Scheuermann Disease or Kyphosis

In 1920, Holger Werfel Scheuermann, a Danish surgeon, described a rigid kyphosis of the thoracic or thoracolumbar spine occurring in adolescents.¹ The disease, now known as Scheuermann disease, manifests itself at puberty and involves ventral wedge formation of one or more vertebral bodies, leading to a rigid kyphotic deformity of the affected segments.^2,3 It is the second most frequent etiologic factor in back pain in children and adolescents following spondylolysis and spondylolisthesis.⁴ Scheuermann disease typically involves the midthoracic spine, with the apex at the T7 and T8 vertebrae.⁵ Sorenson⁶ defined the radiographic diagnosis of Scheuermann kyphosis on the basis of anterior wedging of 5 degrees or more of at least three adjacent vertebral bodies. Scheuermann disease typically involves the thoracic spine but can also occur solely in the thoracolumbar spine in 25% of patients.

Incidence

Scheuermann disease affects between 1% and 8% of the general population.^6,7 In a review of 1384 cadaveric specimens, Scoles et al.⁷ reported a prevalence of 7.4%. Scheuermann disease affects the growing, maturing spine and is usually identified in adolescents between 11 and 17 years of age. In Sorenson’s review, 58% of those affected were male and 42% were female. There are, however, widely divergent reports regarding the relative gender prevalence. Bradford⁸ reported a female-to-male ratio of 2:1. In contrast, Murray et al. reported a 2:1 prevalence in males⁹; 20% to 30% of the patients also have scoliosis. Additionally, there is an increased incidence of spondylolysis in patients with thoracic Scheuermann kyphosis.¹⁰

A familial occurrence of the disease has been described.² Damborg et al.¹¹ reviewed 35,000 twins and found a prevalence of Scheuermann disease of 2.8% (3.6% in males and 2.1% in females). Both the pairwise and probandwise concordance for monozygotic twins was significantly greater than that for dizygotic twins, and the hereditability was 74%. These findings may indicate a strong genetic contribution to the etiology of the condition.

Pathogenesis

The etiology of Scheuermann kyphosis remains unknown.^8,12,13 Many theories have been proposed to explain the progressive wedge shaping of the involved vertebrae. Scheuermann¹ considered the condition a form of avascular necrosis of the ring apophysis that leads to a growth arrest, resulting in wedging of the ventral portion of the vertebral bodies. However, Bick and Copel¹⁴ later showed that the ring apophysis does not contribute to vertebral growth. Furthermore, avascular necrosis has never been identified in affected vertebral segments of patients with the disease.^8,12,15 Schmorl¹⁶ postulated that herniations of disc material through the vertebral end plates (which now bear his name) lead to a loss of disc height and ventral wedging of the vertebral body. Subsequent studies disproved these early theories but have not yet established a cause.

Osteoporosis may be an etiologic factor in the development of Scheuermann kyphosis. Bradford et al.¹⁷ prospectively studied 12 patients with an extensive osteoporosis workup and iliac crest biopsy. They identified increased levels of serum alkaline phosphatase and urinary hydroxyproline, in conjunction with reduced bone mineral density. However, when compared with age-matched controls, no specific relationship could be identified. The authors postulated that Scheuermann disease may be related to a generalized skeletal disease that presents during the adolescent growth spurt. Gilanz et al.¹⁸ subsequently reported on 20 adolescent patients 12 to 18 years of age with Scheuermann kyphosis and could demonstrate no evidence of osteoporosis (as assessed by quantitative CT).

Mechanical factors have also been postulated in the development of Scheuermann kyphosis.^13,17 Strenuous physical activity has been associated with compression of the vertebrae of patients with this disease.¹³ Ogden et al.¹⁹ believe that the term Scheuermann disease is a misnomer; these authors state that the changes noted radiographically are altered remodeling responses to abnormal biomechanical stresses and are not secondary to an underlying disease process. They theorized that the kyphosis occurs first and that the ventral vertebral body is then subjected to increased forces that suppress ventral growth and perpetuate the deformity. The reported success of brace treatment lends support to the mechanical theory.²⁰ Lambrinudi²¹ and others have suggested that the upright posture and tightness of the anterior longitudinal ligament of the spine contribute to the deformity. Most investigators believe that the growth plate becomes disorganized first and the emerging kyphosis follows. The kyphosis and growth plate changes may ultimately potentiate each other. The kyphosis likely results in increased pressure on the vertebral end plates ventrally, allowing for uneven growth of the vertebral bodies with wedging (as per Wolff law).

