The interspace between the sacrum and the transverse process (TP) of L5 is the lumbosacral osteofibrotic tunnel bounded by the ala sacrum inferiorly, the TP L5 cranially, the fifth lumbar neural foramen medially, the lumbosacral ligament anteriorly, and the intertransverse ligament posteriorly.
The lumbosacral ligament typically extends obliquely inferolateral from the TP L5 to the ala sacrum.
The lumbosacral ligament (green arrows), intertransverse ligament (red arrows), sacrum (red asterix), TP of L5 (magenta asterix). P = posterior, A = anterior, Cr = cranial, Ca = caudad.
