More Dogs Than Bones
Dogs and bones go together like peanut butter and jelly, right? Eh, sort of. There are some bones dogs can eat (or technically, chew) and others that could cause serious damage if nibbled or ingested. Bones are meant for recreation, not food. Generally speaking, raw knucklebones from large livestock are safe for dogs to chew. Cooked bones and pieces small enough to be choking hazards are off limits. When and how you give your dog a bone also matters. Keep reading for everything you need to know about canines and bones.
More Dogs Than Bones
If your dog is new to raw bones or has a sensitive stomach, remove any and all bone marrow before allowing them to go to town. Bone marrow is incredibly rich and fatty; while some dogs may handle it well, others could start vomiting or have diarrhea. In fact, Animal Emergency Service advises against feeding dogs with delicate systems bones at all. Stick to chewable treats or hard carrots, instead.
That's because raw and cooked bones can both cause splinters in your dog's mouth and digestive tract, resulting in injury and even death (although this is more common with cooked bones). Here are some of the consequences of a dog chewing on raw or cooked bones.
Small Bones and Circular Bones: Giving any bone that is smaller than your dog's mouth or easily splinters is risky. Both can result in choking hazards as well as trauma to the mouth and intestinal tract. Circular bones are also unfavorable because they can become lodged in the lower jaw of a dog. Dogs are terrified of this, and cutting the bone to free the dog's jaw usually necessitates sedation.
Bone cancer can occur as a primary disease (originates from cells that normally reside in the bone space) or as a metastatic disease (spreads from cancers that arise elsewhere). In humans, most bone malignancies are metastases that arise from tumors outside the bone (breast, prostate). Primary bone tumors are less common, and osteosarcoma (primary bone cancer arising from bone-forming cells) is an orphan disease, meaning that these diseases have such a low prevalence that a general practice physician would not be expected to see more than one case in a year. In dogs, bone cancer also can occur as a primary or metastatic disease, but in contrast to humans, the most common form of bone cancer seen in dogs in the U.S. is osteosarcoma. This is probably due to various factors, including a higher relative risk in large and giant breed dogs to develop the disease over their lifetime (as compared to other dogs, and also to humans), as well as to the low incidence of mammary cancer in female dogs in the U.S. due to the practice of spaying and the relatively low incidence of other carcinomas in dogs that spread to bone in general, such as prostate, lung, colon, and renal cancer as well as of other common cancers of bone such as multiple myeloma. The remainder of this review will focus on the biology and treatment of osteosarcoma.
Osteosarcoma occurs in humans, dogs, and cats. In people, it is predominantly a pediatric disease with peak onset by 15 years of age. It is infrequent in adults, and incidence increases somewhat with age, with a second smaller peak after age 60. Primary osteosarcoma is a rare tumor, with fewer than 1,000 diagnoses per year. However, because of the demographics of the disease (i.e., the adolescent peak), it is considered an oncologic priority. Osteosarcoma is much more common in dogs than in people (15 times). An estimated 10,000 new diagnoses are made yearly, mostly in large and giant breed dogs, and it is seen only rarely in cats.
Osteosarcoma accounts for approximately 85% of bone tumors in dogs. The median age at diagnosis is 8 years, with a small peak of incidence in young animals (younger than 3 years). Still when the effect of body mass is taken into account, the overall risk for any dog to develop primary osteosarcoma is not magnified with increasing age. Dogs heavier than 90-lb account for almost 1/3 of cases, and most tumors in this group occur in the appendicular skeleton (limbs). Dogs under 30-lb account for less than 5% of cases, and in this group, most osteosarcoma occurs in the axial skeleton. In cats, there is no association with size or breed and the frequency of axial tumors is about the same as skeletal tumors.
A major component of this disease in dogs, and possibly in people, appears to be genetic (i.e., heritable). Risk is most accurately defined by body mass, although there is a direct correlation with size as well. In children, osteosarcoma is frequently seen in kindreds with mutations of the retinoblastoma susceptibility gene (RB-1), and this risk is paternally imprinted. In dogs, there are clear breed predispositions. A recent study by Phillips and colleagues published in Genomics (Phillips et al., 2007) showed that the narrow heritability in Scottish Deerhounds was 0.69; in other words, almost 70% of the cause is due to heritable traits. Narrow heritability (h2) is the proportion of the total variability due to genetic factors. It is not surprising heritable factors account for a significant component of risk in Scottish Deerhounds; more than 15% of dogs from this breed die from osteosarcoma. The best-fit model for inheritance of the risk traits in Scottish Deerhounds was a Mendelian major gene with dominant expression. Furthermore, Comstock and colleagues (Comstock et al., 2006) reported at the 2006 Genes Dogs and Cancer meeting (Chicago, IL) there are 4 regions of the genome that appear to be associated with an increased risk of osteosarcoma in Rottweilers, another breed where risk appears greater than what would be attributable to size alone (incidence estimated at more than 12%).
