When to Use MRI for Knee Injury Detection

The Primary care physicians are often confused which test to permit to effectively detect knee injury. Magnetic resonance imaging (MRI) is particularly useful when there is suspected meniscal and ligamentous injuries. The imaging should be preceded by history and physical examination to assess damage of the cartilage, the menisci, and the cruciate and collateral ligaments. Radiography is useful technique for initial evaluation of painful knee and only when arthroscopy is contemplated, MRI should be conducted.

There are a number of reasons for the choice of MRI: it being a non-invasive process does not use ionizing radiation. It also provides multiplanar soft tissue images not obtained by other imaging methods. The sensitivity of MRI for meniscal and cruciate ligament injury is between 75% to 88%. Besides, it can also evaluate synovitis, bone bruise, stress or insufficiency fracture, osteochondral defects, and osteonecrosis where other methods have limitation. MRI can detect specific features of osteonecrosis in elderly women who often get sudden knee pain. MRI can identify other lesions, such as of the knee, usually seen in these women. In such patients, MRI findings of focal replacement of the bone marrow and adjoining edema are specific for osteonecrosis. The MRI is preferred diagnostic tool for acute knee pain as up to 42% less invasive procedure of arthroscopy is performed.

However, the scans need to be checked thoroughly since false positives for meniscal tears are also quite high in MRI. For articular cartilages also the sensitivity of MRI is considerably lower than arthroscopy. MRI has also been shown to reveal cartilage lesions, osteophytes, and meniscal abnormalities in asymptomatic control participants with no history of knee injury or disease. It seems a big drawback of the technique or the clinical interpretations of MRI scan require much experience for correct intervention. The findings on MRI must closely correlate with findings on the history and physical examination.

The comparative evaluation and precautions about MRI scan interpretations are required for effective use of the technique. The knee pain is often referred to MRI scan which is costlier and delays intervention. Moreover, the limitations of the technique have to be regarded. All cartilage and meniscal lesions are not symptomatic and there may be other causes of acute knee pain. MRI is also not useful and offers little for patients in whom changes of degenerative joint disease are evident on radiographs.

Source:

Koplas, M., J. Schills, and M. Sundaram. 2008. The painful knee: Choosing the right imaging test. Cleveland Clinic Journal of Medicine 75(5): 377-384.