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The Sacroiliac Joint After Lumbar Fusion: What Should You Be Watching For?


A Biomechanical Reality 

Lumbar and lumbosacral fusion procedures are widely performed to restore spinal stability, correct deformity, and relieve neural compression. By eliminating pathological motion, arthrodesis often produces meaningful clinical improvement. Yet stability inevitably alters biomechanics. When motion is removed from one region of the spine, mechanical forces must be redistributed elsewhere within the lumbopelvic complex. 

Increasingly, the sacroiliac joint (SIJ) has emerged as a structure that may absorb this shift. 

The SIJ connects the sacrum to the pelvis and functions as a load-transfer interface between the axial skeleton and lower extremities. Although it permits only minimal motion, it plays a critical role in dissipating axial and rotational stress. Because of its anatomical position, fusion particularly when extending to the sacrum may increase mechanical demand across the SIJ. 

 

What This Systematic Review Evaluated 

A 2023 systematic review analyzed 21 studies involving 2,678 patients who underwent thoracolumbar, lumbar, or lumbosacral arthrodesis. The cohort included 1,198 males (44.7%) and 1,480 females (55.2%), with mean ages ranging from 42 to 73 years and follow-up periods extending up to nearly seven years. 

Most included studies were Level III evidence, reflecting moderate heterogeneity in study design, diagnostic criteria, and outcome reporting. The aim was straightforward: determine how frequently SIJ pain and degeneration occur after fusion and identify potential contributing factors. 

 

What the Evidence Suggests 

Reported prevalence of postoperative SIJ pain ranged from 3% to 90% across studies. While this wide variation reflects differences in diagnostic standards and follow-up duration, it underscores that SIJ pain following fusion is not uncommon. 

More consistent patterns emerged when comparing surgical constructs. Patients undergoing fixed arthrodesis fusion constructs that include the sacrum demonstrated substantially higher SIJ pain rates (59%) compared with floating fusions that spared the sacrum (10%). Radiographic findings reinforced this association, with degenerative SIJ changes observed in 75% of post-arthrodesis patients versus 38.2% in control populations. 

Some data suggested that increasing the number of fused levels may elevate risk, with SIJ pain prevalence rising from 5.8% in single-level fusions to over 22% in four-level constructs. Spinopelvic alignment also appeared influential; patients with higher pelvic tilt and incomplete restoration of lumbar lordosis were more likely to experience SIJ pain. 

 

Key Findings from 21 Studies (2,678 Patients) 

What Should You Be Watching For? 

This review does not question the value of spinal fusion. Rather, it highlights a biomechanical consequence that may be underrecognized in postoperative care. 

When lumbar motion is eliminated, the sacroiliac joint may become the adjacent structure responsible for compensatory load absorption. In some patients, this redistribution appears to translate into measurable degeneration and clinically meaningful pain. 

The evidence suggests that risk may be higher when fusion constructs include the sacrum, when multiple levels are fused, or when sagittal alignment is not adequately restored. Importantly, approximately 15% of patients presenting to spine clinics may already have SIJ pain preoperatively underscoring the need for careful baseline assessment. 

At the same time, substantial heterogeneity across studies limits precise incidence estimates. Diagnostic criteria varied, imaging protocols differed, and follow-up durations were inconsistent. What emerges is not a single definitive percentage, but a consistent signal across datasets. 

For spine surgeons and clinicians, the implication is not alarm but awareness. Careful preoperative SIJ evaluation, thoughtful construct selection, and deliberate attention to sagittal balance may influence long-term outcomes. Persistent postoperative pain should prompt consideration of the SIJ as a potential pain generator rather than focusing solely on adjacent segment disease or hardware-related causes. 

Spinal fusion restores stability. This review invites us to consider where that stability redistributes the load and whether the sacroiliac joint may ultimately bear part of that cost. 

 

Interested in Reading the Full Study? 

 
 
 
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