Factors associated with pathological fractures in dogs with appendicular primary bone neoplasia: 84 cases (2007-2013).

OBJECTIVE:To determine the incidence of pathological fractures associated with appendicular primary bone tumors in dogs managed medically and to identify potential risk factors at the time of radiographic diagnosis that may be associated with eventual pathological fracture. DESIGN:Retrospective case series. ANIMALS:84 dogs with primary long bone neoplasia treated medically. PROCEDURES:Medical records for dogs with a diagnosis of primary long bone neoplasia based on results of radiography that was confirmed subsequently at necropsy were reviewed. Owners elected medical treatment at a pain clinic. Data regarding clinical signs, diagnostic testing, pathological findings, and outcome were evaluated. RESULTS:84 dogs met study inclusion criteria with 85 limbs affected. Osteosarcoma was the most common tumor and was identified in 78 of 85 (91.8%) limbs. The median time from diagnosis to euthanasia was 111 days (range, 28 to 447 days). Pathological fractures were identified in 33 of 85 limbs (38%), with the femur most commonly affected, (8/14 [57.1%]), followed by the tibia (9/17 [52.9%]), humerus (10/27 [37%]), radius (5/25 [20%]), and ulna (1/2 [50%]). Logistic regression analysis indicated that tumors arising from long bones other than the radius had odds of eventual fracture 5.05 as great as the odds for tumors of the radius, and lytic tumors had odds of eventual fracture 3.22 as great as the odds for tumors that appeared blastic or mixed lytic-blastic. CONCLUSIONS AND CLINICAL RELEVANCE:Results suggested that radial primary bone tumors were less likely and lytic tumors were more likely to fracture. The overall incidence of pathological fractures secondary to appendicular primary bone neoplasia in this study with patients treated by means of intensive management for bone pain was higher than previously reported.