2 Thoracic Spine

10.1055/b-0035-121462

2 Thoracic Spine

2.1 Transthoracic Approach to the Thoracic Spine T4–T11

R. Bauer, F. Kerschbaumer, S. Poisel

2.1.1 Indications

Kyphosis
Scoliosis
Vertebral body fractures
Tumors
Spondylitis

2.1.2 Choice of Side of Approach

Generally speaking, the thoracic spine can be approached using either right-sided or left-sided thoracotomy. Unless the indication prescribes the side to be used, right-sided thoracotomy is preferable because of the vascular anatomy (the left-sided course of the aorta). However, in the case of scoliosis, thoracotomy is always performed on the side of the convexity.

2.1.3 Dorsolateral Thoracotomy with Rib Resection

With orthopedic indications, the thoracotomy is generally performed with rib resection. This creates better exposure in adult patients and in the case of thoracic deformities associated with spinal deformities. In addition, the resected rib may serve as graft material for vertebral fusion.

2.1.4 Choice of Rib to be Resected

Entry is generally made two ribs above the level of the center of the lesion. Owing to the descending course of the ribs, it is easier to cut along the lower rib in a caudal direction rather than toward the proximal end. If a rib is chosen whose location is too distal, it is difficult to reach the upper end of the deformity. In younger individuals and those in whom the ribs are mobile, it may be possible to reach the vertebra corresponding to the resected rib. If this proves difficult, the segment close to the spine of the next higher rib may be resected through the same approach. The following vertebrae can be reached in favorable circumstances:

Resection of the fifth rib: a T5–T11 approach
Resection of the sixth rib: a T6–T12 approach
Resection of the seventh rib: a T7–L1 approach However, there are exceptions to this rule. In patients with horizontally coursing ribs, resection of the sixth rib may allow vertebrae T5–T11 to be reached. On the other hand, if the ribs describe a sharply descending course, resection of the fifth rib only permits exposure of T6–T11. Finally, in patients with severe spinal curvatures and commensurate thoracic deformities, rib resection thoracotomy may provide access to only two or three vertebrae.

2.1.5 Positioning and Incision

The patient is placed on his or her side. Elevation of the kidney rest or slight tilting of the operating table allows for good extension in the operative field. The skin incision made over the selected rib is slightly S-shaped, curving caudally around the scapula. It is started about four fingerbreadths lateral to the spinous processes and continues forward as far as the chondrocostal border ( Fig. 2.1 ). Next, latissimus dorsi is completely divided transversely to its course ( Fig. 2.2 ). Because of the nerve supply (thoracodorsal nerve) this should be done as far caudally as possible (see Figs. 2.32 and 2.33 ).

Serratus anterior is exposed in the anterior area of the wound. It is now possible to reach behind this muscle under the scapula with the hand and to count off the ribs from cranial to caudal. The first rib usually cannot be palpated, and the first palpable one is therefore, as a rule, the second rib. Serratus anterior is likewise transected, as far caudally as possible to spare, if possible, the long thoracic nerve ( Fig. 2.3 ). The periosteum of the selected rib is divided from posterior to anterior as far as the chondrocostal border, using cutting diathermy ( Fig. 2.4 ), and is initially retracted with a straight raspatory. At the superior margin of the rib, the direction of the cut, in accordance with the course of the intercostal muscles, is from posterior to anterior; at the lower border, it is from anterior to posterior. Hereafter, the rib is completely exposed with a rib raspatory ( Fig. 2.5 ).

**Fig. 2.2** Anatomical exposure of the operative field after transection of the skin and subcutaneous tissue. The muscle fasciae have been removed. 1 Latissimus dorsi 2 Serratus anterior 3 Trapezius 4 Rhomboid major 5 Infraspinatus 6 Teres major 7 Iliocostalis thoracis 8 External intercostal muscle 9 Inferior angle of the scapula

**Fig. 2.3** Anatomical exposure of the operative field after transection of latissimus dorsi and before incision of serratus anterior. The appropriate site of incision is identified by the dashed line. 1 Serratus anterior 2 Long thoracic nerve 3 Lateral thoracic vessels. V–VII Ribs

Following this preparation, the rib is transected anteriorly at the osseocartilaginous boundary and elevated; posteriorly, it is resected with rib shears about two fingerbreadths laterally from the costotransverse joint. The thoracic cavity can now be opened within the bed of the resected rib ( Fig. 2.6 ).

