Simultaneous Anterior-Posterior Approach Through a Costotransversectomy for the Treatment of Congenital Kyphosis and Acquired Kyphoscoliotic Deformities

Smith, John T. MD; Gollogly, Sohrab MD; Dunn, Harold K. MD

Journal of Bone & Joint Surgery - American Volume:
doi: 10.2106/JBJS.D.01795
Scientific Articles
Abstract

Background: Congenital kyphosis and acquired kyphoscoliotic deformities are uncommon but are potentially serious because of the risk of progressive deformity and possible paraplegia with growth. Our current approach for the treatment of these deformities is to use a single posterior incision and costotransversectomy to provide access for simultaneous anterior and posterior resection of a hemivertebra or spinal osteotomy, followed by anterior and/or posterior instrumentation and arthrodesis. To our knowledge, this approach has not been reported previously.

Methods: The medical records and radiographs for sixteen patients who had been managed at our institution for the treatment of congenital kyphosis and acquired kyphoscoliosis between 1988 and 2002 were analyzed. The mean age at the time of surgery was twelve years. The diagnosis was congenital kyphosis for fourteen patients and acquired kyphoscoliotic deformities following failed previous surgery for two. The mean preoperative kyphotic deformity was 65° (range, 25° to 160°), and the mean scoliotic deformity was 47° (range, 7° to 160°). Fifteen patients were managed with vertebral resection or osteotomy through a single posterior approach and costotransversectomy, anterior and posterior arthrodesis, and posterior segmental spinal instrumentation. The other patient was too small for spinal instrumentation at the time of vertebral resection. A simplified outcome score was created to evaluate the results.

Results: The mean duration of follow-up was 60.1 months. The mean correction of the major kyphotic deformity was 31° (range, 0° to 82°), and the mean correction of the major scoliotic deformity was 25° (range, 0° to 68°). Complications occurred in four patients; the complications included failure of posterior fixation requiring revision (one patient), lower extremity dysesthesias (one patient), and late progressive pelvic obliquity caudad to the fusion (two patients). The outcome, which was determined with use of a simplified outcomes score on the basis of patient satisfaction, was rated as satisfactory for thirteen patients, fair for two patients, and poor for one patient.

Conclusions: A simultaneous anterior and posterior approach through a costotransversectomy is a challenging but safe, versatile, and effective approach for the treatment of complex kyphotic deformities of the thoracic spine, and it minimizes the risk of neurologic injury.

Level of Evidence: Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.

Author Information

1 Department of Pediatric Orthopedics, Primary Children's Medical Center, 100 North Medical Drive, Suite 4550, Salt Lake City, UT 84113. E-mail address for J.T. Smith: john.smith@hsc.utah.edu. E-mail address for S. Gollogly: sgollogly@hotmail.com

2 Department of Orthopedics, University of Utah Medical Center, 30 North 1900 East, Room 3B165, Salt Lake City, UT 84132-2302. E-mail address: harold.dunn@hsc.utah.edu

Article Outline

Congenital kyphosis and kyphoscoliosis are uncommon deformities that result from abnormal embryonic development of the spine; specifically, these deformities are the result of segmentation anomalies that affect the longitudinal growth of the spine in the sagittal and coronal planes. The natural history of congenital kyphosis has been well documented1-3 and the deformity has been classified into three types according to the system originally proposed by McMaster and Singh1. Type-I kyphosis, the most common form, results from a partial failure of formation of the anterior part of the vertebral body. This form has the greatest risk of progression with growth and is associated with a 25% risk of anterior cord compression if left untreated1,4. Type-II kyphosis results from an anterior failure of segmentation. The degree of progression is related to the length of the anterior segmentation defect, and this form of kyphosis is associated with a much lower risk of neurologic compromise. Type-III kyphosis is the result of a combination of these anomalies.

Acquired kyphosis at the thoracolumbar junction can develop following extensive laminectomies performed for the treatment of tethered spinal cord syndrome or spinal cord tumors, resulting in neurological dysfunction and pain. Severe deformity often necessitates surgical correction, but such treatment is complicated because of the proximity of the deformity to the spinal cord, scarring from previous surgery, and the lack of adequate posterior bone for fusion.

