Risk Factors for Anterior Cruciate Ligament (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.