A history of unexplained lameness or the presence of a firm mass warrants radiographic assessment (lateral and craniocaudal views) of the affected bone. Features of an aggressive bony lesion may include one or all of the following (see Figure 21.1A–D): a loss of fine trabecular detail of the metaphyseal bone due to lysis, discontinuity of the cortex, periosteal new bone formation (Codman’s triangle), palisading mineralization perpendicular to the bone shaft (‘sunburst effect’), extension of a mass into the adjacent soft tissues, an indistinct transitional zone between tumour and normal bone, inappropriate areas of sclerosis, or pathological fracture. OSA does not cross the articular cartilage, although tumour may extend into soft tissues and to adjacent bones. Primary lesions usually remain monostotic. CT scans, when available, give a more accurate evaluation of the extent of affected bone.

The differential diagnosis for a radiographic aggressive bony lesion includes bone tumour (primary or metastatic), infection (Figure 21.1E) (fungal or bacterial), and (rarely) bone cysts.

Bacterial osteomyelitis is suspected on the basis of history (as contamination from surgery or trauma is more common than haematogenous spread). Mycotic osteomyelitis is a major differential diagnosis in countries where fungal diseases are common as they can be monostotic with preference for metaphyseal lesions and spread is haematogenous; however, most mycotic diseases are polyostotic and associated with pulmonary infiltrates and thoracic lymphadenopathy. Travel history and the signalment of the patient may be indicative of a fungal infection.

A 4-inch, 8–11 G bone biopsy needle is used through a small stab incision in the skin. Two to three biopsies of the centre of the lesion (as determined from radiographs) are taken via the same skin incision (only once the cortex is penetrated). The diagnostic accuracy is 82% for specific tumour type and 92% for differentiating tumour from other causes, and complications are uncommon (Powers et al 1988). Post-biopsy radiographs confirm the position of the biopsy tract. Material for culture and cytology should be taken before fixation in formalin. Fluoroscopy is useful for assisting bone biopsy for axial sites.

This has a diagnostic accuracy of 94% but an increased risk of pathological fracture (Wykes et al 1985).

Aspiration of the intramedullary region is performed through areas of cortical destruction (can be ultrasound guided). In dogs, ultrasound-guided needle aspirations of aggressive appendicular bone lesions indicated sarcoma with a sensitivity of 97% and a specificity of 100% in 32 of 36 cases. When a diagnosis of sarcoma was made on cytology (Figure 21.4), ALKP staining indicated OSA, with a sensitivity of 100% (Britt et al 2007).

Amputation is a pain-relieving procedure, and is considered by many to be the best way to relieve the pain caused by the primary tumour. Amputation alone is considered palliative, although the prognosis is better than no treatment (Spodnick et al 1992, Zachos et al 1999). Amputation with or without adjuvant therapy is the standard treatment for appendicular OSA. There are few contraindications to amputation (see Figure 21.5). Concurrent osteoarthritis may progress more rapidly following amputation, although this may be managed medically and most dogs compensate rapidly. Forequarter (including scapula) amputation is required for thoracic limb lesions. Coxofemoral disarticulation is performed for distal pelvic limb lesions and disarticulation combined with en bloc acetabulectomy is used for proximal femoral lesions. Most clients (42/44) were satisfied with the outcome of amputation, and surprised at the rapidity of their dog’s adaptation. No significant association between adaptation with weight, age or thoracic or pelvic limb amputation was found (Kirpensteijn et al 1999).

This is a palliative treatment for primary and metastatic bone pain. Response and duration of response depend on the size of the lesion, radiation protocol, and whether or not chemotherapy is used in conjunction with radiotherapy. Response (improvement in limb function) occurs in 75–92%, for variable durations (Green et al 2002, Ramirez et al 1999). Reported response duration ranges from 17 to 288 days (median 130 days). In the authors’ experience, dogs with lesions in the proximal humerus do not respond as well as other locations. Typical protocols are 8–9 Gy once weekly for three or four treatments. Radiation should be considered in all patients where surgery is not an option.

The primary OSA is removed and the limb remains functional by the implantation of another material (e.g. bone autograft, bone allograft, steel prosthesis; see Figure 21.6) or by distraction osteogenesis (Withrow & Vail 2007). Intraoperative radiotherapy has been attempted in a few cases (Liptak et al 2004b). Limb sparing may be used where amputation is declined, or dogs have significant pre-existing orthopaedic or neurological disease. It must be stressed that in the vast majority of cases, amputation is the simplest, quickest, cheapest and best method of treating the primary tumour.

For a patient to be suitable for a limb-spare procedure, tumour must be clinically and radiographically confined to the limb and involve <50% of the bone (Withrow & Vail 2007). MRI, CT, nuclear scintigraphy and radiographs may be used to estimate the extent of the tumour (Davis et al 2002, Wallack et al 2002). Pathological fracture is a contraindication due to contamination of soft tissues, although this can be reduced by radiotherapy and neoadjuvant chemotherapy. The most suitable sites are the distal radius and ulna (Withrow & Vail 2007).

Surgeons experienced in limb salvage techniques are not always readily available and only experienced surgeons should perform these techniques.

Cisplatin or carboplatin alone or in combination with doxorubicin have been shown to significantly improve life span. However, irrespective of the protocol employed, the MST remains in the order of 300–365 days with 2-year survival times at 20–25% (Berg et al, 1992 and Berg, Gebhardt, Rand, 1997, Bergman et al 1996, Chun et al 2005, Kent et al 2004, Mauldin et al 1988). Currently, the most widely used protocol is single-agent carboplatin and this is our recommended treatment for middle-aged to older dogs with OSA. Three to four cycles every 3 weeks at 300 mg/m² have resulted in median survival times of 321 days (Bergman et al 1996). Carboplatin (see Chapter 6) has fewer side effects than cisplatin, does not require diuresis prior to administration and can therefore be given on an outpatient basis. Although it is an expensive drug, the fact that administration is easier means that it is more cost effective than cisplatin.

Combination protocols are generally held to be superior to single-agent protocols (see Chapter 6). However, in the management of OSA there seems to be little benefit to a combination protocol for the majority of patients and when balancing toxicity versus long-term benefit, carboplatin as a single-agent stands up well. Studies alternating doxorubicin and carboplatin or doxorubicin and cisplatin at 3-weekly intervals for three to four cycles/drug did not show any survival benefit over three cycles of carboplatin (median 320 days) (Kent et al 2004, Moore et al 2007). Doxorubicin as a single agent (adjunctive to amputation) every 2 weeks for five cycles resulted in an 8-month MST and a 17% 2-year survival rate in 303 dogs (Moore et al 2007). In younger patients that have a poorer prognosis the authors generally combine doxorubicin and carboplatin but until enough studies are carried out on younger patients the true benefit of this combination remains unknown. Greyhounds show significant myelosuppression with carboplatin that usually results in a reduction of dose to around 250 mg/m². Treatment delays because of low neutrophil counts are more common with greyhounds than other breeds and, in the authors’ experience, because of regular dose reduction, these patients appear to have an overall poorer prognosis with shorter survival times.