Achondroplasia

Achondroplasia is the most common skeletal dysplasia requiring treatment of spinal disorders. The genetic defect in fibroblast growth factor receptor 3 function is located at chromosome 4p16.3. Hypochondroplasia has a similar genetic defect with lesser expression, and individuals with hypochondroplasia are taller than individuals with achondroplasia. Achondroplasia is recognizable at birth to allow an early diagnosis in nearly all cases. Short limbs with humeral and femoral shortening (rhizomelia) are present together with the characteristic facial features of frontal bossing and nasal bridge depression. Head size is often large compared with other body segments, and hydrocephalus may be present, although most infants with achondroplasia do not require ventriculoperitoneal shunting. The diagnosis can be confirmed by an anteroposterior spinal radiograph, which even at birth shows narrowing of the interpediculate distances in the lumbar spine.

At birth, an infant with achondroplasia has hypotonia in the trunk and in the extremities, and parents should be advised to expect a modest delay in the infant’s developmental milestones. Generally, children sit by about 6 months of age and walk at about 12 months of age, but children with achondroplasia usually sit independently between 9 and 12 months of age and walk by about 18 to 24 months of age.

The cause of hypotonia remains unclear regarding whether it is constitutional or the result of a partial neurologic deficit. There was speculation that foramen magnum stenosis might be the cause of the hypotonia, but this has been shown not to be the case.² Some hypotonia may result from spinal cord compression at the foramen magnum because there is a relative increased frequency of sleep apnea in infants with achondroplasia, sometimes leading to sudden death.³ Sleep apnea monitors are often used for the first several months in many of these infants, and if sleep apnea is clinically significant, evaluation of potential spinal cord compression at the foramen magnum is needed.^4,5 This evaluation includes not only careful recording of sleep monitor findings, but also sleep laboratory studies for apnea and oxygen saturation levels and computed tomography (CT) and magnetic resonance imaging (MRI) of the brainstem and upper cervical spine.

Somatosensory evoked potential (SSEP) monitoring has been shown to be helpful in establishing the diagnosis of cervical myelopathy in these patients.⁶ If SSEP testing is done, subcortical recording of SSEPs from stimulation of the median nerve is more sensitive and specific in diagnosing high cervical myelopathy than stimulation of the posterior tibial nerve.⁷

There are three major contributing causes that may lead to sleep apnea or respiratory problems in achondroplasia: foramen magnum stenosis, midface hypoplasia, and small chest size. Chest circumference in achondroplasia is generally below the 3rd percentile, but this measurement is the same in infants with or without apneic problems. Midface hypoplasia may lead to snoring and upper airway respiratory compromise and has been implicated as the major reason for repeated otitis media in these children. The most common cause of apnea in infants with achondroplasia is upper cervical spinal cord compression at the foramen magnum, where imaging studies have repeatedly shown a significant decrease in cross-sectional area of the foramen. Although the sagittal plane dimension of the foramen magnum is relatively normal, the loss of area for the spinal cord from the severe side-to-side foramen magnum narrowing, with consequent spinal cord compression, seems to be the underlying cause of apnea in many of these infants.

Previous studies have divided this foramen magnum area compression into two major types—the first involving cervical cord compromise from direct impingement of the posterior rim of the foramen magnum and the second caused by the posterior foramen magnum rim invaginating into the ring of the atlas. In these studies, it is stressed that the neural compression is of the high cervical spinal cord, not of the brainstem itself.⁸ Autopsy studies have noted histologic changes in the upper cervical spinal cord similar to changes seen in the central cord syndrome, and some authors believe that if one avoids placing the head of a young child with achondroplasia in hyperextension, the risk of spinal compression is lessened.⁹ Persistent foramen magnum compression may play a role in the later finding of a syrinx in the cervical spinal cord.¹⁰

Some degree of foramen magnum stenosis is present in essentially all children with achondroplasia. By using CT to measure the size of the foramen magnum, it has been shown that 96% have a foramen magnum size smaller than 3 standard deviations below the mean.⁸ How and whom to treat remains unclear, however. One study of 32 children with achondroplasia showed 28% with a history of sleep apnea and 22% with abnormal sleep study results, both of which improved in the 6 children who had foramen magnum decompression.⁶ Foramen magnum decompression has been reported to be performed more safely and successfully when combined with external ventricular drainage to manage the abnormal cerebrospinal fluid dynamics in this compressive condition.¹¹ Diverse symptoms and signs such as ataxia, incontinence, and respiratory problems have been reported to be successfully treated by foramen magnum decompression and atlas laminectomy in patients ranging in age from 7 months to 30 years.¹² Some authors recommend that prophylactic cervicomedullary decompression be done, even in asymptomatic children, if T2-weighted MRI signal changes in the spinal cord are present.¹³

Although successful foramen magnum decompression has been reported in infants,¹⁴ other authors maintain that if appropriate sleep apnea monitoring is continued until the child is 2 or 3 years old, there is a natural relative increase in the foramen magnum size with growth, relieving enough of the spinal cord compression to avoid the need for surgical treatment.¹⁵ Reported mortality and morbidity rates from foramen magnum decompression are thought by these authors to be greater than if no treatment except sleep monitoring is done. It is rarely necessary to perform foramen magnum decompression in older children or in adults. If a child has required cervicomedullary decompression, there seems to be an increased risk for symptomatic thoracolumbar stenosis requiring laminectomies before adolescence.¹⁶

In the cervical spine below the foramen magnum in achondroplasia, the principal spinal disorder is diffuse spinal stenosis. Although a small spinal canal is present from birth, signs or symptoms of neural compression in the lower cervical spine are usually not noted until middle age or later.¹⁷ At those ages, neural compression results from osteophytes that develop with time from degenerative disc changes. The cumulative effect of previous small cervical spine dimensions and osteophyte compression leads to neurologic deficits that require treatment. If pain or sensory changes in the upper extremities are the only findings, conservative care with a cervical orthosis and anti-inflammatory medications is used initially.

If a motor deficit in the upper or lower extremities is present and pain is unrelieved by nonoperative treatment, laminectomy at multiple levels is needed.^18,19 MRI defines the levels of compression, which are usually multiple. As a result, when laminectomy of the cervical spine is needed in achondroplasia, often most of the cervical spine below the axis needs to have the laminae removed to relieve the neural compression. In addition, these patients may need laminectomies in the thoracic and lumbar spine, and some patients with achondroplasia require laminectomy decompression from the skull to the sacrum.²⁰ Foraminotomies are needed at levels shown on MRI to have neural foraminal stenosis from adjacent osteophytes. After multilevel laminectomy, cervical spine fusion is generally not needed in adults, but in the rare instance that cervical laminectomy in a child with achondroplasia should become needed, there is an increased chance of postlaminectomy kyphosis, and careful follow-up evaluation is needed. Although atlantoaxial instability is commonly seen in some other skeletal dysplasias, this instability is rarely seen in achondroplasia.^21,22

Of all the spinal segments, the middle and upper thoracic spine is the least involved in spinal deformity or cord compression in achondroplasia. The most common spinal deformities and stenosis, with subsequent neurologic problems, occur in the thoracolumbar and lumbar spine. Thoracolumbar kyphosis is usually present at birth to some degree but is more noticeable when the infant begins to sit (Fig. 32–1A). As sitting begins, the entire spine appears kyphotic, at least partly owing to the generalized hypotonia present at this age. Although some authors have advocated limiting infants to a reclined, rather than a fully upright, sitting position to avoid the development of thoracolumbar kyphosis,²³ this does not seem to be necessary in clinical practice. In more than 90% of children with achondroplasia, thoracolumbar kyphosis improves without treatment as the standing position is assumed and lumbar lordosis develops. Because walking typically is achieved by 18 to 24 months of age, this is the time that the resolution of the thoracolumbar kyphosis begins, followed by the gradual continual improvement over the subsequent 2 to 3 years.

