Sacroiliac Joint Injury

Excerpt

Sacroiliac joint injury (SIJ) is a common cause of low back pain (LBP). Posterior pelvic joint pain is frequently used to describe SIJ dysfunction. This articulation connects the spine and pelvis and may be traumatically dislocated in high-energy events, such as motor vehicle accidents, representing a true orthopedic emergency.

The SIJ connects the iliac and sacral auricular surfaces. Injury to this region often produces significant pain localized to the posterior low back and buttock, although referral patterns may vary. The SIJ experiences shearing, torsion, rotational, and tensile forces. Based on its geometry and load-bearing function, the joint has been analogized to a “Chinese finger trap.”

The SIJ plays a critical role in ambulation, as it represents the sole orthopedic connection between the upper and lower body. Structurally, the SIJ is an amphiarthrosis, similar to the pubic symphysis, characterized by limited motion via cartilaginous connections and a relatively stiff synovial joint containing synovial fluid. Sacral and iliac articular surfaces are coated with hyaline cartilage, while dense fibrous tissue reinforces the joint. Normal SIJ motion is limited to a few degrees.

Diagnosing SIJ pathology can be challenging. One difficulty in evaluating SIJ injury is distinguishing it from LBP (lumbago). Specialized provocation tests and diagnostic imaging can assist in making this distinction. The SIJ is a significant contributor to LBP, responsible for about 15% to 30% of cases, and should be routinely considered in differential diagnoses. Pregnant women are particularly vulnerable due to hormonal joint laxity. SIJ fusion reduces joint laxity between the ages of 40 and 50. Pregnancy or fusion-related changes may result in hypermobility or hypomobility, which can exacerbate SIJ pain. Osteoarthritis is a frequent contributor to SIJ dysfunction.

Multiple etiologies and contributing factors underlie SIJ injury. Symptom overlap with other sources of LBP, along with the diverse origins of SIJ dysfunction, complicates diagnosis and management. SIJ injury can be acute, but pain persisting beyond 3 months defines chronic SIJ pain, which occurs when free nerve endings within the joint degenerate or become chronically activated. Pain may be constant or intermittent. Exclusion of lumbar pathology is essential before confirming SIJ dysfunction as the primary cause of back pain, with exceptions including trauma and pregnancy. Infectious causes of SIJ pain are uncommon but can occur in both pediatric and adult populations and are often overlooked.

Excessive joint mobility can result in pain within the SIJ. Conversely, hypomobility is a hallmark of ankylosing spondylitis, a common cause of inflammatory SIJ injury. SIJ dysfunction frequently coexists with mechanical LBP. The SIJ may also be the site of referred pain from the lumbar vertebrae rather than the primary origin. For example, degenerative disc disease at L5 to S1 may be perceived as SIJ pain, although the source is located higher in the lumbar spine.

Multiple referral patterns are observed in SIJ injury, including the posterior thigh, knee, or foot. The posterior thigh is the most common site, occurring in approximately 50% of patients. Management is further complicated by the absence of clearly defined diagnostic and treatment guidelines. Magnetic resonance imaging (MRI) is the preferred imaging modality for evaluating SIJ dysfunction. In addition, radiography-guided anesthetic injection provides a reliable method for confirming SIJ pathology as the source of pain in many cases.

The SIJ is a frequent target for intervention in chronic LBP. Conservative management typically includes physical therapy, home exercise programs, and over-the-counter (OTC) analgesics such as nonsteroidal anti-inflammatory drugs (NSAIDs) or acetaminophen. Corticosteroid injections and radiofrequency ablation (RFA) are viable options when conservative strategies are insufficient. SIJ fusion may be indicated in severe, refractory cases. Patient education is a critical component of management, emphasizing posture, safe lifting techniques, stretching, and regular exercise. Weight reduction should be considered in patients with elevated body mass index to reduce mechanical stress on the joint.