Key Point

• SIJ mechanics indicate that therapists should take a holistic, movement-focused approach to SIJ pain. 

A client reports deep, localized pain on the lower right side of the back that sometimes radiates into the buttocks and posterior of the right thigh. They say the pain gets worse when standing from a seated position or when climbing stairs. The therapist asks the client to point to the location of the pain, and the client pushes into the tissue beside the right side of the sacrum. 

The massage therapist targets the site of the pain, applying cross-fiber friction to the right sacroiliac ligaments and deep kneading and compression to the gluteal muscles, piriformis, and erector spinae. The massage concludes, the client dresses, and the therapist returns to assess the session’s results. The therapist is puzzled and discouraged when the client points higher up on their low back and says, “Now the pain is here.” 

Most of us can relate to the therapist in this scenario because the interplay between the sacroiliac joint (SIJ), pubic symphysis, hip, and lumbar spine is complex and dynamic. However, when we stop chasing pain and take a movement-oriented approach to this body region, we can unravel client pain puzzles by addressing the biomechanical events underlying the dysfunction. 

In this article, we’ll focus on the SIJ by reviewing its anatomy and biomechanics. We’ll discuss SIJ pain and learn techniques that help us support the healthy interplay between the sacrum, spine, and hips. 

Sacroiliac Joint Anatomy

Most massage therapists are familiar with the SIJ. These unique diarthrodial synovial joints serve as the interface between the sacrum and the iliac bones of the pelvis (Image 1). Hyaline cartilage covers the sacral articular surface, while fibrocartilage covers the iliac surface. This arrangement reflects a biomechanical synergy where each type of cartilage plays a role that complements the other.  

The hyaline cartilage on the sacral surface provides a smooth, friction-reducing layer that facilitates the movement of the sacrum relative to the ilium. The smoothness of hyaline cartilage minimizes friction during the limited movements of the SIJ, contributing to the joint’s overall longevity. 

The fibrocartilage on the iliac surface is tougher and denser to withstand high pressure and tensile forces. In addition, the iliac surface of the SIJ is more irregular, and fibrocartilage is more adaptable to irregular surfaces. It fills the gaps and helps stabilize the joint while absorbing and distributing mechanical loads transmitted through the pelvis. 

The articulation of the sacrum and ilium is surrounded by a fibrous capsule containing a joint space filled with synovial fluid. As noted, the articulating surfaces of the sacrum and ilium are not smooth; instead, they are irregular and interlocking, distinguishing the SIJ from all other synovial joints. In early life, the joint surfaces are nearly flat, allowing gliding motions between the sacrum and ilium in all directions. Over a person’s lifetime, these ridges and depressions deepen. By age 30, the joints develop an elevated ridge along the iliac surfaces and a depression along the sacral surfaces, creating a functional interlocking between the two bones that increases the joint’s stability. 

Ligaments of the Sacroiliac Joint 

A dense network of ligaments contributes to the joint’s stability while allowing minimal movement, which helps dissipate loads and forces (Image 2). 

• Interosseous Sacroiliac Ligament—The interosseous sacroiliac ligament (not visible on the diagram) is deep within the joint, filling the irregular space between the sacral and iliac surfaces. It prevents the sacrum and ilium from sliding anterior, posterior, superior, and inferior relative to each other. In other words, it holds the bones together against the incredible forces acting on the pelvis. 

• Anterior Sacroiliac Ligament—This ligament covers the anterior surface of the joint, limiting the posterior rotation of the sacrum relative to the ilium, and countering forward tilting of the sacrum. 

• Posterior Sacroiliac Ligament—This ligament covers the posterior surface of the joint, restricting anterior rotation of the sacrum and supporting the joint against vertical shear forces. A vertical shear force acts parallel to the body’s vertical axis, attempting to slide one part of the body vertically over another part. For example, carrying a heavy load like a tote bag on one shoulder creates an asymmetrical load on the spine. This uneven weight distribution generates a vertical shear force that acts on the SIJ. The weight on one side of the body tends to pull that side down, effectively pulling the pelvis downward relative to the spine on the loaded side. 

• Sacrotuberous Ligament—The sacrotuberous ligament extends from the sacrum to the ischial tuberosity, limiting the posterior and anterior tilting of the sacrum and supporting the joint against rotational forces. Rotational forces attempt to cause rotation of the sacrum relative to the ilium around a theoretical vertical axis that runs horizontally through the joint. Twisting movements, like those involved in playing golf or tennis, involve rotating the upper body. At the same time, the pelvis remains more stationary, creating a twisting force through the spine down to the sacrum. 

• Sacrospinous Ligament—This ligament runs from the sacrum to the ischial spine and works with the sacrotuberous ligament to limit posterior and anterior tilting of the sacrum. 

