Kyphosis

Introduction

Kyphosis is a posteriorly directed (concave) sagittal curvature of the spine, usually involving the thoracic vertebrae. Normal thoracic kyphosis is 20° to 40°, but it can be greater because of a physiologic or pathologic process.¹ Any kyphosis at the thoracolumbar junction or in the lumbar spine is abnormal. A growing child with a thoracic kyphotic deformity greater than 45° should be investigated. In children, these findings are commonly due to Scheuermann, postural, iatrogenic, or congenital kyphosis.

Scheuermann’s Kyphosis

Previously known as idiopathic kyphosis
Most common form of kyphosis in adolescence
Prevalence of 0.4% to 8.3% of the general population¹⁰
Equal male:female ratio, but more common in males when in thoracolumbar/lumbar spine¹⁹
Usually presents in early teenage years
Often associated with spondylolysis (due to increased lumbar lordosis which strain the pars interarticularis) and scoliosis

Postural Kyphosis

Also known as familial round-back deformity
Most common form of kyphosis
More common in females, due to slouching to hide their developing breasts
Usually presents during the adolescent growth spurt
It is not pathologic, but should be included in the differential for kyphosis

Congenital Kyphosis

Further divided into three groups
- Type I: Failure of formation of the vertebral bodies anteriorly
- Type II: Failure of segmentation of the vertebral bodies with an unsegmented bar
- Type III: A combination of Type I and II
Very rare
Often associated with congenital scoliosis, mucopolysaccharidoses, and spondyloepiphyseal dysplasia congenita

Iatrogenic Kyphosis

Most commonly involves the cervical spine
Has been linked to C2 involvement, relatively young patient age, preoperative malalignment, and irradiation

Anatomy

Kyphosis usually involves the thoracic spine. Ideally, thoracic kyphosis should be measured by the sagittal Cobb angle from the endplate of T2 to T12. However, radiographic obstruction due to the shoulders frequently requires that the thoracic kyphosis be determined from T5 to T12.

Pathogenesis

Scheuermann’s kyphosis has a strong hereditary tendency, but the etiology is not known (may be autosomal dominant).¹¹ In 1920, Scheuermann postulated that this form of kyphosis may be caused by avascular necrosis of the cartilage ring apophysis of the vertebral body, but this has not been substantiated.⁹ Other possible etiologies include weakening of the cartilaginous end plate, juvenile osteoporosis, abnormal cartilaginous matrix of the vertebral bodies, or abnormal growth hormone levels.^15-17

Postural kyphosis is normally related to slouching in the young and old with weakened back extensor muscles. The etiology of congenital kyphosis involves either a failure of segmentation or a defect in the formation of the vertebral body elements. Iatrogenic kyphosis is commonly caused by a fracture of the thoracolumbar spine treated non-operatively (especially if the posterior ligaments are disrupted) or extensive laminectomies with or without fusion.^19,21

Natural History

The natural history of postural kyphosis is benign, and the pain usually ends when the child stops growing. Patients with Scheuermann’s kyphosis have the best prognosis when they are skeletally immature, have curves less than 75°, and have vertebral wedging less than 10°. Type III congenital kyphosis has the worst prognosis, with a progression of 5°-8° per year. Paraplegia commonly results if left untreated.⁵ To prevent the progression of iatrogenic kyphosis after extensive laminectomies, preservation of at least one half of each facet is recommended. If that is not possible, arthrodesis is often indicated.

Clinical Presentation

Scheurmann’s kyphosis presents with hyperkyphosis that fails to correct with hyperextension, tight hamstrings, back pain usually located over the apex of kyphosis (more common with lumbar kyphosis), and lower lumbar back pain (due to excessive compensatory lumbar lordosis). Postural kyphosis has a gradual more flexible kyphosis compared to Scheuermann’s kyphosis. It rarely causes pain, and lacks the roentegraphic findings of Scheurmann’s kyphosis.

Congenital kyphosis may be associated with other congenital abnormalities such as congenital scoliosis, mucopolysaccharidoses, and spondyloepiphyseal dysplasia congenita. Iatragenic kyphosis usually presents with pain at the fracture site. The patient may also complain of radiating leg pain and/or neurologic dysfunction.

Imaging and Diagnostic Studies

Obtain standing AP and lateral radiographs, as well as a lateral radiograph with the patient supine on a bolster, which hyperextends the spine to allow evaluation of flexibility. Measure kyphosis using the sagittal Cobb angle between the superior endplate of the upper end vertebra and the inferior endplate of the lower end vertebra.

Scheuermann’s kyphosis is defined by thoracic kyphosis greater than 45° with wedging of 5° or more of at least three adjacent vertebrae, or thoracolumbar kyphosis greater than 30°.² Other common findings include Schmorl’s nodules, an irregularity or flattening of the vertebral endplates, and narrowing of vertebral disc spaces. Later findings include syndesmophytes anteriorly, and facet joint osteophytes posteriorly.

MRI, CT, and bone scans may be used in select patients with associated neurologic findings, and/or severe back pain suspicious for an associated condition such as spondyloysis, tumor, or infection. Obtain an echocardiogram and renal sonogram in patients with congenital kyphosis to look for other congenital abnormalities.²⁴ Assess growth potential by the Risser score or the Greulich and Pyle method.