FIGURE 32–1 A, Lateral spinal radiograph at 6 months of age shows early thoracolumbar kyphosis. Most of these deformities resolve by 2 or 3 years of age. If the apical vertebra remains wedged by age 5 or 6 years, surgery is recommended. B, Lateral radiograph (same child as A) of spine at age 10 years shows persistent wedging of L1 at thoracolumbar junction, which requires anterior and posterior spinal fusion.

A lateral spinal radiograph shows initial relative anterior wedging of the thoracolumbar vertebrae, but this generally resolves as standing and walking occur, with the radiograph showing a gradual filling in of the anterior aspects of the vertebral bodies at the thoracolumbar apex. In the author’s experience, bracing to correct this kyphosis has limited value, and the use of a thoracolumbosacral orthosis (TLSO) is poorly tolerated by many children with achondroplasia, partly owing to the difficulty they have with TLSO wear in reaching their feet owing to their short extremities. An orthosis that uses a soft front while supporting the kyphosis has been reported to be successful,^24–27 although proper patient selection for bracing remains problematic. The use of stretching exercises for the hip flexion contractures (always present in this condition), as a means to decrease lumbar lordosis and control the thoracolumbar kyphosis, has been advocated, but documentation of the effectiveness of this passive stretching program is difficult, particularly when most thoracolumbar kyphoses resolve with no treatment.²⁸

In a few young patients with achondroplasia, thoracolumbar kyphosis does not improve and becomes progressively worse with time. If there is significant wedging of one or more of the thoracolumbar vertebrae at 5 or 6 years of age, surgical treatment is needed to allow partial correction and prevent continued progression of the deformity (Fig. 32–1B).²⁹ This approach is based on review of early childhood x-rays of teenagers later requiring treatment for severe thoracolumbar kyphosis and neurologic deficits. It is generally possible by age 5 or 6 years to determine whether or not the thoracolumbar wedging would improve without treatment or progress to a more severe deformity. Using this approach at this earlier age, the kyphotic deformity generally can be corrected better and more safely, leading to the prevention of localized increased kyphosis and early spinal cord compression.

As thoracolumbar kyphosis increases, so does the compensatory lumbar lordosis. Because the lumbar spine capacity decreases as lumbar lordosis increases, control of the thoracolumbar kyphosis seems to delay the onset of lumbar spinal stenosis symptoms. Whether this early kyphosis fusion will eventually lead to less of a need for decompressive lumbar laminectomy has not been determined. Circumferential fusion of the kyphosis thoracolumbar area in children younger than 2 years has been reported to lead to hypoplastic vertebral bodies and iatrogenic spinal stenosis, apparently as a result of inhibition of circumferential vertebral growth after the fusion.³⁰ In an average-sized individual, it has been shown, however, that the spinal canal achieves its adult dimensions by age 6 years, so circumferential fusion after this age should not lead to iatrogenic stenosis.

In young children with persistent thoracolumbar kyphosis at age 6, the author’s favored surgical technique involves a combined anterior and posterior spinal fusion on the same operative day.²⁹ The child is positioned with a beanbag and tape in a lateral decubitus position with the table tilted about 20 degrees, to allow for simultaneous exposures for the anterior and posterior spinal surgery. Through a thoracoretroperitoneal approach, anterior discectomies are done at three or four levels at the apex of the kyphotic deformity. Because the surgical approach at this level commonly involves an approach through the rib bed of either the 10th or the 11th rib, the portion of the rib removed is saved for an anterior strut graft.

The operating table is then tilted about 20 degrees the other direction to allow exposure of the posterior spine. Through the posterior incision, facetectomies are completed through the levels to be fused, and pedicle screws are placed at the end vertebrae. Because this surgery is usually done on children with no neurologic signs or symptoms, laminectomy is not needed. (If laminectomies are done, there is little bone contact space remaining at the thoracolumbar levels for fusion to occur.) Dual rods are contoured to allow for about 50% correction of the kyphosis and are inserted into the pedicle screws.

Motor evoked potentials and SSEPs must be carefully obtained during and after this correction phase. If there is a change in evoked potentials, the rods are removed. When the evoked potentials have returned to baseline, replacement of the rods, with greater kyphosis bent into these, is done. The final correction is that at which the evoked potentials have remained at baseline and safe correction has been obtained. Decortication of the laminae and transverse processes is done, and bone graft is placed. The table is tilted to its original position, and the rib strut graft is inserted into a channel cut in the apical vertebral bodies to allow the graft to sit into these vertebral bodies as it is anchored in the end vertebrae. Local bone graft is used to graft further the space left by the discectomies. Both wounds are closed in the usual fashion. If the anterior surgery is done first and the strut graft is applied, there is a possibility that this strut graft will displace when the posterior instrumentation and correction occurs. For this reason, the author prefers the simultaneous combined anterior and posterior approaches in the above-described manner.

In the author’s surgical series of more than 25 patients with achondroplasia with kyphotic deformity requiring surgical treatment, more than half have temporarily lost SSEPs at the time of the initial correction of the kyphosis. None of these patients have had permanent neurologic deficit postoperatively. If the SSEPs are lost, however, the rod must be removed and bent into more kyphosis before reinsertion of the rods. Postoperatively, a TLSO brace may be used for about 3 months during the day to allow for some protection for the instrumentation and fusion, but the child remains ambulatory at all times. After 3 months postoperatively, sports activity restrictions are stopped, and full activity is resumed (Fig. 32–2). In another series of 12 immature patients with achondroplasia treated with pedicle screw posterior instrumentation and fusion, no loss of evoked potentials was noted, and overall mean kyphosis correction was 50%.³¹ The exact cause of this neurologic compromise is unclear but may be related to buckling of the ligamentum flavum with kyphosis correction, leading to further spinal canal compromise.

FIGURE 32–2 A 9-year-old boy with achondroplasia had persistent thoracolumbar kyphosis. A, MRI showed kyphosis and failure of anterior vertebral body to form. B and C, Radiographs 2 years after anterior discectomy with strut graft and posterior instrumentation and fusion. Neurologic status remains normal.

An alternative approach has been reported to treat persistent thoracolumbar kyphosis in which spinal instrumentation is placed in the anterior spine rather than in the posterior spine.³² An anterior strut bone graft is placed, and posterior fusion, without instrumentation, is done. This posterior fusion is repeated about 4 months after the initial surgery. A body jacket cast is used for 6 months, and a brace is used for another 3 months. Using this approach in four patients, Ain and Shirley³² obtained solid fusion, kyphosis correction of 23% to 31%, and no worsening of neurologic function.

Although clinically the principal thoracic and lumbar problem in preadolescent children with achondroplasia is persistent thoracolumbar kyphosis, neurologic compromise from spinal stenosis is the most common spinal disorder in teenagers and adults. Lutter and Langer³³ separated these neurologic manifestations into four types: I, progressive, insidious onset; II, intermittent claudication; III, nerve root compression; and IV, acute onset of paraplegia. Types I and II are the most common. In type I, there is a slow but progressive onset of back pain, associated with lower extremity paresthesias and sensory loss.

