What Is Sacroiliitis?
Sacroiliitis is inflammation of the sacroiliac joint (SIJ) — the joint that connects the sacrum to the ilium in the pelvis. The SIJ is a large, ear-shaped joint that transmits loads from the trunk to the lower limbs and absorbs impact forces during gait and running.
It is essential to distinguish two different clinical entities: mechanical sacroiliac dysfunction — a functional alteration without systemic inflammatory process, common in women in the peri- and postpartum period — and inflammatory sacroiliitis — a manifestation of spondyloarthritis such as ankylosing spondylitis and psoriatic arthritis.
This distinction is clinically decisive, because spondyloarthritis requires specific systemic treatment (biologic agents), whereas mechanical dysfunction responds to local measures and rehabilitation. Clinical examination together with laboratory and imaging workup allows this differentiation.
Mechanical vs. Inflammatory
Mechanical dysfunction is the most common cause of sacroiliac pain. Inflammatory sacroiliitis is a manifestation of spondyloarthritis and requires systemic workup.
Diagnosis by Block
Intra-articular block with anesthetic is the gold standard for confirming the SIJ as a pain source — relief of 75% or greater confirms the origin.
Spondyloarthritis
Bilateral sacroiliitis on MRI in a young patient with inflammatory low back pain is a cardinal sign of axial spondyloarthritis.
Epidemiology
The sacroiliac joint is considered the source of pain in 15-30% of patients with chronic low back pain, according to studies that use diagnostic block as the confirmation criterion. Mechanical SIJ dysfunction is more prevalent in women, with peak incidence in the fourth and fifth decades of life.
Inflammatory sacroiliitis, in the context of spondyloarthritis, has an estimated prevalence of 0.1-1.4% in the general population. Ankylosing spondylitis, the prototype of axial spondyloarthritis, has a strong association with the HLA-B27 antigen, present in 90-95% of patients. Symptom onset typically occurs between 15 and 40 years of age, with a male predominance of 2-3:1.
Risk factors for mechanical SIJ dysfunction include pregnancy and postpartum (hormonal ligamentous laxity and mechanical overload), leg-length discrepancy, scoliosis, lumbar fusion (increased stress on the SIJ), pelvic trauma, and athletic activities with asymmetric impact.
Pathophysiology
The sacroiliac joint is an atypical diarthrodial joint: the anterior third is a true synovial joint with hyaline cartilage on the sacral side and fibrocartilage on the iliac side, while the posterior two thirds are a syndesmosis (a strong ligamentous connection). This complex anatomy explains the diversity of pain mechanisms.
SIJ stability depends predominantly on ligaments — especially the posterior interosseous sacroiliac ligament, the strongest in the human body — and on the competence of pelvic stabilizing muscles (gluteus maximus, piriformis, lumbar multifidi). The SIJ innervation is multisegmental (L2-S4), which explains the variable patterns of referred pain.
Pain Mechanisms
MECHANICAL DYSFUNCTION VS. INFLAMMATORY SACROILIITIS
| FEATURE | MECHANICAL DYSFUNCTION | INFLAMMATORY SACROILIITIS |
|---|---|---|
| Mechanism | Overload, ligamentous instability, biomechanical alteration | Autoimmune process with enthesitis, erosion, and sclerosis |
| Typical age | 30-60 years, postpartum | 15-40 years |
| Laterality | Usually unilateral | Bilateral (spondylitis) or alternating |
| Nighttime pain | Uncommon | Characteristic — second half of the night |
| Morning stiffness | Brief (less than 30 min) | Prolonged (greater than 30-60 min), improves with exercise |
| Laboratory markers | Normal | Elevated ESR/CRP, HLA-B27 frequently positive |
| Imaging course | No structural progression | Erosion, sclerosis, progressive ankylosis |
Symptoms
The cardinal symptom of sacroiliitis is pain in the gluteal region, typically below the iliac crest, over or around the posterior superior iliac spine (PSIS). Patients frequently point to the pain with one finger directly over the SIJ — the so-called "Fortin finger test," which has diagnostic value when positive.
