Minimally Invasive Treatment of Thoracic and Thoracolumbar Idiopathic Scoliosis

28 Minimally Invasive Treatment of Thoracic and Thoracolumbar Idiopathic Scoliosis

Peter F. Picetti, Alexander R. Vaccaro, Zachary D. Patterson, David L. Downs, and George D. Picetti III

Abstract

This chapter will describe a new minimally invasive approach for treating single overhang thoracic and thoracolumbar curves. The authors describe the evolution of this new technique through a detailed description of preoperative planning, the actual surgical procedure, and the postoperative care. Case reports and the initial series are included, which demonstrate improved results and decreased complications as the technique has evolved.

Keywords: thoracoscopic minimally invasive scoliosis, one-lung ventilation

28.1 Introduction

Minimally invasive techniques have permitted access to the anterior spinal column without a thoracotomy and its associated potential risk. Surgical approaches may change, but the technical procedure and operative goals remain the same.

Thoracoscopic treatment of lung diseases has been used since Jacobaeus’ work in the early 1900s.¹ In the early 1990s, Regan et al² presented their work on thoracoscopic treatment of spinal disease in Dublin, Ireland. Rosenthal et al³ were the first in print with their technique of thoracic discectomy in 1994. Pollock et al⁴ evaluated the efficacy of thoracoscopic release and posterior fusion versus open release and posterior fusion, and found no statistical difference in correction of Cobb angle. Other studies followed with expanded indications for thoracoscopic surgery in deformity.⁵

Development of endoscopic treatments for spinal disorders began in 1993.²^,³ Initial efforts focused on techniques for release and fusion for kyphosis and scoliosis, followed by an endoscopic technique for hemiepiphysiodesis and hemivertebrectomy for congenital scoliosis.

After having performed more than 150 endoscopic procedures for release and fusion for spinal deformities in the mid-1990s, we set out to develop an endoscopic technique for the instrumentation, correction, and fusion of primary thoracic scoliosis. We performed our first entirely endoscopic instrumentation, correction, and fusion for thoracic scoliosis in October 1996. The goal of this technology in the surgical treatment of idiopathic scoliosis is to perform a safe, reproducible, and effective procedure that results in spinal alignment improvement and balance in all planes and axial derotation comparable to, or better than, that obtained with an open procedure.

Over time, the surgical technique and times have progressively improved with curve correction outcomes similar to open methods, but with the benefits of less soft-tissue disruption and less time to functional recuperation. Once this was accomplished, our next goal was to develop a minimally invasive approach for the treatment of thoracolumbar scoliosis. Challenges to this technique include endoscopically crossing the diaphragm, maintaining retroperitoneal exposure, and attaining and maintaining lumbar lordosis with the use of structural grafting.

28.2 Indications and Preoperative Planning

The endoscopic technique is indicated for single-overhang primary thoracic scoliosis, Lenke type 1A or 1B curve pattern for the direct thoracoscopic technique, and Lenke type 5C curve pattern for the minimally invasive combined approach. These curve patterns can be safely addressed as an isolated fusion without the risk of spinal imbalance.⁶ However, if the patient is kyphotic with this curve pattern, then this technique should not be performed. Because the anterior growth plates are removed with the discectomy and fusion, no further growth can take place. In contrast, the posterior elements continue to grow and an exaggerated kyphosis will result. The technique is contraindicated for double major curves. Finally, this procedure should not be attempted in patients who are not able to tolerate single-lung ventilation.

Patients are selected on the basis of progressive scoliosis and curve type. All curves should be Lenke type 1A, 1B, or 5C.⁶ Patients are evaluated for pelvic obliquity, waist crease, shoulder height difference, degree of rotation, flexibility, and sagittal balance. Complete histories are obtained and all patients undergo physical examination; in addition, 36-inch posteroanterior, lateral, and lateral bending radiographs are obtained. Cobb angles are marked in the standard fashion.

28.3 Surgical Technique

Patient positioning and port placement and anesthesia are the same for both procedures. Early on, we struggled with selecting the optimal location for port placement. In planning for a long fusion, accurate port placement is critical. If placed inappropriately, the port sites are levered against the ribs, and a significant amount of pressure and trauma may be inflicted on the intercostal neurovascular bundle. Patients may complain of postoperative dysesthesia over the anterior chest wall, which can last from weeks to 6 months. Early in the series, port placement was determined by visually compensating for the angle of rotation, which results in suboptimal locations. With the use of Carm fluoroscopy, ports can be placed with great accuracy. As our port placement improved, we no longer saw cases of chest wall numbness and wound issues.

General anesthesia is administered by means of double-lumen intubation in children weighing more than 45 kg. Children weighing less than 45 kg often require selective intubation of the ventilated lung.

The patient is then placed in the direct lateral decubitus position, with the arms forward and elevated at 90 degrees and the elbows flexed at 90 degrees. Hips and shoulders are taped to the operating table, which helps maintain the patient’s correct position throughout the procedure.

