Baastrup Disease (Kissing Spine Syndrome)

Imaging Gallery

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Baastrup disease ("kissing spine syndrome") is a degenerative condition caused by close approximation and impingement of adjacent spinous processes, most commonly at L4-L5. Pain is worse with extension (standing, walking downhill) and improved with flexion—the opposite pattern of disc herniation. An interspinous bursa develops from repetitive friction and appears as T2 hyperintensity on MRI between spinous processes. CT shows sclerosis and flattening of the articulating spinous process surfaces. Distinguish from facet arthropathy (paramedian tenderness) and discogenic pain (flexion-aggravated). Injection into the interspinous bursa is both diagnostic and therapeutic. Conservative management is first-line; refractory cases may require partial spinous process excision.

Baastrup Disease (also called kissing spine syndrome) is a painful condition caused by close approximation of adjacent spinous processes with degeneration of the interspinous ligament and development of an adventitious bursa.

History:

Christian Ingerslev Baastrup, a Danish radiologist, first described this condition in 1933. He noted the characteristic radiographic finding of close approximation of spinous processes in patients with low back pain.

Epidemiology:

Associated Conditions:

Baastrup disease frequently coexists with other degenerative spine conditions. This reflects the common degenerative process affecting multiple structures.

• Facet joint arthropathy (very common)
• Disc degeneration and loss of height
• Spinal stenosis
• Spondylolisthesis

Spinous Process Anatomy

Structure:

The spinous processes are posterior projections from the vertebral arch. In the lumbar spine, they are thick, broad, and quadrilateral, projecting horizontally backward.

Normal Interspinous Space:

Interspinous Ligament

Composition:

The interspinous ligament is composed of three layers:

1. Ventral - thin, close to ligamentum flavum
2. Middle - main bulk, collagen fibers
3. Dorsal - merges with supraspinous ligament

Changes with Degeneration:

With aging and disc degeneration, the interspinous ligament undergoes changes. Loss of disc height brings spinous processes closer together, leading to increased contact pressure. The ligament may undergo myxoid degeneration, cyst formation, and eventually frank bursitis.

Interspinous Bursa

Key Concept:

The interspinous bursa is NOT congenital. It is an adventitious bursa that develops from repetitive friction between adjacent spinous processes. This distinguishes it from congenital bursae elsewhere in the body.

Development:

1. Disc degeneration leads to loss of height
2. Spinous processes approximate
3. Repetitive contact causes friction
4. Adventitious bursa develops to reduce friction
5. Bursa may become inflamed (bursitis)
6. May extend posteriorly or into epidural space (cyst formation)

Mechanism of Disease

Primary Driver:

Loss of disc height (disc degeneration) is the primary driver of Baastrup disease. As the disc loses height, the spinous processes approximate and begin to contact during extension.

Cascade of Changes:

Osseous Changes

Spinous Process Morphology:

Extension Mechanism

Why Extension Hurts:

During lumbar extension, the spinous processes are brought closer together. In Baastrup disease, this causes direct bone-on-bone contact and compression of the inflamed interspinous bursa, generating pain.

Protective Flexion:

Lumbar flexion separates the spinous processes, decompressing the interspinous space. This is why patients often prefer sitting (flexed posture) and have difficulty with prolonged standing or walking (extended posture).

Complications

Dorsal Epidural Cyst:

In some cases, the interspinous bursa may extend posteriorly into the spinal canal, forming a dorsal epidural cyst. This can cause spinal stenosis symptoms (neurogenic claudication) in addition to axial back pain.

Reported in less than 10% of cases but important to recognize on MRI as it may require surgical excision.

Imaging-Based Classification

No universally accepted classification exists, but the following imaging-based staging is useful:

Associated Findings

Often coexists with other degenerative pathology:

History

Pain Characteristics:

Important History Points:

• Duration (usually chronic, insidious onset)
• Occupation (jobs requiring prolonged standing)
• Activities that worsen symptoms (walking downhill, lying prone)
• Activities that improve symptoms (sitting, leaning forward)
• Previous spine problems or surgery

Physical Examination

Inspection:

• May have exaggerated lumbar lordosis
• Antalgic posture (flexed)

Palpation:

• Tender over spinous processes (midline)
• May feel prominent spinous processes
• Paramedian tenderness suggests facet involvement

Range of Motion:

• Extension limited by pain
• Flexion typically full
• May have stiffness from associated degeneration

Provocation Tests:

Neurological Examination:

Typically normal in uncomplicated Baastrup disease. Abnormalities suggest associated stenosis, radiculopathy, or epidural cyst.

Red Flags

Imaging Protocol

X-ray (First Line):

• Lateral view essential
• Shows kissing spinous processes
• Sclerosis of spinous tips
• Loss of disc height at affected levels

CT Scan:

• Best for bony detail
• Shows sclerosis, flattening, enlargement
• Cystic changes within spinous processes
• Useful for surgical planning

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MRI (Most Sensitive):

Diagnostic Injection

Interspinous Bursa Injection:

This is both diagnostic and therapeutic. Response to injection confirms Baastrup disease as the pain generator.

