Spinal surgery

Mineralization and solidification of a movable joint.

Method of incising and accessing the body. The approach is planned according to the type of procedure and location of the disease or injury. Knowledge of the approach helps the circulating nurse and scrub person plan the positioning and instrumentation for the surgical procedure.

Anterior approach

Entering the body through the front of the neck, chest, or abdomen.

Posterior approach

Entering the body through the back of the neck, chest, or lower spine.

Transoral approach

Entering the body through the mouth to the back of the pharynx.

Decompression

Release of spinal pressure with cutting away of segments of the vertebral bone.

Dermatomes

Levels of cutaneous sensory innervation from specific areas of the cord to the peripheral nervous system.

Idiopathic

Unknown or uncertain origin.

Kyphosis

Exaggerated thoracic curvature of the spine.

Lordosis

Exaggerated lumbar curvature of the spine.

Myotomes

Levels of muscle innervation from the spinal cord.

Osteoporosis

Wasting and demineralization of bone.

Paralysis

Decreased ability to move voluntarily.

Paraplegia

Injury between the levels of T1 and T8; with injury between the levels T9 and T10, the individual may be able to sit up.

Hemiplegia

Injury to one side of the nervous system.

Quadriplegia

Injury above the level of T1.

Radiculopathy

Pain that travels up or down a nerve pathway.

Retroperitoneal

Behind the peritoneal cavity without entering the sac.

RSD

Reflex sympathetic dystrophy.

Scoliosis

Lateral curvature of the spine. Can be combined with kyphosis (kyphoscoliosis).

Spondylosis

Bony degeneration of the vertebral column with mineral deposits.

Stagnara wake-up test

The patient is awakened during the surgical procedure and asked to move his or her feet. The patient does not feel pain and is given an amnesic medication.

Stenosis

Narrowing of a passage.

Thenar

The web space between the index finger and the thumb.

Transperitoneal

Through the peritoneal cavity.

Anatomy and physiology of the spinal cord and vertebral column

The vertebral column and spinal cord comprise the posterior aspect of the trunk of the body. The relationship between the bones and nerves is evaluated first from a topographic perspective with assessment of the alignment of specific external landmarks (Fig. 38-1). The external dorsal musculature frames the margins of the surgical landmarks used in planning the posterior incision for spinal surgery (Fig. 38-2).

FIG. 38-1 Topographic landmarks for spinal surgery.

FIG. 38-2 Dorsal surface with muscular borders.

Curvatures of the spine

The configuration of the spinal curvature is dependent on chronologic and idiopathic factors. Each age group, as shown in Figure 38-3,A, displays a different set of normal spinal curves based on physiologic development. Abnormal curvatures can be age related but sometimes idiopathic without consideration for age (Fig. 38-3, B).

FIG. 38-3 Natural and pathologic spinal curves. A, Normal chronologic curves. B, Idiopathic curves.

The spinal cord and spinal nerves

The spinal cord is between 17 and 20 inches (43 to 50 cm) long and passes through a central canal in the vertebral column to the level of the second or third lumbar vertebra (Fig. 38-4). Pairs of spinal nerve roots branch off to each side of the body from 31 segments of the spinal cord as it passes through the vertebrae.

FIG. 38-4 Spinal nerves. *(Modified from Mettler FA:* Neuroanatomy, *ed 2, St Louis, 1948, Mosby.)*

The spinal nerves are as follows:

• Eight pairs cervical

• Twelve pairs thoracic

• Five pairs lumbar

• Five pairs sacral

• One pair coccygeal

The spinal nerves carry sensory and motor impulses between the central nervous system (CNS) and the peripheral nervous system (PNS). The cord is composed of gray matter (cell bodies) on the inside and white matter (nerve fibers) on the outside. This is the exact opposite of the substance of the brain. The ventral nerve roots are the motor axons to the muscles and glands, and the dorsal nerve roots are the sensory dendrites (Fig. 38-5). The dorsal root ganglion is easily entrapped by the bony vertebrae and causes pain and disability.

FIG. 38-5 Spinal innervation of the body.

The cephalad portion of the cord begins at the base of the brain at the foramen magnum.

The first thickened area of the spinal cord is at the C7 to T1 junction, forming the brachial plexus. Compromise of the brachial plexus caused by bony impingement of the cervical or upper thoracic vertebrae results in arm and hand pain and muscular weakness with thenar wasting.

The caudal portion of the spinal cord thickens and ends at L1 to form the conus medullaris before terminating in a fibrous tail known as the cauda equina (horse’s tail; Fig. 38-6). The nerve fibers that extend beyond L2 to L3 form the lumbosacral plexus.

FIG. 38-6 Terminal portion of the spinal cord.

The blood supply to the spinal cord arises from the vertebral artery. The radicular artery of Adamkeiwicz supplies blood to the lower third of the cord. Occlusion of this artery causes paraplegia. Venous drainage is through the intervertebral vein that drains into the azygous venous system.

The meninges cover the cord to the level of the second or third lumbar vertebra. They terminate in a fibrous band (filum terminale) that extends through the lumbar vertebrae and sacrum and attaches to the coccyx. The dura is not attached or continuous with the central canal of the vertebral column.

