Posterior Thoracic and Lumbar Approaches

Sreeharsha V. Nandyala

Alejandro Marquez-Lara

Junyoung Ahn

Kern Singh

ANATOMY

Superficial landmarks enable gross determination of the anatomic level. Proximally, C7 and T1 are the largest spinous processes and may serve as palpable anatomic landmarks. Distally, the intercrestal line approximates the L4-L5 interspace.
There are three layers to the posterior musculature of the spine (FIG 1; Table 1):
- Superficial layer: trapezius, latissimus dorsi, rhomboid major and minor, and the levator scapulae
- Intermediate layer: superior and inferior serratus posterior and the levatores costarum
- Deep layer: erector spinae, transversospinalis, interspinalis, and the intertransversarii
The superficial and intermediate layers receive their nervous supply from peripheral nerves, which are not encountered through the posterior approach (FIG 2). The deep layer receives its nervous supply segmentally from the posterior dorsal rami. There is a large amount of redundancy in the innervation of the deep layer.
- The midline approach is a true internervous plane. Nerve injury occurs only with excessive lateral dissection.
The vascular supply to the deep layer is from segmental branches of the aorta. These vessels enter the operative field at the level of the intertransverse ligament and can be a source of significant bleeding.
The facet joint capsules have a shiny white appearance and the individual fibers can be seen inserting onto the lateral edge of the laminar trough. Care should be taken to avoid violating the capsular fibers, unless that segment is being fused.
The ligamentum flavum has a yellow appearance with the fibers running in a cephalocaudal direction. The cephalad end of the ligament has a broad insertion from the base of the spinous process to between 50% and 70% of the anterior surface of the lamina. The caudal end of the ligament inserts from the superior edge of the lamina to between 2 and 6 mm of the anterior surface of the lamina.⁴
Particularly at the L5-S1 level, the interspace may be widened or the posterior bony anatomy only partly formed. Care should be exercised when exposing this level as inadvertent plunging into the canal may occur.
Laterally, the intertransverse membrane overlies the iliopsoas and protects the neural structures that lie beneath.
In children, the spinous process apophysis has not fused. During dissection, the apophysis is split down to the bone and then elevated with the paraspinal musculature.

FIG 1 • The superficial, intermediate, and deep musculature of the back.

Table 1 Musculature of the Back

Muscle	Origin	Insertion	Innervation	Blood Supply
Superficial layer
Trapezius	Medial third of superior nuchal line of occiput, external occipital protuberance, and ligamentum nuchae; spinous processes of C7-T12	Lateral third of clavicle, acromion, spine of scapula	Motor supply from spinal accessory nerve, sensory fibers from C3 to C4	Transverse cervical artery
Latissimus dorsi	Spinous processes of T7—sacrum, medial third of iliac crest, ribs 9-12, inferior angle of scapula	Floor of bicipital groove	Thoracodorsal nerve (C7, C8)	Thoracodorsal artery
Levator scapulae	Transverse processes of C1-C4	Medial border of scapula	Dorsal scapular nerve (C5), with branches of C3-C4 innervating upper part of muscle	Dorsal scapular artery
Rhomboid major	Spinous processes of T2-T5	Medial border of scapula	Dorsal scapular nerve (C5)	Dorsal scapular artery
Rhomboid minor	Caudal end of ligamentum nuchae, spinous processes of C7-T1	Medial border of scapula	Dorsal scapular nerve (C5)	Dorsal scapular artery
Intermediate layer
Serratus posterior superior	Spinous processes of C7-T3	Ribs 1-4	Intercostal nerves	Posterior intercostals arteries of T1-T4
Serratus posterior inferior	Thoracolumbar fascia, spinous processes of T11-L2	Ribs 9-12	Intercostal nerves	Posterior intercostal arteries, subcostal artery, and L1-L2 lumbar arteries
Levatores costarum	Tip of transverse process of C7-T11 vertebrae	Rib below level of origin	Posterior rami of thoracic spinal nerves	Dorsal intercostal arteries
Deep layer
Erector spinae (vertically oriented and superficial)
Iliocostalis Longissimus Spinalis	Iliac crest, sacrum, transverse and spinous processes of vertebrae, and supraspinal ligament	Ribs, transverse and spinous processes of vertebrae, posterior aspect of skull	Segmental innervation by dorsal primary rami of spinal nerves C1-S5	Segmental supply by deep cervical arteries, posterior intercostal arteries, subcostal artery, and lumbar arteries
Transversospinalis (obliquely oriented and intermediate)
Semispinalis	Transverse processes T1-T12	Spinous processes of C2-T5	Dorsal rami of spinal nerves	Segmental arteries from aorta
Multifi	dus Articular processes of cervical vertebrae, transverse processes of thoracic vertebrae, mammillary processes of lumbar vertebrae, posterior superior iliac spine	Spinous processes of C2-L5	Dorsal rami of spinal nerves	Segmental branches from aorta
Rotatores	Transverse processes	Base of spinous processes above Long skip one level; short attach at level above	Dorsal rami of spinal nerves	Segmental branches from aorta
Deepest muscle
Interspinales	Spinous processes	Spinous processes one level above	Dorsal rami of spinal nerves	Segmental branches from aorta
Intertransversarii	Anterior and posterior transverse processes of cervical vertebrae, transverse and mammillary processes of lumbar vertebrae	Anterior and posterior processes of cervical vertebrae one level above, transverse and accessory processes of lumber vertebrae one level above	Dorsal rami of spinal nerves	Segmental branches from aorta