**Fig. 2.4** Operative site following transection of serratus anterior. The periosteum is split over the sixth rib along the red dashed line. V–VII Ribs

**Fig. 2.5** Operative site following division of the periosteum and enucleation of the sixth rib with a rib raspatory. VI, VII Ribs

**Fig. 2.6** Operative site following rib resection and partial division of the periosteum and costal pleura. 1 Resection stump of the sixth rib 2 Costal pleura 3 Periosteum 4 Lung VII Rib

**Fig. 2.7** Intercostal approach to the pleural cavity. The intercostal muscles are transected between the sixth and seventh ribs. Care should be taken to make the incision at the upper border of the lower rib to avoid injury to the intercostal vessels and intercostal nerve. VI, VII Ribs

2.1.6 Intercostal Thoracotomy

In children and adolescents with a mobile thorax, the thoracotomy may also be performed intercostally. This is indicated especially if only a few vertebrae need to be exposed and the rib is not needed as graft material. Positioning of the patient and the type of incision conform to those used in dorsolateral thoracotomy with rib resection. Following transection of the latissimus dorsi and serratus anterior, the selected intercostal space is entered. As a rule, a plastic probe is inserted between the intercostal muscles and the parietal pleura, above which the intercostal muscles can then be divided with cutting diathermy ( Fig. 2.7 ). The procedure after transection of the parietal pleura again conforms to that for thoracotomy with rib resection.

After complete transection of the pleura, a thoracotomy spreader is inserted, and the thorax is then slowly and cautiously spread. The lung is retracted anteriorly, and a good view is obtained of the vertebrae covered by the parietal pleura ( Fig. 2.8 ).

**Fig. 2.8** Operative site after opening the pleural cavity. The parietal pleura (costal and mediastinal pleura) is preserved. 1 Right lung
2 Diaphragm
3 Esophagus }visible through the parietal pleura
4 Azygos vein }visible through the parietal pleura
5 Intercostal vessels }visible through the parietal pleura
6 Sympathetic trunk }visible through the parietal pleura
7 Greater splanchnic nerve }visible through the parietal pleura

2.1.7 Anatomical Site

The anatomy of the posterior mediastinum and retropleural cavity is shown in Figs. 2.9 , 2.10 , 2.11 .

A brief discussion of the most important anatomical variations of the structures in the posterior mediastinum now follows ( Figs. 2.12 and 2.13 ). Injury to the thoracic duct during exposure of the vertebral bodies should be avoided if at all possible. Chylothorax may otherwise develop as a complication. Fig. 2.12 shows variations in the course of the thoracic duct. This makes it clear that the thoracic duct essentially follows the course of the aorta on the right side. Variations of the azygos and hemiazygos veins are shown in Fig. 2.13 . As a rule, the vertebrae can be accessed through a median transection of the intercostal veins without touching the longitudinal venous systems.

**Fig. 2.9** Anatomical site of the posterior mediastinum and retropleural cavity as seen from the anterior. 1 Ascending aorta 2 Arch of the aorta 3 Brachiocephalic trunk 4 Left internal carotid artery 5 Thoracic aorta 6 Intercostal arteries 7 Abdominal aorta 8 Celiac trunk 9 Superior vena cava 10 Opening of the azygos vein 11 Right brachiocephalic vein 12 Left brachiocephalic vein 13 Accessory hemiazygos vein 14 Azygos vein 15 Hemiazygos vein 16 Intercostal veins 17 Thoracic duct 18 Right vagus nerve 19 Left vagus nerve 20 Esophageal plexus 21 Vagal trunks 22 Sympathetic trunk with ganglia 23 Greater splanchnic nerve 24 Lesser splanchnic nerve 25 Intercostal nerves 26 Subcostal nerve 27 Trachea 28 Esophagus 29 Diaphragm V–XII Ribs

**Fig. 2.10** Anatomical site of the right half of the posterior mediastinum and right retropleural space. 1 Right lung 2 Esophagus 3 Cut edge of the parietal pleura 4 Esophageal plexus of the vagus nerves 5 Thoracic diaphragm 6 Azygos vein 7 Intercostal vessels 8 Sympathetic trunk 9 Greater splanchnic nerve 10 Communicating branches 11 Intercostal nerve I–X Ribs

**Fig. 2.11** Anatomical site of the left half of the posterior mediastinum and left retropleural space. 1 Left lung 2 Thoracic aorta 3 Cut edge of the parietal pleura 4 Accessory hemiazygos vein 5 Sympathetic trunk 6 Communicating branches 7 Greater splanchnic nerve 8 Lesser splanchnic nerve 9 Intercostal nerve 10 Intercostal vessels 11 Thoracic diaphragm I–X Ribs

**Fig. 2.12 a–d** Positional variants of the thoracic aorta, azygos vein, and thoracic duct in relation to the thoracic spine (according to Kubik, 1975). The left-sided position of the topographic unit of thoracic duct–aorta–azygos vein may be regarded as an age-related displacement (83 % of individuals with a left-sided position were over 70 years old). a Left-sided position (36 %). b Middle position (20 %). c Oblique position (17 %). d Right-sided position (6 %).

