Correlation of magnetic resonance images with anatomic features of the equine tarsus

Magnetic resonance imaging of the normal dromedary camel tarsus

Background

Magnetic resonance imaging (MRI) is the most versatile and informative imaging modality for the diagnosis of locomotor injuries in many animal species; however, veterinary literature describing the MRI of the dromedary camel tarsus is lacking. Our purpose was to describe and compare the MRI images of twelve cadaveric tarsi, examined in a 1.5 Tesla MRI scanner, with their corresponding anatomical gross sections. Turbo spin-echo (TSE) T1-weighted (T1), T2-weighted (T2), proton density-weighted (PD), and short tau inversion recovery (STIR) sequences were obtained in 3 planes. Tarsi were sectioned in sagittal, dorsal, and transverse planes. MRI images from different sequences and planes were described and compared with the anatomical sections.

Results

The soft and osseous tissues of the dromedary camel tarsus could be clearly defined on MRI images and corresponded extensively with the gross anatomic sections. The obtained MRI images enabled comprehensive assessment of the anatomic relationships among the osseous and soft tissues of the camel tarsus. Several structure were evaluated that cannot be imaged using radiography or ultrasonography, including the transverse inter-tarsal ligaments, the talocalcaneal ligament, the short dorsal ligament, branches of the short medial and lateral collateral ligaments and the tarsometatarsal ligaments. Specific anatomical features regarding the dromedary camel tarsus were identified, including the fused second and third tarsal bone, an additional bundle of the short medial collateral ligament connecting the talus and metatarsus and the medial and lateral limbs of the long plantar ligament.

Conclusions

MRI images provided a thorough evaluation of the normal dromedary camel tarsus. Information provided in the current study is expected to serve as a basis for interpretation in clinical situations.

Radiographic anatomy of the equine distal tibia

The radiographic anatomy of the equine distal tibia is complex and is not widely described in the current literature. Superimposition and radiographic similarities between the different osseous structures of the equine distal tibia can make it difficult for anatomic localization of pathology. The purpose of this prospective, descriptive, anatomic study was to detail the normal anatomy of the equine distal tibia using routine radiographic projections and CT of the equine tarsus. Radiographic identification of the different osseous protuberances of the distal tibia on three cadaveric limbs was achieved using radiopaque markers and evaluation of multiplanar and 3D CT reconstructions to create anatomical maps. It was found that the lateral malleolus is composed of cranial and caudal protuberances that are superimposed over the intermediate cochlear ridge of the distal tibia on the lateromedial, dorsal 45° lateral-plantaromedial, and dorsal 65° medial-plantarolateral oblique views, thereby hindering visualization of the cranial protuberance of the lateral malleolus. The medial malleolus is a simple rounded protuberance with discrete margins. On the dorsal 65° medial-plantarolateral oblique, the medial malleolus is ill-defined due to superimposition with the talus. The intermediate cochlear ridge of the distal tibia extends in a craniolateral to caudomedial direction, with its cranial protuberance largely superimposed with the calcaneus and talus on the dorsoplantar view. In summary, the distal tibial anatomy is complex and a thorough anatomical reference is necessary when reviewing radiographs of the equine tarsus for pathology. A plantaro 15° distal 85° lateral-dorsoproximomedial oblique projection is proposed to isolate all distal tibial protuberances.

E12 technique: Conventional epoxy resin sheet plastination

Epoxy plastination techniques were developed to obtain thin transparent body slices with high anatomical detail. This is facilitated because the plastinated tissue is transparent and the topography of the anatomical structures well preserved. For this reason, thin epoxy slices are currently used for research purposes in both macroscopic and microscopic studies. The protocol for the conventional epoxy technique (E12) follows the main steps of plastination-specimen preparation, dehydration, impregnation and curing/casting. Preparation begins with selection of the specimen, followed by freezing and slicing. Either fresh or fixed (embalmed) tissue is suitable for epoxy plastination, while slice thickness is kept between 1.5 and 3 mm. Impregnation mixture is made of epoxy E12 resin plus E1 hardener (100 ppw; 28 ppw). This mixture is reactive and temperature sensitive, and for this reason, total impregnation time under vacuum at room laboratory temperature should not last for more than 20-24 hr. Casting of impregnated slices is done in either flat chambers or by the so-called sandwich method in either fresh mixture or the one used for impregnation. Curing is completed at 40°C to allow a complete polymerization of the epoxy-mixture. After curing, slices can be photographed, scanned or used for anatomical study under screen negatoscope, magnification glass or fluorescent microscope. Based on epoxy sheet plastination, many anatomical papers have recent observations of and/or clarification of anatomical concepts in different areas of medical expertice.

