eMedicine Specialties > Physical Medicine and Rehabilitation > Lower Limb Musculoskeletal Conditions

Anterior Cruciate Ligament Injury

Author: Tarek Souryal, MD, Head Team Physician, Dallas Mavericks; Former Chief, Department of Surgery, Division of Orthopedic Surgery, Las Colinas Medical Center; Clinical Professor, Departments of Orthopedic Surgery and Physical Medicine and Rehabilitation, University of Texas Southwestern Medical Center
Coauthor(s): Kenneth Adams, MD, Assistant Professor, Department of Physical Medicine and Rehabilitation, University of Texas Southwestern
Contributor Information and Disclosures

Updated: Jan 2, 2009

Introduction

Background

The anterior cruciate ligament (ACL) originates from the tibial plateau just medial and anterior to the tibial eminence. The ACL tracts from the tibia superiorly, laterally, and posteriorly, to its insertion on the posterior aspect of the medial wall of the lateral femoral condyle. The ACL is composed of 2 bundles, the anteromedial bundle and the posterolateral bundle. The ACL provides 85% of the total restraining force to anterior translation of the tibia. An ACL tear is a common injury that occurs in all types of sports. This injury usually occurs during a sudden cut or deceleration, as it typically is a noncontact injury. The patient states, "I planted, twisted, and then heard a pop." Before the advent of arthroscopic knee surgery in the early 1970s, ACL tear was often a career-ending injury.

Related eMedicine topics:
Anterior Cruciate Ligament Injury [Sports Medicine]
Anterior Cruciate Ligament Pathology
Knee, Anterior Cruciate Ligament Injuries (MRI)

Pathophysiology

Like all ligaments, the anterior cruciate ligament (ACL) is composed of type I collagen. The ultrastructure of a ligament is close to that of tendons, but the fibers in a ligament are more variable and have a higher elastin content. Ligaments receive their blood supply from their insertion sites. The vascularity within a ligament is uniform, and each ligament contains mechanoreceptors and free nerve endings that are hypothesized to aid in stabilizing the joint. Avulsion of ligaments generally occurs between the unmineralized and mineralized fibrocartilage layers. The more common ACL tear, however, is a midsubstance tear. This type of tear occurs primarily as the ligament is transected by the pivoting lateral femoral condyle.

Frequency

United States

Epidemiologic studies estimate that approximately 1 in 3000 individuals sustains an ACL injury each year in the United States. This figure corresponds to an overall injury rate approaching 200,000 injuries annually. This estimate is low for women, because ACL injury rates are estimated to be 2-8 times higher in women than in men participating in the same sports. The average cost for surgical repair of an ACL tear is approximately $11,500. If all ACL injuries were repaired, the associated expenditure for 100,000 procedures would eclipse $2 billion annually.

International

International statistics are not available.

Mortality/Morbidity

Not a single report of mortality was found in 6 different studies examining the morbidity and mortality of anterior cruciate ligament repair. The total number of patients in these combined studies was 363. Morbidity was divided into 5 classes. The first class included patients who were symptomatic with activities of daily living (ADL). The second class included patients who were able to perform all ADL. Patients in the third class were able to perform mildly stressful sports (eg, jogging, swimming, biking, cross-country skiing). The fourth class included patients who were able to perform moderately stressful sports, including baseball, alpine skiing, racquet sports, dance, and lacrosse. The last class included patients who returned to perfect health and were capable of performing very stressful sports, such as soccer, basketball, football/rugby, volleyball, gymnastics, and hockey. Postsurgery status of patients was as follows:

  • Remained class 1 - 3.3%
  • Remained class 2 - 1.4%
  • Attained class 3 - 11.8%
  • Attained class 4 - 17%
  • Returned to class 5 - 66.5%

Race

No known correlation exists between race and occurrence of ACL injuries.

