Anatomische Darstellung des caninen Karpalgelenkes mittels Magnetresonanztomographie und Computertomographie unter besonderer Berücksichtigung der Weichteilstrukturen

摘要

Computed tomography (CT) and magnetic resonance imaging (MRI) were used to study the anatomy of clinically and radiographically normal carpal joints in 12 large-breed dogs that were euthanatised for medical reasons. Preparations made by sectioning the carpal joints from these same dogs were used as controls. Computed tomographic and magnetic resonance images were taken in transverse, sagittal and dorsal planes.The computed tomographic examination focused on the depiction of the ligaments, muscles and tendons of the carpal joint using a soft tissue window. Reconstruction algorithms of a medium-sized kernel proved to be applicable. Window settings with a centre of between 50 and 110 HU and a width of 200 to 300 HU provided the best soft tissue contrast in the carpal region. A single-slice helical third generation CT scanner was used together with software that allowed a multi-planar reconstruction of the transverse slices in sagittal and dorsal planes. A low-field open magnetic resonance unit (0.2 T) was used for MRI. T1 and T2 weighted images with different sequences and different slice thickness were obtained in the transverse, sagittal and dorsal planes. T1 weighted spin echo sequences (TR: 640 ms, TE: 26 ms, slice thickness: 3 mm) provided good quality images. Upon completion of the imaging modalities, the joints were sectioned and anatomical preparations were made. These included cryostat sections and permanent transparent slice plastinations. There was a good correlation between the anatomical structures of the frozen sections and those of the slice plastinations. The computed tomographic and magnetic resonance images and the anatomical sections were compared. Viewing the computed tomographic and magnetic resonance images on a monitor using a navigation system offered more advantages than conventional viewing of single images. Projection of the chosen image together with the corresponding images in the other two planes allowed faster and more precise identification of the anatomic structures than viewing single images alone.The superimposition-free depiction of computed tomographic and magnetic resonance images allowed good visualisation of ligaments, tendons and muscles of the carpal region. Compared to muscles, the tendons and ligaments appeared slightly hyperdense on computed tomographic images and markedly hypointense on magnetic resonance images. The palmar flexor tendons, the strong palmar ligaments and the collateral ligaments could be identified on images generated by CT and MRI. Magnetic resonance imaging was superior to CT for visualisation of the extensor tendons and the weaker dorsal ligaments.Most of the extensor tendons and many of the smaller ligaments and tendons could be seen via MRI. Clear differentiation of the medial collateral ligament and the tendon of the long abductor muscle of the first digit (musculus abductor digiti I longus) was not possible with either CT or MRI. As well, the lateral collateral ligament could not be clearly differentiated from surrounding tissue. The medial and lateral accessory metacarpal ligaments could be depicted on both computed tomographic and magnetic resonance images. The palmar fibrocartilage could also be visualised; on computed tomographic images, it was slightly hyperdense with an irregular border and with MRI, it had a low and irregular signal and could be better differentiated. The ligaments that are situated palmar to the antebrachiocarpal joint space could be seen better on magnetic resonance images than on computed tomographic images. The short digital muscles could be visualised with both imaging modalities, but could not be differentiated from each other. Individual carpal bones could be easily distinguished from each other on magnetic resonance images. On computed tomographic images, these bones could not be differentiated well using a soft tissue window, but could be clearly distinguished using a bone window. Some of the large nerves and vessels could be seen on magnetic resonance images; however, reliable identification of these structures was not possible. Contrast studies are required for identification of individual vessels. Synovial bursae and tendon sheaths were barely recognisable on magnetic resonance images and could not be identified on computed tomographic images. Magnetic resonance imaging was superior to CT for identification of all soft tissue structures of the canine carpus. Therefore, soft tissue injuries of that joint should be evaluated using MRI rather than CT.