Surgical Technique: 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

Surgical Technique
The surgical technique involved in a posterior vertebral column resection (VCR) is quite demanding and requires the operating team to be well versed in spinal deformity surgical techniques. The first important component to a successful operation is appropriate patient positioning on the operating frame. We utilize the OSI "Jackson" operative frame, either the open frame with adjustable pads, or for very small patients, the closed frame utilizing chest rolls. All patients receiving preoperative halo-gravity traction (n=27) are positioned with their halo in a lessened amount of traction weight. There were no patients who had counter-traction performed with femoral traction pins so as to avoid over-distraction of the spinal cord since this is a spinal column shortening procedure. Optimal positioning is important during these lengthy procedures in order to avoid excessive pressure points in the axilla and to maintain stability of the trunk. The use of spinal cord monitoring, including some form of motor tract monitoring is strongly recommended.

A thorough subperiosteal dissection of the exposed posterior vertebral column is required. In revision patients, a preoperative 3D CT scan is helpful to understand posterior vertebral column pathoanatomy prior to surgery, and also to confirm expected pathoanatomy intraoperatively as portrayed by the CT scan. Because of the length of these surgeries and the potential for significant bleeding, it is imperative to minimize epidural and osseous blood loss during these surgeries. This is performed not only with careful subperiosteal stripping of the posterior vertebral elements, but also with the use of adjunctive antifibrinolytics such as Aprotinin (Trasylol) or with Tranexamic Acid. Aprotinin was utilized in all pediatric patients (n=31) during their procedure. While the use in adults was initially performed, it is no longer administered due to the risk of renal failure as recently documented in cardiac literature.(6)

Following exposure, posterior column ligament and facet releases/osteotomies (Ponte type osteotomies in previously unfused spines and Smith-Petersen osteotomies in previously fused regions) may be performed. These often are performed at the apex of scoliosis or kyphoscoliosis deformities to also aid in apical pedicle screw fixation. Secure pedicle screw fixation is then obtained for the appropriate levels which are to be included in the definitive instrumentation and fusion. The use of multiaxial reduction screws (MARS) is quite helpful at strategic positions: 1) the apical concave regions of severe scoliosis, 2) the proximal and/or distal regions of severe kyphosis or kyphoscoliosis, 3) the concave lumbar region of any type of deformity in the lumbar spine. Pedicle fixation will provide stability to the spinal column above and below the resection area which is imperative in preventing and/or treating spinal subluxation which is a real risk with these procedures. All pedicle screws in this series were placed using the free hand technique espoused by Kim and Lenke, et al (7) using anatomic landmarks and a special blunt, curved gearshift. The pedicles were palpated to confirm intraosseous borders, under-tapped by 1 mm, repalpated again to confirm intraosseous borders, and then screws were placed.

In the thoracic spine, 5 to 6 cm of the medial rib associated with the level to be resected is removed. Subperiosteal dissection of the medial aspect of the rib is performed. It is cut approximately 5 to 6 cm lateral to the vertebral attachment and then as much of the rib as possible is removed down to the head anteriorly and is kept intact for later placement on top of the laminectomy defect. This is performed prior to the laminectomy to avoid canal intrusion. In primary procedures, super-periosteal dissection around the lateral aspect of the pedicles and vertebral body is performed using Penfield elevators. The soft tissues and the anterior vasculature are held from harms way with either mailable retractors or special lateral wall vertebral body elevators (PSO tool set®, Medtronic Spinal and Biologics, Memphis, TN). In revision cases, a subperiosteal dissection will be required due to previous scarring, with a similar approach to gain access circumferentially around the vertebra(e) to be resected. In both circumstances, the segmental vessels are kept lateral in a soft tissue cuff and should not be violated.

Next, a wide laminectomy is performed centrally over the apical level(s) which are to be resected. Typically, the entire lamina of the level to be resected, the lamina cephalad to the pedicles above, and caudad to the pedicles below, is removed. Normally, for a one-level resection procedure, a posterior column laminectomy will result in a 5 to 6 centimeter exposure of the dura and neural elements. It is important not to minimize the posterior column exposure to gain thorough access to the spinal cord and/or cauda equina circumferential to aid in the resection procedure and also for visualizing any dural impingement during the correction.

