Sacroiliac Joint Dysfunction

This is a **challenging and frustrating scenario** of **failed SI joint fusion** - defined as **persistent or recurrent pain after SI joint fusion surgery** despite technically successful implant placement. This occurs in **15-30% of cases** and requires a systematic approach to identify the cause and guide management. The patient had appropriate indications for surgery (refractory pain, positive diagnostic injection 85% relief, failed conservative treatment) but has not achieved pain relief despite good implant position. ### Differential Diagnosis for Persistent Pain I would approach this with a broad differential, categorizing causes into **mechanical**, **biological**, **incorrect diagnosis**, and **other pain generators**: **1. Incomplete Fusion (Pseudarthrosis) - Most Common** The CT shows bridging bone but no complete fusion at 9 months. SI joint fusion can take **12-18 months to achieve solid arthrodesis**. Some patients have persistent pain until solid fusion occurs. However, some series show that radiographic fusion does not always correlate with clinical outcome - some patients with incomplete fusion on imaging are pain-free, while others with solid fusion continue to have pain. **2. Hardware-Related Pain** (a) **Implant Prominence/Irritation**: Triangular titanium implants can cause local irritation if they protrude or abut adjacent structures. Examine for focal tenderness over implant trajectory. (b) **Stress Shielding or Adjacent Bone Reaction**: Periosteal reaction or stress concentration around implants, though this usually manifests as implant loosening (not seen here). **3. Incorrect Initial Diagnosis (Misidentified Pain Source)** This is critical to reconsider. Despite pre-operative diagnostic workup showing 85% relief with injection and positive provocative tests, it's possible the SI joint was **not the sole or dominant pain generator**: (a) **Lumbar Facet Arthropathy**: Facet-mediated pain can mimic SI joint pain (buttock pain, positive FABER test which also stresses lumbar spine). The patient may have had **dual pathology** (SI joint AND facets), and fusing the SI joint unmasked persistent facet pain. (b) **Lumbar Disc or Radiculopathy**: L5-S1 pathology can refer pain to buttock and PSIS area. Review pre-operative MRI lumbar spine. (c) **Hip Pathology**: Intra-articular hip pathology (labral tear, femoroacetabular impingement, early arthritis) or extra-articular hip pathology (greater trochanteric pain syndrome, gluteal tendinopathy). Hip pathology can present as buttock pain and give positive FABER test (which stresses hip AND SI joint). (d) **Myofascial Pain or Piriformis Syndrome**: Gluteal muscle or piriformis pain can localize to buttock and PSIS area, positive provocative tests may reflect muscle guarding rather than true SI joint pathology. **4. Adjacent Segment Pathology** Fusion of the SI joint alters biomechanics, potentially increasing stress on adjacent structures: (a) **Contralateral SI Joint**: Increased loading on left SI joint after right fusion may cause left SI joint pain. Examine for left SI joint tenderness and provocative tests. (b) **Lumbar Spine (Especially L5-S1)**: Increased stress on lumbosacral junction after SI fusion. Check for new lumbar symptoms. **5. Chronic Pain Syndrome or Central Sensitization** After prolonged pre-operative pain (18 months failed conservative treatment) and now 9 months post-operative pain, the patient may have developed **chronic pain syndrome** with central sensitization. Pain persists despite removing peripheral nociceptive source. Psychosocial factors (catastrophizing, kinesiophobia, secondary gain from disability) may perpetuate symptoms. **6. Infection (Low-Grade)** Less likely given normal inflammatory markers (CRP less than 5, ESR 12), no systemic symptoms, and no implant loosening. However, **low-grade infection** (Cutibacterium acnes, Staphylococcus epidermidis) can present with persistent pain and normal inflammatory markers. Would expect more local signs (drainage, warmth, erythema). ### Investigations **1. Detailed History and Re-Examination** (a) **Pain Mapping**: Ask patient to point with one finger exactly where her pain is. Is it still precisely over right PSIS (SI joint), or has it shifted to lumbar spine, contralateral SI joint, hip, or become diffuse? (b) **Compare to Pre-Operative Pain**: Is the pain **identical** to pre-operative pain, or has the character/location changed? If identical, suggests persistent SI joint pathology (incomplete fusion) or wrong diagnosis. If changed, suggests new pathology (adjacent segment, hardware irritation). (c) **Functional Impact**: Activities that worsen pain (sitting? walking? stairs?). Pre-operative activities that were most painful - are those still problematic? (d) **Provocative Tests**: Repeat cluster. Are they positive on the **same side** (right - suggests persistent SI joint pathology), **opposite side** (left - suggests contralateral SI joint overload), or **lumbar** (suggests facet or discogenic pain)? (e) **Hip Examination**: Full hip ROM, FABER test (distinguishing hip vs SI pain), impingement tests (FADIR), Stinchfield test (hip flexion against resistance). (f) **Neurological Examination**: L5-S1 radiculopathy? Straight leg raise? Sensory/motor deficits? **2. Advanced Imaging** (a) **CT Scan (Already Done)**: Shows implant position (good), no loosening/fracture/migration, some bridging bone but incomplete fusion. This is not unexpected at 9 months. Reassess at 12-18 months for solid fusion. (b) **MRI Lumbar Spine with Metal Artifact Reduction Sequences (MARS)**: Assess for facet arthropathy, disc pathology, nerve root compression that may have been overlooked pre-operatively or developed post-operatively. MRI also shows soft tissue changes, inflammation, or edema. (c) **Nuclear Medicine Bone Scan or SPECT-CT**: Can localize increased metabolic activity (bone