Urologic function is often impaired, subclinically at first but later leading to incontinence.³⁴ If urologic problems are suspected in the initial stages, voiding cystourethrogram can help to diagnose urinary control problems. If voiding cystourethrogram is abnormal, MRI of the thoracic and lumbar spine is indicated. If significant spinal stenosis is present, laminectomy decompression is needed to reverse the urologic problems. In one series of 22 pediatric patients with achondroplasia with symptoms and signs of spinal claudication and requiring laminectomy surgery, 77% had bladder incontinence. These patients requiring laminectomy at this young age had narrower lumbar interpediculate distances and greater thoracolumbar kyphosis than young patients with achondroplasia not requiring laminectomy.³⁵

In achondroplasia with type II with neurologic manifestations, there is also a slow, progressive onset of symptoms, with the patient first noting a decreased ability to walk distances. Pain and weakness in the legs result when standing and walking occur, and these symptoms are relieved by the patient squatting, sitting, leaning forward, or lying down. These all are spinal positional changes that flex the lumbar spine to allow more room for the cauda equina and relieve the spinal claudication symptoms. It has been shown in a stillborn infant with achondroplasia that the capacity or space within the lumbar spine is nearly doubled by fully flexing the lumbar spine when compared with the extended or lordotic position.²⁸

In this setting, the initial office neurologic examination of the lower extremities may be normal, even if significant spinal stenosis is present. The normal findings may be partly due to the fact that the patient has been sitting in the waiting room with a flexed lumbar spine for a time and has relieved the signs and symptoms of spinal stenosis that are present when standing. It is often helpful to have the patient walk up and down the hall for a few minutes until the symptoms of spinal claudication return, at which time the lower extremity neurologic examination is repeated, often finding weakness, particularly involving the muscles that dorsiflex the ankle. If these physical findings are present and the history suggests spinal claudication, MRI of the thoracic and lumbar spine is needed to evaluate the need for surgical treatment with decompressive laminectomy.

Patients with type III neurologic manifestations have more obvious unilateral radicular signs and symptoms to allow an appropriate diagnosis. A positive straight-leg raising test is present in most cases in the lower extremities. Lumbar spine MRI usually allows for identification of the specific point of femoral or sciatic nerve root compression. Acute paraplegia, or type IV manifestation, is uncommon and probably occurs most often after significant trauma. In most instances, before the trauma, there have been signs or symptoms of one of the other types, most often type I or II.

For any of these types, if neurologic deficits are suspected from the history or shown on physical examination, MRI is indicated to localize the site of abnormality. The problem most common in the interpretation of MRI is to determine which level is causing the neurologic signs or symptoms because there is diffuse stenosis usually present in the lower thoracic spine and the entire lumbar spine. Imaging studies show that the primary stenosis is from the narrowing of the interpediculate distances because the anteroposterior dimension of the spinal canal is relatively more normal until osteophytes from disc degeneration protrude into the spinal canal.^36,37 Occasionally, CT myelography may be used to evaluate for levels of spinal stenosis, but if this is done, the myelographic dye should be placed via cisternal puncture in the upper cervical spine and not by lumbar puncture because lumbar puncture, with loss of cerebrospinal fluid, may lead to increased neurologic deficits in achondroplasia.³⁸

The selection of the surgical procedures best suited to the individual patient with achondroplasia depends on the physical examination and the imaging findings. In a patient with type III neurologic manifestations, a limited laminectomy, disc excision, and foraminotomy generally suffice to relieve the symptoms. More commonly, in the other types of neurologic manifestations, multilevel decompressive laminectomy is the surgical treatment of choice.^39,40 Laminoplasty was reported to be successful for complete relief of symptoms in 71% of 35 patients with achondroplasia and lumbar stenosis, but the use of this procedure has not been widespread.⁴¹ Even if multilevel laminectomy is done in these patients, fusion may not be needed unless there is a preexisting thoracolumbar kyphosis of about 30 degrees or more. If there is preexisting kyphosis at this level, pedicle screw fixation with dual-rod instrumentation is used with no instrumentation, no matter how small, within the spinal canal at the thoracic levels without laminectomy, although posterior pedicle screws can be used with laminectomy.

In situations with marked thoracolumbar kyphosis and multilevel stenosis on MRI, it is often difficult to determine the exact level of neurologic compromise. Generally, if depressed knee and ankle deep tendon reflexes and leg weakness are present, lumbar laminectomy seems to suffice for treatment. If there is MRI evidence of significant anterior spinal cord compression at the apex of a thoracolumbar kyphosis, and hyperreflexia is present together with leg weakness and sensory changes, anterior partial vertebrectomy or posterior pedicle subtraction osteotomy to decompress the anterior spinal cord at the apex of the kyphosis may be needed, in addition to multilevel lumbar and lower thoracic laminectomies. A report of four patients with achondroplasia and marked kyphosis who had decompression through a pedicle subtraction osteotomy noted that there was a mean kyphosis correction of 44%, but that, despite final improvement in neurologic status, transient postoperative weakness was noted in two of the four patients.⁴²

In achondroplastic patients without coincident kyphosis but with neurologic deficits secondary to the diffuse stenosis, multilevel laminectomy is the treatment of choice (Fig. 32–3).^39,40 Before surgery, it is essential to view the entire thoracic and lumbar spine on MRI to assess for all levels of stenosis that may be causing lower extremity weakness. It is important to decompress all levels that appear to have neural compression on MRI, and most often the levels for laminectomy extend from around T10 to S1. If only a single-level or double-level laminectomy is done at what appear to be the most involved areas, recurrence of new symptoms within months of the decompressive surgery is common as new levels of compression develop adjacent to the initial sites of decompression.

FIGURE 32–3 A and B, Radiograph (A) and photograph (B) of multiple-level laminectomy generally needed for spinal stenosis in achondroplasia. If multiple levels are not included, recurrence of symptoms a few months after limited decompression is common.

Because of the severe spinal stenosis present in achondroplasia, with the absence of epidural fat and concurrent loss of most of the subarachnoid space seen at the time of surgery, special precautions and surgical techniques are needed to complete these laminectomies more safely.³⁴ The use of rongeurs within the spinal canal during laminectomy should be limited, owing to the severe stenosis. A postoperative increase in neurologic deficits is common, even if extreme care is taken during the laminectomy procedure. The use of a high-speed bur to transect the lamina on each side just medial to the facet or at the facet level is recommended. After the laminae have been transected, the posterior elements are lifted dorsally with a clamp, with the intent to avoid placing instruments within the stenotic spinal canal, which may injure the neural elements.

Foraminotomies can be done as needed after the laminae are removed, but MRI studies showed that although the foramina in achondroplasia lumbar spines were smaller than in control groups, the percentage of foraminal space occupied by the nerve root was similar between the two groups. The conclusion was that spinal stenosis symptoms arose from the central canal stenosis, not from foraminal stenosis. It would seem that foraminotomies in these patients are usually not needed.⁴³ Unless there is increased kyphosis in the area of laminectomies, the author has noted that fusion may not be needed, even if laminectomies include removal of the facets. It has been reported more recently, however, that 10 skeletally immature patients with achondroplasia required spinal instrumentation and posterior fusion after laminectomies across the thoracolumbar region.⁴⁴

After extensive laminectomy surgery, as described earlier, there may be areas of thinned dura that later form pseudomeningoceles and lead to later neurologic deterioration or pain or both. Using the paraspinal muscles to obliterate the dead space left by removal of the bony laminae seems to be helpful in decreasing the formation of these postlaminectomy pseudomeningoceles.³⁴ Ain and colleagues⁴⁵ reported that 61% of 98 achondroplasia patients undergoing laminectomy surgery had at least one perioperative complication, including 37% with dural tears, 23% with neurologic complications, 9% with infection, and 1 death.

