What MRI to order for Posterior Cruciate Ligament (PCL) injury?

From the Guidelines

For a PCL injury, a standard knee MRI without contrast is the recommended imaging study. This recommendation is based on the high sensitivity and specificity of MRI for diagnosing PCL tears and associated injuries, as well as its ability to provide detailed visualization of ligamentous structures 1. When ordering the MRI, it should be specified as a "Knee MRI without contrast" with a clinical indication of suspected PCL injury. The MRI protocol should include T1-weighted, T2-weighted, and proton density sequences with fat suppression in multiple planes (axial, sagittal, and coronal) 1. Key points to consider when evaluating a PCL injury with MRI include:

• The use of a high-field strength magnet (1.5T or 3T) for optimal visualization of ligamentous structures
• The evaluation of sagittal images, where the PCL normally appears as a continuous band of low signal intensity
• The assessment for complete tears, partial tears, and avulsion fractures
• The evaluation of associated injuries, such as meniscal tears, other ligament injuries, and bone contusions, which is important for treatment planning 1. It's worth noting that while ultrasound (US) has been studied for its potential utility in diagnosing knee injuries, including PCL injuries, its use is limited by technical factors and is not typically recommended as the primary imaging modality for evaluating suspected PCL tears 1.

From the Research

MRI Sequences for PCL Injury

To diagnose PCL injuries, the following MRI sequences can be used:

• T1-weighted spin echo (SE) sequences 2
• T2-weighted SE sequences 2
• Fat-suppression scans, such as short-tau inversion recovery (STIR) sequences 2
• Oblique sagittal fast spin-echo (FSE) proton-density (PD) sequences with the knee positioned in 90° of flexion 3

Positioning for PCL MRI

Positioning the patient with the knee flexed at 90° can help visualize the PCL in a position of greatest length and tension, which may assist in differentiating and identifying PCL injuries 3.

Imaging Modalities for PCL Injury

The following imaging modalities can be used to diagnose PCL injuries:

• Standard x-ray's 4
• Stress views 4
• Magnetic resonance imaging (MRI), which remains the gold standard imaging study for detecting ligament injuries 4

Classification of PCL Injuries

A new classification of acute PCL injuries based on MRI has been proposed, which includes:

• Type I lesions 2
• Type II lesions, which can be further divided into posteromedial fascicle tears and anterolateral fascicle tears 2
• Type III lesions 2
• Type IV lesions, which are characterized by complete interruption of the ligament 2