Posterior Osteotomies of the Spine

 

 

 

 

DEFINITION

Spinal osteotomies encompass a range of techniques involving resection of bone from the spinal column to induce flexibility and correct rigid pediatric spinal deformity. These osteotomies can resect the deformity or create more mobility in the spine to allow for deformity correction.

The types of spinal osteotomies include the following: Ponte osteotomy

Smith-Petersen osteotomy (SPO)

Pedicle subtraction osteotomy (PSO) Vertebral column resection (VCR)

The aim of correction varies from a balanced correction to complete correction in the coronal, sagittal, and axial planes.

A balanced correction improves the deformity by maintaining the skull and trunk over the pelvis without a straight spine while keeping the spine in an acceptable sagittal position.

A complete correction aims to achieve a straight spine in coronal plane with the skull and trunk over the pelvis both in the coronal and sagittal planes.

Achieving good sagittal alignment correlates with improved quality of life in adults. In children, its usefulness is desirable but less obvious because children and young adults can compensate for regional malalignment to maintain balance.

Spinal osteotomies have inherent risks, particularly neurologic deficit and bleeding.

Neurologic deficits can come about directly or indirectly; care must be taken to avoid direct spinal cord contusion, manipulation, or spinal column subluxation in the course of the osteotomy and destabilization procedure. Excessive distraction and conversely significant spinal cord shortening can cause ischemia and neurologic deficit.

Below the conus medullaris, attention should be focused on prevention of nerve root injury.

Multimodality intraoperative neurologic monitoring (IONM) should be employed to detect impending neurologic deficit in real time and allow proper intraoperative intervention and reduce risk of permanent deficit.

Risk of complications is high and should be discussed with the patient's family to manage expectations.

Blood loss may be significant and involve transfusion of blood and/or components. The use of antifibrinolytics such as tranexamic acid (TXA) may reduce intraoperative blood loss.

Transcranial motor evoked potential (TcMEP) monitoring allows direct surveillance of the anterior motor pathway, whereas somatosensory evoked potential (SSEP) allows surveillance of the posterior columnar sensory pathway. The loss of MEP data with normal SSEP registration has been reported to

 

occur with an incidence up to 20%.2

Ponte osteotomy: wide resection of the posterior elements involving removal of the superior and inferior articular facets, the interspinous ligament, the cephalad spinous process with a portion of the lamina, and the ligamentum flavum. Thought to hinge at the posterior longitudinal ligament (PLL) as the fulcrum of correction and may open the disc space anteriorly. Up to 5 to 10 degrees of angular correction is possible for each level where this is performed.

Originally described for kyphosis correction by Alberto Ponte, this technique is now used for scoliosis and lordosis as well as kyphosis due to its versatility.

SPO: wedge-shaped osteotomy through the posterior elements of a previously fused or autofused spine Frequently, this term is used interchangeably with a Ponte osteotomy, but the definition is clear.

PSO: Three-column resection in which the posterior elements, the pedicles, and a vertebral wedge are resected and the fulcrum is at the anterior portion of the vertebral body. This allows for the generation of approximately 30 degrees of lordosis and is commonly used for fixed sagittal imbalance or focal, rigid kyphosis.

VCR: involves complete resection of a vertebra with discs above and below, resulting in three-column destabilization, allowing for significant deformity correction not obtainable by any other means.

A classification of spinal osteotomies (Table 1) is a useful aid to understand the degrees of the spinal releases, destabilization, and power of correction.

Ponte osteotomy or SPO is a grade 2 spinal osteotomy.

PSO is graded as 3 or 4, whereas VCR is graded as 5 or 6, depending on the extent of the resection.

 

ANATOMY

 

Kyphosis of the thoracic spine is normally between 10 and 40 degrees.6

 

 

Lordosis of the lumbar spine averages around 40 to 60 degrees.6 Lordosis is also present in the cervical spine.

 

The C7 plumb line, which is a measure of overall sagittal balance, is a straight line drawn vertically through

the center of the C7 vertebral body that should cross the S1 vertebral body at its posterosuperior edge.6 This is called the sagittal vertical axis (SVA).

 

Vertebral anatomy

 

 

The spinous processes of the thoracic vertebrae are shingled and cover the interlaminar space. The spinous processes of the lumbar vertebrae are more horizontal in profile, especially, at the caudal part of the spinal column. This makes the interlaminar space more uncovered and accessible.

 

The laminae are thicker laterally than medially.

 

 

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Table 1 Spinal Osteotomy Classification

Grade

Anatomic

Resection

Description

 

1

Partial facet

joint

Resection of inferior joint facet and joint capsule

2

Complete

facet joint

Both superior and inferior facets at a spinal segment are resected with

complete ligamentum flavum removal; other posterior elements including lamina and spinous process may be resected (Ponte osteotomy).

3

Pedicle/partial Partial wedge resection of the posterior vertebral body and posterior

body elements with pedicles (PSO)

4

Pedicel/partial Wider wedge resection of a substantial portion of the vertebral body,

body/disc posterior elements with pedicles, and includes resection of one endplate and adjacent intervertebral disc

5

Complete

vertebra and discs

Complete removal of a vertebra and both adjacent discs (VCR)

6

Multiple

vertebrae and discs

Resection of more than one entire vertebra and adjacent discs

(VCR+)

Adapted from Schwab F, Blondel B, Chay E, et al. The comprehensive anatomical spinal

osteotomy classification. Neurosurgery 2014;74:112-120.

