Sacroiliac joint sprain is often caused by improper posture, sudden twisting due to muscle imbalance, and in rare cases, there may be no obvious history of trauma.

bubble_chart Etiology

The sacroiliac joint is composed of uneven, interlocking auricular joint surfaces, stabilized by ligaments of varying lengths at the front and back. The weight of the torso is transmitted through the sacroiliac joint to the lower limbs. In pregnant women, hormonal changes, prolonged bed rest, or the effects of spinal or general anesthesia can lead to sacroiliac joint laxity, compromising its stability. When subjected to external forces, this may result in a sacroiliac joint sprain or dislocation. However, due to the joint's inherent strength and stability, sprains or dislocations are uncommon. In cases of poor posture, muscle imbalance, or ligament laxity, torsional forces can disrupt the alignment of the uneven sacroiliac joint surfaces, widening the joint space. Under negative pressure within the joint cavity, the synovial membrane may be drawn into the joint space, causing impingement and severe pain. Depending on the direction of the sprain, it may lead to either anterior or posterior dislocation of the sacroiliac joint.

(1) Anterior sacroiliac joint dislocation occurs when the hip is extended and the knee is flexed, tightening the quadriceps and iliofemoral ligament, which pull the ilium forward. Meanwhile, the torso, spine, and sacrum rotate backward, causing the ilium to displace anteriorly.

(2) Posterior sacroiliac joint dislocation occurs when the hip is flexed and the knee is extended, tightening the hamstrings, which pull the ilium backward. Simultaneously, the torso, spine, and sacrum rotate forward to the opposite side, creating antagonistic torsion between the sacrum and ilium, leading to posterior rotation and displacement of the ilium.

After a sacroiliac joint sprain, sudden severe pain is felt on the affected side of the sacroiliac region, with limited movement, pale complexion, and even shock. The ipsilateral lower limb dares not bear weight, and the torso tilts forward and toward the affected side. Approximately 20–60% of patients experience radiating pain in the ipsilateral lower limb, mostly in the buttocks, posterior thigh (posterior femoral cutaneous nerve), sciatic nerve distribution area, and the anterior-medial root of the thigh. The causes of radiating pain include:

1. The ligaments, muscles, or other soft tissues near the sacroiliac joint are innervated by the 4th and 5th lumbar nerves and sacral nerves. When the sacroiliac joint is sprained, it can cause reflexive neuropathic pain in these nerves.

2. The sciatic nerve or posterior femoral cutaneous nerve bundles are closely adjacent to the anterior side of the sacroiliac joint and piriformis muscle. When the ligaments around the sacroiliac joint bleed due to sprain, swell, or the piriformis muscle spasms, the nerve bundles can be directly irritated, leading to radiating pain.

3. A sacroiliac joint sprain combined with a lumbosacral joint sprain can also irritate the nerve roots, causing sciatica.

During examination, the following may be observed: Standing posture—the torso tilts toward the healthy side when standing, with the healthy limb bearing weight, the affected foot touching the ground lightly, and the hand supporting the affected hip to reduce movement and pain. Sitting posture—the patient sits with the healthy ischial tuberosity bearing weight, using both hands for support to lessen the load. Bed-lying posture—the patient first sits by the bedside, then uses both hands to support the affected limb to prevent pain in the affected sacroiliac joint. The pelvic separation test is positive, with adductor muscle tension. The sacroiliac rotation test is positive. Straight leg raising is restricted. The posterior superior iliac spine is higher or lower compared to the contralateral side. Tenderness is present at the posterior superior iliac spine.

The anteroposterior X-ray shows unequal heights of the posterior superior iliac spines, while the oblique view reveals widening of the sacroiliac joint space and disorganization of the convex-concave relationship.

bubble_chart Diagnosis

Based on the history of trauma, clinical symptoms, and signs, and with reference to X-ray films, a definitive diagnosis can be made. If the pain immediately disappears after hearing a sound from the sacroiliac joint during traction manipulation, a definitive diagnosis can be established. However, it is necessary to differentiate it from lumbosacral joint sprain and annulus fibrosus rupture.

bubble_chart Treatment Measures

This condition can achieve immediate results through manual reduction. Generally, the "traction technique of separation and realignment" is first employed to release the trapped synovial membrane within the joint and relieve muscle tension. For cases of anterior rotational displacement of the ilium, the affected hip is hyperextended to tighten the quadriceps and iliac ligaments, facilitating the reduction of the anteriorly rotated ilium. After reduction, a wide adhesive tape is applied for circumferential fixation. Functional exercises should begin after three weeks of rest to prevent recurrence.