Combined Anterior and Posterior

Luque described combined approach VCR with a decancellation of the vertebral body, without resection of the disc, for large spinal deformities. ¹⁹ Bradford and Tribus then modified this procedure to include resection of the discs and vertebral bodies through an anterior approach. ²⁰ Spines were instrumented with a posterior approach to achieve large corrections of the coronal and sagittal planes, with a spine shortening procedure. Total surgical times often exceeded 10 hours, and total estimated blood loss exceeded 5,000 mL. As should be expected, complications are common in surgeries of this magnitude. New neurologic deficits may be as high as 20%, with approximately 10% of patients sustaining a permanent neurologic deficit. ²¹ Anterior approaches for VCR carry a risk of pulmonary-associated complications, such as hemothorax, chylothorax, and pneumothorax. Despite the risks of early complications, the long-term results of these surgeries are good with substantial improvements in health-related quality of life (HRQOL) and radiographic parameters.

Posterior Vertebral Column Resection

The first description of a posterior vertebral column resection (pVCR) was given in 1922 when MacLennan reported apical vertebral resection followed by casting for severe scoliosis. ²² Subsequent reports described combined anterior and posterior approaches which, as noted earlier, combined large deformity corrections with long operating times, high blood loss, and frequent complications. Thus, pVCR was introduced as a method to reduce the aforementioned limitations while maintaining the corrective capabilities of apical resection. Suk et al first described the “modern” pVCR, reducing operative times in adult scoliosis cases to 5 hours and blood loss to 4,800 mL, while maintaining excellent corrections in the coronal and sagittal planes. ²³ Neurologic deficit rates were lower than expected, though one must be cautious with retrospective studies as they may underestimate complication rates, particularly new neurologic deficits. ²⁴ There were two cases of permanent paraplegia. This series included congenital and postinfectious spinal deformities, which decreased mean operative times and estimated blood losses. In our experience, AIS is more similar to adult deformities and distinct from congenital scoliosis. As such, extrapolating results and outcomes from congenital resections to AIS is probably inappropriate.

Lenke et al continued to refine techniques of VCR in the pediatric population, with a mean operative time of approximately 9 hours and estimated blood loss of 1,600 mL. ²⁵ Important to note, this cohort did not find a difference in complication rates for anteroposterior VCR versus pVCR nor for staged versus single-stage pVCR. This finding underscores the overall complex nature of these cases and the need for informed consent with parents and patients alike. Intraoperative neurologic monitoring changes were frequent (27%), though there were no permanent neurologic injuries. The cosmetic improvement in these patients was profound, and the authors suggest that Cobb angle comparisons underestimate the benefit to cosmesis. The decrease in estimated blood loss should be noted and may be due to improved surgical technique and experience combined with the use of antifibrinolytics, such as tranexamic acid (TXA). Regardless of 3CO performance, we recommend TXA use in AIS cases with a dosing protocol of 50 mg/kg ideal body weight (IBW) bolus followed by 10 mg/kg/hour infusion until wound closure. ²⁶

Osteotomes/Kerrison

Using a half-inch, straight osteotome the inferior facet is resected to expose the superior facet. The facetectomy is made with a “vertical” cut at the junction of the facet and the lamina, extending approximately 5 mm. A cut through the junction of the pars and the inferior facet completes the facetectomy. The distal portion of the spinous process of the cranial segment is removed with a Leksell rongeur. This exposes the distal lamina and interlaminar space. Next, using the superior facet as a plane for ventral resection, the rongeur removes the distal lamina and ligamentum flavum from the midline. So long as the rongeur does not go ventral to the superior facet, then the dura and spinal cord are “safe.” After removing the ligamentum flavum from the midline, epidural fat will be exposed. A Woodson elevator is used to dissect the plane between the flavum and epidural fat. Using a Kerrison 3, the ligamentum flavum is removed with a small amount of lamina from both the caudal segment and cranial segment. We alternate angling 45 degrees caudal on the caudal lamina and 45 degrees cranial on the cranial lamina while working toward the superior facet and foramen. This technique prevents the creation of a small hole, which requires a forceful insertion of the Kerrison rongeur. Once at the foramen, the superior facet is removed with the Kerrison. One must ensure that the lateral capsule is removed such that the segment is loosened. In cases of a large coronal deformity, the spinal cord may be draped over the medial pedicle along the concavity. In this situation, inserting the Kerrison rongeur into the spinal canal may not be safe. We use a matchstick burr to remove the superior facet down to the ligamentum flavum and capsule. These soft tissues are then bluntly dissected using a Woodson elevator with a dorsally directed force. One should never work toward the spinal cord. These facet resections are performed on both sides, completing the PCO. We pack the foramen with liquefied collagen and a cotton pad (Fig. 15‑1b). Closure of the osteotomy (Fig. 15‑1c) is performed with segmental compression along a concavity in cases of hyperkyphosis. In cases of hypokyphosis, where shortening is to be avoided, our preference is to distract along the concavity, moving from the apex to the cranial and caudal end vertebra. This will provide for coronal plane correction with lengthening of the dorsal column, maximizing correction of thoracic hypokyphosis. Accurate pedicle screw placement is required to minimize screw plowing when compression and distraction are used. One should take care to watch for motion at the bone–screw interface at all portions of the correction to minimize the risk of screw pull-out and loss of fixation.

