Lower back and leg discomfort is common, but the source of this pain is often confused by the similar ways different conditions can manifest. Many people incorrectly use the terms “SI joint pain” and “sciatica” interchangeably. While both conditions can cause significant discomfort in the buttock and leg, they originate from distinct anatomical structures and require different approaches for effective management. Clarifying the nature of each condition is the first step toward an accurate diagnosis and appropriate treatment plan.
Defining Sciatica and Its Source
Sciatica is accurately described not as a diagnosis itself, but as a symptom complex involving pain that radiates along the path of the sciatic nerve. This nerve is formed by the nerve roots that exit the spine from the lower lumbar (L4-L5) and sacral (S1-S3) segments. The pain is neurological in origin, resulting from the irritation or compression of these nerve roots or the sciatic nerve itself.
The pain pattern associated with sciatica is typically sharp, shooting, or electrical, traveling from the lower back or buttock down the back of the leg. The most common cause of nerve root compression is a herniated or bulging lumbar intervertebral disc, but it can also be caused by spinal stenosis or piriformis syndrome. Symptoms often include numbness, tingling, or muscle weakness in the affected leg and foot, which are signs of nerve involvement.
Understanding Sacroiliac Joint Dysfunction
The sacroiliac (SI) joint is a pair of joints connecting the sacrum, the triangular bone at the base of the spine, to the ilium, which is the large bone of the pelvis. These joints are heavily reinforced by strong ligaments and are designed for stability, acting as shock absorbers that transfer forces between the upper body and the legs. SI joint dysfunction refers to pain originating from inflammation (sacroiliitis) or from abnormal motion within the joint.
This dysfunction can be caused by either too much movement (hypermobility) or too little movement (hypomobility) within the joint. The typical pain pattern is localized primarily in the lower back and buttock, often pinpointed to a specific spot near the posterior superior iliac spine. This discomfort is frequently described as a dull ache, and it may refer pain down the thigh, generally not extending below the knee.
Key Differences in Pain Location and Cause
Sciatica and SI joint pain are fundamentally different conditions because one is neurological and the other is mechanical or inflammatory. Sciatica is the result of nerve root pathology, where the pain follows a distinct dermatomal map along the entire course of the sciatic nerve. The pain quality is often a sharp, burning, or shooting sensation, reflecting the irritation of the nerve.
SI joint pain, conversely, is musculoskeletal, arising from the joint or its surrounding ligaments. While SI joint pain can cause “pseudoscitica” by referring pain into the buttock and posterior thigh, the pain is usually concentrated around the hip and rarely travels to the foot. Sciatica pain is worsened by actions that increase pressure on the nerve roots, such as coughing, sneezing, or prolonged sitting. SI joint pain is aggravated by movements that stress the joint, like standing up, climbing stairs, or bearing weight on one leg.
Diagnosis and Condition-Specific Treatments
Distinguishing between these two pain generators relies on a combination of physical examination and diagnostic procedures. A neurological examination for sciatica includes checking reflexes, muscle strength, and performing the straight-leg-raising test, which can reproduce shooting pain below the knee if a nerve root is compressed. Imaging tests like Magnetic Resonance Imaging (MRI) are used to confirm the presence of a herniated disc or spinal stenosis, common causes of nerve compression.
In contrast, SI joint dysfunction is diagnosed using specific provocative physical maneuvers, such as the FABER test or the thigh thrust test, which intentionally stress the joint to reproduce the patient’s pain. The most definitive diagnostic tool is a diagnostic injection, where an anesthetic is precisely injected into the joint under imaging guidance. A significant reduction in pain following the injection confirms the SI joint as the primary source of discomfort.
Because the underlying causes are distinct, the treatment pathways are also customized to the condition. Sciatica treatment focuses on reducing nerve compression and inflammation through oral anti-inflammatory medications, physical therapy emphasizing nerve gliding and spinal mechanics, and targeted epidural steroid injections. Treatment for SI joint dysfunction aims to stabilize the joint and reduce inflammation through specialized physical therapy to strengthen surrounding muscles, anti-inflammatory medications, and therapeutic SI joint injections. For chronic, severe SI joint pain that does not respond to conservative care, minimally invasive procedures like radiofrequency ablation or surgical fusion of the joint may be considered.