Multiple open wrist fractures and dislocation of the distal radioulnar joint from a dog bite injury.

Dogs are commonly kept as household pets, but sometimes pet dogs bite people. We report the case of a 69-year-old man who was bitten by his pet pit bull terrier. The dog bite resulted in multiple open wrist fractures and dislocation of the distal radioulnar joint, requiring surgical debridement, open reduction and internal fixation, and bone grafting. CT of the fractures showed that the dog's maxillary canine teeth had been deeply embedded in the hamate and second metacarpal bones, requiring that the dog's mouth be opened and the teeth disengaged in order to remove the injured limb from the dog.

Introduction

Dogs are commonly kept as household pets. An estimated 68% of US households owned pets in 2017, including 89.7 million dogs [1]. Sometimes, pet dogs bite people, most frequently their owners, household members, or friends. We report the case of a dog bite that caused multiple open wrist fractures and dislocation of the distal radioulnar joint.

Case report

A 69-year-old man presented following dog bite injuries sustained when he attempted to separate 2 pet pit bull terriers fighting with each other in his home. This action resulted in one of them clamping its mouth around his left wrist from the radial side and biting. Reportedly, the patient was unable to dislodge the dog from his wrist for some time. No further details were available regarding the incident or the dogs. At the time of transfer to the medical center, the patient's vital signs were normal. It was determined that his injuries were restricted to the left upper extremity. He had received an initial bolus of antibiotics and tetanus prophylaxis was found to be current. Physical examination showed multiple bite lacerations of the left wrist and forearm. His left hand was neurovascularly intact. Initial radiographs showed a comminuted, impacted open extra-articular fracture of the distal radial metaphysis, with dislocation of the distal radioulnar joint and avulsion fracture of the ulnar styloid process (Fig. 1). Carpal bone fractures were also identified involving the body of the hamate and the triquetrum, and there was also a fracture of the base of the second metacarpal. Noncontrast CT was performed for further evaluation (Fig. 2), confirming the radiographic findings. The penetrating fractures of the body of the hamate and of the base of the second metacarpal have a shape that corresponds to the shape of the maxillary canine teeth, with penetration through the dorsal cortex but not completely through the bones (Fig. 3). The morphology of the distal radial metaphyseal suggests a combination of crushing and shear, perhaps as the dog shook its head and the patient attempted to detach the dog's mouth from his wrist. The dislocation of the distal radioulnar joint and the avulsion fracture of the ulnar styloid process would be consistent with this injury mechanism, and the overall combination of findings is consistent with the animal biting from the radial side of the wrist (Fig. 4). The patient was taken to the operating room where the soft tissue wounds were irrigated and debrided. There were no tendon lacerations. The radius fracture underwent open reduction and internal fixation with placement of an antibiotic-eluting spacer. The hamate fracture with stabilized by percutaneous pins (Fig. 5). Subsequent surgery was performed to remove spacer and fill the void with bone graft. The patient recovered uneventfully.

Fig. 1

A 69-year-old man with dog bite injury of wrist. Wrist radiographs in PA (A), lateral (B), and scaphoid (C) projections show a highly comminuted extra-articular open fracture of the distal radial metaphysis with dislocation of the distal radioulnar joint and avulsion fracture of the ulnar styloid process. There are also fractures of the hamate and base of second metacarpal. Soft tissue gas is present.

Fig. 2

Coronal CT scans of the wrist from dorsal to volar (A)–(E) confirm the radial metaphyseal fractures and the distal radioulnar joint dislocation with avulsion fracture of the ulnar styloid process. There are penetrating fractures of the body of the hamate and base of the second metacarpal.

Fig. 3

Axial CT images through the carpal bones show penetrating fractures of the second metacarpal base (A) and the body of the hamate (B). The direction of penetration is indicated by the white arrows.

Fig. 4

Surface-rendered 3D CT images (A) and (B) show penetrating fractures of the body of the hamate and of the second metacarpal base, as well as the comminuted fractures of the distal radial metaphysis and the dislocation of the distal radioulnar joint. The hypothesized mouth print is indicated by the shadowed area, as determined by the position of the canine penetrations.

Fig. 5

PA (A) and lateral (B) wrist radiographs following treatment. The distal radius fracture has been reduced and internally fixed; the distal radioulnar joint has been reduced; the hamate fracture has been pinned across the fifth CMC joint.

Discussion

Dog bites are common injuries, with an annual incidence estimated at 1.5% of the general population; only 19% of the injuries were severe enough for the victims to seek medical care [2]. Fatalities are rare but often preventable and mostly involve young children [3]. Of dog bite injuries that resulted in ER visits by persons over 15 years of age, injuries to the extremities accounted for 86.2% [4]. Injury diagnoses that included fracture/dislocation comprised only 0.4% of all ED visits for dog bite injuries [4]. Fractures from dog bites appear to be relatively uncommon in the literature; a clinical series of 1616 dog bite injuries in children (under age 18) reported only 4 patients whose treatment included open reduction and internal fixation of fractures (humerus, mandible, radius, and phalanx). The ages of the patients and the exact locations of the fractures were not identified; there was also no enumeration of fractures that were not treated surgically [4]. In a series of 4 dog bites by police dogs, 1 patient had open comminuted transverse fractures of the distal ulna, a cortical violation of the tibia, and soft tissue injuries, and another had nondisplaced fractures of the scaphoid and triquetrum in addition to other soft tissue injuries and gunshot wounds from the human officers [5].

American pit bull terriers are medium-sized dogs with a brachycephalic skull (the width is similar to length) [6]. As a consequence, the 42 permanent teeth are more crowded together than in dogs with longer skull types. The normal adult dog has 42 teeth, 22 on the maxilla, and 20 on the mandible. The maxillary teeth are comprised of 6 incisors, 2 canines, 8 premolars, and 6 molars; the mandibular teeth are comprised of 6 incisors, 2 canines, 8 premolars, and 4 molars. The canines are fang-like, long and pointed, and when the mouth is closed, the mandibular canines lock in front of the maxillary canines in a scissor bite. The molars are used for chewing on bones or similar hard objects. Bite force is higher in larger dogs because of the larger muscles, and in brachiocephalic dogs because of their teeth are less spread apart. [7]. Bite force at the canine teeth is generally less than at the molars because of the greater distance of the anterior portion of the mouth from the muscles of mastication [8], but the application of that force at the tip of a pointed tooth could allow it to fracture the cortex of trabecular bone and penetrate into the medullary space. If the canine teeth have penetrated the victim's bone, as it our case presentation, it would no longer be possible to detach the dog from the limb without opening its mouth and disengaging the canine teeth from the bone. Attempts to shake the dog off the limb or pull the limb away from the dog would be fruitless. This mechanism could also explain how a fictional character in Carl Hiaasen's classic novel, Double Whammy, could meander through the plot with the severed head of a biting pit bull attached to his non-dominant upper extremity [9].