What tests can diagnose medial collateral ligament (MCL), anterior cruciate ligament (ACL), meniscal, and posterior cruciate ligament (PCL) injuries in an active individual with a history of sports participation and possible traumatic knee injury?

Diagnostic Tests for Knee Ligament and Meniscal Injuries

Initial Evaluation Algorithm

Start with plain radiographs (anteroposterior and lateral views) to exclude fractures and bony avulsions, then proceed to MRI as the definitive diagnostic test for all soft tissue injuries including ACL, PCL, MCL, and meniscal tears. 1, 2, 3, 4

Step 1: Plain Radiographs (Initial Screening)

• Obtain two-view radiographs (AP and lateral) first in all patients meeting Ottawa knee rule criteria (focal tenderness, effusion, inability to bear weight) 1, 3
• The lateral view should be obtained with the knee at 25-30 degrees of flexion to evaluate for joint effusion 1
• In patients under 40 years with knee effusion >10 mm on lateral radiograph, proceed directly to MRI as this decreases delayed diagnosis and improves outcomes 3, 4
• Radiographs detect bony avulsion fractures that may accompany ligament tears and guide subsequent imaging decisions 1, 3

Step 2: Clinical Examination Tests (Performed 4-5 Days Post-Injury for Optimal Accuracy)

For ACL injury:

• Lachman test is the most sensitive clinical examination with 84% sensitivity and 96% specificity when performed 4-5 days post-injury 4, 5
• Perform with knee flexed at 20-30 degrees to assess anterior tibial translation 4
• Pivot shift test provides additional assessment 5
• Clinical examination accuracy reaches 88-96% for ACL tears 6, 7

For PCL injury:

• Posterior drawer test and tibial sag test are the primary clinical examination maneuvers 5, 8
• Clinical examination achieves 100% accuracy for PCL tears when performed systematically 7
• Examination under anesthesia during arthroscopy reveals the "floppy ACL sign" and posteromedial drive-through sign 8

For MCL injury:

• Valgus stress testing assesses MCL integrity 5
• Palpation of the medial joint line detects tenderness and potential intra-articular displacement 9

For meniscal injury:

• McMurray's test, Apley's grind test, and bounce test aid in meniscal tear diagnosis 5
• Joint line tenderness on palpation is a key finding 5, 9
• Clinical examination accuracy is 85% for meniscal tears 7

Step 3: MRI (Definitive Diagnostic Test)

MRI is the imaging gold standard for all knee ligament and meniscal injuries with the following performance characteristics:

For ACL tears:

• 92.5% positive predictive value and 92-98.3% overall diagnostic accuracy 2, 4
• Sensitivity and specificity are similarly high for both 1.5T and 3T protocols 4
• Detects associated injuries in 19.7% of ACL cases including posterolateral corner injuries, meniscal tears, and bone contusions that profoundly impact surgical planning 2, 4

For meniscal tears:

• 96% sensitivity and 97% specificity at 3T (though 1.5T shows similarly high accuracy) 3
• Can change management from surgical to conservative in up to 48% of patients presenting with locked knee 1, 3
• Detects bone marrow contusions that predict concomitant soft-tissue injuries 3

For PCL tears:

• MRI remains the gold standard imaging study for detecting PCL injuries 8
• Diagnostic accuracy approaches 100% when combined with clinical examination 7

For MCL tears:

• MRI detects mid-substance tears, avulsions, and rare intra-articular displacement 9
• Identifies associated injuries (PCL tears, meniscal root tears) that commonly occur with high-grade MCL injuries 9

Critical timing consideration:

• Perform MRI within 6 weeks of acute trauma for optimal visualization of certain injuries 2, 3

Alternative Imaging When MRI is Contraindicated

Ultrasound is the recommended first-line alternative:

• 90% sensitivity and 97% specificity for ACL injuries 2, 4
• 88% sensitivity and 90% specificity for meniscal tears (highest specificity of 86% in recent injuries <1 month) 1, 3
• Joint effusion on ultrasound has 91% positive predictive value for internal derangement in acute knee trauma 1, 3
• Major limitation: operator-dependent and cannot adequately evaluate portions of menisci, articular surfaces, or deep intra-articular structures 2, 3

CT scanning has limited utility:

• 87.5-100% sensitivity and 100% specificity for ACL tears, but inferior to MRI for soft tissue evaluation 1, 2, 4
• Use CT only for suspected occult fractures or when ultrasound is unavailable/inconclusive 3, 4
• Lateral tibial plateau depression >11 mm on CT predicts higher risk of lateral meniscus tear 3

Common Pitfalls to Avoid

• Do not skip initial radiographs in acute trauma settings as they guide subsequent imaging decisions and detect fractures 3
• Do not perform clinical examination immediately after injury - wait 4-5 days for optimal Lachman test accuracy as acute pain and swelling reduce examination reliability 4, 8
• Do not order MR arthrography or MRA routinely as they are not indicated for initial diagnosis of ligament or meniscal injuries 1, 3
• In elderly patients (>70 years), recognize that asymptomatic meniscal tears are extremely common - MRI findings must be correlated with clinical symptoms as the majority of people over 70 have asymptomatic meniscal tears 3
• Do not rely solely on MRI in acute phase as severe soft-tissue swelling can obscure findings - combine with clinical examination for optimal diagnostic accuracy 9, 7