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________________ INTRODUCTION •	GOALS o	Update resource on incidence o	expand section to provide an organized summary of the information presented in the article; add a brief description of the anatomy/role of the ACL o	STRUCTURE BASED ON MODEL ARTICLE:

ACL injury occurs when the anterior cruciate ligament (ACL) is either stretched, partially torn, or completely torn.[1] The most common injury is a complete tear.[1]ACL usually causes pain, a popping sound during injury, instability of the knee, and joint swelling within hours of injury. Physical examination typically reveals tenderness around the knee joint, reduced range of motion of the knee, and increased laxity of the joint.

ACL injury is often caused by rapid change in direction, sudden stop, landing after a jump, or direct contact to the knee.[1] It is more common in athletes, particularly those who participate in alpine skiing, soccer, football, or basketball.[1][5] Women are more likely to affected than men in certain sports because of differences in anatomy, muscle strength, and the effect of hormones on ligament integrity. Diagnosis is typically made by physical examination and is sometimes supported by magnetic resonance imaging (MRI).[1]

In individuals with high levels of activity such as competitive athletes, surgical treatment is often required. Surgery involves arthroscopy to replace the ACL with another tendon taken from another area of the body or from a cadaver. After surgery, rehabilitation involves rest, slowly expanding the range of motion of the joint, and strengthening the muscles around the knee joint to support and stabilize the knee joint. In individuals with lower levels of activity, non-operative treatment such as bracing and physical therapy are used.

ACL injury occurs in around 200,000 people per 100,000 in the general population each year. Prevention of ACL injury focuses on proper jumping form, increasing the strength of muscles around the knee, and core strengthening. [original text] Anterior cruciate ligament injury is when the anterior cruciate ligament (ACL) is either stretched, partially torn, or completely torn.[1] The most common injury is a complete tear.[1] Symptoms include pain, a popping sound during injury, instability of the knee, and joint swelling.[1] Swelling generally appears within a couple of hours.[2] In approximately 50% of cases, other structures of the knee such as surrounding ligaments, cartilage, or meniscus are damaged.[1] The underlying mechanism often involves a rapid change in direction, sudden stop, landing after a jump, or direct contact to the knee.[1] It is more common in athletes, particularly those who participate in alpine skiing, soccer, football, or basketball.[1][5] Diagnosis is typically made by physical examination and is sometimes supported by magnetic resonance imaging (MRI).[1] Prevention is by neuromuscular training and core strengthening.[3][4] Treatment recommendations depend on desired level of activity. In those with low levels of future activity, nonsurgical management including bracing and physiotherapy may be sufficient.[1] In those with high activity levels, surgical repair via arthroscopic anterior cruciate ligament reconstruction is often recommended.[1] Surgery, if recommended, is generally not performed until the initial inflammation from the injury has resolved.[1] About 200,000 people are affected per year in the United States.[2] In some sports, females have a higher risk of ACL injury, while in others, both sexes are equally affected.[5] Many people with a complete tear who do not receive surgery are unable to play sports, and may develop osteoarthritis.[2]

__________ ANATOMY •	GOALS o	NEW SECTION describing the basic anatomy of the knee ligaments; include images of knee here o	The knee joint is formed by three bones: the femur (thighbone), the tibia (shinbone), and the patella (kneecap). These bones are held together by ligaments, which are strong bands of tissue that keep the joint stable while an individual is walking, running, jumping, etc. There are two types of ligaments in the knee: the collateral ligaments and the cruciate ligaments. The collateral ligaments include the medial collateral ligament (along the inside of the knee) and the lateral collateral ligament (along the outside of the knee). These two ligaments function to limit sideways movement of the knee. The cruciate ligaments form an “X” inside the knee joint with the anterior cruciate ligament running from the front of the tibia to the back of the femur, and the posterior cruciate ligament running from the back of the tibia to the front of the femur. The anterior cruciate ligament prevents the tibia from sliding out in front of the femur and provides rotational stability. There are also two C-shaped structures made of cartilage called the medial and lateral menisci that sit on top of the tibia in the knee joint and serve as cushion for the bones.

_________________ CLASSIFICATION •	GOALS o	NEW SECTION describing grade 1 vs 2 vs 3 sprains o	Injury to a ligament is referred to as a sprain. The American Academy of Orthopedic Surgeons defines ACL injury in terms of severity and classifies them as Grade 1, 2, or 3. Grade 1 sprains occur when the ligament is stretched slightly but the stability of the knee joint is not affected. Grade 2 sprains occur when the ligament is stretched to the point that it becomes loose; this is also referred to as a partial tear. Grade 3 sprains occur when the ligament is completely torn into two pieces, and the knee joint is no longer stable. This is the most common type of sprain. Around half of ACL injuries occur in conjunction with injury to other structures in the knee, including the other ligaments, menisci, or cartilage on the surface of the bones. For example, a specific pattern of injury called the “unhappy triad” involves injury to the ACL, MCL, and medial meniscus, and occurs when a lateral force is applied to the knee while the foot is fixed on the ground.

