Association Between Posterior Cruciate Ligament Resection and Medial Gap Laxity in Robotic-Assisted Total Knee Arthroplasty

Purpose The posterior cruciate ligament (PCL) is a major stabilizing structure of the flexion space, yet current evidence is inconclusive regarding change in gap laxity associated with its resection. This study aimed to describe the association between PCL resection and knee gap balancing using intra-operative robotic assessment. Methods Records were retrospectively reviewed for primary robotic-assisted total knee arthroplasty (raTKA) from July 2020 to March 2021. Patients were classified into two cohorts based on surgeon preference for flexion gap balancing: either cruciate-retaining (CR) or posterior-stabilized (PS) technique. Knee alignment and gap balancing measurements were collected under manual surgeon stress prior to bone cuts (and after PCL resection in the PS cohort). Medial and lateral compartment flexion-extension laxity measurements were compared using multiple linear regression. Results 98 TKAs were included (59 CR, 39 PS). Linear regression demonstrated a significant association between the PCL-resected/PS cohort and increased medial compartment flexion laxity (3.4mm, p<.001, 95%CI=[2.348, 4.445]) and extension laxity (1.7mm, p=.005, 95%CI [0.533, 2.939]) compared to the PCL-retained/CR group. Non-statistically significant decreases were found in mean lateral flexion laxity (-0.015mm, n.s., 95% CI=[-1.310,1.280]) and lateral extension laxity (-0.029mm, n.s., 95% CI=[-1.313, 1.255]). Conclusion Robotic gap assessment data demonstrates PCL resection in PS TKA is associated with significantly greater medial flexion and extension laxity compared to CR TKA. Surgeons should be aware of these potential asymmetric mechanical differences following PCL resection when utilizing robotic or manual gap assessment and allow for adjustments in the final reconstructive plan.