 

 

Facet joint orientation (supine position) in the thoracic spine is more horizontal to facilitate lateral bending and rotation; in the lumbar spine, the facets are oriented vertically to promote flexion and extension.

 

The ligamentum flavum originates from the superior margin of a lamina and extends cephalad to attach to the inner surface of the lamina above it. The attachment at the cephalad lamina is more lateral compared to the attachment at the caudal lamina which is more medial. Ligamentum flavum is deficient at the midline as it meets at the raphe.

 

 

The thoracic pedicles origination and orientation vary based on their location in the spine.8

 

 

Proximal thoracic spine (T1-T2): The starting point is at the junction between the midpoint of the transverse process and the lamina at the region of the lateral pars. Twenty-five to 30 degrees of medial angulation exists.

 

Middle thoracic spine (T7-T9): The origin of the pedicle is at the junction of the proximal transverse process and lateral to the middle of the base of the superior articular facet. About 5 degrees of medial angulation is present.

 

Lower thoracic spine (T11-T12): The pedicles start at the midpoint of the transverse process and medial to the lateral aspect of the pars. They are perpendicular in the transverse plane to the vertebral body.

 

In deformities such as scoliosis, considerable rotational variability and dysmorphism of thoracic pedicles are encountered.

 

The lumbar superior and inferior articular facets are oriented approximately 45 degrees from the coronal plane with the articular surface facing posterior medially and anterior laterally, respectively. The lumbar pedicle starting point is at the lateral aspect of the pars and the midpoint of the transverse process at the inferior edge of the articular process.

 

 

The upper lumbar vertebral pedicles are perpendicular to the vertebral body in the transverse plane, but the pedicles gradually angle laterally to medial in the lower lumbar region to reach a transverse pedicle angle of 25 to 30 degrees at L5.17

 

Spinal cord and spinal column growth

 

 

There is differential growth between spinal column and spinal cord. For most of the period of fetal development, the spinal cord ends at the lower lumbar spine, but the spinal column grows faster than the neural elements. The spinal cord terminates at the L1 vertebra, which is its final position 2 months after birth.

 

The most rapid growth rate happens in utero. After birth, the first peak growth period of the spine occurs in the first 5 years of life. The second growth peak occurs just prior to and includes puberty.

 

In boys, the remaining growth at age 5 years before the onset of puberty is 18 cm and at the onset of puberty is 13 cm.

 

In girls, the remaining growth at age 5 years before the onset of puberty is 14 cm and at the onset of puberty is 12 cm.

 

Spinal canal achieves 95% of its adult size and 70% of the spinal height at the age of 5 years. The neurocentral synchondrosis closes at the age of 9 years.1, 4

 

The effect of posterior spinal fusion on an immature spine

 

 

Lung growth continues until the age of 9 years. This is supported by a rib-sternal-vertebrae housing. A thoracic spine height of at least 18 to 22 cm is necessary to avoid thoracic insufficiency syndrome.7

 

Assuming growth ceases at 14 years in girls and 16 years in boys, 0.7 mm per year of longitudinal growth per vertebra is lost after spinal fusion in the immature spine for thoracic vertebrae and up to 1.2 mm per

year of remaining growth per lumbar level.4

 

Crankshaft phenomenon—continued anterior growth with a posterior tether (fusion) may cause deformity recurrence through rotation of the previously fused spine.

 

It is postulated that the loss of correction postimplant removal after posterior spinal fusion is less of a problem, as some late anterior column growth helps to buttress the spine against kyphosis.3

PATHOGENESIS

Scoliosis

 

Scoliosis is a spinal curvature with a Cobb angle of greater than 10 degrees measured in the coronal plane. It is typically a three-dimensional (3-D) deformity involving the coronal, sagittal, and transverse planes.

 

Congenital

 

 

This occurs as a result of malformation of vertebral elements due to a failure of formation, failure of segmentation, or a combination of the two.

 

 

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Failure of formation includes hemivertebra and wedged vertebra. Failure of segmentation includes block vertebrae and unilateral bars.

 

There can be mixed deformities with bizarre combinations of the previously discussed as well as rib deformities.

 

Idiopathic

 

 

Three different subtypes were described by James:

 

 

Infantile scoliosis develops between 2 months and 3 years of age.

 

Juvenile scoliosis develops between 3 and 10 years of age and is often associated with intraspinal pathology.

 

Adolescent (adolescent idiopathic scoliosis [AIS]) develops after 10 years of age and prior to skeletal maturity.

 

This classification has now been supplanted by early (usually before age 5 years) and late-onset idiopathic scoliosis, reflecting the velocity of growth prior to age 5 years.

 

Idiopathic scoliosis appears to be a multifactorial process for which the etiology is not yet clearly understood, although may be related to genetics, abnormalities of skeletal growth or the nervous system, biomechanical or biochemical factors, and environmental factors.

 

Neuromuscular

 

 

This is a broad category representing multiple etiologies with various presentations with spastic and paralytic conditions.

 

Some of these conditions include cerebral palsy, Freidreich ataxia, myelomeningocele, and spinal cord injury.

