A spinal instrumentation and fusion procedure remains the standard surgical means of improving and stabilizing progressive adolescent idiopathic scoliosis. Open anterior and posterior techniques have been utilized successfully. In an effort to minimize the approach-related morbidity of the standard open methods, a minimally invasive, thoracoscopic approach was developed to treat thoracic scoliosis.
Patient Positioning and Intraoperative Planning
The levels of the spine selected for instrumentation and fusion typically include all segments in the thoracic curve. The patient is secured in a direct lateral position over an axillary roll with the convex side of the scoliosis up. The legs are scissored and padded to protect the peroneal nerve at the knee, and the arms are positioned with 90° each of shoulder and elbow flexion with a folded pillow placed between the forearms. Full access to the axilla is required.
After the patient has been properly positioned, the image intensifier is used to plan the position of the skin incisions for Thoracoport placement (Fig. 1). With the coronal image-intensifier view, the angulation of each vertebra is drawn on the patient's back, and extended to the lateral aspect of the chest, with a surgical marker, and the planned levels of instrumentation—typically T5 to T12—are numbered. With a direct lateral image-intensifier view, the midlateral position of the vertebral bodies is marked and three incisions (each 2 cm long) are planned to gain access to the involved vertebrae. A single skin incision is sufficient to access three vertebral bodies cephalad and caudad, except at the apex, where an incision will yield access to two vertebrae in either direction. Thus, three incisions provide access for the common eight-level thoracic fusion. These skin incisions will ultimately be manipulated cephalad and caudad along the chest wall to allow for a path between the ribs that is parallel to the frontal plane orientation of each vertebra included in the instrumentation.
The surgical field is widely prepared and draped so that the surgeon has access to the posterior aspect of the ilium for harvest of autogenous bone graft and is able to convert the procedure to an open thoracotomy if needed. An iliac crest bone graft is harvested in all cases to ensure the greatest chance for a rapid intervertebral fusion. In many cases, the graft is supplemented with approximately 10 cm3 of demineralized bone powder to add bulk and growth factors to the graft material.
Operating Room Setup and Anesthetic Considerations
There are a number of special equipment needs for the safe performance of thoracoscopic procedures. High-quality endoscopes (0°, 30°, and 45° angled optics) and video equipment are essential. The video tower is placed on the posterior side of the patient, where the surgical scrub technician also stands. The surgeon and assistant(s) stand anterior to the patient. An endoscopic suction-irrigation device (with the suction connected to a blood recovery system), an ultrasonic dissector, and electrocautery are positioned at the head of the operating table (Fig. 2). The operating table must be compatible with use of the image intensifier.
The primary considerations with regard to anesthesia are related to the need for selective deflation of the lung on the operatively treated side. This is most often accomplished by use of a bronchoscopically visualized double-lumen endotracheal tube. One lumen is placed into the left mainstem bronchus, and the other is placed into the trachea just above the carina.
Surgical Exposure
In addition to the three planned posterior portals overlying the vertebrae, two additional portals are planned along the anterior axillary line. These anterior ports are used primarily for spinal exposure and disc excision, while the posterior incisions are utilized primarily for placement of instruments.
After ipsilateral lung deflation, anterior portals are established with use of a skin incision and blunt dissection through the intercostal muscles. Thoracic trocars, 11.5 mm in diameter, are placed to maintain the path for instrument passage. Immediately after the endoscope is placed into the chest, lung deflation is confirmed. The caudad posterior portal is established to create three working portals to allow exposure of the spine and disc excision. A fan retractor is often required early in the procedure (Fig. 3), before complete atelectasis of the lung has occurred. Placed through the caudad portal, it is attached to a table-mounted holder. The vertebral levels are confirmed with a radiographic marker, and the pleura overlying the spine is opened longitudinally with the ultrasonic scalpel. The segmental vessels are coagulated with this device prior to division (Fig. 4). The plane of dissection lies between the vertebral column and great vessels (azygos vein and aorta). Blunt dissection along with the use of the ultrasonic scalpel provides a nearly bloodless circumferential exposure of the spine (Fig. 5). The displacement of the great vessels and the esophagus is maintained by packing two or three sponges in this tissue plane.