Treatment of congenital kyphosis is among the most challenging surgical problems in the growing spine. Most deformities occur at the thoracolumbar junction. This commonly results in a so-called trapped posterior hemivertebra, the result of anterior failure of segmentation. The resulting growth imbalance produces a varying degree of kyphosis and possibly scoliosis. The complexity of the pathologic anatomy, its proximity to the spinal cord, the abundant vascularity, and difficult access create a high risk of neurological injury and inadequate correction with surgery.

A number of different options have been used for the treatment of congenital kyphosis. Orthotic treatment is considered to be ineffective2,3. Surgery has been recommended, depending on the age of the patient and the type and severity of the deformity. The standard surgical approaches for the treatment of this deformity include posterior arthrodesis1,5,6, combined anterior and posterior arthrodesis1,3,5,6, and excision of the hemivertebra and arthrodesis with internal fixation7-9. Combined anterior and posterior arthrodesis is often recommended for the treatment of severe deformities (those measuring >55°)3,5,6. Theoretically, excision of the hemivertebra would lessen the risk of impingement on the spinal cord during correction of the deformity. However, the posterior hemivertebra can be difficult to visualize during an anterior procedure. There are no standard treatment recommendations for acquired complex kyphoscoliosis because of the varied etiologies.

In 1894, Menard5 provided the first known description of the use of a costotransversectomy for the treatment of a spinal abscess in a patient with tuberculosis. In 1956, Seddon6 provided an update on this technique in the era of modern spine surgery, again noting its utility as a surgical approach to the spine. In 1995, Ahlgren and Herkowitz7 described a modified posterolateral approach to the thoracic spine and found it to be valuable for the biopsy of spinal lesions, the decompression of paraspinal infections, and the treatment of thoracic disc herniations.

Costotransversectomy approaches have been used extensively for a variety of purposes, including the treatment of thoracic disc herniations8, the excision of spinal neurinomas10, and the excision of ventrally based space-occupying intraspinal lesions11. Shono et al.12 described a similar procedure for resection of an isolated nonincarcerated hemivertebra causing kyphoscoliosis. The procedure, which involved the use of a posterior approach for hemivertebral excision followed by segmental spinal instrumentation and arthrodesis, was associated with excellent results. In an effort to improve visualization of the hemivertebra resection, Ruf and Harms13 described a posterior-only approach for excision of the hemivertebra combined with immediate segmental pedicle screw fixation.

Treatment of acquired kyphoscoliotic deformities is challenging because most patients with such deformities have had prior spinal surgery. A variety of spinal disorders such as tethered-cord syndrome or spinal cord tumors require laminectomy at the thoracolumbar junction, placing the patient at risk for the development of thoracolumbar kyphosis.

In 1988, we began to use a posterior-only approach combined with a posterior costotransversectomy for the treatment of congenital kyphosis and acquired kyphoscoliosis. We used this modified approach to provide direct visualization of the trapped nonincarcerated posterior hemivertebra, thereby facilitating excision under direct visualization, or to allow for vertebral resection and osteotomy followed by correction of deformity with use of segmental spinal instrumentation. This approach provides excellent visualization of the thecal sac during excision of the hemivertebra and correction of the deformity, and it also provides sufficient exposure of the adjacent anterior vertebral bodies for the performance of a supplemental anterior arthrodesis through a single posterior approach. The purpose of the present study was to report the results of this procedure in sixteen patients with congenital kyphosis and acquired kyphoscoliosis.

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Materials and Methods

We performed an institutional review board-approved retrospective review of the records of the sixteen patients who had been managed at our institution for the treatment of congenital kyphosis and acquired kyphoscoliosis between 1988 and 2002. The mean age at the time of surgery was twelve years (range, four to sixteen years). Nine patients were male, and seven were female. The diagnosis was congenital kyphosis for fourteen patients (including twelve who had a Type-I deformity, one who had a Type-II deformity, and one who had a Type-III deformity). The remaining two patients had painful, progressive kyphoscoliosis associated with previous extensive laminectomies and failed surgical procedures for the treatment of tethered-cord sydrome. The mean preoperative kyphotic deformity was 65° (range, 25° to 160°), and the mean preoperative scoliotic deformity was 47° (range, 7° to 160°).

