The success of an operation depends on several factors. The doctor will see if it had the desired effect in the spine. Equally important, the patient will report if symptoms are improved.
Often, changes in quality of life (QOL) are weighted as heavily as decrease in pain. Sleeping more, better sleep, and more active sex life are examples of improved QOL for some patients.
Returning to work or sports activities is another measure of treatment success. It's still a success if pain persists, but the patient may only describe the result as "better" rather than "much better."