Recently, Fotiadis et al.²² screened 10,057 students and found 175 children with Scheuermann disease (study group). The length of the sternum was greater in the healthy (control) group. There was a statistically significant difference between the two groups with regard to sternum length. The children with Scheuermann disease were taller in relation to the control group. These authors concluded that the shorter length of sternum than normal has a possible correlation with the appearance of Scheuermann disease. Presumably the shorter length of the sternum increases the compressive forces on the vertebral end plates anteriorly, allowing uneven growth of the vertebral bodies with wedging.

Clinical Features

The onset of Scheuermann disease usually appears around puberty, commonly as kyphosis of the thoracic (type I Scheuermann) or thoracolumbar spine (type II Scheuermann). These two entities differ both in location and by their clinical presentation. The deformity is often attributed to poor posture. This results in a delay in both diagnosis and treatment. Pain is often present; standing, sitting, and heavy physical activity may aggravate the pain (i.e., mechanical pain), which may or may not subside with cessation of growth. Adults who have untreated Scheuermann disease may have severe back pain, especially when the deformity is advanced.

Patients generally present with an angular thoracic or thoracolumbar kyphosis accompanied by a compensatory hyperlordosis of the lumbar spine. Their compensatory lordosis may lead to an increase in pelvic tilt.³ Frequently, the cervical lordosis is increased with forward projection of the head. The kyphosis is fixed and remains apparent on hyperextension of the spine. In rare instances, advanced thoracic kyphosis can lead to thoracic spinal cord compression and paraparesis.²³ Thoracic disc herniation may also be associated with Scheuermann kyphosis, and the patient may present with signs and symptoms of myelopathy.^2,24,25 Pain, when present, is usually at the site of the thoracic deformity. Sorenson described pain as the major symptom in 50% of patients with advanced disease.⁶

Clinical examination often reveals tight hamstrings as well as a popliteal angle of less than 30 degrees and subtle neurologic findings. Tight hamstrings have recently been implicated as a possible cause of sagittal decompensation.²⁶

In addition to the kyphosis of the thoracic spine, affected individuals demonstrate varying degrees of structural scoliosis.^5,15,17 Blumenthal et al.¹³ noted lumbar scoliosis in 85% of 50 patients with type I Scheuermann disease. Spondylolysis and spondylolisthesis are also common in the lumbar spine.^2,17 Ogilvie and Sherman²⁷ observed a 50% incidence of asymptomatic spondylolysis in 18 patients with type I disease. They postulated that the excessive hyperlordosis places stress on the pars of the L4 and L5 vertebrae, resulting in the spondylolysis. Increased cervical lordosis also develops as a compensatory mechanism and causes the head to protrude forward (gooseneck deformity), producing a negative sagittal balance with the C7 plumb line lying posterior to the sacral promontory.⁴

Radiographic Features

Routine radiographic studies obtained for evaluation of the patient with Scheuermann kyphosis should include anteroposterior and lateral radiographs of the entire spine via long films (scoliosis views) and a hyperextension lateral image of the thoracic spine. The lateral radiograph should be obtained with the patient standing, with knees and hips fully extended and arms out and away from the spine. The patient should be looking forward. The lateral radiograph should document the following typical changes of Scheuermann kyphosis:

The abnormal sagittal parameters are determined from the thoracic, thoracolumbar, and lumbar regions of the spine.

