Concern, conversations, and controversy still exist around the optimal treatment for a partial anterior cruciate ligament (ACL) tear. Many surgeons recommend nonoperative treatment, despite evidence that up to 40% of those patients progress to a complete tear. Then again, surgical management comes with an ample array of possible complications. In the February 5, 2020 issue of The Journal of Bone & Joint Surgery, Lian et al. add insight into how best to treat partial ACL tears with their study of rotatory knee laxity in >300 patients with varying severities of ACL injury.
As part of the research undertaken by the PIVOT Study Group, Lian et al. made precise measurements of lateral knee compartment translation (measured with image-based iPad software; see Figure) and lateral compartment acceleration (measured with a surface-mounted accelerometer) during preoperative pivot-shift testing of affected and healthy knees in patients under anesthesia who had the following ACL problems:
- A partial ACL tear (n=20)
- A complete ACL tear (n=257)
- A failed ACL reconstruction (n=27)
With each increasing grade of injury, the authors found progressively increased rotatory laxity, defined as an increased difference in affected-knee-versus-healthy-knee lateral translation and acceleration. They also found a progressive, injury grade-related increase in lateral knee compartment translation in the healthy knees of these patients. In addition, the data suggest that patients who experience a failed ACL reconstruction exhibit increased rotatory knee laxity prior to the event that precipitated the failure.
From these findings and previous evidence that persistent rotatory knee laxity correlates with reduced patient-reported outcome scores and increased rates of meniscal and cartilage damage among patients with ACL injuries, Lian et al. conclude that “an elevated quantitative pivot shift in the case of a partial ACL tear might be an indication for bundle augmentation or ACL reconstruction.”