Clinical Results and Discussion: Vertebral Column Resection (VCR) for Severe Pediatric and Adult Spinal Deformity

Kathy M. Blanke, RN
Washington University School of Medicine
St. Louis, MO

Scoliosis Research Society Paper 13
42nd Annual Meeting
Edinburgh, Scotland
September 5-8, 2007

Results: Clinical
Of the 43 patients, 38 were treated in a single-stage, while 5 were treated in a two-staged fashion. The interval between stages ranged from five to seven days. The average EBL for all patients was 1007 cc, ranging from 375 to 3100 cc. No patient became coagulopathic intraoperatively, and no patient received platelets or fresh frozen plasma. The average operative time was 9 hours 23 minutes, ranging from 4h 52m to13h 40m for all the procedures.

Discussion
The surgical treatment of severe spinal deformity is challenging. Traditionally, a circumferential approach with anterior releases via discectomies, followed by posterior instrumentation and fusion has been the standard of care. The use of a vertebrectomy procedure has been around for quite some time as well, with the first description in 1922 by MacLennan8 who described a posterior apical resection followed by postoperative casting for the treatment of severe scoliosis. Following that, several authors recorded their experiences with vertebrectomies, most commonly for the surgical treatment of congenital scoliosis.(9-17) Then in the modern era of spinal deformity surgery, Bradford (1) was the first to describe the use of a circumferential vertebrectomy on patients with severe structural spinal deformities. His report consisted of 13 patients who underwent a 1 to 7 level (average 3 levels) vertebrectomy. Scoliosis patients had a preoperative curve averaging 117°, correcting to an average 55°. Kyphosis patients had a preoperative curve averaging 112°, correcting to an average 56°. The average estimated blood loss was 5800 cc, and the average operative time was 10.5 hours for these combined procedures. Bradford and Tribus (18) later reported on 24 patients with rigid coronal decompensation who underwent a circumferential vertebral column resection (VCR). The average preoperative scoliosis was 103° corrected by 52%. Importantly, coronal and sagittal imbalances were corrected to an average of 82% and 87% respectively. However, there was an average operative time of over 12 hours, an average blood loss of 5500 mL, and 31 overall complications.

Suk was the first investigator to promote a posterior-only VCR. He believed that there was a reduction in the total operating time, amount of blood loss through this one-stage posterior-only procedure. In 2005, he presented a series of 16 patients (average age 29 years) who underwent a posterior VCR having a minimum 2-year follow-up.(5) His indication for this procedure was scoliosis of more than 80° with flexibility less than 25%. There was an average of 1.3 vertebrae removed, 15 in the thoracic spine and 6 in the lumbar spine. The mean preoperative scoliosis of 109° was corrected to 46° (59% correction). However, complications were encountered in four patients, including one with complete permanent paralysis. He recommended this as an effective alternative for severe rigid scoliosis but cautioned that it was a highly technical procedure and should only be performed by an experienced surgical team. It is important to note, he did not utilize any form of motor tract monitoring during the surgeries, only SSEP monitoring.

Our current series of 43 consecutive patients undergoing posterior-only VCR for severe pediatric and adult spinal deformity is both complimentary and additive to these prior reports. This is the largest reported series on posterior VCRs thus far, and the first from a North American center. In addition, the indications for the procedure were divided into four main groups: severe scoliosis, global kyphosis, angular kyphosis, and kyphoscoliosis. These patients were either in good balance or out of balance prior to their posterior vertebrectomy procedure. These patients would all have undergone a circumferential anterior and posterior procedure versus a circumferential vertebrectomy instead of their posterior VCR. The severe scoliosis cases had a correction rate of 69%, 54% for the global kyphosis cases, 63% for the angular kyphosis cases, and 55% for the combined kyphoscoliosis cases, which is as good as or better than other correction rates reported in the literature by either circumferential or posterior-only vertebrectomy.

Importantly, there were no spinal cord related neurologic deficits in any of these patients in this series, where 40 of the procedures were performed at L1 or cephalad. We attribute this to several factors including the routine use of NMEP monitoring in those patients who had available spinal cord monitoring potentials (n=40 out of 43). In this regard, seven patients lost NMEP data some time during the surgical procedure, most commonly during the actual spinal shortening and correction. The most common reason for lost NMEP data was spinal subluxation which can occur before, during, or even after the corrective procedure. The spine is rendered extremely unstable during this posterior reconstruction, and thus it is imperative to regain primary stability with a dural sac that is free from compression and not excessively shortened ventrally (during kyphotic reconstructions). In three patients (2 with and 1 without available spinal cord monitoring), over-shortening of the ventral spinal cord led to loss of data in one and a failed wake-up test in the other. Restoring appropriate anterior height via a larger anterior cage restored the NMEP data in two, and neurologic function in the other. We also feel strongly about the importance of maintaining normotensive anesthesia during correction and closure of these deformities. We prefer to have the mean arterial pressure (MAP) at least 75 to 80 mm Hg during this time. Occasionally, this will require the adjunctive use of Dopamine as a low-dose inotrope. Often blood products will be given even if the hematocrit seems adequate, as there is a fair amount of hemo concentration that occurs over the course of these procedures depending on the amount of fluids provided by anesthesia. As one might anticipate, the occurrence of NMEP data loss was in patients with a primary or secondary kyphotic malalignment to the spine, with the highest risk being the angular kyphosis group. We recommend strict and vigilant care in these patients which are at a much higher risk of a neurologic deficit during these procedures as they would be in any type of treatment for their deformity.

