What are the differences between spondylitis and spondylosis?

Spondylitis vs. Spondylosis: Key Differences

Spondylitis is an inflammatory disease process involving active inflammation of the vertebral bodies and/or sacroiliac joints, while spondylosis is a degenerative, non-inflammatory condition characterized by wear-and-tear changes of the spine.

Fundamental Pathophysiology

Spondylitis represents chronic inflammatory arthritis that primarily targets the axial skeleton. The disease involves active immune-mediated inflammation affecting:

• Sacroiliac joints (sacroiliitis)
• Vertebral bodies and intervertebral discs
• Entheses (sites where tendons/ligaments attach to bone)
• Can lead to spinal fusion (ankylosis) over time 1, 2

The inflammation is driven by immune dysregulation, strongly associated with HLA-B27 genetic marker (present in 80-95% of cases), and involves the interleukin 23/17 axis 3.

Spondylosis, in contrast, is a degenerative process involving:

• Progressive wear of intervertebral discs
• Posterior joint degeneration
• Osteophyte (bone spur) formation
• Disc herniation and resorption
• No active inflammation 4, 5

Clinical Presentation Differences

Spondylitis (Inflammatory)

• Pain pattern: Inflammatory back pain with characteristic features:
  • Insidious onset before age 40
  • Morning stiffness lasting >30 minutes
  • Improves with exercise, worsens with rest
  • Predominates in second half of night 6
• Systemic features: Fatigue, elevated inflammatory markers (ESR, CRP)
• Extra-articular manifestations: Uveitis, psoriasis, inflammatory bowel disease 7
• Response to NSAIDs: 75% show good/very good response within 48 hours 6

Spondylosis (Degenerative)

• Pain pattern: Mechanical pain
  • Worsens with activity, improves with rest
  • No significant morning stiffness
  • Age-related onset (typically >50 years)
• Symptoms: Axial pain, radiculopathy, or myelopathy depending on nerve compression 4
• No systemic features: Normal inflammatory markers
• Poor NSAID response: Only 15% respond well to NSAIDs 6

Diagnostic Imaging Distinctions

Spondylitis

• Early disease: MRI shows active inflammation (bone marrow edema) before structural damage 6
• Radiographic features:
  • Bilateral, symmetrical sacroiliitis
  • Continuous, symmetrical syndesmophytes (vertical bony bridges)
  • Ossification of intervertebral discs
  • Ankylosis of sacroiliac, intervertebral, and costovertebral joints
  • "Dagger sign" on X-ray 8, 3

Spondylosis

• Radiographic features:
  • Asymmetric osteophytes (often bulging laterally, especially right-sided)
  • Disc space narrowing
  • Posterior joint destruction
  • No ossification of intervertebral discs
  • Sacroiliac joints NOT affected
  • Spinal stenosis may develop 8, 5

Laboratory Findings

Spondylitis

• HLA-B27 positive in 80-95% 3
• Elevated CRP and ESR during active disease 7
• Required for diagnosis alongside clinical and imaging criteria 1, 2

Spondylosis

• Normal inflammatory markers
• No genetic associations
• Diagnosis based purely on clinical and imaging findings 4

Treatment Approach Differences

Spondylitis (Requires Anti-Inflammatory Treatment)

The goal is to control inflammation and prevent structural damage 7:

1. First-line: NSAIDs (continuous use, not as-needed) + physical therapy 1, 2
2. Second-line (if ASDAS ≥2.1 despite NSAIDs): Biologic DMARDs (TNF inhibitors, IL-17 inhibitors) or JAK inhibitors 9
3. Tailored biologics based on extra-articular manifestations:
   • TNF monoclonal antibodies for uveitis or IBD
   • IL-17 inhibitors for significant psoriasis 9
4. Avoid: Long-term glucocorticoids, conventional DMARDs for pure axial disease 1, 2

Spondylosis (Conservative Management)

Most patients managed non-surgically 4:

1. Conservative care: Physical therapy, ergonomic modifications
2. Symptomatic relief: NSAIDs as-needed (not continuous)
3. Surgery: Reserved for persistent radiculopathy or myelopathy with functional disability despite conservative treatment 4

Critical Pitfalls to Avoid

1. Don't confuse inflammatory vs. mechanical back pain: The response to NSAIDs within 48 hours is diagnostically useful—dramatic improvement suggests spondylitis 6

2. Don't miss early spondylitis: Radiographic changes take years to develop. MRI and HLA-B27 testing are essential for early diagnosis 6

3. Don't treat spondylosis with biologics: These expensive immunosuppressive agents have no role in degenerative disease

4. Don't dismiss spondylitis as "just arthritis": Untreated inflammatory disease leads to irreversible spinal fusion and disability. Early aggressive treatment prevents structural damage 6

5. Recognize that sacroiliac joint involvement is pathognomonic for spondylitis: If sacroiliitis is present, it's inflammatory, not degenerative 8