 

Syndromic scoliosis includes causes such as neurofibromatosis, skeletal dysplasias, osteogenesis imperfecta, and Down syndrome.

 

Neurogenic scoliosis includes causes such as Chiari malformation, syringomyelia, and tethered cord.

 

Kyphosis

 

Kyphosis describes flexion of the spine in the sagittal plane beyond 40 degrees in the thoracic spine.

 

Scheuermann kyphosis involves at least 5 degrees of anterior wedging of three consecutive vertebrae, Schmorl nodes, and endplate irregularities (Sorensen criteria).

 

Congenital kyphosis can occur due to failure of formation of the vertebral body, failure of separation of the anterior vertebral body, or a combination of these.

 

NATURAL HISTORY

 

Idiopathic scoliosis

 

 

Progression has been noted to be associated with growth, with the highest risk at or just after peak height velocity and in large curves.

 

Curves of less than 30 degrees in the thoracic spine do not typically continue to progress after maturity.

 

Curves of 50 to 75 degrees at skeletal maturity, especially thoracic curves, have been noted to consistently progress, with rates of progression of around 1 degree per year. Large deformities in adulthood can cause pain, coronal and/or sagittal imbalance, concerns about appearance, and significant disability.

 

A trend toward increased back pain exists in patients with AIS in adulthood, although most patients stated this pain was moderate or less.14

 

Congenital scoliosis: The greatest rate of progression is seen in patients having a unilateral bar with a contralateral hemivertebra, followed by a unilateral bar, and then by two unilateral hemivertebrae.

 

Scheuermann kyphosis: Patients have a tendency for some increase in kyphosis when followed into adulthood and increased back pain when compared to age-matched cohorts.16

 

Congenital kyphosis: These vertebral malformations have the potential to progress rapidly and result in neurologic compromise, especially the posterolateral quadrant failure of formation type of anomaly.

 

PATIENT HISTORY AND PHYSICAL FINDINGS

 

The initial onset of the spinal deformity can be important for assessing the etiology of the condition (ie, congenital, infantile, juvenile, or adolescent scoliosis).

 

Symptoms such as pain may be related to the spinal deformity or may be a sign of other intraspinal pathology and thus should be evaluated.

 

It is important to assess for symptoms of neurologic compromise, such as bowel or bladder incontinence, numbness, tingling, asymmetric reflexes, or weakness.

 

Evaluate for truncal shift, shoulder height asymmetry, and waist asymmetry, as well as the patient's sagittal alignment for kyphosis and lordosis.

 

On the Adams forward bend test, lumbar or thoracic prominences can be evaluated and provide insight in the rotational deformity of the spine.

 

Understanding the underlying medical conditions of the patient is essential when evaluating the risks and goals of these procedures, for example, presence of congenital heart disease or prior thoracotomy or radiation can increase the risk of scoliosis.

 

IMAGING AND OTHER DIAGNOSTIC STUDIES

 

Full-length posteroanterior (PA) and lateral spine erect x-rays are essential to the evaluation and surgical planning for spinal deformities.

 

Bending, traction, and/or bolster films are helpful in determining the flexibility index of the spine and thus the likelihood that osteotomies may need to be done.

 

With complex congenital abnormalities or deformity, computed tomography (CT) scans with 3-D reconstruction provide additional information about the morphology of the spine.

 

A magnetic resonance imaging (MRI) can reveal intraspinal pathology and further anatomic details. Frequently, these are obtained in individuals requiring significant spinal osteotomies due to concern for intraspinal pathology (eg, syrinx, tethered cord).

 

A dual energy x-ray absorptiometry (DEXA) scan may be valuable if there is concern for underlying osteopenia.

 

Consider echocardiogram and renal ultrasound in patients with congenital scoliosis.

DIFFERENTIAL DIAGNOSIS

Congenital scoliosis or kyphosis

Idiopathic scoliosis: infantile, juvenile, or adolescent Neuromuscular scoliosis

Scheuermann kyphosis Prior spinal fusion

 

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NONOPERATIVE MANAGEMENT

 

Nonoperative management typically consists of observation or bracing.

 

 

Observation is typically indicated for scoliotic curves less than 25 degrees in skeletally immature patients and for thoracic kyphosis of less than 60 degrees.

 

Bracing is indicated in skeletally immature children with scoliotic curves of 25 to 40 degrees. Brace use of 13 to 22 hours per day results in a 90% to 93% success rate in avoiding surgical intervention.15

 

Bracing and physical therapy for Scheuermann kyphosis may be used to assist with pain reduction.

 

SURGICAL MANAGEMENT

 

The main goal of spinal osteotomies is to increase the mobility of the spine to aid with deformity correction.

 

The aim of the correction varies from a complete correction in both the coronal and sagittal planes to a balanced correction. A complete correction aims to achieve a straight spine in the coronal plane with the skull over the pelvis both in the coronal and sagittal planes. A balanced correction improves the deformity by maintaining the skull over the pelvis without a straight spine coronally while keeping the spine in an acceptable sagittal position.

 

Determining which osteotomy to perform largely depends on the anatomy, magnitude of the deformity, underlying cause of the spinal deformity, and the experience of the surgeon.

 

A focal deformity over fewer vertebral segments often requires osteotomies that can create more acute correction such as PSO or VCR.

 

A global deformity over more vertebral levels may be adequately addressed using Ponte osteotomies.

