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Edinburgh Spinal Deformity Centre, Edinburgh Royal Infirmary, Edinburgh, UK
King James IV Lecture given at the Annual Congress of the British Orthopaedic Association, International Convention Centre, Birmingham on 12th September 2001
J.R.Coll.Surg.Edinb., 47, April 2002, 475-480
Congenital anomalies of the vertebrae producing a scoliosis, kyphoscoliosis or kyphosis are potentially serious conditions, which can, on occasion, result in an extremely severe rigid spinal deformity with possible spinal cord compression. The key to successful management depends on: (1) Early diagnosis while the curve is still small. (2) Anticipation of the likely prognosis based on the type and site of the vertebral anomaly, the degree of growth imbalance it produces and the amount of spinal growth remaining. (3) Preventing progression of the deformity and this may necessitate surgical treatment in the first few years of life. It is much better to carry out a relatively simple operation to balance the growth of the spine at an early stage than to wait and perform potentially hazardous anterior and posterior spinal surgery as a salvage procedure at a later stage.
Keywords: Congenital scoliosis, congenital kyphosis, natural history, surgery
Congenital deformities of the spine are due to the presence of developmental vertebral anomalies, which produce a localised imbalance in the longitudinal growth of the spine. The term congenital is slightly misleading because it implies that the deformity is present at birth but this is not necessarily so. It is the vertebral anomalies, which are present at birth, and the clinical deformity may not become apparent until later childhood when the diagnosis is made radiographically.
Congenital deformities of the spine are relatively uncommon. However, I have been able to study 670 patients with this type of deformity seen at my Edinburgh Spine Deformity Clinic. This is one of the largest groups of reported patients and has been the subject of a series of publications on the natural history and management of the condition.1-6 I found that all degrees of severity of curvature were seen at all ages. Some patients were first seen in their teenage years with small curves, which progressed minimally. Others presented in the first few years of life with curves, which deteriorated rapidly, becoming extreme deformities at an early age, (Figures 1, 2 and 3) and a few developed spinal cord compression and paraplegia. These severe curves were often rigid, and surgical correction was difficult and dangerous.
Figure 1: Infant girl aged 4 months with a thoracic scoliosis due to a unilateral unsegmented bar on the concavity with 3 adjacent contralateral hemivertibrae on the convexity at the same level. No treatment was given.
Figure 2 & 3: By the age of 9 years and 10 months the scoliosis had increased to 106 degrees and there was marked malalignment of the trunk combined with distortion of the rib cage reducing the vital capacity
The skill in managing a patient with a congenital spine deformity lies not in the ability to perform major complex salvage surgery at a late stage, when there is a severe rigid deformity, but in recognizing those curves with a bad prognosis at an early stage and applying prophylactic surgical treatment to prevent curve progression and possible neurological complications. Planning such treatment requires a thorough knowledge of the natural history of all types of congenital spine deformity and the methods of treatment which are available.
In order to understand the great disparity in prognosis for congenital spine deformities it is necessary to correlate the principles of normal growth of the spine with the pathologic anatomy of the various types of developmental vertebral anomalies that may cause the deformity (Figure 4).
Figure 4
The embryological development of the spine is a very rapid process and the complete anatomical pattern is formed in mesenchyme during the first six weeks of intrauterine life. Once the mesenchymal mould is established the cartilaginous and bony stages follow that pattern. Vertebral anomalies appear during the mesenchymal and early chondrofication stages and are due to either a defect of vertebral formation or a defect of segmentation of the primitive vertebrae. The vertebral anomalies are fully established at birth.
The neural axis also develops during this early embryological period and it is not surprising, therefore, that neural and vertebral malformations often co-exist. In this lecture, I will deal only with ‘closed’ congenital deformities in which the skin overlying the spine remains intact although there may be occult intraspinal anomalies, and not with those who have associated myelomeningocele.
Normal longitudinal growth of the spine occurs at the end plates on the upper and lower surfaces of the vertebral bodies.2 This growth occurs symmetrically and, as a result, the spine grows in a balanced manner without a pathological curvature. However, in the presence of a congenital vertebral anomaly there is an absence or deficiency in a number of growth plates on one side of the spine, resulting in a longitudinal growth imbalance and an increasing curvature as the child grows.
