Posterior condylar offset ratio more precisely reconstructed with robotic arm-assisted total knee arthroplasty when compared to conventional manual technique

AIMS AND OBJECTIVES: The use of robotic-arm assisted total knee arthroplasty promises more precision in TKA implant technique. Precise implantation is elemental in improving functional and radiological outcome after TKA. The posterior condylar offset ratio (PCOR) is one important radiological parameter in total knee arthroplasty (TKA). The PCOR correlates with the maximum range-of-motion of the knee. A decrease of PCOR in TKA could lead to early impingement of the tibial insert with a consecutive decreased flexion range of the knee. The primary objective of this study was to determine differences in PCOR reconstruction after TKA between manual and robotic arm-assisted TKA surgery. MATERIALS AND METHODS: A total of 80 patients undergoing primary TKA performed by one single senior surgeon were included in this prospective study. Two groups (Robotic arm-assisted TKA group, manual TKA group, n=40 patients each) were compared on the basis of hip-knee-ankle angle (HKA), medial proximal tibial angle (mPTA), distal lateral femoral angle (dLFA) and PCOR. Weight-bearing full-leg a.p. radiographs, as well as lateral knee radiographs, were performed pre- and postoperatively. All surgeries were performed with one single posterior stabilized TKA prosthesis type. Statistics consisted of parametric t-testing with a level of significance of p<0.05. RESULTS: Preoperative limb alignment, mPTA and dLFA did not differ in between groups (each p>0.05). Postoperative mean PCOR was larger in the robotic arm-assisted TKA group (0.51 ± 0.05 vs. manual TKA group 0.47 ± 0.05, p=0.006). The absolute mean difference of pre- and postoperative PCOR was higher in the manual TKA group when compared to the robotic arm-assisted TKA group (-0.059 vs. -0.017, p=0.001). Manual TKA group showed a mean relative deviation of 12,03% (± 9,1%) in pre- to postoperative PCOR, whereas a mean relative deviation of 3.9 % (± 4.5%) was found in the robotic arm-assisted TKA group. CONCLUSION: Robotic arm-assisted TKA showed higher precision regarding postoperative PCOR with lower absolute mean differences and less relative deviation in pre- and postoperative PCOR when compared to manual TKA. A precise reconstruction of PCOR correlates with a better functional outcome as shown in previous studies before.