Signs and symptoms of recurrent spinal stenosis may occur years after initial decompressive laminectomies. The most common cause of recurrent stenosis seems to be facet hypertrophy and disc disease, although scar tissue may form over the decompressed dural sac as well. MRI studies with gadolinium enhancement often help to visualize the scar tissue present and where the cauda equina compression has recurred. In one series of eight patients with restenosis, repeat decompression helped improve motor function in some, but three of these patients had significant complications.⁴⁶

In patients with significant thoracolumbar kyphosis and lumbar spine stenosis, both of these conditions can be a possible cause of the underlying neurologic deficit.⁴⁷ In this setting, MRI of the entire spine is used to ascertain all levels of compression. To treat lumbar spinal stenosis and anterior spinal cord compression at the apex of the kyphosis, anterior decompression and fusion at the apex of the kyphosis, together with a posterior multilevel laminectomy and instrumented fusion, is needed.^29,47 Anterior decompression and fusion may be done through an anterior approach by vertebrectomy and strut bone graft fusion at the apex of the deformity or by an approach through the pedicles for anterior decompression with cage and bone graft stabilization. After posterior decompression at multiple levels is completed, pedicle screw and rod instrumentation is inserted, and bone graft is placed to complete the fusion. The pedicle anatomy of the thoracic and lumbar spine has been shown by CT to be markedly different from that of the normal spine. In addition to other findings reported, all pedicles are directed cranially, the pedicle starting points diverge from T9 to L5, and the maximal screw path length is at L2.^48,49 Instead of stainless steel implants, titanium spinal implants are used to obtain better images at MRI if there is a subsequent need to evaluate the spinal cord further.

Diastrophic Dysplasia

Diastrophic dysplasia has several typical features that allow this diagnosis to be made at birth. Although in most countries the incidence is about 1 per 1 million, Finland has a much higher number of patients with this disorder and has been the source of much of the current literature on the natural history of patients with diastrophic dysplasia. There is a genetic defect in diastrophic dysplasia sulfate transportase, and the chromosomal location for this defect is at 5q31-q34.

Characteristic diagnostic features include micromelia with markedly short stature; “hitchhiker’s thumb”; stiff proximal interphalangeal joints of the fingers; severe equinovarus foot deformity; and, within a few weeks of birth, the formation of external ear cysts, which lead to scarring and the classic “cauliflower ear” appearance.⁵⁰ Intelligence is normal. A cleft palate is present in about 25% of these children.

The spine has several areas of involvement in diastrophic dysplasia. All patients have spina bifida of the cervical spine, although symptoms directly related to this anatomic feature do not seem to occur.^51,52 Upper cervical abnormalities seen in some of the other skeletal dysplasias, such as foramen magnum stenosis and atlantoaxial instability, are not present in diastrophic dysplasia.⁵³ The primary cervical spine abnormality in this condition is mid-cervical kyphosis,^54,55 although a review of 122 patients from Finland found only a 4% incidence of cervical kyphosis.⁵⁶ At a young age, many patients with diastrophic dysplasia have mild cervical kyphosis, but most of these cases resolve with time and growth, by an average of 7 years of age.^51,57

Why cervical kyphosis worsens in a few patients and not in most patients is unclear, but the presence of the bifid cervical spinous processes may play a role. In children in whom kyphosis does not resolve by itself, significant wedging of the apical vertebrae can occur. If progressive kyphosis is noted, cervical fusion is indicated to prevent severe deformity. If cervical kyphosis becomes severe, spinal cord compression occurs, and death may result from this cervical spinal cord compression. At autopsy, neuropathologic examination has shown neurolytic changes in the anterior columns of the spinal cord as a result of anterior cord compression, so treatment of progressive kyphosis at an earlier stage is preferable. In these children, with stiffness of all joints a feature of the condition, it is often difficult to elucidate clearly neurologic functional changes, and liberal use of radiography and MRI is necessary to allow for early detection and ongoing evaluation of cervical kyphosis, together with possible spinal cord compression.

In patients with progressive cervical kyphosis, anterior and posterior fusion is recommended for optimal stabilization (Fig. 32–4). A halo brace is used to allow partial correction and postoperative immobilization until the fusion is solid. The kyphotic neck is usually relatively stiff, and aggressive attempts to correct the kyphosis are more likely to lead to iatrogenic neurologic injury. Laminectomy does not have a role here. If there is spinal cord compression that requires treatment, anterior decompression with vertebrectomies at the apex is the surgical approach of choice.

FIGURE 32–4 Lateral cervical spine radiograph of an 8-year-old girl with diastrophic dysplasia 2 years after two-level vertebrectomy with anterior strut graft and posterior fusion for 90-degree kyphosis.

Kyphoscoliosis is the primary spinal disorder in the thoracic spine. In one study, 40% of children with diastrophic dysplasia developed mild to moderate scoliosis.⁵⁸ In these patients, this deformity is not large enough to require treatment except for periodic follow-up, although occasionally a brace is used for a time. About 30% of patients with this condition develop a severe, rigid, progressive thoracic scoliosis associated with a sharply angular mid-thoracic kyphosis. In a more recent study from Finland, of 86 patients with diastrophic dysplasia and scoliosis, 11 cases were severe, 41 cases were “idiopathic-like,” and 33 cases were mild and nonprogressive.⁵⁹

In a review of 43 patients with diastrophic dysplasia,⁶⁰ if significant kyphoscoliosis was to develop, the onset of the spinal deformity was before age 4 years. In another review of 88 patients, 70 had scoliosis measuring an average of 42 degrees (range 11 to 188 degrees).⁶¹ Lung function generally has been shown to be relatively normal in diastrophic dysplasia, but pulmonary function declines with increasing thoracic kyphoscoliosis.⁶²

Imaging studies, such as tomography or three-dimensional CT reconstructions of the spine, often show a wedge-shaped vertebra at the apex of the thoracic kyphoscoliosis, similar to what one would see with a congenital hemivertebra.⁶⁰ Although orthotic treatment can be attempted early if there is flexibility proven on lateral bending radiographs, most of these early-onset deformities are very stiff. The treatment goal is to prevent progressive deformity rather than to wait and treat a severe deformity, an approach that is analogous in many ways to the treatment approach used for congenital scoliosis or kyphosis.

Submuscular spinal instrumentation without fusion to allow continued growth can be used in some cases, if there is a large curve in a young child (Fig. 32–5), but significant flexibility of the spine must be shown before this type of instrumentation treatment. If there is no real correction on lateral bending radiographs, anterior and posterior spinal fusion and posterior spinal instrumentation with modest correction is recommended at the stage at which progression has been proven greater than 50 degrees. Spinal growth in diastrophic dysplasia seems to be complete by about age 8 years, so definitive spinal fusion can be done in this condition at an earlier age than with most childhood spinal deformities with less fear of inhibiting later trunk growth.

FIGURE 32–5 A, Anteroposterior spinal radiograph of a 5-year-old boy with diastrophic dysplasia. Scoliosis was corrected from 70 degrees to 40 degrees by this submuscular rod without fusion. Although braces must still be worn, these rods are useful in this condition in which young children frequently have severe progressive scoliosis. Definitive instrumentation and fusion can usually be accomplished by age 9 or 10 years. B, Radiograph shows progressive kyphosis that often occurs above distraction instrumentation without fusion, if multiple lengthenings are necessary.

