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Perspectives on Modern Orthopaedics

Thoracoscopic Anterior Instrumentation and Fusion for Idiopathic Scoliosis

Sucato, Daniel J. MD, MS

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Journal of the American Academy of Orthopaedic Surgeons: July 2003 - Volume 11 - Issue 4 - p 221-227
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Abstract

Surgical treatment for idiopathic scoliosis has changed rapidly in the last 20 years. Posterior segmental spinal instrumentation was an advance over Harrington instrumentation because it improved correction in the sagittal and coronal planes.1,2 The single solid rod used with anterior surgery was an improvement over the Dwyer cable, especially for thoracolumbar and lumbar curves, because it allowed surgeons to use a rotational maneuver to correct both the sagittal and coronal deformities.1,2 Recently, the single solid rod placed through an open thoracotomy has been used to correct thoracic curves.3,4 Anterior correction of thoracic scoliosis offers the theoretic advantage of better coronal correction because it permits the surgeon to perform diskectomies, provides improvement in the thoracic hypokyphosis seen in idiopathic scoliosis, and saves motion segments. In a prospective study, Betz et al4 demonstrated that anterior surgery improved sagittal plane alignment while saving an average of 2.5 distal motion segments compared with posterior surgery.

In the last decade, indications have increased for endoscopic approaches to thoracic spine surgery. Endoscopy was first used for biopsy and diskectomy as well as for anterior release and fusion, in combination with posterior spinal fusion and instrumentation, to treat severe curves or when there was risk for the development of the crankshaft phenomenon.5-7 The endoscopic approach also has been used to perform an anterior instrumentation, correction, and fusion. Early results are encouraging, but the technique requires further study and improvement.

Patient Selection and Preoperative Planning

The indications for anterior instrumentation and fusion include single thoracic curves or thoracic curves with a compensatory lumbar and/or upper thoracic curve, that is, type IA, IB, or IC curves using the Lenke classification.8 It is important to determine the curve type for preoperative planning so that the appropriate thoracic curve correction is achieved, especially in the setting of a so-called selective thoracic fusion in the IC curve type. The ideal patient for thoracoscopic anterior instrumentation and fusion is one who has a relatively small curve size (50° to 65°) of relative flexibility (>50% flexibility index); is thin (40 to 60 kg), which makes placement and utilization of the portals easier; and is tall, because the sizable chest provides a greater working space and larger vertebral bodies for easier insertion of screws. For surgeons with experience in the technique, the indications can include stiffer curves of up to 75°. The primary contraindication for the procedure is poor pulmonary function, which limits the patient's ability to tolerate single-lung ventilation. All patients should have preoperative pulmonary function tests to assess their ability to tolerate the procedure and to help predict the postoperative course. Pulmonary function test findings below 60% of predicted results are a relative contraindication to anterior thoracic surgery.

Preoperative assessment of the patient should include a physical examination to confirm radiographic findings that the upper thoracic and lumbar curves are compensatory without any structural characteristics. Imaging should include standing lateral and posteroanterior and supine bending right and left radiographs. The lateral radiograph should be used to ensure that excessive kyphosis (>40°) is not present. This is a contraindication for anterior correction because, when compression is used, anterior correction can increase kyphosis.9 Fusion levels for the thoracic curve are determined on the posteroanterior radiograph, using the superior and inferior end vertebrae of the Cobb measurement as the upper and lower end instrumented vertebrae. In a smaller patient or one who has marked tilt of the upper end instrumented vertebrae, a level superior to the end vertebra may be chosen to provide greater fixation because of the risk of cutout of the superior screws. Analysis of the lower end vertebra may reveal that the disk proximal to it is in fact neutral. If so, the more proximal level may be chosen as the lower end instrumented vertebra. Supine bending radiographs are important to confirm that the lumbar and upper thoracic curves are truly compensatory (bend to <25°). Bending radiographs are used to determine the flexibility of the thoracic curve so that a coronal bend may be placed in the rod if the curve is stiff.

