Soft tissue laxity is highly variable in patients undergoing total knee arthroplasty.

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering

Background:

• Achieving balanced medial and lateral gaps is crucial for successful total knee arthroplasty (TKA).
• Soft tissue laxity is a patient-specific factor influencing joint stability, often independent of bone resection planning.

Purpose of the Study:

• To quantify the variability of soft tissue laxity in patients undergoing TKA.
• To assess the predictability of soft tissue laxity based on preoperative knee deformity.

Main Methods:

• Retrospective review of 113 TKA patients.
• Intraoperative dynamic stress examination using a robotic tracking system to measure compartment opening in flexion and extension.
• Analysis of preoperative knee deformity data.

Main Results:

• Significant variability in medial and lateral compartment opening was observed (0-13.4 mm).
• Varus knees showed greater medial compartment opening under valgus stress compared to valgus knees (P<0.0001).
• Valgus knees exhibited greater lateral compartment opening under varus stress compared to varus knees (P<0.0001).

Conclusions:

• Soft tissue laxity in TKA is highly variable and significantly contributes to the post-resection joint gap.
• Preoperative deformity is a poor predictor of the extent of soft tissue laxity.
• These findings necessitate consideration for both measured-resection and gap-balancing techniques in TKA surgery.