• Iliolumbar Ligament—This ligament extends from the ilium to the transverse processes of the L4 and L5 vertebrae. While not directly part of the SIJ, it helps stabilize the lumbosacral junction and can indirectly affect SIJ stability. It limits anterior translation and rotation at the lumbosacral junction. 

A typical SIJ moves about 2–4 millimeters during weight-bearing and forward-bending activities, mainly due to the stretching and tensioning of ligaments. 

Nerve Innervation of the Sacroiliac Joint 

A complex network of nerves innervates the SIJ, including the ventral rami of L4 and L5, superior gluteal nerve, and dorsal rami of L5–S2 (Image 3). There is inconsistency in the nerve supply to the SIJ between individuals, with some demonstrating innervation almost exclusively from the sacral dorsal rami. Because of this overlapping nerve supply, pain originating from SIJ dysfunction can mimic other conditions like lumbar disc disease or hip pathology. This intricate nerve supply may also account for the variable patterns of referred pain that originate with the SIJ. 

Biomechanics of the Sacroiliac Joint 

Along with the pubic symphysis, the SIJ provides stability to the lower back and pelvis, facilitating the mobility of the hips and lumbar spine, which is crucial for walking, bending, lifting, and twisting. Let’s examine the movements available at the SIJ, the form and force closure mechanisms that make the joint stable, and the SIJ’s functions within the dynamic interplay of lower body biomechanics.  

Movement 

Several powerful muscles surround the SIJ, but none are designed to produce active movement at the joint. Instead, muscles like the erector spinae, psoas, iliacus, quadratus lumborum, piriformis, abdominal obliques, glutes, hamstrings, and pelvic floor muscles produce movements at the hip or the lumbar spine, indirectly causing movement or increasing stability at the SIJ.

The subtle motions that occur at the SIJ are nutation and counternutation—movements of the sacrum relative to the ilium that play a significant role in the function and mechanics of the pelvic girdle (Image 4). 

Nutation refers to the anterior and inferior rotation of the sacral base (the upper portion of the sacrum) relative to the ilium. During this motion, the sacral promontory (the superior aspect of the sacrum) moves anteriorly and inferiorly, while the coccyx moves posteriorly and superiorly. In other words, the sacrum tilts forward and down. This action “narrows” the anteroposterior diameter of the pelvic outlet while “widening” the transverse diameter. Nutation increases tension in the sacrotuberous and sacrospinous ligaments, increasing the joint’s stability. 

In counternutation, the sacral base moves posteriorly and superiorly relative to the ilium, and the coccyx moves anteriorly and inferiorly. Now, the sacrum moves backward and upward. Counternutation “widens” the anteroposterior diameter of the pelvic outlet while “narrowing” the transverse diameter. Counternutation decreases tension in the sacrotuberous and sacrospinous ligaments. 

Nutation and counternutation are functional, dynamic responses to various activities and situations. For example, when you walk, the pelvis and sacroiliac joints go through subtle but complex movements to accommodate the transfer of forces from the lower extremities to the spine. 

Transitioning from a sitting to a standing position requires similar adjustments. Nutation occurs as you prepare to stand, providing increased stability in the sacroiliac joint as you load your body weight onto your legs. Nutation also occurs when you lift a heavy object off the ground, creating stability by preventing excessive, anterior-posterior movement that could destabilize the joint. 

In sports that involve rotational movements, like golf or baseball, several dynamic changes between nutation and counternutation occur as the athlete shifts weight, rotates the torso, and adjusts the pelvis to achieve maximum power and precision.

The act of breathing also subtly influences sacral position. Inhalation promotes nutation by engaging the diaphragm and pelvic floor muscles, which pull the sacrum into a nutated position. Exhalation promotes counternutation as these muscles relax. 

Stability 

The SIJ relies on two primary mechanisms for stability. Form closure is the inherent cohesion provided by the joint’s unique interlocking design described previously. Force closure is the dynamic support afforded by surrounding ligaments and muscles. During sacral nutation, the sacrum nods forward and down. This movement tenses several ligaments. As these ligaments become taut, they exert a force on the ilium, drawing it posteriorly and medially. At the same time, muscles around the SIJ, like the gluteal muscles, latissimus dorsi, and thoracolumbar fascia, create tensional forces. The resulting effects compress the SIJ, providing stability. 

Functions 

The sacroiliac joint functions as a shock absorber for the spine, distributes the force of loads from the lower extremities, and stabilizes the weight-bearing side of the body during gait.  

