Indications

Scoliosis

Thoracic scoliosis has various etiologies (idiopathic, neuromuscular, syndrome related) that are frequently not diagnosed and treated until the curve is relatively large and stiff. Anterior surgery has been most frequently used as a means to achieve a complete discectomy and release of the anterior spine; this results in greater curve flexibility and prevents the “crankshaft” phenomenon in young patients. Although no strict guidelines on the magnitude and flexibility of the spinal curvature that requires release have been established, generally curves with a Cobb angle greater than 70 to 75 degrees and a bend correction less than 50% are considered appropriate for release. When sufficient segmental mobility of the released vertebra has been achieved, posterior instrumentation is placed to correct the deformity (Fig. 25–1).

FIGURE 25–1 A and B, Preoperative posteroanterior (A) and lateral (B) radiographs of large stiff curve. C and D, Postoperative posteroanterior (C) and lateral (D) radiographs. Thoracoscopic anterior spinal release and discectomy and combined posterior spinal instrumentation and fusion provide acceptable correction.

Lenke³ reported on a combined anterior VATS release and fusion followed by posterior instrumentation in the treatment of adolescent idiopathic scoliosis that had an average preoperative curve of 82 degrees (range 41 to 125 degrees) with postoperative correction of 70% to 28 degrees (range 5 to 60 degrees). Similarly, Newton and colleagues⁴ reported a series of 112 pediatric spinal deformity cases with an average preoperative curve of 80 degrees that received an anterior release combined with posterior instrumentation and found a 67% correction in idiopathic scoliosis and a 52% correction in neuromuscular scoliosis. More recent studies have called into question the utility of the anterior release, however, in the age of modern segmental pedicle screw instrumentation.^5,6 Suk and colleagues⁶ found an average correction of 66% when posterior pedicle screws alone were used in preoperative thoracic curves of 80 degrees with a flexibility of 45%. Although modern pedicle screw constructs offer a similar correction, an anterior release may still be indicated to optimize coronal and axial plane correction, improve sagittal alignment by increasing thoracic kyphosis, and prevent crankshaft growth.

Children and young adolescents (Risser 0, open triradiate cartilage) with progressive scoliosis are known to be at risk for crankshaft deformity when treated with a posterior fusion alone.⁷ These results were reported for children using hook and wire fixation, however, and not modern pedicle screw instrumentation. Although there has been concern regarding adequate pedicle size in children to accommodate pedicle screws, Catan and colleagues⁸ performed a magnetic resonance imaging (MRI) analysis of thoracic pedicle morphology in preadolescent patients with idiopathic scoliosis and found that the anatomic measurements were compatible with pedicle screw instrumentation. Sarlak and colleagues⁹ reported more recently a series of seven children (average age 7.4 years) with scoliosis with an average preoperative thoracic curve of 56 degrees who were treated with posterior segmental pedicle screw instrumentation and 5 years of follow-up. These authors found a 57% correction rate with no evidence of crankshaft phenomenon in four patients but found a slight increase in Cobb angle and a significant increase in angle of trunk rotation (ATR) suggesting crankshaft phenomenon in two patients.⁹ Given the lack of clear evidence on the appropriate treatment of these cases, an anterior fusion may be a viable option to limit anterior growth and prevent this late increasing deformity.¹⁰ Thoracoscopic disc excision and fusion provides a minimally invasive option and minimizes the risk of pulmonary complications in these young patients with progressive deformity.^11–13

Patients with spinal deformity associated with Marfan syndrome, neurofibromatosis 1, and prior spinal irradiation may have an increased risk of pseudarthrosis after an isolated posterior scoliosis correction. In cases such as these, an anterior fusion procedure may improve the odds of successful arthrodesis, especially when autogenous bone graft is used.⁴