Symptoms of Sacroiliitis / Sacroiliac Dysfunction
- 01
Unilateral or bilateral gluteal pain
Pain localized over the SIJ, frequently pointed out with one finger over the posterior superior iliac spine.
- 02
Unilateral pain on sitting
Pain that worsens when sitting on the buttock of the affected side, leading the patient to sit leaning toward the opposite side.
- 03
Pain on turning in bed
Changes of position elicit pain through shearing of the sacroiliac joint.
- 04
Pain on climbing stairs
Single-leg weight bearing aggravates ipsilateral SIJ pain during the climb.
- 05
Pain referred to thigh and groin
May radiate to the posterior thigh (rarely below the knee) and, less frequently, to the groin.
- 06
Morning stiffness
In the inflammatory form: prolonged stiffness (more than 30 minutes) that improves with exercise. In the mechanical form: brief and improves quickly.
- 07
Nighttime pain (inflammatory form)
In inflammatory sacroiliitis: pain that wakes the patient in the second half of the night, forcing them to get up.
Diagnosis
Diagnosis of sacroiliac pain is challenging because no single clinical test has high sensitivity and specificity. The diagnostic approach combines clinical provocation tests, laboratory workup to exclude or confirm spondyloarthritis, imaging, and confirmatory anesthetic block.
The most accepted diagnostic rule is the presence of three or more positive provocation tests out of five standardized tests, which yields a sensitivity of 94% and specificity of 78% for sacroiliac-origin pain.
🏥Diagnostic Evaluation of Sacroiliitis
Fonte: ASAS guidelines and Laslett criteria
SIJ Provocation Tests (3+ positive = high probability)
- 1.Gaenslen test: hip hyperextension with the opposite side flexed
- 2.Pelvic compression test: lateral pressure on the iliac crests in lateral decubitus
- 3.Pelvic distraction test: posterolateral pressure on the ASIS in supine position
- 4.Sacral thrust test: posterior pressure on the sacrum in prone position
- 5.FABER (Patrick) test: hip flexion, abduction, and external rotation
- 6.Fortin finger test: patient points to the pain over the PSIS with one finger
Workup for Spondyloarthritis
- 1.HLA-B27: positive in 90-95% of ankylosing spondylitis cases
- 2.ESR and CRP: elevated in active inflammatory sacroiliitis
- 3.SIJ MRI: subchondral edema (sign of active sacroiliitis) — fundamental criterion for early diagnosis
- 4.Pelvic radiograph: chronic sacroiliitis with erosion, sclerosis, and ankylosis (New York grades)
- 5.Intra-articular SIJ block: relief of 75% or greater confirms the SIJ as the pain source
DIAGNÓSTICO DIFERENCIAL
Diagnóstico Diferencial
Lumbar Facet Pain
Leia mais →- Bilateral axial low back pain
- Worse with extension and rotation
- No pain on SIJ provocation
Testes Diagnósticos
- Medial branch block
- Facet provocation tests
L5-S1 Disc Herniation
- Radicular pain below the knee
- Positive Lasegue
- S1 neurologic deficit
Testes Diagnósticos
- Lumbar MRI
- Segmental neurologic exam
Piriformis Syndrome
- Deep gluteal pain
- Pain on piriformis palpation
- Pain on prolonged sitting
Testes Diagnósticos
- FAIR test
- Transrectal or transvaginal palpation
Trochanteric Bursitis
- Lateral hip pain
- Over the greater trochanter
- Worse when lying on the side
Testes Diagnósticos
- Trochanteric palpation
- Ultrasonography
Spondylolisthesis
Leia mais →- Palpable step-off in the spine
- Mechanical low back pain
- Slippage on radiograph
Testes Diagnósticos
- Lateral lumbar radiograph
- Dynamic radiograph
Treatments
Treatment of sacroiliitis depends fundamentally on etiology: mechanical dysfunction responds to local measures and rehabilitation, whereas inflammatory sacroiliitis in the context of spondyloarthritis requires specific systemic treatment. Correct identification of the cause is therefore the first therapeutic step.
For mechanical dysfunction, the approach is multimodal: pelvic stabilization exercises, manual therapy, acupuncture, and, in refractory cases, intra-articular block or radiofrequency ablation of the lateral branches of the sacrum.
