Osteosarcomas are malignant, aggressive tumours occurring mainly within the appendicular skeleton, and are considered to be the most common skeletal tumour in dogs (Moores et al, 2003). When cells are damaged, the injured site becomes abundant with changing cells that can display uncontrolled growth. Primitive cells of the interosseous bone called osteoid provide structural support within the body and play a role in the development of osteosarcoma; as the cells mature to create new bone they can become malignant tumours (Dernell, 2003).
There are three types of osteosarcoma:
A periosteal osteosarcoma is a bone surface lesion that includes cortical self-destruction, and a parosteal osteosarcoma is an osseous lesion adjacent to the bone with no cortical destruction (Dernell, 2003). Endosteal osteosarcomas derive from the medullary canal; periosteal and parosteal osteosarcomas derive from the periosteum (Liptak, 2010).
Osteosarcomas found within the hind limb can occur distal to the proximal femur and require a coxofemoral disarticulation, which is the amputation of the hind limb to include the femoral head. As the canine is usually found to adapt well after undergoing amputation, the decision to undertake surgery is popular (Blackwood, 1999). The veterinary surgeon will take into consideration the function of the remaining three limbs; if these are predisposed to other joint conditions it may not be appropriate to remove the affected limb. Another technique available is limb-sparing surgery, where the aim is to remove the localized tumour while leaving as much of the limb to function as normal. This technique can only be used for solitary osteosarcomas as there could be a chance of local reoccurrence if the tumour is not entirely removed (Endicott, 2003).
Canines considered to be predisposed to osteosarcomas are large-breed dogs such as Rottweilers and German Shepherds. However, recent research by Shearin and Ostrander (2010) indicates that long-limbed breeds, such as great danes and deer hounds, have a particular physiology in relation to osteosarcomas and are therefore also considered predisposed to the disease. Providing care for these large-breed dogs is multifactorial, and includes ensuring decubitus ulcers do not occur, cushioning any protruding bony prominences with thick, soft bedding if the canine is recumbent for prolonged periods and turning the patient every few hours — these are fundamental aspects of veterinary nursing.
Initial assessment
Canines who are admitted need a thorough and detailed history, enabling the veterinary surgeon to build up a picture of the dog's current routine. It is vital to gain information about the dog's normal behaviour and habits, such as food quantities or exercise regimens, for when the dog is hospitalized. This could include the owner's perception of the dog's pain levels and any lameness they have noticed since the consultation with the surgeon.
A relatively new nursing model that has been developed for use when admitting patients is the Ability Model (Orpet and Welsh, 2011), which contains a comprehensive patient assessment sheet; use of a pain scoring system or the palpation of superficial lymph nodes may be of benefit when the surgeon is assessing the patient against a baseline status.
Manipulation of the affected limb on admittance should be limited as the limb will be painful. The patient may be carrying it in an abnormal position in comparison with the normal static posture of the animal, as the tumour may be developing at irregular angles. Inflammation will occur at the site because of friction of the developing cells occurring as new bone is being laid down, which creates a firm, immobile mass and causes soft-tissue disruption (Moores et al, 2003).
Radiography
Lateral and cranial caudal survey radiographs will identify the size and spread of the tumour. The nurse can then be aware of which areas of the appendicular skeleton are affected and where to handle with particular care as the patient assessment will highlight areas of discomfort. The veterinary surgeon may require a radiograph of the thorax to check for metastasis. The lungs can be the first place that the cells invade, spreading haematogenously, as they are the initial place of capillary beds encountered post-systemic circulation (Dunlop and Malbert, 2004).
Three views are required of the thorax: left and right lateral views and a ventrodorsal view. It is important to take both of the lateral views as the nondependent lung fields are well aerated and closer to the radiography cassette, which gives for a clearer radiograph and magnification of metastatic lesions for the veterinary surgeon to see, as discussed by Liptak (2010).
The patient will require pain relief as directed by the veterinary surgeon, which has an impact on nursing considerations as some analgesia, such as partial agonists, can cause respiratory depression. Intravenous fluid therapy is administered to help support the circulation of the patient. A solution such as a crystalloid may be used as it contains electrolyte fluid similar to the canine's own isotonic extracellular fluid (Hotston-Moore, 2004). Fluid diuresis will aid in preventing nephrotoxicity from drug therapy (Dernell, 2003), which could affect renal blood flow or collect in the renal tubular epithelial cells and cause disruption to renal function (Dobson, 1998).
Williams and Fowler (1999) suggest that other treatment alongside surgery may include pre- and/or post-operative chemotherapy, which delays the progression of metatastic disease. However, with the development of an osteosarcoma, chemotherapy should be an adjunct to treatment rather than stand-alone therapy (Blackwood, 1999).
Radiotherapy will provide pain relief and will allow the dog to become ambulatory on the affected limb. Therefore limb amputation is only part of the multi-modal treatment required, and nursing patients that are receiving the adjunctive or solitary therapies requires careful planning. Personnel should wear gloves, gowns and masks to prevent contamination of themselves and others when dealing with cytotoxic drugs. The patient's consumables need to be disposed of in cytotoxic waste-disposal containers only, and any urine or feaces deposited in cytotoxic containers as well (Blackwood, 1999). The level and extent of the treatment package can depend on many factors, such as client compliance, cost and treatment availability.
Surgery
Dependent on the progression of the disease and the effect the amputation will have on the remaining limbs, coxofemoral disarticulation for hind limb lesions is one method of removing the tumour, which has proved popular by surgeons (Blackwood, 1999).