 

Preoperative halo-gravity traction may improve some of the severe spinal deformities to the extent that a VCR is averted.

 

Spinal osteotomies typically involve a learning curve. A pathway in developing the skillset of the spinal osteotomies is shown in FIG 1.

 

Preoperative Planning

 

Review of all medical imaging and understanding of the patient's spinal deformity and anatomy is essential.

 

Determining the osteotomies to be performed and the levels at which they will be performed is important as well as the type and levels of spinal fixation. Identifying levels intraoperatively can be difficult.

 

 

 

FIG 1 • There is a graduated progression of spinal osteotomies in that with increasing spinal destabilization comes increased correction power (and risk).

 

 

A preoperative hemoglobin and hematocrit should be drawn. Autologous donor blood may be obtained. The patient should be typed and screened for potential transfusion. Intraoperative cell salvage machine (cell saver) is used to decrease transfusions. TXA is used intraoperatively to reduce blood loss.

 

 

A preoperative urinalysis evaluating for an active urinary tract infection should be obtained. Metabolic panels and clotting profiles should also be evaluated.

 

Skin of the back is evaluated for possible dermatologic conditions (ie, acne or eczema) preoperatively. In patients with myelomeningocele, soft tissue closure with the aid of a plastic surgeon may be required.

 

Preoperative prophylactic antibiotics are administered according to local hospital guidelines.

 

Positioning

 

For posterior exposures, the patient is positioned prone; intubated; gastric tube, esophageal temperature probe, and Foley catheter placed; blood pressure cuff, electrocardiogram (ECG) leads, and pulse oximetry device applied; and neuromonitoring needles inserted. Baseline neuromonitoring signals may be obtained prior to positioning the patient prone on the operative table.

 

A rolled sponge is placed on the mouth as a guard to prevent laceration to the tongue during TcMEP muscle stimulation.

 

The patient is placed on a translucent table in a prone position to allow unobstructed radiographic visualization (FIG 2).

 

It is important to pad pressure areas including the chest, anterior superior iliac spines (ASIS), and patella. A chest bolster is placed in the area of the expected sagittal apex while ensuring the abdomen is hanging free.

 

Care must be taken with positioning of the face. The eyes are checked throughout the case to ensure no external force is being placed on them.

 

The arms are positioned in 90 degrees of external rotation and shoulder abduction less than 90 degrees with the elbows flexed.

Approach

 

Typically, these osteotomies are performed with a posterior midline approach to the spine, although they are also used with combined anterior and posterior approaches.

 

A posterior midline skin incision is made over the levels to be exposed.

 

 

 

 

FIG 2 • Patient positioned for spinal osteotomy surgery in the prone position on a radiolucent frame. The face and orbits are protected, and chest, hips, knees, and feet are padded. The abdomen should hang free to decrease epidural venous bleeding.

 

 

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Anatomic landmarks

 

 

 

The iliac crest demarcates L4-L5 in most patients. T4 is at the level of the scapular spine.

 

C7 is the vertebra prominens, the most prominent spinal process.

 

Dorsal thoracolumbar fascia is incised at the midline along the length of the skin incision.

 

The spinous processes are identified. The unossified apophysis can be easily identified with either a Kelly clamp or hemostat. It is cut sharply down to the bone either with a scalpel or Bovie. A Cobb elevator is used to separate multifidus from the spinal processes and laminae subperiosteally to the lateral edge of the facet joints laterally. The landmarks are identified in a dry operative field.

 

Ensure the cephalad interspinal and intraspinal ligaments are well preserved to minimize the risk of proximal junctional kyphosis.

 

 

Facet joints capsules are denuded once the spinal level is confirmed with an intraoperative fluoroscopy. Partial facetectomy is performed with either an osteotome or ultrasonic bone scalpel.

Ponte Osteotomy

 

This named osteotomy was described by Alberto Ponte in 1987.

 

The osteotomy was classically described as posterior column shortening procedure in a mobile, nonossified spine for Scheuermann kyphosis. Closed wedge osteotomy is performed segmentally.

 

The osteotomy pivots on the mobile anterior disc and anterior longitudinal ligament that acts as a tension band in assisting closure in the posterior element of the spine. The closing force is created by the moment arm of the instrument used which includes pedicle screws, pedicle hooks, laminar hooks, or transverse hooks.

Improved pedicle screw extenders can magnify the corrective force exponentially. In pediatric patients, anterior column lengthening with the discs “open” anteriorly are observed.13

 

It allows an estimated 5- to 10-degree correction at a spinal unit in the sagittal plane. It is indicated when the deformity is global, long, gradual, and sweeping. It is less useful when the deformity is focal in the sagittal plane.

 

 

 

 

FIG 3 • A,B. Preoperative and postoperative radiographs, respectively, of a patient with congenital scoliosis who underwent a hemivertebra resection. C,D. Preoperative and postoperative radiographs, respectively, of a patient with severe, rigid kyphosis who underwent a PSO and instrumented correction and fusion.

 

 

It has also been used in hypokyphotic AIS to recreate normal kyphosis in a reversed manner.11

 

SPO is similar to Ponte osteotomy and sometimes used interchangeably. It was classically described for ankylosing spondylitis patients with the anterior spinal ligaments ossified and fused. Its extended use includes posterior osteotomy in any adjoining vertebra with fusion seen at the posterior elements.

