Comparison of Ultrasound and Magnetic Resonance Imaging for Identifying Soft Tissue Abnormalities in the Palmar Aspect of the Equine Digit.

Damage to the soft tissue structures of the digit is a common source of equine lameness. While magnetic resonance imaging (MRI) allows for the most complete diagnostic imaging of the equine digit, ultrasound is more readily available and less expensive. This prospective diagnostic accuracy study compares ultrasound to MRI for the diagnosis of injuries visible with ultrasound within the digit, including the deep digital flexor tendon (DDFT), collateral sesamoidean ligament (CSL), and navicular bursa. Clinical patients underwent an MRI of the digit and a blinded ultrasound of the digit between the heel bulbs, and results of the two modalities were compared. A total of 70 ultrasound and MRI exams of 45 horses were included. Ultrasound had good sensitivity (85%), moderate specificity (60%), and accuracy of 70% for evaluating the dorsal tearing of the DDFT. Accuracy was lower for navicular bursa effusion (67%), navicular bursa proliferation (61%), and CSL enlargement (61%). Tearing of the DDFT distal to the navicular bone was identified with MRI in 27 limbs, 20 of which also had dorsal damage proximal to the navicular bone identified with ultrasound. Ultrasound evaluation remains a useful screening tool, particularly for the assessment of DDFT tearing proximal to the navicular bone but risks under-diagnosing pathology to the navicular bursa and CSL. Clinically significant concurrent damage to the distal DDFT and other osseous and soft tissues in the hoof capsule is unlikely to be identified without MRI.

Chronic Collateral Sesamoidean Desmopathy in Draft Horses: Magnetic Resonance Imaging and Histopathological Findings.

Desmopathy of the collateral sesamoidean ligament (CSL) is an unusual disorder in draft horses. This study records the magnetic resonance imaging (MRI) features of chronic CSL desmopathy in eight draft horses and confirms these features by histopathology. The recorded chronic CSL desmopathy has usually affected the forelimbs (100%) and commonly bilateral (62.5%). All horses showed positive proximal digital nerve block, positive front digital flexion test, and negative interphalangeal extension test. Radiography revealed no osseous abnormalities in all feet. MRI features of chronic CSL desmopathy included thickening of the ligament with increased moderate intensity in fast low-angle shot, T1 turbo spin echo, and proton density images in the affected part of the ligament. Chronic CSL desmopathy was concomitant with deep digital flexor tendon injury and distal sesamoidean impar desmitis. In most chronic cases of CSL desmopathy, heterogeneous signal intensities were seen with multiple foci of low signal intensities interlaced with increased moderate signal intensities of thickened CSL. Histopathology confirmed the MRI findings and revealed separated bundles and fascicles by septa of less organized and loose connective tissues containing fibroblasts and loose collagen fibers. Multifocal islands of cartilaginous metaplasia, mineralized areas, and dystrophic calcification were observed in the injured ligament. In conclusion, chronic CSL desmopathy may progress to cartilaginous metaplasia and dystrophic calcification. MRI is a beneficial diagnostic and prognostic tool for chronic CSL desmopathy, and histopathology is a gold standard to document the MRI findings associated with CSL dysmopathy in draft horses.

Is the T-ligament a ligament? A histological study in equine cadaver forelimbs.

Foot pain is a frequent cause of lameness in horses and can involve multiple structures within the hoof. The T-ligament (an anatomical structure connecting the synovium of the distal interphalangeal joint, the digital flexor tendon sheath and the navicular bursa) is poorly described. Five pairs of equine cadaver distal forelimbs were collected from a slaughterhouse. Sagittal sections (medial, middle and lateral) were obtained and processed with Haematoxylin Eosin Safran, Unna's Orcein, and Picrosirius red stains. Histological assessment revealed that the T-ligament was covered by the surrounding synovia of the distal interphalangeal joint, the digital flexor tendon sheath and the navicular bursa. Its collagen content was lower (30.01%±10.15) than that of the collateral sesamoidean ligament (89.48%±5.8; P = .0008) and the middle phalanx (85.72%±3.67; P = .0008). Under polarized light microscopy, it showed a slight heterogeneous pattern of birefringence, with angle-related changes. Elastic fibres were more numerous (21.76%±8.72) than in the collateral sesamoidean ligament (0.28%±0.45), or deep digital flexor tendon (0.04%±0.02); and were more densely packed. Mean cell count was higher for the T-ligament than for other tissues (P = .0007). Blood vessels were identified in the T-ligament and were penetrating the deep digital flexor tendon (8/10 limbs, 5/5 horses). In conclusion, the T-ligament looked like a vinculum for the deep digital flexor tendon, with a central elastic core, surrounding loose connective tissue and blood vessels. It is not a ligament. Its clinical relevance still needs to be determined.

