• Psoriatic arthritis. Psoriatic arthritis is a form of arthritis accompanied by the skin disease psoriasis. The skin disease often precedes the arthritis; in a small percentage the joint disease develops before the skin disease. For about 20 percent of people with psoriatic arthritis, the disease involves the spine. In some cases, bony overgrowth can cause two or more vertebrae to grow together, or fuse, causing stiffness.

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• Juvenile Spondylarthropathy. Also called juvenile-onset spondyloarthritis (spinal arthritis), this term is used to describe spondylarthropathies that begin before age 16. In addition to affecting the spine, they may cause pain and inflammation in the joints of the pelvis, hips, ankles and knees. They may also affect other body organs such as the eyes, skin and bowels.

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• Enteropathic arthritis. This is a form of arthritis that occurs in about 5 percent of people with inflammatory bowel disease, which includes ulcerative colitis and Crohn's disease. It commonly affects the sacroiliac joints, causing lower back pain.

Other forms of arthritis and related conditions that can affect the back include:

• Osteoarthritis. The most common form of arthritis of the back, osteoarthritis is a chronic condition characterized by the breakdown of the cartilage that cushions the ends of the bones where they meet to form joints. In the spine, this breakdown occurs in the cartilage of the facet joints, where the vertebrae join. As a result, movement of the bones can cause irritation, further damage and the formation of bony outgrowths called spurs. These spurs can press on nerves, causing pain. New bone formation can also lead to narrowing of the spinal canal, known as spinal stenosis.

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Experts answer your questions about osteoarthritis.

Learn how being overweight can increase your risk of osteoarthritis.

• Rheumatoid arthritis. Rheumatoid arthritis is a chronic inflammatory disease of the joints that occurs when the body’s immune system – which normally protects us from infection – mistakenly attacks the synovium, the thin membrane that lines the joints. Although rheumatoid arthritis most commonly affects the hips, knees, hands, wrists, feet, elbows and ankles, it can also affect the facet joints in the spine, causing pain and, in severe cases, destruction of the joints. This may allow the upper vertebra to slide forward on top of the lower vertebra, a condition called spondylolisthesis. The slipped vertebra may put pressure on the spinal cord and/or the nerve roots where they exit the spine.

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