 

Indications

 

 

 

Stiff AIS with flexibility of less than 50% Hypokyphotic AIS

 

Scheuermann kyphosis

 

Revision surgery for junctional kyphosis

 

Pedicle Subtraction Osteotomy/Hemivertebra Excision

 

Types of PSO

 

 

 

 

Unilateral PSO Asymmetric PSO Symmetric PSO

 

Indications

 

 

Hemivertebra resection is similar in technique to unilateral PSO and most common in congenital scoliosis (FIG 3A,B).

 

 

Asymmetric PSO is indicated in a stiff scoliosis (flexibility of 20% to 40%) with Cobb over 90 degrees. Symmetric PSO is indicated for the following:

 

Severe, rigid Scheuermann kyphosis (FIG 3C,D)

 

Revision scoliosis with significant hypokyphotic thoracic deformity or hyperkyphotic lumbar deformity with fixed sagittal imbalance

 

Vertebral Column Resection

 

Indications

 

 

Stiff scoliosis curve with severe curvature (over 80 degrees) with flexibility of less than 25%.12

 

Fully segmented hemivertebra in which full correction is desirable by resection of entire hemivertebra, discs above and below, and concave disc (FIG 4).

 

 

Circumferentially fused spine (congenital or iatrogenic) Tumor resection for solitary metastasis or primary tumor

 

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FIG 4 • A,B. 3-D CT reconstructions of a patient with a fully segmented hemivertebra and kyphoscoliosis. C,D. Pre- and postoperative erect X-rays of the patient after posterior hemivertebra resection, reconstruction and short-segment fusion with instrumentation.

 

 

TECHNIQUES

• Ponte Osteotomy

  A standard midline approach is used (TECH FIG 1A).

  Resect the inferior articular facets by using an ultrasonic scalpel or chisel bilaterally. Then, extend the resection along the inferior lamina to create a chevron-shaped osteotomy (TECH FIG 1C-E).

  Create an interlaminar window by removing interspinal and intraspinal ligaments (TECH FIG 1B).

  Remove the spinous process with bone cutter to expose the interlaminar space. Keep this bone for use as autologous bone graft.

  Excise the ligamentum flavum with a double-action Leksell rongeur and/or a Kerrison rongeur to expose the underlying epidural fat.

  Place a Woodson dural separator deep to the superior articular facet to protect the exiting nerve root. Use an ultrasonic osteotome or Kerrison rongeur to osteotomize the superior articular facet.

  An epidural vein is commonly present at the lateral edge of the facetal resection. Bleeding is controlled by a combination of bipolar cautery, thrombin-soaked patty, or Gelfoam.

  The exiting nerve roots are decompressed completely.

   

  Multiple symmetric V-shaped gutters are formed, with complete resection of the articular facets bilaterally and spinous processes (TECH FIG 1F-J). In patients with scoliosis, crowding of structures at the concavity of the curve will result in an asymmetric V-shaped gutters; this will aid in coronal correction with distraction.

   

  In an AIS patient with hypokyphosis, the thoracic segment typically has a more lordotic appearance (TECH FIG 1K).

   

  Undercut the osteotomized lamina margin to avoid dural impingement during the closure of the osteotomy.

   

  Pedicle instrumentation is performed at all levels of the Ponte osteotomy. The entry point is created with a burr. In our practice, the freehand technique for pedicle screw insertion is used.

   

  In Scheuermann kyphosis, cantilever reduction technique is used to assist in reduction. Reduction pedicle screws are placed

   

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  strategically at the most caudal levels. Load-sharing principle is followed during reduction.

   

   

   

   

  TECH FIG 1 • Ponte osteotomy. A. The posterior elements of the spine are shown after soft tissue exposure and hemostasis. B. Creating interlaminar window in Ponte osteotomy. C. Removal of the ligamentum flavum with a Kerrison rongeur. D. Removal of the facet with a narrow, double-action Leksell rongeur. E. Completed osteotomy with Gelfoam in vertebral interspace. (continued)

   

   

   

  TECH FIG 1 • (continued) F. Multiple chevron-shaped Ponte posterior column osteotomies used in this case of Scheuermann kyphosis. G,H. Spinous process and inferior facet resection. I,J. Completion of facetectomies with superior articular process and pars interarticularis resection. K. Oblique view of pedicle screw insertion after multiple Ponte osteotomies and distraction for a typical AIS case. (G-K: Courtesy of James Millerick.)

   

   

  In a patient with AIS with hypokyphotic thoracic sagittal alignment, the reduction is achieved first by insetting the concave rod, which is contoured hyperkyphotically. The rod is captured by the pedicle screws mainly by translation. The convex rod, which is contoured hypokyphotically, is reduced by cantilever technique. Differential rod contouring helps to restore the sagittal alignment while achieving derotation. Segmental derotation is performed for further correction in the axial plane if needed.

   

  Negatively charged tricalcium phosphate silica bone graft substitute is placed over the sites of Ponte osteotomy to prevent unwanted ossification in the spinal canal while encouraging fusion externally at the posterior elements.

   

  Decortication of the remaining spinal processes and posterior elements is performed followed by bone grafting. Vancomycin powder is mixed in with the bone graft.