Vertebrae

All vertebrae have similar bony characteristics that form a circular canal to house the spinal cord. The structure of a vertebra includes:

• A thick cylindric body that bears a portion of the weight of the torso.

• Two posterolateral extensions that form the proximal bony vertebral (neural) arch. These extensions form thick pedicles that connect to flatten laminae posteriorly. The laminae connect at the spinous process, forming a circle. Each pedicle has a notch superiorly and inferiorly to seat the vertebrae above and below.

• A transverse wing-shaped spinous process that is formed by the connection of the posterior laminae. The central foramen shapes the spinal canal.

The bony structure of the vertebral column extends from the foramen magnum at the base of the skull to the coccyx (Fig. 38-7, A). The 33 vertebrae, which provide support for the body, vary in size and shape according to location and are separated by flexible discs over the anterior surface of the body (Fig. 38-7, B). Each disc is composed of two parts: an exterior annulus fibrosus and an interior gel referred to as the nucleus pulposus.

FIG. 38-7 Vertebral column. A, Lateral view and posterior view. B, Differentiation of vertebrae.

The seven cervical vertebrae are in the neck and form the secondary curvature. They are lighter weight with a smaller disc-bearing body. The top two cervical vertebrae, C1 atlas and C2 axis, have clearly distinct landmarks. The atlas laminae form a circle around the odontoid process of the axis so the head has a wide range of circular and linear motion (Fig. 38-8). The atlas-axis complex has no disc or spinous process and is considered to be the strongest vertebrae of the cervical portion of the vertebral column.

The 12 thoracic vertebrae articulate posteriorly with the ribs to form a cage around the thoracic organs, forming a primary curvature. The spinous processes are low profile and smaller than the lower vertebrae. The body and discs of the thoracic vertebrae are thinner and are designed to bear minimal weight.

The five lumbar vertebrae are posterior to the retroperitoneal cavity and are designed to carry the heaviest load of the entire vertebral column with the least amount of flexibility. The body and disc of each lumbar vertebra are thick and form a secondary curvature. Figure 38-9 illustrates the combined lumbar vertebra-disc unit.

The five sacral vertebrae are fused in the adult to form the sacrum, and the four fused coccygeal vertebrae form the coccyx (Fig. 38-10). Collectively, these two sets of fused vertebrae form the posterior aspect of the pelvic girdle. Each vertebra is connected to the other by a series of ligamentous fibers (Fig. 38-11). The vertebral column measures about 28 inches (71 cm) in the average-size adult.

The physiologic relationship between the spinal cord, spinal nerves, and bony vertebral column affects multiple body systems if the curvature is misaligned or some pathology changes the size of a foramen or joint. Figure 38-12 illustrates the major organ systems and the corresponding spinal nerves that can cause problems with physiologic functioning.

FIG. 38-12 Physiologic relationship between the spinal cord, spinal nerves, and vertebral column.

Special considerations for spinal surgery

Because of the proximity of the vertebral column to the spinal cord, both neurosurgeons and orthopedic surgeons perform surgical procedures in this area. Many surgeons have attained subspecialty board certification in spinal surgery. Both disciplines use power drills, power saws, microscopes, and computer imaging to correct problems in the spinal column; however, many surgeons feel that spinal surgery is a specialty unto itself because of the multidisciplinary approaches applied in the correction of spinal problems.

Diagnostics

For diagnosis of spinal conditions, computed tomography (CT) is used to detect abnormal bone. CT and magnetic resonance imaging (MRI) are used to evaluate spinal injuries. MRI and myelography outline soft tissue abnormalities, such as disc degeneration, protrusion, or rupture.¹³ Because it is noninvasive and seems as effective, MRI is replacing myelography.

Positioning for spinal surgery

Positioning for spinal surgery can require the patient to be placed in either the supine or the prone position, depending on the type of approach necessary for the planned procedure. Most facilities have specialized OR beds that accommodate the modifications needed for adequate exposure of the surgical site. Some surgical body positions provide distraction of the vertebrae for more direct access to specific regions of the spine.

Considerations for patient positioning include prevention of untoward injury, such as pressure areas, pinch points on jointed tables, falls, wrong site surgery, and venous stasis. Ischemic insult to the area around the eye can result in blindness.¹⁴

Positioning a patient in the prone position is a multistep procedure. The patient is given general anesthesia on the transport cart, intubated, and catheterized. A minimum of four people is needed to turn the anesthetized patient into the prone position onto the specialized OR bed.

A few prone positions simulate kneeling or crouching, which means that the patient may be in a full lift and body flexion before coming into contact with the surface of the OR bed. Figure 38-13 shows the kneeling-crouching position used by some surgeons for lower spine procedures. This posture constricts the patient’s circulation and increases the risk for embolization.

FIG. 38-13 Kneeling-crouching position for spinal surgery.

The Jackson table (Fig. 38-14) and the Jackson-Wilson table with the central arch (Fig. 38-15) are used for posterior spinal incisions. Each type of specialty spinal table allows the surgeon to position the patient for optimal vertebral position and exposure of the surgical site.