On the lower portion of the back, the latissimus dorsi muscle spans over the body. It originates from the spinous processes of the six lower thoracic vertebrae, lumbar and sacral vertebrae and ilium, inserting onto the humerus see Fig. In the deeper part of the back are two large groups of muscles: the erector spinae sacrospinalis and transversospinalis muscles.
The erector spinae consists of three separate groups of muscles that run from the sacrum and iliac crest to the ribs or transverse process of the vertebrae: the iliocostalis lateral , longissimus middle , and spinalis medial; see Fig. The iliocostalis muscle inserts into the angles of the ribs and into the cervical transverse processes from C4 through C6. The longissimus thoracis muscles insert into the thoracic transverse processes and nearby parts of the ribs between T2 and T The spinalis muscle is largely aponeurotic and extends from the upper lumbar to the lower cervical spinous processes.
The transversospinalis muscle group passes obliquely cephalad from the transverse processes to the spinous processes immediately deep to the erector spinae muscle. These muscles fall into three layers.
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The most superficial layer, the semispinalis muscle, arises from the tips of the transverse process and inserts into the tips of the spinous processes. The semispinalis capitis passes from the upper six thoracic transverse processes and lower four cervical articular processes to the occipital bone between the superior and inferior nuchal lines. The semispinalis cervicis muscle starts from the upper thoracic and lower cervical transverse process and attaches to the spinous processes of C2 through C5.
The semispinalis thoracis muscle runs from the transverse processes of the lower six thoracic vertebrae onto the spinous processes of the upper thoracic and the last two cervical vertebrae. The intermediate layer, the multifidus, arises from the sacrum, posterior sacroiliac ligament, accessory processes of the lumbar spine, and articular processes of the thoracic spine and inserts to the spinous processes of the vertebrae up to C2.
Operative Spinal Cord Anatomy | The Neurosurgical Atlas, by Aaron Cohen-Gadol, M.D.
The deepest muscles of this group, the rotators, are small muscles that bridge from the transverse processes to the lamina of the vertebra directly above. The head of a rib articulates with the adjacent parts of its own vertebral body, the vertebra above, and the intervertebral disk between them Fig. The exceptions to this general rule are the first, eleventh, and twelfth ribs, which articulate only with their own vertebral body. On the vertebral body from the second to the tenth level, each rib head has two synovial joints with a vertebral body and intervening radiate ligament enforcing the joint.
These are two independent joint surfaces, separated by the posterolateral position of the intervertebral disk. The inferior articular surface is numbered the same way as the rib and has a height slightly greater than the pedicle, and its posterior limit corresponds to the point of insertion of the pedicle. Its height represents about one third of the height of the body. In contrast, the superior facet represents only half the height of the inferior facet.
The third synovial joint is the costotransverse joint, which is strengthened by superior and lateral costotransverse ligaments Fig. The superior costotransverse ligament joins the neck of the rib to the transverse process immediately above. The ribs are also attached to one another through the intercostal musculature, which originates medially on each superior rib and inserts laterally on its immediately inferior rib.
This strip of muscles contains the intercostal nerve, artery, and vein. Most frequently, the intercostal vein is most cephalad, with the intercostal artery close to it but caudad Fig. The intercostal nerve is frequently found separate from these structures and is located most caudad of the three. Immediately ventral to the intercostal bundle and intercostal muscles lies the pleura. Some neurovascular structures are related to the spine in the posterior mediastinal space.
Between T4 and T7, the aorta has a close relationship with the left lateral surface of the vertebral bodies.
Surgical approaches to the thoracolumbar spine.
It then moves medially to occupy a more anterior position, and at the level of the diaphragm, it is strictly prevertebral. The segmental arteries arise from the posterior surface of the thoracic aorta and run horizontally, following the concavity of the vertebral body. At the level of the foramen, they bifurcate into a radiculomedullary and intercostal branch.
