Kyphosis

Updated: Jan 17, 2018
  • Author: R Carter Cassidy, MD; Chief Editor: Jeffrey A Goldstein, MD  more...
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Overview

Background

Kyphosis refers to the normal apical-dorsal sagittal contour of the thoracic and sacral spine. Normal kyphosis is defined as a Cobb angle of 20-40° measured from T2 to T12. [1, 2]

As a pathologic entity, kyphosis is an accentuation of this normal curvature. Many potential etiologies of kyphosis have been identified. Kyphosis can occur as a deformity solely in the sagittal plane, or it can occur in association with an abnormality in the coronal plane, resulting in kyphoscoliosis. Although pathologic kyphosis can affect the cervical and lumbar spine as well the thoracic spine, cervical and lumbar involvement is uncommon; any kyphosis in these areas is abnormal.

Kyphosis can cause pain and potentially lead to neurologic deficit and abnormal cardiopulmonary function.

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Pathophysiology

The pathophysiology of kyphosis depends on the etiologic factor. The exact cause of Scheuermann disease is still imprecisely defined. Scheuermann postulated that the condition resulted from avascular necrosis of the apophyseal ring. Other theories include histologic abnormalities at the endplate, osteoporosis, [3] and mechanical factors that affect spinal growth. [4] A Danish study demonstrated an important genetic component to the entity. [5]

Postural kyphosis is present when accentuated kyphosis is observed without the characteristic 5° of wedging over three consecutive vertebral segments that defines Scheuermann kyphosis. [6] This is felt to be due to muscular imbalance leading to the round-back appearance of these individuals.

When focal kyphosis occurs after a fracture, more height is lost in the anterior aspect than in the posterior aspect; this is the typical fracture pattern. The angulation can increase as the fracture heals, placing pressure on the spinal cord. Patients with fractures have historically been treated with laminectomy alone, especially in the thoracic spine, and they often had progressive kyphosis at the fracture site. [7, 8]

Postinfectious kyphosis occurs in a manner similar to that just described. Mechanical integrity of the anterior column is lost as a consequence of the infectious process. Bending forces then accentuate the normal sagittal contour.

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Etiology

Many potential causes of kyphosis have been described. [9] Scheuermann disease and postural round back are often identified in adolescents. [10, 11, 12] Congenital abnormalities, such as failure of formation or failure of segmentation of the spinal elements, can cause a pathologic kyphosis. Autoimmune arthropathy, such as ankylosing spondylitis, can cause rigid kyphosis to develop as the spinal elements coalesce.

Kyphosis can also develop as a result of trauma, a spinal tumor, or an infection. Iatrogenic causes of kyphosis include the effects of laminectomy and irradiation, which lead to incompetence of the anterior or posterior column. Finally, metabolic disorders and dwarfing conditions can lead to kyphosis.

This article focuses on kyphosis due to Scheuermann disease and postural, postinfectious, posttraumatic, or iatrogenic etiologies.

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Prognosis

Results of surgical correction vary, depending on the etiology of the deformity.

Malcolm et al reviewed 48 patients and achieved a deformity correction rate of 26% and at least partial pain relief in 98% of patients with posttraumatic kyphosis with anterior and/or posterior fusions. [7]

Lehmer et al studied 38 patients who underwent a single-stage closing wedge procedure to treat posttraumatic and postlaminectomy kyphosis. [13] They obtained a mean correction of 35° with three pseudarthroses. Eight of 14 preoperative neurologic deficits improved, and 76% of the patients treated said they would undergo the surgery again if needed.

Kostuick achieved fusion in 36 of 37 patients receiving anterior-only fusion. [14] Pain significantly improved in 78%, and three of eight patients with paraparesis improved.

Outcomes in Scheuermann kyphosis are similar to those just presented, though the amount of correction achieved may not be correlated with pain relief.

In a series of patients who were treated with a posterior Harrington rod, all had pain relief. However, 16 of 22 lost correction. [15]

Lowe and Kasten used posterior instrumentation to achieve a mean correction of 85° down to 43°. [16]

With anterior-posterior and posterior-only surgery, Speck and Chopin gained an average deformity correction of 40%, and 28 of 45 patients were pain-free. [17] However, four patients had infections, nine lost more than 10° of correction, and one had Brown-Sequard syndrome postoperatively.

Investigators have evaluated advanced techniques, such as osteotomies and new instrumentation. Bridwell et al reported a series of 33 patients treated with pedicle subtraction osteotomy for sagittal imbalance. [18, 19]  The C7 plumb line improved from 16.6 cm positive to 1.7 cm. Pain and Oswestry disability indexes significantly improved. Eight patients had pseudarthrosis, and one had a wound infection. No permanent neurologic injuries occurred.

Video-assisted thoracoscopic release followed by posterior arthrodesis has been successful. In one study, deformity correction was 84.8° to 45.3° in patients with thoracic kyphosis associated with Scheuermann disease. [20] Mean loss of correction was 1.6°, and one hook pulled out. No cases of junctional kyphosis were observed.

In a retrospective study, anterior-posterior correction was compared with posterior-only instrumentation with all pedicle screws. [21] The posterior-only group had significant improvement in terms of blood loss, correction of deformity, and number of complications.

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