with that vertebra will exit through the intervertebral foramen well above
the intervertebral disk so that it will notbe affected by a herniation at that
level. However, a posterolateral herniation (the usual direction) will
impinge on the next lower nerve as it courses toward its associated inter-
vertebral foramen. In this case, pain was distributed along the medial side
of the leg and foot as far as the great toe, the distribution of the saphenous
branch of the femoral nerve (L5). Herniation of the fourth lumbar inter-
vertebral disk between vertebral bodies L4–L5 would affect nerve L5. None
of the other answers (answers a, c, d, and e)are correct.
500.The answer is b.(Moore and Dalley, pp 526–527.)A horizontal line
drawn across the posterior superior iliac crests generally crosses the fourth
lumbar spinous process. Lumbar punctures (spinal taps) are generally per-
formed at the L3–L4 or L4–L5 interspinous space since the spinal cord ter-
minates by L2 in greater than 99% of the adult population. The ligaments
that need to be penetrated in the midline include the supraspinous liga-
ment, the interspinous ligament and the ligamentum flavum (if slightly off
the midline). The needle must pierce both the dura mater and arachnoid
mater in order to collect cerebral spinal fluid (CSF), which should be clear.
The sacral hiatus, which is marked by the sacral cornu and covered by the
sacrococcygeal ligament, is used to gain access to extradural space. None of
the other answers (answers a, c, d, and e)are correct.
Extremities and Spine Answers 603