Manual Stress and Gap Spacer Systematically Underestimate Intraoperative Joint Gaps Compared with a Tensor Device in Robotic-Assisted Total Knee Arthroplasty.

Abstract

Robotic-assisted total knee arthroplasty (TKA) enables precise bone resection based on intraoperative ligament balance. However, commonly used methods for assessing ligament balance-manual varus/valgus stress and gap spacers-may lack accuracy, potentially affecting surgical outcomes. This study compared intraoperative joint gap measurements among 3 techniques: manual stress, gap spacers, and a novel tensor device. This prospective cohort study included 59 varus knees that underwent robotic-assisted TKA with a primary prosthesis. Intraoperative joint gaps were digitally measured in both medial and lateral compartments at full extension and 90° flexion using 3 methods: manual stress, gap spacers, and a tensor device applying 120 N force. Measurements were repeated for reliability, and statistical comparisons were made using one-way analysis of variance. Intramethod reproducibility was assessed using intraclass correlation coefficients (ICCs). Joint gaps measured using gap spacers were significantly smaller than those obtained with the tensor device (p < 0.05), particularly in flexion. Manual stress yielded intermediate values. The tensor device consistently produced the largest joint gaps. ICCs were >0.8 for all methods, indicating high reproducibility, with the tensor showing the highest consistency. However, manual and spacer methods systematically underestimated joint gaps despite their reproducibility. Manual stress and gap spacer techniques underestimate intraoperative joint gaps, potentially leading to unintended ligament laxity in robotic-assisted TKA. The tensor device provides more accurate and reproducible gap assessment, supporting its use for improved intraoperative decision making. Level II Prospective cohort study. See Instructions for Authors for a complete description of levels of evidence.