Posterior Osteotomies of the Spine
Daniel Grant
Leok-Lim Lau
Suken A. Shah
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.
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 body
Partial wedge resection of the posterior vertebral body and posterior elements with pedicles (PSO)
4
Pedicel/partial body/disc
Wider wedge resection of a substantial portion of the vertebral body, 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.
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.
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.Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
