The anterior cruciate ligament (ACL) is located inside the knee joint and provides stability to the knee. ACL injuries occur more frequently in women than men; the reason for this is unknown. The purpose of this study is to determine gender-specific anatomical, hormonal, and demographic risk factors for ACL injury. This observational cohort study will only enroll incoming cadets at the U.S. Naval, Air Force, or Military Academies.

Study hypothesis: Human movement factors, including key kinetics and kinematics of the knee during a jump-landing task, are associated with the rate of ACL injury.

The ACL stabilizes the knee joint by preventing the shinbone (tibia) from sliding forward beneath the thighbone (femur). A hard twist or excessive pressure on the ACL can tear or rupture the ligament, resulting in high levels of short-term disability and extensive rehabilitation. Previous data indicate that women who participate in sports or who are otherwise physically active have higher rates of ACL injury than men; the reason for this is unknown. There are four groups of potential risk factors for ACL injury: environmental, anatomical, hormonal, and biomechanical or neuromuscular. In particular, poor technique when landing from a jump (also known as jump-landing) is proposed as a specific neuromuscular risk factor of interest in this study. This study will determine gender-specific anatomical, hormonal, and demographic risk factors for ACL injury, as well as quantify gender-specific differences in jump-landing technique and other neuromuscular risk factors.

This observational cohort study will enroll 4,800 cadets at the three large U.S. military academies; approximately 50% of those enrolled will be women. Only incoming cadets at the U.S. Naval, Air Force, or Military Academies will be able to participate. Each study participant will undergo a baseline assessment that will include measurement of neuromuscular risk factors using motion analysis, strength testing, and standardized assessment of poor jump-landing technique using the Landing Error Score System (LESS). All participants will be followed for up to 4 years. ACL injuries will be prospectively identified; an injury questionnaire is administered to participants who sustain an ACL injury while they are cadets. Otherwise, there is no further contact.

Inclusion Criteria:

• Incoming cadet at the U.S. Naval, Air Force, or Military Academies

Incoming cadets at the U.S. Naval, Air Force, or Military Academies