Meniscal Lesions: Diagnosis and Treatment

Robert S. P. Fan, MD, Richard K. N. Ryu, MD

Disclosures
In This Article

Imaging

Plain radiographs are generally not helpful in evaluating meniscal lesions other than to rule out other bony or joint pathology. Arthrography has been used extensively in the past with reported accuracy rates of 60% to 97%.[21] The primary disadvantage of arthrography is its invasive nature. Arthrography today has been largely supplanted by magnetic resonance imaging (MRI), which yields accuracy rates as high as 90% to 98%.[21,22] MRI is noninvasive and highly accurate and has a very high negative predictive value.[23]

There is considerable variation in the methodology of knee scanning among imaging centers. Experience of the centers and variations in such equipment as surface coils and magnetic field strength can play a role in determining the imaging protocol of the individual center.

A variety of imaging sequences may be selected. These include routine spin echo, inversion, recovery, fat suppression techniques, gradient recall acquisition in the steady state (GRASS), 3-dimensional Fourier transform imaging, and radial sequences. The repetition time (TR) and echo delay time (TE) can be manipulated to determine contrast during sequencing. This results in T1, T2, and proton density weighting images. To evaluate the menisci, T1 weighting, proton density weighting, or GRASS sequencing is essential to examine the menisci. The GRASS sequencing provides effective T2 weighting. The use of a dedicated circumferential knee coil provides optimal results. The menisci appear dark or low signal intensity on T1 and T2 weighting. Fluid appears as low- to intermediate-signal on T1 and proton density weighting and becomes bright or high signal intensity on T2 and GRASS-weighting images. MRI is ideal for studying the meniscus because of the low signal intensity of the fibrocartilage of the meniscus and the high signal intensity of fluid within a tear.[24]

The normal-appearing meniscus is uniformly low in signal in both T1- and T2-weighted images. It should appear as triangular configurations on both the coronal and sagittal images.

A grading system has been developed to describe abnormal intrameniscal signal. Grade 1 is oval or globular in appearance and does not communicate with any meniscal surface. Grade 2 signal is more linear, but similarly does not communicate with the articular surfaces. Grade 3 signals within the meniscus are linear and should communicate with either superior or inferior articular surfaces. Grades 1 and 2 signals are consistent with intrasubstance myxoid degeneration, whereas grade 3 signal is consistent with a tear[24] (Figures 6A,B).

Figure 6A.

Normal MR imaging of the knee demonstrating intact medial meniscus (arrows).

Figure 6B.

High signal intensity within the posterior horn of the medial meniscus (arrows) extending through the surface, diagnostic of meniscal tear.

In addition, focal alteration of meniscal size or an irregular configuration should raise suspicions of a torn meniscus.

False positives for meniscal pathology are well known. These occur commonly at the junction of the transverse meniscal ligament with the anterior horn of the lateral meniscus, or at the lateral meniscus in the region of the popliteal hiatus. In addition, there is a normal superior recess in the posterior horn of the medial meniscus. Furthermore, the meniscofemoral ligaments of Humphrey and Wrisberg can mimic a tear in the posterior horn on the lateral meniscus.

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