出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/08/30 22:54:23」(JST)
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| Anterior cruciate ligament injury | |
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| Classification and external resources | |
Diagram of the right knee
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| 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.[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.[2] 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,[3] Soccer, 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, 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.
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.[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 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.
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.[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 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.
Right knee-joint, from the front, showing interior ligaments.
Left knee-joint from behind, showing interior ligaments.
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.
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.[8] 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.
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.[9] 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.[10] 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.[11] 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.[12]
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.[13]
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.
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. Sudden falls can be associated with further complications such as fractures and head injury.
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.[14] 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.[15] 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.
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.[16]
Mountcastle et al. performed a study on gender difference in ACL tears in relationship with physical activities.[17] 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.
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