Kyphosis (plural: kyphoses), much less commonly kyphus, is a term used to describe the sagittal curvature of the thoracic spine. Hyperkyphosis is when the kyphosis angle is above the normal range ^5,7.

Pathology

Kyphosis increases with age, with a kyphosis angle of ~25° (range 20-29°) in adolescents and young adults to ~38.5° (range 35-42°) in adults aged over 65 years ^5,7. There appears to be no gender predilection, but it may vary with ethnicity ⁷.

A kyphosis angle >40° has been widely accepted as the threshold for hyperkyphosis, although no published consensus exists ^5,7,9. Using the >40° threshold, the incidence of hyperkyphosis in 60-year-olds and over is ~30% (range 20-40%), and in 70-year-olds and over is ~55% ⁷. Thus, some authors recommend a threshold of >50° ⁵ or >60° ⁷ to avoid overdiagnosis, although an age-adjusted range between 20-60° may be more appropriate ⁷.

Etiology

An increased kyphosis angle is associated with the following:

• normal aging: the degree of kyphosis is mainly related to intervertebral disc degeneration and vertebral body shape with a minor component related to decreased muscle strength ^5,7

• vertebral body fracture

  • spinal compression or wedge fracture, usually related to osteoporosis ⁵

  • traumatic vertebral body fracture ⁶

  • pathological fracture

  • present in ~40% of patients with hyperkyphosis ⁵

  • each vertebral body fracture increases the kyphosis angle by ~4 degrees ⁵

• Scheuermann disease

• spondyloarthropathies

A decreased kyphosis angle is seen in the following condition:

• straight back syndrome

Radiographic features

Plain radiograph

The Cobb angle technique is the most commonly used to assess for kyphosis ^5,6. It is measured on a unsupported erect lateral projection as the angle between two thoracic vertebrae, although the levels used vary in the literature:

• superior endplate of T2 ⁹ or T4 ⁵ or T5 ⁹ (depending on visualization)

• inferior endplate of T12 ^5,9

The Cobb angle technique

• has inter- and intra-observerser variation of 3-5° ⁵

• may overestimate kyphosis if there are concurrent vertebral endplate irregularities ¹

• measuring above the T4 level results in higher kyphotic angles ⁷

Other kyphosis angle measurement techniques include:

• wedge angle ⁶

• alternative Cobb ¹

• vertebral centroid angles ³

• adjacent endplate method ⁶

Treatment and prognosis

Exercise programs and bracing may reduce thoracic hyperkyphosis in adults ⁸.

Hyperkyphosis is associated with reduced physical performance, increased falls, and increased vertebral body fracture risk as well as increased all-cause mortality ^5,7.

History and etymology

Derived from the Greek word kyphōsis, from kyphos meaning humpbacked ⁴.

See also

• lordosis

• scoliosis