Kyphosis — Scheuermann vs Post‑TB

Kyphosis refers to a sagittal plane spinal deformity with excessive posterior convexity. While some degree of thoracic kyphosis is normal (20–40° by Cobb measurement), pathological kyphosis causes pain, deformity, neurological deficit, and cardiorespiratory compromise when severe. Scheuermann kyphosis and post-tuberculous kyphosis (Pott disease sequelae) are two distinct but important causes that differ markedly in aetiology, natural history, severity, and management.

• Normal thoracic kyphosis: 20–40° (Cobb T5–T12); lumbar lordosis: 40–60°; cervical lordosis: 20–35°
• Pathological kyphosis defined as >40° by Cobb measurement in the thoracic spine
• Scheuermann kyphosis: structural kyphosis due to anterior vertebral body growth disturbance during adolescence; typically 45–75°; rarely exceeds 90°
• Post-tuberculous (Pott) kyphosis: results from vertebral body destruction by Mycobacterium tuberculosis; can produce severe sharp angular kyphosis (gibbus deformity) of 90–180°; more common in developing nations and immunocompromised patients
• Other causes of kyphosis: congenital (failure of formation/segmentation), neuromuscular, post-laminectomy, osteoporotic (Schmorl nodes, compression fractures), ankylosing spondylitis

Scheuermann kyphosis is the most common cause of structural thoracic hyperkyphosis in adolescents, affecting approximately 4–8% of the population. It is more common in males and is associated with poor posture, thoracic pain, and cosmetic concern.

Diagnostic Criteria (Sorensen):

• Scheuermann kyphosis: Cobb >45° PLUS anterior wedging of ≥5° in 3 or more consecutive vertebrae — this distinguishes it from postural kyphosis
• Additional features: Schmorl nodes (disc herniations into endplate), irregular endplates, disc space narrowing
• Postural kyphosis: flexible (corrects on prone hyperextension), no vertebral wedging, no endplate changes — does not progress to structural deformity; responds to physiotherapy
• Two types: Type I (classic thoracic, T7–T9 apex), Type II (thoracolumbar, T10–T12 apex — less common; more back pain)

Management:

• Surgical indications: Cobb >70–75°, failure of conservative treatment, progressive neurological deficit (rare but occurs with thoracic disc herniation or intraspinal pathology at apex), severe cosmetic deformity, or chronic disabling pain
• Surgical technique: posterior spinal fusion (PSF) with pedicle screw-rod instrumentation — Ponte osteotomies (posterior element resection) at apex levels to release posterior tension band and allow correction; anterior release via VATS for rigid curves >80°
• Ponte osteotomy: resection of posterior elements (facets, ligamentum flavum) at multiple levels — allows segmental correction of kyphosis through posterior shortening; safe in thoracic spine with intact anterior column
• Fusion levels: typically T2 or T3 to L1 or L2 — must include all wedged vertebrae and restore sagittal balance
• Average correction achievable: 40–50% of Cobb angle

Spinal tuberculosis (Pott disease) accounts for approximately 50% of osteoarticular TB worldwide. Vertebral body destruction, disc space loss, and anterior column collapse lead to progressive angular kyphosis — the gibbus deformity. Despite effective anti-tuberculosis therapy, the deformity often progresses after infection is controlled due to ongoing anterior column deficiency.

Pathophysiology:

• TB typically begins in the anterior vertebral body (paradiscal pattern in adults; central pattern in children) — disc avascular and resistant initially; adjacent endplates destroyed leading to disc involvement
• Anterior column destruction → angular kyphosis → progressive deformity even after infection controlled
• Gibbus deformity = sharp angular kyphosis at the level of vertebral destruction — can reach 90–180°; highest deformity risk with thoracic and thoracolumbar involvement
• Neurological involvement: spinal cord compression from pus, granulation tissue, caseous material, or mechanical kyphosis — paraplegia (Pott paraplegia)
• Pott paraplegia types: active (from inflammatory/infective compression — responds to anti-TB therapy ± surgical decompression) vs healed (from mechanical kyphotic deformity — requires corrective surgery)

Classification of Post-TB Kyphosis:

Surgical correction of post-TB kyphosis is among the most complex and high-risk procedures in spinal surgery. Anterior column reconstruction is the fundamental principle — the destroyed anterior column must be rebuilt and the posterior tension band instrumented.