Computed tomography and magnetic resonance imaging study of a normal tarsal joint in a Bengal tiger (Panthera tigris)

Background

In this research, using computed tomography (CT) and magnetic resonance imaging (MRI), we provide a thorough description of the standard appearance of a right tarsal joint in a Bengal tiger (Panthera tigris). CT scans were performed using a bone and soft tissue window setting, and three-dimensional surface reconstructed CT images were obtained. The MRI protocol was based on the use of Spin-echo (SE) T1-weighted and Gradient-echo (GE) STIR T2-weighted pulse sequences. Magnetic resonance (MR) images were taken in the transverse, sagittal and dorsal planes. We also performed anatomical dissections to facilitate the interpretation of the different structures of the tarsus joint and allow comparisons with CT and MRI images.

Results

The CT images allowed us to observe differences between the bones and soft tissues of the tarsal joint. When applying the bone window setting, the obtained footage showed the anatomy between the medulla and cortex. Additionally, the trabecular bone was delineated. By contrast, the soft tissue window allowed the main soft tissue structures of the tarsal joint, including ligaments, muscles and tendons, to be differentiated. Footage of the main anatomical structures of the standard tiger tarsus was obtained through MRI. The SE T1-weighted images showed the best evaluation of the cortical, subchondral and trabecular bone of the tibia, fibula, tarsus and metatarsus bones. Nonetheless, the GE STIR T2-weighted images allowed us to better visualize the articular cartilage and synovial fluid. In both MRI pulse sequences, the ligaments and tendons appeared with low signal intensity compared with muscles that were visible with intermediate signal intensity.

Conclusions

The results of this CT and MRI study of the Bengal tiger tarsal joint provide some valuable anatomical information and may be useful for diagnosing disorders in this large non-domestic cat.

Magnetic resonance imaging of plantar soft tissue structures of the tarsus and proximal metatarsus in foals and adult horses

Objectives: The object of this study was to describe previously defined soft tissue structures by using spin and gradient sequences in a 0.5 Tesla magnetic resonance system in order to improve the characterisation of tendon and ligaments at the plantar region of the equine tarsus and metatarsus while considering possible age-related variations.

Methods: Cadaveric hindlimbs from twenty-two Warmblood horses with an age range from one month to twenty-five years were examined in spin and gradient echoes. The proximal suspensory ligament from six limbs was dissected to assign the signal intensities histologically. For statistical analysis, horses were divided into two groups (≤3 years and >3 years) for evaluating signal intensity and homogeneity of the plantar tendons and ligaments.

Results: Focal increase of the signal intensity within the deep digital flexor tendon was significantly more present in horses older than three years. Signal alterations of the long plantar ligament were seen without a significant dependency to age. The accessory ligament of the deep digital flexor tendon could not be visualized on all images within the region of interest. The morphology of the proximal suspensory ligament was not affected by age-related changes.

Clinical relevance: Spin and gradient echoes in MRI were suitable to identify and assess soft tissue structures at the plantar aspect of the equine tarsus and proximal metatarsus. Age-related appearance must be considered when interpreting magnetic resonance images.

Post-traumatic osteoarthritis of the ankle: A distinct clinical entity requiring new research approaches

The diagnosis of ankle osteoarthritis (OA) is increasing as a result of advancements in non-invasive imaging modalities such as magnetic resonance imaging, improved arthroscopic surgical technology and heightened awareness among clinicians. Unlike OA of the knee, primary or age-related ankle OA is rare, with the majority of ankle OA classified as post-traumatic (PTOA). Ankle trauma, more specifically ankle sprain, is the single most common athletic injury, and no effective therapies are available to prevent or slow progression of PTOA. Despite the high incidence of ankle trauma and OA, ankle-related OA research is sparse, with the majority of clinical and basic studies pertaining to the knee joint. Fundamental differences exist between joints including their structure and molecular composition, response to trauma, susceptibility to OA, clinical manifestations of disease, and response to treatment. Considerable evidence suggests that research findings from knee should not be extrapolated to the ankle, however few ankle-specific preclinical models of PTOA are currently available. The objective of this article is to review the current state of ankle OA investigation, highlighting important differences between the ankle and knee that may limit the extent to which research findings from knee models are applicable to the ankle joint. Considerations for the development of new ankle-specific, clinically relevant animal models are discussed. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:440-453, 2017.

