Partial Ulnectomy for Distal Ulnar Osteosarcoma in a Giant Breed Dog
VETERINARIAN SPECIALTY CASE STUDY
Prior to surgery a CT scan of the thoracic limbs was performed. The results revealed an aggressive bone lesion arising in the distal portion of the right ulna.
Rascal, 10 year old male neutered Newfoundland, was referred to Animal Specialty Group on 10/9/2016 for evaluation and treatment for a slowly progressive right thoracic limb lameness. The lameness had been noted for the past few weeks. Rascal was started on carprofen; however despite this the lameness progressed. Other than the lameness Rascal has always been a health dog without any underlying medical problems.
On physical exam Rascal’s overall vitals were within normal limits, he weighed 57kg. He had moderate to severe right thoracic limb lameness with pain on palpation of the carpus and distal radius and ulna.
High-detail inspiratory thoracic radiographs were obtained without the aid of sedation or anesthesia and did not reveal any evidence of any underlying pulmonary metastatic disease. Orthogonal views of the affected limb along the distal 1/3 of the ulna revealed loss of sharp sclerotic margination of the medullary bone and cortex with regions of extreme lysis.
Complete blood work revealed an elevated ALT 210IU/L and GGT 17 IU/L, the rest of the results were within normal limits. The ALP value was 44IU/L.
Suspicious bone lesions identified on radiography include:
– primary bone tumors (chondrosarcoma, fibrosarcoma, hemangiosarcoma)
-metastatic bone cancer (multiple myeloma or lymphoma of bone)
-systemic mycoses with bony localization
-rarely bone cysts
5. Surgical Procedure
Prior to surgery a CT scan of the thoracic limbs was performed. The results revealed an aggressive bone lesion arising in the distal portion of the right ulna extending 1.2 cm from the distal margin of the ulna through 12 cm from the proximal margin of the ulna, consistent with a primary bone tumor. The proximal margin of the lesion is approximately 2 cm distal to the distal aspect of the interosseous ligament.
The affected right thoracic limb was circumferentially clipped from just above the elbow to the metacarpal pad. The dog was placed in left lateral recumbency with the affected leg suspended. A caudolateral approach was made over the mid to distal aspect of the right ulna. The lateral digital extensor muscle was separated from the extensor carpi ulnaris to expose the distal ulna. The styloid process was disarticulated. Using an oscillating saw an osteotomy was made approximately 2 cm distal to the interosseous ligament. The distal ulna was completely excised including the styloid process.
Closure was routine. Postoperative radiographs were obtained to evaluate complete excision of the distal ulna. A lateral splint along with a modified Robert Jones bandage were applied. The excised portion of the ulna (3 X 14 cm tissue), was submitted for histopathological evaluation.
Post-operatively Rascal was placed on maintenance fluid and intravenously hydromorphone for pain. Post-operatively a fentanyl patch was applied. Approximately 6 hours post-surgery Rascal was offered food and he ate well. The following day Rascal was transitioned to oral tramadol and carprofen. He continued to do well without any complications. Rascal was discharge on day three post-surgery.
Prior to being discharged the bandage along the right thoracic limb was changed. There was a moderate amount of serosanguinous strikethrough noted; extending all the way from the primary layer through the tertiary layer. The surgical site was still intact and there was a minimal amount of swelling and inflammation noted along the incision site. The lateral splint was applied followed by a modified Robert Jones bandage.
7. Histopathology results
The results of the histopathology revealed a destructive intramedullary neoplasm composed of pleomorphic dendritic and fusiform cell arrangement in sheets and trabeculae. Mitotic index was 15 mitoses per 10 high-power (40x) fields. There was moderate to marked anisocytosis and anisokaryosis.
The histologic features were suggestive of an aggressive phenotype. The closest approach of the neoplastic tissue to the proximal margin was 4.5mm. There was neoplastic tissue breaching through the cortex of the one of the sections and was noted to approach the related soft tissue margin (0.5mm).
Osteosarcoma (OSA) is the most common primary bone tumor in dogs (85-98%) often seen in large to giant breed dogs. Appendicular OSA is highly malignant tumor with < 15 % dogs having clinically detectable metastasis at the time of initial diagnosis, but with 75-90% eventually developing metastatic disease. Lung metastasis are more common to the pulmonary tissues and less commonly to locoregional lymph nodes or other internal organs.
A more recent study evaluating dogs with ulnar osteosarcoma suggests that the rate of metastasis may be lower (50% reported at the time of analysis) or that metastatic lesions take longer to develop in these cases.
Treatment of choice for osteosarcoma consists of controlling disease locally (via complete forequarter amputation, partial ulnectomy, or stereotactic radiosurgery) and systemically (with chemotherapy) to delay the onset of metastatic disease. In this case the owner elected to proceed with partial ulnectomy and follow up with chemotherapy and radiation therapy as needed.
Ulnectomy for distal lesions are often resected more successfully because of the normal separation between the radius and ulna at this level. Proximally located tumors are more difficult due to the close association of the two bones at the interosseous ligament.
In previous literature salvage of the styloid process is recommended to maintain stability of the carpus. Distal ulnectomy with pancarpal arthrodesis has been reported in 5 cases. The need for arthrodesis with complete distal ulnectomy is controversial. It is thought that stability after a distal ulnectomy (without any additional surgical intervention) is maintained by the remaining ligaments in relation to the radius and carpus (short radial collateral lig., palmar radiocarpal lig., dorsal radiocarpal lig.)
While there is a higher risk of local recurrence with partial ulnectomy (compared to amputation), a recent study evaluating dogs with ulnar osteosarcoma that were treated with partial ulnectomy did no worse than dogs that were treated via amputation. In this same study, the overall median survival time of dogs with ulnar osteosarcoma treated with surgery (+/- chemotherapy) was 15 months.
Rascal presented for a 1 week bandage change, there was mild irritation along the incision line which was still intact. Rascal was bearing weight on the operated limb without any overt complications.
Two weeks post-surgery the surgical site was noted to have completely healed and the limb on palpation palpated stable and the splint was replaced with just a modified Robert Jones bandage. Rascal was seen by the ASG Oncology Service where they commenced chemotherapy with a recheck in 3 weeks for second carboplatin injection and CBC (once every 3 weeks for a total of 6 treatments) and possibly commencing radiation therapy.
On 11/12/16, one month post-surgery, orthogonal views of the right thoracic limb revealed new bony grow along the distal aspect of the radius. Concern was expressed for tumor recurrence. Rascal continued to use the limb without any overt complications. He is expected to follow up with the ASG Oncology Service for continued chemotherapy and also potential commencement of radiation therapy.
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