- Email: [email protected]
Adult deformity correction techniques
SE
M I N
SP
I N E
SU
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27 (2015) 159–162
Available online at www.sciencedirect.com
www.elsevier.com/locate/semss
Adult deformity correction techniques Andre Jakoi, MDa,n, Amrit Khalsa, MDa, and Reginald Fayssoux, MDb a
Department of Orthopaedic Surgery, Drexel/Hahnemann University Hospital, Philadelphia, PA Desert Orthopaedic Center, Rancho Mirage, CA
b
abstra ct Adult spinal deformity is a common disorder with an increasing clinical and societal impact based on the aging demographic throughout the world. Adult spinal deformity in the adult population has a significant and measurable impact on health-related quality of life. A significant proportion of this affected populace will require treatment in some form or another. In general, the first-line of treatment is non-operative, but a subset will require operative intervention. Once surgical intervention is chosen, there are numerous methods that may provide surgeons with adequate tools for successful outcomes. The purpose of this review article is to discuss the importance of adult deformity in the spectrum of disorders that affect the spine, to define specific considerations that are useful in guiding an evidence-based approach to care, and to elaborate on the variety of surgical techniques for which to address the issue of spinal deformity. & 2015 Elsevier Inc. All rights reserved.
As the current population continues to age and the size of the elderly population increases, the problem of adult scoliosis is becoming increasingly prevalent. A significant proportion of this populace will require treatment of some kind. As with most spinal patients, conservative care is almost always the initial treatment. However, a small subset of this patient population will have an indication for surgery. Indications may include back pain failing conservative care, progressive leg pain or neurologic deficit, muscle fatigue secondary to spinal imbalance, curve progression, and pulmonary compromise secondary to deformity.1 Many factors need to be considered regarding surgical planning for patients. Overall health of the patient and his/ her expectations are key when initially evaluating patients. Many of the basic principles are similar to that of adolescent idiopathic scoliosis, but there are more factors that need to be appreciated, which make correction more challenging. Those factors include the presence of disc degeneration, facet arthropathy, and osteopenia, which accompanies an older age population. The SRS-Schwab classification is a validated classification system that categorizes adult spinal deformity. The classification includes four coronal curve types (thoracic only,
n
Corresponding author. E-mail address: [email protected] (A. Jakoi).
http://dx.doi.org/10.1053/j.semss.2015.03.015 1040-7383/& 2015 Elsevier Inc. All rights reserved.
thoracolumbar/lumbar only, double curve, and no coronal curve) with three sagittal modifiers (including pelvic incidence minus lumbar lordosis, global alignment, and pelvic tilt). Improvement in sagittal modifiers at 1 year after treatment has been shown to correlate with significantly improved patient-reported outcome measures.2 Adults with primary thoracic curves and flexible lumbar compensatory curves are usually most predictably stabilized by posterior instrumented fusions.1 Thoracoscopic procedures may be offered for the more flexible curves but may not be adequate to maintain balance in adult patients with stiffer compensatory curves.1 End vertebra considerations should include the entire Cobb-measured curve and any additional levels that may aid in coronal balance. Patients with thoracolumbar or lumbar curves with flexible secondary curves are model candidates for anterior correction and fusion with segmentation instrumentation. The anterior procedure has many advantages within this setting. Fewer motion segments, obtaining superior correction, and higher fusion rates are all advantages seen with the anterior procedure.3 Maintaining lumbar lordosis is important, and the use of structural interbody grafts or cages placed anteriorly may allow for this.4–9
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When choosing this technique, it is crucial to make certain that the secondary curves are flexible. If there is a fixed secondary curve, especially a fixed oblique lumbosacral takeoff, this procedure will result in significant coronal imbalance.1 In patients with either spinal stenosis or radiculopathy, decompression is required and a posterior or combined approach may be preferable. Posterior rod fixation is used in conjunction with such osteotomies and fusions in adult deformity. Such constructs can provide both static fixation in combination with pedicle screws and be a tool for maintaining forces such as compression, distraction, and rotation to achieve the desired spinal alignment in multiple planes. Compression forces are often utilized in creating further lordosis in hypolordosis deformities of the lumbar