Anterior Minimally Invasive Surgery in Thoracolumbar Fractures

Philipp Schleicher, Matti Scholz, and Frank Kandziora

Introduction

Minimally invasive surgery (MIS) techniques in thoracolumbar fracture treatment provide access to the thoracic spine and thoracolumbar junction (T4–L2) and to the lumbar spine (L2–L4). The thoracic spine and thoracolumbar junction can be accessed for MIS treatment by a video-assisted mini-open thoracotomy or by a full endoscopic approach—the video-assisted thoracoscopy (VAT). The latter is mainly suitable for noninstrumented cases, because every instrument is introduced into the thoracic cavity via a small thoracotomy.

The lumbar spine can be accessed for MIS treatment down to L4 by a left retroperitoneal approach. Although anterior reconstruction is rarely performed in segments L4-L5 and L5-S1, these levels can be accessed for MIS treatment by an anterior pararectal approach.

Preoperative Planning and Equipment

The key questions to answer in preoperative planning for thoracolumbar fractures are the following:

• Which levels are to be addressed?

• Where are the great vessels (e.g., the aorta) located?

• Where does the diaphragm attach to the spine?

The answers determine the type of approach and from which side it will be performed. A transthoracic approach, either video assisted or fully endoscopic, is possible from T4 to L1 and sometimes even to L2. Between T4 and T7, a right-sided approach is preferred because of the course of the aortic arch and the beating heart, which both obstruct access to the upper thoracic spine on the left side. From T10 to L2, it is advisable to use a left-sided approach, because it is easier to handle the thoracoabdominal aorta with its strong wall than the fragile vena cava. In the transition zone from T8 to T10, right- and left-sided approaches are possible. The choice should be based on preoperative computed tomography (CT) imaging, which displays the location of the aorta.

From L2 to L4, a lumbar retroperitoneal approach without opening of the thoracic cavity is possible. It is usually performed from the left side, because it is easier to handle the aorta rather than the fragile vena cava. In certain cases, for example predominantly right-sided pathology (tumors and infection) as well as in revision cases, a right-sided approach is also possible.

Table 4.1 summarizes the standard approaches based on the index level.

For minimally invasive anterior approaches to the thoracolumbar spine, specialized equipment is necessary. All types of approaches require a self-retaining retractor system (such as the SynFrame, Synthes, West Chester, PA) with retractor blades ranging of sizes 60 to 140 mm. A thoracoscopy unit with cold light source and video camera is required as well, except for the retroperitoneal approach. This unit can optimize camera stability, if the camera can be mounted to the retractor ring. For full endoscopic technique, a fan-like folding endoscopic retractor is essential.

Table 4.1 Summary of Standard Approaches in Anterior Minimally Invasive Surgery Fracture Treatment

Level	Approach
T4–T8	Right-sided transthoracic
T8–T10	Right- or left-sided transthoracic (depending on the aorta)
T10–L2	Left-sided transthoracic
L2–L4	Left-sided retroperitoneal

The instruments commonly used for spinal surgery are available in various sizes (e.g., Cobb elevator, pituitary rongeur, Kerrison pouches, annulus knife, chisels, bipolar forceps, monopolar adapter, etc.). The intended implant system should be checked preoperatively to determine if it is appropriate for MIS application.

Anesthesia

Ventilation issues arise mainly in the transthoracic approach—either full endoscopic or mini-open. Single lung ventilation is required in all full endoscopic procedures and in all procedures above T10. This entails an increased risk of endotracheal tube dislocation during all steps of the operation and prolongs the induction time.

In mini-open procedures below T10, double lung ventilation is possible, but then the positive end-expiratory pressure (PEEP) has to be reduced as much as possible.

During the operation, lung tissue is moved cranially with gentle pressure to facilitate viewing the surgical field. Single lung ventilation, reduced PEEP, and external pressure on pulmonary tissue may lead to an intraoperative iatrogenic ventilation-perfusion mismatch, with corresponding changes in arterial blood gases, mainly a decrease in oxygenation. Postoperatively, pleural effusion and atelectasis are not rare sequelae, so it is strongly advised to perform a lung function workup during the preoperative evaluation process. Monitoring should facilitate repetitive arterial blood gas analyses.

