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Anterior Cruciate Ligament (ACL) Injury

Topic updated on 11/07/17 9:08pm

Snapshot
  • A 27-year-old woman presents to the emergency department for severe pain in the right knee. A few hours prior to presentation, an opposing soccer player strikes her leg from her right side while her foot was planted to the ground. Afterwards, she felt a "pop" sound that was followed by severe knee pain and swelling. After the swelling improved, she feels that her right knee is unstable. On physical exam, the patient has a positive Lachman test. The patient is asked to rest, place ice and compress the knee, and elevate the affected leg. Given her sport demands, a conversation is made on the necessity of surgical reconstruction of the anterior cruciate ligament.
Introduction
  • Clinical definition
    • injury in the form of tear or rupture affecting the anterior cruciate ligament (ACL) in the knee
  • Epidemiology
    • incidence
      • non-contact ACL injuries are more common
    • demographics
      • more common in female athletes
    • risk factors
      • sports (e.g., football, soccer, skiers, and basketball)
      • motor vehicle accidents
  • Pathoanatomy
    • normal anatomy
      • the ACL course
        • originates in the posteromedial aspect of the lateral femoral condyle
        • reaches the anteromedial aspect of the tibia
      • the ACL plays an important role in knee stability 
        • it controls anterior translation of the tibia
          • it also restrains against tibial rotation, varus, and valgus stress
    • pathology
      • contact mechanisms
        • injury that causes hyperextension or valgus deformation of the knee
          • e.g., football injury
        • high-speed motor vehicle accident
      • non-contact mechanisms
        • changing direction, pivoting, or landing that leads to rotation or valgus stress of the knee after sudden deceleration
  • Associated conditions
    • unhappy triad which consists of injury to the 
      • ACL
      • medial collateral ligament
      • medial meniscus
  • Prognosis
    • the majority of athletes are able to return to their sports activities with ACL reconstruction
Presentation
  • Symptoms 
    • feeling a "pop" in the knee
      • thereafter, there is acute swelling and pain
    • unstable or "giving out" knee
  • Physical exam
    • anterior drawer test  
      • the proximal tibia is anteriorly pulled while the patient is supine and the knee is flexed at 90 degrees
        • if there is anterior translation then the test is positive
    • Lachman test 
      • the proximal tibia is anteriorly pulled with one hand, while the other hand stabilizes the distal femur while the knee is flexed at 30 degrees
    • hemarthrosis
Imaging
  • Magnetic resonance imaging (MRI)
    • indication
      • an imaging modality that can confirm the diagnosis
      • if reconstruction is a possibility or to identify concomitant knee pathology
Studies
  • Making the diagnosis
    • can be made based on typical clinical presentation alone
    • can be confirmed by MRI or knee arthroscopy
Differential
  • Meniscal tear
    • differentiating factor
      • patients can have a positive
        • Thessaly test 
        • McMurray test 
        • Apley test 
  • Posterior collateral ligament (PCL) injury 
    • differentiating factor
      • patients can have a positive posterior drawer test
      • trauma is typically due to
        • a motor vehicle accident leading to "dashboard injury"
        • falling on a flexed knee while the foot is plantarflexed
        • direct trauma to the proximal tibia
Treatment
  • Conservative
    • rest, ice, compression, and elevation (RICE) therapy
      • indication
        • management to reduce pain, edema, and hemarthrosis in the acute stage of the injury
          • nonsteroidal anti-inflammatory drugs are typically added
  • Operative
    • surgical reconstruction
      • indications
        • performed in 
          • young and active patients with high demand sports or jobs
          • significant knee instability
            • such as injuries affecting multiple knee structures (e.g., unhappy triad)
Complications
  • Osteoarthritis
  • Arthrosis
  • Sports disability



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Qbank (2 Questions)

TAG
(M1.MK.40) A 23-year-old female college basketball player presents in Sports Clinic after she felt a "pop" in her knee after coming down with a rebound. To examine the patient, you have her lie down on the table with her knees flexed 90 degrees. With your hand around her knee you are able to draw the tibia toward you from underneath the femur. The torn structure implicated by this physical exam maneuver has which of the following attachments? Topic Review Topic

1. The posterior intercondylar area of tibia and the posteromedial aspect of the lateral femur
2. The anterior intercondylar area of tibia and the posteromedial aspect of the lateral femur
3. The patella and tibial tuberosity
4. The lateral epicondyle of the femur and the head of fibula
5. The medial condyle of the femur and the medial condyle of the tibia

PREFERRED RESPONSE ▶
TAG
(M1.MK.4719) A 19-year-old female college soccer player presents to a sports medicine clinic with right knee pain. One day prior she twisted her right knee and felt a “pop” while chasing after a ball. She has since felt severe throbbing knee pain and noticed a rapid increase in swelling around her knee. She is able to bear weight but feels “unstable” on her right leg. On exam, anterior drawer and Lachman’s tests are positive. The physician informs her that she has likely injured an important structure in her knee. What is the function of the structure that she has most likely injured? Topic Review Topic

1. Prevent excess posterior translation of the tibia relative to the femur
2. Prevent excess anterior translation of the tibia relative to the femur
3. Resist excess varus force on the knee
4. Resist excess valgus force on the knee
5. Provide a cushion between the lateral tibial and femoral condyles

PREFERRED RESPONSE ▶

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