Ankylosing Spondylitis

Spine

Overview

Ankylosing spondylitis (AS) is a chronic inflammatory arthropathy primarily affecting the axial skeleton, characterized by progressive spinal fusion and reduced mobility. The condition typically presents in young to middle-aged males with inflammatory back pain and may progress to severe kyphosis and functional limitation. Early diagnosis and management are critical to slow progression and maintain quality of life.

Pathophysiology

AS is an HLA-B27-associated autoimmune condition involving chronic inflammation of the spine and sacroiliac joints. The inflammatory process leads to ossification of spinal ligaments and intervertebral disc fibrosis, progressively fusing vertebrae into a rigid column. This pathological process extends from the sacroiliac joints upward, with inflammation preceding structural changes. Peripheral joint involvement and extra-articular manifestations (uveitis, enthesitis) occur in 30-40% of cases. The rigid spine becomes vulnerable to fracture from minor trauma.

Typical Presentation

Site

Sacroiliac joints, lumbar and thoracic spine; may extend to cervical spine, hips, shoulders, and peripheral joints; entheseal pain at heels, tibial tuberosities, and ribs

Quality

Inflammatory back pain; morning stiffness; night pain often waking patient in second half of night; progressive loss of spinal extension and rotation; peripheral joint pain if involved

Intensity

Highly variable; ranges from mild morning stiffness to severe debilitating pain with progressive functional limitation; inflammatory markers (ESR, CRP) may correlate with symptoms

Aggravating

Prolonged rest and inactivity; morning stiffness (typically >30 minutes, improving with movement); static postures; cold weather; stress

Relieving

Physical activity and exercise; movement and mobilization; NSAIDs; heat application; forward bending in early disease; biologics (TNF inhibitors) in later disease

Associated

Morning stiffness lasting >1 hour; progressive kyphosis and loss of spinal extension; chest wall pain and reduced chest expansion; fatigue; depression and anxiety from chronic disease; uveitis (25% of cases); peripheral arthritis; enthesitis; inflammatory bowel disease connection (10%)

Orthopaedic Tests

Test descriptions are written with AI assistance from standard clinical texts. Where a test lists Sources, its description has been checked against them; those sources are independent and do not endorse OsteoKit. Accuracy figures and grades (A–D) appear only when checked against the published study; tests without one are marked “No accuracy study”.

Further reading: full test procedures are described in standard clinical examination texts, e.g. Magee & Manske, Orthopedic Physical Assessment (7th ed.), and Cook & Hegedus, Orthopedic Physical Examination Tests: An Evidence-Based Approach (2nd ed.).

No accuracy study

Modified Schober Test (Lumbar Flexion)

Procedure

Patient standing. Mark the skin at the level of the dimples of Venus (PSIS), then 10 cm above and 5 cm below. Ask the patient to bend forward as far as possible with knees straight and remeasure the distance between the upper and lower marks.

Positive Finding

A small increase in the distance, meaning reduced lumbar flexion.

Interpretation

Measures lumbar flexion for monitoring. Suspect axial spondyloarthritis in a young adult with back pain lasting months that started gradually, is worse in the morning and in the second half of the night, and eases with exercise but not rest; refer to the GP or a rheumatologist. In established ankylosing spondylitis the fused spine fractures easily: avoid high-velocity thrust to stiff segments, and new spinal pain after even a minor fall needs imaging. A painful red eye with blurred vision suggests uveitis and needs same-day eye review. Spinal and chest mobility measures show how stiff the spine and ribcage are. They are used to monitor axial spondyloarthritis (several are part of the BASMI index), not to diagnose it. Stiffness usually appears late, so normal mobility does not rule out early disease; inflammatory back pain features, blood tests and MRI matter more. The studies cited for the figure previously stored measured mobility in people already diagnosed, or set normal ranges in healthy people; they did not test diagnosis, so no figure is shown.

Sources

No accuracy study

Occiput-to-Wall Distance Test

Procedure

Patient stands with heels and back against a wall, knees straight and chin level. Measure the distance from the back of the head to the wall.

Positive Finding

The back of the head cannot touch the wall.

Interpretation

Shows fixed forward posture of the neck and upper back. A late sign used for monitoring; normal in early disease.

Further reading

No accuracy study

Chest Expansion Measurement

Procedure

Patient standing with hands on head. Place a tape around the chest at the fourth intercostal space (nipple line in men, just below the breasts in women). Measure after full breath out and after full breath in; record the difference.

Positive Finding

Reduced expansion compared with what is expected for age and sex.

Interpretation

Suggests stiffness of the rib joints, usually in established disease. Also reduced with age, lung disease and poor effort, so it does not confirm spondyloarthritis. Spinal and chest mobility measures show how stiff the spine and ribcage are. They are used to monitor axial spondyloarthritis (several are part of the BASMI index), not to diagnose it. Stiffness usually appears late, so normal mobility does not rule out early disease; inflammatory back pain features, blood tests and MRI matter more. The studies cited for the figure previously stored measured mobility in people already diagnosed, or set normal ranges in healthy people; they did not test diagnosis, so no figure is shown.