TREATMENT OPTIONS FOR SACROILIAC PAIN
| TREATMENT | INDICATION | EVIDENCE | CONSIDERATIONS |
|---|---|---|---|
| Pelvic stabilization exercises | Mechanical dysfunction — first line | Moderate | Strengthening of glutes, core, and pelvic floor |
| Pelvic belt (sacroiliac belt) | SIJ instability, postpartum | Moderate | Adjunct to muscle strengthening |
| Acupuncture and laser therapy | Chronic pain, associated muscle component | Moderate | Adjunct to the exercise program |
| Intra-articular block (corticosteroid) | Pain confirmed by diagnostic block | Moderate | Diagnostic and therapeutic simultaneously |
| Radiofrequency of the lateral branches of the sacrum | Refractory pain confirmed by block | Moderate | Cooled RF with better results than conventional |
| Anti-TNF / Anti-IL17 | Inflammatory sacroiliitis (spondyloarthritis) | Strong | Systemic treatment for axial spondyloarthritis |
| Sacroiliac fusion | Pain refractory to all conservative measures | Moderate | Minimally invasive surgery with triangular implants |
Approach to Mechanical Sacroiliac Dysfunction
Phase 1
0-4 weeksInitial Measures and Analgesia
Modification of provocative activities, NSAIDs, pelvic belt if instability is present. Acupuncture for control of acute pain and gluteal and piriformis muscle spasm.
Phase 2
4-12 weeksPelvic Stabilization Program
Progressive strengthening of gluteus medius and maximus, lumbar multifidi, transversus abdominis, and pelvic floor. Pelvic proprioception exercises.
Phase 3
3-6 monthsGuided Interventions
Intra-articular block with corticosteroid for persistent pain. Simultaneously assesses the SIJ as the pain source and provides anti-inflammatory relief.
Phase 4
After conservative failureRadiofrequency or Fusion
Cooled radiofrequency of the lateral branches of the sacrum for confirmed refractory pain. Minimally invasive sacroiliac fusion reserved for selected cases.
Acupuncture and Laser Therapy
Medical acupuncture is a valuable tool in the treatment of sacroiliac pain, acting on both the articular component and the frequently associated myofascial component (trigger points in the gluteal muscles, piriformis, and quadratus lumborum).
Proposed mechanisms of action in sacroiliac pain include modulation of multisegmental nociceptive transmission (L2-S4) corresponding to the SIJ innervation, release of endogenous opioids, modulation of inflammatory mediators, and reduction of periarticular muscle spasm — mechanisms demonstrated mainly in preclinical models and general musculoskeletal pain studies, with clinical translation specific to sacroiliitis still limited.
Low-level laser therapy is proposed as an adjunct for its potential local anti-inflammatory effect and periarticular analgesia. Application with near-infrared wavelengths (808-980 nm) aims to reach adequate depth for the joint. Effects on cartilage regeneration described in preclinical studies do not have established clinical translation in human sacroiliac pain.
Prognosis
The prognosis of mechanical sacroiliac dysfunction is generally favorable. Most patients respond to conservative treatment with pelvic stabilization exercises and acupuncture. In pregnancy-related sacroiliac pain, resolution occurs spontaneously in 70-80% of women within the first 6 months postpartum.
Intra-articular block with corticosteroid provides relief in 60-70% of patients, but the duration is variable (2-12 weeks). Cooled radiofrequency of the lateral branches of the sacrum offers more prolonged relief (6-12 months) with success rates of 50-70% when patient selection is appropriate.
In inflammatory sacroiliitis from spondyloarthritis, long-term prognosis depends on early diagnosis and treatment. Biologic agents have transformed the natural history of these diseases: patients treated early show less radiographic progression, better function, and greater quality of life. Complete ankylosis of the SIJ, when it occurs, may paradoxically reduce pain by eliminating joint movement.
Myths and Facts
Myth vs. Fact
Sacroiliac pain is always caused by pelvic "misalignment."
