D(B) Cooper

An injury to the anterior cruciate ligament can be a debilitating musculoskeletal injury to the knee, seen most often in athletes. Non-contact tears and ruptures are the most common causes of ACL injury. The anterior cruciate ligament (ACL) is an important ligament for proper movement. ACL injury more commonly causes knee instability that does injury to other knee ligaments.[1] Injuries of the ACL range from mild such as small tears to severe when the ligament is completely torn.
There are many ways the ACL can be torn; the ligament tears because it is overstretched. The movements of the knee that can result in a tear is when the knee is straightened more than 10 degrees beyond its normal maximal position (hyperextension) - the lower leg is forced forward in relation to the upper leg. It can happen from a rotational injury when the knee twists when the rest of the body is moving straight.[2] Tears in the anterior cruciate ligament often take place when the knee receives a direct impact at the knee while the leg is in a stable position, for example a standing football player is tackled sideways when his feet are firmly planted.
Torn ACLs are most often related to high impact sports or when the knee is forced to stop suddenly at high speed and when the tibia moves forward in relation to the femur. These types of injuries are prevalent in alpine skiing,[3] Association football, American football, Australian rules football, basketball, rugby, professional wrestling, martial arts, and artistic gymnastics. Research has shown that women involved in sports are more likely to have ACL injuries than men. ACL tears can also happen in older individuals through slips and falls and are seen mostly in people over 40 due to wear and tear of the ligaments. An ACL tear can be diagnosed by a popping sound heard after impact, anterior knee instability, swelling after a couple of hours, severe pain when bending the knee, and when the knee buckles or locks during movement or gives way while standing still with weight on the affected knee.
Contents [hide]
1 Signs and symptoms
2 Causes
3 Evolution
4 Diagnosis
4.1 Anterior drawer test
4.2 Lachman test
4.3 Pivot shift test
5 Prevention
6 Treatment
6.1 Conservative
6.2 Surgery
6.3 Rehabilitation
7 Epidemiology
8 References
9 External links
Signs and symptoms[edit]

Symptoms of an ACL injury include hearing a sudden popping sound, swelling, and anterior instability of the knee (i.e. a "wobbly" feeling). Pain is also a major symptom in an ACL injury and can range from moderate to severe.[4] Continued athletic activity on a knee with an ACL injury can have devastating consequences, resulting in massive cartilage damage, leading to an increased risk of developing osteoarthritis later in life. Other problems include anterior knee instability. ACL injury is a common cause of non contact knee injury in football. Falls occur when the knee gives way sometimes without warning.
Causes[edit]

ACL injuries occur when an athlete stops on a dime or when an athlete plants his foot really hard into the ground (cutting). ACL failure has been linked to heavy or stiff-legged landing; the knee rotating while landing, especially when the knee is in an unnatural position.
Women in sports such as association football, basketball, tennis and volleyball are significantly more prone to ACL injuries than men. The discrepancy has been attributed to differences between the sexes in anatomy, general muscular strength, reaction time of muscle contraction and coordination, and training techniques. A recent study suggests hormone-induced changes in muscle tension associated with menstrual cycles may also be an important factor.[5] Women have a relatively wider pelvis, requiring the femur to angle toward the knees.[6] Recent research also suggests that there may be a gene variant that increases the risk of injury.[7]
The majority of ACL injuries occur in athletes landing flat on their heels. The latter directs the forces directly up the tibia into the knee, while the straight-knee position places the anterior femoral condyle on the back-slanted portion of the tibia. The resultant forward slide of the tibia relative to the femur is restrained primarily by the now-vulnerable ACL.

Right knee-joint, from the front, showing interior ligaments.



Left knee-joint from behind, showing interior ligaments.