Sources

No accuracy study

Tragus-to-Wall Distance Test

Procedure

Patient stands with heels and back against a wall, knees straight and chin level, trying to touch the head to the wall. Measure from the tragus of the ear to the wall on both sides and average.

Positive Finding

A larger distance than before or than expected.

Interpretation

A part of the BASMI mobility index, used to track neck and upper back posture over time.

Sources

No accuracy study

Finger-to-Floor Distance Test

Procedure

Patient stands with feet together and knees straight and bends forward as far as possible. Measure from the tip of the middle finger to the floor.

Positive Finding

A larger distance than before or than expected.

Interpretation

Reflects hip and hamstring flexibility as well as the spine, so it cannot show where the stiffness is. Useful to track change.

Sources

No accuracy study

Lateral Spinal Flexion

Procedure

Patient stands with heels and back against a wall, arms by the sides. Mark the fingertip on the thigh, ask them to bend sideways without leaning forward or lifting the heels, and measure how far the finger slides down. Repeat on the other side and average.

Positive Finding

Reduced side-bending compared with before or with what is expected.

Interpretation

A part of the BASMI mobility index and one of the more useful measures for tracking change. It does not diagnose spondyloarthritis.

Sources

⚠ Red Flags

  • •Spinal fracture risk—minor trauma causing neurological deficits or severe pain in rigid spine
  • •Acute anterior uveitis—sudden eye pain, photophobia, redness requiring urgent ophthalmology review
  • •Cauda equina syndrome—rare but serious; progressive neurological deficit, saddle anesthesia, bowel/bladder dysfunction
  • •Cardiac involvement—conduction abnormalities, aortic regurgitation; refer if palpitations or syncope
  • •Severe progressive kyphosis causing cardiopulmonary compromise
  • •Suspected spinal infection or malignancy in atypical presentations
  • •Uncontrolled inflammatory markers despite therapy—consider rheumatology review

⚡ Yellow Flags

  • •Psychosocial distress and depression related to progressive disability and loss of function
  • •High health anxiety and catastrophizing regarding disease progression
  • •Avoidance behavior and kinesiophobia limiting therapeutic exercise adherence
  • •Social isolation due to reduced mobility and chronic pain
  • •Work-related stress and occupational disability concerns
  • •Poor medication adherence and compliance with biologic therapy
  • •Relationship strain and sexual dysfunction from pain and stiffness
  • •Sleep disturbance from nocturnal inflammatory pain affecting quality of life

Osteopathic Techniques

Refer first

Ankylosing spondylitis needs a medical diagnosis and drug treatment: daily anti-inflammatories first, then TNF inhibitors if they are not enough, with a rheumatologist involved. Regular exercise, postural training and physical therapy are the non-drug foundation. Refer before using manual techniques on the spine.

Rehabilitation Exercises

Spinal Extension and Chest Wall Opening (Wall-Assisted)

PosturalBeginner

Cervical and Thoracic Rotation in Sitting

Range of MotionBeginner

Hip Flexor and Psoas Stretch (Lunge Position)

StretchingBeginner

Abdominal Core Activation (Transverse Abdominis Engagement)

StrengtheningBeginner

Thoracic Spine Mobilization with Foam Roller (Supported Extension)

Range of MotionIntermediate

Quadratus Lumborum Stretch (Supported Side Bend)

StretchingIntermediate

Gluteal and Hip Extensor Strengthening (Bridging with Holds)

StrengtheningIntermediate

Standing Balance and Proprioceptive Training (Tandem Stance)

BalanceIntermediate

Swimming or Water-Based Aerobic Activity

CardiovascularIntermediate

Combined Spinal Rotation and Lateral Flexion (Seated Twist-Reach)

Range of MotionIntermediate

Progressive Spinal Extensors and Back Support (Modified Prone Superman)

StrengtheningAdvanced

Dynamic Balance and Gait Training with Obstacles

BalanceAdvanced

Referral Criteria

  • •Suspected AS diagnosis or confirmation needed—rheumatology referral for HLA-B27 testing, inflammatory markers, and imaging (X-ray, MRI) to confirm diagnosis and assess disease severity
  • •Acute inflammatory flare unresponsive to NSAIDs—consider rheumatology referral for biologic therapy (TNF inhibitors) assessment
  • •Acute anterior uveitis or other eye symptoms—urgent ophthalmology referral
  • •Progressive kyphosis affecting respiratory function or quality of life—orthopedic or spinal surgeon consultation for possible corrective osteotomy
  • •Spinal fracture or neurological symptoms following trauma—emergency imaging and spinal surgery consultation; high risk of serious injury in rigid spine
  • •Severe functional limitation despite conservative management—consider occupational therapy and vocational rehabilitation
  • •Cardiac symptoms (palpitations, syncope) or conduction abnormalities—cardiology referral to assess for aortic regurgitation or conduction disease
  • •Inflammatory bowel disease symptoms—gastroenterology referral for evaluation and coordination of care
  • •Uncontrolled inflammatory markers or inadequate response to current therapy—rheumatology review for optimization of biologic or conventional DMARD therapy
  • •Depression, anxiety, or psychosocial distress affecting adherence—psychology or mental health referral for supportive therapy
  • •Atypical presentation or rapidly progressive disease—return to rheumatology for diagnostic clarification and management adjustment