Some of the most severe cases of kyphoscoliosis the author has seen have been in patients with diastrophic dysplasia (Fig. 32–6). These deformities may be severe enough to cause swallowing difficulties owing to the aberrant path taken by the esophagus. Despite the severity of these deformities, neurologic signs and symptoms related to spinal cord compression in the thoracic and lumbar regions are very rare, in contrast to what is expected from severe kyphotic deformities in general. In patients with diastrophic dysplasia, if neurologic defects or paraplegia is present in conjunction with severe thoracic kyphoscoliosis, the cause is usually iatrogenic, secondary to surgical attempts to instrument and correct the spinal deformity aggressively. There is minimal flexibility in these severe curves, so motor evoked potential and SSEP monitoring is required intraoperatively when spinal instrumentation and fusion is performed to detect early any neurologic changes from overstretching of the spinal cord in the face of a rigid spine. The vertebrae and the spinal canal in this condition are of sufficient size to accept appropriately sized pedicle screws, hooks, and wires or cables as part of spinal instrumentation. A goal in treating patients with scoliosis and diastrophic dysplasia is, however, to detect this deformity early, monitor this closely, and fuse the spinal deformity area before it progresses to a severe degree. Anterior and posterior fusion at an early age for progressive curves seems to be the best approach in treatment to prevent the severe deformity seen in the past in some adults with this condition.⁶³

FIGURE 32–6 A, Anteroposterior spinal radiograph of a girl with diastrophic dysplasia; in this condition, some of the most severe cases of scoliosis and kyphosis seen with skeletal dysplasias are present. B, Tomogram of thoracic spine in a child with diastrophic dysplasia. This tomogram shows a finding common in this condition when severe scoliosis is present at a young age. The resemblance to congenital kyphoscoliosis may help explain why progression may be so rapid and eventual curve magnitude so severe.

Most patients with diastrophic dysplasia also have a marked lumbosacral lordosis. The sacrum itself also develops a lordotic position with growth. This lordosis is exaggerated further by posterior vertebral body wedging that occurs in L5. In addition, owing to hip flexion contractures that are always present, lumbar lordosis is increased even more when the patient is standing. This standing hip and spine position is also partially compensatory for knee flexion contractures, which are common in these patients. In a study of walking difficulties in patients with diastrophic dysplasia, the walking difficulties were only rarely related to low lumbar spinal stenosis, however.⁶⁴ In some patients with diastrophic dysplasia, interpediculate narrowing in the L5 and S1 vertebrae is seen on radiographs and MRI, but decompressive laminectomy is rarely required.^60,61 There is no interpediculate narrowing in the upper lumbar spine.

Spondyloepiphyseal Dysplasia

There are two forms of spondyloepiphyseal dysplasia—the congenita and the tarda types—and they are very distinct from one another.

Spondyloepiphyseal Dysplasia Tarda

Spondyloepiphyseal dysplasia tarda affects only males and is inherited as an X-linked recessive condition. This condition is caused by mutations in the SEDL gene in chromosomal location Xp22.2-p22.1.⁶⁵ At birth, normal body proportions seem to be present, and the diagnosis is commonly not established until late childhood or early adolescence. The trunk is short but not dramatically so; radiographs show platyspondyly,⁶⁶ a characteristic hump-shaped buildup of bone in the central and posterior aspects of the vertebral body, and a delay in ossification of the vertebral ring apophysis. Scoliosis and kyphosis are uncommon; although low back pain may result from a combination of disc degenerative disease and increased lumbar lordosis, the spine is not the most important feature of this condition. Multiple disc herniations have been reported.⁶⁷

The most common reason that patients with spondyloepiphyseal dysplasia present to an orthopaedist is for treatment of hip pain and stiffness (Fig. 32–7).⁶⁵ Premature hip osteoarthritis is a feature of this condition, often starting in the preadolescent years and progressing with age. Increased lumbar lordosis may be exaggerated by hip flexion contractures from hip arthritis. Total hip arthroplasty is commonly needed in early adult life. If this condition is suspected in a child, a family history of the need for hip replacement in early adult life may help make the diagnosis of spondyloepiphyseal dysplasia tarda.

FIGURE 32–7 Anteroposterior radiograph of pelvis shows early abnormalities in hips of a 10-year-old boy with spondyloepiphyseal dysplasia tarda. Note relative flattening of lumbar vertebrae. Hip replacement surgery in early adult life is common in this condition.

Spondyloepiphyseal Dysplasia Congenita

From the spine point of view, spondyloepiphyseal dysplasia congenita is of much more concern than spondyloepiphyseal dysplasia tarda. Inherited as an autosomal dominant condition, spondyloepiphyseal dysplasia congenita has a defect in type II collagen, on the α₁ chain. The chromosomal location of this defect is 12q13.11-q13.2. Other related skeletal dysplasias with type II collagen abnormalities include Kniest syndrome, Stickler syndrome, and Strudwick spondylometaepiphyseal dysplasia.

Spondyloepiphyseal dysplasia congenita is recognizable at birth with imaging findings in conjunction with short-trunk dwarfism.⁶⁸ There is delayed ossification in the vertebral bodies, and coxa vara is present. Hands and feet are of relatively normal size. As the child ages, there continues to be absent or delayed ossification of the femoral heads and irregularities in the epiphyseal and the metaphyseal areas of the long bones. From the medical standpoint, retinal detachment is common in this condition, and the parents need to be aware of this to arrange periodic eye evaluations.

Atlantoaxial instability is the most commonly seen cervical spine problem in children with spondyloepiphyseal dysplasia congenita, with nearly half of children having this finding.^50,69 In infancy, some hypotonia is present, but this should resolve with age. Failure to attain motor milestones progressively in the lower or upper extremities should direct attention to the cervical spine because atlantoaxial instability is often found early in childhood, sometimes at 1 year of age.

Cervical spine radiographs in a young child may be difficult to interpret. In a normal child, there is increased flexibility and motion on flexion and extension compared with an adult, so this has to be taken into consideration. In addition, in spondyloepiphyseal dysplasia congenita, there is a delay in posterior element ossification, so it is even more difficult to delineate clearly instability with flexion and extension radiographs in the upper cervical spine. Because odontoid hypoplasia is the underlying anatomic abnormality, the abnormal motion may be either excessive flexion motion or excessive extension motion (Fig. 32–8).

FIGURE 32–8 A 12-year-old girl with spondyloepiphyseal dysplasia congenita has odontoid hypoplasia and 5 mm of motion between C1 and C2 with flexion and extension. In this instance, abnormal motion is mainly in extension, with front of ring of C1 riding over hypoplastic odontoid. MRI in flexion and extension shows no spinal cord signal change and no apparent compression. Periodic monitoring with flexion-extension radiographs and MRI continues.

Although radiographs are the first step in the evaluation of upper cervical stability, flexion-extension sagittal plane MRI is extremely useful not only to view the anatomic abnormalities, but also to see if there is indentation into the spinal cord or narrowing of the spinal canal in either full flexion or full extension positions. If MRI findings are normal except for odontoid hypoplasia and there is 5 mm or less of motion on flexion and extension lateral cervical spine radiographs, ongoing follow-up is indicated periodically throughout childhood. If there is more than 5 mm of motion with neck extension and flexion or if there is indentation or signal change at the cervical spinal cord, posterior upper cervical spinal fusion is indicated. Laminectomy at the upper cervical spine is generally not needed in patients with spondyloepiphyseal dysplasia congenita and has no role as the only treatment for upper cervical cord compression caused by atlantoaxial instability. If the upper cervical spine sagittal canal diameter is narrowed and myelopathy is present, C1 laminectomy may be indicated in addition to occiput-C2 posterior fusion.⁷⁰

Upper cervical fusion may include only C1 and C2 but commonly extends from the occiput to C2 in these young children; partly owing to the lack of ossification of the posterior elements at this level at this age, this fusion usually is needed. It is more difficult to obtain secure wire fixation of the laminae, and if the instability is excessive, C1 extension movement and overreduction can occur with posterior wiring. To stabilize the upper cervical spine, the author prefers to use a halo brace, applied in the operating room as the first step in the fusion surgery. The number of halo pins used increases in younger children to obtain adequate stability, with six to eight pins usually placed for children younger than 5 years. In these young children, torque screwdrivers are used to tighten the pins to 3 or 4 psi rather than the 6 to 7 psi used in older individuals (Fig. 32–9).

