Collateral ligament laxity in knees: what is normal?

Area of Science:

• Orthopedics
• Biomechanics
• Knee Kinematics

Background:

• Optimal soft tissue balance is crucial for total knee arthroplasty (TKA) success.
• Current consensus on ideal collateral ligament laxity post-TKA remains undefined.

Purpose of the Study:

• Quantify collateral laxity in healthy young volunteers.
• Determine if significant differences in collateral laxity exist between males and females.

Main Methods:

• Measured femorotibial mechanical angle (FTMA) in 267 healthy knees (ages 19-35) using a computer navigation system.
• Applied 10-Nm varus and valgus torque at 0° and 15° flexion to assess ligamentous laxity.
• Utilized independent t-tests and ANOVA for statistical analysis (p<0.05).

Main Results:

• Mean unstressed FTMA was varus (1.2° at 0°, 1.2° at 15°).
• Varus torque increased laxity by 3.1° (0°) and 6.9° (15°); valgus torque by 4.6° (0°) and 7.9° (15°).
• Women demonstrated significantly greater laxity than men under valgus stress (p<0.001 at 15°).

Conclusions:

• Collateral ligament laxity is quantifiable and shows significant inter-individual variability.
• Female subjects exhibit greater ligamentous laxity, particularly under valgus stress, compared to males.
• Findings establish a baseline for evaluating laxity in arthritic and post-TKA knees.