Is it time for a systematic and objective assessment of knee laxity? The impact of objective knee laxity after TKA on patient-reported outcomes: a comprehensive review

PURPOSE: Over the past decade, robot assistance has emerged as an innovative and rapidly advancing tool in total knee arthroplasty (TKA). Despite technological advancements, the evaluation of the soft-tissue envelope during TKA often relies on subjective and rudimentary assessments by the surgeon. This literature review explores the relationship between objective intraoperative and postoperative laxity measurements in the coronal and sagittal planes and patient-reported outcome measures (PROMs) following TKA. METHODS: A literature review was conducted using PubMed/MEDLINE and Embase to identify studies on intra- or postoperative laxity measurements in TKA and their correlation with PROMs. Inclusion criteria required studies on TKA patients with quantifiable coronal and/or sagittal laxity measurements and postoperative PROMs linked to these measurements. RESULTS: Thirty-four studies met inclusion criteria: ten on sagittal laxity, twenty-seven on coronal laxity, and three on both. Follow-up ranged from 1 month to over 8 years. Sagittal laxity thresholds of 5-10 mm under applied loads of 89-133 N were associated with better functional outcomes, whereas excessive (> 10 mm) or overly tight (< 5 mm) laxity correlated with reduced satisfaction. Medial laxity in the coronal plane was linked to lower PROMs, while the impact of lateral laxity on PROMs was less conclusive. CONCLUSIONS: Objective laxity parameters correlate with PROMs, particularly a stable medial compartment throughout the range of motion, while the role of lateral laxity remains unclear. Systematic use of objective soft-tissue evaluations may enhance PROMs. While fixed-force assessments are standardized, personalized approaches with variable forces tailored to individual patients might be needed for optimal outcomes.