Anesthesia Considerations

Maintaining a proper airway during anesthesia is critical to the success of thoracoscopic surgery. To perform anterior instrumentation and fusion, the lung on the convexity of the curve must be deflated, and single-lung ventilation techniques are used. This is typically accomplished with a double-lumen endotracheal tube, which has a bronchial lumen that sits in the dependent mainstem bronchus and a tracheal lumen that lies just proximal to the carina (Fig. 1). The dependent lung is ventilated through the bronchial lumen, while the lung on the convexity of the curve becomes deflated when the tracheal lumen is occluded. It is important to recheck tube placement after the patient is in the lateral decubitus position because, in up to 80% of cases, the tube tends to move distally.10

Figure 1
Figure 1:
Correct positioning of the doublelumen endotracheal tube to ventilate the left lung. The bronchial lumen should be just distal to the carina and the tracheal lumen just proximal to the carina. The tracheal lumen is occluded to allow for selective ventilation of the left lung.

Patients undergoing single-lung ventilation are subjected to significant stresses from the right-to-left shunt through the dependent lung and from that lung's decreased functional capacity, the result of increased intraabdominal pressure and compression from the weight of the mediastinal structures. The high pressures that result can lead to airway leaks or trauma, which can cause pneumothorax. The so-called down lung syndrome, seen most frequently with lengthy surgeries, is characterized by absorption atelectasis, accumulation of secretions, and formation of transudate in the dependent lung. The anesthesiologist needs to be skilled in the technique to minimize the chance of anesthetic complications.11,12

Patient Positioning and Operating Room Setup

The patient is positioned in the lateral decubitus position on a radiolucent operating table with the convexity of the curve up (Fig. 2). An absolutely lateral position is critical, especially during screw placement, and should be checked periodically to ensure that it is maintained throughout the procedure. The patient may be secured using an inflatable radiolucent beanbag or other positioning system. Whatever method is used, the patient's spine must be palpable posteriorly, and the umbilicus visible anteriorly, to allow orientation and exposure in case conversion to an open thoracotomy is necessary. The thoracotomy tray should be available in the operating suite. The arm on the convexity of the curve can usually be positioned out of the sterile field, especially when the upper instrumented level is at T5 or below. However, when the upper instrumented level is above T5, the arm may be incorporated into the sterile field to provide better control of the patient's arm and scapula, making proximal portal placement easier.

Figure 2
Figure 2:
Operating room setup.

One or two surgeons are positioned on the posterior aspect and one on the anterior aspect of the patient. The scrub assistant is usually anterior. The video monitors should be at the head of the table on both sides of the patient to give the surgeons on each side a direct view. The fluoroscopy C-arm unit is brought in anteriorly when screws are placed, with the monitor at the foot of the table.

Although some surgeons perform the diskectomy on the posterior aspect, the anterior position allows better control of posterior penetration beyond the posterior anulus fibrosus and posterior longitudinal ligament. During screw placement and instrumentation, the surgeon may be more comfortable at the posterior aspect of the patient because leaning over the operating room table is then unnecessary, and it is safer to direct the screws slightly anteriorly.

Surgical Procedure Portal Placement

Accurate placement of the portals is critical because they determine the approach for the diskectomies and, more important, the screw starting points and directions. Before the patient is prepared and draped, the spinal levels to be instrumented are located fluoroscopically in the coronal and sagittal planes, and the skin is marked. In general, the incision for the portals should be directly over the rib so that two portals (above and below the rib) can be used for each incision.

