Digital tensioning demonstrates smaller medial and larger lateral gap measurements than manual assessment in robotic‐assisted total knee arthroplasty

PURPOSE: With the increasing use of robotic systems in total knee arthroplasty (TKA), contemporary alignment strategies have increasingly relied on accurate intraoperative gap measurements to achieve optimal soft tissue balance. Digital tensioning devices offer a potentially more objective and reproducible method of gap measurement; however, the relationship between digital and manual gap measurement techniques remains unclear. This study aims to compare gap measurements obtained using a digital tensioning device versus manual tensioning with a Z-retractor, and to explore whether gap discrepancies vary in the medial versus lateral compartment. METHODS: A total of 170 primary TKA cases performed using the CORI robotic system (serial number SN000618, software versions v2.0.1.1 or v2.0.2.0) were prospectively collected from April 2024 to March 2025. Primary TKA cases with complete digital and manual gap measurements obtained according to the study protocol were included; cases with incomplete data or protocol deviation were excluded. All procedures followed a standardised workflow in which the default initial implant position was planned in neutral mechanical alignment. Intraoperative gap measurements were first obtained using the CORI Digital Tensioner (using 100 N medially and 50 N laterally), followed by manual gap assessments using a Z-retractor technique. Gap measurements were compared across the analysed flexion arc. RESULTS: A total of 152 knees were ultimately included, comprising 78 right (51.3%) and 74 left (48.7%) knees. Mean preoperative alignment was 3.72 ± 4.43°, with a mean preoperative range of motion from 6.44 ± 6.06° to 143.34 ± 7.79°. The digital tensioner consistently demonstrated significantly larger lateral gaps compared with manual tensioning, particularly in extension (0°: 2.38 mm vs. 1.63 mm, p < 0.001). Conversely, the digital tensioner produced smaller medial gaps compared to manual tensioning both in extension (-0.92 mm vs. -0.00 mm) and at 100° of flexion (0.79 mm vs. 1.19 mm, p < 0.001). These directional differences were maintained across preoperative alignment and range-of-motion subgroups. CONCLUSION: Gap measurements obtained using a digital tensioner consistently demonstrated greater lateral opening in extension and reduced medial gaps compared to manual assessment. The direction of these differences was maintained across preoperative alignment and preoperative flexion range. While digital tensioning may provide a more standardised approach to intraoperative gap assessment, surgeons should recognise technique-specific measurement differences when interpreting gap data for robotic-assisted TKA planning and soft-tissue balancing. LEVEL OF EVIDENCE: Level II, prospective cohort study.