While arthroscopy is considered the gold standard for evaluating the knee, MRI appears to be superior for detecting meniscal lesions and degeneration. The modality also appears to be less useful than arthroscopy for detecting hemarthrosis.
A German study presented at the European Congress of Radiology used MRI and arthroscopy in order to evaluate chondral and osteochondral fractures in patients with acute injury of the knee.
"The situation is well known where a plain x-ray of the acute injury of the knee joint comes up negative for hemarthrosis, but nevertheless, we still have hemarthrosis because of subtle chondral and osteochondral fractures," said Dr. Klaus Bohndorf of the department of radiology at the Zentralklinikum in Augsburg.
Sixty patients with acute knee injuries were enrolled in the 13-month-long, prospective study. All had hemarthrosis, although x-rays showed negative results. All patients underwent MRI and subsequent arthroscopy. MRI exams were performed with T1-weighted spin-echo, T2-weighted turbo spin-echo, and gradient-echo 2-D sequences. Osteochondral defects of the medial and lateral compartment related to acute injury were noted for each modality.
Out of 120 knee compartments, 10 defects were diagnosed, Bohndorf said. MRI had a sensitivity of 40%, a specificity of 98%, and an accuracy rate of 93%. The positive predictive value was 67% and the negative predictive value was 95%. Arthroscopy had a sensitivity of 70%, a specificity of 99%, and an accuracy of 96%. The positive predictive value was 87%, while the negative predictive value was 97%.
The study concluded that neither modality was ideal for detecting these subtle fractures, especially because MRI is time-consuming and requires an experienced reader.
MRI fared better in an Italian study that compared it to arthroscopy for the assessment of symptomatic meniscal degeneration and medial meniscal cystic involutions.
In 97 patients, MRI was performed using a permanent magnet, low-field dedicated scanner, and T1-weighted, T2-weighted, and fat-supressed sequences. MRI found 12 meniscal lesions that were not seen with arthroscopy. In addition, MR imaging detected localized meniscal degenerative alteration in 69 patients.
"For now, arthroscopy is considered the gold standard," said Dr. Marco Mastantuono from the University of Rome. "But in many respects, MRI is superior for correct therapeutic planning."
By Shalmali Pal
AuntMinnie.com staff writer
April 19, 2000
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