History

A 4-year-old 38.4-kg castrated male Labrador Retriever–Poodle cross was presented to Texas A&M University’s Small Animal Emergency Service because of left thoracic limb lameness. The dog was initially presented to another emergency clinic 4 weeks prior due to licking at the left carpus and favoring the left forelimb. The left carpus was clipped, and a circumferential wound was identified and treated with hydrotherapy, bandage changes, cold laser therapy, and two 1-week courses of clindamycin over that month. The week prior to presentation at our hospital, the dog became non–weight-bearing on the limb. On initial examination at our referral hospital, the dog was bright and alert with vital signs within normal limits. There was a firm, painful swelling over the left distal antebrachium proximal to the carpal joint, and a circumferential dermal scar with a soft, fluid-filled area on the caudomedial aspect of the scar. There was no open draining tract. The dog was non–weight-bearing and knuckling on the left forelimb on gait examination. On neurologic examination, the dog had an absent withdrawal, marked muscle atrophy, and no appreciable deep pain distal to the carpus in the left thoracic limb. Baseline bloodwork showed a mild leukocytosis (WBC count, 17.5 X 10³ WBCs/µL; reference range, 6 X 10³ to 17 X 10³ WBCs/µL), mature neutrophilia (14.35 X 10³ neutrophils/µL; reference range, 0.3 X 10³ to 11.5 X 10³ neutrophils/µL), and mildly elevated globulins (4.1 g/dL; reference range, 1.7 to 3.8 g/dL). All other results were within reference ranges. Radiographic images of the left antebrachium (Figure 1) and stressed and flexed radiographic views of the left carpus were obtained.

View Full Size

Left dorsopalmar (A) and lateral (B) carpal radiographic images of a 4-year-old 38.4-kg castrated male Labrador Retriever–Poodle cross referred because of a 4-week history of left thoracic limb lameness.

Citation: Journal of the American Veterinary Medical Association 261, 8; 10.2460/javma.23.03.0169

• Download Figure
• Download figure as PowerPoint slide

Diagnostic Imaging Findings and Interpretation

Left carpal radiography revealed a defined, radiolucent, nearly circumferential groove in the cortices of the distal aspects of the radius and ulna with an associated smooth periosteal reaction and soft tissue swelling (Figure 2). Flexed and stressed left carpal radiographic images were unremarkable (not shown). Differential diagnoses for the boney changes of the left radius and ulna included a strangulating lesion, incomplete, chronic transverse fracture, or osteomyelitis. Musculoskeletal ultrasonography of the lesion revealed a periosteal reaction with a central fissure parallel to the dermal scar. Within the fissure, a linear, hyperechoic object approximately 1 mm thick was identified running perpendicular to the musculoskeletal structures and able to be traced nearly circumferentially around the limb (Figure 3). There was focal compression of the radial artery by the foreign material with an intramural thrombus. Caudally, the foreign object was deep to the superficial digital flexor tendon. The tendons of the superficial digital flexor, flexor carpi ulnaris, and extensor tendons were moderately to severely enlarged, heterogenous, and irregularly marginated. There was variable loss of normal muscle fiber architecture both proximal and distal to the hyperechoic material and focal echogenic fluid pockets along the dermal scar.

View Full Size

Same images as in Figure 1. A defined, radiolucent groove (arrowheads) and periosteal reaction (arrows) are present nearly circumferentially around the distal aspects of the radius and ulna. There is associated soft tissue swelling around the distal antebrachium.

Citation: Journal of the American Veterinary Medical Association 261, 8; 10.2460/javma.23.03.0169

• Download Figure
• Download figure as PowerPoint slide

View Full Size

Sagittal (A) and transverse (B) ultrasonographic images of the central groove in the region of periosteal reaction (arrowheads) on the dorsal distal aspect of the left radius showing the hyperechoic, shadowing, linear foreign body (arrows) present within the groove. C—Transverse image of the presumed superficial digital flexor and flexor carpi ulnaris tendons (between the white crosses) caudal to the radius. The foreign object (arrow) can be seen to the right of the image. The caudal cortical margin of the radius (arrowhead) is at the bottom of the image. The disorganization and hyperechogenicity of the fibers indicate marked chronic tendinopathy. D—Longitudinal image of the presumed radial artery showing the foreign body (arrow) causing focal compression and a region of internal hyperechogenic material (between the white crosses) representing intramural thrombus.

