Lateral Parascapular Approach to the Upper Thoracic Spine

Obtaining surgical access to the anterior vertebral elements of the upper thoracic vertebrae (T1–6) presents a unique anatomical challenge. The thoracic cage, which narrows significantly as it approaches the thoracic inlet, has an intimate association between the vertebral column and the superior mediastinal structures. The supraclavicular, transmanubrial, and transthoracic approaches to this region give excellent access to limited parts of the upper thoracic spine, but none provides access to all the upper thoracic vertebrae. An anatomically guided procedure, the lateral parascapular extrapleural approach to the upper thoracic spine, allows excellent exposure of all upper thoracic vertebrae for neural decompression, corpectomy, vertebral reconstruction, and simultaneous posterior spinal fixation.

29.2 Patient Selection

Patients with pathology of the upper thoracic vertebrae are candidates for this approach. Many of these lesions may be accessed via typical transthoracic approaches; however, some patients with significant pulmonary disease are poor surgical candidates for such invasive procedures.

The lateral parascapular approach is also ideal for lesions not only involving the vertebral bodies but also extending to the posterior elements and paraspinal musculature. This approach lends itself to resection of lesions and also facilitates anterior and posterior instrumentation.

29.3 Preoperative Preparation

Standard preoperative anesthetic evaluation, including cardiopulmonary assessment, should be obtained. Double-lumen intubation may be useful. Typical laboratory studies including serum chemistries, complete blood count, and coagulation profile are also obtained. Because of the proximity of the great vessels, banked blood should be available, and cell-saver techniques may be considered.

In addition, preoperative plain radiographs and computed tomographic or magnetic resonance imaging scans should be obtained to fully characterize the lesion of interest. In some cases, it can be difficult to localize midthoracic lesions if there is no gross deformity on plain radiographs. Care should be taken to ensure that the correct thoracic level is identified on preoperative imaging (by counting either from the first rib, the last rib, or other bony landmarks). Intraoperatively, C-arm fluoroscopy has most commonly been used for localization; however, more recent adoption of intraoperative three-dimensional scanning, with or without neuronavigation, has improved accuracy.

Lastly, neurologic monitoring may be considered to provide important feedback on possible intraoperative neurologic compromise.

29.4 Anatomy

As with any surgical approach, the key to understanding the lateral parascapular approach is knowledge of the relevant anatomy. The musculature of the upper thoracic spine can be divided into two groups (extrinsic and intrinsic back muscles) and three layers (superficial, intermediate, and deep).

29.4.1 Extrinsic Back Muscles

Extrinsic back muscles are associated with the upper limbs and ribs and act to move structures other than the spine. These muscles constitute the superficial and intermediate muscle layers of the back. The superficial group of muscles is further subdivided into a superficial layer of the superficial muscle group (trapezius muscle, latissimus dorsi) and a deep layer of the superficial muscle group (rhomboids, levator scapulae). The intermediate group of muscles (serratus posterior superior and inferior) aid head rotation and act as weak accessory muscles for respiration:

The trapezius muscle of the superficial layer of the superficial muscle group is the first muscle encountered after the skin incision ( ▶ Fig. 29.1).
Immediately deep to the trapezius muscle lies the deep layer of the superficial muscle group—the rhomboid major, rhomboid minor, and levator scapulae muscles.
Immediately deep to the rhomboids are the intermediate group of muscles. The serratus posterior superior arises from the spinous processes of C6 to T3 and inserts on the second to fourth ribs; it acts to pull these ribs upward during respiratory movements.

Fig. 29.1 Posterior exposure of the cervical and thoracic spine demonstrating the superficial muscular layer in relation to the spinous processes, scapulae, and arterial supply. The superficial muscular layer includes the trapezius, latissimus dorsi, rhomboid major, rhomboid minor, and levator scapulae muscles.

29.4.2 Intrinsic Back Muscles

The next group of muscles encountered is the deep, or intrinsic, muscles ( ▶ Fig. 29.2, ▶ Fig. 29.3). The common functionality of this group of muscles is that they all act to move the spinal column itself. Acting bilaterally, they can extend the vertebral column; acting unilaterally, they can rotate the column toward the contralateral side.

Fig. 29.2 Posterolateral view of the upper thoracic spine after development of a myocutaneous flap that contains the skin and subcutaneous tissues and the trapezius, rhomboid major, rhomboid minor, and serratus posterior superior muscles. The transversospinalis group of muscles (paraspinal muscles), including the semispinalis capitis, spinalis, semispinalis thoracis, and iliocostalis muscles, are demonstrated as they arise from the transverse processes. Upper: Drawing of the three muscular columns of the deep musculature arising from the aponeurotic sheath that originates at the sacrum. m., muscle.

Fig. 29.3 A transverse section of the T4 vertebra, rib, and associated musculature. The superficial muscular layer includes the trapezius and rhomboid major muscles. Deep muscles in the medial and paramedial region include the iliocostalis, longissimus, spinalis, semispinalis, multifidus, and rotatores muscles. m., muscle.

The intrinsic back muscles can be divided into two groups: superficial and deep. The superficial intrinsic muscles include the splenius and erector spinae muscles, which, as a group, diverge as they pass cranially. The splenius muscles function in stabilization and rotation of the skull and neck ( ▶ Fig. 29.1).

The erector spinae complex comprises a group of muscles inferiorly attached to the posterior aspect of the sacrum and iliac crest, sacroiliac ligaments, and sacral and inferior lumbar spines. Superiorly, its attachments fan out and the muscle is divided into three subdivisions:

Iliocostalis (cervicis, thoracis, lumborum)—the most lateral group; attaches to transverse processes and angles of the ribs.
Longissimus (capitis, cervicis, thoracis)—separated from iliocostalis by posterior primary rami of spinal nerves and extends all the way to the skull.
Spinalis (capitis, cervicis, thoracis)—most medial; originates from spinous processes, inserts on spinous processes higher up.

The deep intrinsic muscles include the interspinalis, intertransversarii, rotatores, multifidus, and semispinalis capitis, cervicis, and thoracis muscles (the multifidus and semispinalis muscles together are called the transversospinalis muscles). The deep intrinsic muscles of the back tend to converge as they pass cranially (from origins on vertebral transverse processes to vertebral spines, to the skull at higher levels, or the semispinalis capitis).

29.4.3 Ribs

The head of each rib articulates with the adjacent parts of its own vertebral body, the vertebra above, and the intervertebral disk between them. In the upper thoracic spine, the only exception to this general rule is the head of the first rib, which articulates only with its own vertebral body. In addition to the vertebral articulation, the tubercle of each rib also articulates with the transverse process of its own vertebra ( ▶ Fig. 29.4). The articulation of the head of each rib with two vertebrae is formed by individual beveled facets that form separate synovial joints with the posterolateral surfaces of each vertebral body ( ▶ Fig. 29.5).

Fig. 29.4 Transverse section through a thoracic vertebra and rib demonstrating the costovertebral joint and radiate ligament and the costotransverse joint and associated lateral costotransverse ligament. m., muscle.

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