The consistent findings from this video analysis study showed that the players likely ruptured their ACL immediately after ground contact. 

All players experienced an immediate valgus motion within 40 ms after initial contact (IC). Moreover, the tibia rotated internally during the first 40 ms. 

 

These results suggest that valgus loading is a contributing factor in the anterior cruciate ligament injury mechanism and that internal tibial rotation is coupled with valgus motion. 

 

After the point of injury, external rotation of the tibia was observed. This surprising result explains the previous paradox that external rotation is visually observed in injury situations, whereas the same rotation is found to ease the strain of the ACL in cadaver studies.

 

The new hypothesis for noncontact anterior cruciate ligament (ACL) injury mechanism.

 

 

A, an unloaded knee. B, when valgus loading is applied, the medial collateral ligament becomes taut and lateral compression occurs.

C, this compressive load, as well as the anterior force vector caused by quadriceps contraction, causes a displacement of the femur relative to the tibia where the lateral femoral condyle shifts posteriorly and the tibia translates anteriorly and rotates internally, resulting in ACL rupture.

D, after the ACL is torn, the primary restraint to anterior translation of the tibia is gone. This causes the medial femoral condyle to also be displaced posteriorly, resulting in external rotation of the tibia.

 

The results presented in this article are the result of a long-term effort that was initiated ten years earlier by the Oslo Sports Trauma Research Center, where a model-based image-matching method for reconstruction of human motion was developed.

 

These very time-consuming analyses have been conducted as a Norwegian-Japanese collaboration. Dr. Hideyuki Koga from the Tokyo Medical and Dental University in Japan and the Oslo Sports Trauma Research Center is the first author of this work whereas Dr. Tron Krosshaug has been a developer and supervisor.

 

Read the article in American Journal of Sports Medicine.