and cervical spine or reducing hyperkyphosis of the thoracic spine, often in conjunction with Smith-Petersen osteotomies (SPO) and pedicle subtraction osteotomies (PSO).1 Posterior distraction instrumentation systems are utilized for creating kyphosis when necessary, although more common in pediatric idiopathic scoliosis correction.1 Rotational deformities are also corrected using posterior rod fixation, utilizing derotational techniques converting deformity in the coronal plane to sagittal correction in the setting of scoliosis.10 For a large, rigid deformity, an anterior release is often performed by taking down the anterior longitudinal ligament through an anterior approach. This allows for added mobility for subsequent correction. This technique carries with it greater rates of pseudarthrosis and perioperative morbidity.11 The cantilever bending technique was developed in an effort to forgo the complications of an anterior release, while still achieving powerful correction in a rigid spinal deformity. This technique utilizes two long benders in situ to provide corrective force above and below the apical pedicle screws. This powerful correction relies on the spinal bone–implant interface, which is often the limiting factor for correction in osteoporotic bone.12 Axial vertebral body alignment can also be corrected using derotational techniques. Direct vertebral rotation (DVR) was first described by Lee et al.,14 as a method utilizing derotating posts over bilateral periapical screws in an effort to reduce rib prominence and obviate the need for thoracoplasty.13 Again relying on the spinal bone–implant interface, derotation is best accomplished through several vertebral bodies at once to minimize stress.13–15 As with any instrumentation, risk of implant failure is a consideration with rod fixation. Increased risk of rod fracture has been associated with use in conjunction with a PSO and also the use of cobalt–chrome rods versus titanium. It is speculated that in larger corrections utilizing PSO, rods may be notched by bending instruments and may contribute to failure.16 Of note, a technique of dynamic stabilization without fusion has been advocated to minimize complications associated with traditional pedicle screw–rod constructs with fusion. These systems consist of titanium alloy screws connected by an elastic synthetic compound. This technique has shown to be a safe alternative to a more aggressive instrumented fusion in an elderly population.17
27 (2015) 159–162
1.
Anterior and posterior osteotomies
Reconstruction techniques include anterior and posterior osteotomies, decancellation or pedicle subtraction osteotomies, and vertebral column resection. Anterior osteotomies are performed through the area of a fused disc space. Care must be taken to identify the foramen and the pedicles, especially in patients with a rotational component to the deformity. The posterior cortex is then removed with a curette or a Kerrison rongeur. Posterior osteotomies can be performed by resecting bone in the area of the prior fusion at the fused facet joints, removing osteophytes until mobility is achieved. Many surgeons will place pedicle screws cephalad and caudad to the intended osteotomy site to control reduction and prevent translation after a three-column osteotomy is made, such as a PSO.10 If the facets are completely fused and cannot be mobilized, Kerrison rongeurs are used to remove bone from the midline through the intertransverse foramen. It is best to open the midline with a laminectomy or establish the midline prior to laminectomy. Posterior osteotomies over multiple levels can achieve a significant amount of correction over a large area.6
2. Shortening osteotomies/spinal column resection This procedure is used only for severe and rigid deformities with significant truncal decompensation. The first stage consists of an anterior approach on the convex side of the curve. Multiples osteotomies are performed proximally and distally to the intended resection level. An osteoperiosteal flap is raised over the apical one to three vertebrae, after which the vertebral bodies are decancellated back to the posterior longitudinal ligament. The convex and concave pedicles are removed as far back as possible without risking damage to the dura or the exiting nerve roots. Decancellated bone is then laid loosely down into the defect, while protecting the dura, and the osteoperiostal flap is then sutured over the top.6,7 Usually, most adults are treated in a staged manner, typically 5–7 days after the posterior procedure is performed. After proximal and distal osteotomies are completed posteriorly, the remainder of the spinal posterior elements over the anteriorly resected segments is removed. Thoracoplasty is performed on the convex side, and the apical ribs are resected on the concave side. The convex rod is fixed to the upper portion of the curve above the level of the resection using segmental fixation and is then cantilevered to the spine distally, correcting the curvature and effectively shortening the vertebral column.