The clinical and radiographic characteristics of the sixteen patients are summarized in Table I. Six patients had no known associated spinal cord anomalies or other abnormalities. The remaining ten patients had a variety of associated problems, including tethered spinal cord that had been released prior to correction of the kyphosis (three patients), developmental delay (two patients), seizure disorder (two patients), neurogenic bladder or neuropathy (two patients), and failed prior surgery (five patients). Three patients with myelodysplasia had congenital kyphosis as the primary deformity. None of these patients had typical congenital lumbar kyphosis of myelodysplasia.

In the absence of a validated tool for the assessment of the outcome of spinal surgery in juvenile patients, we completed a subjective and radiographic assessment of clinical outcome. In the course of our retrospective review, a satisfactory outcome was achieved if the patient and the family were satisfied with the results of the operation, there were no obvious and clinically important postoperative complications, the fusion appeared solid, and there was no evidence of hardware failure or progression of deformity during the follow-up period. A fair outcome was achieved if a clinically important postoperative complication was identified but the patient did not require additional surgery. A poor outcome was defined as the need for additional surgery for the treatment of a postoperative complication during the follow-up period.

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Operative Technique

The patient is positioned prone on a radiolucent operating table and is carefully padded and stabilized to allow 30° of table rotation in both directions around the central longitudinal axis. An attempt is made to establish spinal cord monitoring of somatosensory evoked potentials. If acceptable signals are present, they will later serve as confirmation of the absence of spinal cord compression following correction. If acceptable signals cannot be initially obtained as a consequence of preexisting neurologic abnormalities or prior spinal cord surgery, correction of the deformity is accomplished with an additional degree of caution and the adequacy of decompression is confirmed visually. If somatosensory evoked potentials are not obtainable, a wake-up test is performed intraoperatively after correction and instrumentation of the deformity in patients with normal motor function. The back is prepared and draped widely out to the posterior axillary line. A standard midline longitudinal incision is made as needed to treat the deformity. A subperiosteal posterior exposure of the spine is then completed, with the surgeon bearing in mind that the posterior elements may be absent or abnormal in terms of their appearance or thickness or their relationship to adjacent segments.

Fluoroscopy is used to identify the level of the hemivertebra and its associated pedicle, lamina, transverse process, and attached rib. A transverse incision is then made through the paraspinous muscle mass; the incision is centered at the level of the hemivertebra. The adjacent ribs are exposed subperiosteally for approximately 3 cm. For adequate exposure and a sufficiently large operative field, it usually is necessary to resect two ribs at the level of the anomalous vertebral body. Very small hemivertebrae can be removed following the resection of a single rib, whereas the size of the orientation of other anomalous segments requires the resection of as many as three ribs. This decision is made intraoperatively, depending on the extent and complexity of the deformity. Rib resection is usually unilateral and is done on the apex of an associated scoliotic curve. Care is taken to preserve the pleura during rib resection, and a blunt retractor is placed with the tip at the anterior aspect of the vertebral body to define the deep and lateral aspects of the surgical field. If a pleural tear occurs during rib removal, a repair is attempted and the placement of a chest tube is obligatory. Next, the lamina and the pedicle of the hemivertebra are removed, with care being taken to preserve the segmental nerve at that level. The superior and inferior exiting nerve roots are visualized or palpated in order to ascertain their course in the surgical field and to protect them during exposure and removal. A laminectomy at the level of the hemivertebra allows for direct visualization of the dura and intraspinal contents, which are protected, and for hemostasis of the paraspinal venous plexus. This provides excellent visualization of the dural sac and allows gentle retraction and protection during resection of the hemivertebra. The discs and end plates of the body of the hemivertebra are dissected in a subperiosteal fashion and are removed first because they form identifiable anatomic planes for dissection and are relatively avascular compared with the vertebral body itself. Once the hemivertebra has been defined by removal of the superior and inferior intervertebral discs, it is resected as completely as possible. The posterior longitudinal ligament is resected with the posterior portion of the body, and the resection is carried as far anteriorly as possible while preserving the anterior longitudinal ligament.

