CONGENITAL SCOLIOSIS

Congenital scoliosis is a lateral curvature of the spine that occurs as a result of an abnormal vertebral development. Although the defect is present at birth, the abnormality often does not become evident until later growth when an obvious deformity has occurred. Vertebral anomalies causing congenital scoliosis occur through a failure of formation, or a failure of segmentation, or a combination of both.

The prognosis and treatment of the defect relies on assessment of the natural history of specific vertebral anomalies. Early researchers believed congenital scoliosis to be a relatively benign condition with little chance to cause subsequent deformity. Later classic studies have shown consistently, that the contrary is true. McMaster demonstrated that the majority of curves are progressive while only twenty-five percent are nonprogressive.  These authors found that approximately 75% of patients required treatment, and 85% of those untreated progressed to have curves above 40º by maturity.

The tendency to progress is influenced by the type of vertebral anomalies, the location of the defection, and patient’s growth potential. Therefore, an understanding of the natural history of the congenital vertebral anomaly is crucial in order to optimize treatment. The goal of treatment whether operative or non-operative are to achieve or to preserve a stable, balanced spine both in the coronal and sagittal planes, to preserve lung development, and function.

EMBRYOLOGY

Failure of the normal development of the spine in utero leads to vertebral anomalies that may result in congenital scoliosis. Formation of the spine begins during the 4th week of intrauterine development. At this time, the mesoderm differentiates into three areas on either side of the notochord- paraxial, intermediate, and lateral mesoderm. At five weeks, 42 to 44 pairs of somites will form from the paraxial mesoderm. These somites help to structure the vertebra, the bones of the head and the thoracic region and its associated musculature. Each somite differentiates into sclerotome and dermomyotome. The sclerotome is accountable for the development of the spine. The dermomyotome develop the muscle cells and the overlying skin. The cells of sclerotome then migrate towards and around the notochord and neural tube. Once all sclerotomes have migrated, each level will divide into a cranial area of loosely packed cells and a caudal area of densely packed cells. These two layers of cells will form the intervertebral disc. The space between these two layers has been described as a “cell-free space”.

The “cell-free space” is filled with cells migrating cranially from the caudal densely packed layer and forms the annulus fibrosus. The nucleus pulposus is formed inside the annulus from notochord that has not deteriorated. This development extends to such an extent that the caudal portion of one sclerotome condenses with the cephalic portion of the adjacent sclerotome. This condensation forms the precartilaginous vertebral body. Therefore, one complete vertebra requires two somites to interact with each other in order to develop normally.  Failure of this segmentation may result in a congenital bar.

Fusion of adjacent sclerotomes creates the centrum, which further develops into the vertebral body. The cells that originally migrated to the neural tube form the neural arches, which serve to protect the spinal cord, vessels, and nerve roots. These arches consist of two pedicles and right and left laminae. The centrum and the two halves of the vertebral arches develop separately and then to fuse to one another.

Chondrification and then ossification begins during the sixth week after cells have migrated and vertebral structures have begun to fuse. This process is signaled by the notochord and neural tube which initiates the disintegration of the notochord. Primary ossification centers are located, one at the centrum, and one at each side of the vertebral arch. There are also five secondary ossification centers that contribute to the development of growth plates. Failure of formation or the presence of any asymmetry of growth plates or any defect in both chondrification and ossification centers may contribute to a congenital malformation. 

The nervous system of the fetus is derived from the surface ectoderm during the third week of gestation. The neural groove is formed by signals from the notochord and mesenchymal cells. This groove is then folded into a tube which represents the central nervous system. Subsequently, the peripheral nervous system develops from neural crest cells that migrated during the folding process. As the embryo develops, the spinal cord ascends in the canal.

As mentioned previously, the paraxial mesoderm is responsible for the formation of the vertebrae as well as the connective tissue, skin, striated muscle, and the muscles of the head. The other two areas of mesoderm, the intermediate and lateral, are involved in development of the urogenital, pulmonary, and cardiac as well as other systems. Therefore, any abnormality affecting the development of the mesenchyme responsible for bony formation of the spine may also be responsible for defects in other organ systems, such as cardiac, urogenital, and central nervous system defects.

CLASSIFICATION

The natural history of the congenital scoliosis is to great extent determined by the type of vertebral malformation. Abnormalities of the spine can be classified into three main categories:

defects of formation,
defects of segmentation, and
neural defect (not discussed in this review).