3.
Osteotomy classification
There are many osteotomies described to achieve different degrees of correction in both coronal and sagittal plane deformities. Schwab et al.18 recently described a classification system for grading both the extent of bony resection and
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subsequent destabilization in such osteotomies. This system may be used to gauge the varying subtypes in an effort to organize spinal osteotomies based on the degree of correction. Grade 1 osteotomies, the most common being the SmithPetersen osteotomy (SPO) generally provide 51–101 of correction at each level. Always approached from a strictly posterior incision, the bony resection involves partial removal of the inferior articulating facet of the rostral vertebra in addition to joint capsule.18 This is often referred to as an opening wedge osteotomy because the success of the correction is dependent on a mobile anterior column. Concurrently, as the anterior column opens up, the posterior column is closed down, forcing the spine into extension, whether providing further lordosis in the lumbar spine or correcting a hyperkyphotic deformity in the thoracic spine.19–21 This is generally coupled with a fusion followed by posterior compression instrumentation. Asymmetric resection of facet at concurrent levels can also provide correction in the coronal plane if needed. It is essential during pre-operative planning to ensure a lack of bridging osteophytes that will prevent successful opening anteriorly.19 Additionally, one must take into consideration the degree of disc degeneration, as a mobile, healthy disc will provide more correction as the middle column acts as a hinge than a degenerated disc.21 A major risk factor for any anterior lengthening procedure such as the SPO is potential tension put on vascular structures, particularly in the elderly and those with significantly calcified vessels.1 Furthermore, iatrogenic foraminal stenosis is a concern when closing down the osteotomy. A wide foraminotomy is often recommended at the involved spinal level to prevent nerve root compression and subsequent radiculopathy.21 Grade 2 osteotomies encompass the complete removal of both the superior and the inferior facets at a given spinal segment. In addition, the ligamentum flavum is resected, as can other posterior structures including the lamina and spinous process.1 These include a variant of the SPO with a more aggressive facetectomy and the Ponte osteotomy.18,22 These osteotomies provide approximately 101 of correction at each spinal level.20 The same limitations with regard to anterior mobility exist as in grade 1 osteotomies if a limited posterior approach is utilized. The Ponte osteotomy was initially described in the treatment of Scheuermann kyphosis to provide gradual correction at multiple thoracic levels.22 An anterior approach was traditionally described in conjunction with these osteotomies in order to take down the anterior longitudinal ligament disc and perform an interbody fusion. Anterior release and fusion is not without consequences, particularly with the advent of 3column pedicle screw fixation obtainable through posterioronly approach with fusion.19 Grade 3 osteotomies provide even greater correction in the sagittal plane through a single-level bony resection. In general, these osteotomies involve complete removal of the posterior elements with a partial wedge resection of the vertebral body.18 This leaves a portion of the anterior vertebral body intact and is a subsequent closing-wedge osteotomy posteriorly. For this reason, anterior spinal mobility is
27 (2015) 159–162
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nonessential, as no anterior column lengthening is performed. Thus, these osteotomies can be performed in patients with previous circumferential fusions.19,20 The most common resection in this grade is the pedicle subtraction osteotomy. This powerful osteotomy can achieve between 251 and 351 of correction, historically performed in deformities with an apex in the lumbar spine.19 Traditionally, this all-posterior approach begins with removal of all posterior elements at the planned level of resection, including the superior and inferior facets adjacent to the pedicle. After then taking down the pedicle to the level of the posterior vertebral body, the vertebral body is decancellated through each pedicle in a wedge-shaped fashion.19 After thinning and fracturing through the posterior vertebral body cortex, a posterior compression force is applied across the defect hinging on the