Increased slope of the lateral tibial plateau subchondral bone is associated with greater risk of noncontact ACL injury in females but not in males: a prospective cohort study with a nested, matched case-control analysis

Abstract

Background: There is an emerging consensus that increased posterior-inferior directed slope of the subchondral bone portion of the tibial plateau is associated with increased risk of suffering an anterior cruciate ligament (ACL) injury; however, most of what is known about this relationship has come from unmatched case-control studies. These observations need to be confirmed in more rigorously designed investigations.

Hypothesis: Increased posterior-inferior directed slope of the medial and lateral tibial plateaus are associated with increased risk of suffering a noncontact ACL injury.

Study design: Case-control study; Level of evidence, 3.

Methods: In sum, 176 athletes competing in organized sports at the college and high school levels participated in the study: 88 suffering their first noncontact ACL injury and 88 matched controls. Magnetic resonance images were acquired, and geometry of the subchondral bone portion of the tibial plateau was characterized on each athlete bilaterally by measuring the medial and lateral tibial plateau slopes, coronal tibial slope, and the depth of the medial tibial plateau. Comparisons between knees of the same person were made with paired t tests, and associations with injury risk were assessed by conditional logistic regression analysis of ACL-injured and control participants.

Results: Controls exhibited side-to-side symmetry of subchondral bone geometry, while the ACL-injured athletes did not, suggesting that the ACL injury may have changed the subchondral bone geometry. Therefore, the uninjured knees of the ACL-injured athletes and the corresponding limbs of their matched controls were used to assess associations with injury risk. Analyses of males and females as a combined group and females as a separate group showed a significant association between ACL injury risk and increased posterior-inferior directed slope of the lateral tibial plateau slope. This relationship was not apparent when males were analyzed as a group. Multivariate analyses indicated that these results were independent of the medial tibial plateau slope, coronal tibial slope, and depth of the medial tibial plateau, which were not associated with ACL injury.

Conclusion: There is a 21.7% increased risk of noncontact ACL injury with each degree increase of the lateral tibial plateau slope among females but not among males. The medial tibial plateau slope, coronal tibial slope, and depth of the medial tibial plateau were not associated with risk of injury for females or males.

Keywords: anterior cruciate ligament; biomechanics of ligament; injury prevention; knee; ligaments.

Figure 1.

Segmented data (gray lines) relocated to tibial coordinate system. The long axis of the tibial coordinate system is defined by the direction connecting the centroids (black open squares) of the proximal and distal transverse plane outlines of tibial cortical bone (black dotted lines). The proximal outline is made at the transverse level just below the tibial articular cartilage surface. The distal outline is made at an inferior height equal to the anterior-posterior length of the proximal tibia outline. Medial and lateral outlines of the posterior aspects of the tibial cortices are made at the proximal level of the posterior cruciate ligament insertion. The medial-lateral direction of the tibial coordinate system is defined by the direction that passed through the most posterior points of the medial and lateral tibial outlines (black open triangles) and perpendicular to the defined superior-inferior axis. The posterior-anterior direction of the tibial coordinate system is defined as the direction perpendicular to both the defined superior-inferior and medial-lateral directions.

Figure 2.

(A, B) The lateral and medial tibial slopes (LTS and MTS) are defined as the slope of the lines between the anterior and posterior peaks (black open squares) of the lateral and medial tibial compartments, respectively, relative to the line perpendicular to the tibial inferior-superior axis in the posterior direction. Negative LTS and MTS angles indicate a posteriorsuperior directed slope of the plateau, and positive angles (as shown in A and B) represent a posterior-inferior directed slope. A value of 0 indicates the LTS and MTS are perpendicular to the inferior-superior axis of the tibia. (C) The medial tibial depth is defined as the greatest depth of concavity measured perpendicular from the line between the anterior and posterior peaks in the medial compartment (vertical axis scaled up). (D) The coronal tibial slope is defined as the slope of the line connecting the most medial and lateral peaks of the tibial plateau relative to the line perpendicular to the tibial long axis in the lateral direction (medial-lateral axis).