In the upper thoracic region, the first two intercostal spaces are supplied by branches of the costocervical trunk through the highest intercostal artery. Because the aorta is displaced downward and to the left, the upper four intercostal arteries ascend to reach intercostal spaces three through six.
They stretch obliquely across each vertebral body from caudad to cephalad in direct apposition to the periosteum of the vertebral body and are located deep to the azygos and hemiazygos vein, the thoracic duct, and the sympathetic trunk. On the left side, the superior hemiazygos vein occupies a position lateral to the aorta and receives collateral branches down to the sixth or seventh interspace. The azygos vein is lateral to the esophagus on the right side and runs inferiorly to join the superior vein cava at the fourth interspace. At the point where it turns medially, it may receive some branches, which may be divided if necessary Fig.
The sympathetic chain runs vertically and lies atop the heads of the ribs at the anterior edge of the foramina.
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From the intercostal nerves the chain receives the rami communicantes. A section of a few of these will be of no functional consequence as long as the major chain is preserved.
From the inferior thoracic ganglia are derived larger trunks that constitute the splanchnic nerves, and these should be spared. The lateral extracavitary approach LECA is an extension of the costotransversectomy. The more extensive rib resection provides a more ventral and wider operative view across the midline. LECA is indicated for the removal of extradural mass lesions anterior and lateral to the spinal cord or cauda equina, followed by anterior vertebral fusion.
It can be applied for the management of thoracic disk herniation, upper lumbar disk herniation, trauma, tumors, and inflammatory diseases that involve up to three and sometimes four vertebral levels. LECA may not be applicable above the T4 level because of the scapula and below the L4 level because of the iliac crest.
This incision offers access to both the posterior midline and anterior vertebral body through the lateral approach Fig. Skin and subcutaneous tissue are incised and reflected to the extended incision side. The thoracodorsal fascia is then dissected from the midline and is incised along the horizontal skin incision line. The thoracolumbar fascia appears silver to white. When it is dissected and retracted, the lateral branch of the dorsal ramus of the spinal nerve is seen to run over the surface of the muscle layer Fig.
Trapezius or latissimus dorsi muscle is divided with the attached fascia, depending on the level of the lesion.
click here The entire skin, subcutaneous tissue, muscle, and fascia flap are then elevated and retracted laterally. A plane is defined at the lateral aspect of the erector spinae group, and these muscles are elevated as a layer off the ribs and are retracted medially Fig. The endothoracic fascia and pleura are separated using blunt dissection. On identification of the neurovascular bundle, the intercostal nerve is separated from the vessels. The transverse processes and associated intertransversarii muscles are removed. The superior costotransverse ligaments and radiate ligament, post costotransverse ligament, are incised with a scalpel.
After the costovertebral joint is opened, the rib head is elevated out of the field. It is important to remove the rib and transverse process at the articulation to ensure full exposure Fig. Each intercostal nerve is then traced into its respective foramen Fig. A ligature is placed around the nerve, which is cut 3. The retracted nerve roots cause the spinal cord retraction, which enables the surgeon to view the vertebral body across the midline. The parietal pleura is dissected off the vertebral bodies using a Cobb elevator.
If the rami communicantes that connect the nerve root and sympathetic ganglion are divided, the vertebral body can be exposed easily to the ventral tip.
The sympathetic chain is contained within a fascial compartment formed by fusion of the mediastinal and prevertebral fascia over the costovertebral articulation. Displacing the sympathetic chain anterolaterally via subperiosteal dissection reveals the anterolateral surface of the vertebral body, pedicle, and foramen. The segmental arteries are dissected off the vertebral bodies and are divided between clips. The foraminal margins above and below the lesion are defined with a blunt nerve hook.
Care is taken not to dissect into the spinal canal. After identification of the foramen, the pedicle is removed using a combination of rongeurs and thin foot-plated punches. The table is then rotated 15 to 20 degrees away from the surgeon to maximize visualization of the spinal canal. Removal of the pedicle provides the lateral view of spinal cord. Both wrists have traction bands applied to pull the arms down for lateral radiographic imaging during the procedure.