remodeling, inflammation, stress). Increased uptake at **fusion site** suggests ongoing bone remodeling (normal up to 12-18 months) or incomplete fusion. Increased uptake at **adjacent sites** (contralateral SI joint, lumbar facets, hip) suggests adjacent segment pathology. (d) **MRI Pelvis/Hip**: If hip pathology suspected, MRI hip to assess for labral tear, FAI, AVN, gluteal tendon pathology. **3. Diagnostic Injections (Critical for Management Decision)** (a) **Repeat SI Joint Injection (Right)**: Fluoroscopic-guided injection of local anesthetic into the **fused right SI joint**. If greater than 75% relief, suggests the fusion is incomplete and the SI joint remains a pain source. If less than 50% relief, suggests the SI joint is no longer the source (fusion successful biomechanically, or was never the source). (b) **Contralateral SI Joint Injection (Left)**: If right SI joint injection negative but left SI joint tenderness/provocative tests positive, inject left SI joint. Relief confirms contralateral overload. (c) **Lumbar Facet Medial Branch Blocks**: If lumbar facet arthropathy seen on MRI and facet provocation on examination, perform diagnostic medial branch blocks at L4-5 and L5-S1. Relief confirms facet-mediated pain. (d) **Hip Intra-Articular Injection**: If hip examination suggestive, fluoroscopic-guided hip injection with local anesthetic. Relief confirms intra-articular hip pathology. ### Management Options Management depends on findings from investigations and diagnostic injections: **Scenario 1: Incomplete Fusion (Positive Right SI Joint Injection)** (a) **Conservative Management (First-Line)**: Continue physiotherapy, activity modification, NSAIDs. Many fusions mature between 12-18 months. Repeat imaging at 12 months to assess fusion progression. (b) **Revision Fusion**: If fusion fails to progress or patient has severe symptoms, consider **revision SI joint fusion** with bone grafting or biologics (BMP) to promote fusion. Open approach may be needed to debride pseudarthrosis and achieve solid fusion. This is a salvage option with uncertain outcomes. **Scenario 2: Adjacent Segment Pathology (Positive Contralateral SI Joint or Facet Injection)** (a) **Conservative Management**: Physiotherapy targeting new pain source, injections for symptom relief (repeat SI joint injection contralateral side, or facet injections/RFA for facets). (b) **Contralateral SI Joint Fusion**: Rarely indicated, but if severe symptoms and failed conservative treatment, may consider. Risk of bilateral SI joint fusion includes loss of pelvic mobility and increased stress on lumbar spine. (c) **Lumbar Fusion**: If facet pain severe and refractory, may need lumbar fusion (L5-S1 or above depending on pathology). This extends the fusion but carries significant morbidity. **Scenario 3: Incorrect Initial Diagnosis (Negative SI Joint Injection, Positive Alternative Source)** (a) **Treat the Correct Source**: Hip arthroscopy for labral tear/FAI, lumbar facet RFA or fusion for facet arthropathy, piriformis injection or release for piriformis syndrome, etc. (b) **Accept Failed Surgery**: Counsel patient that SI joint was likely not the source, surgery addressed a non-painful joint. Focus on identifying and treating actual pain generator. **Scenario 4: Hardware Irritation (Focal Tenderness Over Implant Trajectory)** (a) **Hardware Removal**: If fusion solid on CT (bridging bone visible) and symptoms localized to hardware, can remove implants. However, risk of recurrent instability if fusion incomplete. Usually wait 12-18 months to ensure fusion solid before hardware removal. **Scenario 5: Chronic Pain Syndrome/Central Sensitization (Negative All Injections, No Identifiable Source)** (a) **Multidisciplinary Pain Management**: Refer to chronic pain clinic for comprehensive approach including psychology (CBT for pain, address catastrophizing), physical therapy (graded functional restoration), medications (neuropathic pain agents like gabapentin, duloxetine, NOT opioids), and interventional pain techniques (spinal cord stimulation if appropriate). (b) **Counsel About Realistic Expectations**: Some patients do not achieve complete pain relief despite technically successful surgery. Goal is functional improvement, not complete pain elimination. ### Key Teaching Points (1) **Failed SI joint fusion occurs in 15-30% of cases**: Despite appropriate patient selection and technically successful surgery, some patients do not improve. Causes include incomplete fusion, incorrect initial diagnosis, adjacent segment pathology, hardware issues, or chronic pain syndrome. (2) **Diagnostic injections are critical for failed fusion workup**: Repeat SI joint injection, contralateral SI joint injection, lumbar facet blocks, and hip injection help identify persistent or new pain sources. Guide management decisions. (3) **Pre-operative diagnostic injection response doesn't guarantee surgical success**: Even with 85% relief from diagnostic injection, the patient may have had dual pathology, or the pain may have evolved post-operatively. (4) **Incomplete fusion at 9 months is not necessarily a failure**: SI joint fusion can take 12-18 months to achieve solid arthrodesis. Repeat imaging at 12-18 months before declaring pseudarthrosis. (5) **Adjacent segment pathology after SI fusion is recognized**: Contralateral SI joint overload and increased lumbar stress (especially L5-S1) can develop after SI fusion. Biomechanical trade-off. (6) **Revision surgery has uncertain outcomes**: Revision SI joint fusion, hardware removal, or extension of fusion to adjacent structures (contralateral SI joint, lumbar spine) should be approached with caution. Ensure correct diagnosis with diagnostic injections before revision. (7) **Chronic pain psychology matters**: After 27 months of pain (18 months pre-op + 9 months post-op), central sensitization and psychological factors may perpetuate symptoms. Multidisciplinary approach needed.