The quality of outcomes studies on arthroplasty has improved dramatically in the recent literature, with an increasing number of prospective randomized studies coming to fruition.
However, given the limited number of prospective randomized studies performed to date, we must also consider retrospective data in our assessment of the arthroplasty outcomes literature.
High-Flexion versus Standard Knee Designs
Kim et al.
conducted a prospective randomized study involving a bilateral total knee arthroplasty model in which a high-flexion design was compared with a standard cruciate-retaining design. Ten men and 240 women had a bilateral total knee arthroplasty in which one knee was treated with a high-flexion implant and the contralateral knee was treated with a standard-flexion design. Patients were assessed at various intervals with use of questionnaires, rating systems, and clinical and radiographic examinations.
After a minimum duration of follow-up of two years, the authors found no significant clinical differences between the groups, revealing that the high-flexion design did not have any advantage over the standard-flexion design.
Kim et al.
also performed a prospective randomized study in which fifty-four patients received a high-flexion prosthesis in one knee and a standard cruciate-retaining prosthesis in the contralateral knee.
Again, the authors found no differences between the groups in terms of knee scores, function, or range of motion at three years.
Minoda et al.
prospectively randomized 171 patients undergoing 181 cruciate-retaining total knee arthroplasties to receive standard implants or implants with a high-flexion femoral component and a polyethylene insert. The patients were followed for one year and were assessed on the basis of range of motion, knee scores, and clinical and radiographic outcomes.
There were no significant differences between groups, although the authors identified a higher average range of motion in the high-flexion group.
Seon et al.
conducted a study in which fifty knees were randomized to total knee arthroplasty with a high-flexion design and fifty were randomized to total knee arthroplasty with a standard design.
The high-flexion design was a cruciate-retaining implant with a high-flexion femoral component and high-flexion polyethylene insert similar to that used in the study by Minoda et al. The authors prospectively followed the patients for a minimum of two years in terms of range of motion, function, and knee ratings.
They found no significant differences between the groups, suggesting that the high-flexion implants alone did not provide improvement in terms of clinical outcome after total knee arthroplasty.
McCalden et al.
also compared a high-flexion design with a standard-flexion design in a prospective randomized study of 100 patients. Fifty patients received a high-flexion posterior-stabilized polyethylene insert, and fifty received a standard posterior stabilized polyethylene insert.
After an average duration of follow-up of 2.7 years, the authors found no differences in range of motion between the implant designs, again suggesting that the implant alone is not associated with clinically important improvement in postoperative flexion.
It appears that high-flexion implant designs do not provide a significant improvement of range of motion after total knee arthroplasty.
We await longer-term clinical results to determine if there are differences in implant survival due to differences in contact stress between high-flexion and standard total knee arthroplasty designs.
