9 Scheuermann’s Kyphosis

Scheuermann’s disease, also known as Scheuermann’s kyphosis, was first described in 1921 by Danish surgeon Holger Werfel Scheuermann. Coined “kyphosis dorsalis juvenilis,” he characterized the condition after several years at the Danish Home for Crippled Children, during which he noticed a recurring pattern of painful kyphosis in many of the adolescents, especially the boys.¹ Unlike other children with “round backs,” radiographs of his patients revealed compression of anterior portions of the vertebral bodies. The recent discovery of Legg–Calve–Perthes disease led him to believe that a similar process was occurring in the spine, with compression of the vertebral bodies secondary to avascular necrosis of the ring apophysis. The modern definition, developed by Sørensen in 1964, of three contiguous vertebral bodies with anterior wedging of at least five degrees,² still uses vertebral body changes as the key pathological feature of the disease. The resultant thoracic hyperkyphosis is what gives patients with the disease their classic appearance. Despite advanced imaging and histopathological studies revealing that many patients have vertebral endplate irregularities (“Schmorl’s nodes”), narrowing of the disc spaces, and premature disc degeneration, the original definition is still utilized today, as none of these secondary findings are necessary to diagnose the disease.

9.2 Epidemiology and Etiology

The prevalence of Scheuermann’s kyphosis is believed to be somewhere between 2 and 8%.^3,4,5 Scoles examined a skeletal collection of over 1,384 spinal columns, finding that approximately 7% of the patients had vertebral changes consistent with the disease.³ One of the most recent series by Makurthou et al⁵ showed an overall rate of 4% in the Dutch population. The disease was found in 4.5% of men compared to 3.6% of women, though this difference was not significant. Despite these findings, the majority of spine surgeons would agree that the typical Scheuermann patient is an adolescent male, as originally was described. The popular belief of what comprises a “typical” Scheuermann patient—namely, an adolescent boy with a high thoracic curve—may lead clinicians to miss atypical presentations of the disease worldwide.⁶

The etiology of Scheuermann’s disease is still unknown, but is postulated to be multifactorial, due to a combination of biological and mechanical factors. Examples of histopathologic findings that have been described include avascular necrosis of the annular apophysis (subsequently disproved), disorganized endochondral ossification of the wedged vertebral body endplates, and increased mucopolysaccharides in degenerated discs between these vertebrae.^3,7 However, it is impossible to know whether these findings are primary or secondary to mechanical conditions acting on the spinal column. The fact that vertebral wedging is partially reversed by bracing treatments suggests that mechanical factors play a role.⁸ From the time of the initial descriptions of the disease, experts have noted mechanical differences among Scheuermann’s patients. Scheuermann himself believed that children who worked heavy labor were more susceptible, and Sørensen’s seminal 1964 text described children with “poor posture” who eventually progressed to having the key radiographic changes of the disease. Lambrinudi theorized that an upright posture combined with a tight anterior longitudinal ligament may contribute to the deformity.⁹ Most likely, there is interplay of biological and mechanical factors, in which a biologically susceptible child is subject to mechanical forces during adolescence, progressing to disease. Discovering which are most important may prove to be an impossible task.

On the other hand, a genetic etiology is perhaps the theory with the strongest supporting evidence. Several families have shown multifactorial inheritance of the condition. In a study of one family with an autosomal dominant pattern of inheritance, McKenzie and Sillence discovered that features of Scheuermann’s disease were found in untested relatives of the proband, and that other chromosomal anomalies were more likely in these family members compared with the general population.¹⁰ The Dutch Twin Registry, a longitudinal database of all twins born in Denmark over the last 130 years, has been crucial in establishing a genetic component of the disease. Damborg et al showed that concordance of the disease was two to three times higher in monozygotic twins compared with dizygotic twins.⁴ They concluded that their findings supported a multifactorial inheritance pattern with a heritability of 74%. Thus, it is most likely that children born with a genetic predisposition into the right mechanical environment are those who eventually develop the condition.