A single anterolateral portal is placed at the apex of the curve in the anterior-to-midaxillary line, and the thoracoscope is placed through this portal. The thoracoscope consists of a camera and a scope that is angled at 30° or 45°. Seen from the anterolateral portal, the spine is horizontal on the monitor; seen from the posterolateral portal, the spine is vertical, giving a good “pipeline” view (Fig. 3). The scope should be oriented to see the disks straight on when the thoracoscope is in the anterolateral portal. This is best achieved by keeping the orientation light from the lens perpendicular to the spine, with the scope handle at the 3-o'clock position when looking at the most cephalad disk (Fig. 4, A) and at the 9-o'clock position when looking at the most caudad disk (Fig. 4, B). This position allows visualization down the axis of the disk space and provides a true anteroposterior view of the vertebral bodies. The posterolateral portals are made under direct visualization. The placement of the most cephalad portal is very important for proper instrumentation. The skin mark initially made under fluoroscopic visualization is used to place a guide pin, which is then assessed using the camera in the anterolateral portal. The ribs should be counted to check the level of the guide pin. If the pin is not sufficiently superior or posterior to allow the surgeon to place the proximal screw, the pin is moved and the portal inserted. The camera may then be placed through that portal to check the position further.

Figure 3
Figure 3:
Thoracoscopic video images. A, With the thoracoscope in the anterolateral portal, the spine is horizontal on the monitor and provides a good assessment of the superior and inferior extent of each vertebral body. B, With the thoracoscope in one of the posterolateral portals, the spine is more vertical on the monitor “pipeline” view, providing a good assessment of the anterior and posterior aspects of the spine. The diaphragm is visible at the top of the image.
Figure 4 A,
Figure 4 A,:
Use of the thoracoscope in the anterolateral portal. To view the proximal (cephalad) portion of the spine, the camera is positioned parallel to the floor and the light source handle is at the 3-o'clock position. The spine appears horizontal on the monitor (inset). B, To view the distal (caudad) aspect of the spine, the camera is positioned parallel to the floor and the light source handle is at the 9-o'clock position. This keeps the spine horizontal on the monitor (inset). C, Portal placement for a typical thoracic idiopathic curve. The anterolateral portal is made in the anterior axillary line at the apex of the curve.

The remaining posterolateral portals are then placed, with close attention paid to the distances between portals and their positions in the anteroposterior and superoinferior directions. Positioning is assessed with the thoracoscope in the anterior portal to ensure that the portals are made directly over the vertebral bodies. A typical portal configuration for a seven- or eight-level instrumentation is a single anterolateral portal and four posterolateral portals (Fig. 4, C). Various portal configurations have been described, including posterolateral portals only or a combination of three anterolateral with three posterolateral portals.

Disk Excision and Bone Grafting

Disk excision is the most important aspect of the procedure. The surgeon incises the pleura in the midvertebral body, then coagulates the segmental vessels. The pleura should be bluntly teased posteriorly past the rib heads and anteriorly around the front of the spine to allow access to the anterior longitudinal ligament and contralateral anulus. Sharp incision of the disk can be made with a scalpel blade or harmonic scalpel. Disk shavers, rongeurs, and curettes are used to excise the disk as completely as possible (Fig. 5). Animal studies comparing open thoracotomy with thoracoscopic techniques have demonstrated comparable amounts of diskectomy.13,14 A quantitative analysis of computed tomography (CT) in 12 adolescent patients (mean age, 13.3 years) demonstrated that a mean of 73% of the disk and end plate was removed, allowing correction from a mean of 55° to a mean of 9°.15

Figure 5
Figure 5:
Axial CT scan of a thoracic disk space after diskectomy and bone grafting done as part of an anterior thoracoscopic instrumentation and fusion. Note the bone graft material (arrows) packed all the way to the opposite side of the disk space and posteriorly. The rod is seen on the right side of the vertebral body.

Autologous rib or iliac crest bone grafts can be used and probably are best placed immediately upon completion of the diskectomy at each level. Bone funnels are used to place the grafts and should start in the depths of the disk space to ensure that the grafts are packed completely.

Screw Placement

Before screws are placed, the patient's position should be rechecked to ensure it is directly lateral. The fluoroscopic image should be at right angles to the vertebral bodies in the anteroposterior projection and is used to confirm that the screw is oriented parallel to the end plate. The thoracoscope is placed in the anterior portal initially to direct the guidewire with respect to the superoinferior starting point and orientation. The thoracoscope is then moved to a posterolateral portal to check the anteroposterior starting point and its direction. The anteroposterior fluoroscopic images are then used to fine-tune the starting point in the superoinferior direction.

