PMC

a Images of sacroiliac joint T2WI in study group. b Images of sacroiliac joint T2WI in control group. c Images of sacroiliac joint Dixon aqueous phase in study group. d Images of sacroiliac joint Dixon aqueous phase in control group. e Images of sacroiliac joint Dixon fat phase in study group. f Images of sacroiliac joint Dixon fat phase in control group

(a) A slice from the superior sub-region of the posterior sacroiliac joint. Boundaries of the posterior sacroiliac joint (in yellow) at the level of the first sacral body in horizontal images. Laterally and medially the region is delimitated by the iliac and sacral bones. It is deep to the posterior sacroiliac ligament (green) posteriorly and deep to anterior cartilaginous portion of the sacroiliac joint (red) anteriorly. (b) A slice from the middle sub-region of the posterior sacroiliac joint. Boundaries of the posterior sacroiliac joint (in yellow) at the level of the second and third sacral bodies. Laterally and medially the region is delimitated by the iliac and sacral bones. It is deep to the posterior sacroiliac ligament (green) posteriorly and deep to the anterior articular cartilaginous portion (red) anteriorly. (c) A slice from the inferior sub-region of the posterior sacroiliac joint. Boundaries of the posterior sacroiliac joint (in yellow) at the level of the third and fourth sacral bodies. Laterally and medially the region is delimitated by the iliac and sacral bones. It is deep to the posterior sacroiliac ligament (green) posteriorly and deep to the anterior articular cartilaginous portion (red) anteriorly. A: anterior, L: lateral, M: medial, P: posterior.

A. Effects of sacrotuberous ligament, biceps femoris muscle, and gluteus maximus muscle on the sacroiliac joint. A; Effects of sacrotuberous ligament (black and gray lines) on the sacroiliac joint. Tension during nutation of the sacrum (black arrow), controlling the sacroiliac joint (dotted line), by increased the sacrotuberous ligament tension (white arrow).
STL: sacrotuberous ligament
B. Effects of biceps femoris muscle (BF) on the sacroiliac joint. Relationship between biceps femoris muscle and the sacrotuberous ligament. The tension (white arrow) in the biceps femoris (*) continues with the superficial fibers of the sacrotuberous ligament and is involved in tension (black arrow) of the sacrotuberous ligament (**).
C. Effect of the gluteus maximus (black and gray lines) on the sacroiliac joint. The sacroiliac joint (dotted line) is compressed and stabilized by the glueus maximus contraction (white arrow).

Figure : Axial view showing sacroiliac joint cortical destruction, erosive changes, and widening.
Figure : Coronal view showing sacroiliac joint cortical destruction, erosive changes, and widening.