Assessment of knee collateral ligament stiffness by strain ultrasound elastography.

BACKGROUND

Knowledge of the biomechanics of the normal collateral ligaments is important to secure optimal stability of the knee following injury. Various in vitro methods have been described in evaluating the biomechanics of these ligaments. However, a method of direct evaluation has not been reported.

OBJECTIVE

To determine the stiffness characteristics of the collateral ligaments of the knee using strain ultrasound elastography.

METHODS

Strain ultrasound elastography was performed on different components of the collateral ligaments in various angles of knee flexion in 18 healthy males (36 ligaments). We measured relative stiffness of the ligaments using strain ratio (SR = target tissue strain/reference strain). A lower strain ratio indicates higher relative stiffness.

RESULTS

There was moderate to excellent intra- and inter-rater agreement for strain ratio measurements in all ligament portions. Strain ratios were lowest at 0° in all three ligaments, indicating high relative stiffness. In the superficial and deep medial collateral ligaments, the strain ratio increased with increasing knee flexion, whereas in the lateral collateral ligament, stiffness showed a tendency to fluctuate.

CONCLUSION

Strain ultrasound elastography is a reliable tool for monitoring relative stiffness of the collateral ligaments of the knee and is easily applied to the routine clinical setting.