According to the Mayo Clinic, “Back pain is a common complaint. Most people in the United States will experience low back pain at least once during their lives. Back pain is one of the most common reasons people go to the doctor or miss work.”
Mechanical back pain is usually caused by problems with the structures of the spine, such as muscle strains, ligament sprains, or herniated discs. It is often triggered by certain movements, positions, or injuries and tends to improve with rest and conservative treatments. Inflammatory back pain, on the other hand, affects the lower back (i.e., the axial spine and sacroiliac joints). It is most often associated with spondyloarthritis.
When determining if back pain is inflammatory in nature, medical experts often take the following into account:
Onset of pain is usually under 35 years of age and is insidious;
Pain persists for more than three months (i.e., it is chronic);
The back pain and stiffness worsen with immobility, especially at night and early morning;
The back pain and stiffness tend to ease with physical activity and exercise;
NSAIDs are very effective in relieving pain and stiffness in most patients.
Note that inflammatory back pain by itself should not be used to diagnose spondyloarthritis. Instead it is a very important characteristic that physicians consider along with other findings such as x-ray or MRI evidence of sacroiliitis, the detection of the gene marker HLA B27, or the history of another related physical finding such as iritis.