Scheuermann Kyphosis

Scheuermann disease is the most common cause of structural kyphosis in adolescents. Vertebral wedging produces an exaggerated thoracic kyphosis that is rigid: it does not correct with hyperextension.

Who. Prevalence is 1-8% of adolescents, varying with the diagnostic criteria used. Males predominate 2:1 on historical figures, although the ratio may be equalising. Presentation peaks in the adolescent growth spurt, 12-17 years, and the diagnosis is often made when parents notice a "round back" or stooped posture. Historically it was associated with heavy manual labour (juvenile disc disorder).

Cause. Multifactorial. There is a genetic component, autosomal dominant with variable penetrance, and mechanical overload during growth compresses the front of the vertebral body. A cartilage endplate abnormality is possible, and the disease is associated with growth plate disorders.

The wedge. Repetitive loading damages the vertebral endplates at the anterior growth plate, and growth becomes asymmetric, the posterior vertebral body growing faster than the anterior. Each affected vertebra contributes more than 5° of wedging. Disc material herniates into the weakened endplates as Schmorl nodes, and disc-space narrowing follows as a secondary degenerative change.

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The consequences. The wedged vertebrae sum to an increased thoracic kyphosis, and the lumbar and cervical regions compensate with hyperlordosis. The pelvis compensates as well, and that compensation is part of the preoperative plan. The soft tissues adapt around the deformity:

• Hamstrings and hip flexors tighten
• The pectorals shorten, tightening the anterior chest wall
• The centre of gravity shifts forward

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Sorensen's criteria (1964) are the standard for diagnosis. Both must be met:

1. Thoracic kyphosis greater than 45°, the Cobb angle on a standing lateral radiograph
2. Three or more consecutive vertebrae, each with anterior height loss and more than 5° of anterior wedging

Some authors use greater than 40° as the kyphosis threshold. The supportive findings are not required for the diagnosis:

• Vertebral endplate irregularities: wavy, irregular endplates
• Schmorl nodes, disc herniation into the vertebral body
• Disc-space narrowing
• Increased AP diameter of the apical vertebrae

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Two types. The apex of the curve separates them. The classic thoracic form is the more common and the better tolerated.

Atypical (lumbar or thoracolumbar) Scheuermann. A distinct, exam-favoured entity, more painful than the thoracic form and more likely to cause functional limitation and pain in adulthood. It is seen most often in adolescent athletes and manual workers (gymnasts, rowers, fast bowlers, weightlifters). Repetitive flexion plus axial loading injures the immature vertebral endplate and ring apophysis, producing Schmorl nodes, endplate irregularity and disc-space narrowing at the thoracolumbar junction, often with little or no visible kyphotic deformity.

It presents as back pain. Activity-related low back pain is the dominant symptom, not a cosmetic round back, and lumbar Scheuermann may present primarily as low back pain rather than visible kyphosis. Recognise it as a cause of "mechanical" adolescent back pain rather than dismissing it as a sprain.

History. Onset is gradual and noticed during the growth spurt. Pain is present in 50%, usually activity-related and localised to the apex. Ask how the back affects sport and sitting tolerance, and whether there is a family history, which may be positive. Neurological symptoms are rare, but ask about weakness and numbness.

Inspection. Standing, the thoracic kyphosis is exaggerated, with a forward head posture and often protracted shoulders; the lumbar lordosis is increased and the cervical spine extended. On the Adams forward bend the kyphosis has an angular apex rather than a smooth curve. Look for the rib hump or asymmetry of an associated scoliosis.

Flexibility. The hyperextension test decides whether the curve is structural. Then test the tight soft tissues: hamstring tightness is very common (straight leg raise), the Thomas test for hip flexor tightness is often positive, and shoulder flexibility shows pectoralis tightness.

Neurology. Examine fully if there are any symptoms, checking reflexes, strength and sensation in the lower limbs. Cord compression is rare but possible with severe kyphosis, and a thoracic disc can herniate into the spinal canal.

Radiographs. A standing lateral spine radiograph with the arms forward on a support is the standard view for measuring kyphosis. The Cobb angle is measured from the superior endplate of the first tilted vertebra to the inferior endplate of the last tilted vertebra, usually T4-T12 or the affected levels. An AP view assesses scoliosis.

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Other imaging. The diagnosis itself is radiographic, and MRI is for the atypical case: it is indicated only for neurological symptoms, to assess the cord and disc. CT is rarely needed, for surgical planning in complex cases, and a bone scan is not routinely indicated.

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Skeletal maturity. It is critical to bracing candidacy. Assess the Risser sign on the iliac crest, with a hand radiograph for bone age if needed.

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The structural, rigid kyphosis of Scheuermann disease must be distinguished from other causes of an increased thoracic or thoracolumbar curve in a young person. Getting this wrong risks bracing a flexible postural curve, which needs only posture training and exercises, or missing infection, tumour or a syndromic/neuromuscular cause.

The decision. Curve size and skeletal maturity set the treatment.

Physiotherapy. The programme covers:

• Core strengthening, especially the extensors
• Hamstring and hip flexor stretching
• Pectoralis stretching
• Postural awareness training
• Activity modification, avoiding heavy lifting

It continues during bracing and after brace weaning, postural awareness is lifelong, and activity is modified if symptomatic.