The rate of deterioration and final severity of a congenital spine deformity is proportional to the degree of growth imbalance produced by the vertebral anomalies. An early onset of the deformity carries a bad prognosis because this indicates a severe growth imbalance, which will continue to skeletal maturity when the growth plates fuse. The greater the growth imbalance, the more severe the deformity. However, the rate of deterioration is not uniform and accelerates during the adolescent growth spurt, which is at its peak in girls around the age of 12 years and in boys at 14 years.
The type of spinal deformity which develops depends on whether the impaired growth occurs unilaterally, producing a pure scoliosis, or lies anterolaterally or anterior to the transverse axis of vertebral rotation in the sagittal plane, producing a kyphoscoliosis or a pure kyphosis. In my series of 670 patients, there was a gradual blending spectrum of deformities with 80% having a scoliosis, 14% kyphoscoliosis and 8% a kyphosis.
The classification of congenital spine deformities is based firstly, on the pattern of curve, ie scoliosis, kyphoscoliosis or kyphosis, and secondly, on the type of vertebral anomaly which produced the deformity. 1,5,8,9 There are two basic groups of anomalies; those due to a defect of vertebral formation and those caused by a defect of segmentation of one or more vertebrae. (Figure 4) There is also a smaller group with mixed or unclassifiable anomalies.
Defect of Formation: A hemivertebra is the commonest cause of a congenital scoliosis and is due to a complete failure of a vertebra to form on one side. Longitudinal growth occurs on the upper and lower surfaces of the hemivertebra, whereas there is an absence of two growth plates on the unformed side. (Figure 4) As the hemivertebra grows, it acts as an enlarging wedge on one side of the spine resulting in an increasing scoliosis. Hemivertebrae may be single or multiple and occur at all levels of the spine. 1,3
Progression of a scoliosis due to a single fully segmented hemivertebra can be difficult to predict and requires careful monitoring. The majority of these curves progress relatively slowly at 1-2 degrees per year and by skeletal maturity can produce a moderately severe scoliosis of over 50 degrees in the lower thoracic and thoracolumbar regions. However, the most pernicious and deforming hemivertebra occurs at the lumbo-sacral junction where it causes the lumbar spine to take-off obliquely from the sacrum and the patient lists to the side producing a significant deformity. A compensatory curve develops above but this is never sufficient to balance the spine and early surgical treatment is required to prevent this deformity from developing. 10
Two fully segmented unilateral hemivertebrae are less common but have a much worse prognosis because there is an absence of four growth plates on the concavity of the curve. These curves progress much more rapidly at 3 to 4 degrees per year and the majority exceed 50 degrees by the age of 10 years. All require early prophylactic surgical treatment.
Two opposing hemivertebrae have a more variable prognosis. If they are close together they tend to balance each other, causing only two small kinks in the spine and minimal cosmetic deformity. However, if the hemivertebrae are widely separated in different regions of the spine, the resulting curves are often unbalanced causing the trunk to list to one side and prophylactic surgical treatment may be required.
Not all hemivertebrae are fully segmented. A semisegmented hemivertebra is synostosed to one of its neighbouring vertebrae and there is relatively little growth imbalance. These curves progress very slowly and no treatment is required. An incarcerated hemivertebra is a small ovoid piece of bone with very poor growth lying in a niche scalloped out of the adjacent vertebrae. In these patients the spine remains straight and no treatment is required.
In treating a congenital scoliosis due to a hemivertebra it is important to appreciate that it is not possible to create growth on the side of the spine, which is not growing. It is only possible to prevent progression by retarding growth on the convexity. In these circumstances a spinal brace is never an alternative to appropriate surgical treatment.