Technique:

• Patient prone
• Fluoroscopic or ultrasound guidance
• Needle into interspinous space at affected level
• Inject local anesthetic and steroid

Interpretation:

• Good relief = Baastrup confirmed as pain source
• Partial relief = may have coexisting pathology
• No relief = consider other diagnosis

Laboratory Studies

Usually not required. If concern for infection or inflammatory arthropathy:

• ESR, CRP (normal in Baastrup)
• HLA-B27 (if concern for spondyloarthropathy)

📊 Management Algorithm

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Treatment Algorithm

Conservative Management (First Line):

Injection Therapy:

Indications:

• Failed conservative management (6-12 weeks)
• Diagnostic confirmation
• Therapeutic trial

Technique:

• Fluoroscopic or ultrasound-guided
• Into interspinous space at affected level(s)
• Corticosteroid and local anesthetic

Outcomes:

• 60-70% good response reported
• May need repeat injections
• Duration of relief variable

Surgical Management

Indications:

• Refractory to conservative and injection therapy
• Epidural cyst causing neurogenic symptoms
• Significant functional impairment

Surgical Options:

Disease Complications

Dorsal Epidural Cyst:

• Extension of interspinous bursa into spinal canal
• May cause spinal stenosis symptoms
• Requires surgical excision

Adjacent Level Disease:

• Ongoing degeneration may affect other levels
• May develop Baastrup disease at other levels

Treatment Complications

Injection-Related:

• Infection (rare)
• Bleeding
• Temporary numbness
• Steroid side effects (if repeated)

Surgical Complications:

Long-Term Outcomes

Natural History:

Without treatment, Baastrup disease typically follows a chronic, waxing and waning course. Progressive degeneration may lead to increasing symptoms over time.

Prognosis:

With appropriate treatment (conservative, injection, or surgery), prognosis is generally good. Most patients achieve adequate pain control with conservative measures.

Spinous Process Excision Protocol

Day 0-1:

• Mobilization: Same day or next morning mobilization
• Wound care: Drain rarely required
• Pain management: Oral analgesia usually sufficient
• Activity: Sitting and standing tolerated

Week 1-2:

• Activity: Walking as tolerated
• Wound check: 10-14 days for suture removal
• Restrictions: Avoid heavy lifting, extension, bending
• Return to sedentary work: Often by 1-2 weeks

Week 2-6:

• Progressive activity: Gradual return to normal activities
• Physical therapy: Core strengthening, flexibility exercises
• Avoid: Repetitive extension movements
• Return to manual work: 4-6 weeks typically

Long-term:

• Follow-up: 6 weeks, 3 months, then as needed
• Maintenance: Ongoing core strengthening program
• Activity modification: Avoid prolonged extension

Treatment Outcomes by Modality

Prognostic Factors

Favorable:

• Isolated Baastrup disease without stenosis
• Single level involvement
• Good response to diagnostic injection
• No epidural cyst

Unfavorable:

• Multilevel involvement
• Associated spinal stenosis or facet arthropathy
• Workers' compensation claims
• Poor response to injection

Patient Satisfaction

• Conservative management: 50-60% satisfied
• Post-injection: 60-70% good/excellent
• Post-surgery: 70-85% good/excellent pain relief

Baastrup disease is managed in Australia according to established principles of conservative-first approach with injection therapy for refractory cases.

Imaging:

MRI is readily available through public and private radiology services. Specific protocols for lumbar spine include sagittal T2 and STIR sequences that demonstrate interspinous bursitis and bone marrow edema.

Injection Therapy:

Interspinous bursa injections are performed by pain medicine specialists, interventional radiologists, and spine surgeons under fluoroscopic or ultrasound guidance. These procedures are typically bulk-billed when clinically indicated.

Surgical Management:

Surgical treatment for refractory Baastrup disease, including spinous process excision and epidural cyst decompression, is performed at major spine surgery centers. These cases are often discussed at multidisciplinary meetings, particularly when associated pathology such as stenosis is present.

1. Baastrup CI. On the spinous processes of the lumbar vertebrae and the soft tissues between them, and on pathological changes in that region. Acta Radiologica. 1933;14(1):52-55.
2. Maes R, Morrison WB, Parker L, et al. Lumbar interspinous bursitis (Baastrup disease) in a symptomatic population: prevalence on magnetic resonance imaging. Spine. 2008;33(7):E211-5.
3. Mitra R, Ghazi U, Guthikonda M. Baastrup's disease: an often missed etiology for back pain. J Pain Res. 2011;4:137-141.
4. Filippiadis DK, Mazioti A, Argentos S, et al. Baastrup's disease (kissing spines syndrome): a pictorial review. Insights Imaging. 2015;6(1):123-128.
5. Chen CK, Yeh L, Resnick D, et al. Intraspinal posterior epidural cysts associated with Baastrup's disease: report of 10 patients. AJR Am J Roentgenol. 2004;182(1):191-194.