9.3 Natural History

The natural history of Scheuermann’s disease is relatively benign, though many patients often find themselves with lower back pain later in life. The theory behind this observation is that to preserve sagittal balance, the hyperkyphosis of the thoracic region leads to hyperlordosis of the lumbar region, causing undue stress on the lumbar back musculature and facet joints distal to the apex of the deformity, accelerating normal degenerative changes and leading to increased back pain in middle age.¹¹ In a seminal study out of the University of Iowa in which 67 Scheuermann’s patients were followed for 32 years, adult patients had higher rates of intense back pain, but were not significantly disabled by their condition when compared to age-matched controls.¹² In a more recent work, Ristolainen et al surveyed 80 patients with Scheuermann’s after a 37-year follow-up period, comparing their responses to those from a national census survey of age-matched adults.¹¹ Their findings were similar to the Iowa study, in that there were no differences in employment rates, but increased rates of constant back pain and sciatic pain in the past 30 days. Adult Scheuermann’s patients also found themselves having more difficulty mounting stairs and carrying 5-kg loads. Perhaps most concerning, the patients reported an overall lower quality of life (6.4 vs. 7.6 on a visual analog scale [VAS], p < 0.001), and a lower general health status (age-adjusted 6.4 vs. 7.3, VAS scale, p < 0.001). Interestingly, the degree of kyphosis did not correlate with the self-reported quality of life, back pain, or overall health. Data on whether surgery for the disease influences these outcomes is still unknown, as follow-up data through this time period using modern techniques are currently unavailable.

Given that Scheuermann’s disease may present as kyphotic deformity in the thoracic, thoracolumbar, or lumbar regions, a classification system may be used to distinguish these varieties.¹³ Type I disease, the typical presentation, includes thoracic kyphosis and three or more contiguous wedged vertebral bodies ( Fig. 9.1). Type II patients have kyphosis in the thoracolumbar/lumbar region, a more atypical form, and may only have one or two wedged vertebral bodies, though they tend to show higher rates of Schmorl’s nodes and disc space narrowing on radiographs ( Fig. 9.2). Some authors propose that those with type II disease have a distinct natural history compared to type I patients, responding better to nonoperative treatment, though this has yet to be shown in a longitudinal series.¹³

Neurological complications as a result of the disease are rare, though rate of progression, local anatomical variations, and degree of kyphosis are all felt to be factors that increase a patients’ risk. For example, a high degree of kyphosis with a sharp degree of vertebral wedging is likely a risk factor for neurologic complication, given the way the spinal cord drapes over such a deformity. On the other hand, any neurologic anomalies in the region (e.g., dural cysts) will put a patient at high risk for complication.¹⁴ Lastly, as patients age, the accompanying disc degeneration often puts them at a higher risk of experiencing complications such as thoracic disc herniation.

Fig. 9.1 A 22-year-old otherwise healthy woman presents with thoracic back pain, progressive in severity over the past 7 years. Physical therapy was unsuccessful in alleviating her symptoms. Preoperative imaging revealed a 92-degree thoracic kyphosis with apex at T7–T8, with a stable sagittal vertebrae at L1 (a,b). Preoperative MRI demonstrated no herniated discs or spinal cord/dural abnormalities in the region of the deformity (c). Note the relative inflexibility of curve on the supine MRI. She underwent posterior fusion from T2 to L1 with Smith–Peterson osteotomies at levels T6–9. The patient was discharged from the hospital on postoperative day 4. One month later, she developed a distal postoperative seroma that was treated with incision and drainage and a short course of oral antibiotics. Postoperative imaging 8 months later (d,e) demonstrates correction of the kyphosis to 47 degrees and good sagittal balance, with resolution of her back pain.

