Distal border fragments of the equine navicular bone: association between magnetic resonance imaging characteristics and clinical lameness.

Distal border fragments of the navicular bone are increasingly being detected due to the improved capabilities of magnetic resonance imaging (MRI), but their clinical significance remains unclear. The purpose of this retrospective study was to describe the location, size, and frequency of fragments in a cohort of horses presented for MRI of the foot and to compare MRI findings with severity of lameness. Archived MRI studies and medical records were searched from March 2006 to June 2008. Horses were included if a distal border fragment of the navicular bone was visible in MRI scans. Confidence interval comparisons and linear regression analyses were used to test hypotheses that fragments were associated with lameness and lameness severity was positively correlated with fragment volume and biaxial location. A total of 453 horses (874 limbs) were included. Fragments were identified in 60 horses (13.25%) and 90 limbs (10.3%). Fifty percent of the horses had unilateral fragments and 50% had bilateral fragments. Fragments were located at the lateral (62.2%), medial (8.89%), or medial and lateral (28.9%) angles of the distal border of the navicular bone. There was no increased probability of being categorized as lame if a fragment was present. There was no significant difference in fragment volume across lameness severity categorizations. Confidence intervals indicated a slightly increased probability of being classified as lame if both medial and lateral fragments were present. Findings indicated that distal border fragments of the navicular bone in equine MRI studies are unlikely to be related to existing lameness.

Use of intravenous gadolinium contrast in equine magnetic resonance imaging.

The use of intravenous gadolinium contrast during equine magnetic resonance imaging (MRI) is a new technique that has been infrequently used in clinical imaging. This article describes the development of an effective contrast dose and the use of gadolinium contrast in clinical equine MRI. Gadolinium contrast improves lesion conspicuity across a broad range of lesion types. Contrast-enhanced MRI is potentially a valuable imaging tool in the assessment of the equine athlete.

Comparison of radiography, nuclear scintigraphy, and magnetic resonance imaging for detection of specific conditions of the distal tarsal bones of horses: 20 cases (2006-2010).

OBJECTIVE: To describe pathological findings identified with MRI in the distal tarsal bones of horses with unilateral hind limb lameness attributable to tarsal pain and to compare the usefulness of MRI with that of radiography and nuclear scintigraphy in evaluation of this region. DESIGN: Retrospective case series. ANIMALS: 20 lame horses. PROCEDURES: In all horses, MRI, radiography (4 standard projections), and nuclear scintigraphy of the tarsus had been performed. Horses were excluded if the results of all 3 imaging modalities were not available or if lameness was detected in more than 1 limb. Pathological changes identified with MRI were cross-referenced with the findings determined with other imaging modalities. RESULTS: Compared with MRI findings, the following lesions were identified with radiography: medullary and subchondral bone sclerosis in 9 of 16 horses, pathological changes related to osseous hyperintensity in 0 of 10 horses, and osteoarthritis in 5 of 8 horses. Standard radiographic projections did not aid in the identification of fracture of the distal tarsal bones (3 horses). Location of increased radiopharmaceutical uptake with nuclear scintigraphy corresponded with the location of pathological changes detected with MRI in all horses. The intensity of the radiopharmaceutical uptake on nuclear scintigraphic images did not correspond with the severity of the pathological changes identified with MRI. CONCLUSIONS AND CLINICAL RELEVANCE: Radiography was unreliable for the detection of pathological changes related to osseous hyperintensity identified with MRI, fracture, and subchondral bone sclerosis in the equine tarsus. Nuclear scintigraphy was effective in localizing pathological changes, but MRI provided superior anatomic detail.

Evaluation of three miniplate systems for fracture stabilization in pigeons (Columba livia).

Bone plates are rarely used in avian fracture management for several reasons, and until recently, there was no plating system considered appropriate for use in birds with a body mass less than 500 g. To evaluate 3 different miniplate systems in avian fracture repair, 3 groups (A, B, and C) of 6 pigeons (Columba livia) each were used. The left ulna and radius of the pigeons were transected, and the ulna was stabilized. In group A, a 1.3-mm adaption plate was used. In group B, a limited contact system was created with washers that were placed between a 1.3-mm adaption plate and the bone. The intention was to reduce the compression of the periosteum and vascular damage to the bone. In group C, a 1.0-mm maxillofacial miniplate was used. Healing was evaluated with radiographs after 14 and 28 days. A flight test was conducted on day 28; the birds were then euthanatized, and the wing was dissected. Birds in group A with the adaptation plate achieved the best flight results (100%). In group B birds, no effect of the limited contact concept was visible at necropsy, and a high percentage of the screws had loosened, leading to failure (33%). The maxillofacial miniplates of group C birds were too weak and bent (100%). These results indicate that the adaption plate 1.3 met the desired requirements. To improve the system, further trials, with smaller drill bits and with screws having a smaller thread pitch, are recommended.

Magnetic resonance imaging of acquired trigeminal nerve disorders in six dogs.

The medical records and magnetic resonance (MR) images of dogs with an acquired trigeminal nerve disorder were reviewed retrospectively. Trigeminal nerve dysfunction was present in six dogs with histologic confirmation of etiology. A histopathologic diagnosis of neuritis (n=2) or nerve sheath tumor (n=4) was made. Dogs with trigeminal neuritis had diffuse enlargement of the nerve without a mass lesion. These nerves were isointense to brain parenchyma on T1-weighted (T1W) precontrast images and proton-density-weighted (PDW) images and either isointense or hyperintense on T2-weighted (T2W) images. Dogs with a nerve sheath tumor had a solitary or lobulated mass with displacement of adjacent neuropil. Nerve sheath tumors were isointense to the brain parenchyma on T1W, T2W, and PDW images. All trigeminal nerve lesions enhanced following contrast medium administration. Atrophy of the temporalis and masseter muscles, with a characteristic increase in signal intensity on T1W images, were present in all dogs.