Summary

In robotic-assisted total knee arthroplasty, using a tensor to evaluate soft tissue balance allows for the adjustment of medial gaps between extension and flexion.

Abstract

Objective

In total knee arthroplasty (TKA), achieving medial knee stability is reported to affect postoperative ambulation function and patient satisfaction. Therefore, to overcome the concerns of the gap balancing technique, medial gap technique has been developed and recently performed. Medial gap technique focuses on medial knee stability and allows lateral physiological laxity. This report presents our experience with adjusting soft tissue balance focusing on medial knee stability using the ROSA (Robotic Surgical Assistant) Knee system (Zimmer Biomet, Warsaw, IN).

Methods

This study included 119 patients with varus osteoarthritis undergoing primary Cruciate-Retaining (CR) TKA in 62 knees and Posterior-stabilized (PS) TKA in 57 knees (Persona; Zimmer Biomet, Warsaw, IN ) using the ROSA Knee system. The surgeries were performed with a medial parapatellar approach. The medial soft tissue release was limited by femoral and tibial osteophyte removal and deep medial collateral ligament (MCL) release within 1cm from medial tibial plateau. Lateral physiological laxity was allowed to avoid excessive medial releases. The femoral distal resection and tibial resection angles were determined based on mechanical alignment, with adjustments for varus-valgus alignment within 2 degrees according to the soft tissue balance. Subsequently, the Zimmer FuZion Tensor was used to evaluate soft tissue balance between extension and flexion before posterior femoral condyle resection, determining the femoral rotation angle and implant size to achieve equal medial gaps. After implant placement, ROSA Knee was used to manually apply varus-valgus stress at extension and flexion positions to measure the medial and lateral implant gaps (MIG, LIG) at each position.

Results

The average values of implant gaps were as follows: MIG at extension: 2.0 mm, MIG at flexion : 1.8 mm, LIG at: extension 3.2 mm, and LIG at flexion: 3.3 mm. The medial gap difference between flexion and extension positions (flexion MIG - extension MIG) was 0.6 mm, with a gap difference of 2 mm or more observed in 5 knees (4.2%).

Discussion

The ROSA knee system is a robotically assisted semi-autonomous surgical system with some specific characteristics. The aim of this collaborative robotic system is to improve the accuracy and reliability of the bone resections and the ligament balancing. In robotic-assisted total knee arthroplasty, using a tensor to evaluate soft tissue balance allows for the adjustment of medial gaps between extension and flexion. Further studies are needed to address the adjustment of soft tissue balance, including lateral laxity.