Bicruciate Substituting Design Does Not Improve Maximal Flexion in Total Knee Arthroplasty

Background: An important factor in the functional results after total knee arthroplasty is the achieved maximal flexion. The main purpose of this study was to compare the maximal knee flexion one year after surgery in patients who received either the bicruciate substituting knee system or the conventional posterior stabilized system.

Methods: In a prospective randomized controlled trial, 124 patients presenting with osteoarthritis received the bicruciate substituting or the conventional posterior stabilized prosthesis. The primary outcome was the maximum flexion angle at one year postoperatively on a lateral radiograph made with the supine patient using manual force to bend the knee. Secondary outcomes were active flexion (lying and standing), the Knee Society Score, the Patella Scoring System score, the University of California Los Angeles score, the number and type of adverse device effects, and visual analog scale satisfaction up to two years postoperatively. The outcome measures of both groups were compared using one-sided t tests and non-parametric alternatives, with a significance level of p < 0.05.

Results: No significant differences between the two groups were observed in maximal flexion on radiographs and in active flexion at baseline. The median maximal flexion on radiographs was 127° (range, 83° to 150°) for the bicruciate substituting group and 125° (range, 74° to 145°) for the conventional posterior stabilized group. The two groups showed comparable two-year results with respect to the Knee Society Score, the Patella Scoring System, the University of California Los Angeles score, and visual analog scale satisfaction. In the bicruciate substituting group, forty-one adverse device effects in twenty-six patients were reported, including three total system revisions and fourteen manipulations under anesthesia, compared with the conventional posterior stabilized group, in which sixteen adverse device effects were observed in thirteen patients, including six manipulations under anesthesia (p = 0.012).

Conclusions: Patients who receive a bicruciate substituting system compared with those who receive a conventional posterior stabilized system have comparable knee flexion characteristics and clinical and functional outcomes but more complications by two years after total knee arthroplasty.

Level of Evidence: Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.