Fig. 9.2 A 15-year-old obese, otherwise healthy adolescent girl presents with progressive kyphotic deformity. The kyphosis was first noted at the onset of puberty, but quickly progressed through her growth spurt. She denies any neurologic symptoms. Preoperative imaging revealed thoracolumbar kyphosis of 100 degrees, apex at the T10–T11 disc (a,b). CT imaging shows the flexibility of the curve with the patient supine (c). Before surgery, she underwent pulmonary function testing given her obesity combined with the severity and age of onset of her kyphosis. Posterior spinal fusion was performed from T3 to L3, with Smith–Peterson osteotomies at T9–L1, after which the spine was flexible enough as to not require a pedicle subtraction osteotomy. A third rod using open dominoes was attached given the length of the construct and sharp angulation of the preoperative deformity. One-month postoperative imaging displays a correction to 50 degrees with good sagittal balance and no hardware complications (d,e).

The typical presentation of Scheuermann’s kyphosis has not changed in the near century since the disease was first described. Though the majority of patients present in adolescence (typically around the time of late puberty, ages 13–17), adult presentations of the disease are also known.¹⁵ However, whether these patients developed the disease at a later age or did not pursue treatment until adulthood remains a mystery. Often, patients seeking treatment for the disease will present with two symptoms—back pain and cosmetic concerns. If present, the characteristics of back pain should be described in detail—typically, it is present just distal to the apex of the deformity. In patients who present later in life, they may present with complaints of lumbar spondylosis, as the compensatory lumbar hyperlordosis may predispose them to this condition. Other complaints in more severe forms of the disease include difficulty maintaining horizontal gaze. Neurological complaints are atypical and should prompt further workup. Similarly, even in severe forms of the disease, cardiac and pulmonary symptoms are extremely rare and almost always associated with an alternative diagnosis. With regard to past medical history, patients are typically healthy, as Scheuermann’s disease is not associated with other anomalies. Some authors propose a higher rate of sex chromosome abnormalities in certain familial forms of the disease, but this has not yet been corroborated.¹⁰

The differential diagnosis for Scheuermann’s disease is broad. Particularly, any secondary cause of vertebral wedging must be ruled out. Postural kyphosis, or “round back syndrome,” must be separated as this condition is benign and will resolve with nonsurgical modalities such as physical therapy aimed at strengthening the core and paraspinal musculature. Other diagnoses that must be considered in the evaluation include tumor, vertebral body fracture, neuromuscular conditions, and congenital vertebral abnormalities. In particular, multiple anomalies should prompt thorough evaluation for other causes. With proper imaging studies and a thorough medical history, other conditions can usually be ruled out.

The physical examination is particularly helpful in distinguishing postural kyphosis from Scheuermann’s disease. Though both have kyphosis while upright, the patient with postural kyphosis will have resolution of the deformity upon hyperextension. The presence of the kyphotic hump upon hyperextension is essential for the diagnosis of Scheuermann’s disease, as it marks a fixed curve unlikely to resolve without intervention. The examiner should have the patient perform an Adams forward bend test, which will highlight the position of the deformity as either in the thoracic or thoracolumbar region. Furthermore, any scoliosis of the lumbar region can be appreciated, as this will be necessary later when determining the lowest instrumented vertebrae. Lastly, all patients should undergo a thorough skin evaluation to rule out neuromuscular disorders such as neurofibromatosis, which can also present with sharp thoracic deformity.

9.5 Imaging Studies

Standing long-cassette anterior−posterior (AP) and lateral radiographs are mandatory in the patient evaluation and invaluable for preoperative planning. In particular, patients should stand with the shoulders and elbows fully flexed forward so that the finger tips are resting on the clavicles. This position allows for the best visualization of the upper thoracic spine. The patient should assume a natural standing posture, with the knees fully extended. The pelvis and hips must be included in the view for calculation of pelvic parameters such as pelvic incidence, pelvic tilt, and sacral slope, which may influence the amount of correction necessary to achieve sagittal balance.¹⁶ Supine AP, lateral, and upright flexion and extension¹⁷ views can be helpful in evaluating the flexibility of the curve and the intervertebral discs at the most proximal and distal ends of the deformity. Though not direct correlates, the curve flexibility can be estimated on supine magnetic resonance imaging (MRI) or computed tomography (CT) imaging. Radiographs with “Cotrel’s traction” are also used as a formal method to quantify the flexibility of the curve.¹⁸

