Spondyloarthritis & Ankylosing Spondylitis

What are spondyloarthritis and ankylosing spondylitis?

Spondyloarthritides are inflammatory joint disorders that primarily affect the spine and the sacroiliac joints—often in young adults.

In simple terms, these are conditions in which the immune system causes chronic inflammation in joints, ligaments, and tendon insertion sites (entheses). The typical pattern includes:

• back and neck pain with stiffness, particularly in the morning or after rest,
• improvement with movement rather than with rest,
• potential progressive “fusion” of vertebrae over time.

Ankylosing spondylitis (AS) is the classic and most characteristic form of spondyloarthritis, predominantly involving the spine and sacroiliac joints. In advanced stages, the spine may become “one rigid structure” (“bamboo spine”), highly fragile and prone to fractures.

What types of spondyloarthritis exist?

Ankylosing spondylitis is the most typical form, but it belongs to a broader family of disorders.

Main categories of spondyloarthritis:

• Ankylosing spondylitis (AS) – predominant involvement of the spine and sacroiliac joints, progressive ankylosis, classic “bamboo spine.”
• Psoriatic arthritis – association of skin/nail psoriasis with arthritis, sometimes with spinal involvement.
• Reactive arthritis (Reiter syndrome) – arthritis following infection (urogenital or gastrointestinal), which may also affect the spine.
• Enteropathic arthritis – in patients with inflammatory bowel disease (Crohn’s disease, ulcerative colitis).
• Undifferentiated spondyloarthritis – cases with clinical features of spondyloarthritis that do not meet criteria for a specific category.

All share common features (inflammatory back pain, enthesitis, frequent HLA-B27 positivity) but differ in overall clinical presentation and associated organ involvement.

How common are they and who is at higher risk?

Ankylosing spondylitis (AS) is relatively uncommon and often affects individuals in their most productive years.

The prevalence of AS in the general population is approximately 0.1–0.2%, with a clear male predominance (roughly 3:1). Nevertheless, women are also affected, often with a more subtle or atypical presentation.

Risk factors include:

• HLA-B27 positivity.
• Family history of spondyloarthritis.
• Onset of chronic back pain at a young age (often < 40 years).
• Coexisting psoriasis, inflammatory bowel disease, or prior infections.

Early recognition of the features of inflammatory back pain in young adults is critical to avoid delays in diagnosis and treatment.

Pathophysiology & the role of HLA-B27

Spondyloarthritides are autoimmune inflammatory disorders with a particular predilection for entheses and spinal joints.

HLA-B27 is a major histocompatibility complex (MHC) molecule involved in antigen presentation to T lymphocytes. In genetically predisposed individuals (HLA-B27 and other genes), environmental triggers—often infections—may lead to:

• enthesitis – inflammation at tendon/ligament insertion sites,
• arthritis of the sacroiliac and spinal joints,
• new bone formation and development of syndesmophytes along the spine.

Over time, repeated cycles of inflammation and repair result in ankylosis of adjacent vertebrae, producing the characteristic “bamboo spine” and profound stiffness.

Key symptoms – what does “inflammatory” pain mean?

The pain pattern differs from typical “mechanical” low back pain—this distinction is essential for early recognition.

Features of inflammatory spinal pain include:

• Onset before age < 40–45 years.
• Insidious, gradual onset (not acute after exertion or injury).
• Morning stiffness > 30 minutes, with difficulty moving the back.
• Pain during the second half of the night that may wake the patient.
• Improvement with activity/exercise, not with rest.
• Alternating buttock pain (reflecting sacroiliac involvement).

Additional manifestations may include:

• pain at enthesis sites (heels, Achilles tendon, plantar fascia),
• pain/swelling in peripheral joints (hips, shoulders, knees),
• fatigue or low-grade fever during inflammatory flares.

Extra-articular manifestations (eyes, skin, bowel, heart)

Spondyloarthritides are not confined to joints—they may affect multiple organ systems, necessitating multidisciplinary care.

Common extra-articular features:

• Ocular – acute anterior uveitis (painful red eye with photophobia and blurred vision).
• Dermatologic – psoriasis, skin lesions, or vasculitis depending on the subtype.
• Gastrointestinal – association with inflammatory bowel disease (Crohn’s disease, ulcerative colitis), abdominal pain, diarrhea.
• Cardiovascular – aortitis, valvular disease, conduction abnormalities (in advanced disease).

