Anterior cruciate ligament injury

Anterior cruciate ligament injury
Classification and external resources
Diagram of the right knee
ICD-10	S83.5
ICD-9	844.2
eMedicine	pmr/3

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 than does injury to other knee ligaments. 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. Tears in the anterior cruciate ligament often take place when the knee receives a direct impact from the front of the thigh 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 make sharp changes in movement and during abrupt stops from high speed. These types of injuries are prevalent in alpine skiing, American football, Australian rules football, basketball, rugby, professional wrestling, martial arts, artistic gymnastics, Ultimate (sport), and association football. 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, 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.

Signs and symptoms

Symptoms of an ACL injury include hearing a sudden popping sound, swelling, and 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. 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 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

ACL injuries occur when an athlete rapidly decelerates, followed by a sharp or sudden change in direction (cutting). ACL failure has been linked to heavy or stiff-legged landing; as well as twisting or turning the knee while landing, especially when the knee is in the valgus (knock-knee) position. But other positions can cause the ACL to tear.

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. Women have a relatively wider pelvis, requiring the femur to angle toward the knees. Recent research also suggests that there may be a gene variant that increases the risk of injury.

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 lateral 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.

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

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  Left knee-joint from behind, showing interior ligaments.

Diagnosis

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

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. 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

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. 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. 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. 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, Dr. Joseph Torg.

Pivot shift test

• 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

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.

Treatment

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. These include cartilage/meniscus injuries, bone bruises, PCL tears, posterolateral injuries and collateral ligament injuries.

Conservative

A torn ACL is less likely to restrict the movement of the knee. When tears to the ACL are not repaired it can sometimes cause damage to the cartilage inside the knee because with the torn ACL the tibia and femur bone are more likely to rub against each other. Immediately after the tear of the ACL, the person should rest the knee, ice it every 15 to 20 minutes, provide compression on the knee, and then elevate above the heart; this process helps decrease the swelling and reduce the pain. The form of treatment is determined based on the severity of the tear on the ligament. Small tears in the ACL may just require several months of rehab in order to strengthen the surrounding muscles, the hamstring and the quadriceps, so that these muscles can compensate for the torn ligament. Falls associated with knee instability may require the use of a specific brace to stabilize the knee. Women are more likely to experience falls associated with the knee giving way. Sudent falls can be associated with further complications such as fractures and head injury.

Surgery

Main article: ACL reconstruction

If the tear is severe, surgery may be necessary because the ACL cannot heal independently, as there is no blood supply to this ligament. Surgery is usually required among athletes because the ACL is needed in order to perform sharp movements safely and with stability. The reconstructive surgery is usually done several weeks after the injury in order to allow the swelling and inflammation to go down. During surgery the ACL is not repaired, instead, it is reconstructed using other tendons in the body. There are three different types of ACL surgery. Patella tendon-bone auto graft and hamstring auto graft are the most common and preferred and tend to produce the best results. For the Patella tendon-bone auto graft, the central 1/3 of the patella tendon is removed along with a piece of bone at the attachment sites on the kneecap and tibia. The advantages of using this method is that the patella tendon and ACL are relatively the same length and it uses a bone to bone attachment which most surgeons agree is much stronger than other healing methods. Disadvantages of this method is common anterior knee pain due to the removal of bone from the kneecap. For the hamstring auto graft, two tendons are taken from the hamstring muscles and wrapped together to form the new ACL. Advantages of this method are less pain associated with post surgery healing than that of the patella tendon-bone graft due to the fact no bone is removed, and the small incision. The disadvantage of this method is that the new ligament takes longer to heal since there is no bone to bone healing and the tendon to bone connection takes relatively long to become rigid. After the surgery, rehabilitation is required in order to strengthen the surrounding muscles and stabilize the joint.

There are two main options for ACL graft selection, allograft and autograft. Autografts are the persons own tissues, and options include the hamstring tendons or middle third of the patella tendon but it is not known which is best. Allografts are cadaveric tissue sourced from a tissue bank. Each method has its own advantages and disadvantages; hamstring and middle third of patella tendon having similar outcomes. Patellar grafts are often incorrectly cited as being stronger, but the site of the harvest is often extremely painful for weeks after surgery and some patients develop chronic patellar tendinitis. Replacement via a posthumous donor involves a slightly higher risk of infection. Additionally, donor grafts eliminate tendon harvesting which, due to improved arthroscopic methods, is responsible for most post-operative pain.

