Psoriatic arthritis tends to develop in the large joints, particularly in the hands and feet. However, it can also affect the spine, causing pain in the back and pelvic area. Psoriatic arthritis is most common in people with psoriasis or individuals with a family history of the disease. When psoriatic arthritis affects the spine, doctors refer to it as axial arthritis, meaning that it affects the spine, shoulders, or hips. Axial arthritis occurs in up to 50 percent of people with psoriatic arthritis. If this type of arthritis affects the spine, it often affects the extremities as well.