Screws are placed beginning at the apex of the curve, with the starting point of the screw just anterior to the rib head. The screws are directed slightly anteriorly to avoid the spinal canal and to be in the midaxial plane of the rotated apical vertebral bodies. This screw orientation allows for rotational correction during rod insertion and compression. As screws are placed proximal and distal to the apex, the starting holes move slightly more anteriorly. The cephalad screws are the most difficult to place accurately with good purchase because the vertebral bodies are smaller, the rib heads obscure more of the vertebral bodies, and the proximal portals are often not ideally placed. The proximal screws must be placed with great care and attention to anatomic landmarks to ensure that these screws are not too posterior, which could lead to spinal canal penetration, but are posterior enough to allow secure purchase in good bone stock (Fig. 6). It is often necessary to remove the rib heads at T5 and T6 to gain good access to the vertebral bodies at these levels.

Figure 6
Figure 6:
Axial CT scan of a thoracic vertebral body after anterior thoracoscopic instrumentation and fusion. The starting position of the screw is just anterior to the rib head. The outline of the aorta is seen at approximately 1 o'clock, just posterior to the left mainstem bronchus. The screw has one to two threads engaging the opposite cortex; however, the screw tip is close to the aorta.

Present instrumentation systems are modifications of open anterior instrumentation systems, with all instruments made to fit through a 10.5-mm-diameter portal. Screws in sizes from 5.5 to 7.5 mm and rods in 4.0-, 4.5-, and 4.75-mm diameters are available. The proximity of the aorta to the vertebral bodies in the upper and midthoracic spine limits the amount of bicortical screw purchase that can be achieved16 (Fig. 6). In the lower thoracic spine in a patient with idiopathic scoliosis, the aorta is positioned more anterior to the vertebral body. Newer instruments allow the surgeon to place screws without the use of the guide wire, which can lead to complications with inadvertent advance across the vertebral body.

Rod Insertion and Correction Maneuvers

The stiffness of the curve, the purchase of the most proximal screws, and whether maximum correction is desired (Lenke IA curve) will determine whether a small coronal bend should be placed in the rod before inserting it into the chest. In taller patients with smaller, more flexible curves and larger vertebral bodies, no coronal bend in the rod is necessary. In patients with a very lordotic thoracic segment, a kyphotic bend can be placed in the rod.

The rod is inserted through the distal or proximal posterolateral portal and grasped within the chest with a rod grabber so that it can be seated into the screws in one step. The rod is initially seated distally to help control the length of rod that protrudes distal to the screw and prevent it from pushing against the diaphragm.

Two correction maneuvers are performed: compression and cantilever. Because the rod is essentially straight in the coronal plane, in contrast with the deformity, the rod can be seated only in the distal three or four screws. Initially, compression is performed across these screws, followed by cantilevering the rod down into the remaining proximal screws. After the rod is captured in the proximal screw heads, compression is then completed at these levels with care taken to avoid excessive force on the top screws. The securing plugs are then tightened fully. The surgeon must be sure to place the guide sleeve over the screw or grasp the rod to produce a countertorque to prevent screw migration or “plowing.” Anteroposterior and lateral radiographs or fluoroscopic images should be checked to ensure that all screws are safely positioned and that correction is adequate in the coronal and sagittal planes.

Pleural Closure and Chest Tube Insertion

The pleura can be closed to help decrease chest tube output, limit development of lung adhesions, and contain the bone graft in the disk space. Diaphragmatic repair is incorporated into the pleural closure when the instrumentation extends to T12 or L1. The pleura is closed with an Endostitch device (US Surgical, Norwalk, CT), running a suture beginning distally and another beginning proximally, which then meet in the center so that they can then be tied easily. A chest tube is placed through the incision of the most distal posterior portal skin incision. Because of the single, small-diameter rod, all patients should wear a brace during the day (when not sleeping) for the first 3 months.