SALINE ARTHROGRAPHY OF THE DISTAL INTERPHALANGEAL JOINT FOR LOW-FIELD MAGNETIC RESONANCE IMAGING OF THE EQUINE PODOTROCHLEAR BURSA: FEASIBILITY STUDY.

Abnormalities of the deep digital flexor tendon, navicular bone, and collateral sesamoidean ligament can be difficult to visualize using magnetic resonance imaging (MRI) if bursal fluid is absent. The use of saline podotrochlear bursography improves podotrochlear apparatus evaluation, however, the technique has disadvantages. The objective of this prospective feasibility study was to describe saline arthrography of the distal interphalangeal joint as an alternative technique for improving MRI visualization of the deep digital flexor tendon, navicular bone, collateral sesamoidean ligament, and podotrochlear bursa, and to compare this technique with saline podotrochlear bursography. Eight paired cadaver forelimbs were sampled. Saline podotrochlear bursography or saline arthrography techniques were randomly assigned to one limb, with the alternate technique performed on the contralateral limb. For precontrast and postcontrast studies using each technique, independent observers scored visualization of the dorsal aspect of the deep digital flexor tendon, palmar aspect of the navicular bone, collateral sesamoidean ligament, and podotrochlear bursa. Both contrast techniques improved visualization of structures over precontrast MR images and visualization scores for both techniques were similar. Findings from this study demonstrated that saline arthrography is feasible and comparable to saline podotrochlear bursography for producing podotrochlear bursa distension and separation of the structures of the podotrochlear apparatus on nonweight bearing limbs evaluated with low-field MRI. Clinical evaluation of saline arthrography on live animals is needed to determine if this technique is safe and effective as an alternative to saline podotrochlear bursography in horses with suspected pathology of the podotrochlear apparatus.

Avaliação radiográfica e ultrassonográfica do aparato podotroclear de cavalos Quarto de Milha diagnosticados com síndrome do navicular / Radiographic and ultrasonographic evaluation of the podotrochlear apparatus in American Quarter horses diagnosed with navicular syndrome

O objetivo deste estudo foi avaliar as alterações do aparato podotroclear de 22 cavalos da raça Quarto de Milha acometidos pela síndrome do navicular utilizando o acesso transcuneal. Esses equinos foram submetidos ao exame radiográfico e ultrassonográfico. No exame radiográfico foi observado a presença de invaginação sinovial de diferentes tipos, além de calcificação da bursa podotroclear e tendão flexor digital profundo, entesiófitos, osteófitos e alteração do limite córtico-medular. No exame ultrassonográfico observou-se alterações da bursa podotroclear, aderência e irregularidades nos bordos do tendão flexor digital profundo, diminuição do coxim digital, calcificação do ligamento sesamóide distal ímpar e irregularidade da superfície flexora do osso sesamóide distal. Todos os equinos que apresentavam alterações radiográficas também apresentaram alterações no exame ultrassonográfico compatíveis com a síndrome do navicular. O exame ultrassonográfico utilizando o acesso transcuneal foi um método prático e eficiente para avaliação das lesões do aparato podotroclear dos eqüinos, sendo um método complementar ao exame radiográfico.

The objective of this study was to evaluate radiographically and ultrasonographically the podotrochlear apparatus using a transcuneal approach in 22 American Quarter horses suffering from navicular syndrome. On the radiographs, different forms of synovial invaginations, calcification of the podotrochlear bursa and deep digital flexor tendon, enthesophyte and osteophyte formation, and changes in the cortical-medullary margin were observed. On the ultrasound scans, changes of the podotrochlear bursa, adhesions and irregularities at the surface of the deep digital flexor tendon, the digital cushion area reduction, calcification of the impar distal sesamoideal ligament, and irregularities of the flexor surface of the distal sesamoid bone were observed. Radiographic and ultrasonographic abnormalities compatible with navicular syndrome were present in all patients. Ultrasonography using transcuneal approach was a practical and efficient method to evaluate podotrochlear apparatus injuries in equine, thus being a complementary method to radiography.