To the authors’ knowledge, this is the first published report providing description of the high field MRI appearance of the normal dromedary camel tarsus. The clinically relevant osseous and soft tissue structures of the dromedary camel tarsus were described and corresponded well with the gross anatomic sections. The obtained information in the current study appointed that MRI enabled assessment of structures inside the tarsus (soft and bony tissue) that otherwise cannot be visualized by other means and offers the opportunity to diagnose lesions within the tarsus that cannot be diagnosed through other imaging modalities [17]. MRI permitted viewing of the camel tarsus in three planes and obtaining information of cartilage, cortical bone, subchondral bone, trabecular bone, cancellous bone, ligaments, and tendons which is not all possible with other available diagnostic imaging tools. This enables the clinicians to interpret the tarsus in different angles and accurately detect the problem. The obtained results are in agreement with the conclusions reported earlier, that MRI offers the best evaluation technique of all anatomical structures, particularly soft tissues, of the tarsal joint in horse, cattle, dog and cat [3, 12–16].
The protocol demonstrated in this study was designed to optimize evaluation of various structures in the dromedary camel tarsus, although it was longer than that expected in clinical patients. This was to afford comprehensive reference images of the clinically normal camel tarsus to assist interpretation of MRI images in clinical situations. The used sequences were extensive in every plane so that an optimal protocol could be determined. Typical protocols utilized in clinical situations utilize short sequence acquisition time in order to shorten the time of general anesthesia or deep sedation during examination and also decrease the cost of examination. The spin-weighted sequences (T1, T2, PD and STIR) provided excellent anatomic definition and satisfying tissue contrast of the bony and soft tissue structures in the dromedary camel tarsus. T1 and PD images were excellent for the detailed anatomic assessment of the tarsal structures and identification of articular cartilage. The fat-suppressed sequence (STIR) and T2 images provided better visualization of synovial fluid [5, 12, 18].
Knowledge of the normal anatomy and signal intensity of various tissues are crucial for correct interpretation of MRI scans obtained from lame patients. In the present study, synovial fluid had high signal intensity in STIR, PD and T2 images that was unlike T1- weighted images. Similar findings were reported in horse [3]. It was not possible to define a clear limit between the subchondral and cortical bones as a result of similar low signal intensity. This was convenient with horse tarsal joint [13]. The corticocancellous junction was regular and clearly defined, as mentioned for the bovine tarsus [14]. Cancellous bone had heterogeneous intermediate to high signal intensity where the bone of the trabeculae had low signal intensity and fat in the bone marrow filling the trabecular spaces had high signal intensity. This agreed with those reported in horse [13]. Articular cartilage had homogenous intermediate signal intensity adjacent to the low signal of subchondral bone at articular interfaces. Congruous findings were reported in horse [19]. The tarsocrural joint capsule, synovial tissue and synovial fluid had low to intermediate signal intensity similar to those reported in bovine tarsus [14]. Tendons, collateral ligaments and the long plantar ligament of the dromedary camel had low signal intensity and the inter-tarsal ligaments had heterogeneous signal intensity. Similar findings were reported in horse [10, 20].
Joint disease is a significant problem and the use of imaging techniques to detect the specific tissue affected is critical to implementation of successful treatment strategies. Radiography and ultrasonography are commonly used to detect joint disease and injury but have limitations. Radiography lacks direct viewing of articular cartilage and other soft tissues, and fails to detect early or subtle bone changes [8]. Ultrasonography reveals soft tissue detail including articular cartilage, but is operator dependent, limited to bone surface and anisotropy of the ultrasound beam angle can influence articular cartilage appearance [21]. Diagnostic arthroscopy visualizes articular cartilage and other joint structures with high sensitivity; although, it is invasive and deep cartilage and bone are not observed without superficial cartilage disruption [22]. MRI is currently considered the most sensitive technique for detecting bone pathology including osteonecrosis, osteomyelitis and trauma, such as bone contusion and un-displaced fractures, as well as articular cartilage pathology and soft tissue lesions. Unlike radiography and ultrasonography, MRI provides cross-sectional and three-dimensional evaluation with different imaging sequences that can be used to target the examination to the potential site of the lesion [4].
High field MRI provided comprehensive assessment of the dromedary camel tarsus. Results of the present study indicated that signal intensity varied according to the used sequence and investigated structure in the normal dromedary camel tarsus. Interpretation of MRI images is a challenge and obliges a good knowledge of anatomic detail and familiarization to the normal MRI appearance of the region of interest in order to diagnose the problem with confidence. Further studies are warranted to determine the clinical application of high field MRI in the dromedary camel tarsus.