There are multiple principles that we have gleaned over the past five years of performing these challenging procedures. First, there appears to be no reason to approach these patients circumferentially. In more severe scoliosis, kyphosis, and kyphoscoliosis deformities, the vertebral body is located posteriorly. In addition, as Suk (3,4,5) has suggested, the main advantage of a posterior-based VCR is simultaneous control of the spinal column and access to the neural elements circumferentially to closely follow the both during correction of the deformity. Thus, there is excellent access to the dural tube circumferentially to confirm absence of any type of impingement due to either subluxation or retained bony/disc material during the corrective procedure. This certainly makes the procedure safer from a neurologic prospective.

From a technical perspective, there are several factors that are extremely important including the use of a wide laminectomy from the outset. We prefer now to perform a laminectomy from the inferior pedicles of the level above the resection, distal to the superior pedicles of the level below the resection. There is always a residual laminectomy defect following closure to allow for egression of the dural sac posteriorly in order to avoid dorsal impingement, and allow access to assess the ventral aspect of the dural sac. Another important factor is that it is absolutely imperative to have stable pedicle screw fixation above and below the resected area to maintain spinal alignment, avoid and/or treat subluxation, and provide for adequate correction and final construct stability. (7,19)

Because of the severe instability produced by this approach, it is imperative to have a temporary rod or rods placed to prevent subluxation prior to going ventral into the anterior column and even sometimes before that. The liberal use of multiaxial reduction screws (MARS) is also very helpful in very strategic instrumentation positions including the concave apex of severe scoliosis, the cephalad or caudal aspect of a kyphotic reconstruction, and immediately caudal to the resected area. Because the lower spine and hips are usually in extension on the operating room table, it is most common that the distal spinal column will tend to migrate ventrally following the resection and during the closure of the vertebrectomy site, which tends to put ventral pressure on the more proximal limb of the neural elements. This can be remedied by using MARS just caudal to the resection area to translate the distal fragments posteriorly to reduce this subluxation.

For the vertebral resection procedure, the use of a high-speed diamond-tipped burr such as the Midas Rex AM8 (Medtronic, Fort Worth, TX), is extremely beneficial. The apical concave pedicles of a scoliosis or kyphoscoliosis, and the ventral vertebral body bone of long-standing angular kyphosis cases are extremely cortical in nature. This bone is very difficult to resect with curettes or rongeurs, and "painting" the bone away with a high-speed burr while protecting the neural elements/dural sleeve with Penfield-type retractors, has proven extremely helpful. In addition, the use of an anterior structural cage is also essential for avoiding ventral spinal cord buckling or excessive shortening which occurs during closure especially in a kyphotic malalignment. This also allows procurement of an anterior arthrodesis from the endplates above and below following the discectomies both above and below the resected area. To cover the laminectomy site and also help procure a posterior arthrodesis, any ribs that are excised during thoracic-level vertebrectomies are bivalved longitudinally and placed cancellous surface ventral over the remaining laminar segments above and below as a "bridge" graft.

Lastly, as evidenced by prior reports, these surgeries have a very high neurologic risk. This is in part due to the severe nature of the deformity, and in part due to the instability created in order to correct these deformities with segmental instrumentation.20 Thus, it is imperative to use intraoperative spinal cord monitoring with some form of motor tract monitoring to provide early detection of data loss, which allows for immediate correction of the causation. In our series, of the 40 cases that had monitoring out of which seven lost data, we were fortunate to have the NMEP data return quickly with the aid of prompt and precise surgical techniques. While difficult to prove, it is certainly realistic that our neurologic complication rate would have been much higher without the early detection that is obtainable with the use of multimodality spinal cord monitoring.

In conclusion, a posterior-based VCR is a safe but challenging technique to treat severe primary or revision pediatric and adult spinal deformity. In this consecutive series of 43 patients, there have been no spinal cord-related, wound, instrumentation and fusion complications thus far. Intraoperative spinal cord monitoring, especially some form of motor tract monitoring, is mandatory to prevent spinal cord-related neurologic complications. This posterior-only approach also allows for dramatic radiographic and clinical correction of these severely deformed patients.