CT scan analysis of implant mating comparing APA versus TEA in simultaneous bilateral TKA: One technique per knee.

BACKGROUND: The optimal landmark for setting femoral component rotation in primary TKA remains a debate. This study compares the Anterior-Posterior Axis (APA) versus the Transepicondylar Axis (TEA) in patients undergoing simultaneous bilateral TKA, where one reference line was randomized to each knee. Implant mating was assessed via post-operative CT scans.

METHOD: The study included 32 patients with osteoarthritis in both knees with similar varus deformities. All patients underwent the same surgical procedure on both knees, aside from the selected femoral rotation axis line: APA randomized to one side and TEA to the contralateral. Post-operative CT scans were performed in extension to assess in-vivo mating.

RESULTS: CT scan analysis showed mean rotation of the femoral implant externally rotated relative to the radiographic TEA with no significant difference between the APA and TEA groups (p = 0.28). Tibial implant rotation was also externally rotated to the radiographic TEA with no significant difference (p = 0.59). Femoral-tibial implant mating showed a mean external rotation of the tibia relative to the femur in both groups: 0.86 ± 4.0° external rotation in the APA group and 0.23 ± 3.7° external rotation in the TEA group. There was no significant difference between groups (p = 0.52). The range of mating mismatch was 15° in the APA group and 16.5° in the TEA group.

CONCLUSIONS: When using a measured resection, posterior referencing technique, post-operative femoral-tibial implant mating measured by CT scan showed no superiority comparing the APA method versus the TEA method.

LEVEL OF EVIDENCE: 2 Randomized prospective study.