Petplan's most common claim for the month of March 2016 was for Intervertebral Disk Disease. Most people associate this problem with the Dachshund breed, but IVDD can occur in many canine breeds and less frequently in cats.
I'm going to point you to a webpage that does a good job explaining the different types of IVDD with illustrations and how it is diagnosed and treated - both medically and surgically.
Next, watch this video as a neurologist talks about IVDD:
Watch this video that shows a surgeon actually teasing the disk material away from the compressed spinal cord and removing it with suction.
It is important to read a sample policy when doing your research before purchasing pet insurance for your pet. Some companies have an extended waiting period for IVDD to be covered after you buy the policy. Some company policies restrict all future coverage for IVDD if your pet has been diagnosed (and recovered) prior to purchasing a policy - even if it occurs in a different area of the spinal canal.
Notice the average expense for treating this disease in the table above. It can be much more expensive than this if diagnostics such as a myelogram, CT scan or MRI are done followed by surgery and rehabilitation. Sometimes pets need all of these things to have the best chance of returning to full function and pet insurance can certainly help with the costs.