How is the posterior approach of surgical treatment for idiopathic scoliosis performed?

Updated: Dec 02, 2020
  • Author: Charles T Mehlman, DO, MPH; Chief Editor: Jeffrey A Goldstein, MD  more...
  • Print
Answer

The major superficial muscles of the back are not often directly visualized during posterior surgical approaches for scoliosis, but they must not be forgotten. These muscles include the trapezius, the rhomboid major, the rhomboid minor, and the latissimus dorsi. Using an animal model, Kawaguchi et al showed that significant posterior muscle injury can be induced by the pressure exerted by surgical retractors. [132] This certainly makes a case for intermittent removal and replacement of such retractors during the course of posterior spinal surgery.

The route for exposure of the posterior spinal elements passes through the cartilaginous apophyses of the spinous processes. These structures, often referred to as the cartilaginous caps, are systematically split in the midline to allow sequential subperiosteal dissection of the spinous processes, laminae, facet joints, and transverse processes.

The laminae of the thoracic vertebrae spread out from the midline like wings and flow upwards (cranially) in the direction of the transverse processes. The facet joints of the thoracic spine are shingled in a coronal plane in such a way that the inferior facet that contributes to each joint is located posteriorly and the superior facet is located anteriorly. The thickness of the interior and superior facets of the thoracic spine is in the range of 3-5 mm. [133] The thoracic facet joints are located a mere 7-11 mm from the midline of the posterior spine.

Progressing from the thoracic to the lumbar spine, important differences are noted. The V-shaped laminae of the thoracic spine give way to the butterfly-shaped laminae of the lumbar spine. This orientation change is important for the surgeon to remember when exposing these bony elements. The facet joints of the thoracic spine, which are oriented in more of a coronal plane, transition into the more sagittally oriented facet joints of the lumbar spine. The transverse processes of the thoracic spine, which seem to flow directly up and away from the laminae, change significantly in the lumbar spine so that they are no longer in close proximity to the laminae and are located anterior and inferior to the lumbar facet joints.

The ribs are also obviously absent in the lumbar vertebrae. What some consider a rib remnant does persist and is referred to as a mammillary body or mammillary process. It is most pronounced near the thoracolumbar junction but may be identified on nearly all of the lumbar segments. In the sagittal plane, one must also appreciate that the normal gentle kyphosis of the thoracic spine reaches its apex at about the T7-9 region. Below this, a rather definite transition to lumbar lordosis occurs, with an apex around the L3 level.

Thoracic kyphosis is typically in the range of 20-40° (Cobb measurements usually taken from the top of T3 to the bottom of T12). Some authors have stated that up to 50° of thoracic kyphosis should be considered normal. [134] Normal lumbar lordosis is considered by some to range from 35º to 55° (Cobb measurements usually taken from the top of L1 to the top of L5).


Did this answer your question?
Additional feedback? (Optional)
Thank you for your feedback!