Sex

According to numerous studies, female athletes sustain a greater number of anterior cruciate ligament (ACL) injuries than do male athletes. These results are well supported in 2 different papers. The first paper, by Arendt and Dick, showed that female athletes sustained significantly higher incidences of ACL injuries than their male counterparts did when competing in collegiate soccer and basketball.1 The authors' data demonstrated that women have a 2.4 and a 4.1 times greater chance of incurring ACL injury when compared with males in soccer and basketball, respectively. A second paper, by Hutchinson and Ireland, reported that female athletes competing in the 1988 Olympic basketball trials sustained 81% of ACL injuries during the trials.2

Age

Anterior cruciate ligament injuries occur most commonly in individuals aged 14-29 years. These years correspond to a high degree of athletic activity.

Clinical

History

Obtain as much information as possible directly from the patient. The important facts can be clarified by asking questions about the following:

  • Mechanism of injury
  • Pain
  • Feeling/hearing a pop
  • Feeling knee give out
  • Ability to continue playing sport
  • Swelling
  • Loss of knee motion
  • History of previous knee injury

Physical

Up to 50% of patients with acute knee injuries who report feeling or hearing a snapping or popping sound are found to have an anterior cruciate ligament (ACL) injury. A hemarthrosis almost always is present because of the vascular supply to the ACL. When a complete ligamentous tear occurs, pain may begin immediately, followed by resolution. Immediately following injury, minimal effusion or spasm is present, so ACL injury usually can be identified easily. Several hours after injury, effusion and spasm make diagnosis of an ACL tear more difficult.

To determine the patient's normal amount of laxity, examine the uninjured knee first.

  • Perform the Lachman test.
    • This test is performed with the knee in 30° of flexion, with the patient lying supine.
    • Using one hand on the anterior aspect of the distal femur and a second hand behind the proximal tibia, attempt to displace the tibia forward from the femur.
    • A positive Lachman occurs when no endpoint is encountered. The degree of excursion may also indicate an ACL tear.
  • Another test to detect ACL tears is the anterior drawer.
    • Perform this test with the knee at 90° of flexion, with the patient lying supine.
    • Place both hands behind the proximal tibia and attempt to displace the tibia forward from the femur.
    • If there is more than 6 mm of tibial displacement, an ACL tear is suggested.
    • The anterior drawer test is not very sensitive and has been found to be positive in only 77% of patients with complete ACL rupture.
  • Many other diagnostic tests exist (eg, Slocum test, pivot-shift test), but Lachman and anterior drawer tests are used most commonly.

Causes

Anterior cruciate ligament (ACL) injuries haveno single cause. ACL injuries can be related to extrinsic factors and intrinsic factors. Numerous studies document the fact that poor levels of conditioning correlate directly with increased levels of injury. Research also has demonstrated that improved conditioning results in reduced numbers of injuries.

  • Body and movement factors3
    • The first 2 factors, body movement and positioning, play a big role in ACL injuries.
    • Noyes and colleagues demonstrated that most ACL injuries (ie, 78%) occur without contact.4 Most of these injuries occur upon landing after a jump. The Noyes study involved only female basketball players, but the capacity of the knee to plant and turn or to absorb the shock of a jump is relevant to men and women in all sports.
  • Muscle strength
    • Muscle strength is the last of the extrinsic factors that affect the ACL. The hamstring is an ACL agonist working in concert with the ACL to prevent anterior tibial translation. Conversely, the quadriceps acts as an antagonist to the ACL, generating force that promotes anterior tibial translation. Ideally, a balance exists between these opposing forces to protect the knee; however, the quadriceps averages 50-100% greater muscle strength than does the hamstring.
    • Strength coaches often emphasize quadriceps strengthening and ignore hamstring strengthening, further exacerbating the inequality.
  • Several intrinsic factors can contribute to ACL injuries.
    • Joint laxity is one such factor. Significant controversy surrounds this topic, because published studies are contradictory about whether or not increased laxity contributes to ACL injuries. Acasuso-Diaz and colleagues concurred with Kibler and coauthors that a strong relationship exists5,6 ; however, reports by Godshall and by Jackson and colleagues maintained that ACL laxity does not predispose to ACL injury.7,8
    • The Q angle is the acute angle between the line connecting the anterior superior iliac spine, the midpoint of the patella, and the line connecting the tibial tubercle with the same reference point on the patella. Theoretically, larger Q angles signal increases in the lateral pull of the quadriceps muscle on the patella and put medial stress on the knee. Shambaugh and colleagues studied 45 athletes and found that the average Q angles of athletes sustaining knee injuries were significantly larger than were the average Q angles for players who were not injured.9 Because lower extremity alignment cannot be altered, no recommendation can help to minimize the athlete's risk of ACL rupture; however, the dynamic position of the tibia can be improved with internal rotation exercises for the tibia (eg, medial hamstrings).
    • A narrow intercondylar notch may be a predictive factor for ACL rupture. According to various reports, athletes who sustain ACL injuries often have narrow notch widths compared with fellow athletes with uninjured knees. The notch width index (NWI), defined by Souryal and colleagues, is "the ratio of the width of the intercondylar notch to the width of the distal femur at the level of the popliteal groove on a tunnel view radiograph." Another study by Souryal and coauthors established that NWI measurements fall along a Gaussian curve, indicating that measurement is reproducible.10,11 Results showed that athletes sustaining ACL injuries had the lowest NWIs. The critical NWIs were calculated as being 1 standard deviation below the gender-dependent mean. Athletes falling into this critical range, according to reported data, are 26 times more susceptible to ACL injuries than are other athletes.

