Practice Essentials
Scheuermann thoracic kyphosis (Scheuermann disease) is a structural deformity of the thoracic spine, defined by anterior wedging of at least 5° of three or more adjacent thoracic vertebral bodies. [1, 2] Further radiographic findings include Schmorl nodes and endplate narrowing. Although the etiology of Scheuermann kyphosis remains unknown, the natural history and treatment indications are well described. [3] The incidence of Scheuermann kyphosis is estimated to be as high as 8-10% in adolescents aged 10-12 years. [4, 5]
Both adolescents and adults can develop symptoms associated with Scheuermann kyphosis. Adolescents typically develop a progressive cosmetic deformity, which first brings them in for medical attention, whereas adults with long-standing deformity typically develop pain as an indication for treatment.
Bracing has been demonstrated to be an effective treatment modality for the adolescent with a progressive deformity, whereas pain often responds to nonoperative care, including physical therapy and anti-inflammatories in both adolescents and adults. In patients with a progressive deformity, refractory pain, or neurologic deficit, surgical correction may be indicated.
Historically, surgical care of Scheuermann kyphosis has shadowed surgical care of idiopathic scoliosis. The role of surgical care for adolescent kyphosis was debated in the sparse literature before 1960. In 1962, Paul Harrington introduced the Harrington rod to augment the surgical correction of scoliosis. In 1965, Moe presented his nonoperative and operative results from a posterior approach in the treatment of adolescent kyphosis. Postoperative curve progression and a high pseudoarthrosis rate complicated the posterior-only approach. [6]
Once a patient with Scheuermann kyphosis, either adult or adolescent, reaches a surgical threshold, the surgeon's aims are essentially the same:
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To obtain a solid arthrodesis throughout the length of the kyphosis with appropriate correction of the deformity
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To alleviate pain
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To improve spinal alignment
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To preserve motion segments
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To reduce risk for junctional kyphosis
There are three main surgical options:
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Posterior-only approach
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Anterior-only approach
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Combined approach using both anterior and posterior techniques
Single approaches, either solely anterior or solely posterior, typically have been reserved for deformities that exhibit partial ability for correction on a hyperextension film. Combined approaches typically have been mandated for more substantial deformities. (See Treatment.)
Combined anterior and posterior surgical approaches for Scheuermann kyphosis were first popularized in the 1970s. These techniques increased fusion rates and correction and remain the foundation of current surgical approaches. Subsequent innovations included simultaneous thoracoscopic anterior release with postinstrumented fusion. Current surgical recommendations in symptomatic Scheuermann disease aim to achieve well-balanced sagittal alignment, preserve motion segments, and reduce the risk of junctional kyphosis. [5]
Pathophysiology
Although the etiology of Scheuermann kyphosis is not fully understood, the histologic and pathologic findings are well described. Radiographically, the presence of three adjacent wedged vertebral bodies of at least 5° each is pathognomonic for Scheuermann kyphosis. Anatomic findings include a thickened anterior longitudinal ligament (ALL) with narrowed intervertebral disks. The vertebral bodies are wedged, and traumatic disk herniations through the endplates are consistent findings. In addition, the spinopelvic orientation of these patients has shown a more horizontally oriented sacrum as compared with a control group of patients who do not have Scheuermann kyphosis. [7]
The collagen-to-proteoglycan ratio in the matrix of the endplate in patients with Scheuermann kyphosis has been described as low in comparison with that in patients without the condition. This relative decrease in collagen has been hypothesized to lead to an alteration in the ossification of the endplate and, thus, to altered vertebral body growth.
Finally, osteoporosis has been postulated to play a role in the pathology and etiology of Scheuermann kyphosis. Bradford reported on 12 patients with Scheuermann kyphosis who were prospectively studied with an extensive osteoporosis workup, including an iliac crest biopsy. [8] Some of the patients with Scheuermann kyphosis were demonstrated to have a mild form of osteoporosis, though a causal relation between this finding and the development of Scheuermann kyphosis was not established.
A follow-up study by Gilsanz reported on 20 adolescent patients aged 12-18 years with Scheuermann kyphosis who demonstrated no evidence of osteoporosis as measured by quantitative computed tomography (CT). [9]
Bradford, however, had surmised that the osteoporosis was transient and somehow led to altered vertebral growth and, thus, to the formation of Scheuermann kyphosis. [8] This etiologic hypothesis remains a subject of debate.
Etiology
The proximate cause of Scheuermann kyphosis remains to be determined. Scheuermann initially hypothesized that avascular necrosis of the ring apophysis led to premature cessation of growth anteriorly and subsequent wedging of the vertebral body. Bick et al quickly countered that theory by showing that the ring apophysis has no effect on anterior longitudinal growth since it is not part of the cartilaginous physis. [10] Schmorl later postulated that traumatic herniations of disk material through the vertebral endplates led to subsequent loss of disk height and anterior vertebral wedging. This theory was also disproved.
