Neoplasia: a common cause of forelimb lameness
Lauren Deahl, DVM, Residency Trained in Surgery
Veterinary Specialty & Emergency Center
Musculoskeletal neoplasia is a common cause of forelimb lameness in dogs. In some cases, this may be in the form of an obvious tumor or may present as a subtle or intermittent lameness. A thorough physical and orthopedic examination should be performed in all dog diagnosed with a suspected musculoskeletal neoplasm to evaluate for evidence of metastatic disease and plan the most appropriate treatment.
The most common primary bone tumor, osteosarcoma, accounts for 85% of all skeletal neoplasia.
Other primary bone tumors include chondrosarcoma, hemangiosarcoma, fibrosarcoma, lymphoma and plasma cell tumors. Osteosarcoma most commonly occurs in large to giant breed dogs. Breed predispositions include Rottweilers, Great Danes, Dobermans, Golden Retrievers, Saint Bernards and Irish Wolfhounds. Although osteosarcoma is typically a disease of middle age to older dogs (median age 7 years) a biphasic age distribution has been identified with a subset of dogs ages 1-2 years affected. Over 90% of osteosarcoma lesions are monostotic and rarely cross cartilage.
Approximately 75% of osteosarcomas are seen within the appendicular skeleton. Osteosarcoma is most often seen within the metaphyseal regions of long bones. The distal radius is the most common site (23%) in the forelimb followed by the proximal humerus (18%). The ulna is less common (2.6%). Osteosarcoma is highly malignant with up to 90% of dogs eventually developing metastatic disease. Negative prognostic factors include a higher body weight, location in the proximal humerus, large tumor size, ALP elevation, tumor necrosis and histologic grade.
Surgery alone is considered palliative for osteosarcoma, as microscopic metastatic disease is considered present in all cases and chemotherapy is indicated after surgery. Radiation therapy and limb sparing procedures can also be considered for certain tumors. Other primary bone tumors are uncommon but may be suspected in dogs with an unusual signalment or anatomic location. Chondrosarcoma is the second most common primary bone tumor and is relatively uncommon.
1 High grade aggressive medullary osteosarcoma of the distal radius in a 8 year old greyhound.
Compared to osteosarcoma, it is associated with a much lower metastatic rate. Metastatic cancer can spread to bone from almost any other malignancy and a careful physical exam and thorough work up should be performed to rule out a primary cancer.
Limb amputation is recommended in dogs with a tumor of soft tissues or bone located on a limb that is unresectable without amputation and to address the local tumor in dogs with osteosarcoma. The two main techniques used for amputation of the thoracic limb are removal of the scapula along with the limb or disarticulation at the scapulohumeral joint. Removal of the scapula is preferred and is most commonly performed. The technique for forelimb amputation is described elsewhere (Small Animal Surgery, Fossum 4th edition, Veterinary Surgery Small Animal Tobias and Johnson 1st ed.)
Function after amputation is typically good to excellent, even in large breed dogs and most owners are satisfied with their pet’s function. Owners should be informed that dogs recovering from a forelimb amputation may have more difficulty ambulating initially compared to a pelvic limb amputation. Although the presence of severe degenerative joint disease in remaining limbs may be a contraindication, amputation can still be successful in dogs with a mild to moderate degree of degenerative change in remaining limbs. Complications of amputation include hemorrhage, seroma formation, dehiscence and infection.
Tumors of the digit often present as a cause of lameness or due to the presence of a mass. Most digit tumors are neoplastic. The most common type of digit tumor is squamous cell carcinoma (SCC), followed by malignant melanoma. Occasionally, squamous cell carcinoma may involve multiple digits.
Other digit neoplasms include mast cell tumors, soft tissue sarcoma, plasmacytomas, among others.
Non-neoplastic lesions can also be identified on the digit and include pyogranulomatous inflammation, epithelial inclusion cysts, histiocytomas, basal cell tumors and benign adenexal tumors. Because many neoplastic digit lesions can metastasize, full staging prior to surgery is recommended. Radiographs of the affected foot are recommended as malignant tumors often show evidence of bone lysis. For most tumors confined to the digit, wide surgical excision has been shown to improve outcome, however, when large tumors are present a limb amputation may be necessary.
Metastatic disease is common with 13-26% of dogs with SCC and 28-38% of dogs with malignant melanoma being diagnosed with metastatic disease at some point. Digit amputations for suspected neoplasia most commonly involve removal of the entire digit with disarticulation at the metacarpophalangeal joint or with transection of the affected metacarpal bone using bone cutters. Skin is preserved for closure and digital arteries and veins are ligated. Closure is performed routinely and a soft padded bandage or splint is used for 1-2 weeks. Activity restriction is recommended until the wound heals.
Soft tissue sarcomas are a group of mesenchymal tumors that comprise 15% of all skin tumors and 7% of all subcutaneous tumors and are commonly identified. Although these tumors are an uncommon cause of lameness, many are locally aggressive and can invade limb muscles and tissues to cause lameness.
The most common tumors of the joint include synovial cell sarcoma, histiocytic sarcoma, myxomas and other sarcomas. Affected dogs typically present with a lameness or joint swelling. Occasionally, a palpable periarticular mass is present. Large greed, older dogs are most commonly affected. These tumors can be difficult to differentiate, even with standard biopsy and special immunohistochemical stains are often required once a biopsy has been performed. An incisional biopsy of the tumor is recommended to determine tumor type and plan for the most appropriate treatment. Advanced imaging (CT scan) may be recommended for diagnosis and surgical planning. In general, amputation is recommended for treatment of most synovial tumors following staging for gross metastatic disease.
Dr. Lauren Deahl is a residency-trained surgeon at the Veterinary Specialty & Emergency Center. The Veterinary Specialty & Emergency Center operates state-of the-art emergency and specialty veterinary hospitals that are open 24/7/365 in Levittown PA, Philadelphia PA and Conshohocken PA. For more information about our world-class emergency and specialty care, please visit VSEC on the web at www.VSECVET.com.