1. A lateral vertebral radiograph of the lumbar region acquired during myelography of the dog in this case. Note the widening and lucency of the caudal physis of L5 with loss of normal physeal margins and pathologic fracture of the caudal end plate. The caudal L4 vertebral body and the L5 vertebral body have increased opacity. There is no evidence of static or dynamic compression of the spinal cord at the level of the physeal fracture.

Cerebrospinal fluid was collected from the cerebellomedullary cistern at the time of the myelogram. Analysis of the fluid revealed a total protein concentration of 24 mg/dl (normal ≤ 25 mg/dl) and a nucleated cell count of 6 cells/μl (normal ≤ 5 nucleated cells/μl) consisting of small lymphocytes and nonphagocytic macrophages. Aerobic bacterial culture of the cerebrospinal fluid yielded no growth.

The patient's physical examination and radiographic findings were consistent with vertebral physitis. However, we could not rule out a traumatic fracture or neoplastic or metabolic process affecting the physis. The owner declined additional diagnostic tests such as bacterial cultures of the blood and urine and fluoroscopic-guided aspiration of the vertebra.

We suspected a bacterial cause of the vertebral physitis and initiated treatment with cephalexin (22 mg/kg orally every 8 hours for three weeks). Analgesia was provided by transdermal administration of fentanyl (2.8 μg/kg). After three days of therapy, the dog developed mucopurulent nasal discharge and began sneezing. Enrofloxacin (5 mg/kg orally b.i.d. for 20 days) and metronidazole (22 mg/kg orally b.i.d. for seven days) were added to treat a presumptive upper respiratory tract infection and in an attempt to prevent pneumonia. The fentanyl patch was removed, and the patient was discharged with instructions to the owner to firmly restrict exercise at home.

On reevaluation seven days later, the patient had mild mucopurulent nasal discharge. Pain was not evident on palpation of the vertebral column, but the dog's gait remained stiff and short-strided in the pelvic limbs. Three weeks after the initial examination, the antibiotic therapy was discontinued.

Four weeks after the initial examination, the dog was reevaluated for recurrent crying, panting, and shaking. The patient was in extreme pain upon palpation of the lumbar vertebrae; however, the gait remained unchanged from previous examinations. Complete blood count and serum chemistry profile results were within reference ranges. Cystocentesis was performed, and a urinalysis revealed a moderate amount of a mixed population of bacteria that were predominantly bacilli. Aerobic bacterial culture of the urine grew > 10⁵ colonies/ml of Escherichia coli and > 10⁵ colonies/ml of Enterococcus species. An aerobic bacterial culture of the blood yielded no growth. The results of immunofluorescent antibody testing for Brucella canis were negative.

2. A lateral vertebral radiograph taken on Day 28 revealed degenerative changes of the caudal physeal region of L5 and bony callus formation ventral to the physeal fracture.