Genetic factors have also been mentioned in etiologic discussions surrounding Scheuermann kyphosis. Halal reported on five families in which Scheuermann kyphosis appeared to transfer in an autosomal-dominant mode of inheritance. [11] Zaidman et al performed clinical and genetic investigations to confirm the autosomal dominant inheritance pattern and found an associated mutant major gene, as well as the candidate genes IHH, PAX 1, and SOX9. [12]
Skogland [13] and Ascani [14] proposed other theories that Scheuermann kyphosis is based on a genetic inheritance. [13] Skogland reported on 62 females aged 9-18 years, whose mean height was an average of 2.5 standard deviations (SDs) above average. Of these 62, 18 had thoracic kyphosis of more than 40°, with 11 additional participants having vertebral anomalies consistent with Scheuermann kyphosis.
Damborg et al found a heritability of 0.74 in Scheuermann's disease, with a lower threshold in men than women. [15]
Ascani also presented work demonstrating a similar correlation between Scheuermann kyphosis and height. He demonstrated increased levels of growth hormone as well. [14]
A study by Hershkovich et al suggested that height and body mass index (BMI) are associated with the risk and severity of spinal deformities in adolescents. [16] The study, which included 103,249 males and females aged 17 years who had been diagnosed with some degree of kyphosis or scoliosis, found that in underweight males and females, spinal deformities were significantly more common and were more likely to be severe. Greater height was also associated with increased risk and greater severity of spinal deformities in males and females.
Mechanical factors have been postulated as a cause for Scheuermann kyphosis. [17] Scheuermann initially noted a higher incidence of kyphosis in industrial workers and found that hyperextension bracing was helpful in curbing the progression of Scheuermann kyphosis; these findings would support a mechanical etiology.
Wood et al postulated that biomechanical stresses may alter the remodeling response in the vertebral bodies. [18] This, in turn, may result in increased compressive forces on the anterior part of the vertebral body, which may stunt growth and lead to Scheuermann kyphosis. Bracing provides evidence in favor of this etiologic hypothesis by virtue of its success as a nonoperative treatment for this disease. However, the radiographic and histologic changes of Scheuermann kyphosis have not yet been demonstrated to be secondary or primary in the development of Scheuermann kyphosis.
Epidemiology
The prevalence of Scheuermann kyphosis is estimated to be 4-8% of the general population. Sorensen reported a prevalence of 0.4-8.3%. [2] Scoles et al reported on 1384 cadaveric specimens and noted a 7.4% prevalence of Scheuermann kyphosis. [19] The incidence may be as high as 8-10% in adolescents aged 10-12 years. [4, 5]
Although the prevalence of Scheuermann kyphosis is generally accepted as being essentially equal in males and females, there has been some debate regarding this finding in the literature. Bradford et al reported a female-to-male ratio of 2:1 for Scheuermann kyphosis. [20, 21] Meanwhile, Murray et al reported the exact opposite finding, with a 2.1:1 male-to-female ratio. [22] In Sorenson's work, 58% of the patients were male, and 42% were female. [2]
Prognosis
Outcome and prognosis depend on the individual patient and treatment rendered. Generally, a patient with moderate-to-mild Scheuermann kyphosis rarely requires surgery or even bracing. These patients can be managed with education, guidance, and overall encouragement to resume and maintain normal activity levels. Aggressive use of exercise and judicious use of anti-inflammatory medications can augment this regimen.
The outcome and prognosis of bracing treatment is more controversial. While the brace is in place, approximately a 50% correction of the deformity should be expected. However, once the brace is removed, a gradual loss of correction is expected over time.
Sachs et al reported on 120 patients reviewed 5 years after discontinuance of bracing [23] ; 69% of these patients had maintained at least 3° of improvement over their presenting radiographs. Other authors have presented similar results. Sachs also reported that the prognosis was less favorable if the presenting curve was 74° or more. One third of these patients failed bracing therapy and progressed to needing surgery.
There is a relative lack of patient-based outcome studies in patients who have undergone surgical correction of Scheuermann kyphosis, though a number of retrospective reviews have reported high patient satisfaction ratings, as have some studies with insufficient numbers of control subjects. Surgical correction of the deformity affords predictable restoration of normal thoracic kyphosis, thus halting progressive deformities. Reasonable pain relief and resumption of normal activities also are reflected in multiple retrospective reviews.
Graat et al carried out a cohort study that assessed long-term (mean follow-up, 18 y) clinical and radiologic outcomes in 29 patients who underwent surgical treatment of Scheuermann kyphosis via either a posterior approach (n = 13) or a combined anterior-posterior approach (n = 16). [24] Radiologic results were disappointing, but these did not correlate with clinical outcome scores, which were good. Outcomes were better with the combined approach than with the posterior approach.
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Preoperative lateral radiograph of patient with 85° thoracic deformity secondary to Scheuermann kyphosis.
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Postoperative lateral radiograph demonstrating two-rod leverage technique after anterior release allowing reduction of deformity to 47°.
