Evidence-Based Answer
It is highly accurate in diagnosing injury to the anterior cruciate ligament (ACL) (strength of recommendation [SOR]: A, prospective blinded cohort studies) and posterior cruciate ligament (PCL) (SOR: B, limited number of prospective blinded cohort studies).
Insufficient data are available to evaluate the effectiveness of magnetic resonance imaging (MRI) for diagnosing injuries to the medial collateral ligament (MCL) and lateral collateral ligament (LCL).
Evidence summary
Ligamentous knee injuries from trauma are common. In 2003, patients made about 19.4 million visits to the doctor because of knee problems.1 The ACL is the most often injured knee ligament. The incidence of ACL injury is approximately 200,000 annually in the United States; 100,000 ACL reconstructions are performed each year.2,3 A complete tear of the ACL can lead to significant knee instability and, unless repaired, may limit physical activity and quality of life.
In contrast, PCL injuries don’t often cause significant instability and generally respond to nonsurgical treatment; they have less impact on a patient’s quality of life. Surgery for PCL injury is usually reserved for elite athletes and unstable injuries. MCL and LCL injuries also are generally treated nonsurgically with rehabilitation and bracing; they normally don’t require arthroscopic evaluation and repair.
An effective alternative to arthroscopy
Arthroscopy with direct visualization of the ligamentous structures is considered the gold standard for diagnosing intra-articular ligamentous knee injuries, but it’s invasive and costly. Although clinical examination is helpful in identifying injured ligaments, it may lead to unnecessary arthroscopies when used alone because of the high false-positive rate. MRI has been shown to be an effective tool for accurately diagnosing ligamentous knee injury.2,3
MRI offers high sensitivity for detecting ACL, PCL tears
Several prospective studies have compared MRI with arthroscopy for diagnosing ACL and PCL tears (TABLE).4-8 All enrolled patients had sustained knee trauma and had had a clinical exam that suggested ligamentous injury. MRI and arthroscopy were performed regardless of MRI findings. The surgeons performing arthroscopy were blinded to the MRI results.
Although MRI equipment and techniques varied in all the studies, the sensitivity and specificity remained consistently high for detecting ACL injuries. Thin-slice views, special oblique views, and a fast spin-echo technique didn’t improve either the sensitivity or specificity compared with conventional techniques or views, nor did decreasing the time interval from injury to imaging.5,9,10 Prospective studies of PCL injuries also revealed high sensitivity and specificity with MRI.
No data on MRI for MCL and LCL injuries
No prospective studies are available to assess the accuracy of MRI for suspected MCL and LCL injuries; however, MRI would likely not affect treatment or clinical outcomes, as both of these injuries are typically treated nonsurgically.
Recommendations
The American Academy of Orthopaedic Surgeons supports MRI as an effective tool for evaluating knee injury,1 and offers recommendations and guidelines for treating ligamentous knee injury based on the findings of clinical examination and MRI. The Academy states that MRI is invaluable in preventing unnecessary surgery, and recommends it whenever ligamentous injury is suspected.
Acknowledgements
The opinions and assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the US Air Force medical Service or the US Air Force at large.