Eighty percent of deformities can be classified using this generalization. The remaining 20% represent a combination of anomalies or are too severe to classify. The specific type of deformity has prognostic value and the choice of treatment protocol is based upon identifying the type of anomaly present. 

Defects of Vertebral Formation

Failure of formation is due to a defect of a structural component of a vertebra. This may present as an absence of any portion of the vertebra including: the anterior, anterolateral, posterior, posterolateral, and lateral portions. Thus, the type of deformity (i.e. Scoliosis, kyphosis, or kyphoscoliosis) depends on the area affected or the regions in which the normal growth is altered. One of the most common causes of congenital scoliosis is the presence of hemivertebra. This anomaly represents a unilateral failure of formation of the lateral half of the vertebral body and its associated pedicle and hemilamina. Unilateral rib is usually associated with the existing vertebral body if the anomaly is located in thoracic spine. A wedge vertebra is usually due to a unilateral partial failure of formation of one of the chondrification centers. The hemivertebra may be associated with different degrees of segmentation and the sub-classification determines the likelihood and degree of curve progression. A hemivertebra can be fully segmented, semi-segmented, or nonsegmented. A posterior based hemivertebra (anterior failure of formation) results in congenital kyphosis (not discussed in this review).

Fully Segmented Hemivetebra

A fully segmented hemivertebra has normal disc spaces and growth plates at the cephalad and caudad positions. It is completely separate from the adjacent vertebral bodies allowing growth to occur at both the upper and lower poles. The fully segmented hemivertebra acts as a wedge as it grows producing a curve that commonly deteriorates steadily at 1 to 2 degrees per year. 9 8 Lower thoracic and thoracolumbar region anomalies may progress faster. The lower lumbar anomaly may cause torso decompensation as a result of oblique take of the spine from the sacrum. If two hemivertebra are located on one side with in curvature, progression is likely to be greater than if only one defect is present.

Semi-Segmented Hemivertebra

A partially segmented hemivertebra is fused to one of the adjacent vertebral bodies. It has only one functional disc, either cephalad or caudad. These curves progress less rapidly and are usually less than 40 degrees at skeletal maturity

Non-Segmented Hemivertebra

A nonsegmented hemivertebra is fused to the neighboring vertebrae at both the cephalad and caudad poles. Therefore, there are no disc spaces and growth plates associated with this type of anomalous vertebral body. This vertebral body has little growth potential and is associated with minimal progression.

Incarcerated Hemivertebra

An incarcerated hemivertebra is smaller and more ovoid in shape than the non-segmented hemivertebra. The adjacent vertebral bodies conform in their shape which tends to compensate for the mal-developed hemivertebra which is “tucked into” the spinal column. Although this type of anomaly is associated with cephalad and caudad disc spaces, these spaces are usually narrow and have poor growth potential. The pedicle of an incarcerated hemivertebra is in line with adjacent pedicles. Curvature associated with this anomaly may slowly progress but rarely exceeds 20 degrees in magnitude.

Non-incarcerated Hemivertbra

A nonincarcerated hemivertebra has a pedicle that is outside the pedicle line of adjacent levels and tends to be fully segmented. Associated curvatures have greater potential for progression than with incarcerated hemivertebra. The anomaly is usually fully segmented.

Hemimetameric Shift

Multiple hemivertebra can exist either on one side or on contralateral sides of the spinal column. In hemimetameric shift (HMMS) or hemimetameric segmental displacement, two or more hemivertebra are present on contralateral sides of the spine and there is at least one normal vertebra between them. As previously mentioned, two pairs of somites form one segmental spinal unit. Some believe that the simultaneous development of these matching somite pairs occur independently. A caudal shift of a somite pair can occur if these somites are not at the same developmental phase. Therefore, there will be a shift back at a more caudal level and a mismatch. If further insult occurs at the critical time of formation, hemivertebra are produced on contralateral sides of the spine. This is found in up to 11% to 15% of cases of congenital scoliosis. It is more common in thoracic region where it tends to have a more benign course. However, hemivertebra located at the lumbosacral junction or those far from each other tend to lead to more rapid progression of the deformity, often requiring surgical intervention. 5

Defects of Vertebral Segmentation

Failure of segmentation occur when adjacent somites or their related mesenchyme fail to fully separate, this results in the partial or complete loss of a growth plate in the affected area. Fusion of the facets and disc spaces occurs on the affected side of the vertebral column and curve progression is dependent on the location and the number of vertebrae affected. It may occur the unilaterally or bilaterally.