Early Results

In one series of 28 girls (average age, 12.1 years) with a mean preoperative curve of 55° (range, 46° to 78°), the mean postoperative curve at 1 year was 14° (74.5% correction)15 (Fig. 7). Complications included six proximal screws that partially pulled from the vertebral body at the time of compression in four patients; two screws that cut out at the time of insertion because of small vertebral bodies in two patients; guidewire migration into the spinal canal in one patient, with resultant dural leak without neurologic sequelae; and asymptomatic pseudarthrosis in one patient who underwent a posterior spinal fusion.15

Figure 7
Figure 7:
Preoperative anteroposterior (A) and lateral (B) radiographs of a 13-year-old girl with a 56° right thoracic idiopathic curve with a notable trunk shift to the right and hypokyphosis (panel B). Anteroposterior (C) and lateral (D) radiographs 1 year after anterior thoracoscopic instrumentation from T5 to T12, with near-complete correction of the coronal plane deformity and restoration of the normal sagittal profile.

Picetti and Bueff17 reported followups over 2 years on 50 patients (mean age, 12.7 years) with a mean preoperative curve of 58°. Improvements in techniques resulted in enhanced correction and fewer complications over the course of this series. Mean curve correction was 50.1% in the first 10 patients and 68.6% in the last 10. Surgical time improved from a mean of 6 hours 6 minutes in the initial 30 cases to 3 hours 58 minutes in the last 10 cases. Mean blood loss was 266 mL. The chest tube was in place for a mean of 2.25 days (range, 1 day to 5 days), and hospital stay averaged 2.9 days (range, 2 to 7 days). Reported complications included one screw pullout, three patients with chest wall numbness, five mucous plugs, one wound revision, and two rod fractures. A demineralized bone matrix product was used in the initial patients, resulting in a high incidence of pseudarthrosis; however, only 1 patient of the remaining 35 had a pseudarthrosis when autologous rib graft was used.17

Complications

There are no published series of patients who have had thoracoscopic instrumentation and fusion for idiopathic scoliosis, so the prevalence of complications is not known. However, complications that have been presented and discussed at scientific meetings can be categorized as anesthesia-related and surgical. The anesthesia-related complications include the down lung syndrome, with significant atelectasis present on the initial chest radiograph; inability to tolerate single-lung ventilation and conversion to an open technique or posterior spinal fusion; inability to obtain single-lung ventilation because of difficulty in tube placement; and pneumothorax secondary to high airway pressures.12 Because this procedure is new and technically demanding, the incidence of complications can be high, especially early in the surgeon's experience. Complications that can occur during surgery include blood vessel injury, lymphatic injury with resultant chylothorax, guide-pin migration into the opposite side of the chest with resultant pneumothorax,18 distal migration or plowing of the screw when the rod is seated proximally or is compressed, and screw cutout at the time of screw insertion.

Summary

The endoscopic approach to curve correction, instrumentation, and fusion for spinal deformity is anewtechnique that promises improved patient care because it limits the surgical incision and chest wall compromise, improves postoperative pain and pulmonary function, and enhances cosmesis. Compared with posterior instrumentation, anterior instrumentation by either open or thoracoscopic approach can save fusion levels while improving three-dimensional correction. However, no studies have directly compared thoracoscopic instrumentation and fusion with open anterior and/or posterior procedures, making any conclusive statements impossible. Amulticenter prospective study may be needed to fully elucidate the advantages this technique may have and to help define the exact indications for a thoracoscopic approach to treat scoliosis.

Several important issues must be kept in mind. First, the proposed advantages have not been confirmed through scientific study. Second, the technique continues to evolve to decrease the duration of surgery while maintaining the safety of the procedure. Third, screw migration and proximity of screws to important softtissue structures need further study. Finally, this is a technically demanding procedure with a steep learning curve and may not be appropriate for all surgeons who treat spinal deformity.

