Summary
This study elucidates morphological differences of the lateral tibial cartilage geometry including middle and posterior cartilage slope as well as correlations to meniscal geometry of ACL deficient knees in comparison to ACL intact knees
Abstract
Background
ACL deficient knees have shown to undergo changes in the morphometry of the articular cartilage, especially of the lateral compartment shortly after ACL injury. Changes in cartilage slopes are among the previously described most relevant alterations. With internal tibial rotation, the lateral tibiofemoral contact area is moved from the middle tibial cartilage slope towards the steeper posterior tibial cartilage slope. Middle and posterior tibial cartilage slope may therefore have independent roles regarding the risk of ACL injury. The purpose of this study was to elucidate morphological differences of the lateral tibial cartilage geometry including middle and posterior tibial cartilage slope as well as correlations to meniscal geometry of ACL deficient knees in comparison to ACL intact knees.
Methods
A cohort of 50 consecutive patients with isolated ACL injury from 2021-2022 was matched with 50 control patients without ACL injury or meniscal injury according to age, sex and BMI. MRI was assessed and the following geometrical features of the lateral compartment were measured: middle tibial cartilage slope (MCS), posterior tibial cartilage slope (PCS), meniscal slope (MS), meniscal wedge angle (MWA), and cartilage slope angulation (MCS-PCS). Cartilage slope measurements were performed in the center of the posterolateral lateral segment of the lateral tibial plateau and the longitudinal tibial axis was established according to Hudeck. The aforementioned measuerment techniques have shown excellent intra- and inter-rater reliability, which extends to the novel cartilage slope angulation measurement introduced in this study.
Results
ACL injured knees showed a significantly increased middle and posterior lateral tibial cartilage slope with 6.86°(SD 4.81°) and 21.83° (SD 7.64°), respectively, in comparison to ACL intact knees with 2.62° (SD 2.85°) and 13.4° (SD 4.25°), respectively (p <.0001; p<.0001). The angulation between MCS and PCS (cartilage slope angulation) was increased in ACL deficient knees with 15.0° (SD 6.12°) compared to 10.69° (SD 4.13°) in ACL intact knees (p < .0001). The meniscal slope was significantly increased in ACL deficient knees with 4.1° (SD 5.19) in comparison to ACL intact knees with -1.0° (SD 3.85°); (p < .0001). MWA was 39.01° in ACL deficient knees and 37.2° in ACL intact knees with no significant between-group-difference. MWA was significantly positively correlated to the posterior tibial cartilage slope in both ACL deficient (r = 0.81; p < .0001) and ACL intact knees (r = 0.56; p = .001). The median time from ACL injury to MRI was 4 weeks. No correlation was found between time from ACL injury to MRI and cartilage slope.
Conclusion
ACL deficient knees showed increased middle and posterior cartilage slopes as well as increased cartilage slope angulation compared to ACL intact knees. The resulting steeper drop-off may influence the risk of ACLR failure.