anterior margin of the vertebral body.20 Although the PSO does provide more correction than lowergrade osteotomies like the SPO, this larger osteotomy has been shown to have greater blood loss and higher rates of neurologic deficits. Furthermore, bony quality must be a consideration as osteoporotic bone can lead to collapse at the osteotomy in addition to iatrogenic kyphotic deformity.20 Grade 4 osteotomies involve a resection similar to that of the PSO, but they remove additional body to the extent that at least a portion of the adjacent disc is taken. This type of osteotomy is not as well described; however, a recent study by Murrey et al.23 described a method similar to the PSO, with the addition of a complete resection of the superior endplate and disc. This transpedicular decompression and osteotomy can achieve 251–301 of correction per level and offers the ability for anterior decompression from a posterior approach. Blood loss again is a major concern, like the PSO, and must be taken into consideration.23 Grade 5 osteotomies involve the complete resection of a vertebral body with both the cephalad and the caudal discs.18 Commonly referred to as a vertebral column resection, when the resection is extended beyond a single level, it becomes a grade 6.18,19 The VCR can be performed through a single posterior approach and a combined anterior–posterior approach. It is indicated for fixed trunk translation, rigid spinal deformities of more than 801 in the coronal plane, and severe column asymmetry such as a hemivertebra.20 Preoperative planning is of utmost importance when deciding the number of vertebral bodies to resect based on the angle of the curve. Sharp curves may be amenable to a single-level resection, while long, sweeping curves may require the resection of multiple levels in order to both achieve correction and prevent undue tension on neural elements.19 The anterior thoracolumbar approach is generally taken along the costal margin through the rib and rectus muscle, utilizing a retroperitoneal approach. After mobilization of the great vessels, piecemeal resection of the vertebral body is carried out until the dura is reached.19–21 The posterior approach through the standard dorsal incision can finish resection of the pedicles and posterior elements and preparation of adjacent posterior fusion instrumentation. The posterior-only approach, after removing the posterior elements, allows the resection of the vertebral body through a dural tube, bypassing the neural elements.1 VCR is associated with a high rate of complications including blood loss, infection, dural tear, and neurologic injury.21
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Even with these complications, VCR is a safe and effective procedure for correcting severe fixed angular deformities in both the coronal and the sagittal planes.19
r e f e r e n c e s
1. Rothman-Simeone. Adult Deformity Section. Text book 'The Spine' 6th edition. Elsevier Saunders. 2. Smith JS, Klineberg E, Schwab F, et al. Change in classification grade by the SRS-Schwab Adult Spinal Deformity Classification predicts impact on health-related quality of life measures: prospective analysis of operative and nonoperative treatment. Spine. 2013;38(19):1663–1671. 3. Cotler JM, Cotler HB. Spinal Fusion: Science and Technique. New York: Springer-Verlag; 1990;407. 4. Gertzbein SD, Betz R, Clements D, et al. Semirigid instrumentation in the management of lumbar spinal conditions combined with circumferential fusion: a multicenter study. Spine. 1996;21:1918–1925. 5. Koustuik JP, Errico TJ, Gleason TF. Techniques of internal fixation for degeneration conditions of lumbar spine. Clin Orthop. 1986;203:219–231. 6. Weinstein SL. Bristol-Myers Squibb/Zimmer award for distinguished achievement in orthopedic research. Long-term follow-up of pediatric conditions: Natural history and outcomes of treatment. J Bone Joint Surg Am. 2000;82:980–990. 7. Boachie-Adjei O, Bradford DS. Vertebral column resection and arthrodesis for complex spinal deformities. J Spinal Disord. 1991;4:193–202. 8. Bradford DS, Tribus CB. Vertebral column resection for the treatment of rigid coronal decompression. Spine. 1997;22:1590–1599. 9. Gill JB, Levin A, Burd T. Longley: corrective osteotomies in spine surgery. J Bone Joint Surg Am. 2008;90(11):2509–2520. 10. Aebi M. The adult scoliosis. Eur Spine J. 2005;14:925–948. 11. Kim YB, Lenke LG, Kim YJ, Kim YW, Bridwell KH, Stobbs G. Surgical treatment of adult scoliosis: is anterior apical release and fusion necessary for the lumbar curve? Spine. 2008;33 (10):1125–1132.
