Abstract
BackgroundDiagnosing partial tears of the medial meniscus (MM) posterior root is difficult. The aim of this study was to evaluate diagnostic values involved in conventional magnetic resonance imaging (MRI) features of MM posterior root tears (MMPRTs) and find other MRI-based findings in patients with partial MMPRTs.MethodsEighteen patients who had arthroscopically confirmed partial MMPRTs were included. As a control, 18 patients who underwent partial meniscectomy for other types of MM tears were evaluated. Isolated partial MMPRTs were classified into the following three types: type A, accurate partial stable tear (cleavage < 1/2 of root width); type B, bridged unstable root tear (cleavage ≥ 1/2 of root width); type C, complex horn tear expanded to the root. Conventional MRI-based findings of MMPRTs were evaluated between two groups (n = 23). Posterior root irregularity, bone marrow spot, and ocarina-like appearance showing several condensed circles in triangular meniscal horn (ocarina sign) were also evaluated.ResultsPosterior root irregularity and bone marrow spot were frequently observed in the partial MMPRTs (47.8%), compared with the other MM tears (P = 0.007 and 0.023, respectively). The ocarina sign was detected in 69.6% of patients with partial MMPRTs. A significant difference between two groups was observed in a positive ratio of ocarina sign (P < 0.001). Types A, B, and C of the partial tear/damage were observed in three, eight, and seven patients, respectively. The ocarina sign was the most common MRI finding in each type of partial MMPRT.ConclusionsThis study demonstrated that a characteristic MRI finding, “ocarina sign,” was frequently observed in patients with partial tear/damage of the MM posterior root. The ocarina sign was the most common MRI finding in several types of partial MMPRTs. Our results suggest that the ocarina sign may be useful to diagnose unnoticed partial MMPRTs.Level of evidence: IV, retrospective comparative study.
Highlights
Diagnosing partial tears of the medial meniscus (MM) posterior root is difficult
The incidence of the MM posterior root tear (MMPRT) was higher in women compared with that of other MM tears (P = 0.005, Table 1)
A giraffe neck sign was observed in 21.8% of the magnetic resonance imaging (MRI) with partial MMPRTs (P = 0.049)
Summary
Diagnosing partial tears of the medial meniscus (MM) posterior root is difficult. A radial tear sign (radial linear defect) with complete discontinuity of the posterior root and fluid gap on axial images has high diagnostic value in the diagnosis of MMPRT [4–6]. MM medial extrusion sign is often observed in the other types of MM tears and has a lower accuracy for detecting MMPRT compared with giraffe neck, cleft, ghost, and radial tear signs [5, 6]. These signs are clinically useful to detect complete tears of the MM posterior root. Diagnosing partial tear and/or pathological damage of the MM posterior root is still difficult
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