Figure. No caption a...
Figure. No caption a...

The anomalous pattern of segmental vascularity that often accompanies these deformities can make adequate hemostasis difficult to achieve and often is responsible for the substantial blood loss that is encountered during the procedure. Gaining control of a bleeding vessel at the deep limit of the surgical field often requires a combination of adequate aspiration, bipolar cautery, thrombin-soaked gel foam, direct pressure, and time. Once the hemivertebra has been removed, the adjoining end plates are denuded to expose cancellous bleeding bone. A wedge that approximates the desired amount of correction is created in the anterior column, with care being taken to preserve the anterior longitudinal ligament so that it serves as a rotational hinge and stabilizing restraint to translation during correction. The resected hemivertebra is morselized for bone graft and is placed loosely in the anterior aspect of the gap left by the resection. For patients with acquired kyphoscoliosis without an associated hemivertebra, a decancellation osteotomy14 of the apical vertebra is performed under direct visualization.

Following resection of the hemivertebra, posterior spinal instrumentation is placed for correction of the deformity. The pattern of fixation that is used depends on the type of the deformity and the preference of the surgeon. Our current preference is to use pedicle screws at least two vertebrae caudad to the level of the resection and a combination of pedicle screws and hooks cephalad to the level of the resection, depending on the specific deformity and the ease of pedicle navigation. Given the relative ease of placing pedicle screws inferior to the deformity, we typically begin by inserting pedicle screws at the inferior limit of the instrumentation. We then proceed superiorly with pedicle screw fixation until the superior limit of the instrumentation is reached or the difficulties of pedicle navigation warrant a switch to pedicle, lamina, or transverse process hooks, as appropriate. Fluoroscopy is used to confirm satisfactory placement of the fixation points. Two rods are contoured to approximate the desired amount of correction and are attached to the inferior points of fixation. A combination of cantilever bending and translation forces are then applied, and the deformity is slowly corrected to approximate the normal sagittal and coronal balance of the spine. During this process, the dura and its contents can be directly inspected for signs of compression by visualizing and palpating the anterior aspect of the thecal sac at the level of the hemivertebra and the apex of correction. If compression of the thecal sac or neural elements does occur with correction of the overall deformity, additional bone can be resected at the point of compression if it can be seen or palpated. If there are changes in somatosensory evoked potentials during correction and there is not an obvious source of compression, the etiology of the compromise is thought to be vascular and the rods are recontoured to reduce the amount of correction. With a combination of these maneuvers, the deformity can be corrected without compromising the contents of the spinal canal.

A standard posterior spinal arthrodesis is then completed (Figs. 1-A and 1-B). Our preference is to use local autogenous bone and supplemental morselized allograft bone. A surgical drain with a closed self-suctioning reservoir is placed, a chest tube is placed into each hemithorax that has been violated by a pleural opening, and the wounds are closed in a routine fashion. The patient is mobilized with the assistance of a physical therapist on the first or second postoperative day, depending on the comfort level. An orthosis was not used postoperatively for any patient in the present series. Specific activity restrictions that avoid bending, twisting, heavy lifting, and sporting activities are maintained for six months.

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Results (Table II)

All sixteen patients were managed with vertebral resection through a simultaneous anterior and posterior approach to the spine that involved a single posterior midline incision and a costotransversectomy. All but one of the patients had an anterior and posterior spinal fusion and posterior segmental spinal instrumentation; the remaining patient was too small for spinal instrumentation at the time of vertebral resection. The mean correction of the major kyphotic deformity was 31° (range, 0° to 82°), and the mean correction of the major scoliotic deformity was 25° (range, 0° to 68°). The mean duration of follow-up was 5.0 years (range, 2.0 to twelve years).

Four patients had a major complication. One patient had a failure of posterior instrumentation that necessitated revision surgery, one patient had development of persistent lower extremity dysesthesias of uncertain etiology, and two patients had radiographic evidence of late progression of pelvic obliquity caudad to the fusion. There were no substantial neurological injuries affecting bowel or bladder function or muscle strength in the lower extremities.

