If you have been treated for spinal stenosis in the lumbar area it is possible that you already had arthritis in that area.
Acctually, in most of the cases spinal stenosis results from osteoarthritis-related bone damage.
When osteoarthritis is found in a young patient, it is due to other condition, which needs to be identified (known as secondary osteoarthritis).
Also, secondary osteoarthritis can be a side effect of your recent surgery.
Surgery to the joint structures, can lead to a case of osteoarthritis.

Talk with your orthopedic surgeon about your arthritis!