Fig. 6

40 year old specimen. A-D, Transversal cross-sections (A, C) and matched ultrasonographic (US) views (B, D; for orientation, see insets) at the level of the posterior superior iliac spine (PSIS) showing a superficial lumbar multifidus (LM) and the origin fibers (*) of erector spinae (ES) lateral and deep to it. ES originates from the PSIS and from the dorsal ligaments of the sacro-iliac joint (SI-J). Figs. A, B are just caudal to fig. C, D. (A) S1 = dorsal spine S1. (B) Matched US view with curvilinear transducer 3.6 MHz in human volunteer. At this level, LM is the only superficial muscle (demarcated by white dotted line). Deep to it the origin fibers of ES (*) can be discerned at the dorsal part of the sacro-iliac joint (SI-J) as separate structure with a different echogenic composition compared to LM. (C) S1 = dorsal spine S1. (D) Same curvilinear view as in Fig. B showing the different ultrasonographic composition of the ES fibers (demarcated by white dotted line), deep and lateral to LM