• Shock Absorption—When the foot strikes the ground during walking, running, or any weight-bearing activity, there’s an immediate ground reaction force that travels upward through the lower extremity. This force travels through the foot, ankle, knee, and hip before reaching the pelvis. The SIJ helps dissipate this force by providing a slight give or cushioning effect. The ligaments surrounding the SIJ stretch minimally, helping distribute the force over a larger area and preventing it from concentrating in one region.

• Torque Conversion—The SIJ also acts as a torque converter. The pelvis rotates slightly around its longitudinal axis during activities like walking or running. This rotational force, or torque, is transmitted across the SIJ. The SIJ, due to its shape and orientation, helps convert this rotational force into vertical and horizontal forces, which are then transmitted up to the spine or down to the lower extremities.

• Force Transmission—Besides converting forces, the SIJ also plays a significant role in transferring forces between the spine and lower extremities. When we lift a heavy object, the axial load from the spine is transmitted through the SIJ to the hips and legs. Conversely, forces from the legs during activities like jumping are transferred up through the SIJ to the spine.

• Weight-Bearing Stability—When we walk, there’s a point during the gait cycle where one leg is in the air (swing phase), and the other is bearing the body’s entire weight (stance phase). Along with other hip stabilizers, the SIJ acts as a supportive brace on the weight-bearing side, ensuring the pelvis remains level and doesn’t tilt excessively to one side. This function is primarily achieved due to the ligamentous support and the force-closure mechanism provided by the surrounding soft tissue.

Through this discussion, we understand the SIJ is intricate, balancing the need for stability with the requirement for minor mobility. The joint’s design reflects its critical role in linking the spine to the lower extremities and distributing loads efficiently.

Sacroiliac Joint Dysfunction 

Low-back pain is a common health concern affecting 80 percent of the US population at some point during their lifetimes.¹ SIJ pain accounts for 15–30 percent of chronic cases.² SIJ dysfunction often arises from faulty spine, hip, and pubic symphysis mechanics, injury, repetitive stress, and pregnancy. Here are some common causes for SIJ dysfunction: 

• Pronounced lordosis and vertebral misalignment place additional stress on the SIJ, wearing on the cartilage. 

• Muscular imbalances, such as tight hip flexors or hamstrings, can tilt the pelvis anteriorly or posteriorly, straining ligaments. 

• Ligament adhesions can restrict hip joint movements, causing misalignments that trigger compensatory changes at both the hip and SIJ. 

• The pubic symphysis and SIJ operate in tandem. During walking, as one hip advances, there’s slight motion at the pubic symphysis and counternutation at the contralateral SIJ. Dysfunction in one often results in compensatory changes in the other. 

• SIJ pain also arises from traumatic causes like a fall onto the buttocks, indirect injury from a motor vehicle collision, or sudden, repeated heavy lifting (e.g., moving into a new house).

• Repetitive stress injuries occur from leg length discrepancies, scoliosis, lumbar lordosis, and sports like golf and bowling. 

• Pregnancy causes SIJ pain from weight gain, increased lumbar lordosis, hormone-induced ligament laxity, and trauma associated with delivery. 

Anything that disrupts the biomechanical interplay of the SIJ, spine, and hips can lead to greater stress on the SIJ and osteoarthritis. For example, studies show that previous spinal joint fusion, where two or more vertebrae are joined together using bone grafts or metal hardware, increases the speed of SIJ degeneration and the occurrence of SIJ pain. Similarly, people with hip osteoarthritis typically experience a higher prevalence of SIJ pain.

Sacral Torsion 

Sacral torsion is a term used in osteopathic medicine to describe a condition where the sacrum twists around an oblique axis. An oblique axis is the imaginary line that runs diagonally from the anterior of the sacrum on one side to the posterior of the sacrum on the opposite side. 

A triggering factor, like muscle imbalances, injury, or poor posture, causes one side of the sacrum to move anteriorly and the other side to move posteriorly. Now, the ilium might respond by rotating or tilting to compensate. This rotation is subtle because the SI joints don’t allow for much movement. However, even small shifts can significantly impact the biomechanics of the pelvis and lower back, causing muscles to tighten, weaken, or spasm, manifesting pain, changes in gait, and further compensatory changes in the lumbar spine, hips, and even the upper body. 

Symptoms of Sacroiliac Joint Pain 

Symptoms of SIJ pain vary, but generally include pain localized to one side of the lower back inferior and medial to the posterior superior iliac spine and below L5. Pain can radiate to the buttocks, groin, and occasionally down the back of the thigh, but rarely beyond the knee. SIJ pain is exacerbated by movement, standing up from a seated position, climbing stairs, or during prolonged sitting or standing.  

Getting to Harmony

We’ve learned that the SIJ must function harmoniously with the spine, hips, and pubic symphysis to fulfill its functions as a shock absorber, torque converter, force transmitter, and weight-bearing stabilizer during gait. Instead of focusing on the gluteal muscles and SIJ ligaments to address SIJ pain, take a holistic approach using movement, graded exposure stretches, and an understanding of biomechanics to return this region to balance. 