The surgery is typically undertaken arthroscopically, with tunnels drilled into the femur and tibia at approximately the original ACL attachments. The graft is then placed into position and held in place. There are a variety of fixation devices available, particularly for hamstring tendon fixation. These include screws, buttons and post fixation devices. The graft typically attaches to the bone within six to eight weeks^{[citation needed]}. The original collagen tissue in the graft acts as a scaffold and new collagen tissue is laid down in the graft with time. Hence the graft takes over six months to reach maximal strength.^{[citation needed]}

After surgery, the knee joint loses flexibility, and the muscles around the knee and in the thigh tend to atrophy. All treatment options require extensive physical therapy to regain muscle strength around the knee and restore range of motion (ROM). For some patients, the lengthy rehabilitation period may be more difficult to deal with than the actual surgery. In general, a rehabilitation period of six months to a year is required to regain pre-surgery strength and use.^{[citation needed]} This is very dependent on the rehabilitation assignment provided by the surgeon as well as the person who is receiving the surgery. External bracing is recommended for athletes in contact and collision sports for a period of time after reconstruction. It is important however to realize that this type of prevention is given by a 'surgeon to surgeon' basis; all surgeons will prescribe a brace and crutches for post surgery recovery. Total usage time is one month. After surgery, no sports are allowed for 6 to 7 months. Whether the ACL deficient knee is reconstructed or not, the patient is susceptible to early onset of chronic degenerative joint disease.

Rehabilitation

The rehabilitation process is a very important to reconstruction. The process to regain full use of the joint is long and rigorous. The doctor will start the patient on the rehabilitation program, which is broken down into phases:

Phase 1: Early rehabilitation consists of short-term management, i.e. management of pain and swelling while regaining movement.

Phase 2: In weeks 3 and 4, the pain should be subsiding and the patient will be ready to try more things on an unsteady knee. Joint protection during this step is emphasized. The patient will be able to start doing exercises such as mini wall sits and riding stationary bikes. The aim is to be able to bend the knee 100 degrees.

Phase 3: Weeks 4 and 6 are the controlled ambulation phase. At this point the patient will be doing the exercises from phase 2 plus some more challenging ones. The patient will try to get their knee to bend 130 degrees during this stage. The aim during this period is to focus heavily on improving balance.

Phase 4: This is the moderate protection phase, covering weeks 6 to 8. In this period the patient will try to obtain full range of motion as well as increase resistance for the workouts.

Phase 5: This is the light activity phase, covering weeks 8 to 10. Rehabilitation during period places particular emphasis on strengthening exercises, with increased concentration on balance and mobility.

Phase 6: This is the return to activity phase, lasting from week 10 until the target activity level is reached. At this point the patient will be able to start jogging and performing moderately intense agility drills. Somewhere between month 3 and month 6 the surgeon will probably request that the patient perform physical tests to monitor the activity level. When the doctor feels comfortable with the progress of the patient, s/he will clear that person to resume a fully active lifestyle.

Epidemiology

Mountcastle et al. performed a study on gender difference in ACL tears in relationship with physical activities. The researchers performed an epidemiology study on young athletic populations. Previous studies found that women that participate in the same physical activities as men are more at risk for ACL injuries. The authors hypothesize that the frequency rate for males and females in the athletic and college aged population is the same. The study looked at college graduation classes from 1994-2003 at major institutions. The players who received a whole tear were examined for apparatus of injury and the type of sport they played when the injury occurred. The authors calculated the accident rate, opinion of danger, gender incidents, class year, and the accident rate differentiating men and women. There were 353 ACL injuries in 10 classes during the span of the study. The researchers calculated a 4-year accident proportion of 3.24 per 100 students for men, and 3.51 for women. Overall, the ACL injury rate not including male-only sports was substantially greater in women with an incidence ratio of 1.51 (pg 5). Women are more likely to get injured at gymnastics courses with an incidence ratio of 5.67; with an indoor obstacle course test the rate is 3.72; and there is a 2.42 incidence ratio on basketball. The authors concluded that there is slim gender difference in gender ACL tear. On the other hand, there were significant gender differences in ACL injury rates when particular specific sports and physical activities were compared.

A notable finding is that women are three times more likely to have an ACL injury than men, due to variations of hormone levels and greater ligament strength in men than in women. Most importantly, there is substantial difference in neuromuscular coordination and control in landing—women have less hip and knee flexion. Women also have wider Q angles than men, and this combined with their weakened hip strength makes them more prone to an ACL tear. This is seen especially in Women's Basketball and Volleyball. Athletic trainers and team physicians advise female athletes to adapt an ACL conditioning program.

Female susceptibility

Since the Title IX enactment that made it illegal to discriminate in the education system based on gender in the USA, the percentage of female athletes has risen considerably. By 1998, the percentage of girls participating in high school level sports was ten times the amount that had participated in the previous decade, rising from 3.7% in 1971 to 33% in 1998. With female participation in high-level competition sports on the rise, doctors were finding more and more instances of anterior cruciate ligament (ACL) injuries. According to ACL Tears in Female Athletes, seventy percent of ACL related injuries occur during athletic competition. Of this seventy percent, a majority of ACL tears occur during sports that require quick stopping, cutting, and rapid changes of direction—sports like soccer, basketball and lacrosse. When the National Collegiate Athletic Association (NCAA) compared statistics from these high-risk sports where male and female athletes have similar equipment and rules, they found that ACL injuries occurred two to eight times more likely in females than in males. Doctors have studied a combination of environmental, hormonal, neuromuscular and biomechanical factors that make the female athlete more prone to ACL tears and have used this information to determine ways to prevent future injury. There are many environmental factors that come in to play with female athletes. The first deals with the friction between shoes and surface type. Surfaces that increase friction between player and field of activity can alter the movements of athletes and increase their risk of injury. One such example is drier surface. They increase the friction between shoe and surface therefore increasing risk of ACL injury, whereas wet surfaces have the opposite effect. Doctors still remain controversial over whether artificial turf increases or decreases risk of tears although there has been evidence to support both. The type of shoe, as mentioned earlier also plays a role. Cleat size and shape specifically seems to trigger injury where fewer injuries have been correlated to smaller and fewer cleats. The other environmental factor is knee bracing. Although many females chose to wear a brace on their knee to prevent injury, their actual effect on preventing injury remains controversial. Prophylactic, functional, and postoperative are all types of braces that have been used to prevent ACL injuries or reinjuries. Prophylactic bracing has been shown to improve the knee’s resistance to lateral movement twenty to thirty percent in a controlled experimental setting. On the contrary, a study done by Houston and Goemans found that braced collegiate athletes have a higher incidence of ACL tears that those athletes who don’t wear one. There is also research that suggests no difference in strength, laxity or function in the braced and non-braced knee, however most studies support that wearing a brace does not reduce injury to the knee or ACL.

