Rana SH, Farjoodi P, Haloman S, Dutton P, Hariri A, Ward SR, Garfin SR, Chang DG.
Sacroiliac joint (SI) pain is increasingly being recognized as a
source of low back pain. Injections and percutaneous type procedures are
performed to treat symptomatic joints. However, there are limited studies
available assessing the anatomy of the SI joint in vivo among patients with pain.
The purpose of this study was to provide more precise information on
the dimensions and orientation of the SI joint using a new technique for the
radiographic evaluation of this joint.
Three dimensional computed tomographic (CT) reconstructions of the
pelvis were formatted from 100 SI joints in 50 patients who had clinically
indicated abdominal/pelvic scans. These images were manipulated to evaluate the
SI joint in multiple planes and measure its dimensions, area, and relationship to
anatomic landmarks such as the anterior superior iliac spine (ASIS) and posterior
superior iliac spine (PSIS).
Of the 50 patients, 23 were men and 27 women. Their mean age was 47.6
years (± 18.1). The SI joint consists of a superior limb which measures 39.7 mm
(± 4.8) in length, and an inferior limb which measures 54.3 mm (± 5.1), oriented
at an angle of 100.1° (± 8.1) to one another. The mean area of the joint was
1276.8 mm² (± 189.8). The horizontal distance from the ASIS to the front of the
superior SI joint is 75.4 mm (± 8.4). The horizontal distance from the PSIS to
the back of the superior SI joint is 43.9 mm (± 5.6). The joint stretches 7.5 mm
(± 5.9) cephalad and 38.1 mm (± 6.4) caudal to the PSIS, and 35.4 mm (± 8.8)
cephalad and 10.2 mm (± 11.4) caudal to the ASIS.
CT scans were performed with patients lying supine, while most SI
joint procedures are performed with a patient prone. However it is doubtful that
the bony anatomic landmarks would change appreciable in this largely immobile
joint. These patients were seen in the emergency department for a variety of
conditions related to abdominal and pelvic pain, and not exclusively for SI joint
Treatment of the SI joint by surgeons and interventionalists is
hampered by the limited number of anatomic studies in the literature. Our study
presents the SI joint as a 2-limbed structure, sitting from slightly above the
level of the PSIS rostrally to slightly below the level of the ASIS caudally.
Palpation of these landmarks may assist in directing physicians to the joint. To
begin an interventional pain procedure, with a patient lying prone, this data
supports tilting the x-ray image intensifier 10 degrees caudal past the vertical
anteroposterior (AP) view for optimal approach of the SI joint's inferior limb.
The needle entry should be about 44.1 mm (1.75 inches) caudal to the PSIS. The
image intensifier should have a 12 degree left lateral oblique view for injection
of the right SI joint, and a 12 degree right lateral oblique view for the left SI
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