Editing Retroperitoneum (section)

== Posterior abdominal wall ==

* '''Table for Musculature of the Posterior and Lateral Abdominal Wall'''
* '''Flank muscles'''
** '''Layers:'''
*** '''Skin'''
*** '''Subcutaneous fascia'''
*** '''External oblique'''
**** '''Inferior border of the aponeurosis of the external oblique forms the inguinal ligament'''
*** '''Internal oblique'''
*** '''Transversus abdominus'''
**** Named because of the transverse direction of its muscle fibers
*** '''Transversalis fascia'''
**** '''Crosses the midline anteriorly''' '''and fuses with the lumbodorsal fascia posteriorly'''
**** Continuous with the endopelvic fascia
** '''External oblique, internal oblique, and transversalis fascia are each invested in a layer of fascia'''
** These flank muscles function to flex, extend, and rotate the trunk and provide compression of the abdominal contents.
* '''Psoas, Iliacus, Quadratus Lumborum, and Erector Spinae'''
** Psoas major
*** Travels along the pelvic brim posterior to the inguinal ligament
** '''Psoas minor'''
*** '''Functions in flexion of the thigh at the hip joint'''
*** Innervated by the anterior rami of L1, L2, and L3
*** May be absent in some individuals
** '''Iliacus'''
*** '''Functions in flexion of the thigh at the hip joint'''
** Quadratus lumborum
*** Lies posterior and medial to the psoas muscle
** Erector spinae (sacrospinalis)
*** Large group of back muscles
** Insert figure

* '''Spine'''
** '''Consists of:'''
*** '''7 cervical vertebrae'''
*** '''12 thoracic vertebrae'''
*** '''5 lumbar vertebrae'''
*** '''Sacrum'''
*** '''Coccyx'''
** '''The spinal cord terminates in the cauda equina at spinal column level L2'''
*** '''In the adult,'''
**** '''The lumbar cord is situated between T9 and T11 vertebrae.'''
**** '''The sacral cord is situated between the T12 to L2 vertebrae'''
** '''Spinal cord segmental levels are defined by their roots but are not always situated at the corresponding vertebral levels'''
*** '''When discussing spinal cord injury, one must be careful to specify vertebral column level versus spinal segmental level'''
**** For example, the C8 cord segment is situated in the C7 vertebra while the T12 cord segment is situated in the T8 vertebra.
**** '''In this distal end of the spinal cord (conus medullaris), the spinal cord segments are named for the vertebral body at which the nerve roots exit the spinal canal.'''
***** Thus, although the sacral spinal cord segment is located at vertebral segment L1, its nerve roots run in the subarachnoid space posterior to the L2 to L5 vertebral bodies until reaching the S1 vertebral body, at which point they exit the canal.
***** Therefore, '''all of the sacral nerves that originate at the L1 and L2 spinal column levels run posterior to the lumbar vertebral bodies until they reach their appropriate site of exit from the spinal canal.''' '''This group of nerve roots running at the distal end of the spinal cord is commonly referred to as the cauda equina.'''
***** Conus medullaris vs. cauda equina
****** The most distal bulbous part of the spinal cord is called the '''conus medullaris''', and its tapering end continues as the filum terminale. Distal to this end of the spinal cord is a collection of nerve roots, which are horsetail-like in appearance and hence called the '''cauda equina''' (Latin for horse's tail)§
* '''10th, 11, and 12th ribs'''
** The lower ribs function to protect the retroperitoneal structures from traumatic injury. '''Fracture of these lower ribs should lead to a high clinical suspicion for injury to the retroperitoneal structures'''
** '''The 11th and 12th ribs must be distinguished from the other ribs because they have no anterior connection with the sternum and are often referred to as floating ribs. These ribs are of clinical significance during palpation for the marking of a surgical incision'''
** '''The intercostal vessels and nerves travel''' between the internal intercostal and innermost intercostal muscles, within the costal groove '''on the caudal margin of the superior rib'''