Contraindications

As suggested earlier, the small size of the patient is a relative contraindication to thoracoscopy. Lung deflation is more difficult in these cases because standard size double-lumen and bronchial blocking endotracheal tubes are too large. Another contraindication is the presence of a markedly reduced working distance between the chest wall and the spine. In severe cases of scoliosis, the reduced distance limits the field of vision (the endoscope is too close to the spine to obtain any perspective) and the maneuverability of the working instruments. A minimum distance of 2 to 3 cm of working space between the rib cage and the spinal column is required to provide adequate visualization. If the distance is less than 2 cm, thoracoscopy is not advised. Body weight of less than 30 kg is a relative contraindication because the relative benefits of thoracoscopy seem to be reduced in small patients.²⁶

Visualization of the surgical field is mandatory in all surgical approaches, and it may be compromised in thoracoscopic surgery by incomplete deflation of the lung or pleural adhesions that prevent collapse away from the chest wall and spine. Pleural adhesions (Fig. 25–2) can be anticipated in patients with a history of prior ipsilateral thoracic surgery or significant pulmonary infection, both of which should discourage the surgeon from using the thoracoscopic approach.

FIGURE 25–2 Endoscopic view of pleural adhesions indicated by arrows A and B.

Surgical Technique

Much of the equipment required for spinal thoracoscopy is common to all endoscopic surgery. An endoscope (10-mm diameter, 0- and 45-degree angle viewing), video camera, light source, and monitor have become standard in nearly all modern operating rooms. Access through the chest wall between the ribs is maintained with plastic tubular “ports.” These ports provide a path to place the endoscope and working instruments into the chest cavity.

Patient positioning has traditionally been in the lateral decubitus position (Fig. 25–3). Some studies have suggested that in select cases prone positioning may be possible, avoiding the need to reposition the patient for the posterior procedure or even allowing simultaneous anterior release and posterior instrumentation.^27–29 Although the ability to convert to an open approach may be restricted, it has been shown that the prone position does not adversely affect postoperative pulmonary function.³⁰ This approach necessitates a more posterior portal placement, however, and may limit the anterior extent of spinal exposure and disc excision.

FIGURE 25–3 Diagrammatic setup in operating room shows position of surgeon, assistants, scrub nurse, and monitor for endoscopic surgery.

The role of the anesthesiologist is crucial in the success and safety of thoracoscopic surgery.³¹ Spinal cord monitoring is advised using somatosensory and transcranial motor evoked potentials. Complete ipsilateral lung deflation is essential to prevent lung parenchymal injury from passing instruments and to allow visualization of the spine. Double-lumen endotracheal tubes are preferred in patients large enough (>45 kg) to accept these devices. In children (<45 kg), selective intubation of a single lung is often required as an alternative. A small balloon advanced into the main stem bronchus blocks ventilation to the lung on the operative side. In nearly all patients with normal preoperative pulmonary function, single-lung ventilation can be tolerated. The surgeon and anesthesiologist should be aware of the increased risk of developing postoperative mucous plugs as a result of single-lung ventilation.

After lung deflation, portals are established through the chest wall (Fig. 25–4). The orientation of these portals may vary depending on the pathology, although in most cases of deformity release and fusion they are best placed in a linear relationship along the anterior axillary line. Owing to the site of diaphragm insertion, the inferior portals require a slightly more posterior placement to maintain an intrathoracic position. Initial exposure of the spine often requires gentle retraction of the lung, at least until it becomes completely atelectatic (Fig. 25–5). The vasculature including the azygos vein and subclavian artery is identified before the introduction of surgical instruments to prevent inadvertent injury (Fig. 25–6). The vertebral levels are confirmed by identifying the first rib partially hidden beneath the subclavian artery and counting down distally (Fig. 25–7). Division of the pleura overlying the spine may be performed either longitudinally, over the length of the spine to be fused, or transversely, at each disc space.

FIGURE 25–4 Proper placement of portals is necessary for multilevel discectomies with the patient in lateral position.

FIGURE 25–5 Intraoperative endoscopic view of fan retractor (A) placed on lung (B) to aid in complete deflation.

FIGURE 25–6 Endoscopic view of thoracic cavity shows spine (asterisk), segmental vessels, azygos vein (arrow), and atelectatic lung.