Unilateral Failure of Segmentation

Unilateral failure of segmentation results in the formation of a unilateral bar, one of the most common causes of congenital scoliosis. [4 5 11 12] A bar lacks longitudinal growth while the unaffected side is permitted to grow, leading to the development of a scoliotic deformity. The degree of deterioration is based upon the rate of growth of the unaffected side and the extent of involvement of the unsegmented bar. Associated curves tend to progress rapidly at a rate of 2º to 6º per year. By 10 years of age, most curves exceed 50 degrees. This anomaly may not be evident on radiographs until it ossifies around the age of 3 to 4 years.

A small percentage of patients may possess a combination of defects of both formation and segmentation, creating a complex structural abnormality. It is possible to encounter patients with a unilateral unsegmented bar and a contralateral hemivertebra located in the convexity of the curve at the same level as the bar. This anomaly occurs in approximately 11% of cases of congenital scoliosis. It has the highest risk of progression and produces the most serious degree of deformity of all of the anomaly subtypes. These curves progress at an average of 6 degrees per year, and in the thoracolumbar spine, up to 14 degrees per year. They may exceed 60 degrees by age 4. [4 5 8 9 10 11 12]

Bilateral Failure of Formation

Bilateral failure of vertebral segmentation leads to the formation of a block vertebra. The associated disc spaces are narrow or fused. The symmetrical bilateral restriction of longitudinal growth leads to the development of a shortened segment without significant scoliosis. This anomaly may occur in the cervical spine. If multiple cervical vertebrae are involved, it is termed Klippel-Feil syndrome. 7 On occasion, the growth arrest is asymmetric. However, the curves that result from this asymmetry progress slowly and usually do not exceed 20 degrees in magnitude. [4 5 8 10 11 12]

ETIOLOGY

Although some rare hereditary syndromes (e.g. Jarcho-Levin syndrome, spondylocostal dysostosis, Klippel-Feil syndrome) are associated with congenital scoliosis, it is generally thought that the defects of congenital scoliosis and the result of an intrauterine environmental insult that occurs during crucial periods of spinal development. Originally, it was believed that there was a hereditary origin of congenital scoliosis in up to 5%-10% of cases. Studies have shown that an anomaly present in one monozygotic twin is usually not present in the other. Recently, abnormalities of genes involved in mouse somitogenesis have been found in association with human spinal deformities. Disrupting genes in the “notch pathway”, involved in somatogenesis, produces somite segmentation defects and vertebral anomalies in mice. Therefore, an interaction of environmental factors and the genes that play a role in regulation of somite segmentation is thought to occur in congenital vertebral deformities such as congenital scoliosis. There is not likely to be a sole factor involved in its pathogensis. Animal studies have also shown that a hypoxic insult at the development stage equivalent to a 6 week human embryo causes spinal anomalies similar to those seen in congenital scoliosis. Fetal exposure to thalidomide, lovastatin, or certain progestron/estrogen compounds may increase the incidence of these anomalies as well. In summary, the majority of vertebral anomalies have a multifactorial basis. 

NATURAL HISTORY

The clinical manifestations of congenital vertebral anomalies, such as progressive scoliosis and spinal deformity, occur as a result of asymmetrical spinal growth in and around anomalous vertebrae. The sum total growth of the spine occurs at the endplate surfaces of the vertebrae. Therefore, congenital scoliosis results from an asymmetric deficiency in either the number of growth plates or their rate of growth. It was originally thought to be a benign condition, but this is clearly false for many patients. 3 4 5 Winter, et al. noted that 25% of cases were not progressive, 25% progressed slowly, and 50% progressed rapidly. McMasters and Ohtsuka found that 11% of their patients did not have curve progression, 14% progressed slowly, and 75% progressed rapidly, requiring surgical intervention. They noted that 36% of those treated no-operatively had curvature of 40º-60º and 28% had curvature greater than 60º at skeletal maturity. They also observed that congenital deformity tended to be more rigid and structural curve compared to other types of pediatric scoliosis.

