Background

The presence of bone bruise (BB) after Anterior Cruciate Ligament (ACL) injury is increasingly considered for the understanding of injury mechanisms and residual knee laxity. Recent studies demonstrated an association between the presence of BB and both increased knee ambulatory laxity and worst clinical outcomes. Furthermore, the presence of lateral femoral notch sign (FNS) has been association with knee rotational laxity.

Purpose

To evaluate the association between the intensity of BB and both intraoperative rotatory laxity and lateral FNS. The hypotheses were that (I) more intense BB would be associated with higher intraoperative rotatory laxity and (II) with the presence of lateral FNS.

Methods

Twenty-eight with MRI images at maximum 3 months after ACL injury were included. The intensity of BB was evaluated according to the ICRS scale, and patients were divided into two groups, none-to-mild (G1) and moderate-to-deep (G2), for lateral femoral condyle, lateral tibial plateau, medial femoral condyle, medial tibial plateau. The intraoperative laxity was evaluated through a surgical navigation system through three different tests: Internal-external rotation at 30° and 90° of knee flexion (IE30 and IE90), and pivot-shift test. The KOOS score was also collected for each patient. The t-test (p<0.05) was used to compare the two groups. Furthermore, the presence of lateral FNS was assessed and inserted in a logistic regression with sex, age, and presence of meniscal lesions.

Results

For the tibial medial plateau, the G2 showed significantly higher IE rotation (Effect Size>1.1 – very strong, p<0.05) in all the tests performed with the surgical navigation system. Furthermore, the intensity of BB on the tibial medial plateau was strongly associated with the presence of lateral FNS (OR=30.4, p=0.05). For the tibial lateral plateau, the G2 group showed lower clinical outcomes in KOOS SYMPTOMS (Effect Size=0.983 – very strong, p=0.019).

Conclusion

Bone edema on medial tibial plateau was associated with intraoperative rotatory instability in ACL-deficient knees. This was further confirmed by the strong association with the presence of lateral FNS. The increased rotatory laxity in presence of medial tibial plateau BB could indicate a stronger tibiofemoral impact during the ACL injury mechanism and the risk for increased post-operative laxity.