FIGURE 25–7 Peanut dissector is used to palpate first rib (A). Second rib (B) is most obvious.

Treatment of the segmental vessels (Fig. 25–8) may be similarly individualized with either division or preservation, depending on the needs of the case or preference of the surgeon. In most cases, the authors prefer a longitudinal pleural exposure with division of the segmental vessels using Harmonic laparoscopic coagulating sheers (Ethicon Endo-Surgery, Cincinnati, Ohio). Division of the segmental vessels allows greater anterior spinal exposure for more complete annular release. Blunt dissection of the pleura to the contralateral side of the spine is performed exposing approximately 270 degrees of the disc perimeter. After division of the pleura, any remaining areolar tissue is divided, and packing sponges are used to create a space between the anterior spine and the pleura.

FIGURE 25–8 After division of pleura (A), Harmonic laparoscopic coagulating sheers are applied to segmental vessel (B).

Possible levels that can be accessed thoracoscopically are T2-L1. Exposure of the T12-L1 disc and L1 vertebral body requires division of a small segment of the diaphragm insertion, which can be accomplished by extending the pleural incision distally into the diaphragm. The proximal thoracic spine in the right chest is often covered by the confluence of the segmental veins, which may appear daunting at the T3 and T4 levels. With slow cautious use of the ultrasonic devices, these vessels can be sealed and divided safely, however, exposing the upper thoracic spine. Disc excision techniques are similar to techniques used in open surgery. An annulotomy is performed with the electrocautery or Harmonic scalpel. A rongeur is an excellent tool for most of the disc excision. Specially designed endoscopic rongeurs are available in extended lengths with various angles (straight, up, right, left) to reach the depths of each disc space (Fig. 25–9).

FIGURE 25–9 A, Discectomy can be done with rongeur or curet or both with complete removal of anulus fibrosus, nucleus pulposus, and both endplates of cartilage. B, Appearance after multilevel discectomies completed. Empty disc space can be temporarily packed with Surgicel for hemostasis control before application of bone graft.

Awareness of the discectomy path is vital to avoid damage to the neural elements and to prevent excess bone excision, which causes increased bleeding and suboptimal visualization. An angled curet may also be used to remove residual endplate cartilage and expose the cancellous bony surface required for fusion. Bleeding from the bone can be limited by using the avascular plane of dissection between the cartilage endplate and the vertebral body in immature patients. The key to a comprehensive discectomy is optimal visualization deep into the disc space; this not only allows complete removal of all disc tissue, but also prevents injury to the posterior longitudinal ligament and neural elements.

When the discectomy is complete, either allogeneic cancellous or autogenous (rib or iliac crest) bone graft is placed into the disc space with an endoscopic tubular plunger (Fig. 25–10). The method and type of bone grafting also seems to be important to the success of arthrodesis. This may be crucial only in selected cases; however, all patients are at some risk for pseudarthrosis after posterior instrumentation and fusion procedures. In a study of 112 patients treated with an anterior release followed by posterior instrumentation, Newton and colleagues⁴ compared the grade of arthrodesis between patients who received autogenous versus allogeneic bone graft. These authors found the disc space was fused in 88% of the autograft group compared with 72% of the allograft group at 2-year follow-up.⁴ When autograft is not available, either allograft bone or demineralized bone matrix may be used because they have been shown to result in similar fusion rates.^4,32 Although autogenous bone graft is optimal for patients at greatest risk for pseudarthrosis, the risk-to-benefit ratio must be analyzed on a case-by-case basis.

FIGURE 25–10 Morcellized bone graft (arrow) is introduced into disc space using tubular plunger (asterisk).

Outcomes

The thoracoscopic approach has several advantages compared with an open thoracotomy approach. These advantages, including pulmonary function, reduced recovery period, less pain, and improved cosmesis, are realized, however, only if the efficacy of the spinal procedure equals that of open surgery. Experimental animal and clinical studies suggest comparable efficacy in experienced hands. Several studies have been conducted to evaluate the learning curve necessary to be experienced in this technique.^12,33,34 Newton and colleagues¹² found that there was a slight decrease in operative time throughout the course of the first 65 patients treated at their institution and concluded that thoracoscopy had a steep but not prohibitive learning curve. In a more recent study by Son-Hing and colleagues,³³ the learning curve was found to be short with appropriate training and resulted in an excision of a greater amount of disc tissue and a decrease in operative time, while providing similar curve correction to an open thoracotomy.