The degree of the thoracic curve should always be measured using the Cobb method, by measuring the angle between the superior endplate of the most proximal vertebrae and the inferior endplate of the most distal vertebrae. Normal thoracic sagittal kyphosis is commonly accepted as 20 to 50 degrees of kyphosis from T2 to T12 using the Cobb method. Patients with Scheuermann’s disease will show multiple abnormalities on standing plain films, especially in the sagittal plane. Radiographs must be evaluated for vertebral wedging of at least 5 degrees in three contiguous vertebrae. The patient with two or less does not qualify as having Scheuermann’s disease, rather “round back” deformity (note, this does not apply in those patients with thoracolumbar kyphosis). The kyphosis in patients with round back deformity usually corrects on supine radiographs. On the other hand, a Scheuermann patient has a fixed hyperkyphosis in the thoracic or thoracolumbar region, ranging from 55 degrees to well over 100, with only partial to no correction on supine films. There is also a compensatory hyperlordosis. In a balanced sagittal spine, this hyperlordosis is expected to be approximately 10 to 30 degrees more than the thoracic kyphosis.¹⁹ The compensatory hyperlordosis is responsible for the negative sagittal balance often seen in patients with the disease.

MRIs should be strongly considered in all patients in whom another diagnosis is suspected or in any patient undergoing surgery.²⁰ Cervical, thoracic, and lumbar MRIs are essential to rule out anomalies such as extradural cysts, degenerated discs about the levels of deformity, and stenosis of the thoracic canal. Dangers around the spinal cord must be identified preoperatively, as such pathology may cause neurologic compromise after surgical reduction of the deformity. A CT scan is also obtained by most experts, as the deformed vertebral bodies may require atypical pedicle screw trajectories.

9.6 Nonoperative Treatment

As with most conditions, the decision to treat should be based on the alleviation of the chief complaint—usually pain and/or cosmetic concerns. Experts vary in their decisions regarding which patients will improve with nonoperative treatment. In general, patients with flexible curves less than 75 degrees, no neurologic deficit, and minimal cosmetic complaints have the greatest chance of improving with nonoperative treatment. Asymptomatic adult patients almost always require no treatment at all. Nonoperative management is aimed at reducing the mechanical factors contributive to the pathological process. For those electing nonoperative treatment, the primary modality is bracing. Sachs followed 274 patients treated with a Milwaukee brace from the ages of 12.5 to 16 years old, and reported results up to 24 years after bracing was discontinued.⁸ In patients who wore the brace consistently, 76/110 showed improvement, and 24 worsened. An initial kyphosis of 74 degrees or more universally required spinal fusion. After bracing, the kyphosis tended to correct by approximately 50%, but some of this initial correction was lost over time. Overall, at 24 years, 69% of patients showed improvement. Much like the case in adolescent idiopathic scoliosis, consistent brace wear in this age group can be difficult to achieve. The brace must be worn at least 16 hours a day. A regimen consisting of brace wear during school and at night is preferred, as this allows the patient to achieve the minimal amount of time in the brace while permitting healthy activity during free time outside of school. Of note, brace wear must be started before the child has reached skeletal maturity, as this will let the vertebral bodies to correct some of the wedging during growth. In the Sachs study, the angulation of the vertebral bodies improved from an average of 7.8 to 6.8 degrees in skeletally immature patients treated with bracing. The choice of brace is very clinician-dependent. Though the Milwaukee braces were used in the past, the impracticality and discomfort of this device has made it less favorable. The majority of Scheuermann’s curves can be encompassed with a thoracic lumbar sacral orthosis (TLSO) brace, which is the choice of most physicians today.

Physical therapy is the second component of nonoperative management of the disease. Hamstring stretching should be incorporated to alleviate the increased tension in the distal part of the curve. Trunk extensor and core strengthening will also help alleviate the back pain associated with the hyperkyphosis. A series by Weiss et al of 351 Scheuermann’s patients treated with physical therapy showed a reduction in pain from 16 to 32%.²¹ Of note, these patients underwent daily sessions consisting of hours of physiotherapy, with multiple modalities employed, including osteopathy, manual therapy, and McKenzie exercises. Though adherence to such an intensive regimen may be impractical to accomplish in a clinical setting, the principles should be applied in any course of nonoperative treatment.