The prognosis for curve progression in patients with congenital scoliosis is based upon 3 factors: the type of anomaly, the location of the anomaly, and the age of the patient.  A unilateral unsegmented bar with contralateral hemivertabra has the worst prognosis for curve progression, while block vertebra has the most benign curve. [11 12 14] A curve can occur in the upper thoracic (33%), lower thoracic (31%), thoracolumbar (20%), lumbar (11%), or lumbosacral (5%) spine. Thoracolumbar curves have the greater tendency to progress followed by lower thoracic and upper thoracic curves. Deformity progression may occur through skeletal maturity and beyond.  Curve progression is most likely to occur during two periods of accelerated growth. The first of these periods is within the first two years of life, during which most curves become evident. The second period occurs during the adolescent growth spurt, between ages 10 to 13 in females and approximately 2 years later in males. This progression may also be seen after maturity in severe deformity. 5 10

ASSOCIATED ANOMALIES

Various extra-spinal and spinal anomalies may be associated with congenital scoliosis. The genitourinary tract, cardiac system, and spinal cord are the most common sites for these abnormalities. The incidence of these associated anomalies has been estimated to be between 30% to 60%. The VACTERL syndrome is one the most common associated syndrome. It includes vertebral anomalies, imperforate anus, cardiac abnormalities, tracheoesophageal fistula, renal dysplasia, and limb malformations. One study noted a 61% incident of this syndrome in congenital scoliosis. The Klippel-Feil syndrome in which associated congenital fusion of cervical vertebra is found may be noted. This syndrome has been classically identified by its triad of low posterior hair line and short and stiff neck. 7 Sprengle deformity, an elevation of the scapula, is caused by failure of proper descent of the scapula in utero. This is believed to be due to a similar process of failure of segmentation seen in congenital spinal anomalies. Goldenhar syndrome or oculoauricular vertebral dysplasia is uncommonly foundings. It consists of unilateral malformation of the ear and facial hypoplasia with associated upper thoracic congenital scoliosis.

Rib anomalies such as absent ribs, extra ribs, or rib synostosis are also commonly associated with congenital scoliosis. Severe deformation of the rib cage may occur as a result of large thoracic curvature. If this proceeds before age 8, it may interfere with pulmonary development and results in restrictive lung disease. In spondylothoracic dysostosis or Jarcho-Levin syndrome (right), there are multiple associated posterior rib fusions which constrict the thorax and eventually results in respiratory failure. In spondylocostal dysostosis, the ribs are not severely involved but there is marked shortening of the trunk.

Intraspinal abnormality has been associated with congential scoliosis at rates ranging between 18% and 58%. 22   This is due to the close linkage of the development of the spinal cord with that of vertebral column. It is important to detect these anomalies because they may restrict the movement of the spinal cord, potentially causing neurologic abnormality with corrective surgery.

Diastematom yelia is a sagittal split in either the spinal cord or cauda equina. This split is caused by an osseous or fibrocartilagenous spur arising from adjacent vertebral bodies. Tethered cord may be caused by fibrous bands, a tight filum terminale, ectopic nerve root, or arachnoid adhesions or may be associated with diastematomyelia. The incidence of intraspinal anomalies in decreasing frequency is tethered cord, diastematomyelia, syringomyelia, diplomyelia (true division of the cord), and low lying conus. 26 27 Basu, et al. found the incidence of intraspinal abnormality to be higher among patients with deformities classified as failure of formation. Diastematomyelia is associated with unilateral bar with contralateral hemivertebra. 22 Interestingly, a hemimetamaric shift pattern has a very low association with intraspinal anomalies of 6%. 13

Although spina bifida occulta and more significant vertebral anomalies have a similar etiology, a recent study by Winter et al showed no significant relationship between these two.

Other Congenital Defects

Defects of other organ systems are found in up to 30% to 60% of patients with congenital scoliosis. 22 22 23   Genitourinary system anomalies present in 20% to 40% of patients. This high incidence is due to the fact that the mesoderm is responsible for formation of both vertebrae and the mesonephron, the predecessor of the genitourinary system. The medial region of the mesoderm forms the vertebrae and the anterolateral area forms the mesonephron. The most common genitourinary abnormality is renal hypoplasia. Horseshoe kidney, unilateral renal agenesis, ectopic kidney, duplication, urethral anomalies, and reflux are also associated with congenital scoliosis. Recognition of this association is important in this patient population because up to 25% of these anomalies require interventional therapy such as surgery or hemodialysis.