Harmonic/Ultrasonic Osteotome

Ultrasonic osteotomes are also used to perform posterior-based osteotomies. ²⁷ These coagulate the exposed, bleeding bone upon completion of the osteotomy and may reduce blood loss. To perform a PCO, the inferior facetectomy is performed using the harmonic osteotome and the ligamentum flavum is removed with a Kerrison rongeur. The harmonic osteotome is then used to cut through the superior facet at the level of the cranial aspect of the pedicle. This disconnects the cranial vertebra from the caudal vertebra and completes the osteotomy. The superior facet fragment may be left in place. In our experience, it has not caused symptomatic foraminal stenosis. The correction maneuvers follow as above.

Pedicle Subtraction Osteotomy/Schwab Type 3 and 4

As previously mentioned, PSOs in the treatment of AIS are uncommon and are more likely used in a revision situation. If one is considering a PSO in a primary AIS case, then it is worthwhile to review the work of Lewis et al and know that several PCOs across segments with open disc spaces may provide a similar correction. ⁶ Essential to any 3CO (PSO or VCR) is adequate fixation above and below the level of the resection. Without this, instability may lead to neurologic injury and/or pseudarthrosis. We recommend a minimum of three levels above and below, the exception being L4 PSO, where two sets of pedicle screws and iliac screws are appropriate and adequate.

After placement of implants, we plan the dorsal resection. The goal of the dorsal resection is decompression of the midline neural elements (most frequently the cauda equina) and the creation of a “superforamen” that will allow for safe passage of two nerve roots. As such, all dorsal elements just distal to the pedicle of the cranial segment to the cranial pedicle of the caudal segment must be removed. For example, with an L4 PSO, the distal two-thirds of the L3 lamina and pars interarticularis, the whole dorsal element of L4, and the superior facet and cranial lamina of L5 are removed to be flush with the pedicle. To facilitate this resection, we will score the edges of the resection with a matchstick side-cutting burr. The cuts are completed with osteotomes and the fragments are removed en bloc and reserved for the bone graft. The exiting roots must be traced out of the foramen and confirmed free and without compression. In revision surgeries, with prior laminectomy it is necessary to remove all postlaminectomy membrane and scar from the dura. If it is not removed, then the thickened dura can buckle with osteotomy closure, causing spinal stenosis and possibly a neurologic deficit. We find a no. 15 blade scalpel useful in scar removal. In the event of a dural opening, it is linear and easier to repair than many other possible variations.

After removal of the dorsal elements, the transverse process (in the lumbar spine) is amputated at the junction with the vertebral body. We leave the transverse process fragment, with the underlying psoas attachments, for decortication after closure, to assist with a posterolateral fusion. At the junction of the vertebral body and the transverse process, a Penfield 1 and electrocautery subperiosteally dissect to the front of the spine. Some of this can be done with larger elevators, though it is important to remain subperiosteal to avoid injury to a segmental artery, which can create frustrating bleeding. This dissection proceeds to the front of the spine (approximately 10 o’clock and 2 o’clock). A sponge or metal spoon is then placed in this dissected plane. A temporary rod is placed on the side opposite the initial pedicle resection.