The C-arm is then used to mark the levels, port sites, and the mini-open site below the diaphragm for the thoracolumbar approach. Port site placement is key for the procedures. The ports are placed to enable the surgeon to reach the superior and inferior levels of the spine to be instrumented. The C-arm is used to identify the levels as well as to assist in positioning in the anteroposterior plane, correcting for spinal rotation ( Fig. 28.1).

Thoracic surgery assistance is required initially. Two endoscopic monitors are used: one monitor faces the patient and the other monitor is placed posterior to the patient and spine surgeon to allow visualization for the thoracic surgeon. The spine surgeon is positioned at the patient’s back. This positioning allows all instruments to be directed away from the spinal cord. Standing behind the patient also orients the surgeon in the same direction as the endoscopic view, thereby avoiding the necessity to navigate the external landmarks of the ribs and spine to a mirror image on the screen.

Patient positioning is checked to confirm a direct lateral decubitus position, with the concave side of the curve down. The orientation provides a reference to gauge the anteroposterior and lateral direction of guide wires and screws.

After lung deflation, the initial port is usually placed in the sixth or seventh interspace in line with the spine for the thoracic curves and positioned according to the amount of spinal rotation. The superior-most portal is selected first for the thoracolumbar curves. Preoperatively, the initial skin incision mark is placed with the aid of the C-arm. Inserting the first port at this level will avoid injury to the diaphragm, which is normally more caudal. Once the port is placed, digital inspection of the port is made to ensure that the lung is deflated and no adhesions exist.

The endoscope is then inserted into the chest, and additional ports are placed under direct visualization. Port incisions are usually made directly over the ribs, two interspaces apart. This allows port placement above and below the rib at each level, enabling a surgeon to reach two levels through a single skin incision. Three or four incisions are used for the thoracic curves and three for the thoracolumbar, depending on the number of levels to be instrumented. The ports are 10.5 to 11.0 mm in size.

28.3.1 Exposure and Discectomy

The pleura is incised longitudinally along the entire length of the spine to be instrumented. The pleura is dissected off the spine (vertebral bodies and discs) from the anterior longitudinal ligament anteriorly to the rib heads posteriorly ( Fig. 28.2). Next, the electrocautery is used to incise the disc annulus. The disc is removed in standard fashion using various endoscopic instruments. Once the disc is completely removed, the anterior longitudinal ligament is thinned from within the disc with a pituitary rongeur. The ligament is thinned to a flexible remnant that is no longer structural but is still able to contain the bone grafts. The disc and annulus are removed posteriorly to the rib head. Once the disc is evacuated and the end plate is completely removed, the disc space is inspected directly with the endoscope ( Fig. 28.3). The end plates are then rasped to a homogeneous bleeding surface, and the disc space is packed with Surgicel to control end-plate bleeding. All of the thoracic discs are removed in this fashion.

For the thoracolumbar curves, the T12–L1 disc can be removed from the thoracic cavity depending on where the diaphragm inserts. If the diaphragm inserts below the T12–L1 disc space, the exposure of the disc does not require taking down the diaphragm. Conversely, if the diaphragm inserts above the disc space, then the disc is removed from the retroperitoneal approach below the diaphragm. The lumbar retroperitoneal approach is next performed for the thoracolumbar curves. This is accomplished via an 11th rib approach. In cases where the instrumentation is planned to extend down to L2, the skin is marked over the L1–L2 disc space. This allows for surgical access from the T12–L1 disc space to the L2 vertebral body. If the instrumentation is planned to extend down to L3, the skin is marked over the center of the L2 vertebral body. This allows for surgical access from the L1 disc vertebral body to the L2 vertebral body. If the instrumentation is to extend only to L1, a retroperitoneal approach may be performed to access the T12–L1 disc space and the L1 vertebral body. The surgical approach to L1 is usually initially attempted through the thoracic cavity. This, however, can lead to extensive retraction of the diaphragm.

Fig. 28.1 (a) The C-arm is placed in the posteroanterior plane at the distal level to be instrumented with a rod as a marker. A skin marker is used to mark the levels to be instrumented. (b) Posteroanterior C-arm image of the rod marker parallel to the end plates of the distal level. (c) The C-arm in position in the lateral plane using the rod marker to determine the port location.

Fig. 28.2 Intraoperative view through the endoscope showing the hooked Bovie incising the pleura cephalad to caudad along the axis of the spine over the middle of the vertebral bodies.

Fig. 28.3 Intraoperative view through the endoscope of a completed discectomy; the opposite side annulus is visible, and the complete cartilaginous end plate removal of both vertebral bodies is seen.

Fig. 28.4 (a) The 3-cm incision is made over the 11th rib. (b) The rib is subperiosteally dissected. (c) The rib has been amputated anteriorly and is ready for removal with the endoscopic rib cutter.

