KNEE KINEMATICS DURING LAXITY TESTING FOLLOWING ROBOTIC-ASSISTED AND CONVENTIONAL MECHANICAL TOTAL JOINT REPLACEMENT

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Abstract

Robotic-assisted surgery has become an increasingly attractive option for orthopaedic surgeries, specifically in its use for total knee replacement (TKR). Despite the allure, characterization of the outcomes of robotic-assisted surgery against conventional manual methods remains to be investigated. Therefore, this study aims to characterize kinematics of TKR knees following robotic-assisted and conventional arthroplasty through loaded laxity testing. We hypothesize that robotic-assisted TKR will result in less variable kinematic behavior at end range of motion than its conventional counterparts. Seven pairs of TKR knees were used in this study. For each pair, one surgery was performed using conventional manual methods, while the contralateral side utilized a VELYS robotic-assisted solution (DePuy Synthes). All TKRs were performed by the same surgeon and used a cruciate retaining rotating platform (CR RP) implant system. The knees were mounted onto a VIVO joint motion simulator (Advanced Mechanical Technologies Inc.). Once installed, specimens were pre-conditioned via a baseline loading protocol that involved cycling though the flexion arc from 15 to 90 degrees, while reducing the joint with 30 N of compression. Next, laxity was assessed via applied isolated (1) 4 Nm internal/ external (IE) rotation torques, (2) 8 Nm varus/ valgus (VV) rotation torques, and (3) 40 N anterior, and 80 N posterior forces. Each was performed at discrete positions of 15, 30, 60 and 90 degrees of knee flexion. Laxity outputs were adjusted for joint behavior during baseline to mitigate and mounting biases and account for specimen-specific joint behavior, and conventional TKR and robotic-assisted TKR knees were compared via paired two-tailed t-tests for each combination of flexion angle and tested degree of freedom. At 90° flexion, external rotation laxity was significantly different between the groups (P=0.04), with conventional TKR knees exhibiting greater rotation (26.5° ± 9.1°) than robotic- assisted TKR knees (18.3° ± 3.5°). This is complemented by the observed trend of the difference between conventional and robotic TKR knee external rotation laxity limits increasing with each flexion angle”: 15.8° ± 8.1° [conventional] and 14.1° ± 4.1° [robotic-assisted] at 15 degrees, 20.2° ± 7.2° [conventional] and 18.5° ± 5.6° [robotic-assisted] at 30 degrees, and 21.9° ± 7.2° [conventional] and 19.0° ± 5.2° [robotic-assisted] at 60 degrees. No other statistically significant differences were identified. The results of the current study suggest that while conventionally done TKR may result in comparable joint laxity than those done using conventionally methods, through most of the flexion arc, the latter provides greater stability in external rotation in high flexion (namely 90°). However, observed laxity differences may be compensated for in the opposite direction, resulting in a balanced total laxity envelope. These findings could provide a greater understanding of patient outcomes and inform surgical decision making to cater to a patient's desired functional outcome.