Hemodynamic management should anticipate a blood loss of about 500 to 1,500 mL.1,2

Positioning

The patient is placed in the lateral decubitus position, either right or left, depending on the selected approach. All pressure points should be padded properly using Gelfoam. The lower fibular head (N. peroneus) and the lower axilla (brachial plexus) should be given special attention, because these structures are particularly at risk. The upper arm shall be placed in an anteverted and only slightly abducted position. Excessive abduction should be avoided, to prevent traction damage on the brachial plexus of the upper arm and to facilitate free movement of the thoracoscope.

Placing the upper leg in a slightly flexed position reduces tension on the psoas muscle, which facilitates its mobilization during the operation. Putting the greater trochanter on the hinge joint of the operating table makes it possible to distract the intercostal spaces or the space between the rib cage and iliac crest during the operation. This facilitates access, especially in patients with smaller statures.

During positioning and draping, unhindered motion of the C-arm around the patient should be ensured.

The surgeon stand at the back of the patient, the assistant surgeon stands at the front of the patient, and the nurse stands beside the assistant surgeon.

The displays of the image intensifier and thoracoscopy unit are placed at the foot of the patient, so they are visible to the entire surgical team (Fig. 4.1).

Fig. 4.1 Setup in the operating room. The surgeon stands at the back of the patient and the assistant surgeon faces the surgeon. The fluoroscopy and thoracoscopy monitors are placed at the feet of the patient.

Mini-Open Transthoracic Approach

Localization and Skin Incision

Under fluoroscopic control, the fractured vertebra and the adjacent vertebral bodies are identified. Their anterior and posterior borders and the upper and lower end plates are marked on the skin. If bisegmental stabilization (corpectomy) is to be performed, the skin incision runs from the posterior edge of the lower end plate of the vertebral body above the fracture to the anterior edge of the upper end plate of the vertebral body below the fracture. If monosegmental stabilization is to be performed, the skin incision runs from the midpoint of the posterior wall of the vertebral body above the fracture to the midpoint of the anterior wall of the fractured vertebral body.

The skin incision must be adapted to the location of the intersecting rib. The skin incision is usually not longer than 4 to 8 cm.

Surgical Preparation

The skin, subcutaneous tissues, and the underlying latissimus and serratus muscles are incised in line down to the rib to be exposed. The intercostal muscles are dissected strictly at the cranial border of the guiding rib. The parietal pleura is then incised without injuring the lung. A rib spreader can be inserted to facilitate visualization into the thoracic cavity.

At this point, either PEEP reduction or instituting single lung ventilation is desirable.

The thoracoscope is now inserted via the mini-thoracotomy, and the pleural cavity is checked for adhesions or anatomic variants. The lung is mobilized cranially and secured with a moist swab. The viewing portal is then established under thoracoscopic control. It should be placed about two intercostal spaces away from the mini-thoracotomy. If the fracture is at T7 or above, the viewing portal is usually caudal to the mini-thoracotomy. If the fracture is below T7, the viewing portal is normally cranial to the mini-thoracotomy. In the anteroposterior direction, the viewing portal is typically placed centrally in relation to the thoracotomy; if posterior wall removal is sought, a more anteriorly position may facilitate control (Fig. 4.2).

A stab incision (2 cm) is made, and the intercostal muscles and the parietal pleura are dissected under thoracoscopic control at the upper rim of the rib to avoid injury to the intercostal vessels and nerve. A blunt trocar is inserted. Then the thoracoscope is moved to the viewing portal and fixed to the retractor system.

At this point the visibility of the spinal column is usually still obstructed by the diaphragm caudally and the lung cranially. They are retracted gently by the use of self-retaining retractor blades. The great anterior vessels and the anterior border of the spinal column should be clearly identified by gentle palpation with a swab and secured by another retractor blade.

Then the index vertebra must be securely identified. Fracture hematoma or special anatomic features, such as prominent osteophytes, should also be identified. A Kirschner wire (K-wire) is inserted into the suspicious disk space and the correct level is affirmed fluoroscopically. The parietal pleura is incised with electrocautery along the longitudinal axis of the spine, in the midline between the anterior and posterior border. It is easiest to start the cut at the level of the disk space, which will appear as avascular “hills.” This avoids incidental bleeding from the segmental vessels, which run like a creek through the “valley” in the middle of the vertebral body. They are identified by gentle blunt preparation with a gauze swab and then clipped or coagulated.