Congenital heart defects are also found to be associated with the presence of congenital scoliosis at rates up to 26%. 22 Congenital heart defects are also associated with the presence of Klippel-Feil syndrome. Severe curvature may exacerbate existing cardiopulmonary dysfunction. 33 These anomalies may be fatal and early recognition is essential.

Other rare anomalies are associated with congenital scoliosis such as absent uterus and vagina, cleft palate, cleft lip, preauricular ear tags, and mandibular hypoplasia.

PATIENT EVALUATION

The evaluation of the patient with congenital scoliosis must include an assessment for associated anomalies. A thorough history regarding prenatal drug exposure, pre and post natal development, past medical history, ambulatory status and balance, neurological development, and other systemic reviews including genitourinary and cardiopulmonary systems should be performed. 

The patient examination should include an assessment of general appearance to observe for facial and trunk abnormalities or limb deficiency. The skin should be assessed. Mid line skin abnormalities such as a dimple, nevus, hairy patch, sinus tract, or lipoma may indicate the presence of an intraspinal anomaly. Gait is evaluated to rule out neurological or lower extremity abnormalities. A thorough neurologic evaluation including motor, sensory, and reflex examination should be done. Pathological reflexes such as ankle clonus and Babinski reflexes are assessed. Subtle neurological abnormality may be indicated by the presence of asymmetric calf and/ or thigh circumference, cavus foot, curled toes, and/ or mild limp. The spine is evaluated with patient in a standing position. Shoulder, scapula, waist asymmetry, and torso decompensation is often noted. The shoulder is elevated on the side of the curve convexity and the head is often tilted to the concavity. A forward bending test is done to evaluate for associated rib deformity. In some cases, the rib deformity may be minimal despite significant scoliosis due to a lack of rotational deformity. Pelvic obliquity may be seen with rigid lumbar or lumbosacral curves.

Spinal radiographs should be performed in all patients with suspected congenital scoliosis. They are necessary to identify the types and the locations of curves present. High quality standing or sitting upright (for non-ambulators) anteroposteior and lateral radiographs on a 14 x 56 inch film should be obtained. Careful examination of the lateral radiograph for presence of concomitant kyphosis or lordosis should be included in the radiographic assessment.  A posterolateral quadrant or corner hemivertebra may be missed resulting in progressive kyphoscoliosis if the lateral raiodiograph is not examined carefully. A coned-down radiograph is also helpful in defining the spinal anomaly (ies). After identifying the type of anomaly on the anteroposterior radiograph, the number of viable growth plates should be determined on either side of spine to assess the potential for growth imbalance and progressive curvature. A high quality MRI or CT scan with coronal and sagittal reformats may assist in this regard. 

Descriptions of curves are determined based on the direction in which the apex points, the levels in which the primary curves occur, presence of compensatory curves, and sagittal deformity and sagittal balance. The degree of curvature is established using the standard Cobb.  

Follow up radiographic assessment should be performed with serial standing radiographs at 3-6 month intervals depending the age of the child and the degree of curvature. This enables the surgeon to monitor ongoing curve progression and to time operative intervention. At each visit, the current radiograph should be compared to the both the previous and the original radiograph so that an accurate definition of the curve progression can be gained. Progression of greater of 5º should be considered significant. 

All patients should undergo MRI evaluation of the spine if they exhibit positive neurologic findings or if an operative correction is planned. This allows for the identification of intraspinal anomalies. This is crucial since the highest rate of postoperative paralysis in the correction of scoliosis occur in patients with congenital scoliosis as reported in the morbidity and mortality report of the Scoliosis Research Society. 28  The study should include the brain to rule out Arnold Chiari malformation r hydrocephalus, the cervical, thoracic, and lumbosacral spine. MRI may also help to identify the type of vertebral anomaly in difficult cases although this is best assessed on CT scan. Several recent studies have documented poor correlation between physical examination and MRI findings. The incidence of occult intraspinal anomalies on MRI have been reported to be anywhere from 30% to 41% with neurological findings detecting only 36% to 65% of those patients. 26 27 28 This could suggest that MRI should be obtained routinely in all patients with congenital scoliosis. In patients with neurological deficit in which neural compressive lesions are not clearly delineated on MRI or in patients in whom MRI is contraindicated, CT myelography should be performed.