Next, the pedicles to be resected are encircled, and removal of the vertebral body is started. Prior to removing the anterior body, a temporary, stabilizing rod should be placed and attached to at least two or three pedicle screws both above and below the resection area. Classically, a unilateral rod is used, however, in severe angular kyphotic or kyphoscoliotic deformities, bilateral rods are recommended to prevent spinal subluxation. The vertebral body resection begins by gaining access to the cancellous bone of the vertebral body through a lateral pedicle-body entrance. Next, curetting of the cancellous bone of the body is performed saving the bone for later bone graft. We have noted that bleeding occurring with a vertebral corpectomy is significantly less in the thoracic spine then when performing similar procedures in the lumbar spine. For a scoliosis or kyphoscoliosis deformity, resecting the apical concave pedicle can be quite challenging since it is very cortical, and in a pure scoliosis deformity, the entire spinal cord/dural sac is resting on the medial concave pedicle which does not have any ventral vertebral body associated with it since the body is swung lateral and dorsal in its rotated position on the convexity. In this regard, using a small, high-speed burr (we prefer the Midas Rex® AM8 [Medtronic, Fort Worth, TX]) is helpful to carefully burr away the cortical bone along this concave region. Thus, in scoliosis and kyphoscoliosis deformities, the majority of the vertebral body will be removed from the convexity of the deformity since that is where the vertebral body is located. We prefer to perform the concave resection of the pedicle prior to the convex removal so there is no bleeding into this dependent concave region. This also allows the concave spinal cord to drift somewhat more medial and remove tension prior to going to the convexity for completion of the corpectomy. The entire body is removed except for the anterior shell, as we like to keep a thin rim of bone intact on the anterior longitudinal ligament (ALL) for fusion purposes. However, if this bone is cortical then it must be thinned to allow easy closure of the resection area.

Next, discectomies both above and below are performed using curettes as needed. It is important not to violate the endplates of the superior and inferoadjacent regions as placement of a structural intracorporeal cage may be required. The last part of the vertebral resection will be the posterior vertebral body wall or floor of the spinal canal. Here it will be essential to control epidural bleeding with the judicious use of bipolar cauterization, topical hemostatic agents such as FloSeal® (Baxter U.S., Deerfield, IL), Gelfoam® (Pharmacia, Kalamazoo, MI), and cottonoids. The dural sac must be circumferentially freed and exposed and then separated from the epidural venous complex as well as the posterior longitudinal ligament (PLL). This posterior vertebral wall must be removed in its entirety with reverse-angled curettes, Woodson elevators, or a specialized posterior wall impactor (PSO tool set®, Medtronic Spinal and Biologics, Memphis, TN) which are utilized to impale the posterior wall into the ventral defect that has been created. It is imperative that the ventral spinal cord is completely free of any bony prominences to avoid impingement during closure. This is especially true at the disc levels, especially above but also below, as there tends to be osteophytic lipping in that region which can cause ventral compression if not removed.

At this point, the resection is complete and closure of the resected area with compression forces is performed. The spinal column is always shortened, not lengthened, with convex compression performed as the main correcting technique. This is performed either with individual pedicle screws in primary cases where a good bony grip of the vertebrae is found, or in a construct-to-construct closure mechanism utilizing dominoes at the apex of the resected area. In this method, closing from a construct rod above to a construct rod below to distribute the forces of correction over several levels is performed. It is imperative to compress slowly as subluxation and/or dural impingement can occur along the way. In any deformity that has a degree of kyphosis (GK, AK, and K+S), we place an anteriorly based structural cage to prevent over-shortening of the deformity, and it also acts as a hinge to provide further kyphosis correction. Typically, the spinal column will be shortened by 1 to 1.5 cm, an appropriate height and length cage will be inserted, and then further closure onto the cage to make it snug and fixed will be performed as a final correction maneuver. Once closure has been fully performed, a permanent contralateral rod is placed with appropriate correction maneuvers performed. Then the temporary closing rod is removed and a permanent, final rod is placed on the contralateral side as well. Appropriate compression and distraction forces, in situ contouring, and other correction techniques may be performed always being mindful of any resultant affect on the resected area with respect to subluxation or dural impingement. Next, adequate alignment is confirmed by intraoperative radiographs. Decortication and bone grafting follow with copious amounts of local graft obtained from the resection procedure. The laminectomy defect is covered with the previously harvested ribs for the costotransversectomy approach. These ribs are split in half longitudinally with the cancellous surface placed along the entire laminectomy defect from the lamina above to the lamina below. This creates a rib "bridge" of bone to protect the dura as well as to provide a posterior onlay fusion. The rib is held in place with sutures or a crosslink if there is room and no prominence. To confirm the absence of impingement, final implant security is documented as well as a final circumferential check of the exposed dura. The vast majority of these procedures (n=38) were performed in a single stage with the remaining (n=5) treated with a 2-staged procedure.