Discectomy
Thorough removal of disc material is critical to the success of this procedure, both from the standpoint of gaining curve correction and to achieve a solid fusion. The plastic Thoracoports should be adjusted between intercostal levels to provide optimal access and visualization at each level. One portal is parallel to the disc and is used for the discectomy tools (rongeurs and curets). The adjacent portal is used for the 45° endoscope and is positioned such that viewing is also parallel to the disc space (Fig. 6). The anulus is incised with the ultrasonic scalpel, and the discectomy is initiated with a specially designed upbiting pituitary rongeur. Beginning in the concavity, the end plates of the vertebra cephalad and caudad to the disc are identified (Fig. 7). The discectomy is initiated in the concavity as this is the most dependent aspect and any blood will flow away from the remaining disc. The discectomy progresses laterally to the convex rib head and to the depth of the posterior longitudinal ligament (Fig. 8). Cartilage is removed from the end plates, and hemostasis is maintained by packing the disc space with oxidized cellulose polymer. Once all of the required discs have been excised, the caudad one or two levels are grafted with a combination of morsel-ized iliac crest autograft and an allograft fibular strut (Fig. 9). The use of structural graft at the caudad levels prevents excessive kyphosis at the thoracolumbar junction. The fibular allograft is placed directly through the skin and chest wall after the plastic Thoracoport has been removed. The cancellous iliac crest autograft is delivered through a plunger device after being run through a bone mill.
Instrument Placement
Following the discectomy, laterally directed vertebral body screws are placed at each level through the middle and cephalad posterior portals. Proper placement of these portals is critical to facilitate proper orientation of the screws and is therefore reconfirmed with Kirschner wires placed through the chest wall to the spine (and viewed with the image intensifier) before the incisions are made. These incisions are generally just anterior to the lateral border of the scapula. Blunt dissection through the latissimus dorsi and intercostal muscles is performed, and access is maintained with a 15-mm-diameter trocar (Figs. 10-A, 10-B, and 10-C). At this point, direct visualization through this portal is possible to confirm appropriate placement directly lateral to the vertebral body. A screw path is initiated with an awl and tap, with the entry site in the middle of the vertebral body just anterior to the rib head (Figs. 11-A and 11-B). Screw length is determined with a calibrated ball-tip probe, with planning for bicortical purchase with 1 to 3 mm of screw penetration of the far cortex. The 15-mm portal is adjusted to each interspace, allowing screws to be placed at each desired level parallel to the superior and inferior end plates of the vertebra. The screws are generally 6.5 mm in diameter, with a cancellous thread pitch and blunt tips; they are available in 2.5-mm length increments. The image intensifier is used to confirm the appropriate length and position of each screw prior to rod placement.
Rod Placement
The endoscopic connection of a rod remains one of the challenges of this technique and requires specialized instruments for assembly and compression of the components. The most important aspect of rod placement is achieving appropriate insertion and alignment of the screws. Rod length is established with a calibrated malleable template, with anticipation of 1 to 1.5 cm of compression (shortening of the spine). After final cutting of the rod, it is contoured to the desired kyphosis and anticipated residual scoliosis. A hex end on the rod and an endoscopic rod holder allow maintenance of the proper rod orientation as it is placed through the inferior portal and set into the cephalad screw heads (Fig. 12).
The rod is captured in the cephalad screws with locking nuts and secured in the correct rotational orientation. Each interspace is filled with bone graft, and the next screw is sequentially captured, compressed, and locked to the rod. An endoscopic compressor placed through an anterior incision (without the trocar in place) allows interver-tebral compression in a manner very similar to that used in the open approach (Fig. 13). Compression and cantilevering of the rod into position are the two main methods of deformity correction. Insertion of the rod into the more caudad screws often requires the use of a specialized approximating device designed for the limited skin incisions (Fig. 14). Final correction is confirmed radiographically.
