A 2 yr old male mixed-breed dog presented limping on a forelimb. Soft tissue swelling was minimal, but there was a definite soft tissue injury to the skin distally that appeared acute.Radiographs were made of the antebrachium. What is the diagnosis? The radiographic diagnosis is a destructive lesion with marked cortical destruction in the distal radius cranially and medially. The radiocarpal joint is luxated (arrow) and there is poorly identified injury to the distal radius laterally. A general soft tissue injury is present without any pattern of air within the soft tissues. A pattern of shadows of increased density is superimposed over the distal antebrachium. The ulna appears unaffected. In addition, a radiopaque object is present in the soft tissues cranial to the elbow joint without any associated changes in the elbow joint. What is the etiology of the lesion? Consider the following possible etiologiesCongenital and developmental - these lesions usually are characterized by an error in bone development. The marked bony destruction with bone fragments makes this etiology unlikely Nutritional/metabolic - these lesions are usually generalized, are polyostotic and often symmetrical. This lesion is focal in one bone making this etiology unlikelyTraumatic - the presence of well identified bone fragments plus the radiocarpal joint injury suggests this as a possible etiology - however, what would cause a comminuted fracture of this type in only bone and leave the adjacent bone unaffected - could this be a pathologic fracture through a bone tumor? - how does the pattern of soft tissue density influence the etiology?Infectious/inflammatory - these lesions are usually characterized by periosteal or reactive new bone with underlying focal destructive lesion(s) - the absence of any secondary bony production tends to rule this etiology unlikelyNeoplastic - most neoplastic lesions are destructive with a pattern of reactive new bone that can be minimal or marked - the pattern of acute cortical destruction supports a primary bone tumor originating from the medullary cavity - however, no reactive new bone is present Degenerative - most degenerative lesions involve a joint with presence of an arthrosis - this lesion affects the radiocarpal joint but the primary lesion is definitely within the distal radius with secondary injury to the adjacent joint How should the pattern of soft tissue density influence the diagnosis?How does the single radiopaque object adjacent to the elbow influence the diagnosis?The radiographic diagnosis is a gunshot wound from a high energy bullet that caused the comminuted radial fracture and then exited the limb - the bullet left minimal metallic evidence within the soft tissues of the bullet tract - the injury is typical in that in addition to the fracture it caused cavitation within the soft tissues with subsequent collapse that caused injury to the radiocarpal joint that is distant from the bullet tract - the maximum diameter of this temporary cavity may be approximately 30 times the size of the original missile track - therefore, tissues at a distance from the original wound may be damaged and adjacent bones may be injured without having been struck directly by the missile or any secondary bony fragment - the absence of any reactive new bone plus the presence of sharply defined bony fragments tells of the acute nature of the lesion.The presence of the airgun pellet adjacent to the elbow joint may complicate the radiographic diagnosis - however, the airgun pellet is not related to the acute injury from the bullet and has no clinical importance - the airgun pellet is probably an old lesion and only suggests the nature of the society in which the dog lives interestingly, the owners chose not to have the patient treated which sometimes suggests something concerning the circumstances of the injury - the additional use of oblique views would have made evaluation of the injury easier.