Tumor size is prognostic (the larger the tumor, the worst the prognosis), as is age (younger dogs do worse). Serum ALP levels also are predictive. Dogs with pre-operative levels of ALP> 110 U/L carry a worse prognosis than dogs with ALP
Osteosarcoma in dogs is a treatable, but generally not curable disease. Even now, the decision usually boils down to "leg or life". Survival times of approximately 1 year (or about 10% of a lifetime) are achievable for 50% of dogs with osteosarcoma treated using the current standard of care (50% of cases), and some dogs can survive 5 - 6 years after diagnosis. The standard of care is surgery (amputation of limb sparing surgery) with adjuvant chemotherapy. The choice of chemotherapy drugs does not seem to have a great impact on survival, so anticipated toxicity, quality of life, and cost tend to be driving factors. At present, the drug of choice for most cases is carboplatin. Chemotherapy is only recommended when the primary tumor is removed. It is ineffective in cases that are not surgical candidates. It is important to note that this tumor does not respond well to other treatments, and anything other than standard of care should be considered palliative. No herbal or "alternative" treatments, including Artemisin, have shown efficacy in controlled clinical trials.
Surgery is the mainstay for local control. In most cases, it provides immediate pain relief with high level of function. The only contraindication is poor structural soundness (not size). Case selection and an experienced surgeon (and recovery team) are important. Physical therapy and rehabilitation appear to improve quality of life and both patient and owner satisfaction. Complementary therapies like massage also may be beneficial. Complications are more frequent with limb sparing surgeries, where infection is the most common adverse event. Curiously, dogs that get infections at the surgical site and that respond well to antimicrobial therapy have better outcomes than dogs that do not get infections. This has been postulated to be secondary to activation of antitumor immune responses as a bystander effect of the response to the infection.
Radiation therapy provides local control and is palliative. The use of radiation therapy offers no added benefit to overall survival. Generally, there are no side effects and more than 70% of treated dogs show improvement, especially regarding pain. However, dogs that are not treated surgically remain at very high risk to develop pathologic fractures. An approach using Stereotactic RadioSurgery (STS) was recently adapted for use in dogs and is available at various institutions in the U.S. (e.g., University of Florida, Colorado State University, and others). It is too early to determine how this approach will compare to conventional surgery or limb-sparing surgery.
Other adjuvant therapies have been tested. Non-specific immunotherapy using an agent called L-muramyl-tripeptide-phosphatidylethanolamine (L-MTP-PE or 3-mifamurtide) as an add-on to amputation + cisplatin showed a median survival of 14 months with 40% of dogs surviving 2 years (Kurzman et al., 1995). This compound is being tested again as a possible addition to the current standard of care, and it recently was shown to improve survival for children with osteosarcoma when combined with standard of care therapy. No other therapies have shown any promise so far, although there are numerous ongoing clinical trials using compounds that activate the immune system (TNF, FasL) or targeted drugs (Rapamycin). An example of one such trial was recently published (Paoloni et al., 2009), and although improvement over the standard of care was marginal, it documents the infrastructure available to investigate new approaches for this disease.
There are many causes of limping and lameness in young dogs. Most of these are relatively minor and resolve without medical or surgical intervention. However, there are other causes that are more serious and, if not treated promptly, may result in permanent lameness or lead to debilitating arthritis. The large breeds of dogs (typically dogs whose adult weight is over fifty or sixty pounds) have several bone diseases that occur during the period of rapid growth that happens up to two years of age.
Because of the possibility of permanent lameness, your veterinarian will recommend diagnostic testing if lameness or pain lasts more than 7 to 14 days. X-rays are usually performed to investigate persistent lameness or pain in young dogs. Several radiographs of each affected leg are necessary in order to get an accurate assessment of various bones and joints. In many cases, this will require a short-acting anesthetic or sedative in order to achieve the optimal positioning for diagnostic purposes. In dogs under 6 to 7 months of age, x-rays can be challenging to interpret due to the presence of growth physes or "growth plates." To reach the diagnosis, it may be necessary to have the x-rays examined by a veterinary radiologist. 041b061a72