Background The most common movements that occur during anterior cruciate ligament (ACL) injuries in soccer are “pressing” movements. There are currently no accurate kinematic descriptions of joint kinematics in pressing movements in defensive situations.

Objective To describe the knee and hip joint kinematics during pressing actions in soccer in order to identify kinematic patterns in high-risk situations for ACL injuries.

Design Case study

Setting Competitive level, division-1 amateur female soccer league in Japan.

Participants Five video sequences involving 4 collegiate soccer players.

Assessment of Risk Factors The high-risk pressing situations were determined by the large distance between trunk and foot placements in the sagittal plane.

Main Outcome Measurements The knee and hip joint kinematics using model-based image-matching technique.

Results The mean knee flexion angle at initial contact (IC) was 13°; it had increased by 11° (95% CI: 3°–14°) 40 ms after IC. As for knee adduction and rotation angles, the knee positions were close to neutral at IC, and only minor knee angular changes occurred later in the sequences. The mean hip flexion was 25° at IC, and had increased by 22° (95% CI: 11°–32°) 100 ms later. The hip was also externally rotated 7° at IC, and gradually rotated internally, reaching 10° of internal rotation 100 ms after IC.

Conclusions In contrast with previously reported injury-causing situations, the present knee did not experience rapid knee valgus and increased internal rotation. The hip displayed a smooth transition after IC, which contrasted with previously reported hip kinematics of substantial internal rotation and static hip flexion in injury situations. This study suggests that the observed sudden changes in knee valgus and rotation, as well as the static hip flexion seen in ACL injury situations are unique to such situations, supporting the view that these characteristics likely contribute to the injury mechanism.