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12. Chang K. Cantilever bending technique for treatment of large and rigid scoliosis. Spine. 2003;28(21):2452–2458. 13. Cuartas E, Rasouli A, O’Brien M, Shufflebarger H. Use of all-pedicle-screw constructs in the treatment of adolescent idiopathic scoliosis. J Am Acad Orthop Surg. 2009;17: 550–561. 14. Lee SM, Suk SI, Chung ER. Direct vertebral rotation: a new technique of three-dimensional deformity correction with segmental pedicle screw fixation in adolescent idiopathic scoliosis. Spine. 2004;29:343–349. 15. Rushton P, Grevitt M. Do vertebral derotation techniques offer better outcomes compared to traditional methods in the surgical treatment of adolescent idiopathic scoliosis? Eur Spine J. 2014;23:1166–1176. 16. Smith Justin S, Shaffrey Ellen, Klineberg Eric, et al. Prospective multicenter assessment of risk factors for rod fracture following surgery for adult spinal deformity. J Neurosurg Spine. 2014;21(6):994–1003. 17. Di Silvestre M, Lolli F, Bakaloudis G, Parisini P. Dynamic stabilization for degenerative lumbar scoliosis in elderly patients. Spine. 2010;35(2):227–234. 18. Schwab F, Blondel B, Chay E, et al. The comprehensive anatomical spinal osteotomy classification. Neurosurgery. 2014;74(1):112–120. 19. Gill JB, Levin A, Burd T, Longley M. Corrective osteotomies in spine surgery. J Bone Joint Surg Am. 2008;90:2509–2520. 20. Bridwell KH. Decision making regarding Smith-Peterson vs. pedicle subtraction osteotomy vs. vertebral column resection for spinal deformity. Spine. 2006;31(19):5171–5178. 21. Daubs MD, Lenke LG, Cheh G, Stobbs G, Bridwell KH. Adult spinal deformity surgery: complications and outcomes in patients over age 60. Spine. 2007;32(20):2238–2244. 22. Geck MJ, Macagno A, Ponte A, Shufflebarger HL. The Ponte procedure: posterior only treatment of Scheuermann's kyphosis using segmental posterior shortening and pedicle screw instrumentation. J Spinal Disord Tech. 2007;20(8): 586–593. 23. Murrey DB, Brighman CD, Kiebzak GM, Finger F, Chewning SJ. Transpedicular decompression and pedicle subtraction osteotomy (eggshell procedure): a retrospective review of 59 patients. Spine. 2002;27(21):2338–2345.
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27 (2015) 159–162
Available online at www.sciencedirect.com
www.elsevier.com/locate/semss
Adult deformity correction techniques Andre Jakoi, MDa,n, Amrit Khalsa, MDa, and Reginald Fayssoux, MDb a
Department of Orthopaedic Surgery, Drexel/Hahnemann University Hospital, Philadelphia, PA Desert Orthopaedic Center, Rancho Mirage, CA
b
abstra ct Adult spinal deformity is a common disorder with an increasing clinical and societal impact based on the aging demographic throughout the world. Adult spinal deformity in the adult population has a significant and measurable impact on health-related quality of life. A significant proportion of this affected populace will require treatment in some form or another. In general, the first-line of treatment is non-operative, but a subset will require operative intervention. Once surgical intervention is chosen, there are numerous methods that may provide surgeons with adequate tools for successful outcomes. The purpose of this review article is to discuss the importance of adult deformity in the spectrum of disorders that affect the spine, to define specific considerations that are useful in guiding an evidence-based approach to care, and to elaborate on the variety of surgical techniques for which to address the issue of spinal deformity. & 2015 Elsevier Inc. All rights reserved.
As the current population continues to age and the size of the elderly population increases, the problem of adult scoliosis is becoming increasingly prevalent. A significant proportion of this populace will require treatment of some kind. As with most spinal patients, conservative care is almost always the initial treatment. However, a small subset of this patient population will have an indication for surgery. Indications may include back pain failing conservative care, progressive leg pain or neurologic deficit, muscle fatigue secondary to spinal imbalance, curve progression, and pulmonary compromise secondary to deformity.1 Many factors need to be considered regarding surgical planning for patients. Overall health of the patient and his/ her expectations are key when initially evaluating patients. Many of the basic principles are similar to that of adolescent idiopathic scoliosis, but there are more factors that need to be appreciated, which make correction more challenging. Those factors include the presence of disc degeneration, facet arthropathy, and osteopenia, which accompanies an older age population. The SRS-Schwab classification is a validated classification system that categorizes adult spinal deformity. The classification includes four coronal curve types (thoracic only,
n
Corresponding author. E-mail address: [email protected] (A. Jakoi).