Evolution[edit]

ACL tears occur for two reasons: the failure load of the ligament and the mechanical load applied to it. Female ACLs will fail at relatively lower loads than males, and female pelvic anatomy also predisposes women to higher mechanical loads on the knee. The combination of these factors leads to an increased likelihood – four to six times – for females to tear their ACLs than males.[8]
There are both proximate and ultimate causes for the increased susceptibility of women to ACL tears. Proximate, or immediate, causation is that women have wider pelvises than men. This widened pelvis creates a wider valgus knee angle: with wider hips, the femur must angle towards the knee at a wider angle. This difference in skeletal anatomy between men and women makes women more susceptible to ACL tears due to greater rotational force placed upon the knee.[9]
Underlying this proximate cause is the ultimate cause of male and female anatomical divergence due to the influence of sex hormones. Before puberty, there is no observed difference in frequency of ACL tears between the sexes. Changes in sex hormones, specifically increased estrogen and progesterone in women, make possible many of the anatomical changes necessary for successful reproduction and childbirth. Through the influence of sex hormones, female pelvises widen during puberty. The proximate cause of increased likelihood of ACL tears in women thus stems from the ultimate cause of differences in sex hormones between males and females.
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. Sex hormones, the ultimate cause of ACL tear differences, create differences in ligament 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.[8]
While these sex hormones may appear detrimental to women in terms of sports injuries, they are necessary for childbirth and thus are an intrinsic part of the evolution of the human species. Females face an evolutionary trade-off in anatomy between a body adapted for efficient bipedal movement and one adapted for successful childbirth. Trade-offs, a common theme in the history of human evolution, occur when humans evolve a change in physiology in order to reduce illness or injury (in this case, death in childbirth). This change may have deleterious effects on another aspect of human physiology: in the case of pelvic anatomy, a too-wide pelvis would not be able to be supported by gluteal muscles and would be an inefficient means of bipedal locomotion.
Applied to female pelvic width, a narrower pelvis would reduce valgus knee angle, leading, among other things, to lower rates of ACL tears and other physical benefits like a more efficient stride and running gait. Yet this narrow pelvis would constrain childbirth, possibly resulting in the death of the mother and child. Thus, throughout human history, women with wider pelvises had higher rates of survival in childbirth and passed on these wider-hipped genes to their offspring.
Pelvic width was constrained by the trade-off between locomotion and childbirth: wider pelvises offered a fitness advantage up to a certain point, where they became a liability due to decreased bipedal abilities. Pelvic width thus could not expand as wide as it might to make childbirth easier, due to the necessity of human bipedal locomotion. Humans evolved from quadruped primates who had only the physiological capabilities for inefficient, infrequent bipedal locomotion. Evolutionary adaptations like larger, more powerful gluteal muscles allowed humans to stabilize their hips and trunk during bipedal locomotion. Multiple theories exist about why bipedalism conferred a reproductive advantage. Bipedalism allowed humans to use their hands to carry food, was a more efficient form of long-distance transportation than quadrupedal locomotion, improved thermoregulation by reducing the amount of skin exposed to direct sunlight (the top of the head vs. the entire back), and permitted humans to engage in persistence hunting. East Africa was changing from a forest to a grassland when bipedalism first evolved in humans' ancestors approximately 8 million years ago, and the new behaviors it enabled them to engage in would have made them better fit to survive in this changed environment.[10]
Thus female pelvic width is a trade-off, where childbirth is easier but not as easy as it might be in other quadruped primates; and bipedal locomotion is efficient but not as efficient as it might be with narrower hips. These sex differences in locomotion underlie differential rates of ACL injury in men and women.
Diagnosis[edit]



Anterior cruciate ligament tear seen on MRI. T1 left, right PDW.
The pivot-shift test, anterior drawer test and the Lachman test are used during the clinical examination of suspected ACL injury. The ACL can also be visualized using a magnetic resonance imaging scan (MRI scan).
An ACL tear can present with a popping sound heard after impact, swelling after a couple of hours, severe pain when bending the knee, and buckling or locking of the knee during movement.
Though clinical examination in experienced hands is highly accurate, the diagnosis is usually confirmed by MRI, which has greatly lessened the need for diagnostic arthroscopy. MRI has a higher accuracy than clinical examination in detecting ACL tears when multiple ligaments are torn. This is of particular benefit if there is a coexisting posterolateral corner injury. Addressing the posterolateral corner injury at the time of ACL reconstruction will prevent premature graft failure.
Anterior drawer test[edit]
The anterior drawer test for anterior cruciate ligament laxity is one of many medical tests used to determine the integrity of the anterior cruciate ligament.[11] It can be used to help diagnose sprains and tears.
The test is performed as follows: the patient is positioned lying supine with the hip flexed to 45° and the knee to 90°. The examiner positions himself by sitting on the examination table in front of the involved knee and grasping the tibia just below the joint line of the knee. The thumbs are placed along the joint line on either side of the patellar tendon. The index fingers are used to palpate the hamstring tendons to ensure that they are relaxed; the hamstring muscle group must be relaxed to ensure a proper test. The tibia is then drawn forward anteriorly. An increased amount of anterior tibial translation compared with the opposite limb or lack of a firm end-point indicates either a sprain of the anteromedial bundle of the ACL or a complete tear of the ACL. This test should be performed along with other ACL-specific tests to help obtain a proper diagnosis.
Lachman test[edit]