References

1. Lenke LG, Bridwell KH, Blanke K, Baldus C, Weston J: Radiographic results of arthrodesis with Cotrel-Dubousset instrumentation for the treatment of adolescent idiopathic scoliosis: A five to ten-year follow-up study. J Bone Joint Surg Am 1998;80:807-814.
2. Richards BS, Herring JA, Johnston CE, Birch JG, Roach JW: Treatment of adolescent idiopathic scoliosis using Texas Scottish Rite Hospital instrumentation. Spine 1994;19:1598-1605.
3. Lenke LG, Betz RR, Bridwell KH, Harms J, Clements DH, Lowe TG: Spontaneous lumbar curve coronal correction after selective anterior or posterior thoracic fusion in adolescent idiopathic scoliosis. Spine 1999;24:1663-1672.
4. Betz RR, Harms J, Clements DH III, et al: Comparison of anterior and posterior instrumentation for correction of adolescent thoracic idiopathic scoliosis. Spine 1999;24:225-239.
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7. Regan JJ, Guyer RD: Endoscopic techniques in spinal surgery. Clin Orthop 1997;335:122-139.
8. Lenke LG, Betz RR, Harms J, et al: Adolescent idiopathic scoliosis: A new classification to determine extent of spinal arthrodesis. J Bone Joint Surg Am 2001;83:1169-1181.
9. Clements DH, Betz RR, Lowe TG, Lenke LG, Newton PO: Abstract: Adolescent idiopathic scoliosis with excessive thoracic kyphosis: Comparison of anterior versus posterior instrumentation for maintaining correction. Scoliosis Research Society 35th Annual Meeting Book. Rosemont, IL: Scoliosis Research Society, 2000, p 97.
10. Desiderio DP, Burt M, Kolker AC, Fischer ME, Reinsel R, Wilson RS: The effects of endobronchial cuff inflation on double-lumen endobronchial tube movement after lateral decubitus positioning. J Cardiothorac Vasc Anesth 1997; 11:595-598.
11. Dieter RA Jr, Kuzycz GB: Complications and contraindications of thoracoscopy. Int Surg 1997;82:232-239.
12. Sucato DJ, Girgis M: Bilateral pneumothoraces, pneumomediastium, pneumoperitoneum, pneumoretroperitoneum, and subcutaneous emphysema following intubation with a double-lumen endotracheal tube for thoracoscopic anterior spinal release and fusion in a patient with idiopathic scoliosis. J Spinal Disord Tech 2002;15:133-138.
13. Huntington CF, Murrell WD, Betz RR, Cole BA, Clements DH III, Balsara RK: Comparison of thoracoscopic and open thoracic discectomy in a live ovine model for anterior spinal fusion. Spine 1998;23:1699-1702.
14. Newton PO, Cardelia JM, Farnsworth CL, Baker KJ, Bronson DG: A biomechanical comparison of open and thoracoscopic anterior spinal release in a goat model. Spine 1998;23:530-536.
15. Sucato D, Kassab F, Dempsey M: Abstract: Thoracoscopic anterior spinal instrumentation and fusion for idiopathic scoliosis: A CT analysis of screw placement and completeness of discectomy. Scoliosis Research Society 36th Annual Meeting Book. Rosemont, IL: Scoliosis Research Society, 2001, p 90.
16. Sucato DJ, Duchene C: MRI analysis of the position of the aorta relative to the spine: A comparison between normal patients and those with idiopathic right thoracic curves. J Bone Joint Surg Am, in press.
17. Picetti GD III, Bueff HU: Abstract: Endoscopic instrumentation, correction and fusion of thoracic curves in idiopathic adolescent scoliosis. Scoliosis Research Society 35th Annual Meeting Book. Rosemont, IL: Scoliosis Research Society, 2000, p 110.
18. Roush TF, Crawford AH, Berlin RE, Wolf RK: Tension pneumothorax as a complication of video-assisted thorascopic surgery for anterior correction of idiopathic scoliosis in an adolescent female. Spine 2001;26:448-450.
© 2003 by American Academy of Orthopaedic Surgeons