FIGURE 32–9 A, Lateral cervical spine radiograph shows occipitoaxial wiring and fusion in an 18-month-old boy with spondyloepiphyseal dysplasia. Atlantoaxial instability was present on flexion-extension lateral neck radiographs. Flexion MRI showed spinal cord compression. After fusion, motor development of upper and lower extremities improved dramatically. B, An 18-month-old boy with spondyloepiphyseal dysplasia had occipitoaxial fusion for atlantoaxial instability. Reduction was obtained preoperatively by this halo brace, which was left on intraoperatively and for 3 months postoperatively. In children of this age, six or eight halo pins are generally necessary for fixation.

Placement in the halo brace in the operating room is done before prone positioning so that turning the patient under anesthesia is safer for the cervical spine. Obtaining evoked potentials in the upper and lower extremities should be considered before placing the child prone and again after the child is positioned for posterior upper cervical surgery. The back of the halo brace is removed, and radiographs of the atlantoaxial area are obtained to confirm that anatomic alignment is present before surgical preparation and draping. The posterior neck and the iliac crest are prepared and draped into the surgical field.

In cervical spine surgery in a young child, care is taken to avoid exposing more of the posterior laminae than is needed because unintended extension of the intended fusion levels can occur just from periosteal stripping of distal laminae. The author prefers to fuse from the occiput to C2, in most cases without any wiring or instrumentation. The occiput is cleared subperiosteally, as are C1 and C2 to just lateral to the facets. A high-speed bur is used to remove the outer layer of cortex on the occiput, and a squared-off “box” is constructed at the base of the occiput for placing the bone graft. A corticocancellous piece of iliac crest bone, long enough to extend from the occiput box to the distal aspect of the C2 lamina and wide enough to cover both sides of the lamina at C1 and C2, is carefully removed from the lateral posterior iliac crest. It is important to ensure this corticocancellous bone graft is long enough to extend from the occiput to C2. Extra strips of cancellous bone graft are also obtained. This bone graft is bent using bone benders and trimmed so that the proximal end fits nicely into the occipital box and the lower end contacts the C1 and C2 laminae on each side.

Decortication of the laminae of C1 and C2 is completed with a high-speed bur, and cancellous bone graft is laid directly on the decorticated laminae. The corticocancellous strips are placed dorsal to the cancellous bone, and a two-layer or three-layer muscle closure is used to hold the corticocancellous bone strips firmly in place. The author has used this technique on many occasions. Employing halo brace immobilization for 3 months, the author has not noted slippage of the graft in children of this age, even without internal fixation. In a series of patients with skeletal dysplasia (including several with spondyloepiphyseal dysplasia congenita) treated for atlantoaxial instability, 92% achieved a solid fusion, and 88% had improvement in neurologic function.⁷¹

Instability or stenosis is not a problem in the thoracic and lumbar spine in this condition, although some degree of spinal deformity may be seen. Platyspondyly is present throughout but does not seem to cause much of a problem; a mild thoracolumbar kyphosis that does not require treatment may be present. If there is a progressive scoliosis, orthotic treatment with a TLSO is initially tried and often is sufficient treatment. If there is progressive scoliosis, posterior segmental spinal instrumentation and spinal fusion is possible using standard-sized spinal implants because the spine in patients with spondyloepiphyseal dysplasia congenita has a normal spinal canal size. As in all cases of spinal instrumentation for scoliosis, spinal cord monitoring is used intraoperatively.

Pseudoachondroplasia

Pseudoachondroplasia is a short-limbed form of dwarfism that is inherited in an autosomal dominant fashion and has a defect in cartilage oligomeric matrix protein. This defect is located at chromosome 19p13.1. This dysplasia is not usually diagnosed at the time of birth largely because the facial appearance is normal. Although the body proportions are similar to proportions found in achondroplasia, there is a great deal of difference between these two dysplasias.

In pseudoachondroplasia, there is a normal facial appearance; epiphyseal and metaphyseal changes are evident in the long bones on radiographs; and spinal radiographs show flattened vertebral bodies with a central, anterior tonguelike projection and normal interpediculate distances throughout the spine (Fig. 32–10). The primary orthopaedic problems in this dysplasia that require treatment are the angular deformities of the lower extremities requiring corrective osteotomy (often more than once) and premature osteoarthritis of the hips requiring total hip arthroplasty at a relatively early age.

FIGURE 32–10 Lateral radiograph of spine of a 6-year-old boy with pseudoachondroplasia shows characteristic vertebral shape, with anterior mid-vertebral projections, seen in this dysplasia.

Despite the radiographic appearance of some vertebral flattening, trunk height is relatively normal. Increased lumbar lordosis is common, partly from the spine itself and partly from hip flexion contractures. Proximal femoral extension osteotomies can improve lumbar lordosis if the lordosis remains flexible, but this lordosis becomes more fixed with increasing age. Thoracic kyphosis often initially appears as compensatory to lumbar lordosis, but with time and growth, it may become a fixed and progressive deformity that requires treatment. Orthotic treatment is used initially, but surgery may be needed, particularly if anterior vertebral body wedging is seen on radiographs. This is not the type of kyphosis seen with achondroplasia, in which one or two apical vertebrae are involved, but is caused by multiple levels, each having a lesser amount of wedging. Scoliosis may be seen, but there is nothing characteristic of this in pseudoachondroplasia. If spinal instrumentation and fusion becomes necessary for either kyphosis or scoliosis, standard-sized spinal instrumentation can be used. In contrast to achondroplasia, in which no instrumentation should be placed within the spinal canal, patients with pseudoachondroplasia have a normal-sized spinal canal.

Atlantoaxial instability, a condition essentially never seen in achondroplasia, is not unusual in pseudoachondroplasia. This instability may be due partly to the generalized laxity present in all joints in this dysplasia and is not usually a result of odontoid hypoplasia seen in other skeletal dysplasias. Upper cervical instability caused by os odontoideum has been reported in 60% of 15 patients with pseudoachondroplasia, but no surgery was needed in this group.⁷² It is recommended that before any orthopaedic procedures that require anesthesia, flexion and extension lateral cervical radiographs should be obtained to evaluate these patients for instability. If atlantoaxial instability is diagnosed, posterior atlantoaxial instrumentation and fusion is needed (Fig. 32–11).

FIGURE 32–11 A and B, MRI of cervical spine in a boy with pseudoachondroplasia shows marked narrowing of spinal cord at atlantoaxial level, with flattening of spinal cord seen on transverse cuts. Flexion-extension lateral cervical spine radiographs showed 9 mm of atlantoaxial motion. Posterior atlantoaxial fusion is needed in these cases.

