What is the correct technique for performing the anterior and posterior drawer test of the knee, how are the findings interpreted for ACL or PCL injuries, and what management is recommended if the test is positive?

Drawer Test of the Knee

The Lachman test is superior to the anterior drawer test for detecting ACL injuries, with 81.8% sensitivity versus 40.9% for the anterior drawer, while the posterior drawer test at 90° flexion is the most sensitive and specific test for PCL injuries. 1, 2

Anterior Drawer Test Technique

Patient Positioning

• Patient supine with knee flexed to 90 degrees 3, 1
• Hip flexed to approximately 45 degrees 3
• Foot stabilized by examiner sitting on it 3

Execution

• Examiner grasps proximal tibia with both hands, thumbs on tibial plateau 3
• Apply anterior force to translate tibia forward on femur 3
• Compare side-to-side laxity with contralateral knee 3

Interpretation for ACL Injury

• Positive test: Excessive anterior translation of tibia relative to femur 1
• Sensitivity: Only 40.9% overall, dropping to 22.2% in acute injuries (<2 weeks) 1
• Specificity: 95.2% 1
• Critical limitation: The anterior drawer is a poor diagnostic indicator, especially acutely, because excessive swelling and pain limit examination accuracy within 48 hours of injury 4, 1

Lachman Test Technique (Preferred for ACL)

Patient Positioning

• Patient supine with knee flexed to 15-30 degrees 3, 5

Execution

• One hand stabilizes distal femur 3
• Other hand grasps proximal tibia 3
• Apply anterior force to tibia while stabilizing femur 3

Interpretation for ACL Injury

• Positive test: Excessive anterior translation with soft or absent endpoint 3, 1
• Sensitivity: 81.8% overall, 77.7% in acute injuries 1, 2
• Specificity: 96.8% 1
• Advantage: Produces maximal tension in the ACL, making it more reliable than anterior drawer 5
• The Lachman test maintains high accuracy even under anesthesia and is the preferred clinical test for ACL evaluation 1, 2

Posterior Drawer Test Technique

Patient Positioning

• Patient supine with knee flexed to 90 degrees 6
• Hip flexed 6

Execution

• Examiner grasps proximal tibia with both hands 6
• Apply posterior force to translate tibia backward on femur 6
• Observe for posterior tibial displacement 6

Interpretation for PCL Injury

• Positive test: Excessive posterior translation of tibia relative to femur 6
• Sensitivity and specificity: Very high for PCL tears 6
• Enhanced by posterior sag sign: With knee flexed 90°, observe lateral profile for apparent disappearance of tibial tubercle due to gravity-assisted posterior displacement 6
• This combination of posterior drawer and sag sign is highly sensitive and specific for PCL injury 6

Diagnostic Accuracy Summary

ACL Injury Detection

• Lachman test: 81.8% sensitive, 96.8% specific - PREFERRED TEST 1, 2
• Anterior drawer: 40.9% sensitive, 95.2% specific - unreliable, especially acutely 1
• Pivot shift: 81.8% sensitive, 98.4% specific 1
• When Lachman and pivot shift are both positive, ACL injury diagnosis is highly accurate; when both negative, ACL injury is essentially ruled out 1

PCL Injury Detection

• Posterior drawer test: Very sensitive and specific 6
• Posterior sag sign: Enhances diagnostic accuracy when combined with posterior drawer 6

Management When Tests Are Positive

Initial Imaging

• Radiographs first if patient meets Ottawa Knee Rules criteria: inability to bear weight immediately, inability to flex knee to 90°, or focal bony tenderness 4
• Obtain minimum two views (AP and lateral) with knee at 25-30° flexion 4

Advanced Imaging for Ligament Injury

• MRI is the next study when radiographs are negative but ligament injury suspected 4
• MRI shows 97% diagnostic accuracy for ACL injuries and identifies exact injury location in 93% of cases 4
• MRI has superior contrast resolution for evaluating meniscal and ligamentous injuries compared to CT 4

Treatment Decision Framework

For ACL Injuries:

• Autograft preferred over allograft, particularly in young and active patients, to improve outcomes and decrease graft failure rates 4
• Bone-tendon-bone (BTB) autograft reduces graft failure and infection risk but increases anterior/kneeling pain 4
• Hamstring autograft reduces anterior and kneeling pain but may have higher graft failure rates 4
• Nonsurgical management risks persistent instability and additional meniscal/cartilage injury 4

For PCL Injuries:

• Conservative treatment recommended for isolated, complete midsubstance tears 6
• Intensive quadriceps exercises emphasized with <2 weeks immobilization 6
• Surgical treatment indicated if PCL avulsion fragment is displaced 6
• Outcome depends more on quadriceps strength than residual posterior laxity 6

Critical Pitfalls

• Reexamine at 3-5 days post-injury to distinguish partial from complete tears, as acute swelling limits initial examination accuracy 4
• Do not rely on anterior drawer alone in acute settings - sensitivity drops to 22.2% within 2 weeks of injury 1
• Grade III sprains show swelling, hematoma, pain on palpation, and positive drawer test - 96% have lateral ligament rupture when all four present 4
• Avoid manipulation before radiographs unless neurovascular deficit or critical skin injury present 4