What are the recommended tests for diagnosing Anterior Cruciate Ligament (ACL) and Posterior Cruciate Ligament (PCL) injuries?

Recommended Tests for ACL and PCL Ligament Injuries

For diagnosing ACL and PCL injuries, MRI is the gold standard imaging test, while the Lachman test is the most reliable physical examination test for ACL injuries and the posterior drawer test is the primary test for PCL injuries.

Physical Examination Tests for ACL Injuries

Primary Tests

1. Lachman Test

   • Highest diagnostic accuracy with sensitivity of 79% and specificity of 91% 1
   • Positive predictive value of 95% and negative predictive value of 82% when performed by an experienced clinician 2
   • Technique: Patient supine with knee flexed 20-30°, stabilize femur while pulling tibia anteriorly
   • Positive test: Increased anterior translation with soft/mushy end-feel

2. Lever Sign Test

   • High sensitivity (82%) and specificity (88%) 1
   • Lowest negative likelihood ratio (0.21), making it valuable for ruling out ACL injuries 1
   • Technique: Fist placed under proximal calf, downward force applied to distal femur
   • Positive test: Heel remains on examination table (doesn't rise)

3. Pivot Shift Test

   • Highest specificity (96%) and positive likelihood ratio (11.60) 1
   • Lower sensitivity (55%) but excellent for confirming ACL injury 1
   • Technique: Apply valgus and internal rotation force while extending the knee
   • Positive test: Anterior subluxation of lateral tibial plateau that reduces with flexion

4. Anterior Drawer Test

   • Sensitivity of 78% and specificity of 91% 1
   • Positive predictive value of 87% and negative predictive value of 90% 2
   • Technique: Patient supine with knee flexed 90°, pull tibia anteriorly
   • Positive test: Excessive anterior translation of tibia

History Finding with High Diagnostic Value

• Report of a "popping" sensation during trauma has 100% specificity and positive predictive value for ACL injuries in children and adolescents 2

Physical Examination Tests for PCL Injuries

1. Posterior Drawer Test

   • Primary test for PCL injuries
   • Technique: Patient supine with knee flexed 90°, push tibia posteriorly
   • Positive test: Excessive posterior translation of tibia

2. Posterior Sag Sign (Gravity Drawer Test)

   • Technique: Patient supine with hips and knees flexed to 90°
   • Positive test: Posterior displacement of tibia due to gravity

Imaging Studies

Initial Imaging

• Plain Radiographs (X-rays)
  • Recommended as initial imaging study for acute knee trauma 3, 4
  • Cannot directly visualize ligament tears but may show:
    • Segond fracture (lateral tibial plateau avulsion) - highly associated with ACL tears
    • Avulsion fractures at ligament attachment sites
    • Joint effusion (>10mm on lateral view has 91% positive predictive value for internal derangement)
    • Lipohemarthrosis (indicating intra-articular fracture)

Definitive Imaging

• MRI

  • Gold standard for diagnosing ACL and PCL injuries 3, 4
  • For ACL tears: Sensitivity of 79-100% and specificity of 95-100% 3
  • For PCL tears: Accuracy of 100% for tibiofibular ligament tears 3
  • Advantages:
    • Directly visualizes ligament tears
    • Detects associated injuries (meniscal tears, bone contusions)
    • Identifies anterolateral ligament injuries often associated with ACL tears
    • Can determine location and classification of tears to guide surgical planning 3
    • Can change management from surgical to conservative in up to 48% of patients with locked knee 3

• MRI-based Indirect Signs

  • PCL Index: Ratio of the shortest distance between femoral and tibial PCL attachments to the distance from that line to the PCL arc tip 5
    • Normal: 5.01 ± 0.76
    • Complete ACL tear: 2.88 ± 0.74
    • Partial ACL tear: 3.09 ± 0.23
  • PCL Line: Line drawn parallel to posterior margin of distal PCL and extended proximally 6
    • Positive sign (doesn't intersect femoral medullary cavity) predicts ACL injury

Supplementary Imaging Tests

• Ultrasound

  • For ACL tears: Accuracy of 91% compared to arthroscopy 3
  • Can dynamically assess ligament laxity during stress maneuvers 3
  • Limited by technical factors and operator dependence

• CT Arthrography

  • For ACL tears: Accuracy of 71% 3
  • Less commonly used due to radiation exposure and invasiveness

Functional Performance Tests for Return to Play

For monitoring rehabilitation progress and determining readiness to return to sports:

• Single Leg Hop Test and Crossover Hop Test
  • Only tests with sufficient evidence for reliability, validity, and responsiveness 3
  • Limb Symmetry Index (LSI) >90% recommended as cut-off for return to play
  • For pivoting/contact sports, LSI of 100% is recommended 3

Clinical Algorithm for Diagnosis

1. Obtain history (mechanism of injury, presence of "pop," instability)
2. Perform physical examination tests (Lachman, lever sign, pivot shift, and anterior/posterior drawer tests)
3. Order plain radiographs to rule out fractures and identify indirect signs
4. If physical examination suggests ligament injury or results are equivocal, proceed to MRI
5. Use functional performance tests to monitor rehabilitation progress and determine return to play readiness

Common Pitfalls to Avoid

• Relying solely on the anterior drawer test, which has lower sensitivity than the Lachman test
• Failing to recognize that a negative physical examination does not rule out ACL injury, especially in acute settings with pain and swelling
• Overlooking associated injuries (meniscal tears, bone contusions) that may require additional treatment
• Neglecting to assess for rotational instability with the pivot shift test, which may indicate more complex injury patterns