A 3-year-old spayed female Labrador Retriever was brought to the Veterinary Teaching Hospital at Washington State University with a history of progressive left forelimb lameness of > 1 year's duration. Previously, at 10 months of age, the dog had a long oblique proximal ulnar fracture and radial subluxation of the left antebrachium following an unwitnessed traumatic event. The ulnar fracture was repaired with a Steinmann intramedullary pin and a single cerclage wire. Because the present owner was not the original owner, it was unknown whether the dog had developed or retained a left forelimb lameness after the fracture healed. At 15 months of age, the dog was shot with a lead-based bullet in the left elbow. The dog was adopted by the present owner 9 months after the shooting incident, and the circumstances surrounding the injury, including the type of firearm, nature of the bullet, or treatments administered, were not explained by the previous owner to the new owner. At some point between being shot and being adopted by the new owner, the intramedullary pin had been removed. The circumstances and rationale for its removal were unknown. The dog had a left forelimb lameness when it was acquired by the new owner, and in the year since the dog was acquired, the lameness had progressed in severity. The lameness was exacerbated by exercise and progressed from weight bearing to non–weight bearing after walking approximately 1 city block.
The dog appeared to be alert with normal mentation, weighed 31.7 kg (69.7 lb), and was judged to be moderately overweight (body condition score, 4/5). The dog stood with the left elbow abducted and the right elbow in a normal position. There was a moderate weight-bearing left forelimb lameness at a walk and trot. After a short period during the gait evaluation, the lameness progressed from weight bearing to intermittently non–weight bearing. Moderate joint effusion and crepitus were detected during palpation of the left elbow joint, and the dog resisted elbow joint extension.
A firm subcutaneous mass was palpable on the caudal aspect of the left antebrachium between the proximal and middle thirds of the ulna. This was presumed to be a fibrous tissue callus surrounding the ulnar cerclage wire. There were no other abnormal findings on the physical examination.
The dog was sedated with acepromazine (0.05 mg/kg [0.023 mg/lb], IV) and butorphanol (0.2 mg/kg [0.09 mg/lb], IV) for bilateral orthogonal-view radiographic examination of the elbow joints. Mediolateral and craniocaudal views of the left elbow joint revealed multiple metallic fragments in and around the joint space (Figure 1). Progression of osteoarthritis in the 21-month interval since the initial shooting injury was present as osteophyte formation on the head of the radius, the proximal joint margin of the olecranon, and the medial and lateral aspects of the distal portion of the humerus. Radiographs of the right elbow were interpreted to be normal. The dog's PCV and plasma total protein concentration were 50% and 7.8 g/dL, respectively.
Craniocaudal and mediolateral radiographic views of the elbow joint of a dog with lead arthropathy. Notice the 7- to 9-mm bullet fragment in the joint space in the preoperative views (A and B), which is absent in the postoperative views (C and D).
Citation: Journal of the American Veterinary Medical Association 232, 6; 10.2460/javma.232.6.886
The dog was anesthetized for arthroscopic examination of the left elbow joint. Bupivacaine (3 mL; 0.5% solution) was instilled into the area of the left brachial plexus for local analgesia. Carprofen (4.4 mg/kg [2 mg/lb], SC) was administered before surgery.
The left elbow was aseptically prepared, and arthroscopy was performed with a 10-cm, 30° fore oblique, 2.3-mm arthroscope.a A caudomedial arthroscopic portal was used to explore the elbow joint. Moderate synovial hyperplasia and hyperemia were noted. Multiple full-thickness articular cartilage erosions were seen involving the trochlea of the humerus and the ulnar trochlear notch. The areas void of articular cartilage were surrounded by fibrillated cartilage. Pinpoint dark objects, presumably metal fragments, were visible adhered and incorporated into the proliferative synovium. The anconeal process and medial side of the medial coronoid process appeared normal. A 7- to 9-mm bullet fragment (measured via radiographs) was observed in the lateral compartment of the elbow joint (Figure 2). Although the fragment was freely moveable when manipulated with a right angle probe, its size prevented movement through the humeral-ulnar articulation into the medial compartment of the elbow joint. Adjacent articular cartilage erosion and fibrillation suggested local mechanical trauma induced by the fragment.
Arthroscopic image of an intra-articular lead bullet fragment in a dog's elbow joint. The bullet fragment (center) can be seen between the humerus (H) and the trochlear notch of the ulna (TN). * = Right-angle probe.
Citation: Journal of the American Veterinary Medical Association 232, 6; 10.2460/javma.232.6.886
A craniomedial instrument portal was used to aid in removing the bullet fragment. The fragment was soft and fragmented further when grasped, which necessitated removing the fragment in multiple sections. Fibrin and hyperplastic synovium were removed with a mechanical shaver. Microfractures were created in exposed subchondral bone with a micropick and mallet in an attempt to stimulate neovascularization and fibrocartilage formation. The joint was thoroughly lavaged with lactated Ringer's solution. Radiography performed immediately after surgery confirmed the removal of an intra-articular metal fragment but revealed the continued presence of periarticular and intraosseous metal fragments (Figure 1).
