A comparison of standard and high-flexion knees: are we getting what we expected?

Some patients have been less than satisfied with flexion after total knee arthroplasty (TKA). As early designs provided limited flexion, companies have developed high-flexion designs. We conducted a study to compare flexion between 2 standard and 3 high-flexion designs and to compare clinical and radiographic postoperative flexion. Clinical and radiographic measurements were obtained by 3 independent orthopedists. Clinical flexion, with the patient maximally bending his or her knee as far as possible, was measured with a goniometer, recorded, and compared with measurements from lateral radiographs of the knee in the same position. A total of 144 knees (108 patients) were included in the study. Mean preoperative flexion was 110° for both groups, and mean postoperative flexion was 111° clinically and 109° radiographically for the standard designs, and 114° clinically and 117° radiographically for the high-flexion designs (P<.05). The groups had similar preoperative and postoperative Knee Society knee and function scores. Measurements obtained by the 3 independent examiners were highly correlated. Compared with the standard designs, the highflexion designs demonstrated statistically significantly more flexion, though the clinical increase in flexion was relatively small (3º).