In performing the retroperitoneal approach, a 3-cm incision is performed over the previously determined skin incision site to expose the 11th rib. The 11th rib is exposed by mobilizing the incision as far anteriorly and posteriorly as possible. Once the rib has been subperiosteally dissected, it is removed with the endoscopic rib cutter. This is accomplished by freeing the rib anteriorly from the soft tissue and placing the jaw of the rib cutter under the rib and the foot over the top and sliding the rib cutter as posteriorly as possible. Once this is done, the rib is amputated. Using this technique, almost the entire rib can be harvested for bone graft ( Fig. 28.4).

Dissection is then carried under the T12 rib, through the oblique muscles into the retroperitoneal space and onto the psoas, spine, and diaphragm. Spinal retractors are placed. A plane is developed between the line of the crus of the diaphragm and the psoas. The psoas is retracted posteriorly, and the discs and end plates are exposed and removed in the standard fashion. Once all the discs have been removed, more graft may be harvested via the thoracic portals.

28.3.2 Graft Harvest

Ports are removed after completion of the discectomies. Next, the rib graft is harvested. Handheld retractors are used to expose each rib to be harvested. The port site is retracted anteriorly as far as possible, and the rib is dissected subperiosteally. Dissection is carried posteriorly as far as the port site can be retracted.

Using the endoscopic rib cutter, two incisions 8 to 10 cm apart are made on the superior aspect of the rib. These incisions are perpendicular to the rib and extend only halfway across the rib. An osteotome is used to cut through the rib along the longitudinal axis until the perpendicular incisions are connected. The rib section is removed and morselized. Other rib sections are removed until sufficient bone graft has been harvested. This technique produces adequate amounts of graft and preserves the lower half of each rib, thus protecting the intercostal nerve and decreasing postoperative pain. The graft harvest is performed at this time to limit the stress placed on the remaining rib.

For the thoracolumbar curves, the disc spaces of the lower thoracic and lumbar are sized for structural graft application. Femoral rings are cut and contoured into a tapered shape to produce the desired lordosis, kyphosis, or neutral alignment at each level. The contoured grafts are packed with the morselized rib graft and impacted into the respective disc spaces ( Fig. 28.5).

The degree of lumbar graft angulation or taper is decreased as they are placed at more proximal levels. At times, the lower thoracic vertebrae are of a size that accommodates a smaller structural graft such as a humeral ring rather than a femoral ring. An alternative to allograft is metal or synthetic cages. These also provide anterior column support and can be used to produce the desired degree of lordosis or kyphosis.

28.3.3 Screw Placement

The segmental vessels, which have not been disturbed until now, are grasped at midvertebral body level and cauterized with the electrocautery.

The Kirschner wire (K-wire) guide is placed onto the vertebral body just anterior to the rib head. The position is then checked with the C-arm to be sure the wire will be parallel to the end plates and in the center of the body. Next, the inclination of the guide is checked in the lateral plane by examining the chest wall and rotation ( Fig. 28.6a, b). The guide should be in a slightly posterior to anterior inclination; this will direct the K-wire away from the spinal canal. If any concern arises as to the K-wire placement in the lateral plane, a lateral image with the C-arm can be obtained to confirm the location. Once the guide is correctly aligned, the K-wire is inserted into the appropriate cannula and drilled into the vertebral body parallel to the end plates to the opposite cortex. Care must be taken when placing screws transcortically to avoid segmental vessel injury on the opposite side. The position is confirmed with C-arm fluoroscopy as the wire is being inserted.

The length of the K-wire in the vertebral body can be determined by a scale on the upper section of the K-wire at the top of the guide. The guide is removed, and the staple awl guide is placed over the K-wire. The awl is used to make a starting point in the vertebral body and the staple is tapped and placed over the K-wire. The K-wire is grasped and held to prevent migration. The staple awl guide is removed and the tap is placed over the K-wire and the near cortex of the vertebral body is tapped as the K-wire is held in place.

The appropriate-sized screw is placed over the K-wire and advanced. The wire is again grasped to keep it from advancing while the screw is being inserted. The wire is removed when the screw is approximately three-fourths of the way across the vertebral body. The screw direction can be checked with the Carm as it is advanced and seated against the vertebral body ( Fig. 28.7a–c). The screw should penetrate the opposite cortex for bicortical purchase. Using the rib heads as a reference for subsequent screw placement helps ensure that the screws are in line and yield proper spinal rotation. If each screw is placed in the same position and orientation on each vertebral body, also accounting for rotation, the screws will align in a V pattern and will aid in derotation of the spine during rod placement. If a screw is inserted more than a few millimeters deeper than the rest of the screws, reduction of the rod into the screw head may be difficult.

Once all the screws have been placed, the Surgicel is removed and the graft is inserted in those discs that do not already contain a structural graft. This is the most important part of the operation. A small amount of graft is inserted into the disc space, and the rasp is then used to push the graft all the way to the opposite side. The disc is completely “backfilled” in this fashion. The periosteum is elevated on the edges of the vertebral bodies, and a mound of graft is placed over the disc space and the edges of the vertebral bodies ( Fig. 28.8).