Abstract
INTRODUCTION
Unicompartmental knee arthroplasty (UKA) has been shown to have many benefits over conventional Total Knee Arthroplasty (TKA), but has also been shown to be technically difficult. In fact, technical error is the most common cause of premature failure in UKA. Bicompartmental arthroplasty (BKA) has the potential to perform like TKA with the benefits of UKA. We describe the initial experience with customized alignment guides and implants for UKA and BKA, manufactured based upon preoperative CT scan.
MATERIALS AND METHODS
Twenty three implants in 19 patients were implanted and followed for a minimum of three months postoperatively. Knee society scores and SF-12 scores were collected preoperatively and postoperatively. Radiographs were analyzed with image analysis software for malposition and loosening.
RESULTS
There were 11 female patients who received 12 implants, and 8 male patients who received 11 implants. There were 8 BKA(7 med + pfj; 1 lat + pfj) and 15 UKA (13 medial, 2 lateral). The average age was 69.3 years (range 53-91). Length of followup was average 8.9 months (range 3-19). By 1 month postoperatively, all patients had gained at least 90 degrees of flexion (avg 109; range 90-130) and all were off assisted devices. By 3 months postoperatively, average KSS had improved from 52.8 to 89.6 (pain); 50.9 to 69.9 (function). SF-12 scores for PCS and MCS increased from 34.6 to 39.3 and 50.3 to 55.3, respectively. There was no difference in functional outcomes between UKA and BKAs. Radiographic analysis showed that no implants overhanged bone by more than 1 millimeter in any dimension. Two of 23 tibial components were placed in greater than 10 degrees of varus (so-called outliers). Conversely, 9/19 tibial components were outliers placed in more than 7 degrees of posterior slope or in reverse slope. The femoral components were designed to be placed parallel to the longitudinal axis of the femur, and 19/23 were within 3 degrees. Interestingly, there was a tremendous amount of variation between patients. There were no postoperative complications. In one case, the tibial component was not completely seated to the bone preparation level. Otherwise, there were no intraoperative complications. No revisions have been performed and none are pending.
CONCLUSIONS
Customized implants are designed to match the patient anatomy as closely as possible, without duplicating gross malalignment or malposition. This study shows that this technology reliably allows placement of UKA and BKA devices within acceptable alignment parameters, with excellent short-term functional results. Interestingly, BKA components performed as well as UKA components, suggesting that a certain percentage of traditional TKA patients can expect UKA-like function after BKA instead of TKA. Of course, much longer followup is required to determine rates of failure from progressive arthritis or device wear. Nevertheless, current customized UKA and BKA components are safe and effective.
