LA Radiology Overview

Case reveal

Findings:

Within the distal epiphysis of the radius extending proximally to the level of the distal physis, there is severe moth-eaten osteolysis identified. The surrounding trabecular bone is sclerotic. A mild amount of ill-defined decreased mineral opacity is present within the medial aspect of the distal radial metaphysis, adjacent to the physis, with a minimal amount of periosteal proliferation adjacent to the medial aspect of the physis.
Circumferentially surrounding the carpus, the soft tissues are severely thickened, with multiple gas bubbles in the soft tissues on the medial aspect of the distal radial diaphysis.

Summary

Aggressive distal radial epiphyseal, physeal and probable distal metaphyseal lesion and severe soft tissue swelling. The gas bubbles within the medial soft tissues may be iatrogenic secondary to arthrocentesis, or from gas producing bacteria.

Conclusion

Septic physitis and epiphysitis with secondary septic arthritis.

A little bit more…

Septic arthritis in the foal can be cause from a periarticular wound infection, inoculation of the joint by a puncture wound, or by hematogenous inoculation. The hematogenous route is the most common, and bacteremia and septicemia are the most common risk factor, often due at failure of transfer of passive immunity.
Blood supply to the metaphysis is provided by the nutrient artery, however, in young foals exist transphyseal vessels that connect the metaphyseal and epiphyseal blood supply. This connection allows bacteria located preferentially in the synovial membrane and subchondral bone.

art — Figure 1. Illustration of the arterial blood supply to an equine neonatal joint showing the relationship between the nutrient artery, the synovial capillary network, and the epiphyseal vessels (Hardy, 2006).

There are four types of hematogenous articular infection described:
- Type S or synovial: resulting from inoculation of the synovial membrane without bone involvement.
- Type E or epiphysis: infection of the subchondral bone
- Type P or physis: infection of the physis on the metaphyseal side if the growth plate is identified
- Type T in premature foal where infection of the small tarsal or carpal bone is seen.

Figure 2. Possible routes of bacterial inoculation of a joint: A, B, and C are hematogenous, resulting in synovial membrane infection (A), epiphyseal infection (B), and physeal infection (C). In C, the joint capsule attachment includes the physis; therefore, inoculation of the physis will result in septic arthritis. If the physis is extra articular, then septic arthritis does not always occur concurrently to septic physitis. (D) Joint inoculation from a puncture wound. (E) Joint inoculation from a contiguous soft tissue infection (Hardy, 2006)

The more common types in young foal are S and E. Metaphyseal infection occurs in older foals because of the closure of transphyseal vessels occurs after 7-10 days old. Multiple joint involvements are common.
The more common organism isolated from perinatal foal are: Actinobacillus sp, E. coli, Klebsiella sp, Pseudomonas sp, and Salmonella sp. In older foals, is more common Gram-positive organisms such as Streptococcus sp.
Bone involvement may include osteitis, osteomyelitis, physitis, osteoarthritis, or fracture that communicates or is related to the affected joint.
Contrast radiography, such as fistulograms and contrast arthrography, can be used to help determine communication of a wound with a neighboring joint or can help to identify cartilaginous defects not seen on routine radiographs.
Cartilage or bone involvement negatively influences the prognosis and necessitates more aggressive surgical treatment.

References

Diagnosis and treatment of septic arthritic. Morton, A.J. (2005) Vet Clin equine Vol 28, pp627-649.
Etiology, diagnosis and treatment of septic Arthritis, Osteoitis, and Osteomyelitis in foals. (2006) Clin Tech Equine Pract 5:309-317.
The normal and abnormal equine neonatal musculoskeletal system. Levine, D. (2015) Vet Clin Equine Vol 31, pp601-613.