Thirteen patients had a satisfactory outcome; that is, both the patient and the family were satisfied with the results of the operation, there were no obvious and clinically important postoperative complications, the fusion appeared solid, and there was no evidence of hardware failure or progression of deformity during the follow-up period. Two patients had a fair outcome; that is, they had a substantial postoperative complication but did not require additional surgery. One patient had a poor outcome because additional surgery was needed for the treatment of a postoperative complication during the follow-up period. Specifically, a catastrophic failure of the initial posterior instrumentation necessitated revision anterior and posterior surgery for stabilization. Despite this additional surgery, the patient believed that the overall outcome was satisfactory; nevertheless, the result was rated as poor because of the need for a second major surgical procedure.

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Discussion

The natural history of congenital kyphosis has been well described in the literature1-3,15,16. Although less common than congenital scoliosis, congenital kyphosis is associated with a greater risk of anterior cord compression and neurologic compromise with growth and progression of the deformity if left untreated16. Early intervention to prevent progression of the deformity and to allow for some correction with growth is currently recommended3,16. In a review of ninety-four patients in whom progressive congenital kyphosis had been treated after the age of five years, Winter et al.3 recommended a posterior arthrodesis for curves of ≤50° and a combined anterior and posterior arthrodesis for curves of >50°. McMaster and Singh16 also recommended that all children with Type-I or III congenital kyphosis should be managed with posterior arthrodesis without instrumentation before the age of five years and before the kyphosis exceeds 50°. In this group of younger patients, the authors reported that posterior arthrodesis alone resulted in a mean correction of 15° with growth, from a mean preoperative deformity of 43°. Among patients who had been managed with posterior arthrodesis without instrumentation alone, with and without cast application, at the age of six years or more, there was limited correction of only 9° from a mean preoperative deformity of 70°, and there was a substantial rate of pseudarthrosis or kyphosis progression during the follow-up period (mean, 6.6 years). The authors recommended anterior release, strut-grafting, and posterior arthrodesis with instrumentation (if possible) for these older patients and for patients in whom the curve exceeds 60°.

Kim et al.15 noted that correction of kyphosis may occur with continued growth in patients with Type-I and III deformities, especially when a posterior arthrodesis is performed when the patient is two years old or less. In their study of twenty-six cases of surgically treated congenital kyphosis and kyphoscoliosis, a variety of surgical techniques were used. Five patients with a mean age of sixteen months underwent posterior arthrodesis without instrumentation alone, with improvement of the mean kyphotic deformity from 49° to 26°. Pseudarthrosis developed in two patients, necessitating subsequent posterior augmentation or anterior arthrodesis. Five patients with a mean age of 13.6 years underwent posterior arthrodesis with instrumentation, with improvement of the kyphotic deformity from 59° to 29°. Seven patients with a mean age of sixteen months underwent anterior release or vertebral resection followed by posterior arthrodesis, with improvement of the kyphotic deformity from 48° to 22°, whereas nine patients with a mean age of 11.5 years demonstrated improvement from 77° to 37° after the same procedure. The authors did not report the amount of intraoperative blood loss. They did not comment that spinal instrumentation reduced the need for subsequent augmentation of the fusion and was associated with a low prevalence of pseudarthrosis. Two of the twenty-six patients in that study had development of a postoperative neurological deficit, and the authors identified a number of risk factors for neurologic injury: an older age at the time of correction, combined anterior and posterior arthrodesis procedures, more severe deformity, and preexisting spinal cord compromise.