Both the vertebral wedging and kyphosis should be measured by the Cobb method. When evaluating serial radiographs to document progression, care should be taken to ensure that the same end-vertebral bodies are measured each time. The normal range of thoracic kyphosis is 20 to 45 degrees on a standing lateral radiograph^28–30 as measured by the Cobb method. Normal kyphosis increases with age and is slightly greater in women than in men.^31,32 Ventral wedge compression of one or more vertebral segments in association with kyphosis is the hallmark radiographic feature in Scheuermann disease.¹ Wedging of at least 5 degrees of three or more vertebrae is diagnostic of Scheuermann disease. The kyphosis in Scheuermann disease is usually incompletely reducible with postural and positional changes. The vertebra with the greatest ventral deformity is located at the apex of the kyphotic curve. The kyphosis may approach 100 degrees in advanced cases with a compensatory hyperlordosis of both the cervical and lumbar spine.³

Early in the progression of the disease, the end plates may appear irregular.^3,5,16,33 The changes have been described as moth-eaten and relate to growth retardation rather than to a destructive process.⁵ As the disease progresses, the growth plates appear sclerotic, but despite interspace narrowing the change is not associated with interbody fusion. The absence of fusion helps distinguish Scheuermann disease from other kyphotic deformities of the spine.^5,8,13

An MRI before surgery is recommended to rule out any incidental thoracic disc herniation, epidural cyst, or possible spinal stenosis. The literature has shown such exceptional cases in various reports of neurologic complications in Scheuermann kyphosis.^2,24,25,29 The MRI also assesses the lumbar spine discs, because disc degeneration of the lumbar spine may explain, in some cases, the pain rather than the kyphotic deformity itself.

It is important to differentiate Scheuermann kyphosis from a postural roundback deformity. Adolescents with postural roundback deformity have a slight to moderate increase in the degree of thoracic kyphosis (usually ≤60 degrees), which is less acutely angulated and may be associated with an accentuated lumbar lordosis. This type of kyphosis is flexible and not associated with muscle contractures. There is also a normal appearance of the vertebrae without evidence of wedging, end-plate irregularity, or premature disc degeneration on imaging.^4,33,34

Natural History

The natural history of Scheuermann disease remains very controversial. The condition tends to be symptomatic during the teenage years. However, in the late teenage years, it often produces less pain. If the residual kyphosis in these patients remains less than 50 to 60 degrees, there is usually little discomfort in adult life.³⁵ In a long-term follow-up study, Sorenson noted pain in the thoracic region in 50% of patients during adolescence, with the number of symptomatic patients decreasing to 25% by the time of skeletal maturity.⁶ Later, other authors offered a contrasting view, stating that adults with Scheuermann kyphosis have a higher incidence of disabling back pain than the normal population.^2,8 Murray et al.⁹ performed a study in 67 patients with Scheuermann kyphosis diagnosed by Sorenson’s criteria (i.e., physical examination, trunk strength, radiography, a detailed questionnaire, and pulmonary function testing). The patients had an average kyphotic deformity of 71 degrees, and average follow-up was 32 years. An age-matched comparison group was used as a control. Normal or above-normal averages for pulmonary function were found in patients in whom the kyphosis was less than 100 degrees. Patients in whom the kyphosis was greater than 100 degrees and the apex of the curve was in the first to eighth thoracic segments had restrictive lung disease. The authors concluded that patients may have functional limitations but that these did not result in severe limitations due to pain or cause major interference with their lives. Lowe and Kasten state that adults with greater than 75 degrees of kyphosis can have severe thoracic pain secondary to spondylosis that can limit their activity.³⁶

In summary, patients experience wide variations in the natural history of Scheuermann kyphosis. Thoracic Scheuermann kyphosis greater than 100 degrees can be associated with reduced pulmonary function. There appears to be a subset of patients with refractory symptoms that justify the risk associated with intensive treatments such as bracing and surgical management.

Treatment

The management of patients with symptomatic Scheuermann kyphosis ranges from observation to combined ventral and dorsal reconstructive surgery. Treatment is based on the severity of the deformity, the presence of pain, and the age of the patient. The recommended treatment should be tailored to the individual on the basis of deformity progression, the severity of the curve, and symptomatology.