Robotic-Arm Assisted Total Knee Arthroplasty More Accurately Restored the Posterior Condylar Offset Ratio and the Insall-Salvati Index Compared to the Manual Technique; A Cohort-Matched Study.

INTRODUCTION: Despite the demonstrated success of modern total knee arthroplasty (TKA), it remains a procedure that involves sophisticated preoperative planning and meticulous technique to reconstruct the mechanical axis, achieve ideal joint balance, and restore maximal range-of-motion (ROM). Recently, robotic-arm assisted TKAs have emerged as a promising new technology offering several technical advantages, and it is achieving excellent radiological results, including establishing the posterior condylar offset ratio (PCOR) and the Insall-Salvati Index (ISI). Studies have demonstrated that these parameters are surgically modifiable, and their accurate restoration (fewer mean differences) correlate with improved final joint range-of-motion. However, there is a paucity of studies that evaluate these parameters in light of performing robotic-arm assisted TKA. Therefore, in this study, we aimed to compare: 1) PCOR and 2) ISI restoration in a cohort of patients who underwent robotic-arm assisted versus manual TKA.

MATERIALS AND METHODS: We evaluated a series of 43 consecutive robotic-arm assisted (mean age 67 years; range, 46 to 79 years) and 39 manual total knee arthroplasties (mean age 66 years; range, 48 to 78 years) performed by seven fellowship-trained joint reconstructive surgeons. All surgeries were performed using medial para-patellar approaches by high-volume surgeons. Using the Knee Society Radiographic Evaluation System, preoperative and four-to six-week postoperative radiographs were analyzed to determine the PCOR and patella height based on the ISI.

RESULTS: The mean postoperative PCOR was larger in manual TKA when compared to the robotic-assisted cohort (0.53 vs. 0.49; p=0.024). The absolute mean difference between pre- and postoperative PCOR was larger in manual when compared to robotic-arm assisted TKA (0.03 vs. 0.004; p=0.01). In addition, the number of patients who had postoperative ISI outside of the normal range (0.8 to 0.12) was higher in the manual cohort (12 vs. 4).

CONCLUSION: Patients who underwent TKA using robotic-arm assisted technology had smaller mean differences in PCOR which has been previously shown to correlate with better joint ROM at one year following surgery. In addition, these patients were less likely to have values outside of normal ISI, which means they are less likely to develop patella baja, a condition in which the patella would impinge onto the patellar component, leading to restricted flexion and overall decreased ROM.