Preoperative considerations
Patient preparation
Patient preparation includes a full hind-quarter clip. This involves taking off the hair from the full circumference of the limb, leaving the hock and distal limb unclipped, and then taking the clip up to the lumbar region and then ventrally to allow the surgeon to manipulate the limb peri operatively. When clipping veterinary nurses should be mindful that vigorous skin scrubbing can cause neoplastic cells to migrate within the surrounding area of the tissues (Lascelles and White, 1999). Bandaging the limb distally to allow the surgeon to manipulate the limb when scrubbed up is advised. This can be done with an open-weave bandage and secured with a cohesive bandage, taking the bandage above the hock to allow for anchoring when suspending the limb for scrubbing. The limb is then scrubbed with a chlorohexidine solution and left ready for the surgeon (Figure 1).
Factors affecting the patient's predisposed susceptibility to infection include:
All of these parameters must be considered when nursing and preparing the canine with an osteosarcoma for theatre. The veterinary nurse preparing the patient should wear a hat, gloves and scrubs in theatre to minimize the risk of infection as the patient's immunity may be reduced. The condition of the patient can hinder the recovery time, as the metabolism of drugs will be reduced and poor circulation results in decreased transport of white blood cells.
Analgesia
The surgery being performed ensures the patient will have the majority of the pain removed from within the limb itself. However, the benefits of analgesia include preventing post-operative pain and enabling a shorter recovery period. Signs of pain need to be identified; making a note of the dog's demeanor and temperament pre operatively can be a good aide in monitoring pain post operatively. Indications of pain can include tachycardia, tachypnoea, aggression, depression and a delay in wound healing (Hofmeister et al, 2007).
Postoperative considerations
Wound healing
The skin incision will have sealed within 6–12 hours after the operation (Bacon, 2007), unless it is impeded by the immune system. The immune system may be compromised by chemotherapy, which can be given post operatively as an adjuvant treatment to delay the reoccurrence of neoplastic cells and to potentially eradicate micrometastatic disease (Brooks, 2010).
As the patient may hinder the process of wound healing, applying a buster collar to prevent interference is key. The wound does not require bandaging and should be checked when the canine has recovered from anaesthesia and until the patient is discharged.
Cancer cachexia and diet
Cancer cachexia results from a metabolic derangement coinciding with the cancer, which may have developed before weight loss. Post operatively the patient should be fed less carbohydrates and protein. Additionally, lipid metabolism should be considered when dealing with cancer cachexia as lipids, carbohydrate and protein are the sources the tumour will use to proliferate. A poor nutritional status can cause lethargy and the tumour can use the body's supply of protein; immunosuppresion can lead to abnormalities in lipid metabolism (Ogilvie, 2003).
Food fed post operatively should be warmed to allow the smell to become more evident to the patient, and only fresh food should be left (Ackerman, 2008). Food left alongside the patient for long periods must be avoided, particularly if the dog is nauseous as it could develop a food aversion. If the patient is anorexic and the different nutritional nursing strategies do not work, the veterinary surgeon may consider appetite stimulants such as cyproheptadine. These work relatively quickly within the anorexic canine, and should be given in conjunction with tempting the dog with appetizing food. A diet such as warmed chicken and rice is recommended post surgery as it is easily digestible. However, Lumbis and Chan (2008) advocate that the patient with neoplasia should be given foods containing less carbohydrate and more omega 3 fatty acids, as these inhibit the tumour behaviour with a possibility of improving remission.
The food intake during the hospital stay is calculated on the following sum (Chandler, 2008):
Refeeding energy requirements (kcal) = (30 × current body weight in kg) + 70.
This enables the patient to receive sufficient food to recover from the surgical procedure. Feeding tubes can be used if the canine persists to be anorexic, but this is beyond the scope of this article.
Physiotherapy and rehabilitation
Client compliance plays a large role in the dog's recovery, and veterinary nurses can provide an invaluable connection between the owner and the practice. Educating the owner on the implications of poorly adhered to recovery plans can prove valuable; after the dog has received major surgery its owner needs to continue with the recovery plan. Advocating rehabilitation maximizes the patient's recovery.
Cold compression around the wound can help reduce swelling immediately post operatively, which can be given alongside any anti-inflammatory medication that may be prescribed by the veterinary surgeon.
Ambulatory function for these patients can occur within hours after surgery (Blackwood, 1999). The veterinary nurse should assist the dog when initially standing to instil confidence and give reassurance while it learns to re-establish effective weight distribution. Placing a sling underneath the canine will enable the nurse to take the dog's weight when it is initially trying to stand. This will instil confidence, allowing the dog to walk forward and establish its first gait pattern with only three limbs, which may take some time (Figure 2). Continuing to assist the dog until it has established balance, coordination and how to urinate and defaecate is essential to its recovery. Building the muscles around the remaining hind limb is key, and will depend on the canine's tolerance. Dogs will benefit from assessment and treatment from a chartered veterinary physiotherapist to achieve the best potential for rehabilitation after surgery.
Conclusions
Canines presenting with osteosarcoma are often in considerable pain and have some loss of limb function. Careful assessment, including metastasis, other limb stability, patient health, cost and owner compliance can indicate coxofemoral disarticulation to successfully treat this condition. Nursing these patients involves dietary intervention as well as implementing a recovery plan, which should be continued by the owner. Nurses play a key role in helping the canine regain balance and confidence when walking on three limbs. After discharge, physiotherapy can further improve mobility.