History

Most ACL injuries may be diagnosed through a careful history emphasizing mechanism of injury coupled with a good physical examination. Remember that a previous ligamentous injury may be the cause of instability. When discussing the history, be sure to document mechanism of injury for this episode and any previous episodes.

Noncontact injury

An audible pop often accompanies this injury, which often occurs while changing direction, cutting, or landing from a jump (usually a hyperextension/pivot combination). Within a few hours, a large hemarthrosis develops.

Patients usually are unable to return to play, secondary to pain, swelling, and instability or giving way of the knee.

Contact and high-energy traumatic injuries

These injuries often are associated with other ligamentous and meniscal injuries. The classic "terrible triad" (ACL, MCL, and medial meniscus tears) involves a valgus stress to the knee with resultant acute injury to the ACL and MCL; however, the medial meniscus tear is now thought to occur later, as a result of chronic ACL deficiency.

Physical Examination

An organized, systematic physical examination is imperative when examining any joint. The Dutch Orthopaedic Association clinical guidelines for the treatment of ACL injury recommend the Lachman test, pivot shift test, and anterior drawer test for diagnosis.^[18] Note that a study found the sensitivity of these tests is lower in obese patients (body mass index of ≥30) than in those who are not obese.^[19]

Immediately after the acute injury, the physical examination may be very limited due to apprehension and guarding by the patient.

The examiner should begin with inspection, looking for any gross effusion or bony abnormality. An immediate effusion indicates significant intra-articular trauma. According to Noyes et al, in the absence of bony trauma, an immediate effusion is believed to have a 72% correlation with an ACL injury of some degree.

Assess the patient's range of motion (ROM), especially looking for lack of complete extension, secondary to a possible bucket-handle meniscus tear or associated loose fragment.

Palpation of bony structures may suggest an associated tibial plateau fracture.

Palpation of the joint lines to evaluate a possible associated meniscus tear. Palpation over the collateral ligaments to suggest any possible injury (sprain) of these structures. Up to 50% of ACL ruptures have associated meniscal injuries; acute injuries are likely to have associated injuries of the MCL and meniscus.

Ligamentous laxity may be difficult to detect in the acute situation. The Lachman test, as shown in the image below, is the most sensitive test for acute ACL rupture. Since the Lachman test must be performed when the patient is relaxed, it is often better to conduct this test prior to manipulating the painful knee.

Proper technique for the Lachman test.

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The knee is placed in a position of 20-30° of flexion. The femur is stabilized with a nondominant hand, and an anteriorly directed force is applied to the proximal calf.

The amount of displacement (in mm) and the quality of endpoint are assessed (eg, firm, marginal, soft). Asymmetry in side-to-side laxity or a soft endpoint is indicative of an ACL tear. Although difficult to measure, a side-to-side difference of greater than 3 mm is considered abnormal.

Other ligamentous tests are less reliable especially for primary care providers who may not have as much experience in using these maneuvers. The pivot shift test, as shown in the image below, is performed by extending an ACL-deficient knee, which results in a small amount of anterior translation of the tibia in relation to the femur. During flexion, the translation reduces, resulting in the "shifting or pivoting" of the tibia into its proper alignment on the femur.

The pivot shift test.

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The pivot shift test is performed with the leg extended, the foot in internal rotation, and a valgus stress is applied to the tibia. Flexion causes a reduction of the anteriorly subluxed tibia at approximately 20-30°.

The anterior drawer test, as shown in the image below, may be influenced by hamstring spasm in the acutely injured knee; thus, this test is considered the least reliable.

Anterior drawer test: Note the anterior excursion of the tibia in relationship to the femur.

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This test is performed with the patient supine and the knee flexed to 90°. The examiner can sit on the patient's foot and grasp around the patient's calf with both hands. An anterior force is applied, and tibial excursion is compared to the unaffected knee.

Differential Diagnoses

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Media Gallery

Proper technique for the Lachman test.
Anterior drawer test: Note the anterior excursion of the tibia in relationship to the femur.
The pivot shift test.
MRI displaying a ruptured anterior cruciate ligament.

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Author

Matthew Gammons, MD Assistant Clinical Professor, Department of Family and Community Medicine, Medical College of Wisconsin; Medical Director, Castleton State College; Consulting Staff, Vermont Orthopaedic Clinic and Killington Medical Clinic

Matthew Gammons, MD is a member of the following medical societies: American Academy of Family Physicians, American College of Sports Medicine, American Medical Society for Sports Medicine, American Society of Mechanical Engineers

Disclosure: Received income in an amount equal to or greater than $250 from: Up to Date.

Coauthor(s)

Evan Schwartz, MD Director of Orthopedic Surgery, St John's Queens Hospital, New York Medical College; Assistant Professor, Department of Surgery, Albert Einstein School of Medicine

Evan Schwartz, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Orthopaedic Society for Sports Medicine

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Chief Editor

Sherwin SW Ho, MD Associate Professor, Department of Surgery, Section of Orthopedic Surgery and Rehabilitation Medicine, University of Chicago Division of the Biological Sciences, The Pritzker School of Medicine

Sherwin SW Ho, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, Arthroscopy Association of North America, Herodicus Society, American Orthopaedic Society for Sports Medicine

Disclosure: Received consulting fee from Biomet, Inc. for speaking and teaching; Received grant/research funds from Smith and Nephew for fellowship funding; Received grant/research funds from DJ Ortho for course funding; Received grant/research funds from Athletico Physical Therapy for course, research funding; Received royalty from Biomet, Inc. for consulting.

Additional Contributors

David T Bernhardt, MD Director of Adolescent and Sports Medicine Fellowship, Associate Professor, Department of Pediatrics/Ortho and Rehab, Division of Sports Medicine, University of Wisconsin School of Medicine and Public Health

David T Bernhardt, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Sports Medicine, American Medical Society for Sports Medicine

Disclosure: Nothing to disclose.

Acknowledgements

The authors and editors of Medscape Drugs & Diseases gratefully acknowledge the contributions of previous author John D Hubbell, MD, to the development and writing of this article.