 The high rate of congenital cardiac and urogenital defects associated with congenital scoliosis should lead the clinician to evaluate for the presence or absence of these defects. Echocardiogram should be employed to evaluate the heart.  B-mode ultrasonography has been shown to be a reliable replacement for intravenous pyelogram as a screening tool for genitourinary anomalies. However, if this study is inconclusive, an intravenous pyelogram should be performed. Although most of these abnormalities are benign, up to 1/3 will require treatment. 22

TREATMENT

The goals of treatment of congenital scoliosis are to prevent and/or arrest curve progression and/or cardiopulmonary disease, to correct spinal deformity, to obtain a balanced stable spine, and to preserve function and mobility. McMasters has noted three key factors in gaining optimal results in these patients: early recognition, anticipation of prognosis, and prevention of deterioration. 8 This may be achieved by non-operative or operative methods.

Non-Operative Treatment

Bracing is not nearly as successful in the treatment of congenital scoliosis as it is in the treatment of idiopathic scoliosis. It may be helpful in controlling long flexible congenital or compensatory curves in the pre-adolescent stage. Bracing may be utilized in the post-operative period to control flexible compensatory curves. Nonetheless, most progressive congenital curves fail to respond to bracing. Bracing should not be employed in situations of severe imbalance, in congenital lordosis or kyphosis, in skeletally mature patients, or in the presence of a rigid curve such as those associated with unilateral failure of segmentation. Winter, et. al. have recommended the use of the Milwaukee brace which has a less adverse effect on pulmonary function. It can also be used to treat upper thoracic curvature and to control abnormal head tilt by using a head extension. 38

Operative Treatment

It is commonly accepted among surgeons that it is better to have a short but relatively straight torso than to be shorter and more crooked. This statement aptly describes the goal of surgical management of congenital scoliosis. The basic objective of surgical management is to arrest the progression of deformity. Multiple surgical options exist. The surgery performed depends on the age of the patient, the type and location of the curve, the length and the magnitude of the curve, and the presence of intraspinal abnormalities. For curves associated with rapid deterioration, surgery should be performed before further progression can occur. Operative interventions are classified into three main categories:

Prophylactic stabilization procedures

Hemiepiphysodesis (convex growth arrest)

Excision of hemivertebra

Arthrodesis in situ.

Correction of flexible curvature

Arthrodesis with corrective casting

Arthrodesis with corrective instrumentation

 Correction of rigid deformity

Osteotomies and/or Verteberectomy

HEMIEPIPHYSODESIS

This procedure is performed to arrest the growth at the convexity of the curve. It is the ideal surgical procedure to manage curves that are caused by unilateral failure of vertebral formation. The goal of this procedure, described originally by MacLennan in 1922, is to stabilize the curvature and to allow slow correction of deformity by taking advantage of continued growth on the concavity of the curvature. This advantage is lost when applied to the curve that results from unilateral failure of vertebral segmentation because the concavity of this curve bears no significant growth potential. 

Many authors have found it best suited to patients less than 5 years of age with a fully segmented hemivertebra with curvature less than 70º that corrects to less than 40 degrees on side bending films.  Contradictions to this procedure include local kyphosis and unilateral failure of segmentation. The disadvantages are the slow process of correction and the unpredictable result due to uncertainty of growth potential on the concavity.

The procedure is performed as a combined anterior and posterior growth arrest. The anterior spine is approached utilizing a method that allows for optimal exposure of the defect, whether by thoracotomy, thoracoabdominal, or retroperitoneal abdominal approach. Discectomy and bone grafting is performed at the level and the side of the hemivertebra as well as a level above and a level below. A posterior approach and convex fusion is then performed by stripping the posterior musculature and then fusing the facet joints at the same levels as done anteriorly. Patients are immobilized for 3 to 6 months postoperatively with either a cast or brace.

Transpedicular hemiepiphyseodsis and posterior arthrodesis has been advocated as a single approach that avoids the morbidity associated with the anterior approach. King, et. al. published their results on 9 patients with an average age of 9.1 years at the time of procedure. The average preoperative curve measured 52º. Successful growth arrest was reported in all but 4 cases in which the deformity progressed more than 10º.  Keller, et. al. reviewed their series of 16 patients with an average age of 4.8 years. At surgery preoperative mean curve magnitude was 36º. They noted that 37% of patients improved, Although the outcome of this technique is promising there has been no report on long term follow up to maturity at this time.

