Background Excessive tibiofemoral compression has been shown to rupture the Anterior Cruciate Ligament (ACL) as axial tibia load may produce an anterior shear force to the proximal lateral tibial plateau.

Objective To quantify and compare the amount of Tibial Anterior Shear Force (TASF) during three different landing styles.

Design Controlled Crossover Design.

Setting Controlled Laboratory.

Participants 20 healthy volunteers (10 M, 10 F; 23.4±3.6 years, 171.0±9.4 cm, 73.3±12.7 kg) without history of lower extremity ligamentous injuries.

Interventions Biomechanical data were collected from three different landings; (1) self-selected (SS), (2) leaning forward (LF), and (3) upper body upright (UR). TASF was calculated from the sagittal plane knee joint reaction force, and assuming that the posterior slope of the lateral tibial plateau was 15° and that joint reaction force occurred on the lateral knee.

Main outcome measures Maximum TASFs (TASFmax) normalised by body weight (N), Sagittal plane angle of the ground reaction force (GRF) vector relative to the longitudinal axis of the tibia at TASFmax (GRF_Angle, positive direction indicates GRF is inclined more anteriorly than the tibia in sagittal plane).

Results LF produced the least amount of TASFmax whereas UR produced the largest amount of TASFmax (LF=0.54±0.06, SS=0.95±0.10, UR=1.30±0.11). GRF_Angle in UR was the largest while no difference in GRF_Angle was observed between LF and SS (LF=−3.4°±2.2°, SS=0.2°±1.2°, UR=4.2°±1.1°).

Conclusions It has been reported that GRF pushes the tibia posteriorly during landing, slacking the ACL. However, our research demonstrated GRF_Angle may push the tibia anteriorly and straining the ACL for certain sagittal plane body positions during landing. Based on the TASF calculations, the risk of ACL injuries may depend on the sagittal plane body positions during landing, as well as other factors which increase the lateral TASF, such as valgus knee loading and the amount of the posterior slope on the lateral tibial plateau.