Comparison of cross-sectional anatomy and computed tomography of the tarsus in horses

OBJECTIVE

To compare computed tomography (CT) images of equine tarsi with cross-sectional anatomic slices and evaluate the potential of CT for imaging pathological tarsal changes in horses.

SAMPLE

6 anatomically normal equine cadaveric hind limbs and 4 tarsi with pathological changes.

PROCEDURES

Precontrast CT was performed on 3 equine tarsi; sagittal and dorsal reconstructions were made. In all limbs, postcontrast CT was performed after intra-articular contrast medium injection of the tarsocrural, centrodistal, and tarsometatarsal joints. Images were matched with corresponding anatomic slices. Four tarsi with pathological changes underwent CT examination.

RESULTS

The tibia, talus, calcaneus, and central, fused first and second, third, and fourth tarsal bones were clearly visualized as well as the long digital extensor, superficial digital flexor, lateral digital flexor (with tarsal flexor retinaculum), gastrocnemius, peroneus tertius, and tibialis cranialis tendons and the long plantar ligament. The lateral digital extensor, medial digital flexor, split peroneus tertius, and tibialis cranialis tendons and collateral ligaments could be located but not always clearly identified. Some small tarsal ligaments were identifiable, including plantar, medial, interosseus, and lateral talocalcaneal ligaments; interosseus talocentral, centrodistal, and tarsometatarsal ligaments; proximal and distal plantar ligaments; and talometatarsal ligament. Parts of the articular cartilage could be assessed on postcontrast images. Lesions were detected in the 4 tarsi with pathological changes.

CONCLUSIONS AND CLINICAL RELEVANCE

CT of the tarsus is recommended when radiography and ultrasonography are inconclusive and during preoperative planning for treatment of complex fractures. Images from this study can serve as a CT reference, and CT of pathological changes was useful.

Animal models for cartilage regeneration and repair

Articular cartilage injury and degeneration are leading causes of disability. Animal studies are critically important to developing effective treatments for cartilage injuries. This review focuses on the use of animal models for the study of the repair and regeneration of focal cartilage defects. Animals commonly used in cartilage repair studies include murine, lapine, canine, caprine, porcine, and equine models. There are advantages and disadvantages to each model. Small animal rodent and lapine models are cost effective, easy to house, and useful for pilot and proof-of-concept studies. The availability of transgenic and knockout mice provide opportunities for mechanistic in vivo study. Athymic mice and rats are additionally useful for evaluating the cartilage repair potential of human cells and tissues. Their small joint size, thin cartilage, and greater potential for intrinsic healing than humans, however, limit the translational value of small animal models. Large animal models with thicker articular cartilage permit study of both partial thickness and full thickness chondral repair, as well as osteochondral repair. Joint size and cartilage thickness for canine, caprine, and mini-pig models remain significantly smaller than that of humans. The repair and regeneration of chondral and osteochondral defects of size and volume comparable to that of clinically significant human lesions can be reliably studied primarily in equine models. While larger animals may more closely approximate the human clinical situation, they carry greater logistical, financial, and ethical considerations. A multifactorial analysis of each animal model should be carried out when planning in vivo studies. Ultimately, the scientific goals of the study will be critical in determining the appropriate animal model.

In search of clinical truths: equine and comparative studies of anatomy

The importance of correlating anatomical studies with diagnostic and therapeutic approaches in practice has long been recognised. Such studies in the horse have, until recently, lagged behind this discipline in human medicine and surgery. Clinical techniques by which this correlation is achieved include radiography, ultrasound, computed tomography and magnetic resonance imaging. This review presents published literature on the subject and, in addition, describes the part played by plastination, a recently developed technique for the preservation of biological specimens. In this, tissue fluids and part of the lipids are replaced by certain polymers yielding specimens that can be handled without gloves, do not smell or decay, and even retain microscopic properties of the original sample. The technique has proved to be a useful tool to correct previously presented anatomical descriptions and is one now favoured by human surgeons. Studies of the horse employing this technique include those of the temporomandibular joint and tarsus. The aim of the review is to stimulate further correlations of anatomical structure and equine medical and surgical procedures, thereby advancing knowledge and understanding in practice and teaching.