Anterior Cruciate Ligament Injury: Current Understanding of Risk Factors

Reconstruction of the anterior cruciate ligament (ACL) is a common surgical procedure with an estimated 50,000 procedures in the US annually. Injury of the ACL often requires costly treatment, extensive rehabilitation, and results in early osteoarthritis. While ACL ruptures occur secondary to a complex interplay of multiple variables, a number of risk factors have been identified that increase risk of ACL rupture. We will analyze a variety of identified risk factors including anatomic, neuromuscular control, hormonal, genetic, and external variables. In terms of intrinsic risk factors, multiple recent studies have identified neuromuscular risk factors that put the ACL at risk for injury. These studies show differences in neuromuscular control of knee joint mechanics, hamstring muscle strength and core stability in patients who sustain ACL injury. Anatomical variants between individuals, genders and races have also been implicated as risk factors for ACL injury. These risk factors include femoral intercondylar notch width, tibial slope geometry, ACL dimensions, and generalized ligamentous laxity. Studies have sought to evaluate the interactions between absolute femoral notch width, notch width index, and intercondylar notch shape and how these factors relate to ACL injury risk. Postulating that an increased anterior directed shear force on the tibia correlates with higher incidence of ACL injury, studies have identified an increased posterior inferior directed tibial slope and shallow medial depth of the tibial plateau, as significant risk factors for ACL injury. Newer research suggests that meniscal geometry factors into this equation as well. Other studies have suggested that decreased ACL volume is a contributing factor, while further studies propose that ACL injury risk can be predicted as a factor of generalized joint laxity. Lastly, prior ACL injury and reconstruction have been implicated as risk factors for future knee injury. Patients undergoing ACL reconstruction are at higher risk for contralateral ACL injury and ACL rerupture post reconstruction compared to individuals without prior ACL injury. Additionally, hormonal and genetic factors have been connected to ACL injury. After estrogen and progesterone receptor sites were found on the ACL, multiple studies have analyzed hormone levels and ACL rupture risk. Overall, the results of these studies are varied and controversial, but suggest an increased risk in the pre ovulatory menstrual cycle phase. Genetic studies have shown specific mutations that place patients at risk for ACL injury and other tendon injury. Also, a study has shown that patients with an ACL rupture were more than 4 times as likely to have a relative with history of ligament injury.