Summary

Knee laxity increased bilaterally during the first year after non-surgically treated ACL injury and knee laxity was weakly associated with knee function and perceived knee stability.

Abstract

Background

Knee laxity in the non-surgically treated ACL injured knee joint may increase further over time due to excessive load exposure to the secondary restraints. However, there are no data on an objective measure of the clinical course of knee laxity. Further, the importance of knee laxity for recovering knee function and patients’ perception of knee instability and fear of reinjury at different timepoints after ACL injury is uncertain.

Objectives: To analyse changes in knee joint laxity between 3, 6, 12 and 24 months after non-surgically treated ACL injury and to analyse associations between knee joint laxity and knee function, self-reported knee stability, fear and confidence at different timepoints during recovery. A secondary aim was to compare knee joint laxity at 3 months between patients who did not have an ACLR within 24 months after the ACL injury and patients who had not undergone an ACL reconstruction at the 3-month follow-up but had an ACL reconstruction later.

Method

Design: Prospective cohort study, part of the NACOX study.

Participants: 125 patients (67 males, mean age 25.0 ± 7.0 years) with acute ACL injury.

Main outcome: At 3, 6, 12 and 24 months after injury, knee joint laxity was measured using KT-1000 arthrometer. Self-reported knee function was assessed using the International Knee Documentation Committee Subjective Knee Form (IKDC-SKF). Confidence and fear were assessed with two questions from the ACL-Return to Sport after Injury (ACL-RSI) scale. Subjectively perceived knee joint stability was assessed using a single question.

Results

Knee laxity increased bilaterally from 3 to 12 months, and in the non-involved knee from 3 to 24 months (p?0.05), although mean change was below 1 mm.
Side-to-side difference in knee laxity was correlated with IKDC-SKF (r=-0.283, p=0.016) and self-reported perception of knee stability in rehabilitation/sport activities (r=-0.315, p=0.007) at 6 months, but not at 3, 12 and 24 months. There was no correlation between side-to-side difference in knee laxity and confidence and fear.
At assessment 3 months after the ACL injury, side-to-side difference in knee laxity did not differ between patients who did not have an ACL reconstruction within the 24-month follow-up period (mean side-to-side difference 3.56, 95% CI 2.90-4.24, n=65) compared to patients who had an ACL reconstruction after the 3-month assessment (mean side-to-side difference 4.00, 95% CI 3.13-4.87, n=42) (mean group difference -0.43, 95% CI -1.51-0.65, p=0.429).

Conclusion

Knee laxity increased bilaterally during the first year after non-surgically treated ACL injury. Knee laxity was weakly associated with knee function and perceived knee stability at 6 months after injury.

Clinical implications: The increase in laxity over time in the ACL injured knee could be attributed to excessive load on secondary restraints. Patients with non-surgically treated ACL injury might also develop increased laxity in the non-involved knee over time, which may be interpreted as an adaption towards the injured knee. The present findings could contribute to the basis for treatment decisions after ACL injury. However, the mean change in knee laxity was below 1 mm and might be of limited clinical significance.