http://dx.doi.org/10.1053/j.semss.2015.03.015 1040-7383/& 2015 Elsevier Inc. All rights reserved.
thoracolumbar/lumbar only, double curve, and no coronal curve) with three sagittal modifiers (including pelvic incidence minus lumbar lordosis, global alignment, and pelvic tilt). Improvement in sagittal modifiers at 1 year after treatment has been shown to correlate with significantly improved patient-reported outcome measures.2 Adults with primary thoracic curves and flexible lumbar compensatory curves are usually most predictably stabilized by posterior instrumented fusions.1 Thoracoscopic procedures may be offered for the more flexible curves but may not be adequate to maintain balance in adult patients with stiffer compensatory curves.1 End vertebra considerations should include the entire Cobb-measured curve and any additional levels that may aid in coronal balance. Patients with thoracolumbar or lumbar curves with flexible secondary curves are model candidates for anterior correction and fusion with segmentation instrumentation. The anterior procedure has many advantages within this setting. Fewer motion segments, obtaining superior correction, and higher fusion rates are all advantages seen with the anterior procedure.3 Maintaining lumbar lordosis is important, and the use of structural interbody grafts or cages placed anteriorly may allow for this.4–9
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When choosing this technique, it is crucial to make certain that the secondary curves are flexible. If there is a fixed secondary curve, especially a fixed oblique lumbosacral takeoff, this procedure will result in significant coronal imbalance.1 In patients with either spinal stenosis or radiculopathy, decompression is required and a posterior or combined approach may be preferable. Posterior rod fixation is used in conjunction with such osteotomies and fusions in adult deformity. Such constructs can provide both static fixation in combination with pedicle screws and be a tool for maintaining forces such as compression, distraction, and rotation to achieve the desired spinal alignment in multiple planes. Compression forces are often utilized in creating further lordosis in hypolordosis deformities of the lumbar and cervical spine or reducing hyperkyphosis of the thoracic spine, often in conjunction with Smith-Petersen osteotomies (SPO) and pedicle subtraction osteotomies (PSO).1 Posterior distraction instrumentation systems are utilized for creating kyphosis when necessary, although more common in pediatric idiopathic scoliosis correction.1 Rotational deformities are also corrected using posterior rod fixation, utilizing derotational techniques converting deformity in the coronal plane to sagittal correction in the setting of scoliosis.10 For a large, rigid deformity, an anterior release is often performed by taking down the anterior longitudinal ligament through an anterior approach. This allows for added mobility for subsequent correction. This technique carries with it greater rates of pseudarthrosis and perioperative morbidity.11 The cantilever bending technique was developed in an effort to forgo the complications of an anterior release, while still achieving powerful correction in a rigid spinal deformity. This technique utilizes two long benders in situ to provide corrective force above and below the apical pedicle screws. This powerful correction relies on the spinal bone–implant interface, which is often the limiting factor for correction in osteoporotic bone.12 Axial vertebral body alignment can also be corrected using derotational techniques. Direct vertebral rotation (DVR) was first described by Lee et al.,14 as a method utilizing derotating posts over bilateral periapical screws in an effort to reduce rib prominence and obviate the need for thoracoplasty.13 Again relying on the spinal bone–implant interface, derotation is best accomplished through several vertebral bodies at once to minimize stress.13–15 As with any instrumentation, risk of implant failure is a consideration with rod fixation. Increased risk of rod fracture has been associated with use in conjunction with a PSO and also the use of cobalt–chrome rods versus titanium. It is speculated that in larger corrections utilizing PSO, rods may be notched by bending instruments and may contribute to failure.16 Of note, a technique of dynamic stabilization without fusion has been advocated to minimize complications associated with traditional pedicle screw–rod constructs with fusion. These systems consist of titanium alloy screws connected by an elastic synthetic compound. This technique has shown to be a safe alternative to a more aggressive instrumented fusion in an elderly population.17
27 (2015) 159–162
1.
