The SI joint is a pair of small joints connecting the sacrum, the triangular bone at the base of the spine, to the ilium bones of the pelvis. These joints act as shock absorbers, transferring the weight of the upper body to the legs, and typically have a very limited range of motion. When supporting ligaments become loose or damaged, the resulting hypermobility causes instability and pain, known as SI joint dysfunction. This instability is a common cause of lower back pain requiring targeted stabilization.
Causes and Indicators of SI Joint Instability
Instability in the SI joint arises when the normal mechanics of the joint are disrupted, leading to excessive movement. Common causes include hormonal changes, especially during pregnancy when relaxin loosens the pelvic ligaments. Trauma, such as a fall or motor vehicle accident, can also strain or tear the ligaments surrounding the joint. Degenerative arthritis is another factor that can compromise the joint’s integrity.
Asymmetrical movements or gait patterns may contribute to chronic instability by placing uneven stress on the joint. The resulting pain is often localized below the belt line, near the dimples of the lower back. This discomfort can radiate into the buttock, groin, or down the back of the thigh, sometimes mimicking sciatica. A sharp increase in pain when transitioning from sitting to standing, standing on one leg, or turning over in bed is a telling indicator.
Immediate External Support for Stabilization
Addressing acute SI joint pain involves immediate external support to limit excessive movement and allow irritated structures to calm down. Using a sacroiliac joint belt, also called a trochanteric belt, is a common non-invasive strategy. This device provides circumferential compression across the pelvis, physically squeezing the joint to reduce hypermobility. The belt should be worn low around the hips, about two inches below where a standard belt sits, to ensure proper placement over the SI joint.
The SI belt supports the joint ligaments directly and does not cause atrophy of the back muscles, making it suitable for longer-term use during activities, unlike a lumbar corset. Modifying daily movements is equally important, including avoiding high-impact activities like running or jumping. Limiting single-leg weight-bearing actions, such as climbing stairs or carrying objects on one side, helps reduce shearing forces across the joint.
Proper positioning during rest can significantly reduce nighttime pain by maintaining pelvic neutrality. When sleeping on the back, placing a pillow underneath the knees helps reduce the arch in the lower spine and stabilize the pelvis. Side sleepers should lie on the non-painful side and use a firm pillow between the knees and ankles. This prevents the top leg from rotating the pelvis forward, keeping the hips stacked and minimizing strain on the stabilizing ligaments.
Active Stabilization Through Targeted Exercise
While external support helps with acute pain, long-term stabilization requires strengthening the deep muscle groups that internally support the pelvis. Rehabilitation focuses on the “inner unit” of the core, including the transverse abdominis, gluteal muscles, and adductors. These muscles create a muscular corset that controls the subtle movements of the SI joint, allowing the body to create its own internal stabilization system.
Glute Bridge
The Glute Bridge is a foundational exercise for activating the gluteus maximus, a major pelvic stabilizer. Lie on your back with knees bent and feet flat, then engage your abdominal muscles to gently flatten your lower back. Squeeze the glutes to lift the hips until the body forms a straight line from the knees to the shoulders. The lift must come from the glutes, not the lower back, to target the hip extensors without stressing the SI joint.
Bird-Dog
The Bird-Dog focuses on coordinated core and spinal stability. Begin on your hands and knees with a neutral spine, imagining balancing a glass of water on your lower back to maintain a steady torso. Slowly extend one arm straight forward and the opposite leg straight back, ensuring the pelvis does not rotate or shift sideways. The movement should be slow and controlled, only lifting the limb to the height where the torso remains perfectly level.
Clamshell and Adductor Squeezes
The gluteus medius, a smaller muscle on the side of the hip, is targeted effectively with the Clamshell exercise. Lying on your side with knees bent and feet together, keep your feet touching as you slowly lift your top knee, resembling an opening clamshell. It is important to prevent the top hip from rolling backward during the lift, ensuring the movement is isolated to the hip abductors. Inner thigh squeezes, which engage the adductor muscles, can be performed by placing a small ball or pillow between the knees and squeezing gently.
Medical and Interventional Treatments
When conservative measures, including a stabilization exercise program, fail to provide lasting relief, a physician may recommend medical interventions. A common non-surgical option is a corticosteroid injection, which delivers anti-inflammatory medication directly into the SI joint. These injections confirm the joint as the source of pain and provide therapeutic relief that may last several weeks or months.
If pain returns quickly after an injection, radiofrequency ablation (RFA) may be considered. RFA uses heat generated by radio waves to interrupt the pain signals transmitted by the nerves that supply the joint, potentially offering relief for up to a year. For severe, chronic instability that has not responded to other treatments, SI joint fusion is a surgical option. This minimally invasive procedure places implants across the joint to encourage the bones to fuse together, eliminating movement and creating permanent stability.