More on Anterior Cruciate Ligament Injury

Overview: Anterior Cruciate Ligament Injury
Differential Diagnoses & Workup: Anterior Cruciate Ligament Injury
Treatment & Medication: Anterior Cruciate Ligament Injury
Follow-up: Anterior Cruciate Ligament Injury
References
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Further Reading

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Keywords

anterior cruciate ligament injury, ligament, knee surgery, ligaments, knee injury, knee injuries, torn ACL, ACL injury, ACL reconstruction, torn ligament, knee ligaments, anterior cruciate ligament, anterior cruciate, ligament tear, ACL tear, anteromedial bundle, posterolateral bundle, hemarthrosis, Segond fracture

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Contributor Information and Disclosures

Author

Tarek Souryal, MD, Head Team Physician, Dallas Mavericks; Former Chief, Department of Surgery, Division of Orthopedic Surgery, Las Colinas Medical Center; Clinical Professor, Departments of Orthopedic Surgery and Physical Medicine and Rehabilitation, University of Texas Southwestern Medical Center
Tarek Souryal, MD is a member of the following medical societies: American Orthopaedic Society for Sports Medicine
Disclosure: Nothing to disclose.

Coauthor(s)

Kenneth Adams, MD, Assistant Professor, Department of Physical Medicine and Rehabilitation, University of Texas Southwestern
Kenneth Adams, MD is a member of the following medical societies: American Academy of Physical Medicine and Rehabilitation, American Medical Association, and Texas Medical Association
Disclosure: Nothing to disclose.

Medical Editor

Robert E Windsor, MD, FAAPMR, FAAEM, FAAPM, President and Director, Georgia Pain Physicians, PC; Clinical Associate Professor, Department of Physical Medicine and Rehabilitation, Emory University School of Medicine
Robert E Windsor, MD, FAAPMR, FAAEM, FAAPM is a member of the following medical societies: American Academy of Pain Medicine, American Academy of Physical Medicine and Rehabilitation, American College of Sports Medicine, American Medical Association, International Association for the Study of Pain, Physiatric Association of Spine, Sports and Occupational Rehabilitation, and Texas Medical Association
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

Michael T Andary, MD, MS, Residency Program Director, Professor, Department of Physical Medicine and Rehabilitation, Michigan State University College of Osteopathic Medicine
Michael T Andary, MD, MS is a member of the following medical societies: American Academy of Physical Medicine and Rehabilitation, American Association of Neuromuscular and Electrodiagnostic Medicine, American Medical Association, and Association of Academic Physiatrists
Disclosure: allergan Honoraria Speaking and teaching

CME Editor

Kelly L Allen, MD, Regional Medical Director, IMX-Medical Management Services
Disclosure: Nothing to disclose.

Chief Editor

Consuelo T Lorenzo, MD, Consulting Staff, Department of Physical Medicine and Rehabilitation, Alegent Health Care, Immanuel Rehabilitation Center
Consuelo T Lorenzo, MD is a member of the following medical societies: American Academy of Physical Medicine and Rehabilitation
Disclosure: Nothing to disclose.

 
 
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