There are various internal factors that play a role in the increased amount of ACL injuries found in females. Female body structures as well as certain hormones are the leading contributors to this epidemic. Females have a wider pelvis, shorter femurs, and less developed thigh muscles than males, which can cause stress from impact and movement to lie on specific ligaments or tissues rather than on the muscles themselves. “These differences form a more lateral proximal reference point, increase lateral pull of the quadriceps muscle on the patella and put medial stress on the knee” Women have larger quadriceps angles than men which determine the force the quads put on the patella during leg extension. When this angle is larger, the quadriceps have a greater pull on the patella, causing increased stress on the knee. Women lack the same neuromuscular spurt that males undergo during puberty. This spurt directly correlates with an individual’s strength and coordination, and these muscles are what stabilize the knee and protect it. Without this, women’s bodies bear more of the stress of physical activity on their joints rather than on their muscles. The hyperextension of the knee means that the ACL is more likely to tear. According to Dr. C. David Geier, an orthopedic surgeon and director of the Medical University of South Carolina Sports Medicine program, there is a difference in neuromuscular patterns and activities in females compared to males. Female athletes are more likely to land and turn with their knees straight compared to males who tend to do so with bent knees. ACL injuries have also been reported to be more common during menstruation. Certain female hormones can affect bone, muscle, and tissue in the body. During menstruation, estrogen receptors near the ACL may cause it to become more relaxed, which increases its likeliness for injury. The hormone relaxin, found in females during pregnancy, is also related to the loosening of this ligament.

Most ACL injuries are due to non-contact events. This means that prevention techniques are an important possibility for active people. Though there are many prevention techniques for ACL injuries many are not gender specific. Some of the key factors when talking about injury prevention include training, flexibility, and knowledge. Probably the most important factor in prevention would be the training aspect. Researchers suggest neuromuscular training to help greatly reduce the chance of ACL injury. Many women compared to men have insufficient training, which could explain the increased amount of ACL injuries. In this training, strength should play an important role. Strengthening the surrounding muscles of the ACL can help in preventing an injury. These muscles in particular include the quads and hamstrings. In general women have weaker legs including the important muscles located around the ACL. Studies have shown that women rely too much on quad strength and less on hamstring strength when these muscles should be used almost equally. This poses a problem because increased quad muscles in addition to the decreased knee and hip flexion and valgus knee angles and movements is the reason for the greater number of ACL tears in women over men. In addition, the decrease in hip extension causes women to compensate by landing with a stiff knee. This is very dangerous to the ACL. Overall, neuromuscular training is an effective prevention technique for ACL injuries however timing also plays a big role in this method. Gregory Myer, a researcher at Cincinnati Children’s Hospital in Ohio, conducted a study that proved the earlier females start this neuromuscular training the more effective it will be. Myer found that females who had been introduced to neuromuscular training before age fourteen were 72% less likely to hurt the ligaments in their knee. This is compared to women who started preventative training at twenty had the same risk as women who did not participate in the training. Another important aspect in prevention of ACL injuries is knowledge. Studies have shown that many injuries are due to awkward movements or positions while participating in sport. These can be reduced though knowledge of what can or cannot be harmful to the ACL. There are numerous programs that not only build up strength in the knee and leg but also inform the participants about causes and preventions of this injury. One major example of this would be that women are more prone to partaking in rapid deceleration. This is detrimental to the anterior cruciate ligament however some women may not know this fact. With these programs and other forms of education women would be informed about this and be able to stop decelerating rapidly and learn to gradually slow down. Although no prevention technique can guarantee the absence of ACL injuries, women should partake in early, active and smart training to strengthen and prevent problems with the anterior cruciate ligament.

External links

• Educational site
• The Knee Library — Articles pertaining to knee injuries
• Vermont Safety Research — Tips for knee friendly skiing
• ACL Injury in Martial Arts
• Torn ACL prevention and recovery
• ACL Injury Prevention – The Evidence Mounts, Science of Soccer Online
• ACL Injury — A simple patient guide.
• Anterior cruciate ligament tear