Citation: Journal of the American Veterinary Medical Association 261, 8; 10.2460/javma.23.03.0169

• Download Figure
• Download figure as PowerPoint slide

Treatment and Outcome

A surgical exploration was performed and identified an intact, elastic foreign body deep to the dermal scar. The elastic band was in contact with the radius and ulna medially and laterally. Flexor tendons were visibly thickened and irregular with no normal tendons or transected tendon ends identified. After lavage, a piece of tissue and sterile swab were submitted for aerobic and anaerobic bacterial culture. The dog remained in the hospital for 2 days postoperatively with daily bandage changes. The dog received methadone (0.1 mg/kg, IV, q 8 h), cefazolin (22 mg/kg, IV, q 90 min perioperatively), and crystalloid IV fluid therapy the day of surgery before being transitioned to carprofen (2 mg/kg, PO, q 12 h) and cephalexin (26 mg/kg, PO, q 12 h) the day after surgery. A caudal splint was placed for 2 weeks postoperatively and then downgraded to a fitted carpal brace to provide support for potential injury to the flexor tendons. Intraoperative cultures yielded no strict anaerobes, 1+ growth of Pasteurella dagmatis, and 2 contaminants. Cephalexin was continued for 15 days based on the culture and susceptibility results. The owner identified the foreign material as an elastic hair tie used by their young daughter. At the 1- and 2-week postoperative rechecks, the dog was bearing weight well with the splint in place and was toe touching when the splint was removed. At 10 weeks postoperatively, the dog had a grade 1 to 2/5 left forelimb lameness (similar with and without a brace in place), decreased range of motion of the left carpus, and marked thickening just proximal to the left carpus. The owners reported that the dog was doing well at home and able to go on long walks without signs of pain.

Comments

Reports of subcutaneous rubber band foreign bodies in the veterinary literature are rare. There are several reports in the human literature, particularly in children, which has been referred to as rubber band syndrome (RBS).¹ The rubber band can migrate through the skin and subcutaneous tissues over months to years, which results in swelling at the level of, or distal to, the constriction. In later stages, the constriction can affect the neurovascular structures, resulting in pain and loss of function of the distal extremity.¹ There is a similar case report² in a young cat that was presented with a 6-month history of waxing and waning swelling of the distal antebrachium, draining tract, and circumferential dermal scar. Radiography of the affected limb showed concentric osteolysis with mild periosteal proliferation. An elastic band was removed during surgical exploration.² In humans, the hallmark presentation is a circumferential dermal scar with a draining tract.¹ These clinical signs are consistent with the few case reports in veterinary medicine, including the present case. The rubber band’s migration through the skin and subcutaneous tissue occurs slowly and appears relatively painless in children until the neurovascular structures are affected.¹ This differs from osteomyelitis, which tends to be painful.

In chronic cases where the band is in contact with bone, there may be a “constriction sign” visible on radiography, with circumferential osteolysis and periosteal reaction.² Periosteal reaction in the distal limbs of dogs can be classified in terms of their extent (monostotic or polyostotic), their location on the bone, and the radiographic appearance of the lesion. In this case, a focal area near the distal radial metaphysis was affected. Differential diagnoses include a strangulating lesion, incomplete, chronic transverse fracture, or osteomyelitis. However, osteomyelitis would be expected to have characteristics of an aggressive bone lesion, such as cortical or medullary destruction, irregular margins of the periosteal reaction, or an indistinct zone of transition between the periosteal reaction and normal cortical bone, none of which were present in this case.

The presence of a well-defined, thin, linear radiolucent groove within the periosteal reaction was a highly unusual finding. Periosteal reaction around chronic foreign material near long bones is commonly seen with metallic surgical implants, which has been described radiographically in dogs.³ Whereas metallic foreign bodies are easy to identify on radiography, wooden or plastic foreign bodies have similar radio-opacity to soft tissue and can often only be identified by their effect on surrounding structures or additional imaging modalities. In abdominal imaging, ultrasonography can be a sensitive and specific diagnostic for identification of linear foreign bodies, such as rubber bands, hair ties, or string, within the gastrointestinal tract.⁴ Musculoskeletal ultrasonography has been used to identify radiolucent foreign bodies in the limbs of horses⁵ but is less frequently used in companion animals. This report illustrates the usefulness of musculoskeletal ultrasonography in a small animal patient for identification of a radiolucent foreign body. Additionally, sonographic evaluation of the soft tissues in the region of the foreign body aided in noninvasive characterization of damage to regional musculotendinous and vascular structures.

In the present case, it is unknown how long the rubber band had been present on the distal antebrachium, but the migration deep to the flexor tendons suggests at least a several-month history. This case highlights the importance of closely examining the skin surrounding an area of swelling in a companion animal, including clipping the fur. Rubber band syndrome should be considered as a differential diagnosis in companion animals presenting for a circumferential swelling and wound or scar even if the patient does not have an open draining tract or overt signs of pain. In these cases, radiography and ultrasonography have characteristic findings that support a diagnosis of RBS. A hyperechoic structure running perpendicular to the musculoskeletal structures in the distal antebrachium should raise concern for RBS. With surgical removal, children and companion animals have a good prognosis and return to normal function, especially with early intervention.