Summary

A novel test capturing knee wobbling during single leg squat to evaluate dynamic knee stability for patients with anterior cruciate ligament injury

Abstract

Background

Patients with anterior cruciate ligament (ACL) injury often suffer knee instability. However, there is lack of standard motion test for evaluation of dynamic knee stability after ACL injury. We propose using the single-leg squat-and-hold (SLSH) task with kinematic analysis to objectively measure dynamic knee stability in ACL patients since knee instability can be visualized as a wobbling knee during weight bearing exercises.

Objective

(1) to compare knee kinematic variations capturing knee wobbling during SLSH between ACL subjects and healthy controls; and (2) to detect the changes in knee kinematic variations during SLSH following ACL reconstruction(3) To correlate the kinematic variables with self-reported knee function

Study design & Method: 25 ACL-deficient participants (mean age: 25.0 ± 6.3 years) who were scheduled for ACL reconstruction were recruited. 18 healthy limbs from 18 healthy subjects who were matched with gender, age, BMI and activity level were randomly selected as control group. All the subjects were instructed to perform the SLSH task with maintaining knee flexion angle of 45° for 10s. Knee kinematics involving both the magnitudes and the frequency of the motion fluctuation (flexion-extension, abduction-adduction and internal-external rotation) during SLSH was captured by 3D motion analysis system (VICON) and analysed. Self-reported knee function was evaluated by Lysholm and the International Knee Documentation Committee scoring system (IKDC). The ACL-deficient participants were tested one month pre-operatively and three months post-operatively.

Results

Compared to the control limbs, the ACL involved limb exhibited greater variation in range of flexion-extension(z=2.831;p=0.005; ES=1.00) and varus-valgus(z=4.185;p<0.001;ES=1.53), and higher frequency of motion fluctuation in flexion-extension(z=3.023;p=0.003;ES=1.09) and varus-valgus(z=4.189;p<0.001;ES=1.29).Variation in range of flexion-extension(z=-2.373;p=0.018; ES=0.92), frequency of motion fluctuation in flexion-extension(z=-2.073;p=0.038;ES=0.69) and varus-valgus(z=-2.284 ;p=0.022 ;ES=0.87) were found reduced three months after ACL reconstruction. Increased frequency of knee varus-valgus was correlated with lower IKDC score(r=-0.328, p=0.034).

Conclusion

Knee wobbling is more prominent in ACL-deficient patients before ACLR. Knee wobbling movements presented as increased frequency of knee varus-valgus was associated with poor knee function. Evaluation of the knee kinematics capturing knee wobbling during SLSH may help to identify poor knee stability in a safe manner. Implementing the SLSH task with kinematic analysis appears to be a potential useful assessment for evaluating and monitoring dynamic knee stability after ACL injury.