Anterior and posterior osteotomies
Reconstruction techniques include anterior and posterior osteotomies, decancellation or pedicle subtraction osteotomies, and vertebral column resection. Anterior osteotomies are performed through the area of a fused disc space. Care must be taken to identify the foramen and the pedicles, especially in patients with a rotational component to the deformity. The posterior cortex is then removed with a curette or a Kerrison rongeur. Posterior osteotomies can be performed by resecting bone in the area of the prior fusion at the fused facet joints, removing osteophytes until mobility is achieved. Many surgeons will place pedicle screws cephalad and caudad to the intended osteotomy site to control reduction and prevent translation after a three-column osteotomy is made, such as a PSO.10 If the facets are completely fused and cannot be mobilized, Kerrison rongeurs are used to remove bone from the midline through the intertransverse foramen. It is best to open the midline with a laminectomy or establish the midline prior to laminectomy. Posterior osteotomies over multiple levels can achieve a significant amount of correction over a large area.6
2. Shortening osteotomies/spinal column resection This procedure is used only for severe and rigid deformities with significant truncal decompensation. The first stage consists of an anterior approach on the convex side of the curve. Multiples osteotomies are performed proximally and distally to the intended resection level. An osteoperiosteal flap is raised over the apical one to three vertebrae, after which the vertebral bodies are decancellated back to the posterior longitudinal ligament. The convex and concave pedicles are removed as far back as possible without risking damage to the dura or the exiting nerve roots. Decancellated bone is then laid loosely down into the defect, while protecting the dura, and the osteoperiostal flap is then sutured over the top.6,7 Usually, most adults are treated in a staged manner, typically 5–7 days after the posterior procedure is performed. After proximal and distal osteotomies are completed posteriorly, the remainder of the spinal posterior elements over the anteriorly resected segments is removed. Thoracoplasty is performed on the convex side, and the apical ribs are resected on the concave side. The convex rod is fixed to the upper portion of the curve above the level of the resection using segmental fixation and is then cantilevered to the spine distally, correcting the curvature and effectively shortening the vertebral column.
3.
Osteotomy classification
There are many osteotomies described to achieve different degrees of correction in both coronal and sagittal plane deformities. Schwab et al.18 recently described a classification system for grading both the extent of bony resection and
SE
M I N
SP
I N E
S
U R G
subsequent destabilization in such osteotomies. This system may be used to gauge the varying subtypes in an effort to organize spinal osteotomies based on the degree of correction. Grade 1 osteotomies, the most common being the SmithPetersen osteotomy (SPO) generally provide 51–101 of correction at each level. Always approached from a strictly posterior incision, the bony resection involves partial removal of the inferior articulating facet of the rostral vertebra in addition to joint capsule.18 This is often referred to as an opening wedge osteotomy because the success of the correction is dependent on a mobile anterior column. Concurrently, as the anterior column opens up, the posterior column is closed down, forcing the spine into extension, whether providing further lordosis in the lumbar spine or correcting a hyperkyphotic deformity in the thoracic spine.19–21 This is generally coupled with a fusion followed by posterior compression instrumentation. Asymmetric resection of facet at concurrent levels can also provide correction in the coronal plane if needed. It is essential during pre-operative planning to ensure a lack of bridging osteophytes that will prevent successful opening anteriorly.19 Additionally, one must take into consideration the degree of disc degeneration, as a mobile, healthy disc will provide more correction as the middle column acts as a hinge than a degenerated disc.21 A major risk factor for any anterior lengthening procedure such as the SPO is potential tension put on vascular structures, particularly in the elderly and those with significantly calcified vessels.1 Furthermore, iatrogenic foraminal stenosis is a concern when closing down the osteotomy. A wide foraminotomy is often recommended at the involved spinal level to prevent nerve root compression and subsequent radiculopathy.21 Grade 2 osteotomies encompass the complete removal of both the superior and the inferior facets at a given spinal segment. In addition, the ligamentum flavum is resected, as can other posterior structures including the lamina and spinous process.1 These include a variant of the SPO with a more aggressive