History
A 9-month-old entire female German Shorthaired Pointer presented with a 2-month history of right forelimb weight-bearing lameness. On physical examination, the dog had a firm, nonmobile swelling (40 X 30 mm) on the right distolateral antebrachium.
Diagnostic Findings and Interpretation
A CT (Aquilion Lightning 160; Canon Medical Systems ANZ Pty Ltd) of both forelimbs captured pre- and postcontrast images in a soft tissue algorithm and precontrast images in a bone algorithm. The bone algorithm of the right limb showed a well-defined bony projection from the distolateral cortex of the radius that projected proximo laterally to penetrate the ulna (Figure 1), resulting in cortical disruption, expansile lysis, and chronic remodeling of the ulna. The bony projection had a distinct cortex and medulla continuous with the underlying radius. The distal ulnar and radial physes were closed. The presumptive CT diagnosis was a distal radial osteochondroma with pressure necrosis and penetration of the adjacent ulna causing expansile lysis and chronic remodeling. The left limb was normal and of equal length to the right and had closed distal ulnar and radial physes.
Computed tomographic images from a 9-month-old entire female German Shorthaired Pointer presenting for a 2-month history of right forelimb lameness and a 2-week history of swelling of the right distal antebrachium. Sagittal (A) and dorsal (B) preoperative CT images show the osteochondroma projecting from the distolateral radius (arrowhead), penetrating the ulna with lytic expansion of the ulna (star). A sagittal (C) CT image shows preoperative surgical planning: distal osteotomy (b) 27 mm proximal from the distal styloid process (a) and proximal osteotomy (c) 35 mm proximal to b. Transverse (D) images show the right (R) and left (L) radius (r) and ulna (u) at comparable levels of cross section with expansile lysis and cortical fracture of the ulna from the penetrating radial osteochondroma (arrowhead). Window width, 2,700 HU; window level, 350 HU; 1-mm slice thickness.
Citation: Journal of the American Veterinary Medical Association 262, 10; 10.2460/javma.24.06.0418
Treatment and Outcome
Ulnar ostectomy and excision of the radial bony projection was planned based on CT measurements (Figure 1). The dog was premedicated with medetomidine (7 µg/kg, IM) and methadone (0.2 mg/kg, IM) followed by induction of anesthesia with propofol (1.5 mg/kg, IV). The dog was intubated and maintained under general anesthesia with isoflurane in oxygen. A radial, ulnar, median, and musculocutaneous nerve block was administered by use of ropivacaine (2.7 mg/kg). Intraoperative medication included acetaminophen (10 mg/kg, IV, q 8 h), fentanyl (1 µg/kg, IV, as needed [PRN]), medetomidine (1 µg/kg, IV, PRN), and cefazolin (22 mg/kg, q 90 min). The dog received lactated Ringer solution at 120 mL/h throughout surgery.
With the dog in left lateral recumbency, the right forelimb was free-draped and covered with antimicrobial adhesive drape (Ioban; 3M Co) and the distolateral ulna was exposed through a skin incision. The periosteum was elevated from the distal ulna; a distal osteotomy 27 mm proximal from the distal styloid process and a proximal osteotomy 35 mm proximal to the distal osteotomy allowed removal of the affected ulnar segment with a sagittal saw. The bony projection was excised from the radial cortex with rongeurs (Figure 2), and the cortical bone was smoothed with a bone burr. Medullary tissue from the ulnar segment was submitted for aerobic bacterial culture and sensitivity testing. The ulnar segment and radial bony projection were fixed in formalin for microscopic examination. Radiographs of the right forelimb taken immediately postoperatively confirmed excision of the radial bony projection and affected ulnar segment (Figure 3).
Medial view of the ostectomized ulnar segment (left) with defect (white arrowheads) from penetrating radial osteochondroma from the dog described in Figure 1. Radial osteochondroma (right): the black arrowhead identifies the origin from the radius, and the star identifies the tip that penetrated the ulna.
Citation: Journal of the American Veterinary Medical Association 262, 10; 10.2460/javma.24.06.0418
Mediolateral (A) and craniocaudal (B) immediate postoperative radiographs from the dog described in Figure 1 show 28-mm ostectomy defect and the location of radial osteochondroma excision (arrow). Mediolateral (C) and craniocaudal (D) radiographs at 45 weeks postoperatively show new bone at the ulnar ostectomy margins (arrowheads) with remaining 28-mm defect and remodeling at the radial osteochondroma excision site with no evidence of recurrence (arrow).
Citation: Journal of the American Veterinary Medical Association 262, 10; 10.2460/javma.24.06.0418
The dog received meloxicam (0.1 mg/kg, IV, q 24 h), acetaminophen (10 mg/kg, IV, q 8 h), trazodone (100 to 200 mg, PO, q 8 h PRN), and methadone (0.2 mg/kg, IV, q 4 h) for 24 hours postoperatively. The dog was discharged the following day with meloxicam (0.1 mg/kg, PO, q 24 h for 10 days) and trazodone (100 to 200 mg/kg, PO, q 8 h PRN).