Hurler Syndrome (Mucopolysaccharidosis Type I)

Although an infant with Hurler syndrome appears normal at birth, short stature becomes apparent early along with delays in motor and mental development. Thoracolumbar kyphosis is present at birth but often is not noted initially, even though anterior beaking of the apical vertebral bodies is seen if radiographs were obtained. By 2 years of age, corneal clouding, coarse facial features with a large tongue and large lips, stiff joints, and hernias are obvious, and further motor and mental deterioration is noted. Many of these physical signs develop in the 1st year of life, and early diagnosis is key to an improved prognosis. Laboratory studies show excessive dermatan sulfate and heparan sulfate secretion. Atlantoaxial instability may be present.^78,79

In the past, surgical treatment was not usually indicated for the spine or hip abnormalities seen in Hurler syndrome because death in early childhood was expected. More recently, bone marrow transplantation and enzyme replacement therapy have been used in these patients, however, with significant improvement in quality of life, survival, and life expectancy. Although these therapies can delay or prevent cardiac and neurologic deterioration in Hurler syndrome, numerous orthopaedic manifestations are present that usually require treatment, such as progressive thoracolumbar kyphosis or atlantoaxial instability.^80,81 In one group of 10 patients followed for a mean of 8.7 years after bone marrow transplantation, all showed a decrease, however, in the amount of odontoid dysplasia.⁸² In another group of patients with Hurler syndrome who underwent bone marrow transplantation, high lumbar kyphosis was the most common spinal problem seen (Fig. 32–12).⁸³

FIGURE 32–12 A and B, Lateral spine radiograph (A) and MRI (B) of a 6-year-old child with Hurler syndrome who has received a bone marrow transplant. Although underlying metabolic condition is treated well with bone marrow transplant, the spine and other orthopaedic problems seen in this condition need to be followed closely as growth progresses.

Hunter Syndrome (Mucopolysaccharidosis Type II)

Hunter syndrome is a lysosomal storage disease with a defect in iduronate-2-sulfatase that leads to a buildup of certain glycosaminoglycans and adverse neurologic effects. It is inherited in a X-linked recessive manner, affecting only males, and appearance at birth is normal. These children grow normally for about 2 years, at which time an abnormality is suspected. Life expectancy may extend well into adult life, although death in the 2nd decade of life may occur because of cardiopulmonary problems. Some noncharacteristic vertebral changes are present, but lumbar kyphosis may be marked and require surgical treatment.⁸⁴ Evaluation of the upper cervical spine is needed because MRI studies may show anterior spinal cord compression secondary to a thickening of the soft tissue posterior to the odontoid, owing to deposition of the mucopolysaccharide.⁸⁵

Morquio Syndrome (Mucopolysaccharidosis Type IV)

As with the other MPS syndromes, patients with Morquio syndrome appear relatively normal at birth and for the first year or so, at which time parental concern may be raised by a change in physical features and a developmental delay. The thoracolumbar kyphosis characteristic of this condition is present at birth but may not be noted initially. If kyphosis is noted, it may be confused with congenital kyphosis because the child otherwise appears relatively normal. Thoracolumbar kyphosis in Morquio syndrome differs radiographically from congenital kyphosis: The spine in Morquio syndrome has anteroinferior vertebral beaking of the vertebral bodies adjacent to the apical wedged vertebra, whereas congenital kyphosis from a hemivertebra rarely involves more than one level.

As the child becomes older, short stature is more noticeable, together with genu valgum, pectus carinatum, and corneal clouding. Laboratory findings include increased keratan sulfate in the urine and a defect in N-acetyl-hexosamine 6-sulfate sulfatase in fibroblasts. Radiographs of long bones show irregularities in ossification of epiphyses, and hip subluxation is common with growth. Decreased exercise tolerance and decreasing ability to walk longer distances is common with increasing age in childhood and before adolescence. This decreased exercise tolerance may be a result of the hip instability and knee valgus, but evaluation of the cervical and thoracolumbar spine is necessary to rule out spinal cord compression as the cause of progressively decreasing exercise tolerance.

The most common spinal problem requiring treatment is odontoid hypoplasia, which leads to atlantoaxial instability.^55,86–88 Compression at the upper cervical spine is compounded by the frequent presence of an anterior soft tissue mass from the deposition of mucopolysaccharide. Odontoid hypoplasia is present in most children with Morquio syndrome, and evaluation of the cervical spine is needed before orthopaedic surgery for the hips or legs.⁸⁹ Instability is most often noted between 6 and 12 years of age. Lateral cervical spine radiographs are obtained in flexion and extension, and if there is more than 5 mm of motion, posterior upper cervical spinal fusion is needed.

In addition to instability, there is extradural soft tissue thickening, which is a contributing cause to the compression here that is often worse than is apparent from the radiographs alone.⁹⁰ As with other dysplasias, if the radiographs are unclear regarding what instability may be present, a sagittal view MRI study with the neck in flexion and in extension is useful. When instability is present, posterior cervical fusion has been shown to be beneficial even with long-term follow-up.^71,91 The author prefers occipitoaxial fusion without instrumentation, using iliac crest bone graft for fusion and a halo brace for immobilization for 3 months until fusion is complete (Fig. 32–13). In some children with Morquio syndrome, there may be mid-cervical or lower cervical spine stenosis or instability below the atlantoaxial level. The more levels of the cervical spine that require decompression and fusion, the harder airway access becomes, owing to a combination of limited neck motion and a progressive pectus carinatum deformity.

FIGURE 32–13 A and B, Lateral extension and flexion cervical spine radiographs show increased and abnormal motion at C1-2 associated with odontoid hypoplasia in a 9-year-old child with Morquio syndrome. C, MRI of cervical spine shows signal change within spinal cord at C1-2 indicative of instability at this spinal level with cord compression. D, Lateral cervical spine radiograph after occiput-to-C2 posterior fusion.

Thoracolumbar kyphosis is present at birth, and the degree of kyphotic deformity often does not progress significantly. Most of the time, serial examination and lateral spinal radiographs with the child standing suffice for management. If there is documented kyphosis progression with growth, a TLSO can be used, although in the author’s experience this brace is not tolerated well by these children because it is an additional impediment to their limited ability to move about. It may be difficult to differentiate diminished lower extremity function between the lower extremities themselves (hip and knee problems) and thoracolumbar spinal cord and cauda equina compression. MRI of the thoracolumbar kyphosis often shows some degree of intrusion of the protruding discs on the thecal sac, to the extent of causing some spinal cord flattening.

In a young child, use of instrumentation inside the spinal canal has been known to cause neurologic deficits in the lower extremities in some cases (Fig. 32–14). If it is determined that surgery is needed to treat thoracolumbar kyphosis, it may be safer to combine pedicle screw instrumentation and fusion with multilevel laminectomy (Fig. 32–15) or to use anterior spinal instrumentation.⁹²

FIGURE 32–14 A, Lateral radiograph of 1-year-old child with Morquio syndrome. B, MRI shows kyphosis with wedged vertebra at apex and impression on spinal cord at kyphosis apex. C, Lateral radiograph after instrumentation and fusion. D, Myelogram obtained because of slowly developing neurologic signs and weakness in lower extremities a few days postoperatively shows spinal cord compression. E, Lateral radiograph in cast after removal of instrumentation. Neurologic recovery was complete. Anterior instrumentation or later pedicle screw instrumentation in the older child should be considered to avoid placing hooks into small spinal canal.

FIGURE 32–15 A and B, Lateral spinal radiographs before (A) and 7 months after (B) laminectomy and spinal fusion in a teenager with thoracolumbar kyphosis associated with Morquio syndrome. Although most kyphotic deformities in Morquio syndrome are minimally progressive or nonprogressive, careful follow-up with growth is needed. Surgical treatment is indicated with progressive kyphosis despite bracing and when abnormal neurologic signs and symptoms are present. If neurologic deficit is present, atlantoaxial region should be evaluated carefully. Instability here is common in Morquio syndrome.

(Courtesy of Marc A. Asher, MD, Kansas City, KS.)

