The purpose of this prospective, double-blind study was to determine if, when using high-flexion total knee components, there was an advantage to using either a posterior cruciate-retaining or posterior cruciate-substituting design from the standpoints of range of motion or functional outcomes. Two hundred and fifty patients received a high-flexion posterior cruciate retaining prosthesis in one knee and a high-flexion posterior stabilized total knee prosthesis in the contralateral knee. Hence, each patient served as their own internal control. Patients were assessed clinically by determining range of motion, both radiographically and functionally, with use of the knee rating systems of the Knee Society and the Hospital for Special Surgery. In addition, each patient completed the Western Ontario and McMaster Universities Osteoarthritis (WOMAC) questionnaire. The authors found there was no difference in the range of motion or in the clinical and radiographic results between knees that received a high-flexion cruciate-retaining or stabilized prosthesis.
The major strength of this study is that it is a prospective, randomized study. The two types of knee prosthesis designs were used (one in each knee) in patients who were undergoing bilateral procedures under the same anesthesia. The study was adequately powered and hence is a Level-I study. Furthermore, patients were assessed clinically, radiographically, and by functional outcome. Weaknesses of the study were that this was an Asian population of predominantly female patients and that the findings may not necessarily be generalizable to other populations. In addition, when bilateral procedures are performed, it may be difficult to separate the functional outcome for one of the individual knees. I believe that the strengths of this study outweigh the weaknesses; however, the limitations of any study must be born in mind when interpreting the data.
This article is important in light of the continuing debate between advocates of cruciate-retaining and cruciate-substituting designs. Most recently Chaudhary et al.1 performed a Level-I, prospective, randomized study of 100 patients who had noninflammatory osteoarthritis and were undergoing primary total knee arthroplasty. They found that, overall, the two groups (patients with posterior cruciate-sparing and posterior cruciate-substituting designs) had a similar range of motion of the knee over the initial two-year postoperative period. In addition, they found that a satisfactory range of motion had been achieved by three months postoperatively and that it continued to be maintained at the time of final assessment.
The other design variable in this study is high flexion. High flexion is a "hot topic"; however, there is relatively little objective data to date regarding its advantages and disadvantages as compared with those of conventional designs. Cates et al.2 performed an in vivo comparison of knee kinematics in subjects who received either a posterior stabilized or a cruciate-retaining high-flexion total knee prosthesis; these authors found that subjects in both groups demonstrated excellent weight-bearing ranges of motion and kinematic patterns that were similar (but with less magnitude) to those of the normal knee. Kim et al.3 assessed the range of motion of standard and high-flexion posterior stabilized knee prostheses in a prospective randomized study. They found that after a minimum duration of follow-up of two years, there were no significant differences between the groups of patients with regard to range of motion or clinical and radiographic parameters except for posterior femoral condylar offset. Lastly, Nutton et al.4 performed a prospective, randomized, double-blind study to assess the functional outcome and range of flexion following total knee replacement with standard and high-flexion components. There were a total of fifty-six patients, half of whom received each design, and patients were assessed preoperatively and at one year after operation. The authors found no significant difference in outcome, including maximum knee flexion, between patients who received the standard design and those who received the high-flexion design of this implant.
In summary, this prospective, randomized, Level-I study adds to our knowledge base regarding the issue of posterior cruciate-retaining compared with posterior cruciate-substituting designs, specifically with respect to high-flexion femoral components. The debate, however, will continue between cruciate-retaining and cruciate-substituting designs, with strong advocates on each side of the discussion. Level-I data, such as provided by this study, provides important objective evidence with respect to these important design issues.
*The author did not receive any outside funding or grants in support of his research for or preparation of this work. The authors, or a member of his immediate family, received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from a commercial entity (DePuy, Smith and Nephew, and Zimmer).
1. Chaudhary R, Beaupré LA, Johnston DWC. Knee range of motion during the first two years after use of posterior cruciate-stabilizing or posterior cruciate-retaining total knee prostheses. A randomized clinical trial. J Bone Joint Surg Am. 2008;90:2579-86.
2. Cates HE, Komistek RD, Mahfouz RM, Schmidt MA, Anderle M. In vivo comparison of knee kinematics for subjects having either a posterior stabilized or cruciate retaining high-flexion total knee arthroplasty. J Arthroplasty. 2008;23:1057-67.
3. Kim Y-H, Sohn K-S, Kim J-S. Range of motion of standard and high-flexion posterior stabilized total knee prostheses. J Bone Joint Surg Am, 2005;87:1470-5.
4. Nutton RW, van der Linden ML, Rowe PJ, Gaston P, Wade FA. A prospective randomised double-blind study of functional outcome and range of flexion following total knee replacement with the NexGen standard and high flexion components. J Bone Joint Surg Br. 2008;90:37-42.