How do I determine if I have a positive Anterior Cruciate Ligament (ACL) and Posterior Cruciate Ligament (PCL) test?

How to Determine if ACL and PCL Tests are Positive

A positive Anterior Cruciate Ligament (ACL) test is indicated by abnormal anterior tibial translation, while a positive Posterior Cruciate Ligament (PCL) test is indicated by abnormal posterior tibial translation during specific clinical maneuvers.

ACL Testing Techniques

Lachman Test (Most Accurate)

• Position: Patient supine with knee flexed at 20-30 degrees
• Technique: Stabilize femur with one hand while pulling tibia forward with the other hand
• Positive sign: Increased anterior translation compared to uninjured knee with a soft or absent endpoint
• Interpretation: Best test for ruling out ACL tears with sensitivity of 86% and specificity of 91% 1

Anterior Drawer Test

• Position: Patient supine with knee flexed at 90 degrees, foot stabilized
• Technique: Pull tibia forward while stabilizing the foot
• Positive sign: Excessive anterior movement of tibia relative to femur
• Interpretation: Less reliable than Lachman test with sensitivity of only 20% and specificity of 88% 1

Pivot Shift Test

• Position: Patient supine, knee extended
• Technique: Apply valgus stress and internal rotation while slowly flexing the knee
• Positive sign: Sudden reduction of anteriorly subluxated lateral tibial plateau at 20-40 degrees of flexion
• Interpretation: Highest positive predictive value for ACL tears but lower sensitivity (18-48%) 1

PCL Testing Techniques

Posterior Drawer Test

• Position: Patient supine with knee flexed at 90 degrees
• Technique: Push tibia posteriorly while stabilizing the foot
• Positive sign: Excessive posterior movement of tibia relative to femur
• Interpretation: Primary test for PCL injury

Posterior Sag Test (Gravity Drawer)

• Position: Patient supine with hips and knees flexed at 90 degrees
• Technique: Observe profile of knee from lateral side
• Positive sign: Posterior displacement of tibia due to gravity
• Interpretation: Useful for moderate to severe PCL injuries

Grading Systems

ACL Injury Grading

• Grade 1: 1-5 mm of anterior translation (mild tear)
• Grade 2: 6-10 mm of anterior translation (partial tear)
• Grade 3: >10 mm of anterior translation (complete tear) 2

PCL Injury Grading

• Grade 1: 1-5 mm of posterior translation (partial tear)
• Grade 2: 6-10 mm of posterior translation (partial tear)
• Grade 3: >10 mm of posterior translation (complete tear) 3

Common Pitfalls and Considerations

• Muscle guarding can produce false negative results - ensure patient is relaxed 1
• Acute injuries with significant pain and swelling may limit test accuracy 2
• Compare with contralateral uninjured knee for reference 3
• Combined injuries (both ACL and PCL) may mask individual ligament instability patterns 2
• Chronic injuries may present with different stability patterns due to secondary restraint adaptation 3

Objective Measurement

• KT-1000 arthrometer can provide quantitative measurement of anterior-posterior tibial translation 3
• Side-to-side difference of >3mm is considered abnormal for both ACL and PCL 2

Imaging Correlation

• MRI findings such as the PCL line sign (a line drawn along the posterior margin of the distal PCL that doesn't intersect the femoral medullary cavity) can help confirm ACL injury 4
• Clinical tests should be correlated with imaging findings for definitive diagnosis 2