Abstract
INTRODUCTION
There is ongoing debate about the possible advantages of unicompartmental (UNI) knee replacement versus total knee replacement (TKR), such as for young, active patients. The purpose of this study was to investigate functional, radiographic, and device survivorship outcomes of UNI knee replacement with a newer generation UNI through 2-years post-op.
METHODS
A retrospective review of 188 cemented, fixed bearing unicompartmental (UNI) knee replacements implanted between January 2009 and June 2012 at 3 centers. The purpose of this study was to evaluate the survivorship, reasons for revision, radiographic and clinical results. A chart review was performed to collect demographics, operative details, American Knee Society (AKS) scores and adverse events (AE) through 2-years post-op. Kaplan-Meier (KM) device survivorship rates for the partial knee construct were estimated for post-op years in which at least 40 subjects had later follow-up. The definition of revision was the removal of any component for any reason, and device survivorship was the lack of revision. The time variable was the time to revision if the knee had been revised, or the time to last clinical follow-up or death if the knee had not been revised.
The average follow-up was 2.03 years (SD=0.4). The mean age was 64 years (SD=10.5), 56% of the patients were 65 years or younger, mean BMI was 27.5 kg/m2 (SD=4.9), 60% of patients were women, and 89% had a diagnosis of OA (9.6% had AVN). Data were collected through April 2015.
RESULTS
The KM device survivorship was 98.7% at 2 years (95% CI: 94.8–99.7%) (Figure 1). There were 3 revisions, 2 of which were prior to 2 years post-op (Figure 2) Overall, there were 23 operative site adverse events, including the 3 revisions. The most common AE was arthralgia (4.3%).
There were no observations of lucencies, osteolysis, stress shielding, or femoral notching.
At 2-years post-op the average AKS score was 89.9 points (N= 138, SD=11); 84% were in the good to excellent range. The average improvement from pre-op baseline at 2-years was 37.4 (N=117, SD=18). The average improvement in pain was 30 points (N=124, SD=15) on a 0–50 point scale, with 70% having no pain and 20% having mild pain at 2-years. Preoperatively, the average flexion was 118 degrees (N=152, SD=12.7o), which improved to 126 degrees (N=148, SD=9.4 o) at 2-years; average change from pre-op was 7.1 degrees (N=136, SD=12.2 o). Preoperatively, the average extension was 1.9 degrees (N=152, SD=3.6 o) which improved to 0.5 degrees (N=148, SD=1.6 o) at 2-years; average change from pre-op was a 1.4 degree improvement (N=136, SD=3.6 o).
DISCUSSION
Overall results demonstrated excellent 2 year survivorship for this newer generation UNI, consistent with published national registry results for the class of UNIs. The clinical results demonstrated excellent pain relief and improvements in motion compared to preoperative. It will be of interest to investigate longer term outcomes of UNI knee replacement in a larger patient population, with a focus on younger, more active patients (younger than 60), perhaps with an emphasis on the quality of life.
