Erector Spinae in the Lumbar Region
Examining the transverse section at the lumbar spine allows description of different approaches to the posterior aspect of the spine:

1.  The most common approach is directly in the midline.  This allows for good bilateral exposure.  

2.  The para-median (‘Wiltse’) approach is via the layer between the multifidus and the longissimus muscles.  In this plane, which is relatively bloodless, the dissection goes to the junction of the base of the transverse process and the facet joint.  
 
3.  An approach can also be made lateral to the erector spinae group.  In this case dissection is between the erector spinae and the transversus abdominis muscles.

These approaches allow surgeons access to lateral pathology such as a lateral disc prolapse (Slide 1 and Slide 2), which would be extremely difficult through a midline approach.