From the Guidelines
For a knee injury from sudden hyperextension while hiking with swelling on the medial aspect, an MRI without contrast is typically sufficient and recommended as the initial imaging study. This recommendation is based on the most recent and highest quality study available, which suggests that MRI has many distinct advantages for the evaluation of the injured knee in the setting of negative radiographs 1. The majority of patients who present with acute knee injuries sustain soft-tissue injuries rather than osseous injuries, and MRI is a proven valuable tool in the treatment decision-making process, allowing earlier surgical intervention by obtaining a more accurate diagnosis 1.
Key Points to Consider
- Contrast is generally not necessary for evaluating most common knee injuries such as meniscal tears, ligament injuries (like MCL, ACL, or PCL tears), or bone contusions that may result from hyperextension trauma.
- The non-contrast MRI provides excellent visualization of soft tissues, ligaments, tendons, cartilage, and bone marrow edema.
- Before getting the MRI, a clinical evaluation by a healthcare provider is necessary to perform specific tests to assess ligament stability and meniscal integrity.
- While waiting for imaging, following the RICE protocol (Rest, Ice, Compression, Elevation) and taking over-the-counter pain relievers like acetaminophen or NSAIDs if not contraindicated can help manage symptoms.
- The medial swelling suggests possible injury to structures on the inner side of the knee, such as the medial collateral ligament or medial meniscus, which are commonly affected in hyperextension injuries.
Importance of MRI in Knee Injury Evaluation
- MRI can diagnose the patterns and severity of bone marrow contusions that frequently have an association with the specific mechanisms of injury and can predict associated soft-tissue injuries 1.
- MRI can facilitate diagnosis of the anterolateral ligament injuries that have frequent association with ACL injuries and anterolateral knee instability 1.
- MRI is proven helpful in detection and characterization of posterolateral corner injuries, which can be associated with the ACL ruptures and, if missed, may lead to considerable morbidity 1.
From the Research
Indications for MRI in Knee Injury
- MRI is an effective imaging tool for assessing knee injuries, including those resulting from hyperextension 2, 3.
- The pattern of abnormalities seen on MRI depends on the mechanism of trauma and the position of the joint at the time of injury 2.
- MRI can help diagnose various knee injuries, including anterior cruciate ligament (ACL) tears, meniscal tears, and ligament sprains 3, 4, 5.
MRI Findings in Hyperextension Injuries
- Hyperextension of the knee can lead to impingement of the ACL against the intercondylar notch roof (INR) 6.
- MRI cinematography can be used to analyze the interaction between the ACL and the INR in hyperextension 6.
- The average extension angle at the beginning of impingement was found to be -6.3 +/- 3.8 degrees 6.
Use of Contrast in MRI
- Although the provided studies do not specifically address the use of contrast in MRI for knee injuries, MRI with or without contrast can be used to evaluate knee injuries, depending on the specific clinical question and the presence of certain symptoms or signs, such as medial swelling 4, 5.