ACL tear Causes may include: * Changing direction rapidly (also known as "cutting") * Landing from a jump awkwardly * Coming to a sudden stop when running * A direct contact or collision to the knee (e.g. during a football tackle or a motor vehicle collision) These movements cause the tibia to shift away from the femur rapidly, placing strain on the knee joint and potentially leading to rupture of the ACL. About 80% of ACL injuries occur without direct trauma. Risk factors include female anatomy, specific sports, poor conditioning, fatigue, and playing on a turf field. Female predominance Female athletes are two to eight times more likely to strain their ACL in sports that involve cutting and jumping as compared to men who play the same particular sports. NCAA data has found relative rates of injury per 1000 athlete exposures as follows: * Men's basketball 0.07, women's basketball 0.23 * Men's lacrosse 0.12, women's lacrosse 0.17 * Men's football 0.09, women's football 0.28 The highest rate of ACL injury in women occurred in gymnastics, with a rate of injury per 1000 athlete exposures of 0.33. Of the four sports with the highest ACL injury rates, three were women's – gymnastics, basketball and soccer. Differences between males and females identified as potential causes are the active muscular protection of the knee joint, differences in leg/pelvis alignment, and relative<unk>  laxity caused by differences in hormonal activity from estrogen and relaxin. Birth control pills also appear to decrease the risk of ACL injury. Dominance theories Femur with Q angle: the angle formed by a line drawn from the<unk>  superior iliac spine through the center of the patella and a line drawn from the center of the patella to the center of the tibial tubercle Some studies have suggested that there are four neuromuscular imbalances that predispose women to higher incidence of ACL injury. Female athletes are more likely to jump and land with their knees relatively straight and collapsing in towards each other, while most of their bodyweight falls on a single foot and their upper body tilts to one side. Several theories have been described to further explain these imbalances. These include the<unk>  dominance, quadriceps dominance, leg dominance, and trunk dominance theories. The<unk>  dominance theory suggests that when females athletes land after a jump, their muscles do not sufficiently absorb the impact of the ground. As a result, the<unk> s of the knee must absorb the force, leading to a higher risk of injury. Quadriceps dominance refers to a tendency of female athletes to preferentially use the quadriceps muscles to stabilize the knee joint. Given that the quadriceps muscles work to pull the tibia forward, an overpowering contraction of the quadriceps can place strain on the ACL, increasing risk of injury. Leg dominance describes the observation that women tend to place more weight on one leg than another. Finally, trunk dominance suggests that males typically exhibit greater control of the trunk in performance situations as evidenced by greater activation of the internal oblique muscle. Female athletes are more likely to land with their upper body tilted to one side and more weight on one leg than the other, therefore placing greater rotational force on their knees. Hormonal and anatomic differences Before puberty, there is no observed difference in frequency of ACL tears between the sexes. Changes in sex hormone levels, specifically elevated levels of estrogen and relaxin in females during the menstrual cycle, have been hypothesized as causing predisposition of ACL ruptures. This is because they may increase joint laxity and extensibility of the soft tissues surrounding the knee joint. Ongoing research has observed a greater occurrence of ACL injuries in females during ovulation and fewer injuries during the follicular and luteal phases of the menstrual cycle. Study results have shown that female collegiate athletes with concentration levels of relaxin that are greater than 6.0 pg/mL are at four times higher risk of an ACL tear than those with lower concentrations. Additionally, female pelvises widen during puberty through the influence of sex hormones. This wider pelvis requires the femur to angle toward the knees. This angle towards the knee is referred to as the Q angle. The average Q angle for men is 14 degrees and the average for women is 17 degrees. Steps can be taken to reduce this Q angle, such as using orthotics. The relatively wider female hip and widened Q angle may lead to an increased likelihood of ACL tears in women. ACL, muscular stiffness, and strength During puberty, sex hormones also affect the remodeled shape of soft tissues throughout the body. The tissue remodeling results in female ACLs that are smaller and will fail (i.e. tear) at lower loading forces, and differences in<unk>  and muscular stiffness between men and women. Women's knees are less stiff than men's during muscle activation. Force applied to a less stiff knee is more likely to result in ACL tears. In addition, the quadriceps femoris muscle is an antagonist to the ACL. According to a study done on female athletes at the University of Michigan, 31% of female athletes recruited the quadriceps femoris muscle first as compared to 17% in males. Because of the elevated contraction of the quadriceps femoris muscle during physical activity, an increased strain is placed onto the ACL due to the "tibial translation<unk> ly".
Anterior cruciate ligament injury
Tibial plateau fracture
Posterior cruciate ligament injury
Knee dislocation  Knee dislocation  1
Medial knee injuries
Pes anserine bursitis
Patellar dislocation
Patellar subluxation syndrome