The concept of "misalignment" or "subluxation" of the SIJ lacks robust scientific evidence. Sacroiliac pain results from inflammatory, degenerative, or mechanical-overload processes of the joint and its ligaments, not from "vertebrae out of place."
Sacroiliitis is a disease only of older adults.
Inflammatory sacroiliitis (spondyloarthritis) predominantly affects young adults between 15 and 40 years of age. Mechanical dysfunction is common in women in the peripartum period. Degenerative osteoarthritis of the SIJ increases with age.
Sacroiliac pain always radiates down the leg like sciatica.
Pain referred from the SIJ generally does not extend below the knee. It may radiate to the buttocks and posterior thigh, but radiation below the knee is more suggestive of lumbar radiculopathy. The predominant location is over the SIJ in the buttock.
If the SIJ MRI is normal, it cannot be sacroiliitis.
MRI is highly sensitive for active inflammatory sacroiliitis, but mechanical dysfunction may have a normal MRI. Intra-articular anesthetic block is the gold standard for confirming the SIJ as a pain source, regardless of imaging findings.
When to Seek Medical Help
Frequently Asked Questions about Sacroiliitis
The sacroiliac joint (SIJ) connects the sacrum (base of the spine) to the ilium (pelvic bone). It is responsible for transmitting forces from the trunk to the lower limbs. Pain may arise from mechanical dysfunction (overload, ligamentous instability, postpartum) or from inflammatory sacroiliitis (spondyloarthritis). The SIJ is richly innervated by multiple nerve segments (L2-S4), generating referred pain to the buttocks, thigh, and, occasionally, groin.
Mechanical dysfunction results from overload, ligamentous instability, or biomechanical alteration; it is more common in postpartum women and responds to exercise and local treatment. Inflammatory sacroiliitis is a manifestation of spondyloarthritis (ankylosing spondylitis, psoriatic arthritis), affects young adults, presents with nighttime pain and prolonged morning stiffness, and requires systemic treatment (anti-inflammatories and biologics). Workup with HLA-B27, inflammatory markers, and SIJ MRI distinguishes the two.
Diagnosis combines clinical provocation tests (Gaenslen, compression, distraction, sacral thrust, FABER) — three or more positive yield a sensitivity of 94%. The Fortin finger test (patient points to the pain over the PSIS) is simple and useful. Laboratory workup (HLA-B27, ESR, CRP) and SIJ MRI assess inflammatory sacroiliitis. Intra-articular block with anesthetic (relief greater than 75%) is the gold standard for confirming the SIJ as the pain source.
Yes. Acupuncture acts through multisegmental modulation of nociception (L2-S4), release of endogenous opioids, reduction of periarticular inflammation, and relaxation of muscles in spasm (glutes, piriformis, quadratus lumborum). The Baliao points (at the sacral foramina) and trigger points in the gluteal musculature are particularly effective. Laser therapy complements with a direct anti-inflammatory effect over the SIJ. Combination with pelvic stabilization exercises enhances results.
Yes. Sacroiliac pain affects 20-30% of pregnant women, especially in the third trimester, due to ligamentous laxity (relaxin hormone), weight gain, and shift of the center of gravity. Postpartum, resolution is spontaneous in 70-80% of women within the first 6 months. Pelvic stabilization exercises, sacroiliac belt, and acupuncture are safe and effective both during pregnancy and postpartum.
Spondyloarthritides are a group of inflammatory diseases that affect the spine and peripheral joints, including ankylosing spondylitis, psoriatic arthritis, and reactive arthritis. Bilateral sacroiliitis is the cardinal sign of axial spondyloarthritis. They predominantly affect young adults, with a strong genetic association (HLA-B27). The characteristic symptoms are inflammatory low back pain (nighttime, with prolonged morning stiffness, that improves with exercise). Treatment with biologics may modify progression.
An initial cycle of 8 to 10 sessions, performed 1-2 times per week, is recommended. Response is assessed by reduction of pain in provocative activities (sitting, climbing stairs, turning in bed). Patients with chronic pain may benefit from biweekly maintenance sessions. In postpartum dysfunction, shorter cycles (4-6 sessions) may be sufficient, combined with the pelvic strengthening program.
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