   

   

  Layered closure is performed with the goal of a watertight closure. Placement of drain is controversial and is not part of our practice.

• Hemivertebra Excision

   

  Patient is positioned and a midline posterior approach performed.

   

  Pedicle screws instrumentation is performed with the freehand technique one or two levels cephalad and caudad to the level of interest depending on the indications. (Longer fusions to span the deformity are needed in patients with contralateral bar formation and rib synostosis.)

   

  Perform a partial facetectomy with either chisel or ultrasonic osteotome at the level above and below the

  hemivertebra to expose the underlying superior articular facets.

   

  The pedicle of the hemivertebra at the level of interest is cannulated with a pedicle probe prior to further releases.

   

   

  Ponte osteotomy is performed at the level of interest and one or two levels above and below it. Remove the caudal half of the hemilamina above and cephalad half of the hemilamina below.

   

  Complete hemilaminectomy at the hemivertebra level is done by thinning the lamina with a small rongeur and burr and finally resecting it piecemeal with a Kerrison rongeur.

   

   

  A temporary rod is inserted on the opposite array of pedicle screws prior to further destabilization. The pedicle is disconnected from all the posterior elements.

   

  At the thoracic level, costotransversectomy is performed for one or two levels depending on the size of the hemivertebra.

   

  Sharp dissection along the axis of the rib for about 2 to 3 cm on the bony surface 2 to 3 cm laterally from the costotransverse joint.

   

  Subperiosteal dissection using Alexander elevator around the rib segment, taking care to preserve the neurovascular bundle along the inferior costal margin of the rib.

   

  The rib is resected with a Giertz-Stille rib cutter or ultrasonic osteotome.

   

   

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  The transverse process of the thoracic rib is amputated using ultrasonic osteotome or conventional osteotome.

   

  The costotransverse joint and costovertebral joint are dissociated with a combination of sharp and blunt dissection.

   

  The extracavitary approach allows extrapleural approach to the lateral aspect of the pedicle and lateral part of the vertebral body.

   

  At the lumbar region, the transverse process is amputated at the base. The exiting nerve root from the hemivertebral level is protected. The psoas muscle is separated from the vertebral body with periosteal elevator subperiosteally. The retroperitoneal plane is developed into the ventral aspect. The plane is kept opened with a pair of specialized angled retractors or malleable retractors.

   

  Decancellation of the vertebral body using eggshell technique

   

  The pedicle track is expanded with a series of curettes while maintaining the integrity of the pedicle walls. This allows access to the vertebral body. The cancellous bone at the vertebral body is shelled out with curettes of various sizes and angles without breaching the cortex.

   

  The lateral wall of the pedicle is intentionally breached. This facilitates the lateral angulation of the curette to reach the medial limit of the hemivertebra.

   

  The concavity of the deformity acts as a pivot for closure. A curette is placed as medially as possible intraosseously at the hemivertebra. This is confirmed with an intraoperative fluoroscopy.

   

  Care is taken to preserve the posterior cortex of the vertebral body and medial and inferior walls of the pedicle until the last stage of the operation. The former two protect the dura, whereas the latter protects the exiting nerve root.

   

  The discs cephalad and caudad to the hemivertebra are removed.

   

  The inferior wall of the pedicle is removed with Kerrison rongeur while protecting the exiting nerve root. This is followed by the medial wall.

   

  A posterior tamp is used to collapse dorsal cortex of the vertebral body anteriorly to the shell-out vertebral

  body. The fracture wall is then removed.

   

  A temporary rod is placed at the ipsilateral pedicle screws.

   

  Gradual compression is performed across the osteotomy site to close it.

   

  The temporary rods are exchanged out with permanent rods and final compression/distraction is performed for correction (see FIG 4C,D).

• Symmetric and Asymmetric Pedicle Subtraction Osteotomy

   

  Patient is prepared, exposed as discussed earlier.

   

  Ponte osteotomy is performed at the apex of the deformity.

   

  Pedicles are cannulated with the freehand technique spanning two or three levels cephalad and caudad to the level of interest.

   

  The pedicles at the level of interest are disconnected from the posterior element as detailed earlier. Caudal half of the lamina above the level of interest is resected to avoid impingement during closure.

   

  At the thoracic level, two-level costotransversectomy centered at the level of PSO is performed. Extracavitary approach is developed.

   

  At the lumbar region, the transverse processes are amputated at the base. The exiting nerve roots from the cephalad level are protected. The psoas muscles are separated from the vertebral body with periosteal elevator subperiosteally. The plane is developed into the ventral aspect bilaterally. The plane is kept opened with a specialized retractor or a malleable retractor.

   

  Decancellation of the vertebral body is performed bilaterally from the pedicles with series of curette of different sizes. Ensure the posterior wall is thinned with reverse curette.

   

  A symmetric wedge of bone or asymmetric wedge of bone is removed with small osteotome bilaterally. The first cut is at the superior roof of the foramen parallel to the superior endplate. The second cut is wedge-shaped. Asymmetric wedge is created in patient with concurrent coronal deformity.

   

  The posterior wall is fractured with a posterior tamp anteriorly.

   

   

   

  The wedge of bone is removed piecemeal with curettes, reverse curettes, and pituitary rongeurs. The temporary rods are compressed sequentially. Dura is inspected and palpated gently for buckling. The temporary rods are sequentially exchanged out for full-length, precontoured, permanent rods.

