Proximal tibial bony and meniscal slopes are higher in ACL injured subjects than controls: a comparative MRI study.

PURPOSE: Increased tibial slope is reported as a risk factor of non-contact anterior cruciate ligament (ACL) injury, but the effect of the soft tissues on slope remains unclear. The primary aims of this study were to compare the tibial bony and soft tissue slopes between patients with and without ACL injury, and to investigate the relationship between the meniscal slopes (MS) and the tibial bony slope. Our hypothesis was that the menisci would correct the inclination of the bony tibial slope towards the horizontal.

METHODS: Using magnetic resonance imaging (MRI), the lateral and medial tibial slopes (LTS, MTS) and lateral and medial meniscal slopes (LMS, MMS) were compared in 100 patients with isolated ACL injury and a control group of 100 patients with patello-femoral pain and an intact ACL.

RESULTS: Repeated-measures analysis of variance showed good inter- and intra-observer reliability for both bony and soft tissue slopes (ICC (0.88-0.93) and (0.78-0.91) for intra- and inter-observer reliability, respectively). The LTS and MTS were significantly greater in the ACL injury group (10.4 ± 3.1 and 9.4 ± 3.3) than in the control group (7.3 ± 3.4 and 7.0 ± 3.7). Similarly, the LMS and MMS were significantly greater in the ACL injury group (4.7 ± 4.7 and 6.0 ± 3.4) than the control group (0.9 ± 4.8 and 3.7 ± 3.6). In both groups, the lateral bony tibial slope was greater than the medial bony tibial slope, but the medial soft tissue slope was greater than the lateral soft tissue slope.

CONCLUSION: Increased tibial slopes, both bony and meniscal, are risk factors for ACL injury. As the meniscus tends to correct the observed slope towards the horizontal, loss of the posterior meniscus may potentiate this effect by increasing the functional slope.

LEVEL OF EVIDENCE: III.