• Radical anterior debridement and bone grafting (Hong Kong procedure): classic approach — anterior debridement of all diseased tissue, decompression of cord, bone grafting of anterior defect with rib/fibula/iliac crest autograft or titanium cage; shown to prevent progression and aid neurological recovery
• Combined anterior-posterior surgery: anterior reconstruction (cage + bone graft) + posterior pedicle screw fixation — provides 360° stability; necessary for severe kyphosis correction
• Posterior-only pedicle subtraction osteotomy (PSO) or vertebral column resection (VCR): increasingly used for severe rigid post-TB kyphosis — allows significant correction from single posterior approach; very high blood loss and neurological risk; requires experienced spinal surgeon
• Vertebral column resection (VCR): complete removal of one or more vertebrae — allows correction of severe angular deformity (>90°); highest risk procedure; IONM mandatory; estimated blood loss 1–5 litres
• Anti-TB chemotherapy must be continued for minimum 2–3 months before elective corrective surgery — reduces active infection burden; mandatory RIPE therapy (rifampicin, isoniazid, pyrazinamide, ethambutol)
• Implants in active TB: titanium implants can be used in active disease with adequate debridement and antibiotic cover — do not need to wait for complete infection resolution for decompression surgery

• Scheuermann: disc herniation and myelopathy — approximately 30–40% of Scheuermann patients have thoracic disc herniations at apex levels; symptomatic herniation causing myelopathy requires anterior discectomy + fusion or thoracoscopic approach; cannot correct with posterior-only procedure alone if cord compressed anteriorly
• Flat back syndrome after Scheuermann correction: excessive flattening of lumbar lordosis during thoracic correction — leads to sagittal imbalance, chronic low back pain, and difficulty standing erect; meticulous sagittal balance restoration and appropriate LIV selection (L1–L2) mitigate this risk
• Post-TB: paradoxical response — neurological deterioration shortly after starting anti-TB therapy due to immune reconstitution inflammatory response (IRIS); does not mean treatment failure; continue therapy; steroids may be helpful
• Posterior-only VCR for post-TB kyphosis: technically feasible for curves up to 100–120° in experienced hands; requires temporary posterior distraction rod, sequential removal of all anterior and posterior elements, cage reconstruction, and posterior instrumentation; blood loss and neurological risk are extremely high — discuss openly with patients
• Children with TB kyphosis: ongoing growth after anterior column destruction causes progressive deformity — called the "buckling" phenomenon; anterior fusion at the site of disease combined with posterior instrumentation prevents this; crankshaft-equivalent progression in children with TB is a major long-term concern

• Scheuermann diagnostic criteria: Cobb >45° + ≥5° anterior wedging in ≥3 consecutive vertebrae
• Postural kyphosis: flexible on hyperextension, no wedging, no structural change — does not require surgery
• Scheuermann surgery: >70–75°; Ponte osteotomies for posterior release; anterior release for rigid curves >80°
• Post-TB kyphosis: sharp angular gibbus; can reach 180°; Pott paraplegia from anterior cord compression
• Pott paraplegia: active type (inflammatory — responds to anti-TB ± decompression) vs healed type (mechanical — requires corrective surgery)
• Hong Kong procedure: anterior debridement + bone graft — gold standard for active Pott with neurological compromise
• VCR: complete vertebral resection for severe angular deformity — highest risk spinal procedure; IONM mandatory
• Anti-TB RIPE therapy: 6–9 months; minimum 2–3 months before elective corrective surgery
• Titanium implants safe in active TB with adequate debridement
• Flat back after Scheuermann correction = sagittal imbalance = chronic pain; meticulous LIV selection and lordosis restoration essential