younger patients with higher functional demands.

In the past decade, there has been an improved understanding of the kinematics of the human knee. Recent studies using modern methodologies have challenged the concept of the four-bar link model of human knee motion and obligatory femoral rollback. In vitro testing, fluoroscopic analysis, and sophisticated imaging have allowed a more accurate depiction of knee motion. This improved understanding of knee kinematics has impacted knee replacement design.

Although knee replacement clearly is a highly effective procedure, traditional outcome measures in terms of knee scores have been relatively crude. Newer technologies have permitted a more sophisticated analysis of the effect of implant design on knee kinematics and wear of the articulation. Metrology has permitted quantification of wear and creep more accurately. Robotics has permitted the analysis of discreet interventions and changes in implant design on knee kinematics. Design changes can be evaluated in vivo with fluoroscopic analysis. Fluoroscopic evaluation of patients who had total knee arthroplasty can more carefully analyze the effect of design change and surgical technique on knee kinematics from a three-dimensional standpoint. Through a better understanding of knee kinematics, implant design and surgical technique should evolve to allow better functional outcomes even in patients with higher physical demands. This requires careful evaluation of design changes using state of the art techniques.

In this symposium, these issues are addressed. Kinematics of the human knee are presented from several standpoints using various evaluation techniques. The effects of implant design on kinematics and wear are assessed. In addition, the effects of design on torque and rotational constraint are analyzed. Considerations related to mobile-bearing total knee replacements are presented. Finally, the effect of femoral component design on patellar function and the need for resurfacing is addressed.

Traditional concepts concerning knee kinematics and knee replacement design are challenged by articles in this symposium. The reader should be able to appreciate current methodologies for evaluation of knee kinematics and begin to appreciate our current level of understanding of how implant design effects kinematics after total knee replacement.