The presence of such manifestations strengthens the suspicion of spondyloarthritis and requires close collaboration among rheumatologists, ophthalmologists, gastroenterologists, and cardiologists.

How is the diagnosis made (clinical, laboratory, imaging)?

There is no single definitive test—the diagnosis relies on a combination of clinical features, laboratory findings, and imaging.

Key components:

• Clinical evaluation – history of inflammatory back pain, stiffness, enthesitis, peripheral arthritis, and extra-articular manifestations.
• Laboratory testing – inflammatory markers (ESR, CRP), HLA-B27 testing (positive in many, but not all patients).
• Plain radiographs – particularly of the sacroiliac joints and the spine.
• MRI of sacroiliac joints and spine – detects early inflammatory changes (bone marrow edema, inflammatory discitis) before permanent structural damage becomes visible on X-ray.

Importantly, early referral to a rheumatologist is essential. The earlier appropriate therapy is initiated, the greater the likelihood of slowing or preventing ankylosis and permanent deformity.

What do X-rays show & what is “bamboo spine”?

Imaging changes reflect chronic inflammation, ossification, and ankylosis—and correlate with the risk of deformity and fracture.

Characteristic radiographic findings in ankylosing spondylitis:

• Sacroiliitis and fusion of the sacroiliac joints – among the earliest imaging signs.
• Marginal syndesmophytes – vertical bony bridges along the spine connecting vertebral bodies.
• “Bamboo spine” – advanced disease in which the spine appears as a continuous, rigid column.
• “Squared” vertebrae – loss of normal vertebral concavity due to chronic inflammation.
• Spondylodiscitis – inflammatory erosion at the disc–vertebral junction, often at the thoracolumbar junction.

For the neurosurgeon, this ankylosed, ossified, and often osteopenic spine signifies extreme fragility— effectively behaving like a long bone and prone to fracture even after minor trauma.

Initial management – the role of rheumatology & biologic therapies

The cornerstone of treatment is systemic rheumatologic therapy aimed at controlling inflammation and slowing structural damage.

Main pillars of conservative management:

• Non-steroidal anti-inflammatory drugs (NSAIDs) – first-line therapy for pain and stiffness, with possible disease-modifying effects when used continuously.
• Physiotherapy and exercise – daily stretching, respiratory exercises, and posture training to maintain mobility and prevent kyphotic deformity.
• Biologic agents (e.g., anti-TNF, IL-17 inhibitors) – for moderate to severe disease or when NSAIDs are insufficient, aiming to improve symptom control and quality of life.
• Management of comorbidities – osteoporosis/osteopenia, cardiovascular risk, bowel disease, and others.

The goals are reduction of inflammation, preservation of mobility, and prevention of deformity and fractures. Neurosurgical care becomes relevant in advanced stages or when spinal complications arise, in close collaboration with the rheumatologist.

When is neurosurgical intervention required?

In most cases, treatment is medical. Spine surgery is reserved for patients with serious complications or deformity.

Typical indications for specialized spinal surgery include:

• Spinal fractures in an ankylosed spine – often highly unstable, even after minor trauma (low-energy falls, impacts).
• Neurological deficit (weakness, numbness, myelopathy) due to stenosis, ossification of the posterior longitudinal ligament, or deformity-related fracture.
• Severe kyphotic deformity causing imbalance, impaired ambulation, inability to maintain horizontal gaze (abnormal chin–brow angle), respiratory compromise, or functional disability.
• Painful pseudoarthrosis (non-union fracture) with chronic, refractory pain.

These procedures are often technically demanding, involving long-segment fusions, osteotomies, and meticulous preoperative planning to achieve spinal balance, deformity correction, and protection of the spinal cord.

Daily life & exercise – what should I pay attention to?

Active patient participation is essential. Posture, exercise, and injury prevention play a major role in long-term outcomes.

Practical recommendations:

• Daily stretching and posture training – exercises to maintain thoracic, cervical, and hip extension and avoid persistent flexed posture.
• Low-impact exercise – walking, swimming, cycling, and flexibility/balance exercises.
• Injury prevention – avoid high-risk activities (contact or extreme sports), especially in advanced ankylosis.
• Ergonomic adaptations at home and work – supportive seating, correct screen height, frequent movement breaks.
• Smoking cessation – smoking adversely affects bone health and systemic inflammation.

In patients with an already ankylosed and fragile spine, any head, neck, or back trauma must be approached with great caution: prompt imaging (CT/MRI) is often required to exclude occult fractures.