The studies by McMaster and Singh16, Winter et al.17, and Kim et al.15 suggest that whereas early posterior arthrodesis is effective in the younger child, it is not sufficient for the older child who presents with congenital kyphoscoliosis and a substantial deformity. The deformities that arise in older children as a consequence of an abnormal hemivertebra present a difficult surgical challenge. Some degree of vertebral resection often is required in order to achieve satisfactory correction of the deformity, and this is not possible through a posterior-only exposure and fusion. A combined anterior and posterior arthrodesis for the treatment of kyphoscoliosis has inherent limitations. With use of separate approaches, it is not possible to expose and resect the hemivertebra from the anterior side, to perform spinal instrumentation, and to observe the effects of posterior correction on the contents of the spinal canal during surgery. The adequacy of the anterior decompression must be estimated prior to closing the anterior incision and proceeding to the posterior approach for instrumentation and correction of the deformity. This limitation can be overcome by performing a surgical resection of the hemivertebra and correction of the deformity through the same posterior approach. While a posterior-only approach for resection of the hemivertebra seems to be technically challenging and fraught with risk to the neural elements, several published reports have described acceptable clinical outcomes in association with this technique12,13. Increasing familiarity with anterior and posterior column surgery through a posterior approach has resulted in a tendency to fuse both columns at a younger age. For example, Ruf and Harms18 recently reported on twenty-eight consecutive cases of congenital scoliosis in very young children who underwent hemivertebra resection through a posterior-only approach at a mean age of 3.3 years. We concur with their conclusions that this procedure permits excellent correction in the frontal and sagittal planes and produces a short-segment fusion that allows for normal growth in the unaffected parts of the spine, and we add that it also avoids the uncertainties associated with unbalanced growth of the anterior column that may lead to progression, recurrence, or crankshaft-type deformities.

The location of a typical hemivertebra makes it amenable to resection from the posterior approach. The anomalous vertebral body is located at the apex of the kyphosis, and several authors have reported excellent visualization of the hemivertebra during resection from a posterior approach. In addition, the surgical dissection required to remove the hemivertebra exposes the neural elements that are at risk of compression during correction of the deformity. It should be noted that substantial blood loss should be anticipated during this procedure. We speculate that large losses of blood are a result of the combination of an anomalous vascular supply to the hemivertebra, exposure of the cancellous surfaces of end plates of the adjacent vertebral bodies, and the technical difficulty of obtaining hemostasis in the depths of the operative field.

Shono et al.12 recently reported the results of one-stage posterior hemivertebra resection and posterior segmental spinal instrumentation in a study of twelve patients with congenital kyphoscoliosis who were between eight and twenty-four years of age. The procedure was associated with satisfactory correction of both the scoliosis (from 49° to 18°) and the kyphosis (from 40° to 17°). The authors reported no postoperative neurologic complications, a 100% union rate, and a mean blood loss of 600 mL. They commented that visualization of the pathologic hemivertebra was enhanced by removal of the adjoining rib. This approach was thought to be safe and effective for adolescents with congenital kyphoscoliosis, and the authors concluded that the single-stage posterior approach was effective for resection of an isolated hemivertebra in the thoracic and lumbar spine. Ruf and Harms13 described a similar approach for hemivertebra resection in a study of twenty patients ranging from less than two years of age to fourteen years of age. The approach, which emphasized limited segmental fixation with use of pedicle screws, was associated with correction of the scoliotic deformity from 41° to 14° and correction of the kyphotic deformity from 24° to 11°. Again, the authors were able to achieve excellent visualization of the hemivertebra as well as of the effects of correction of the deformity on the adjacent neural structures. The mean blood loss was 635 mL. In a subsequent report on patients who were five years of age or less18, twenty-eight children with a mean age of 3.3 years were managed with a posterior-only approach with transpedicular instrumentation. The mean scoliotic deformity was corrected from 45° to 13°, and the mean kyphotic deformity was corrected from 22° to 10°. The authors reported no neurologic complications, one infection, three cases of implant failure, and a mean blood loss of 496 mL.

Two patients in the present series were treated for acquired kyphoscoliosis. Both had had extensive, repeated laminectomies for the treatment of tethered-cord syndrome and subsequently had had development of progressive, painful kyphoscoliosis at the thoracolumbar junction. Neither patient had undergone instrumentation and fusion at the time of the laminectomies. The use of the costotransversectomy approach following the failure of previous surgery allows for excellent visualization of the spinal cord during correction of the deformity.

In conclusion, we believe that congenital kyphosis and acquired kyphoscoliosis can be safely corrected with use of a one-stage posterior approach to the spine. The addition of a costotransversectomy approach to the anterior part of the spine allows excellent visualization during resection of a hemivertebra and also allows access to the anterior column for fusion, but substantial blood loss should be anticipated. We recommend arthrodesis of the entire deformity and stabilization with use of pedicle fixation where possible. ▪

The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Investigation performed at Primary Children's Medical Center, Salt Lake City, Utah

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