_______________________ SIGNS AND SYMPTOMS •	GOALS o	simplify terminology and update content An individual may feel or hear a "pop" in their knee during a twisting movement[6] or rapid deceleration, followed by an inability to continue participation in the sport and swelling of the knee joint within 24 hoursearly swelling from hemarthrosis. This combination is said to indicate a 90% probability of ACL rupture.[7] An individual may experience instability in the knee once they resume walking and other activities, and they may feel their knee is "giving out". Pain while walking, loss of full range of motion, and tenderness discomfort along the joint line are also common symptoms of an ACL injury.[8] The swelling and pain may resolve on its own; however, the knee will remain unstable and returning to sport may result in further damage to the knee. ________ CAUSES •	GOALS o	NEW SECTION: will discuss the mechanism by which ACL injury occurs, and also absorb several previous sections (ligament/quads/trunk and leg dominance, prevention) ACL injury most commonly occurs when an individual stops suddenly or plants his or her foot hard into the ground (cutting). ACL injury also has been linked to heavy or stiff-legged landing; the knee rotating while landing, especially when the knee is in an unnatural position. The ACL is responsible for providing stability in knee rotation, as it prevents the tibia from shifting in front of the femur.[2] Many ACL injuries occur when an athlete lands flat on their heels. This movement 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. ACL injuries also can be caused by direct contact or trauma, such as in a motor vehicle collision or from a tackle in football. A severe form of ACL injury caused by direct contact is called the "unhappy triad," also known as the "terrible triad," or "O'Donoghue's triad." The "unhappy triad" involves injury of the anterior cruciate ligament, the medial collateral ligament, and the medial meniscus.[9] Sex-related differences[edit] Women in sports such as association football, basketball, and tennis are 2-10 times more likely to have an ACL injury than men in certain sports significantly more prone to ACL injuries than men. The discrepancy has been attributed to gender differences in anatomy, general muscular strength, reaction time of muscle contraction and coordination, differences in leg/pelvis alignment, and effect of hormones like estrogen and relaxin on ligament strength. and training techniques. Gender differences in ACL injury rates become evident when specific sports are compared.[10] A review of 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.[11] According to recent studies, female athletes are two to eight times more likely to strain their anterior cruciate ligament (ACL) in sports that involve cutting and jumping as compared to men who play the same particular sports (soccer, basketball, and volleyball).[12] Differences between males and females identified as potential causes are the active muscular protection of the knee joint, the greater Q angle putting more medial torque on the knee joint, relative ligament laxity caused by differences in hormonal activity from estrogen and relaxin, intercondylar notch dimensions, and muscular strength.[12][13] Hormonal and anatomic differences[edit] 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.[12] 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.[14] 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[edit] 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 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.[15] 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 anteriorly".[16] Ligament dominance[edit] The increased risk of anterior cruciate ligament injury among female athletes is best predicted by the motion and loading of the knee during performance situations.[17]The ligament dominance theory suggests that females typically perform athletic movements with greater knee valgus angles. A greater amount of stress is placed on the ACL in these situations because there is high activation of the quadriceps muscles despite limited knee flexion, limited hip flexion, greater hip adduction, and a large knee adductor moment.[18][19] Additionally, females typically land with their tibia rotated internally or externally.[20] As a result of increased knee valgus stress, ground reaction forces are greater and laterally directed.[21] Quadriceps dominance[edit] Ligament dominance is observed when there is excessive movement in the frontal plane to accommodate limited movement in the sagittal plane. This is caused by weakness in the hamstring muscles or reliance on the strength of the quadriceps muscles.[19] This quadriceps dominance theory identifies when the hamstring muscles are notably weaker than the quadriceps muscles. As a result, knee stability in performance situations depends on the quadriceps due to a discrepancy in the pattern in recruiting quadriceps and hamstring muscles.[22] Trunk and leg dominance[edit] Other theories used to explain the increased risk of ACL injury among female athletes include the trunk dominance and leg dominance theories. 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. Leg dominance suggests that females exhibit greater kinematic leg asymmetry in knee valgus angles, hip abduction, and ankle abduction in performance situations.[18]

