Radiographic and Clinical Comparisons of a Modern Symmetrical Versus Asymmetrical Implant Design in Primary Total Knee Arthroplasty.

Background: While asymmetrical, left/right specific, femoral, and tibial components are commonly used in modern total knee arthroplasty (TKA), the recent introduction of a modern symmetrical, left/right nonspecific, design may afford benefits as a result of reduced implant and instrumentation requirements. Given the symmetrical trochlear design of left/right nonspecific femoral components, some concerns over patient outcomes and patellar tracking may exist. The purpose of this study was to compare the clinical and radiographic outcomes in a symmetrical TKA design to a more commonly used asymmetrical femoral component.

Methods: There were 225 patients (246 knees) who underwent TKA at an academic center with an implant featuring a symmetrical tibial and femoral component, which features a double 9° Q-angle trochlear design instead of left/right specific trochlea, and were compared to a matched historical cohort of 235 patients (236 knees) who had asymmetrical femoral components. All surgeries in both groups were performed using a similar posterior referenced, measured resection technique. Patient demographics, patient-reported outcomes (PROs), complications, knee range of motion, and radiographic analysis performed by an independent observer, including patellar tilt and displacement, were assessed. Chi-square and t-tests were used. There were no significant demographic differences between groups.

Results: There were no differences in PROs, failures, or complications at one year (P > 0.05). Radiographic patellar tracking was similar between groups with the exception of the symmetrical TKA demonstrating significantly less patellar tilt (0.5 versus 3.1°, P < 0.0001). There was no significant difference in preoperative or postoperative range of motion between the groups (P = 0.49 and P = 0.25).

Conclusions: The symmetrical femoral design demonstrated similar PROs and outcomes to an asymmetrical design. Despite some concern that patellar tracking could be worse in a symmetrical implant, the modern symmetrical TKA design demonstrated less patellar tilt and overall appears to perform clinically similarly to an asymmetric anatomic design.