The dog received cefazolin (22 mg/kg [10 mg/lb], IV, q 90 min) during the surgery and polysulfated glycosaminoglycanb (4.4 mg/kg, SC) immediately after surgery. A cold compress was applied to the elbow for 10 minutes and a soft bandage was placed and left for 24 hours to minimize swelling after surgery. The dog was discharged the following day with instructions for the owner to assist with passive range-of-motion exercises (gentle repeated flexion and extension), restrict exercise, and gradually increase low-impact exercise (slowly increasing walks) over the course of 4 weeks.
Follow-up assessments were performed via telephone reports from the owner. Four weeks after surgery, the owner reported that there was a marked improvement in the lameness. It was also reported that the dog continued to bear weight on the limb for the entire length of walks allowed during the period (approx 8 blocks distance). Four months after surgery, the owner reported further improvement, describing a subtle lameness that was noticeable only after prolonged exercise.
Discussion
Reports of intra-articular foreign bodies in dogs are rare and include the removal of a canine tooth crown from a dog's elbow joint via arthrotomy1 and the ultrasonographic detection of an intra-articular porcupine quill that was subsequently retrieved from a dog's elbow joint during necropsy.2 Radiolucent intra-articular foreign bodies are difficult to diagnose radiographically, and radio-opaque foreign bodies can be difficult to localize accurately as intra-articular versus periarticular. Arthroscopy is therefore a good method of diagnosing as well as treating intra-articular foreign bodies because it provides superior inspection of the joint space, foreign material, and damage to intrasynovial structures, compared with radiography and ultrasonography.
Current literature suggests that the presence of intra-articular lead results in direct chemical toxicosis as well as mechanical trauma. Reports in human literature describe a delay of several years for the clinical signs of arthritis to develop after the initial healing of a gunshot wound to a joint. Humans frequently have radiographic, gross, histologic, and ultrastructural evidence of subsynovial lead accumulation.3–8 Over time, the radiographic appearance of a joint progresses to form a so-called lead arthrogram, in which the joint capsule is diffusely radio-opaque, which completely obscures the joint. On the basis of the findings in a case series of 3 humans with lead arthropathies and subsynovial lead accumulation, it was hypothesized that lead fragments may be dissolved by synovial fluid over time.3 Histologic and ultrastructural examination of 2 lead arthropathy cases resulted in the findings of intracellular accumulations of lead, calcium, and phosphorus complexes in the mitochondria of macrophages, osteoclasts, and synoviocytes, as well as extracellular incorporation of the same accumulations in subsynovial interstitium and newly forming trabecular bone.5 Trabecular bone with lead accumulations had abnormally sparse osteoclastic activity as well as focal areas of necrosis. These findings led the authors to conclude that there was a direct toxic effect of lead on the cells of joint tissues. In experimentally induced lead arthropathy in which lead cylinders were implanted into rabbit femoral condyles such that they would not mechanically interfere with joint motion, investigators found a higher degree of osteoarthritis than in control rabbits with stainless-steel implants.9,10 Because of direct chemical toxicosis, it is recommended to remove any lead exposed to synovial fluid even if it does not mechanically interfere with motion.
Although intrasynovial bullet fragments are frequently reported in human literature, there are no such specific reports in dogs. In a previous report of a lead pellet found in the pastern of a horse with a 6-month history of lameness, there was no mention of radiographic signs of subsynovial lead accumulation (lead arthrogram), but extensive black granular pigment in the synovium was detected histologically.11 Radiography of the dog in this report did not reveal a lead arthrogram. However, in comparing the radiographs obtained directly after the gunshot wound and 21 months later, there was dispersal of metallic densities within and around the joint over time. This dispersal pattern could have been caused by mechanical erosion of soft tissue by the bullet fragments and the subsequent lodging of fragments into these erosions. Whether this dispersal pattern was also attributable in part to synovial dissolution and lead precipitation in the subsynovial tissue is unknown. Although not performed on this case, results of synovial histologic or electron microscopic examination with inspection of the subsynovial tissue for lead may have supported the theory of lead dissolution and subsequent precipitation in this case.
Bullets imbedded in soft tissues are generally not considered a concern regarding systemic lead absorbtion and toxicosis because the foreign material is walled off by fibrous tissue and because lead does not dissolve well in serum (or, presumably, extracellular fluid). Exceptions are in cases of lead bathed in CSF or synovial fluid. There are numerous reports5,6,8 of systemic lead toxicosis secondary to intra-articular lead in humans. There are no such reports in the veterinary literature. In a recent clinical report8 involving a man with symptoms of systemic lead toxicosis who had a gunshot wound to the right elbow joint 6 years prior, serum lead concentration was high (143 μg/dL [reference range, < 10 μg/dL]) and synovial fluid lead concentration was > 1,000 μg/dL. The dog in this report did not have a clinical history or clinical signs suggestive of systemic lead toxicosis, but a CBC with morphologic evaluation of RBCs, serum lead concentration, and synovial fluid lead concentration would have helped to determine whether subclinical lead toxicosis was present secondary to intra-articular lead.
The dog reported here with a lead bullet–induced arthropathy improved clinically following arthroscopic removal of the fragments from the left elbow joint. On the basis of the clinical outcome of this case and information available in the literature, removal of intra-articular foreign material is indicated to reduce mechanically induced articular cartilage damage and synovitis. Lead may cause direct chemical toxicosis to joint tissues and therefore may warrant removal even if the foreign body is not thought to mechanically interfere with joint motion. Intra-articular lead has been reported to cause systemic toxicosis in humans, and this may be an additional reason to remove intra-articular lead foreign bodies in other animals.
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