Bracing. For the skeletally immature patient (Risser 0-3, more than 1 year of growth remaining) with a kyphosis of 50-75° who is compliant. A Milwaukee brace, which extends to the chin, or a TLSO is worn 16-23 hours a day until skeletal maturity, then weaned over 6-12 months, with exercises continued throughout. Compliance is the key determinant of bracing success.

Atypical (lumbar) disease. Management is load-based and symptom-driven: relative rest from the offending sport, activity modification, core and hamstring rehabilitation, and analgesia. Bracing is reserved for refractory pain rather than for cosmesis, and surgery is almost never required. Most settle with skeletal maturity, although the segment carries a higher long-term degenerative/disc risk.

When to operate. The indications for surgery are:

• Kyphosis greater than 75°, the most common indication
• Progressive kyphosis despite bracing
• Intractable pain not responsive to conservative care
• Neurological deficit, which is rare (thoracic disc or cord compression)
• Cosmetic concern in a skeletally mature patient

The operation. Posterior-only fusion is now the most common, and modern techniques favour it with multiple-level osteotomies; anterior release is rarely needed. The goals are to correct the kyphosis to the 40-50° range, achieve solid fusion, maintain sagittal balance and relieve pain.

Posterior spinal fusion with instrumentation is the standard approach for Scheuermann kyphosis.

Principles. Preserve the lower lumbar lordosis to avoid a flat back, and achieve correction with compression rather than distraction. These principles are essential for durable correction and for avoiding junctional complications.

Fusion levels. Level selection is the main way to prevent junctional kyphosis.

• Proximally, include the proximal end vertebra, the most cephalad vertebra of the measured kyphotic Cobb. Stopping short of it leaves an uninstrumented kyphotic segment that becomes proximal junctional kyphosis (PJK).
• Distally, extend the construct to the sagittal stable vertebra (SSV), the most proximal vertebra touched by the posterior sacral vertical line (a vertical line from the posterosuperior corner of S1), and at least to the first lordotic disc. Stopping above the SSV, in particular at or above the first lordotic vertebra alone, leaves the lower curve unbalanced and predisposes to distal junctional kyphosis (DJK).

Which distal rule is best is still debated; the Controversies section below sets out the argument.

How much to correct. Conventional teaching adds a third rule, avoid over-correction: aim toward a physiological kyphosis of about 50°, matched to pelvic incidence, rather than a straight spine, with gentle proximal fixation. The Scheuermann-specific data make that rule less secure than level selection. In the largest operative series PJK was associated with greater residual kyphosis and a LOWER percentage correction, so under-correction is at least as much a concern as over-correction, and the role of correction magnitude is unsettled.

Combined anterior-posterior surgery. Reserved for severe, rigid curves (greater than 80-90°), and now less commonly needed with modern posterior osteotomy techniques. The anterior release, through a thoracotomy or thoracoscopic approach, removes the discs at multiple levels (usually 4-6) and releases the anterior longitudinal ligament; an anterior strut graft may be added. Posterior instrumentation and fusion follow as above, in the same or a staged procedure, and more correction is achievable with the anterior release. The costs are higher morbidity than posterior-only surgery, pulmonary complications from the thoracotomy and a longer operative time.

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Proximal junctional kyphosis. The most common complication after kyphosis surgery, and the dominant complication of Scheuermann surgery, occurring at the level above the instrumentation. In the largest Scheuermann operative series, PJK of 10° or more affected 32% of patients, and distal junctional kyphosis 5%. The established risk factors:

• Poor bone quality
• Stopping the construct short of the proximal end vertebra
• Disruption of the posterior ligamentous complex at the upper instrumented vertebra
• Malaligned global sagittal balance

The dependable levers are level selection and soft-tissue preservation at the top of the construct, not a fixed correction target.

After bracing. Bracing is effective in preventing progression if the criteria are met, but it rarely achieves significant correction of established deformity. Long-term function is good for curves less than 75°, and back pain may persist, though it is usually manageable.

After surgery. Satisfaction rates are high, greater than 90%, with correction from an average of 75° to 45-50° and pain improvement in most patients. Return to full activities takes 6-12 months, and long-term fusion outcomes are generally good.

Global Epidemiology:

• Reported prevalence 1-8% of adolescents, varying with the diagnostic threshold (greater than 40° vs greater than 45°) and the population screened
• Danish twin data estimate heritability at 0.74 with an underlying population prevalence near 1.9% and an approximately 2:1 male predominance
• Peak presentation in the pubertal growth spurt (roughly 12-17 years), reflecting the period of maximal anterior vertebral growth

There is no single international consensus number: thresholds differ because evidence is largely retrospective and outcome measures vary. The common thread is structural confirmation plus skeletal maturity to decide between bracing and surgery.

Anterior release has largely fallen out of routine use because posterior column osteotomies achieve comparable correction - a meta-analysis of 13 studies and 1,147 patients found posterior-only surgery with osteotomies matched combined anterior-posterior results, while posterior-only surgery without osteotomies corrected about 5.6° less - but its precise residual role in the most rigid curves is still individualised rather than protocol-driven.

Landmark natural-history, genetic-epidemiology, bracing, and operative studies are summarised with the actual sample sizes and conclusions of each paper.