Orthopedic surgery is fairly common in dogs. It’s usually needed to repair broken bones or damaged joints (e.g., cranial cruciate ligament tears or severe hip dysplasia), and oftentimes, metal implants (screws, plates, pins, etc.) remain in the dog’s body from that point on.
Dogs usually heal uneventfully after orthopedic surgery involving metal implants, but as is the case with any type of treatment, complications can occur. Most complications arise early on in the healing process (infections, delayed healing, etc.), and are therefore obviously associated with the initial injury and/or surgery. However, one especially devastating complication—cancer—can develop years after surgery involving metal implants.
Metal orthopedic implants have long been associated with an increased risk of cancer at the surgical site in both veterinary and human patients, but the complication is rare enough that it doesn’t get discussed as often as it should. A recent study looked at the characteristics of implant-associated neoplasia (cancer) in dogs and provided a nice review of what we know about the subject. Here are the paper’s highlights.
Medical records of dogs with tumors associated with metallic implants (cases) treated between 1983 and 2013 were reviewed. Two dogs with naturally occurring osteosarcoma (controls) were matched to each case on the basis of tumor location, age, and sex.
Osteosarcoma was the most common tumor, accounting for 13 of 16 implant-associated tumors. Three case dogs had a diagnosis of histiocytic sarcoma, fibrosarcoma, and spindle cell sarcoma. The specific tumor diagnosis within the category of implant-associated neoplasia… affects prognosis and treatment. For example, the patient with fibrosarcoma in the present case series died of an unrelated disease process 3 years after amputation. Other tumors diagnosed in this study, such as OSA or histiocytic sarcoma, are generally not associated with such prolonged survival times.
Median time from implant placement to diagnosis of neoplasia was 5.5 years (range, 9 months to 10 years).
In 1 study of OSA in dogs, 12 of 264 (4.5%) dogs had tumors identified in bones with previous fractures, 7 of which were treated with surgical implants. In another study of 130 fractures in dogs, 5 (3.8%) OSAs were identified at the site of fracture, all of which were repaired with surgical implants.
Large-breed dogs are predisposed to the occurrence of naturally occurring OSA, and most implant-associated bone tumors have been reported in these breeds, a finding mirrored in the present study. Very few implant-associated bone tumors have been reported in small-breed dogs or cats.
Many initiating factors have been hypothesized to play a role in the development of implant-associated sarcomas. Investigators have shown that many implant materials, including commonly used stainless steel and titanium, have potential carcinogenic properties. Corrosion products from metallic implants have been associated with malignancy, and corrosion has been seen in more than 75% of stainless steel components in human retrieval studies. Other reported hypotheses for the development of implant-associated sarcomas include tissue damage from the initial trauma, osteomyelitis [bone infection], or both, which imply that the metallic implants may be associated with but not causally linked to the occurrence of these tumors.
None of this should stop you from pursuing orthopedic surgery for your dog if he or she truly needs it. Implant-associated cancer is rare, after all, but it is important for owners to be aware (and for veterinarians to acknowledge) that life-threatening complications can arise years after surgery.
Dr. Jennifer Coates
Implant-associated neoplasia in dogs: 16 cases (1983-2013). Burton AG, Johnson EG, Vernau W, Murphy BG. J Am Vet Med Assoc. 2015 Oct 1;247(7):778-85.