Aerobic culture did not result in bacterial growth. On microscopic examination, the radial bony projection was composed of trabecular bone with aggregates of crushed necrotic bone intermixed with fibrous connective tissue. At the tip of the bony projection, there was a < 1-mm aggregate of tissue that resembled crushed hyaline cartilage (Figure 4). Microscopic findings supported the presumptive CT diagnosis of osteochondroma.
Photomicrographs of both lesions from the dog described in Figure 1. Radial osteochondroma (A) photomicrograph shows the necrotic cartilage cap (arrowheads) and trabecular bone body (star). Ulna (B) photomicrograph shows the defect from the penetrating radial osteochondroma (arrowheads) with surrounding necrotic bone, fibrin, and hemorrhage (white star) and fibrosis (black star). H&E stain, sections decalcified; bar = 500 µm.
Citation: Journal of the American Veterinary Medical Association 262, 10; 10.2460/javma.24.06.0418
The cortex of the ulnar segment had multifocal fragmentation replaced by aggregates of necrotic bone, fibrin, hemorrhage, and fibrosis. The marrow cavity was replaced by similar material (Figure 4). There was occasional new bone throughout the ulnar cortex, extending into the periosteum and marrow cavity. Microscopic findings were consistent with ulnar necrosis, remodeling, and fracture, as observed on CT.
Skin sutures were removed at 2 weeks postoperatively; the dog was sound at a walk and trot. At 16 weeks postoperatively, the dog was also sound at a walk and trot. Orthogonal radiographs of the right antebrachium showed a persistent ulnar ostectomy gap of 28 mm. The proximal and distal ends of the ulnar ostectomy gap were irregular but well-defined with smoothly marginated bone. The radial cortex had mild irregularities at the site of osteochondroma excision. Radiographs at 45 weeks postoperatively showed the ulnar ostectomy gap unchanged at 28 mm. Bony remodeling at the ostectomy and osteochondroma excision sites was static. There was no evidence of osteochondroma recurrence (Figure 3).
Comments
Osteochondromas are a benign condition that develops in young, growing dogs and are characterized by a cartilage-capped bony projection arising from the surface of bone that develops from endochondral ossification.1 This Case Report describes an unusual conformation of radial osteochondroma with intramedullary penetration of the adjacent ulna, causing expansile lysis of the ulna in a dog. In this case, the osteochondroma was identified on CT as a solitary bony projection from the distal radius. The distal antebrachium is a recognized predilection site for osteochondromas in dogs.1 Osteochondromas in this location are not always associated with clinical signs, become static at skeletal maturity in dogs, and rarely necessitate surgical intervention.1 While impingement and pressure necrosis of the adjacent bone in the distal antebrachium has been reported,1 the radial osteochondroma in this dog caused necrosis, intramedullary extension, and expansile lysis of the ulna, which has not been previously described. This resulted in lameness that necessitated surgical intervention.
A distal ulnar ostectomy removed the affected segment of ulna, and the radial osteochondroma was excised from the radial cortex with rongeurs. Lameness resolved quickly. There are 2 documented cases of dogs with osteochondromas of the distal ulna1 and distal radius2 impinging on the adjacent bone that required surgery to treat lameness. Power2 described a 33-month-old racing Greyhound with a distal radial osteochondroma impinging on the adjacent ulna causing lameness. The osteochondroma was removed, and the dog was reported sound at the 1-month follow-up. No follow-up radiographs were obtained. Le Roux et al1 reported a 20-month-old pit bull–type dog with an osteochondroma of the distal ulna and a concurrent radiolucent defect in the radius. The osteochondroma was removed from the ulnar cortex, and the dog was reported sound with no radiographic evidence of recurrence at 8 months postoperatively. Both cases had osteochondroma confirmed on microscopic examination.
Although microscopic examination is required to confirm a diagnosis of osteochondroma, characteristic features on CT allow a presumptive diagnosis. In the bone algorithm, the osteochondroma had a pathognomonic appearance: a smooth bony projection with a distinct cortex and medulla continuous with the radius.3
Microscopically, the osteochondroma was composed of primarily trabecular bone, with a small area at the tip resembling crushed cartilage. Osteochondromas are primarily composed of trabecular bone that is continuous with the underlying parent bone, sometimes with a hyaline cartilage cap.4 The cartilage cap becomes ossified with skeletal maturity and may be absent when there is pressure necrosis on an adjacent structure.4 The dog of this report had reached skeletal maturity at the time of CT, and pressure against the ulna explained the absence of a sizeable cartilage cap.
The last follow-up radiograph at 45 weeks postoperatively showed cortical irregularities at the site of osteochondroma excision consistent with remodeling but no evidence of recurrence.The ulnar ostectomy gap remained at 28 mm; nonunion following distal ulnar ostectomy in dogs is expected and clinically inconsequential since the distal ulna (excluding the distal styloid process) is not an active forelimb stabilizer.5
This case documents an unusual conformation of a distal radial osteochondroma with pressure necrosis, penetration, and intramedullary extension of the osteochondroma into the adjacent ulna, resulting in localized expansile lysis and lameness in a dog. The dog was successfully treated with ulnar ostectomy and osteochondroma excision. At 45 weeks postoperatively, the dog was sound with no radiographic evidence of osteochondroma recurrence.
Acknowledgments
None reported.
Disclosures
The authors have nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.
Funding
The authors have nothing to disclose.
References
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