Three Pathways between the Sacroiliac Joint and Neural Structures

Images of a 36-year-old man with left-sided lower back, posterior hip, and thigh pain, who sustained an offshore work-related lifting injury.

A, Anteroposterior arthrogram of the inferior aspect of the left SIJ shows a normal inferior recess (r), bead of contrast within the joints margins (arrow), and collection of contrast medium escaping through a ventral tear (VT).

B, Lateral view confirms that the collection of contrast medium escaping through a ventral tear (arrow) is remote to the needle tip, which is in the inferior aspect of the capsule.Symbols: 1, body of S1; 2, body of S2; 3, body of S3.

C, Same projection as that shown in B except with a wider field of view. Arrow indicates ventral tear.

D, Offset opposite lateral arthrogram discloses an intact ventral capsule (arrowheads) on the contralateral side compared with a disrupted capsule with a ventral tear (arrows). White arrow points to the needle in inferior aspect of right SIJ.

E, Post-arthrography axial CT scan obtained at the S2 level (bone window/level settings), with contrast medium in both SIJs. Presacral collection of contrast medium is evidence of a left ventral capsular tear (open arrow). Contrast medium contracts the lumbosacral plexus elements (arrowheads).

F, Line drawing of the ventral hemipelvis, which allows contrast medium to escape and contact the neural elements of the sacral plexus (interrupted lines). The inset shows the torn fibers of the ventral capsule allowing contrast medium to leak slowly.

Capsular attention (ie, focal capsular bulge) and schism in a 28-year-old man with an insidious onset of lower back pain.

A, Concentric area of ventral capsular attenuation is displayed at soft-tissue settings (arrowheads) of this postarthrography axial CT scan obtained at the S2 level.

B, Markedly attenuated area of the ventral capsule and sacroiliac ligament allows seepage of contrast medium in a feathery, wispy dispersal pattern (ie, schism with indistinct margins) into the presacral region (arrow).

A 42-year-old laborer with back pain and occasional posterior right lower extremity pain to the calf. A potential pathway between the SIJ and anterior ramus of S1 is present.

A, Arthrogram of the anteroposterior view reveals contrast medium extending (dotted line) into the S1 dorsal foramina (1). Symbols: 2, S2 dorsal foramina; 5, pedicle of L5.

B and C, Axial and direct coronal postarthrography CT scan through the S1 foramina (soft-tissue window/level settings). Contrast is observed in the right S1 dorsal foramina on both scans (arrowheads).

D, Compare this axial CT scan at the S1 level in another patient after bilateral SIJ arthrography to the above case. The arrowheads point to the S1 anterior rami bilaterally. Notice on the right how contrast medium encircles the S1 segmental root.

E, Line drawing of the dorsal view of the pelvis and L5−S1 motion segment. Small arrowheads on the right indicate where the ilium has been “resected” to reveal the SIJ; the dorsal ligaments have been stripped away. The fine wavy arrow indicates contrast medium tracking subligamentously from the SIJ to the S1 dorsal-sacral foramina. The small curved arrow (at the top of the right SIJ) indicates contrast medium extravasating from the superior aspect of the right SIJ into the right L5 root canal. The discontinuous lines indicate the L5 segmental nerve roots.