   

  The dura is covered.

   

   

  Bridging autologous rib grafts are placed across the resection site. A layered closure is performed.

• Vertebral Column Resection

 

Patient is positioned and exposed as described in the previous section.

 

Ponte osteotomy is performed at the apical region of the deformity as detailed previously.

 

Pedicles spanning three or four levels cephalad and caudad to the level of interest are cannulated with pedicle gearshift via the freehand technique, taking care to preserve the medial wall of the pedicles especially at the level of VCR.

 

At the thoracic level, three-level costotransversectomy centered at the level of VCR is performed (TECH FIG 2A).

 

At the lumbar region, the transverse processes are amputated at the base. The exiting nerve roots from the cephalad level are protected. The psoas muscles are separated from the vertebral body with periosteal elevator subperiosteally.

 

Pedicle screws are inserted at the levels both cephalad and caudad to the level of resection.

 

Complete laminectomy is performed at the level of interest. The caudad portion of the lamina above and the cephalad portion of the lamina below are also resected (TECH FIG 2B).

 

P.744

 

 

 

TECH FIG 2 • Important sequential steps in VCR in the thoracic spine. A. Bilateral transverse process and rib head resection to allow exposure of the lateral vertebral walls. B. Shaded area indicates laminectomy needed for dural exposure. C. Pedicles are resected and thoracic nerve roots are tied off. D. Blunt finger dissection of lateral and anterior vertebral body prior to retractor placement. E. With the dura protected and temporary rods implanted to prevent spinal instability, the vertebral body is resected with a burr, rongeurs, or ultrasonic device. F. A structural cage filled with autologous bone is placed anteriorly to provide anterior column support and prevent excessive spinal shortening; additional autograft cancellous bone is placed around the cage and laterally. G. The temporary stabilizing rods are replaced with the final rods, and compression/distraction is performed as needed for correction; dura is inspected for compression or buckling. (Courtesy of James Millerick.)

 

 

Thoracic roots may be sacrificed and ligated sharply between ties to improve the working space.

 

The pedicles are disconnected from the posterior elements (TECH FIG 2C); TcMEPs are reconfirmed, and the mean arterial pressure (MAP) is raised to over 80 mm Hg.

 

 

A single temporary rod is placed on the convexity of the curve to maintain stability. Lateral vertebral walls are dissected.

 

The dissection is completed with blunt dissection using index fingers from the subperiosteal plane developed, aiming to meet the tips of fingers at the ventral aspect of the vertebral body (TECH FIG 2D).

 

This plane is kept open with specialized retractors.

 

Vertebral body is decancellated with a series of curettes, reverse curettes, and pituitary rongeurs via the pedicle (TECH FIG 2E). Posterior wall of the vertebral body is thinned out with the reverse curettes.

Pedicle is then removed leaving the medial wall of the pedicle and posterior wall of the vertebral body intact to protect the dura and spinal cord.

 

Cephalad and caudal discectomies are performed bilaterally.

 

Medial wall of the pedicle is carefully removed with 2-mm Kerrison rongeur, whereas the posterior wall is pushed anteriorly with a posterior tamp.

 

The convex temporary rod is compressed.

 

A cage filled with morselized autologous graft is inserted into the void (TECH FIG 2F). Additional tricortical autograft from the resected rib can be placed.

 

Both temporary rods are secured.

 

The temporary rods are compress sequentially. Dura is inspected and palpated gently for buckling with a Penfield elevator.

 

 

The temporary rods are sequentially exchanged out for full-length, permanent rods (TECH FIG 2G). The dura is covered.

 

 

Bridging autologous rib grafts are placed across the resection site. A layered closure is performed (TECH FIG 3).

 

P.745

 

TECH FIG 3 • A. Achondroplastic patient with severe thoracolumbar kyphosis. B. This was corrected with posterior VCR at T12, L1, and L2 (grade 6 osteotomy) and posterior instrumented fusion.

 

 

 

PEARLS AND PITFALLS
	All spinal osteotomies ▪ Exposure at a wrong level may result in premature autofusion in pediatric patients. Maintain normotensive anesthesia with MAP of at least 75-80 mm Hg during osteotomy. On table traction with skull tong and femoral skin or skeletal traction assist in spinal reduction. Neuromonitoring is essential throughout the procedure. Prepositioning baseline is needed in patients with large curve. Monitoring should not cease till the closure of the skin.     Ponte osteotomy ▪ Ultrasonic osteotome resection minimizes epidural bleeding during facet resection. It is particularly useful in the concave part of the scoliosis where there is often crowding of dysplastic structures. Symmetric resection of the articular facet processes is essential to

 

 

 

 

	preserve coronal balance in Scheuermann kyphosis.     Pedicle subtraction ▪ Temporary rods can be overbent at the coronal plane at the concavity osteotomy— of the curve to improve the working space at the hemivertebra. unilateral     VCR ▪ Thoracic exiting nerve roots could be sacrificed to create more working space. The nerve is sharply ligated between ties. Temporary rod is necessary to prevent translation during destabilization. Care is taken to avoid spinal translation during reduction. The caudal segment often translates posteriorly, whereas the rostral segment often translates anteriorly.     What do you do ▪ Check neuromonitoring equipment. when the ▪ Reverse the last step in the reduction. neuromonitoring ▪ Increase the patient's blood pressure. signals disappear? ▪ Ensure patient is normothermic. Transfuse patient to maintain hemoglobin. Ensure adequate decompression at the site of osteotomy. Loosen the set screws. Remove the reduction rods if needed (in a stable spine). Ensure proper decompression and avoid dural buckling. Order a Stagnara wake-up test.