Lachman test
The knee is flexed at 30 degrees
Examiner pulls on the tibia to assess the amount of anterior motion of the tibia in comparison to the femur
An ACL-deficient knee will demonstrate increased forward translation of the tibia at the conclusion of the movement
The Lachman test is an orthopedic test used for examining the anterior cruciate ligament (ACL) in the knee for patients where there is a suspicion of a torn ACL.[12] The Lachman test is recognized by most authorities as the most reliable and sensitive clinical test for the determination of anterior cruciate ligament integrity, superior to the anterior drawer test commonly used in the past.[citation needed] To do this, lay the patient supine on an examination table. Put the patient's knee in about 20–30 degrees flexion, also according to Bates' Guide to Physical Examination the leg should be externally rotated.[13] The examiner should place one hand behind the tibia and the other on the patient's thigh. It is important that the examiner's thumb be on the tibial tuberosity. On pulling anteriorly on the tibia, an intact ACL should prevent forward translational movement of the tibia on the femur ("firm endpoint").
Anterior translation of the tibia associated with a soft or a mushy endpoint indicates a positive test. More than about 2 mm of anterior translation compared to the uninvolved knee suggests a torn ACL ("soft endpoint"), as does 10 mm of total anterior translation. An instrument called a "KT-1000" can be used to determine the magnitude of movement in mm.
This test can be done in an on-the-field evaluation in an acute injury setting, or in a clinical setting when a patient presents with knee pain. In either situation, ruling out fracture is important in the evaluation process. Also when evaluating the integrity of the ACL, it is important to test the integrity of the MCL, because this is a common ligament torn in an ACL injury as well.[14] This test is named after orthopaedic surgeon, John Lachman, the late Chairman of the Department of Orthopaedic Surgery and Sports Medicine at Temple University School of Medicine in Philadelphia, PA. The original publication describing the test was submitted by one of his colleagues, Joseph Torg.[15]
Pivot shift test[edit]
Person lies on one side of the body
Knee is extended and internally rotated
Doctor applies stress to lateral side of the knee, while the knee is being flexed
A crash felt at 30 degrees flexion indicates positive test.
Prevention[edit]

Research has shown that the incidence of non-contact ACL injury can be reduced anywhere from 20% to 80% by engaging in regular neuromuscular training that is designed to enhance proprioception, balance, proper movement patterns and muscle strength.[16]
Treatment[edit]

The ACL primarily serves to stabilize the knee in an extended position and when surrounding muscles are relaxed; so if the muscles are strong, many people can function without it. Fluids will also build the muscle.
The term for non-surgical treatment for ACL rupture is "conservative management", and it often includes physical therapy and using a knee brace. Lack of an ACL increases the risk of other knee injuries such as a torn meniscus, so sports with cutting and twisting motions are strongly discouraged. For patients who frequently participate in such sports, surgery is often indicated.
Patients who have suffered an ACL injury should always be evaluated for other knee injuries that often occur in combination with an ACL tear.

Willis McGahee was ridiculously fast in college, tore his acl and was never close to that speed again.

HFNY said:

I found a Bleacher Report article on futbol non-Americano that says ACL tears don't affect straight line speed 18 months after the surgery.

CASE CLOSED.

Case closed, indeed. If Bleacher Report said it, cook it.