Recent research at Louisiana State University Veterinary Teaching Hospital in The Department of Comparative Biomedical Sciences focused on the use of MRIs to diagnose septic arthritis in foals with septicemia.
Advantages of MRI use for foal diagnosis
Because magnetic resonance imaging is the current standard in imaging the distal extremity in adult horses, the researchers performed this study to assess the use of MRIs for diagnosing the distal extremities of foals with septicemia.
Septicemia and its secondary complications, such as septicarthritis and osteomyelitis, remain a common, often severe,rapidly progressive clinical problem in neonatal foals.
Although radiography is often used, it has limited ability to detect early bony changes. Because magnetic resonance imaging is the current standard in imaging the distal extremity in adult horses because it allows assessment of the cartilage, subchondral bone and bone marrow cavity, as well as the joint capsule and surrounding ligaments, the researchers performed this study to assess the use of MRI's for the distal extremity of foals.
The purpose of this original study was to establish the MRI protocols for the extremities in foals and describe the MRI findings associated with septic arthritis. Researchers hypothesized that the use of MRI would be more sensitive for the presence and extent of osteomyelitis and joint effusion than radiography, and that MRIs would have the ability to show cartilage damage, which is not possible with radiography.
Diagnostic methods used for foals
- Affected septic arthritis group: Foals less than 6 months of age with distal extremity joint pain, heat, swelling, lameness and fever, and a joint fluid analysis positive for inflammation of either the fetlock, carpus or tarsus and diagnosed clinically with sepsis.
- Control group: Foals less than 6 months of age negative for septic arthritis.
- Distal extremity joints were scanned in a 1.5T magnet (Hitachi Echelonâ¢) with a human knee coil. Foals were scanned under general anesthesia with client consent. Cadaver limbs from foals humanely euthanized for reasons unrelated to this study were scanned within 24 hours of euthanasia.
- Routine radiographic exams were performed on each joint.
- All images were examined by a board-certified radiologist.
The MRI and radiographic findings were compared for both groups of foals.
Results of research using MRI in diagnosing foals with septicemia
- A total of 10 foals (six live, four cadaver) for a total of 23 joints were included in the study. Ages ranged from 1.5 weeks-16 weeks.
- Five of the 10 septic joints (three foals) had bony abnormalities not present in controls.
- Tenosynovitis was detected as sheath effusion with a heterogeneous intensity on T2 weighted (T2W) and Proton Density (PD) sequences in the long and common digital extensor tendon in one affected foal with no bony lesions.
What researchers learned in their study of foals
- Epiphyseal, physeal, metaphyseal, articular and subchondral bone signal abnormalities were detected in five out 10 affected joints of septic foals that could not be detected radiographically prior to MRI exam.
- A hyperintense zone surrounded by a hypointense halo in affected foals is similar to the MRI characteristics of osteomyelitis in humans.
- The increased hyperintense signal indicates an active lesion, and the areas of decreased hypointense signal indicate a non-active lesion, most likely sclerosis or necrosis.
- Joint lavage performed prior to MRI could contribute to the presence of joint distention and mixed signal and amorphous appearance within the joint in some foals. However, the same findings were present in two foals without prior joint lavage. Fibrous adhesions are likely responsible for this finding.
- MRI is more sensitive than radiography in the detection of early bony lesions due to osteomyelitis and of articular involvement within the joints in the distal extremities of foals diagnosed clinically with septic arthritis.
- Further investigation is warranted to examine a larger population to determine the prognostic value of the presence of MRI abnormalities in the joints of septic foals.
- MRI may represent a new âone imagingâ modality for septic foals in the future.