Several experimental studies have been done to analyze the extent of disc excision possible with thoracoscopic techniques. Biomechanical evaluations of the instability resulting from discectomy were equivalent between open and endoscopic approaches in various animal models.^34–37 The extent of endplate bony exposure has also been shown to be similar with the two approaches experimentally.^34,38 In a histomorphometric study of 32 pigs (160 discs), Zhang and colleagues³⁴ found that there was not a learning curve associated with the amount of disc material excised (>50% in 94% of the discs in this study), but a learning curve was present for the thoroughness of the endplate excision in thoracoscopic discectomy. Because the purpose of the endplate excision is to remove the growth potential and expose a cancellous bony surface for fusion, added care must be taken during the endplate removal step of this procedure.

The clinical results of thoracoscopic anterior release and fusion in patients with spinal deformity have been generally favorable although poorly controlled.³⁹ Although there was an increase in the use of this method during the 1990s, it has since declined in popularity with the widespread adoption of posterior segmental pedicle screw instrumentation. Despite more recent studies that have called the necessity of this technique into question for large, stiff curves, there may be a subset of patients who benefit from this procedure.^5,6,40 Studies by Luhmann and colleagues⁵ and by Suk and colleagues⁶ looked at curves with an average of 80 degrees main thoracic Cobb angle and an average flexibility of 45%. Both groups of investigators concluded that a similar coronal correction can be achieved with posterior segmental pedicle screw fixation as with a combined anterior and posterior procedure. These studies did not examine deformity on the extreme end of curves greater than 100 degrees with less than 25% flexibility, however. In a more recent study of 21 patients with an average preoperative Cobb angle greater than 110.5 degrees and flexibility of 13%, Yamin and colleagues⁴⁰ found a staged procedure to provide a safe and effective treatment with a mean correction rate of 65.2%. These authors recommended that patients with a Cobb angle greater than 80 degrees and flexibility less than 20% should be treated with a staged anterior release and posterior pedicle screw instrumentation with the addition of halo-pelvic traction to correct the deformity.⁴⁰

Evaluation of VATS perioperative and postoperative data reveals an increase in operative time compared with open thoracotomy but a decrease in blood loss, chest tube drainage, and pulmonary morbidity and an increase in patient satisfaction. The time to perform thoracoscopic surgery has ranged from 90 minutes to 4 hours with a decrease in operative time as experience is gained. The total operative time per disc level excised averages 20 to 40 minutes. Studies on the learning curve for VATS have been performed by Newton and colleagues¹² as well as by Son-Hing and colleagues.³³ VATS operative time decreased 26% to 30% and operative time per disc decreased 15% to 24% between the first seven and last seven patients in both series.^12,33 As surgeons gain experience with improved thoracoscopic techniques, instrumentation, and training, the operative time has been shown to be less for VATS compared with an open approach.³³

The reported blood loss and chest tube drainage have been comparable to open procedures with blood loss generally averaging less than 300 mL.^12,33,41,42 In cases of excessive blood loss, conversion to open thoracotomy may be required. The incidence of major complications for either VATS or open thoracotomy is less than 1%.^12,33,43 The most common complications associated with VATS are pulmonary, such as atelectasis, pleural effusions, pneumothorax, and excessive chest tube drainage.^12,33,42,43 Faro and colleagues⁴⁴ compared pulmonary function after an open versus a thoracoscopic anterior procedure and found that pulmonary function recovered more quickly with VATS, and this difference was maintained after 2 years of follow-up. As with all anterior spinal surgery, these risks exist and must be minimized. Although the instrumentation, techniques, and support for VATS continue to improve, this approach is technically demanding, and proper training is essential to the success of this procedure.