**Fig. 2.13 a–f** Morphologic and positional variants of the azygos and hemiazygos vein system (according to Adachi, 1933; Cordier et al., 1938; and our own observations). a “Classic type.” 1 Azygos vein 2 Hemiazygos vein 3 Accessory hemiazygos vein b Absence of anastomosis between the azygos and hemiazygos veins. c Multiple arcade formations and age-related arcuate leftward displacement of the azygos vein. d Cranioaortic arc of the hemiazygos vein. e Lateroaortic arc of the azygos vein and absence of communication between the azygos and hemiazygos veins. f Multiple prevertebral anastomoses; absence of the hemiazygos vein.

**Fig. 2.14** Schematic representation of the segmental blood supply of the spinal cord. The “critical supply zone” is indicated by an arrow (according to Dommisse, 1974 and Kahle et al., 1976). C1, C8, T5, T10, L1, L5 Spinal nerves

2.1.8 Blood Supply of the Spinal Cord

The vascular supply of the spinal cord is of special significance for spinal surgery. The major supply systems will therefore be briefly discussed below ( Figs. 2.14 and 2.15 ).

The spinal cord is supplied by two different arterial systems; on the one hand, by the vertebral arteries, which give off in a caudal direction two posterior spinal arteries and one anterior spinal artery, and on the other hand, by branches of the posterior intercostal arteries.

With respect to the transthoracic approach to the spine, only the latter arteries will be considered—these are the spinal branches of the posterior branches of the posterior intercostal arteries (cf. Fig. 2.15 ). The segmental arteries, which reach the spinal cord via the interspinal foramina and anastomose with the anterior spinal artery, are exceedingly variable in number and caliber so that a division into types does not appear possible. At least two and at most 16 spinal branches have been observed (Domisse, 1974) that advance toward the spinal cord at various levels and contribute to its blood supply. The vessel with the largest caliber is the great radicular artery (Adamkiewicz′s artery), which in 80 % of cases arises from a left posterior intercostal artery between the seventh thoracic and the fourth lumbar vertebra (most often between the ninth and 11th thoracic vertebrae).

**Fig. 2.15** Schematic representation of the blood supply of the vertebral canal and spinal cord on a transverse section (according to Crock et al., 1977). The arrows point to the appropriate ligation sites. 1 Posterior intercostal artery 2 Posterior branch 3 Spinal branches 4 Muscular and cutaneous branches

It should be noted, without minimizing the importance of Adamkiewicz′s artery, that it alone is hardly sufficient to supply the caudal segments of the spinal cord. There are in fact several medullary nutrient arteries at different levels that play a vital role in maintaining the supply of the spinal cord. This is consistent with the experience of spinal surgeons who, particularly in the treatment of scoliosis, have ligated between four and 16 segmental arteries without causing any neurologic dysfunction. At any rate, it seems prudent to protect the segmental spinal arteries insofar as the surgical procedure allows.

In the spinal cord, there is a zone of cervical enlargement, a thoracic zone, and a zone of lumbar enlargement. The number and size of the branches supplying the cervical and lumbar cord are greater than those in the thoracic cord. Thus, the thoracic cord is described as a watershed. The “critical supply zone” of the spinal cord generally lies between the fourth and ninth thoracic vertebrae. It is in this zone that the greatest caution should be exercised during surgery.

In exposing vertebrae by the anterior approach, it is important to transect the segmental arteries as far forward as possible; also, the vessels should be dissected free only over a short distance in a posterior direction ( Fig. 2.15 ). The arterial arcades that join the segmental arteries outside and inside the vertebral canal are thus preserved. To avoid damage to the spinal branches, the vessels should not be electrocoagulated near the intervertebral foramen.

2.1.9 Site of Thoracotomy in Scoliosis

( Figs. 2.16 and 2.17 )

In scoliosis, thoracotomy is always performed on the side of the convexity. Owing to the severe torsion of the vertebral bodies and the posterior rib-hump on the convex side, contact is often made immediately after thoracotomy with the spine, which is situated only a few centimeters under the resected rib. The large thoracic vessels generally do not, or do not completely, follow the line of the curvature, and are therefore usually found on the concave side. This means that in left-sided thoracotomy for thoracic scoliosis with a left-sided convexity, the aorta is generally located on the right of the spine.