A convex growth arrest procedure (combined anterior and posterior convex hemiephiphysiodesis) is the optimum form of early prophylactic surgical treatment for a fully segmented hemivertebra.11,12 This procedure is best applied to patients younger than 5 years of age with a scoliosis less than 40 degrees. The object of the surgery is to balance the growth of the spine by preventing further unbalanced growth on the convexity at the site of the hemivertebra. Theoretically, this should allow the scoliosis to correct slowly by means of continuing growth on the concavity. (Figures 5 and 6)
Figure 5: Infant aged 2 years with a 33 degree right thoraco-lumbar scoliosis due to a single fully segmented hemivertebra at L1. A combined anterior and posterior convex growth arrest procedure was performed
Figure 6: By the age of 13 years 2 months the curve had improved to 9 degrees
Excision of a hemivertebra is theoretically attractive as a prophylactic procedure because it removes the primary cause of the scoliosis, which is the enlarging wedge on the convexity at the apex of the scoliosis.13-15 The hemivertebra is excised both anteriorally and posteriorally through the same combined two stage surgical approach as used for a convex growth arrest procedure. This creates a wedge osteotomy of the spine which, when closed, produces maximum correction and realignment of the spine. However, the majority of hemivertebrae, except for a lumbo-sacral hemivertebra, do not cause significant imbalance and are probably more safely treated by a convex growth arrest procedure, which does not require opening into the spinal canal. The best results of a hemivertebra excision are obtained when surgery is carried out at an early age before the compensatory curves become fixed.
Defect of Segmentation: A unilateral unsegmented bar is the second most common cause of a congenital scoliosis and is due to a unilateral failure of vertebral segmentation affecting two or more vertebrae. The mean length of the bar is usually over three vertebrae. The unsegmented bar does not contain any growth plates and, therefore, does not grow longitudinally, whereas some degree of growth occurs on the opposite side of the spine. The rate of progression and final severity of the scoliosis depends not only on the extent of the bar but more importantly on the growth potential on the convexity which drives the curve. 11 This produces a much greater deformity than a single hemivertebra. These curves progress at a mean 5 degrees per year and usually exceed 50 degrees by the age of 10 years. All of these patients require early surgical treatment, preferably before the age of 5 years.
A congenital scoliosis due to an unsegmented bar has a bad prognosis. However, there is a smaller less well recognised group of patients who have an even worse prognosis. (Figures 1, 2 and 3) These patients have not only a unilateral unsegmented bar but also one or more hemivertebrae on the contralateral side at the same level. These hemivertebrae produce an even greater growth imbalance than if there had been a unilateral unsegmented bar alone.4,16 The mean length of the bar is over three vertebrae with a mean two contralateral hemivertebrae. This causes the most severe and rapidly progressive of all types of congenital scoliosis and, without treatment, these curves deteriorate at 6 degrees or more per year and usually exceed 50 degrees by the age of four years. All require very early surgical treatment, as soon as the diagnosis is made.
The ideal treatment for a congenital scoliosis due to a unilateral unsegmented bar, with or without contralateral hemivertebrae, is to recognise the poor prognosis at an early stage when the curve is small and perform a spinal fusion to prevent further progression.17A convex growth arrest procedure or simply dividing the unsegmented bar will not correct this type of deformity because there is no growth potential in the unsegmented bar on the concavity of the curve.
The object of an early prophylactic spine fusion is to stabilise the curve at an early stage by creating a solid thick fusion that will stop the unbalanced growth of the spine. This usually necessitates a combined anterior and posterior fusion to control the severe spinal growth imbalance in these patients. The best results are achieved when the surgery is carried out before the age of two years.4,17 The argument that an early spine fusion will stunt the growth of the spine in these young patients is of no relevance because the unsegmented bar is not contributing to vertical height and only making the spine more crooked. There is no perfect treatment and it is much better to have a short relatively straight patient, with a fused spine, than a patient with an unfused spine, who is severely deformed and even shorter because of the severe spinal curvature.
In an older child with a moderate deformity, partial correction of the scoliosis may be attempted at the time of spine fusion but correction only occurs in the mobile segments above and below the unsegmented bar. The object of surgery is to achieve overall balance of the spine rather than excessive correction of the congenital curve which could be dangerous.16,17
A magnetic resonance imaging scan of the spine is essential in all patients before intra-operative correction of the deformity is attempted using spinal instrumentation. This may reveal the presence of an intra spinal anomaly, such as a diastematomyelia, that could be tethering the cord. A diastematomyelia has been reported in 5 to 20% of patients with a congenital scoliosis and, if the spur is not removed, these patients could develop serious neurological complications due to traction on the spinal cord at the time of correction of the scoliosis. 1,19-22 Of the various types of scoliosis, the congenital variety carries the highest risk of neurological complications after intraoperative correction. 23
Patients who present at a late stage, with a severe rigid deformity causing significant spinal imbalance or fixed pelvic obliquity, require correction by means of an anterior and posterior closing wedge osteotomy of the vertebral column combined with spinal instrumentation, to maintain correction and an extensive fusion of the whole of the curvature.4A closing wedge osteotomy decreases the neurological risk by relaxing the neural structures and distraction must never be applied. This is a complex and potentially hazardous surgical salvage procedure which should never be necessary. All of these patients would have been much better treated by prophylactic surgery, to balance the growth of the spine, at a much earlier stage.
