Pre-resection ligament balance more frequently reproduces joint line orientation compared to inverse-kinematic workflow in robotic total knee arthroplasty.
Academic Article
Overview
abstract
PURPOSE: Robotic total knee arthroplasty (TKA) enables the acquisition of ligament balance data at various stages in the surgical workflow to inform implant planning. This study aims to compare pre-resection joint balancing versus inverse-kinematic workflows on implant positioning, joint line obliquity and coronal plane alignment of the knee (CPAK) phenotype. METHODS: A single-surgeon single-institution series of 422 primary posterior-cruciate sacrificing TKAs using a digital ligament tensioner was reviewed. The first 213 cases assessed gaps after tibial and before femoral resections (tibia-first group) in an inverse-kinematic alignment (iKA) workflow. The subsequent 174 cases assessed gaps before any bone resections (pre-resection group) in a femur-first kinematic alignment (KA) workflow. Native and postoperative medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA) were compared using Wilcoxon rank-sum tests, and CPAK phenotype distributions were compared using chi-square tests. RESULTS: Mean preoperative MPTA and LDFA were within 0.5° between groups. Postoperative measurements differed between tibia-first and pre-resection for both MPTA (88.3° ± 1.5° vs. 86.7° ± 1.7°, p < 0.001) and LDFA (90.7° ± 2.1° vs. 89.4° ± 2.4°, p < 0.001). The tibia-first group had greater preoperative to postoperative change in MPTA (0.7° ± 1.3° vs. -0.5° ± 1.7°, p < 0.001), LDFA (2.5° ± 1.7° vs. 1.4° ± 1.5°, p < 0.001) and joint line obliquity (3.2° ± 2.5° vs. 0.9° ± 2.6°, p < 0.001). The pre-resection group had more patients whose CPAK phenotype did not change postoperatively (35% vs. 25%, p < 0.05), and fewer patients with CPAK changes > 1 (9% vs. 29%, p < 0.001). Final mediolateral balance was within 1 mm of neutral for both groups throughout flexion. CONCLUSIONS: While both techniques achieved a similar balance, a pre-resection ligament balancing workflow better restored native joint line obliquity and CPAK phenotype compared to an iKA workflow. LEVEL OF EVIDENCE: Level III.
