Non-linear, compartment-specific gap widening with rising distraction forces highlights the need for individualised,...

Achieving balanced soft tissue tension is crucial for successful total knee arthroplasty (TKA), yet remains challenging. This study investigated the effect of standardised distraction forces on medial and lateral femorotibial gap sizing during robotic-assisted TKA, with particular attention to specific patient characteristics like gender and age.

In this prospective single-center cohort study, 238 patients (83 males, 155 females; mean age 70 ± 9.6 years) undergoing primary robotic-assisted TKA were enroled. A force-controlled ligament tensioner applied distraction forces of 100, 150, 200 and 250 N at 5° and 90° of flexion. Medial and lateral joint gaps were recorded intraoperatively via the MAKO® Robotic-Arm Assisted Surgery System. Subgroup analyses were performed for gender and age categories, and stiffness was calculated as the slope of force-displacement curves.

Gap widening increased non-linearly with higher distraction forces, with greater expansion in the lateral compartment, particularly in flexion. Female patients demonstrated significantly larger medial gap increases at forces ≥ 150 N compared to males (p < 0.01; small effect sizes). Age had a comparatively minor influence, with statistically significant differences limited to older subgroups (80-90 years). Gender-based differences were found in gap behaviour. Female patients showed greater gap increases and lower medial stiffness, particularly at higher distraction force between 150-250 N than males.

The results underline the need for individualised, force-adaptive balancing, where robotic real-time gap analysis may help to optimise stability and reduce the risk of postoperative instability (caused by under-tensioning), stiffness (caused by over-tensioning), or pain.

Level II.