___________ DIAGNOSIS o	GOALS o	provide explanations of the various exam maneuvers; remove section on laximetry Manual tests[edit] Most ACL injuries can be diagnosed through physical examination of the knee and comparison to the other, non-injured knee. When a doctor suspects ACL injury in a patient who reports a popping sound in the knee followed by swelling, pain, and instability of the knee joint, they can perform several tests to evaluate the damage to the knee. These tests include the pivot-shift test, anterior drawer test, and Lachman test are used during the clinical examination of suspected ACL injury. The Lachman test is recognized by most authorities as the most reliable and sensitive test, and usually superior to the anterior drawer test.[23] 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 can be accurate, the diagnosis is usually confirmed by using an arthrometer or MRI,which can provide a better image of the soft tissues like ligaments and cartilage around the knee. which have greatly lessened the need for diagnostic arthroscopy and which have a higher accuracy than clinical examination. It may also permit visualization of other structures which may have been coincidentally involved, such the menisci or collateral ligaments. as a meniscus, or collateral ligament, or posterolateral corner of the knee joint. An xray may be performed to evaluate whether one of the bones in the knee joint was broken during the injury. Laximetry[edit] Laximetry is a reliable technique for diagnosing a torn anterior cruciate ligament.[24] MRI scan[edit]

Anterior cruciate ligament tear seen on MRI. T1 left, right PDW. MRI is perhaps the most used technique for diagnosing the state of the ACL but it is not always the most reliable technique. In some cases, the ACL cannot be seen because of the blood surrounding it. Other forms of evaluation that may be used in case physical examination and MRI are inconclusive are arthrometry and stress imaging. Arthrometry is …Stress imaging is … (Rohman 2016) _____________ TREATMENT •	GOALS o	briefly explain procedures and differences in grafts; change subsections to non-surgical vs surgical, include rehabilitation subsection The term for nonNon-surgical treatment for ACL rupture is also referred to as "conservative management", and it often includes physical therapy and using a knee brace. Instability associated with ACL deficiency increases the risk of other knee injuries such as a torn meniscus, so sports with cutting and twisting motions are problematic and surgery is often recommended in those circumstances. Patients who have suffered an ACL injury should be evaluated for other injuries that often occur in combination with an ACL tear and include cartilage/meniscus injuries, bone bruises, PCL tears, posterolateral injuries and collateral ligament injuries. When a combination injury occurs, surgical treatment is usually advised.[2] Conservative[edit] Nonsurgical Treatment A torn ACL will not heal without surgery (i.e. the torn pieces will not come back together to form a functional ligament).is less likely to restrict the movement of the knee. Not repairing tears to the ACL 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 a 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 it 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 require only 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. o	If the knee remains stable enough to allow for walking and the patient does not plan to participate in high level of activity, doctors will recommend bracing and physical therapy. Immediately after a tear of the ACL, the person should follow the RICE model: rest, icing for 15-20 minutes every 2 hours, compression, and elevation. This process helps decrease the swelling and reduce the pain. A brace may be used to protect the knee form instability, and crutches may be used to prevent weightbearing while the knee is healing. As swelling goes down, physical therapy will begin to restore function to the knee and strengthen the surrounding muscles (hamstring and quads) so that the muscles can compensate for the torn ligament and stabilize the knee. Surgery[edit] Treatment Main article: Anterior cruciate ligament reconstruction If surgery is decided upon, either because obvious instability interferes with activities of daily living, or because the knee is subject to repeated, severe, provocative maneuvers, such as the case of the competitive athlete involved in cutting and rapid deceleration etc., then several issues need to be decided upon. •	Timing. Immediate repair is usually avoided and initial swelling and inflammatory reaction allowed to subside. •	Choice of graft material, autograft or allograft. •	Choice of anterior cruciate ligament augmentation, patellar tendon or hamstring tendon.[27] These issues are fully explored in anterior cruciate ligament reconstruction. o	Surgery if 1) patient is an athlete whose sport involves jumping, cutting or pivoting, 2) more structures than just the ACL are damaged 3) knee is buckling during everyday activities 4) patient is young and active

_________________ REHABILITATION o	GOALS o	NEW SECTION regarding the rehab process o	If an individual with an ACL injury receives surgery, rehab will first focus on range of motion of the joint, then on strengthening the surrounding muscles to protect the new ligament and stabilize the knee. Finally, functional training specific to the activities required for certain sports is begun. o	It may take six or more months before an athlete can return to sport after surgery

___________ PROGNOSIS o	GOALS o	NEW SECTION regarding outcomes of nonsurgical vs surgical management o	Include few sentences/paragraph on impact on professional athletic career (using the McMahan Guardian article) o	From earlier section: Not repairing tears to the ACL 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. (Orthoinfo) o	Factors that increase risk of arthritis include severity of the initial injury, injury to other structures in the knee, and level of activity following treatment. (Mayo)

