Abstract
Background
Multiple retrospective studies have compared UC with traditional bearings and shown comparable results and outcomes when looking at clinical and radiologic variables, complications rates, and implant survivorship; however, debate still exists regarding the optimum bearing surface. The present study seeks to determine whether there are any preoperative patient demographic or medical factors or anatomic variables including femoral condylar offset and tibial slope that may predict use of a UC bearing when compared to a standard CR group.
Methods
The study cohort consisted of 117 patients (41 males, 76 females) who underwent primary TKA with the senior author. The implants utilized were either the CR or UC polyethylene components of the Zimmer Persona Total Knee System. Insert selection was based on intraoperative assessment of PCL integrity and soft tissue balancing. Patient demographics (age, gender, BMI) and co-morbidities (hypertension, diabetes, depression, cardiac disease, and lung disease) were recorded. Intraoperative variables of interest included extension and flexion range of motion, estimated blood loss (EBL), tourniquet time, and polyethylene and femoral component sizes. We calculated change in tibial slope and femoral condylar offset from pre- to post-surgery and computed the percentage of patients for whom an increase in tibial slope or femoral condylar offset was determined. Postoperative variables, including length of stay, complication rates and reoperation rates, were recorded. All dependent variables were compared between patients who received the UC component and patients who received the CR component. Continuous variables were assessed using independent samples t-tests, while categorical variables were compared using the chi-square test of independence.
Results
There were 39 patients who received a UC insert and 78 patients who received CR insert. Patient age (p = 0.58), BMI (p = 0.34), or sex distribution (p = 0.84) did not differ between the UC and CR groups. Mean LOS (3.59 vs. 3.08; p = 0.017), EBL (54.5 vs. 46.7; p=0.021), and tourniquet time (61.2 vs. 57.4; p=0.032) were greater for the UC group. Intraoperative implant variables, including polyethylene component (p = 0.49), femoral component (p = 0.56), use of a narrow femoral component (p = 0.85), and patellar component size (p = 0,83), were similar between groups. Additionally, preoperative (p = 0.46) and postoperative (p = 0.19) condylar offset and preoperative (p = 0.66) and postoperative (p = 0.23) tibial slope were not different between the groups. However, the proportion of patients for whom tibial slope increased postoperatively was greater for the UC group compared to the CR group (43.6 vs. 21.8% respectively, p=0.018).
Conclusions
Our results showed that no preoperative medical co-morbidities or demographic factors predicted use of the UC bearing; however, postoperative tibial slope was increased for a greater number of patients who received the UC implant. Patients who have an increase in their slope from their native anatomy during tibial preparation may require additional balancing of the flexion gap, and use of a UC component may be beneficial in this particular group of patients.