facetectomy and the Ponte osteotomy.18,22 These osteotomies provide approximately 101 of correction at each spinal level.20 The same limitations with regard to anterior mobility exist as in grade 1 osteotomies if a limited posterior approach is utilized. The Ponte osteotomy was initially described in the treatment of Scheuermann kyphosis to provide gradual correction at multiple thoracic levels.22 An anterior approach was traditionally described in conjunction with these osteotomies in order to take down the anterior longitudinal ligament disc and perform an interbody fusion. Anterior release and fusion is not without consequences, particularly with the advent of 3column pedicle screw fixation obtainable through posterioronly approach with fusion.19 Grade 3 osteotomies provide even greater correction in the sagittal plane through a single-level bony resection. In general, these osteotomies involve complete removal of the posterior elements with a partial wedge resection of the vertebral body.18 This leaves a portion of the anterior vertebral body intact and is a subsequent closing-wedge osteotomy posteriorly. For this reason, anterior spinal mobility is
27 (2015) 159–162
161
nonessential, as no anterior column lengthening is performed. Thus, these osteotomies can be performed in patients with previous circumferential fusions.19,20 The most common resection in this grade is the pedicle subtraction osteotomy. This powerful osteotomy can achieve between 251 and 351 of correction, historically performed in deformities with an apex in the lumbar spine.19 Traditionally, this all-posterior approach begins with removal of all posterior elements at the planned level of resection, including the superior and inferior facets adjacent to the pedicle. After then taking down the pedicle to the level of the posterior vertebral body, the vertebral body is decancellated through each pedicle in a wedge-shaped fashion.19 After thinning and fracturing through the posterior vertebral body cortex, a posterior compression force is applied across the defect hinging on the anterior margin of the vertebral body.20 Although the PSO does provide more correction than lowergrade osteotomies like the SPO, this larger osteotomy has been shown to have greater blood loss and higher rates of neurologic deficits. Furthermore, bony quality must be a consideration as osteoporotic bone can lead to collapse at the osteotomy in addition to iatrogenic kyphotic deformity.20 Grade 4 osteotomies involve a resection similar to that of the PSO, but they remove additional body to the extent that at least a portion of the adjacent disc is taken. This type of osteotomy is not as well described; however, a recent study by Murrey et al.23 described a method similar to the PSO, with the addition of a complete resection of the superior endplate and disc. This transpedicular decompression and osteotomy can achieve 251–301 of correction per level and offers the ability for anterior decompression from a posterior approach. Blood loss again is a major concern, like the PSO, and must be taken into consideration.23 Grade 5 osteotomies involve the complete resection of a vertebral body with both the cephalad and the caudal discs.18 Commonly referred to as a vertebral column resection, when the resection is extended beyond a single level, it becomes a grade 6.18,19 The VCR can be performed through a single posterior approach and a combined anterior–posterior approach. It is indicated for fixed trunk translation, rigid spinal deformities of more than 801 in the coronal plane, and severe column asymmetry such as a hemivertebra.20 Preoperative planning is of utmost importance when deciding the number of vertebral bodies to resect based on the angle of the curve. Sharp curves may be amenable to a single-level resection, while long, sweeping curves may require the resection of multiple levels in order to both achieve correction and prevent undue tension on neural elements.19 The anterior thoracolumbar approach is generally taken along the costal margin through the rib and rectus muscle, utilizing a retroperitoneal approach. After mobilization of the great vessels, piecemeal resection of the vertebral body is carried out until the dura is reached.19–21 The posterior approach through the standard dorsal incision can finish resection of the pedicles and posterior elements and preparation of adjacent posterior fusion instrumentation. The posterior-only approach, after removing the posterior elements, allows the resection of the vertebral body through a dural tube, bypassing the neural elements.1 VCR is associated with a high rate of complications including blood loss, infection, dural tear, and neurologic injury.21
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Even with these complications, VCR is a safe and effective procedure for correcting severe fixed angular deformities in both the coronal and the sagittal planes.19
r e f e r e n c e s
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