Maroteaux-Lamy Syndrome (Mucopolysaccharidosis Type VI)

Children with Maroteaux-Lamy syndrome appear normal at birth, and short-trunk dwarfism is noted by age 2 or 3 years. Many of the physical features resemble Hurler syndrome, but intelligence is normal. Diagnostic findings include increased urinary excretion of dermatan sulfate and arylsulfatase B deficiency in fibroblasts and white blood cells. This syndrome typically has hip involvement, which on radiographs resembles Legg-Perthes disease. Stenosis at the level of the foramen magnum and upper cervical spine, probably resulting from thickening of the posterior longitudinal ligament, can be improved by laminectomy when neurologic symptoms and signs are present.⁹³ Thoracolumbar kyphosis is common, and the vertebrae are flattened on spinal radiographs. Laminectomy may be needed if MRI findings correlate with lower extremity loss of function. Spinal fusion should be considered for progressive kyphotic deformity. Spinal cord monitoring is essential, and pedicle screw instrumentation should be attempted because placing implants within the spinal canal has been known to lead to iatrogenic neurologic deficits.

Kniest Syndrome

The clinical features of Kniest syndrome are closely related to the features found with spondyloepiphyseal dysplasia congenita. Life expectancy and intelligence are normal. Imaging findings outside of the spine include metaphyseal widening of the long bones, coxa vara, delay in epiphyseal ossification, and sometimes angular deformity of the lower extremities.^94,95 These children walk with a marked external foot progression angle because of femoral external rotation. The presence of coronal and sagittal vertebral clefts has been reported in 63% of infants with Kniest syndrome and may be helpful in establishing a diagnosis.⁹⁶

Odontoid hypoplasia with resultant atlantoaxial instability is the most common spinal problem requiring treatment.⁹⁷ Use of flexion-extension lateral cervical spine radiographs or flexion-extension sagittal view MRI allows for serial evaluation of this instability to determine any need for posterior occipitoaxial fusion. The criteria for surgery and surgical technique are the same as described earlier for spondyloepiphyseal dysplasia congenita. Scoliosis is common but because of the limited trunk growth does not always require treatment. Periodic thoracolumbar spine radiographs are indicated, however, for evaluation and identification of patients who would benefit from either orthotic or surgical treatment. If surgical treatment is needed, small but standard spinal instrumentation can be used. Finally, excessive lumbar lordosis is present, in part from the spine and in part from the expected hip flexion contractures usually present. Because proximal femoral osteotomy is often used to treat coxa vara and external femoral rotation, it is recommended that this femoral osteotomy also include an extension component, which allows some correction of the flexible component of the excessive lumbar lordosis.

Metatropic Dysplasia

Metatropic dysplasia is rare; the name is derived from the apparent change in body proportions with increasing age. This condition seems to be not only a disorder of endochondral ossification, but also seems to be associated with defects in the longitudinal proliferation and maturation of chondrocytes and in the production of normal matrix. The uncoupling of endochondral and perichondral growth seen in this condition may explain why the long bones are dumbbell-shaped, as is seen on radiographs in this dysplasia.⁹⁸ As growth occurs, the trunk becomes disproportionately short owing to flattened vertebrae and scoliosis or hyperkyphosis. Life expectancy usually extends into early adulthood. Scoliosis or kyphosis appears early in childhood and is difficult to manage. Orthotic management is attempted early, but growing rod instrumentation without fusion with or without apical fusion should be considered in young children with severe scoliosis. Definitive spinal instrumentation and fusion, commonly involving anterior and posterior fusion, is usually needed by preadolescence if not earlier.

Odontoid hypoplasia has also been reported to be commonly present in this condition and may require upper cervical fusion.⁹⁹ More recently, cervical spinal stenosis has been reported to be a common feature of this condition, and decompressive laminectomy may be needed in addition to fusion in the upper cervical spine.¹⁰⁰ An additional feature of metatropic dysplasia that should be considered is the presence of enlarged ventricles on head CT scans.

Mucolipidoses

There are some parallels between MPS syndromes and mucolipidoses (ML) even though the underlying metabolic defect is different, with thoracolumbar kyphosis being present in ML type II and type III. In ML type II, there are physical features similar to the features of Hurler syndrome; children with this type usually die in early or middle childhood. ML type II and type III have a similar biochemical abnormality, but ML type III has milder clinical manifestations, and life expectancy extends well into adult life. Progressive thoracolumbar or upper lumbar kyphosis is treated with posterior spinal instrumentation and fusion, usually anterior and posterior. Carpal tunnel syndrome is common in ML type III and requires median nerve decompression often in adolescence.

Chondrodysplasia Punctata

Also known as Conradi-Hünermann syndrome, chondrodysplasia punctata can be diagnosed at birth by short limbs; ichthyosis; flat facial features; and, in particular, radiographic findings of punctate calcification in the epiphyses at the ends of the long bones. These stippled epiphyses are present even in very young children. Coronal and sagittal vertebral clefts are present in 79% of infants with this dysplasia.⁹⁶

Atlantoaxial instability, in one reported case leading to death from cervical cord compression,¹⁰¹ and upper cervical stenosis can be seen, so cervical spine imaging is needed in chondrodysplasia punctata (Fig. 32–16).^102–105 Scoliosis is common and often has its onset in early childhood. There are two main types of scoliosis: One slowly progresses with growth, and the other is a dysplastic type that is rapidly progressive. Orthotic treatment may suffice in curves with slower progression, but spinal instrumentation and anterior and posterior fusion is needed in larger dysplastic curves.¹⁰⁶ Growth hormone has been successful in some patients in improving their final height. Life expectancy and intelligence are normal if the child survives the newborn period.

FIGURE 32–16 A, Lateral cervical spine radiograph in a 7-year-old girl with chondrodysplasia punctata shows cervical stenosis with cervical spinal cord compression, leading to weakness when walking. B, Lateral cervical spine radiograph 1 year after C1 laminectomy and occipitocervical posterior fusion, with neurologic signs and symptoms resolved.

Camptomelic Dysplasia

The most prominent feature in camptomelic dysplasia at birth is bowing of the long bones of the lower extremities. Delayed ossification of the mid-thoracic pedicles is very useful in helping to establish this diagnosis. Cervical kyphosis is reported in 38%,¹⁰⁷ and spinal cord injury as a result of this cervical kyphosis has been reported.¹⁰⁸ Scoliosis and thoracic hyperkyphosis develop very early in childhood and often develop into severe deformity. Many of these children die in early childhood from pulmonary causes. Orthotic treatment is difficult because of the pulmonary compromise seen in these children. If patients survive past early childhood and have progressive kyphoscoliosis, spinal instrumentation and fusion has been reported to be successful.¹⁰⁷

Parastremmatic Dysplasia

Parastremmatic dysplasia is an exceedingly rare, short-trunk dwarfism associated with angular deformity of the lower extremities. Radiographs show abnormalities at the epiphyseal and metaphyseal regions of the long bones. Spinal radiographs show flattened vertebral bodies with irregular endplate ossification. Kyphoscoliosis is present in nearly all cases, and either orthotic or surgical treatment, depending on the severity of the deformity, is indicated as these patients survive to adulthood.

Spondyloepimetaphyseal Dysplasia with Joint Laxity

Early development of severe and progressive kyphoscoliosis during infancy is seen in spondyloepimetaphyseal dysplasia with joint laxity. Left untreated, this deformity leads to death in early childhood resulting from either spinal cord compression or cardiorespiratory failure in most patients.¹⁰⁹

Spondylometaphyseal Dysplasia, Kozlowski Type

The Kozlowski type of spondylometaphyseal dysplasia is a short-trunk dwarfism that is usually not diagnosed until preschool age. Platyspondyly causes the short trunk, and kyphosis is common. Life expectancy is normal, and the kyphotic deformity needs to be followed and treated according to how severe it becomes.¹¹⁰