EXCISION OF HEMIVERTEBRA

Excision of a hemivertebra was first performed in 1928 by Royle. The goal of procedure was to remove the anomaly prophylacticly and to achieve deformity correction by using the excision as a wedge osteotomy. Poor results were reported due to a high rate of pseudoarthrosis and neurological complications in subsequent years. 45  In the late 1960’s, the procedure was refined by Leatherman and Dickenson into a two-stage operation consisting of anterior and posterior procedures. A mean correction of 43% was obtained and only two neurologic deficits occurred out of a total of 60 cases. The accepted indications for this procedure are for the treatment of lumbosacral hemivertebra with oblique take off of the sacrum and imbalance, apparent leg length discrepancy, and truncal imbalance in patients at an early stage of growth before the compensatory curves have become rigid. 12    

Hemivertebra excision is performed by removing the hemivertebra and the adjacent discs. The vertebra is removed anteriorly to the dura and anterior half of the pedicle and morselized graft is placed. This is followed by removal of the remaining pedicle and hemilamina by a posterior approach. Instrumentation is performed if the local anatomy allows otherwise cast immobilization is performed. The procedure may be performed in one or two stages.

A number of authors have reported correction ranging from 40% to 67% without significant neurological complication using the one or two-stage technique. Several centers have reported on hemivertebra excision performed from a posterior approach alone in which a decancellation is performed. This avoids the morbidity of the anterior approach and is particularly useful for lower lumbar hemivertebra in which the vascular anatomy and psoas musculature makes the anterior approach challenging. 

EARLY ARTHRODESIS IN-SITU

The goals of early fusion in-situ are to stabilize a flexible curve in order to prevent severe curvature, chest deformity and restrictive lung disease, and torso imbalance. This is optimally applied to cases of a unilateral bar which is recognized to have a poor prognosis if left untreated. The best outcomes are obtained if the surgical intervention is undertaken as soon as the anomaly is recognized, including both upper and lower end vertebra are in the fusion. In-situ arthrodesis may be performed by a posterior or combined anterior-posterior approach.

 Posterior spinal arthrodesis alone includes posterior striping of the muscles and fusion of the posterior elements in-situ without correction, leaving the anterior structures intact. The fusion is obtained by postoperative cast immobilization or instrumentation if there are adequate bony elements..  Posterior fusion alone is rarely indicated in this population due to the high incidence of Crankshaft phenomenon with persistent anterior growth in a young child.  The exception is the case of kyphoscoliosis with the anterior or anterolateral-based bar.

The crankshaft phenomenon was first recognized in 1957. It has been defined as continues anterior spinal growth in the presence of a solid posterior fusion resulting progression of lateral curvature of more than 10º and worsening vertebral rotation. It has been correlated with the number of open anterior growth centers and the number of years remaining of growth. Kesling, et. al. showed two positive correlations with this phenomenon: surgery performed on a young patient and curvature over 50º. The incidence of crankshaft was 15% in this series, less common than with other types of pediatric scoliosis. 64

Combined anterior and posterior arthrodesis has been presented as an alternative to the limited posterior fusion. This combined procedure bears the advantage of limiting chance of Crankshaft phenomenon, allowing for a greater degree of correction, and obtaining a solid fusion. 4 8 9 The indications are young age at the time surgery, severe growth imbalance, and unilateral unsegmented bar with contralateral hemivertebra. This procedure does bear the potential for increased morbidity associated with the anterior procedure.

DEFORMITY CORRECTION AND ARTHRODESIS

Large flexible congenital curvatures over 40º can be treated with instrumented or uninstrumented corrective surgery. A posterior approach is indicated for curvatures less than 70º, while more rigid curves over 70º may be treated by anterior release and fusion followed by posterior fusion. The goal of surgery is to restore coronal and sagittal balance. This is best applied to patients over 8-10 years of age.

Uninstrumented fusion with corrective casting has a very low neurological complication rate; however, curve correction is lower and pseudoarthrodesis rate is higher than instrumented procedures. Due to concern of neurological complications, compressive maneuvers are favored over direct distraction when instrumentation is employed in congenital scoliosis. Pre-operative MRI screening of the spine is essential prior to surgery for congenital scoliosis to assess for intraspinal anomalies that will increase neurological risk. Intra-operative spinal cord monitoring and the Stagnara wake-up test should be routinely utilized to monitor spinal cord integrity during surgery. 

