Spondylosis L2-L3. A 12-year-old Shih Tzu has arched back

"My dog has more muscular front legs than the back," the owner said. "The back leg muscles are withered and my dog could not walk properly. The owner wondered why the dog had very weak back legs and an arched back. I noted that she made the dog wear diapers too.

"The arched back is due to pain behind the rib cage," I said. This was a case of spondylosis deformans, a chronic disease of degenerated intervertebral discs. In this disease, the joints between the vertebral bones become unstable as the intervertebral discs become abnormal and unable to act as cushions to absorb shocks when the dog jumps.

Bony spurs called osteophytes form on the sides of the vertebral bone, as can be seen in this dog's X-rays.

"Blood test showed high total white cell count and neutrophils, indicating a bacterial infection of the blood," I explained to her the blood test results.  The dog had skin diseases which would have had led to such infections.

 TREATMENT
1. None if there is no pain.
2. In this dog, there is some pain of arched back and wasting of the back leg muscles. Painkillers may be prescribed. Weight loss is not necessary as he is not fat. Physical therapy and exercise are not practical.
3. Surgery if the spinal cord is compressed. This will be costly.

REFERENCE: Spondylosis deformans

http://www.vcahospitals.com/main/pet-health-information/article/animal-health/spondylosis-deformans-in-dogs/2141