Diagnostic Imaging for ACL and PCL Injuries

Primary Imaging Algorithm

The American College of Radiology recommends obtaining knee radiographs first to exclude fractures or bony avulsion injuries, particularly in patients under 40 years with knee effusion, before proceeding to advanced imaging 1
Radiographs serve as the screening tool before proceeding to advanced imaging, according to the American College of Radiology 1
MRI achieves 92.5% positive predictive value and 92-98.3% overall diagnostic accuracy for ACL tears, making it superior to all other imaging modalities, as stated by the American College of Radiology 1
Both 1.5T and 3T MRI protocols provide similar high sensitivities and specificities for ACL tears, so routine 3T imaging does not significantly improve accuracy over 1.5T, according to the American College of Radiology 1

MRI identifies concomitant injuries in 19.7% of ACL cases, including posterolateral corner injuries that, if missed, lead to considerable morbidity, as reported by the Journal of the American College of Radiology 2, 3
Lateral bone contusions on MRI correlate with high-grade pivot-shift and lateral meniscal lesions, predicting injury patterns, according to the Journal of the American College of Radiology 3, 1
MRI detects anterolateral ligament injuries more frequently within 6 weeks of acute trauma compared to delayed imaging, as some injuries resolve or become less visible with chronicity, as stated by the Journal of the American College of Radiology 3

MRI changes management from surgical to conservative in up to 48% of patients presenting with locked knee, according to the Journal of the American College of Radiology 3
Precise ACL tear location and classification on MRI assists preoperative planning for ligament preservation techniques, as reported by the Journal of the American College of Radiology 3

CT has 87.5-100% sensitivity and 100% specificity for ACL tears but remains inferior to MRI for soft tissue evaluation, according to the American College of Radiology 1
CT is appropriate only for suspected occult fractures or bony avulsion injuries, not for routine ligament assessment, as stated by the American College of Radiology 1
Ultrasound achieves 90% sensitivity and 97% specificity for ACL injuries but is operator-dependent and provides limited visualization of cruciate ligaments, according to the American College of Radiology 1, 4
Ultrasound cannot adequately evaluate portions of menisci, articular surfaces, or deep intra-articular structures, as reported by the Journal of the American College of Radiology 2
SPECT has lower sensitivity, specificity, and accuracy than MRI for meniscal and ligament injuries, according to the Journal of the American College of Radiology 3

Do not rely on CT for soft tissue ligament evaluation, even though it has high specificity for ACL tears—MRI remains superior for comprehensive assessment, as stated by the American College of Radiology 1
Avoid delayed MRI imaging beyond 6 weeks when anterolateral ligament injury is suspected, as injuries may become less visible, according to the Journal of the American College of Radiology 3
Do not skip radiographs before MRI, as they exclude fractures and guide appropriate imaging selection, as recommended by the American College of Radiology 1
Do not assume isolated ligament injury—MRI's ability to detect bone contusions predicts development of focal osteoarthritis 1 year after trauma, as reported by the Journal of the American College of Radiology 2, 3