9.7 Operative Treatment

General indications for operative treatment include kyphosis greater than 75 degrees, persistent back pain not responsive to conservative measures, and unacceptable cosmesis. Of note, the decision to pursue surgical correction is not based on curve magnitude alone. In a prospective cohort study in which the decision to operate was based on surgeon and patient decision, Polly and colleagues reported that patients with higher body mass indices (BMIs) and worse pain scores were more likely to undergo operative treatment, while maximal sagittal Cobb’s angle did not differ between the cohorts (73 + 11 degrees operative cohort vs. 70 + 12 nonoperative cohort, p = 0.011).²² The issue of how dissatisfaction with appearance impacts decision making deserves special consideration, as many adolescents are unhappy with their appearance. The higher BMIs found in the operative cohort speak to the delicacy of determining whether an adolescent’s negative self-image is normal or causing significant distress. Severe deformities may be catastrophic in their effect on a young adult’s ego and subsequent personal development. Validated health-related quality-of-life forms, such as the Scoliosis Research Society questionnaires, can be particularly helpful in determining if their deformity is causing frank disability secondary to concerns over appearance. Perhaps most importantly, the adolescent or young adult who wishes to undergo surgery for Scheuermann’s kyphosis, for any indication, must be able to engage in an informed discussion about the risks and benefits of the procedure. In particular, the surgeon should stress that patients may need to undergo future revision surgery. The reoperation rate for proximal or distal junctional kyphosis is much higher in this patient population compared with adolescents undergoing spinal fusion for adolescent idiopathic scoliosis.²⁰ Lastly, patients must understand that while surgery can greatly improve concerns over appearance, back pain is a residual complaint in many subjects.²³

Reduction of the deformity and spinal fusion are the two basic principles on which surgery is based. Reduction is universally achieved through posterior, with or without, anterior releases. This is the key to surgical correction, as the deformity will not reduce without satisfactory release, especially posteriorly. Modern techniques almost universally employ a posterior-only approach with success. Posterior column osteotomies, performed by wide excision of the interlaminar posterior elements and facets, can achieve approximately 5 to 10 degrees of correction per level.²⁴ These are the workhorse of the surgical correction of Scheuermann’s disease. The majority of experts are almost always able to achieve satisfactory correction with posterior column osteotomies at multiple levels, and very rarely need to use three-column osteotomies for patients with an isolated diagnosis of Scheuermann’s disease.

Once reduction is achieved, solid spinal fusion is essential for maintenance of the reduction. Spinal fusion techniques used for surgery for Scheuermann’s kyphosis have always correlated with those used in the treatment of adolescent idiopathic scoliosis. Harrington rods were the primary mode of instrumentation used in historical treatments of the disease, but these were plagued by high rates of pseudoarthrosis and rod breakage. Segmental instrumentation was the next wave that replaced Harrington rods. With the advent of Luque rods, surgeons had more control over the position of the vertebral bodies, but the neurological complications and difficulty associated with sublaminar wires, as well as the high rates of proximal junctional kyphosis, made this form of instrumentation fall out of favor. Cotrel–Dubousset instrumentation, first developed with a hybrid of hooks and screws, was utilized by many surgeons with good results.²³ However, the popularization and refinement of the pedicle screw allowed for a rigid form of posterior fixation with far fewer of the complications associated with earlier instrumentation ( Table 9.1).

