Purpose: Cartilage canals are minute channels present in the articular-epiphyseal cartilage-complex (AECC) in growing humans and animals. Failure of blood vessels contained within these canals has a key role in the pathogenesis of osteochondrosis (OC) in animals and is presumed to be important in the development of juvenile OC in humans. Investigating the role of blood supply provided via cartilage canals in the pathogenesis of OC is hampered by the lack of non-contrast imaging modalities capable of visualizing these vessels in vivo. The purposes of the present study were: 1) to use ultra high field magnetic resonance imaging (MRI) to visualize cartilage canals in intact femoral condyles and humeral trochleae of young pigs ex vivo and compare the MRI results with histology and micro-computed tomography (μCT) of the contralateral, barium perfused limbs; and 2) to use similar techniques to visualize these vessels in vivo.
Methods: For the ex vivo studies, the left pelvic and thoracic limbs of three euthanized pigs, aged 1, 3 and 6 weeks, were perfused with barium sulfate. Subsequently, the left distal humeri and femora (OC predilection sites) were harvested and imaged using μCT. The right distal humeri and femora were harvested unperfused, and imaged using susceptibility weighted imaging (SWI) at 9.4 T. After imaging, the right distal humeri and femora were routinely prepared for paraffin histology, and serial sections (5μm) were cut at 50 μm intervals. Images of serial sections stained with HE or toluidine blue were stacked, and the 3-D MRI data were resliced in a matching plane to allow comparison. 3-D reconstructions of vessels were created from MRI data and compared with 3-D reconstructions of the μCT data of the contralateral limbs. For the in vivo studies, a 25-day-old pig was anesthetized and both stifle joints were imaged using SWI in a 7 T human whole body MR scanner. After the completion of the MRI study, the pig was euthanized and the femoral condyles were harvested and processed for histology as described above.
Results: Vessels contained in the cartilage canals were clearly identified in the MRI images (A) and their locations matched those observed in the histological sections (B) both ex vivo (upper panel - distal humerus) and in vivo (lower panel - femoral condyle).