Subligamentous Thecal Sac Indentation

Subligamentous thecal sac indentation occurs when intervertebral disc material herniates beneath the posterior longitudinal ligament, pressing into and indenting the front (ventral) surface of the protective dural membrane (the thecal sac) that surrounds the spinal cord and cerebrospinal fluid Spine InfoRadiopaedia. On MRI, this appears as a focal inward deformity of the thecal sac contour without rupture of the ligament itself.

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Anatomy of the Posterior Longitudinal Ligament

Structure

The posterior longitudinal ligament (PLL) is a dense band of longitudinal collagen fibers, denser and more compact than the anterior longitudinal ligament, especially over intervertebral discs, where its fibers fuse with the disc annulus fibrosus NCBI.

Location

The PLL runs inside the vertebral canal along the posterior surfaces of vertebral bodies, extending from the axis (C2) down to the sacrum NCBI.

Origin & Insertion

• Origin: Deep fibers arise between adjacent vertebral bodies, attaching firmly to the posterior edge of the annulus fibrosus at each intervertebral disc NCBI.

• Insertion: Superficial fibers span multiple vertebrae, inserting onto the posterior aspects of the vertebral bodies, allowing some flexibility while reinforcing the canal Wikipedia.

Blood Supply

Vascularization is provided by segmental arteries (e.g., posterior intercostal, lumbar, iliolumbar), which send small branches through the vertebral canal to nourish the PLL and adjacent dura Kenhub.

Nerve Supply

The PLL is innervated by the recurrent meningeal (sinuvertebral) branch of the spinal nerves, forming ascending and descending plexuses that penetrate the ligament and posterior annulus fibrosus NCBI.

Functions

1. Limits Hyperflexion of the spine, preventing excessive forward bending Wikipedia.

2. Stabilizes Vertebral Bodies by reinforcing intervertebral spaces and resisting shear forces NCBI.

3. Restricts Posterior Disc Herniation, guiding extruded material to remain subligamentous rather than free in the canal Wikipedia.

4. Provides Nociceptive Feedback, as it contains a high density of pain receptors, contributing to back pain when strained Wikipedia.

5. Aids Annulus Fibrosus Repair by serving as an anchoring scaffold for healing torn annular fibers NCBI.

6. Conveys Proprioceptive Information through mechanoreceptors, helping the central nervous system monitor spinal position and movement NCBI.

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Types of Subligamentous Indentation

• Subligamentous Protrusion: A contained bulge under the PLL without rupture of outer fibers, causing mild to moderate thecal sac indentation Radiopaedia.

• Subligamentous Extrusion: Disc material tears through the annulus fibrosus but remains under the PLL, often leading to more pronounced sac indentation and potential neural compromise Radiopaedia.

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Causes

Common causes of subligamentous thecal sac indentation include degenerative and mechanical stresses, trauma, and pathological lesions Spine InfoRadiology Assistant:

1. Degenerative disc disease

2. Herniated (prolapsed) disc

3. Spinal stenosis

4. Spondylolisthesis

5. Acute trauma (falls, accidents)

6. Vertebral fractures

7. Epidural lipomatosis

8. Spinal tumors (primary or metastatic)

9. Epidural abscess (infection)

10. Facet joint osteoarthritis

11. Ligamentum flavum hypertrophy

12. Ossification of the PLL (OPLL)

13. Congenital spinal canal narrowing

14. Rheumatoid arthritis

15. Disc calcification

16. Obesity-induced mechanical overload

17. Chronic corticosteroid use (lipomatosis)

18. Ankylosing spondylitis

19. Paget’s disease of bone

20. Degenerative spondylolisthesis

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Symptoms

Patients may experience a range of symptoms, depending on location and severity Spine Info:

1. Localized back pain

2. Radiating leg or arm pain (radiculopathy)

3. Tingling (paresthesia)

4. Numbness in affected dermatome

5. Muscle weakness

6. Reduced reflexes

7. Gait disturbance

8. Muscle spasms

9. Sharp shooting pain with movement

10. Pain worsening with flexion or extension

11. Night pain disrupting sleep

12. Stiffness after rest

13. Claudication-like symptoms in spinal stenosis

14. Bowel or bladder dysfunction (if severe)

15. Saddle anesthesia (perineal numbness)

16. Sensory loss in saddle area

17. Difficulty standing or walking

18. Postural imbalance

19. Hyperreflexia (if cord affected)

20. Lhermitte’s sign (electric shock sensation)

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Diagnostic Tests

Evaluation combines imaging and functional studies Spine InfoRadiopaedia:

1. MRI of the spine

2. CT scan

3. CT myelography

4. Plain X-rays (AP/lateral)

5. Flexion-extension radiographs

6. Discography

7. Electromyography (EMG)

8. Nerve conduction studies (NCS)

9. Myelogram

10. Bone scan

11. Ultrasound (limited use)

12. Somatosensory evoked potentials (SSEPs)

13. Motor evoked potentials (MEPs)

14. Blood tests (inflammatory markers)

15. Complete blood count (infection)

16. ESR/CRP (infection, inflammation)

17. CT-guided biopsy (tumor)

18. Open MRI (for claustrophobic patients)

19. Dynamic MRI (motion studies)

20. Physical exam maneuvers (e.g., straight leg raise)

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Non-Pharmacological Treatments

First-line management emphasizes non-drug approaches PubMedAAFP:

1. Superficial heat packs

2. Cold therapy (ice)

3. Massage therapy

4. Acupuncture

5. Spinal manipulation (chiropractic)

6. Therapeutic exercise

7. Multidisciplinary rehabilitation

8. Mindfulness-based stress reduction

9. Tai chi

10. Yoga

11. Motor control exercise

12. Progressive relaxation

13. Electromyography biofeedback

14. Low-level laser therapy

15. Operant therapy

16. Cognitive behavioral therapy (CBT)

17. Spinal traction

18. Aquatic therapy

19. Posture correction training

20. Ergonomic workstation adjustments

21. Core stabilization exercises

22. Pilates

23. Manual therapy (mobilization)

24. Transcutaneous electrical nerve stimulation (TENS)

25. Ultrasound therapy

26. Laser therapy

27. Acupressure

28. Breathing and relaxation exercises

29. Kinesio taping

30. Neurofeedback therapy

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Drugs

Pharmacologic options are used when non-drug measures are insufficient American College of PhysiciansNCCIH:

1. Ibuprofen (NSAID)

2. Naproxen (NSAID)

3. Diclofenac (NSAID)

4. Celecoxib (COX-2 inhibitor)

5. Ketorolac (NSAID)

6. Acetaminophen (analgesic)

7. Cyclobenzaprine (muscle relaxant)

8. Baclofen (muscle relaxant)

9. Tizanidine (muscle relaxant)

10. Gabapentin (anticonvulsant)

11. Pregabalin (anticonvulsant)

12. Duloxetine (SNRI)

13. Amitriptyline (TCA)

14. Tramadol (opioid-like)

15. Oxycodone (opioid)

16. Morphine (opioid)

17. Codeine (opioid)

18. Lidocaine patch (topical analgesic)

19. Capsaicin cream (topical)

20. Prednisolone (oral corticosteroid)

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Surgical Options

Reserved for refractory or severe cases Radiology AssistantSpine Info:

1. Microdiscectomy

2. Laminectomy

3. Laminotomy

4. Foraminotomy

5. Spinal fusion (PLIF/TLIF)

6. Artificial disc replacement

7. Microendoscopic discectomy

8. Endoscopic discectomy

9. Epidural lysis of adhesions

10. Ossified PLL decompression

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Prevention Strategies

Evidence supports exercise and ergonomics for preventing recurrence PubMedHarvard Health:

1. Regular exercise combined with education

2. Proper lifting technique (bend knees, not back)

3. Maintaining good posture

4. Regular walking programs

5. Core strengthening exercises

6. Ergonomic adjustments at work/home

7. Maintaining a healthy weight

8. Adequate calcium & vitamin D intake

9. Medium-firm mattress support

10. Smoking cessation

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When to Seek Medical Attention

Red-flag signs warrant prompt evaluation WikEMWebMD:

• Severe or progressive neurological deficits

• New bowel or bladder incontinence/retention

• Saddle anesthesia (perineal numbness)

• Unrelenting night pain or weight loss

• Fever, chills, systemic infection signs

• History of cancer or severe trauma

• Age < 18 or > 50 with new onset pain

• Anticoagulant use with back pain

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Frequently Asked Questions

1. What does “subligamentous thecal sac indentation” mean?
   It means that disc material has pushed under the posterior longitudinal ligament and is pressing into the front of the thecal sac that surrounds the spinal cord Spine Info.

2. How is it diagnosed?
   MRI is the gold standard for visualizing indentation of the thecal sac and assessing the extent of subligamentous herniation Spine Info.

3. What causes this condition?
   It most often results from degenerative disc disease or a tear in the disc annulus, but trauma, tumors, or ligament ossification can also lead to it Radiopaedia.

4. What symptoms should I expect?
   Symptoms range from localized back pain to radiating limb pain, numbness, tingling, and in severe cases, weakness or bowel/bladder issues Spine Info.

5. Can it improve without surgery?
   Yes—many cases respond to non-pharmacological treatments like exercise and manual therapy, especially when the indentation is mild PubMed.

6. When is surgery necessary?
   Surgery is considered if severe neurological deficits develop, or if conservative care fails after 6–12 weeks with ongoing pain or functional decline Radiology Assistant.

7. What is the long-term outlook?
   With appropriate management, most people recover well; persistent symptoms occur in a minority, often related to incomplete decompression or ongoing degeneration Radiopaedia.

8. Can this cause permanent nerve damage?
   If untreated when severe (e.g., cauda equina signs), it can lead to lasting deficits; early intervention reduces this risk Wikipedia.

9. How can I manage mild symptoms at home?
   Heat, gentle stretching, core exercises, and proper body mechanics can ease pain; always follow professional guidance American College of Physicians.

10. Are there risks with massage or acupuncture?
    When performed by trained providers, these therapies are safe and can help reduce pain, though minor soreness or bruising may occur PubMed.

11. Will I need pain medication long-term?
    Most patients taper off once symptoms improve; long-term opioid use is discouraged due to dependency risks American College of Physicians.

12. Is physical therapy beneficial?
    Yes—targeted PT improves strength, flexibility, and posture, reducing recurrence PubMed.

13. Can spinal manipulation help?
    Spinal manipulation may provide short-term relief, but benefits vary by individual PubMed.

14. How soon will I feel better?
    Acute symptoms often improve within weeks; chronic cases may take months of combined therapies PubMed.

15. How do I prevent recurrence?
    Maintain regular exercise, good posture, ergonomic work habits, and healthy weight to lower risk of future thecal sac indentation PubMed.

Disclaimer: Each person’s journey is unique, treatment plan, life style, food habit, hormonal condition, immune system, chronic disease condition, geological location, weather and previous medical  history is also unique. So always seek the best advice from a qualified medical professional or health care provider before trying any treatments to ensure to find out the best plan for you. This guide is for general information and educational purposes only. Regular check-ups and awareness can help to manage and prevent complications associated with these diseases conditions. If you or someone are suffering from this disease condition bookmark this website or share with someone who might find it useful! Boost your knowledge and stay ahead in your health journey. We always try to ensure that the content is regularly updated to reflect the latest medical research and treatment options. Thank you for giving your valuable time to read the article.

The article is written by Team Rxharun and reviewed by the Rx Editorial Board Members

Last Updated: May 03, 2025.

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