Winter, et. al. demonstrated the efficacy of this approach in 290 patients. Instrumentation allows for a greater degree of correction than arthrodesis with external stabilization with a cast or brace. Two neurological complications occurred, both in the instrumented cases. 63

OSTEOTOMY AND ARTHRODESIS

Severe, rigid scoliosis as a result of untreated congenital scoliosis is characterized by marked truncal decompensation, fixed pelvic obliquity may also occur. The most severe deformities are often associated with mixed vertebral anomalies and rib anomalies such as synostosis. The treatment of these severe, rigid congenital deformities with decompensation is optimally treated with some form of Osteotomy and arthrodesis. Options include multiple anterior-posterior osteotomies with posterior instrumentation, vertebral column resection performed from an anterior-posterior approach, posterior-based decancellation procedures, or posterior-based vertebral column resection. 

The goals of surgery are to restore spinal balance and to preserve or restore pulmonary function. These patients often have significant restrictive lung disease and are at risk for pulmonary failure. In some cases, pulmonary function is improved by this salvage procedure. These procedures are associated with a high rate of complications including neurological injury, severe blood loss, and pseudoarthrodesis.

RECENT ADVANCES

Recent advances in the treatment of spinal deformity have been applied to the correction of congenital scoliotic deformity.

Intermittent Rod Distraction

Grass, et. al. described a procedure that employs posteriorly placed subcutaneous rods to distract curves by slow, intermittent distraction. The mechanism is controlled by a subcutaneous extender. Fusion is performed at the end of the process of repeated distraction. Curve correction ranged between 48% and 62% in their series. No neurologic complications were incurred but there were two infections (out of three patients). The authors suggest that this procedure be considered in patients with a high risk of neurological complication from a single-stage corrective procedure.

Halofemoral Traction 

Arlet, et. al. reported the use of halofemoral traction to progressively correct a 145 degree curve in a patient with preoperative restrictive lung disease and cor pulmonale. After adequate correction over a period of three weeks, instrumented fusion was performed obtaining satisfactory curve correction and improving lung vital capacity. The authors suggest the usefulness of this procedure in patients with high risk, “very severe” congenital scoliosis.

Thoracoscopy

Multiple authors have reported on the efficacy of thoracoscopic surgery employed in the correction of idiopathic scoliosis. Thoracoscopy is believed to be associated with a lower level of morbidity in comparison to traditional thoracotomy when anterior release is necessary for curve correction. Although some studies have included patients with congential scoliosis, no exclusive series of congential scoliosis has been reported to this date. Thoracoscopic hemivertebra resection has also been reported. 

Expansion Thoracoplasty

An alternative to spinal instrumentation in young children and toddlers with severe congenital scoliosis is the method of expansion thoracoplasty. The procedure, recently reported by Campbell and Hell-Vocke, includes the use of an expandable titanium prosthetic device employed on the concavity of a curvature between ribs. The theoretical advantage of the procedure is that it allows for continued development of the thoracic cavity and lungs by maintaining growth and vertical lengthening of the spine while reducing chest wall deformity. The authors reported their data on 21 patients with unilateral unsegmented bar adjacent to convex hemivertebrae who had undergone this procedure. These patients had significant growth of the concave side of the thoracic spine about 7.9 mm/yr and the convex side of about 8.3 mm/yr.

SUMMARY

Congenital scoliosis is a potentially serious condition. It should be diagnosed in an early stage in order to anticipate the prognosis based on the type and site of anomaly, the amount of spinal growth remaining, and the degree of growth imbalance they create. It is associated with other systemic defects including genitourinary, cardiac, and intraspinal anomalies. Appropriate screening for these abnormalities should be performed. Deterioration of the deformity must be prevented. Deformity that is at risk for progression requires immediate surgical treatment. It is much better to do a simple operation to balance spinal growth early on than to wait and perform a more dangerous salvage procedure when the deformity is severe and the patient’s cardiopulmonary status may be compromised. New developments such as thoracoscopic procedures or expansion thoracoplasty may play an increasing important role in the treatment of severe curves.

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