Baastrup's Disease
Spinous process impingement causing midline low back pain with extension
ICD-10: M48.20 · lumbar condition
Baastrup's disease, also called "kissing spine" syndrome, is a condition in which adjacent lumbar spinous processes make contact during lumbar extension, leading to friction, bursitis, and pain at the interspinous space. First described by Christian Baastrup in 1933, it results from loss of intervertebral disc height causing the posterior elements to approximate and allowing the tips of adjacent spinous processes to contact each other. The condition most commonly affects the lower lumbar spine (L4–L5, L3–L4) in middle-aged to elderly patients with significant disc degeneration and lumbar hyperlordosis. A characteristic interspinous bursa forms between the opposing bony surfaces, which can become inflamed and tender. On MRI, the bursa appears as a high-T2 fluid collection between the spinous processes, and the opposing bone surfaces may show reactive sclerosis and marrow edema. Pain is typically midline, worsened by lumbar extension and prolonged standing, and relieved by forward flexion or sitting. Direct midline palpation over the interspinous space reproduces tenderness. Treatment includes fluoroscopy-guided interspinous corticosteroid injection, which is both diagnostic and therapeutic. Interspinous spacer devices can maintain the interspace in extension, and surgical spinous process resection is reserved for refractory cases.
Anatomy & Pathology
The spinous processes of adjacent lumbar vertebrae are separated by the interspinous ligament and supraspinous ligament under normal circumstances. When disc height decreases, the distance between spinous process tips narrows. With repeated extension movements, opposing spinous processes can contact each other directly, compressing the interspinous ligament and eventually eroding the cortical bone. The space may fill with a bursa that can become acutely painful when inflamed.
Symptoms
- Midline low back pain at the interspinous space
- Pain worsened by lumbar extension (standing, walking) and relieved by flexion
- Point tenderness directly over the affected interspinous space
- Pain provoked by backward bending and walking downhill
- Associated lumbar disc degeneration and hyperlordosis
- Interspinous bursa swelling palpable in thin patients
- Absence of radicular leg pain in isolated cases
Causes & Risk Factors
- Lumbar disc height loss causing posterior element approximation
- Lumbar hyperlordosis increasing posterior element compression
- Aging and multilevel disc degeneration
- Repetitive lumbar extension loading (manual labor, hyperextension sports)
- Obesity increasing lumbar lordotic stress
Treatment Options
Conservative
- Fluoroscopy-guided interspinous bursa corticosteroid and local anesthetic injection
- Physical therapy emphasizing lumbar flexion exercises and reduction of hyperlordosis
- NSAIDs for acute inflammatory bursitis
Surgical
- Interspinous process spacer device (e.g., X-STOP) to maintain interspinous gap in extension
- Spinous process resection (partial or complete) of the impinging processes
- Lumbar fusion at the affected level if concurrent instability or disc disease requires structural reconstruction
When to see a spine specialist
See a spine physician if midline low back pain worsens consistently with lumbar extension and standard treatments have not helped. Baastrup's disease can be easily confirmed by fluoroscopy-guided interspinous injection — relief with local anesthetic confirms the diagnosis. Most cases respond well to injection therapy without surgery.
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Search spine specialists →Frequently Asked Questions
How is Baastrup's disease diagnosed?
MRI is the primary diagnostic tool, showing contact or near-contact of adjacent spinous processes, an interspinous bursa (high T2 signal fluid), and reactive endplate changes (sclerosis, marrow edema) at the spinous process tips. Plain radiographs may show sclerosis of opposing spinous process surfaces. Confirmation is obtained by fluoroscopy-guided injection of local anesthetic into the interspinous bursa — pain relief within minutes confirms the diagnosis.
Is Baastrup's disease common?
It is frequently underdiagnosed. Interspinous bursitis and spinous process impingement are common incidental MRI findings in older adults with disc degeneration, but the syndrome is a pain source in a meaningful subset. It should be specifically considered in patients with midline low back pain that is strongly extension-dependent and whose pain does not fit a facet, disc, or sacroiliac pattern.
Can an interspinous spacer device cure kissing spine?
Interspinous spacer devices (most studied for lumbar spinal stenosis) work by maintaining spinal flexion and opening the posterior elements when the patient stands. They can effectively relieve both neurogenic claudication and Baastrup-related pain in carefully selected patients. However, they are not appropriate for all patients, and some studies show reoperation rates of 15–20% over 5 years. They are best considered when conservative care has failed and the patient wishes to defer or avoid fusion.
Related Conditions
Sources
- Baastrup C. On the spinous processes of the lumbar vertebrae. Acta Radiol. 1933.
- Maes R, et al. "Kissing spine" and interspinous bursitis on MRI. Skeletal Radiol. 2008.