Wound Closure
After completion of the instrumentation procedure and removal of the paravertebral packing sponges, wound closure is initiated. An endoscopic suturing device is utilized to perform a running closure (2-0 suture) of the pleura (Fig. 15). The chest is irrigated, and a chest tube is placed prior to closure of the skin incisions.
The patient is instructed to wear a thoracolumbosacral or-thosis when out of bed for three months postoperatively.
INDICATIONS:
This procedure is for patients with a right thoracic adolescent idiopathic scoliosis for which thoracic-only instrumentation is indicated (generally Lenke type-1 curves). Ideal cases are relatively small-magnitude flexible curves requiring instrumentation between T5 and T12 (Figs. 16-A through 16-D). By definition, these patients are also candidates for a posterior surgical procedure. The decision regarding the best approach for each individual patient is a topic of substantial research and debate. An anterior approach has been thought to allow improved restoration of the sagittal alignment. Disc excision results in anterior column shortening, particularly important in the apical region of the curve, which is often locally lordotic. Anterior thoracic correction has also often been achieved with fewer levels of fusion than used in posterior hybrid instrumentation constructs. Although the thoracoscopic approach appears to have advantages over the open anterior approach with regard to postoperative pain and pulmonary function, these advantages are less clear relative to the use of current posterior techniques. As posterior pedicle screw techniques have become more common in patients with adolescent idiopathic scoliosis, the improved correction and construct stability achieved with posterior instrumentation have made the thoracoscopic approach less commonly favored by patients and surgeons. The best indication today seems to be the patient having a major objection to a scar on the back, although saving a caudad level (i.e., not including it in the fusion) may be possible in some thoracic curve patterns.
CONTRAINDICATIONS:
Scoliosis of >70°A side-bending thoracic curve of >35°OsteopeniaInsufficient vertebral size to accommodate the anterior vertebral screwsDouble thoracic scoliosisStructural lumbar scoliosisPrior intrathoracic surgeryAn inability to tolerate single-lung ventilation
Scoliosis of >70°
A side-bending thoracic curve of >35°
Osteopenia
Insufficient vertebral size to accommodate the anterior vertebral screws
Double thoracic scoliosis
Structural lumbar scoliosis
Prior intrathoracic surgery
An inability to tolerate single-lung ventilation
PITFALLS:
The greatest pitfall of the procedure is underestimating the importance of the discectomy and fusion technique. Single-rod anterior instrumentation systems have a greater risk of failing (approximately 5% fail) as a result of delayed union or nonunion at any of the levels of attempted fusion. It is suggested that the surgeon have substantial experience to master this aspect of the procedure (by performing it as a component of a combined anterior release/fusion and posterior instrumentation/fusion procedure) before attempting a fully endoscopic anterior instrumentation and fusion procedure.
Other pitfalls include failure to maintain strict hemostasis, complete lung deflation, and proper positioning of the endoscope, all of which are critical for visualization during the procedure. There are numerous points during the operation where untoward events—an inability to selectively deflate the lung, the occurrence of uncontrolled bleeding, or malpositioned screws preventing capture of the rod—may preclude safe completion of the procedure. The backup plan always includes conversion to an open procedure and/or proceeding with posterior instrumentation.
AUTHOR UPDATE:
Since completing a series of operations with this technique, we have converted nearly completely to the posterior approach for the correction of thoracic adolescent idiopathic scoliosis. This is not because the technique does not result in good or excellent outcomes but because contemporary posterior techniques allow a greater degree of correction with a lower risk of implant failure. Patients with particular concerns about the appearance of the scar associated with a posterior procedure and who are willing to wear a postoperative brace remain those most likely to choose thoracoscopic anterior instrumentation over a modern-day posterior technique.