There are numerous causes of sacrum, or sacroiliac, joint pain. According to the Sports Injury Clinic website, the sacroiliac, or SI joints, are located near the tailbone and connect the hip bones with the sacrum, which is a large, triangular bone situated at the base of the spine. The SI joints move less than many of the spinal joints, and they are strongly reinforced by ligaments. However, SI joints are a common location for low back pain or discomfort.
Leg Length Inequality
A leg length inequality or a difference in leg length can cause SI joint pain or discomfort. According to podiatrists Mark A. Caselli and Edward C. Rzonca at the Podiatry Today website, leg length inequalities or asymmetries are the third most common cause of running injuries, occurring in 60 to 90 percent of the population. There are two principle types of leg length inequalities that can cause SI joint pain: structural and functional. Structural leg length inequalities are caused by an actual anatomical shortening of one or more bones in the lower extremity, whereas functional leg length inequalities may be caused by muscular weakness or imbalance, pelvic inflexibility and other causes. According to Caselli and Rzonca, SI joint pain due to a leg length inequality is often felt on the short extremity side, along with pain on the part of the knee facing away from the body, trochanteric bursitis, Achilles tendinitis and pain with occasional weakness on the outer portion of the foot.
Sacroiliac Joint Dysfunction
SI joint dysfunction can cause SI joint pain. The Physio Advisor website states that during certain spine and hip movements, stretching or compressive forces are applied to the SI joints and their surrounding ligaments. If the forces applied to the SI joints and their ligaments are too large for the joint to accommodate, SI joint injury or SI joint dysfunction may occur. According to the Physio Advisor website, SI joint dysfunction can be caused by movements that recruit low back and pelvis structures and tissues, including bending, sitting, lifting, and arching or twisting the spine along with the weight-bearing forces that accompany activities such as running or jumping. SI injury and the onset of SI joint dysfunction can be immediate, if caused by trauma, or gradual, if caused by repetitive forces applied to the joint over time.
Inflammatory Joint Disease
Inflammatory joint diseases can cause SI joint pain. According to the Spine Universe website, inflammatory and degenerative arthritis, such as osteoarthritis and rheumatoid arthritis, are a common cause of SI joint pain. Ankylosing spondylitis, which is a chronic inflammatory disease characterized by pain and progressive stiffness in the spinal joints, including the SI joints can also cause pain. Osteoarthritis, also known as degenerative joint disease, is one of the most common and debilitating joint conditions affecting older adults, states the American Academy of Family Physicians or AAFP. The AAFP also notes that SI joint osteoarthritis often involves bone spurs that bridge the ilia with the sacrum. Rheumatoid arthritis is a painful chronic inflammatory disorder that may affect the SI joints and is more common in women than men. Ankylosing spondylitis affects the SI joints early in the disease process, causing pain and inflammation. Over time, as the disease progresses, the vertebrae become fused, which increases the risk for spinal fractures.