_____________ PREVENTION Interest in reducing non-contact ACL injury has been intense and the observed, increased liability of the female sex in some sports has added to this. The International Olympic Committee, after a comprehensive review of preventive strategies, has stated that injury prevention programs have a measurable effect on reducing injuries, and that applies particularly to women.[25] Further, paying attention to the balance of strength between hamstrings and quadriceps will help prevent the ACL from being overpowered by over-emphasized quadriceps strength. It is also stressed that landing forces should be reduced together with emphasizing proper landing technique. It has been previously reported that landing on the heel, rather than forefoot with progressive transfer of weight to the heel, is potentially injurious to the ACL because of the hyperextension forces created. The closer the knee is to full extension, the more likely this is to occur.[26] Accordingly, it is generally recommended that injury prevention programs stress these principles. ________________ EPIDEMIOLOGY o	GOALS o	Include updated incidence, expand with more demographics (gender, age, etc). Include special populations here as a subsection o	AAOS lists varying estimates of the risk for women at 2-10 times higher than the risk of injury for men (resource?)

There are around 200,000 ACL tears each year in the United States, with over 100,000 ACL reconstruction surgeries per year. Over 95% of ACL reconstructions are performed in the outpatient setting. The most common procedures performed during ACL reconstruction are partial meniscectomy and chondroplasty.[28]

Young athletes[edit] High school athletes are at increased risk for ACL tears when compared to non-athletes. This risk increases with certain types of sports. Among high school girls, the sport with the highest risk of ACL tear is soccer, followed by basketball and lacrosse. The highest risk sport for boys was basketball, followed by lacrosse and soccer.[29] Children and young athletes may benefit from early surgical reconstruction after ACL injury. Young athletes who have early surgical reconstruction of their torn ACL are more likely to return to their previous level of athletic ability when compared to those who underwent delayed surgery or nonoperative treatment. They are also less likely to experience instability in their knee if they undergo early surgery.[30]

________________ NOTABLE CASES o	GOALS o	NEW SECTION on three famous athletes who had ACL tears o	Derrick Rose, American basketball player (Conway) o	Adrian Peterson, American football (USA today) o	Gale Sayers, American football (link to Wikipedia page – jump to 1968-1969 R knee injury and comeback season)

_____________ REFERENCES o	GOAL: replace reference <2010 o	Topics of older articles include – ♣	Meta-analyses ♣	Injury prevention ♣	Gender-specific ♣	Sport-specific ♣	Surgery ♣	Microbio (estrogen receptors and fibrin microblasts) ♣	Biomechanics of injury ♣	International Olympics Comittee "Anterior Cruciate Ligament (ACL) Injuries-OrthoInfo - AAOS". orthoinfo.aaos.org. March 2014. Archived from the original on 5 July 2017. Retrieved 30 June 2017. ^ Jump up to:a b c d e f g "ACL Injury: Does It Require Surgery?-OrthoInfo - AAOS". orthoinfo.aaos.org. September 2009. Archived from the original on 22 June 2017. Retrieved 30 June 2017. ^ Jump up to:a b Hewett, T. E.; Ford, K. R.; Myer, G. D. (2006). "Anterior cruciate ligament injuries in female athletes: Part 2, a meta-analysis of neuromuscular interventions aimed at injury prevention". Am J Sports Med. 34 (3): 490–8. doi:10.1177/0363546505282619. PMID 16382007. ^ Jump up to:a b Sugimoto D, Myer GD, Foss KD, Hewett TE. 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Jump up^ Rohman, Eric M.; Macalena, Jeffrey A. (2016-03-16). "Anterior cruciate ligament assessment using arthrometry and stress imaging". Current Reviews in Musculoskeletal Medicine. 9 (2): 130–138. doi:10.1007/s12178-016-9331-1. ISSN 1935-973X. PMC 4896874 . PMID 26984335. Jump up^ P Renstrom; A Ljungqvist; E Arendt; B Beynnon; T Fukubayashi; W Garrett; T Georgoulis; T E Hewett; R Johnson; T Krosshaug; B Mandelbaum; L Micheli; G Myklebust; E Roos; H Roos; P Schamasch; S Shultz; S Werner; E Wojtys; L Engebretsen (June 2008). "Non-contact ACL injuries in female athletes: an International Olympic Committee current concepts statement". Br J Sports Med. 42 (6): 394–412. doi:10.1136/bjsm.2008.048934. PMC 3920910 . PMID 18539658. Jump up^ Boden BP, Sheehan FT, Torg JS, Hewett TE (Sep 2010). "Non-contact ACL Injuries: Mechanisms and Risk Factors". J Am Acad Orthop Surg. 18 (9): 520–27. PMC 3625971 . PMID 20810933. Jump up^ Mohtadi, NG; Chan, DS; Dainty, KN; Whelan, DB (Sep 7, 2011). 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Q angle image wikicommons