 

 

 

P.746

POSTOPERATIVE CARE

 

Postoperative care may vary based on the patient's preoperative status and intraoperative findings.

 

 

Bracing is usually not necessary with stable spinal instrumentation and fusion. The ultimate plan should be individually tailored according to patient's demand and situation.

 

Perioperative antibiotics are continued for 24 hours postoperatively.

 

The patients are mobilized to a chair on postoperative day 1 and begin walking on postoperative day 2. They are allowed to weight bear as tolerated and ambulate as tolerated.

 

At 6 months, patients are allowed to return to most sports.

OUTCOMES

Spinal osteotomies have considerable morbidity with increased operative time and blood loss.

Geck at al5 reported an average correction of 9.3 degrees per osteotomy for Ponte osteotomy at 2-year follow-up. There were no reoperations for nonunion or instrumentation failure. None of the patients had neurologic complications. One case of delayed infection in the cohort of 17 patients was reported. Two (12%) of the patients had junctional kyphosis.

In hemivertebra resection, 70% main curve correction rate can be expected in children aged 1 to 6

 

years.10 In this cohort of 28 patients, Ruf and Harms10 reported one case of infection, two pedicle fractures, and three implant failures.

A recent study evaluating the complications of VCR by a group of experienced surgeons from multiple

centers was reported by Lenke et al.9 The average operative time was 545 minutes and estimated blood loss averaged 1610 mL. Six of the 147 patients underwent an operative irrigation and débridement for wound infection. Overall, the complication rate was 58% and a third of the cases had IONM changes; fortunately, there were no permanent neurologic deficits in this series.

These techniques should be used by individuals familiar with the procedures and the inherent complications.

 

 

COMPLICATIONS

Neurologic injury Pseudarthrosis Hardware failure Loss of correction Infection

Proximal or distal junctional kyphosis or progressive scoliosis Pneumothorax

Great vessel injury Pancreatitis

Superior mesenteric syndrome

 

 

REFERENCES

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2. Cheh G, Lenke LG, Padberg AM, et al. Loss of spinal cord monitoring signals in children during thoracic kyphosis correction with spinal osteotomy: why does it occur and what should you do? Spine 2013; 33:1093-1099.

    

    

3. Cook SM, Asher M, Lai S, et al. Reoperation after primary posterior instrumentation and fusion for idiopathic scoliosis. Toward defining late operative site pain of unknown cause. Spine 2000;25:463-468.

    

    

4. Dimeglio A. Growth of the spine before age 5 years. J Pediatr Orthop B 1992;1:102-107.

    

    

5. Geck MJ, Macagno A, Ponte A, et al The Ponte procedure: posterior only treatment of Scheuermann's kyphosis using segmental posterior shortening and pedicle screw instrumentation. J Spinal Disorders Techniques 2007;20:586-593.

    

    

6. Joseph SA Jr, Moreno AP, Brandoff J, et al. Sagittal plane deformity in the adult patient. J Am Acad Orthop

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7. Karol LA, Johnston C, Mladenov K, et al. Pulmonary function following early thoracic fusion in non-neuromuscular scoliosis. J Bone Joint Surg Am 2008;90:1272-1281.

    

    

8. Kim YJ, Lenke LG, Bridwell KH, et al. Free hand pedicle screw placement in the thoracic spine: is it safe?

   Spine 2004;29:333-342.

    

    

9. Lenke LG, Newton PO, Sucato DJ, et al. Complications after 147 consecutive vertebral column resections for severe pediatric spinal deformity: a multicenter analysis. Spine 2013;38:119-132.

    

    

10. Ruf M, Harms J. Posterior hemivertebra resection with transpedicular instrumentation: early correction in children aged 1 to 6 years. Spine 2003;28:2132-2138.

     

     

11. Shah SA, Dhawale AA, Oda JE, et al. Ponte osteotomies with pedicle screw instrumentation in the treatment of adolescent idiopathic scoliosis. J Spine Deformity 2013;1:196-204.

     

     

12. Suk SI, Chung ER, Kim JH, et al. Posterior vertebral column resection for severe rigid scoliosis. Spine 2005;30:1682-1687.

     

     

13. Tsutsui S, Pawelek JB, Bastrom TP, et al. Do discs “open” anteriorly with posterior-only correction of Scheuermann's kyphosis? Spine 2011; 36:E1086-E1092.

     

     

14. Weinstein SL, Dolan LA, Spratt KF, et al. Health and function of patients with untreated idiopathic scoliosis: a 50-year natural history study. JAMA 2003;289:559-567.

     

     

15. Weinstein SL, Dolan LA, Wright JG, et al. Effects of bracing in adolescents with idiopathic scoliosis. N Engl J Med 2013;369:1512-1521.

     

     

16. Wood KB, Melikian R, Villamil F. Adult Scheuermann kyphosis: evaluation, management, and new developments. J Am Acad Orthop Surg 2012;20:113-121.