Intraoperative Gap Balance and Laxity During Total Knee Arthroplasty

A retrospective, multi-center cohort study analyzing intraoperative gap balance and laxity during total knee arthroplasty (TKA) demonstrated that better clinical outcomes are associated with varus gap balance rather than equal medial and lateral gaps. Additionally, researchers found that medial laxity in both extension and flexion negatively correlated with postoperative clinical outcomes, suggesting that medial release to correct ligament imbalance may not be necessary. Their study was presented at the American Academy of Orthopaedic Surgeons 2025 Annual Meeting in San Diego, CA.

Orthopaedic surgeons often use medial release during TKA to correct ligament imbalance in knees with varus deformity, but this approach carries risks of medial and anterior-posterior instability. A certain degree of lateral laxity may be required to facilitate medial pivot motion and achieve optimal range of motion in the knee. This study aimed to determine whether intraoperative gap balance and joint laxity influence postoperative clinical outcomes.

Researchers prospectively collected data from 656 knees undergoing TKA with a single posterior-stabilized implant across 11 centers. Intraoperative measurements of the varus-valgus gap angle and joint gap at both extension and 90° flexion were obtained using a tensor device under a distraction force of 178 N. Medial and lateral gaps were calculated from the center gap and varus-valgus angle, while medial and lateral joint laxity were determined by subtracting polyethylene thickness from the joint gap. Correlations between these intraoperative variables and clinical outcomes, were assessed using the Knee Society Score (KSS) and 2011 KSS at 1 month, 1 year, and 2 years postoperatively.

The average varus gap angle was 1.5° (standard deviation [SD] = 3.1°) in extension and 1.0° (SD = 4.3°) in flexion. Medial and lateral laxity in extension averaged -1.4 mm (SD = 2.7) and -0.6 mm (SD = 3.2), respectively, while the corresponding values in flexion were 2.4 mm (SD = 3.9) and 3.0 mm (SD = 3.9). The polyethylene thickness was slightly greater than the medial and lateral gaps in extension.

A positive correlation was observed between the varus gap angle in flexion and KSS knee score (r = 0.107, P = 0.027), KSS function score (r = 0.140, P = 0.004), 2011 KSS symptoms (r = 0.132, P = 0.006), and 2011 KSS functional activities (r = 0.105, P = 0.030) at two years. Conversely, medial laxity in extension correlated negatively with KSS function score at 1 month (r = -0.110, P = 0.009) and 2 years (r = -0.097, P = 0.045), 2011 KSS symptoms at 2 years (r = -0.130, P = 0.007), and 2011 KSS functional activities at 1 month (r = -0.087, P = 0.039) and 2 years (r = -0.118, P = 0.015). Similarly, medial laxity in flexion negatively correlated with 2011 KSS symptoms at 1 year (r = -0.112, P = 0.016). Lateral laxity in both extension and flexion had minimal impact on KSS and 2011 KSS outcomes.

"Better clinical outcomes are obtained with varus gap balance than with equal medial and lateral gaps,” the study authors concluded. “Medial laxity in extension and flexion can lead to inferior postoperative clinical outcomes and functions. Medial release to correct ligament imbalance seems unnecessary during TKA."

Reference
Nakamura S, Kuriyama S, Nishitani K, Morita Y, Matsuda S. Medial laxity during total knee arthroplasty leads to inferior postoperative clinical outcomes and functions. Presented at: American Academy of Orthopaedic Surgeons. March 10-24; San Diego, CA. Accessed March 6, 2025. https://submissions.mirasmart.com/AAOS2025/Itinerary/PresentationDetail.aspx?evdid=193.