The classification of congenital kyphosis and kyphoscoliosis is very similar to that for congenital scoliosis. The kyphotic deformity may be due to either an anterior failure of formation of a vertebra or an anterior failure of segmentation of two or more vertebrae; there can be a mixture of these anomalies. In contrast to a congenital scoliosis, however, a kyphotic deformity, due to a failure of vertebral formation resulting in a posterior hemivertebra or a posterolateral quadrant vertebra, progresses much more rapidly than one due to a failure of vertebral segmentation.
Congenital kyphosis and kyphoscoliosis are much less common than a congenital scoliosis but potentially more serious because they can, on occasion, lead to spinal cord compression and paraplegia. The reason for this is that a posterior hemivertebra or a posterolateral quadrant hemivertebra are unstable. As a result, the hemivertibra tends to extrude backwards into the spinal canal causing anterior spinal cord compression at the apex of the angular kyphosis, as the deformity increases. 5,9 In contrast, neurological complications only occur in congenital scoliosis as a consequence of an associated intraspinal anomaly and are not caused by direct pressure on the spinal cord by the deformity.
Neurological complications and severe deformity can be prevented if the patient is treated prophylactically at an early age, when the kyphosis is small, by a posterior spine fusion to balance the growth of the spine. Delayed treatment for severe deformity or spinal cord compression requires much more difficult and potentially hazardous anterior and posterior spine surgery.6,9 The spine is approached anteriorally through a thoracotomy or thoraco-abdominal exposure to release the deformity and, if necessary, decompress the spinal cord combined with an anterior rib or fibula strut graft to obtain correction. Early stability may be obtained by a vascularised anterior rib strut graft. This is followed by a second stage posterior spine fusion with instrumentation to maintain correction.
Laminectomy and pre-operative traction are both absolutely contra-indicated if there is spinal cord compression. Traction initially corrects the mobile compensatory curves above and below the more rigid kyphosis. This lengthens the vertebral column and pulls the spinal cord against the unyielding apex of the kyphosis, resulting in further neurological deterioration. Laminectomy is ineffective because the spinal cord is not compressed posteriorally, and removal of the posterior bony structure destabilises the spine, resulting in more rapid progression of the kyphosis and greater anterior spinal cord compression.
Congenital anomalies of the vertebrae producing a scoliosis, kyphoscoliosis or kyphosis, are potentially serious conditions, which can on occasion, result in an extremely severe rigid spinal deformity with malalignment of the body and possible spinal cord compression. Ideally, these anomalies should be diagnosed at an early stage when the curve is small. Congenital vertebral anomalies are frequently diagnosed in infants on radiographs taken for other reasons, before there is an obvious clinical deformity. These radio-graphic findings should not be ignored because they may provide an opportunity for early prophylactic treatment, before a clinical deformity develops. At this time, it is possible to anticipate prognosis based on the type and site of the vertebral anomalies, the degree of growth imbalance they produce and the amount of spinal growth remaining. Deterioration of the deformity must always be prevented. A deformity which is at risk of progression or spinal cord compression requires immediate prophylactic surgical treatment, no matter how young the patient. It is much better to carry out a relatively simple operation to balance the growth of the spine at an early stage than to wait and perform potentially hazardous anterior and posterior spinal surgery, as a salvage procedure, when the deformity is severe or there is spinal cord compression.
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Copyright: 15 October 2001
Correspondence: Professor Michael J McMaster, Edinburgh Spinal Deformity Centre, Edinburgh Royal Infirmary, Edinburgh, U.K.