Quantitative Magnetic Resonance Imaging and Histological Comparison of Normal Canine Menisci

The purpose of this observational study was to establish normative data for the canine menisci using magnetic resonance imaging (MRI).

Ten fresh stifles from five normal male Beagles were obtained from animals with no known lameness. Conventional MRI and ultrashort echo time (UTE) imaging were performed and T₂* values calculated. Five stifles were assessed histologically.

The caudal horn of the medial meniscus had significantly prolonged T₂* values (4.6 ± 1.27 ms; p = 0.002) as compared with the cranial horn of the medial meniscus (3.25 ± 0.86 ms), and the cranial (3.06 ± 0.54 ms) and caudal (3.64 ± 0.72 ms) horns of the lateral meniscus. Histology demonstrated normal tibial, femoral, interior and peripheral meniscal margins, and normal cellularity. The medial meniscus was noted to be obliquely oriented to the scan plane compared with the relatively perpendicular orientation of the lateral meniscus as compared with the bore of the magnet in a limb-extended orientation.

Variability of MRI UTE T₂* is seen in the normal canine meniscus, with prolongation of the caudal horn, medial meniscus. Prolongation may be due to magic angle effects, as the medial meniscus of the Beagle is not perpendicular to the axis of the main magnetic field. Canine meniscal injury is a common sequela to cruciate tear, and detecting meniscal damage is important for directing patient care. The non-invasive quantitative MRI technique of UTE imaging can be used for the evaluation of collagen orientation, while acknowledging inherent regions of prolongation.