Notes

1. Jan Hartvigsen et al., “What Low Back Pain Is and Why We Need to Pay Attention,” Lancet 391, no. 10137 (June 2018): 2356–67, https://pubmed.ncbi.nlm.nih.gov/29573870. 

2. Ali Kiapour et al., “Biomechanics of the Sacroiliac Joint: Anatomy, Function, Biomechanics, Sexual Dimorphism, and Causes of Pain,” International Journal of Spine Surgery 14, supplement no. 1 (February 2020): 3–13, https://pubmed.ncbi.nlm.nih.gov/32123652. 

Myoskeletal Alignment Techniques for SIJ Dysfunction and Pain

These eight methods provide good results and are applicable within most larger routines for the SIJ, lower back, and hips. These techniques should not feel painful, so discontinue anything that is too challenging for the client or elicits pain. Perform each technique on both sides of the body. 

Distract-Compact the Hip—The client is supine with their right knee flexed and their foot resting flat on the table. Snake your right arm around and through the popliteal space and grasp your left arm above the elbow. First, pull the client’s thigh to distract the hip, then push the thigh toward the pelvis to compact the hip. Repeat this movement two or three times. With the client’s hip distracted, ask the client to pull their hip toward the therapy table against your resistance to a count of five and relax. Distract and compact the client’s hip two or three times, ending with the hip distracted. 

Mobilizing the SI Joint—With the client’s knees flexed and their feet resting on the table, snake your left arm under the client’s right knee and grasp the client’s left thigh just above the knee. Grasp the client’s right ankle with your right hand and gently push the ankle downward while lifting the client’s hip with your left arm. Lean both of the client’s knees away from your body and ask the client to hike their right hip against your resistance to a count of five. Pull the right knee inferiorly and medially as the client relaxes. Repeat this technique on both sides as the counterforce posteriorly rotates the client’s right ilium while the medial force helps mobilize a fixated right SIJ.

Iliosacral Alignment Technique Part 1—The client is supine with their knees flexed and feet flat on the therapy table. Their feet can be close together or a shoulder-width apart. Place your elbow against the medial surface of one knee and the palm of the same arm against the medial surface of the other knee. Instruct the client to push their hips up into a bridge while squeezing their knees together against your resistance. Ask the client to lower their hips back to the therapy table while continuing to squeeze into adduction. Repeat this technique three times and then move on to part 2. 

Iliosacral Alignment Technique Part 2—Move the client’s feet and knees together and brace the lateral side of the knees. Ask the client to abduct their knees against your resistance. Again, ask the client to bridge up and down while you continue to brace the lateral sides of the knees. 

Sacral Roll—With the client prone, place your right hand on top of the client’s sacrum and your left hand on top of the right. Drop your body weight into both hands and begin rolling the sacrum counterclockwise. Your palms move along the sacral border to contact the SIJ ligaments. Avoid dropping into the gluteal muscles as you move in a 360-degree circle around the sacrum.

Piriformis and SIJ Release—With the client prone, face away from the client. Flex the client’s left knee to 90 degrees and hook the client’s foot behind your back. Use your right ulna bone to contact the ipsilateral long dorsal SIJ ligaments. You’ll feel the piriformis and other “deep 6” rotators as your forearm sinks deep into the fascia. As you abduct the client’s flexed leg, it creates an internal femoral rotation, which allows your forearm to palpate for tightness in the hip’s external rotators. Ask the client to push their foot against your arm to a count of five and then relax. As the client relaxes, bring their leg to the next restrictive barrier and repeat 3–5 times to improve piriformis flexibility. Now, lift the client’s leg slightly (from the same position) while your forearm applies static pressure on the inferior border of the SI joint.

Sacral Base Decompression—With the client prone, stand at the head of the table and place your right hand on the client’s sacrum and your left forearm on the thoracolumbar fascia. Drop your body weight into the right hand with firm (not painful) pressure, moving the sacrum inferiorly. Your left forearm resists this motion at the thoracolumbar fascia by gently pulling the tissue headward. Ask the client to tilt their pelvis 3–4 times slowly to enhance this release.

Sacral Torsion Technique—The client is in a sidelying position with flexed knees. Grasp the client’s right wrist with your left hand. Place your right hand on the inferior sacral border with a soft palm. Create a counterforce by pulling gently with your left hand while bracing with your right hand. Ask the client to shrug their shoulder toward their ear to a count of five while you resist and then relax. As the client relaxes, increase the counterforce by gently pulling with your left hand while resisting with your right. Repeat this procedure 3–5 times.