Resection of the pedicle and vertebral body follows, protecting the exiting and traversing roots with Penfield retractors or nerve root retractors. We prefer to use a box-shaped osteotome to remove the pedicle and as much vertebral body as possible. When using the box-shaped osteotome, two cuts are needed. The first cut is positioned to remove the cranial portion of the pedicle and the disc. The second cut connects the two, cutting the caudal pedicle and vertebral body. Using an osteotome ensures that no lip of the pedicle is left behind. If this is not removed, then it may impinge upon the exiting root and cause a neurologic deficit after osteotomy closure. The distal osteotomy cuts should be straight ahead or angled cranially to the superior endplate. Resection of the vertebral body distal to the pedicle will create too large a void for simple closure and may complicate placement of an appropriately sized cage if needed, as the lumbar roots preclude placement of large devices. The resection of the vertebral body proceeds using curettes to remove the cancellous bone, preserving the dorsal vertebral body, the ventral cortical body, and the lateral walls. All of these provide stability to the osteotomy. It is important to reserve the cortical portion of the anterior vertebral body. The integrity of this bone will allow for maximum sagittal plane correction through the osteotomy. Any thinning of this bone will weaken it and allow for some collapse during osteotomy closure, which will reduce the angular correction. After removing the cancellous body, the lateral walls are removed with a Leksell rongeur. A stabilizing rod is placed on this side and the same process is performed on the contralateral side. Once the contralateral lateral wall is removed, only the dorsal vertebral body remains. We replace the stabilizing rod to prepare for the removal of the dorsal wall. A Woodson elevator passes underneath the dural sac to ensure no adhesions are present. We will dissect from the disc above to the disc below to ensure all is free. Next, the Woodson is passed under the dural sac so that the tip is seen on the contralateral side. A posterior wall impactor or a large down-pushing curette passes opposite the Woodson as the Woodson is removed. This ensures that no dura mater is caught by the impactor. The posterior wall impaction proceeds with one person holding the impactor in place with two hands, stabilized on the body. Perfect control of this tool is needed to ensure safety and minimize the risk of a ventral dural opening or neurologic injury. Often, the posterior wall can be removed with two impactions. The fragments are removed from the void and the osteotomy is now ready for closure.

There are multiple techniques for closing a PSO. Our preferred technique is to use an articulating bed, where the anesthesiologist bends the bed into lordosis, closing the osteotomy over the stabilizing rods. The surgeon can watch the thecal sac in the midline and the exiting roots through this action to ensure no neural impingement or tension. Closure with an articulating bed also removes the need for compression on screws, which maintains their purchase and integrity. If an asymmetric closure is needed, one can tighten the set screws a bit more on the side that should remain longer, to put some friction in the construct on that side and limit closure. The set screws should not be tight, as this will cause failure at the pedicle–bone interface.

A second method for closure is known as a “construct to construct” or en bloc closure. This technique distributes screw plowing forces over multiple levels, when compared with simply compressing screws around the osteotomy together. A second benefit is that sagittal plane corrections and positions are established prior to the lordosing osteotomy closure. This is an advantage because there is some risk to reciprocal kyphosis in mobile segments around the level of the osteotomy, which will result in less global change in the sagittal plane and potentially result in undercorrection. The constructs above and below the osteotomy are linked via domino connectors, with a third rod on each side. Compression then ensues through the domino connectors thereby distributing the force over the construct. The set screws in the domino are tightened and remain a part of the final configuration.

After closure, the dura must be inspected for compression. Compression can result from inadequate resection of the cranial or caudal lamina. If a Woodson elevator cannot pass freely underneath the lamina, more is resected. There is inevitably dural buckling after the closure. The dural infolding is inspected to ensure that it is mobile and not fixed in place. When probed with a Woodson elevator, the buckling should “run” up and down the midline in response. If it is fixed, then there is a risk of spinal stenosis from the dural buckling, which can cause a neurologic deficit. Duraplasty with a dural substitute can be required in these situations. This is a particular concern in cases of laminectomy membranes, which stiffen the dura. Finally, the nerve roots should be inspected in the foramen. The foramen should be opened and both exiting nerve roots should be tracked from the dural sac and out the foramen to ensure that no compression or tension exists.

Rib autograft or allograft can be placed over the midline deficiency both to encourage fusion and to protect the dura from compression due to bone graft. ²⁸ The lateral gutters are decorticated and bone graft harvested from the osteotomy to ensure a posterolateral fusion.