Design modifications may improve range of motion following posteriorly stabilized total knee replacement: a matched pair study.

BACKGROUND: Our institution's latest knee implant design modifications aimed to decrease anterior knee pain, reduce the amount of bone that is resected in the femoral box, and improve range of motion. QUESTIONS/PURPOSES: Does this new knee design achieve desired clinical improvement in our patient population? This study was designed to compare our new design to that of its predecessor in a matched pair analysis.
METHODS: A consecutive group of 100 knees underwent total knee arthroplasty using the newer box reamer (BR) posterior-stabilized design was matched by age, gender, and body mass index (BMI) to patients with the classic posterior-stabilized (PS) component. Average follow-up was 29.6 months (range 21-47) in the new group. Preoperative range of motion (ROM) and clinical scores, such as Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Knee Society Scores, were obtained and compared to the patients' most recent follow-up. Manipulation under anesthesia (MUA) and revision of the implant for any reason were also analyzed. Ability to attain ROM of >120°, >130°, and >140° was also determined in each cohort.
RESULTS: At 2-year follow-up, 41% of BR knees achieved >130° flexion compared with 19% in the PS design group. WOMAC improved from pre-op 47 to 80 at 1 year in the newer BR design group and 48 to 80 in the classic PS design group. There were 9 MUAs in the newer BR design group compared with 14 in the classic PS design group. There were three revisions in the PS group and none in the BR group.
CONCLUSIONS: Design improvements to this newer knee allowed more patients to achieve greater flexion and appear to have achieved clinical and design goals of the engineering modifications.