Classification

Winter and Hall have classified kyphosis into 15 major groups:³

I. Postural disorders

II. Scheuermann’s kyphosis

III. Congenital disorders

A. Failure of segmentation
B. Failure of formation

IV. Paralytic

A. Polio
B. Anterior horn cell disease
C. Upper motor neuron disease (eg, cerebral palsy)

V. Myelomenigocele

VI. Posttraumatic

A. Acute
B. Chronic
C. With or without cord damage

VII. Inflammatory

A. Tuberculosis
B. Other infections

VIII. Postsurgical

A. Postlaminectomy
B. Postexcision (eg, tumor)

IX. Inadequate fusion

A. Too short
B. Pseudoarthrosis

X. Postirradiation

A. Neuroblastoma
B. Wilm’s tumor

XI. Metabolic

A. Osteoporosis (juvenile or senile)
B. Osteogenesis imperfecta

XII. Developmental

A. Achondroplasia
B. Mucopolysaccharidosis
C. Other

XIII. Collagen disease (eg, Marie-Strumpell)

XIV. Tumor (eg, histiocytosis “X”)

A. Benign
B. Malignant

XV. Neurofibromatosis

Treatment

Nonoperative Treatment

Young adolescents with a kyphotic deformity of less than 50° and no evidence of progression may be observed. Postural kyphosis can usually be managed with patient education in proper sitting and standing posture. Pain is managed with non-steroidal anti-inflammatory drugs. Exercise programs and stretching of the hamstrings and back are used to prevent excessive lordosis and hamstring contractures (usually not beneficial unless used in conjunction with brace treatment). Lumbar Scheuermann's kyphosis tends to be non-progressive, and its symptoms usually resolve with the use of nonsteroidal anti-inflammatory drugs and activity modification.²⁰

Bracing is used to correct thoracic kyphosis with curves of 50° to 75° with correction to 40°, or if the patient continues to have pain despite non-operative treatment. Braces are usually worn for 16 to 23 hours until apical wedging is corrected, and then just at night until skeletal maturity. The Milwaukee brace is used for thoracic curves, or if the curve progresses greater than 60°. The TSLO brace is used for curves below T-8. Bracing has a limited role in the long-term management of iatrogenic kyphosis, but can be used to prevent progression until skeletal maturity when the patient is a better candidate for surgery.

Surgical Treatment

Surgery is indicated for thoracic kyphosis greater than 75°, rigid kyphosis greater than 55°, persistent back pain unresponsive to non-operative treatment, or related neurologic deficit. Surgery usually involves an anterior release with interbody fusion (prevents growth of vertebral bodies) followed by posterior spinal fusion.

Thoracic Scheuermann's kyphosis patients with curves less than 65° or bending correction less than 50° may be treated with posterior spinal fusion alone, patients with curves greater than 70° should be treated with combined anterior and posterior fusions.^13,14

Congenital kyphosis usually requires surgical treatment, and is recommended with curve progression of 10° or more since radiographic landmarks are harder to determine in these patients. Congenital kyphosis patients less than 5 years old with curves less than 55° may be treated with posterior spinal fusion, since some correction will occur with continued growth.^6,8 Anterior and posterior spinal fusion is indicated for children more than 5 years old with curves greater than 55°.^7,8

Iatrogenic kyphosis requires surgery if there is thoracolumbar kyphosis, increasing kyphotic deformity, pain, or increasing neurologic deficits. The surgery involves anterior corpectomy and strut-grafting, or combined anterior and posterior decompression with fusion (for severe deformities). A halo fixator is used after surgery to prevent graft dislodgment, spinal malalignment, and pseudarthrosis.

Outcome

Bradford et al showed that Milwaukee brace treatment for Scheuermann’s kyphosis patients improved vertebral wedging and kyphosis by 49% and lumbar lordosis by 36%.¹²
Lonner et al compared the anteroposterior approach to the posterior-only approach for the treatment of Scheuermann’s kyphosis and found that the anteroposterior approach led to slightly better maintenance of kyphosis at follow-up, but had a higher complication rate.²⁵
Jalanko et al compared the anteroposterior and posterolateral approaches for treating congenital kyphosis and found a higher rate of minor complications in the patients treated through a posterolateral approach (40% versus 8%).²⁷
McGrit et al conducted a retrospective comparison of patients treated with laminectomy or laminoplasty after intramedullary tumor resection, and found the rate of iatrogenic deformity was lower after laminoplasty.²⁶

Complications

Intra-operative Complications

Blood loss
Neurologic injury
Vascular injury
Direct trauma
Ischemia
Pneumothorax

Post-operative Complications

Infection
Hematoma
Neurologic deterioration
Pneumonia
Ileus
Pulmonary embolism

Delayed Complications

Pseudarthrosis
Failed instrumentation
Loss of correction
Adjacent level degeneration
Back pain

Pearls and Pitfalls

Scheuermann's kyphosis, postural kyphosis, iatrogenic kyphosis, and congenital kyphosis are the most common kyphotic deformities in children.
The possibility of a spinal cord injury, myelodysplasia, post-tuberculosis infection, achondroplasia, or inherited metabolic storage disease should be considered when diagnosing a patient with a kyphotic deformity.
The appropriate diagnosis is necessary to determine the correct management based on the clinical presentation of kyphosis, its progression, and the patient’s skeletal maturity.

Controversy

There is a debate about the number of wedged vertebra (1-3) to include in the radiographic findings of Scheuermann’s kyphosis.^2,10,13
The benefits of bracing for Scheuermann’s kyphosis remain controversial due to the small amount of retrospective data.¹⁸
The lowest instrumented vertebra for spinal fusion is debated due to the need to achieve good coronal correction, while preserving as much lumbar movement as possible (most recommend using the stable vertebra).

References

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