Achieving accurate ligament balancing using robotic-assisted unicompartmental knee arthroplasty

Abstract

Unicompartmental knee arthroplasty (UKA) allows replacement of a single compartment in patients with limited disease. However, UKA is technically challenging and relies on accurate component positioning and restoration of natural knee kinematics. This study examined the accuracy of dynamic, real-time ligament balancing using a robotic-assisted UKA system. Surgical data obtained from the computer system were prospectively collected from 51 patients (52 knees) undergoing robotic-assisted medial UKA by a single surgeon. Dynamic ligament balancing of the knee was obtained under valgus stress prior to component implantation and then compared to final ligament balance with the components in place. Ligament balancing was accurate up to 0.53 mm compared to the preoperative plan, with 83% of cases within 1 mm at 0°, 30°, 60°, 90°, and 110° of flexion. Ligamentous laxity of 1.31 ± 0.13 mm at 30° of flexion was corrected successfully to 0.78 ± 0.17 mm (P < 0.05). Robotic-assisted UKA allows accurate and precise reproduction of a surgical balance plan using dynamic, real-time soft-tissue balancing to help restore natural knee kinematics, potentially improving implant survival and functional outcomes.

Figure 1

Ligament balancing was measured throughout various angles during the flexion-extension cycle relative to tibia and mechanical axis. (a) The colored dots represent measurements during femoral range of motion. (b) Intraoperative screenshot of the robotic system showing ligament balance at 0°, 30°, 60°, 90°, and 110° of flexion before resection, with the trial component in place, and after implantation.

Figure 2

Analysis of ligament balance at various degrees of knee flexion. The intraoperative balance plan was similar measurements obtained after component implantation at 0°, 60°, 90°, and 110°. At 30°, ligament balance was relatively loose and surgically corrected, revealing a significant difference (*P < 0.05) between the balance plan and measurements after component implantation.

Figure 3

At 0° (a), 60° (c), 90° (d), and 110° (e), ligament balance between 1 mm and −1 mm was achieved in 81% to 93% of cases. At 30° (b), 76% of cases were balanced between 1 mm and −1 mm due to a necessary increase in ligament tightness.