In the 1990s, patients with Scheuermann’s disease were treated with combined anterior and posterior fusion, the merit of which is still debated today.²⁸ The refinement of video-assisted thoracoscopic surgery (VATS) has allowed for anterior release of the thoracic spine without a significant increase in operation times and with a smaller number of thoracic cavity complications compared to those associated with an open anterior approach.²⁹ Despite this technology, there are several morbid complications associated with the anterior approach that are not present with posterior-only surgery.^25,28,29,30 Lee et al compared AP to posterior-only fixation, finding that combined techniques led to longer operation times and higher rates of complications.²⁵ Out of 39 patients (21 AP), 8 complications occurred in the AP group, including one spinal cord injury resulting in paraplegia. Shi et al found that patients who underwent posterior fixation with VATS anterior release had similar operating times compared to those who underwent posterior-only fixation; however, 4 out of 24 patients who underwent VATS had a complication of the thoracic cavity (two chylothorax and two hemothorax, respectively).²⁸ Thus, the authors’ preferred technique is posterior-only fusion, as a similar degree of correction may be obtained while avoiding the complications associated with the anterior approach.^24,31

A special note must be made regarding short-segment anterior-only fusion, a technically challenging technique first performed in 1996. Utilized by only a select number of spine surgeons worldwide, this procedure is aimed at patients with mild-to-moderate deformity whose primary complaint is pain. During the time that the procedure was pioneered, advanced imaging technologies allowed researchers to view the degenerated discs and vertebral body endplate changes for the first time, leading to the theory that these structures were the primary source of the patient’s pain. Thus, proponents of this technique argue that eradicating the pain generators through discectomy and interbody fusion alleviates the patient’s chief complaint. The challenging procedure involves extensive rib head resection to allow for complete discectomy and the placement of angled cages to partially correct the kyphosis. Anterior spinal instrumentation is used to stabilize the construct, which must be protected with a pleural flap or Gore–Tex membrane to prevent mediastinal injury. Thus, a vast majority of spine surgeons forgo this technique in favor of posterior-only approaches, but still obtain excellent results.

Good sagittal balance and appropriate correction of the deformity are the goals of surgical treatment. Generally, 50% correction of the kyphosis is appropriate, as any more than this has been shown to subject patients to higher rates of proximal junctional kyphosis.²³ The amount of correction necessary in each individual will vary based on the parameters that influence balance, such as the pelvic incidence. To achieve sagittal balance, the C7 plumb line should be restored so that it falls through the superior–posterior corner of the S1 body. Choosing the proper level of instrumentation is equally important in ensuring a good outcome. For most thoracic curves, T2–T3 will be the upper instrumented vertebrae, similar to patients with adolescent idiopathic scoliosis. The lowest instrumented vertebrae should be the stable sacral vertebrae (SSV), which may be determined by drawing a vertical line through the posterior–superior corner of S1.³² The most superior vertebrae inferior to the apex of the kyphosis that touches this line is considered the SSV. Ideally, the SSV will be the lowest instrumented level (the authors’ preferred technique).³² However, similar to controversies in fusion levels in adolescent idiopathic scoliosis, some authors have been more selective with their fusion and have had acceptable results by fusing to the vertebrae below the first lordotic disc (FLD), which is often one level superior to the SSV.³³ The ability of shorter fusions to lead to satisfactory results in certain cases may be explained by the concept of construct symmetry, described as an equal number of levels fused cranial and caudal to the apex of the kyphosis.^18,33 Conversely, a patient with a thoracolumbar apex may require fusion past the SSV to ensure a symmetrical construct. Kim et al, in a series of 44 patients who underwent posterior-only fusion to the SSV or FLD, found that patients who were fused to the FLD had a higher rate of revision surgery for distal junctional kyphosis compared to those fused to the SSV.³⁴ Since hyperkyphosis is accompanied by lumbar hyperlordosis, the surgeon may be tricked into believing a disc is lordotic when it is actually neutral or even kyphotic. Thus, fusing to the SSV is often the safer option to prevent reoperations for distal junctional kyphosis. Lastly, if a patient has lumbar scoliosis, the surgeon may need to extend the fusion distally in order to ensure a stable construct, employing the concepts described by Lenke.³⁵ Other factors, such as degenerated discs or inflexible segments, may also need to be taken into consideration when determining the fusion levels. For these reasons, extensive preoperative planning is mandatory.

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