Disc slip
Ahmad Muneeb, MBBS
Synonyms and keywords: Intervertebral Disc Displacements; Disc Displacements, Intervertebral; Disc Displacement, Intervertebral; Intervertebral Disk Displacements; Disk Displacements, Intervertebral; Disk Displacement, Intervertebral; Intervertebral Disk Displacement; Disks, Prolapsed; Slipped Disk; Disk Prolapse; Discs, Slipped; Herniated Disks; Slipped Discs; Herniated Disc; Disks, Slipped; Disk, Prolapsed; Prolapsed Disk; Disc, Slipped; Prolapses, Disk; Slipped Disc; Discs, Prolapsed; Discs, Herniated; Prolapsed Discs; Disks, Herniated; Disk, Herniated; Herniated Disk; Prolapse, Disk; Disk Prolapses; Prolapsed Disc; Disc, Herniated; Disc, Prolapsed; Slipped Disks; Disk, Slipped; Herniated Discs; Prolapsed Disks

# Overview
Intervertebral disk slip consists of 2 main parts, nucleus pulposus the central part, and annulus fibrosus the peripheral part. Intervertebral disc slip occurs when nucleus pulposus protrudes through annulus fibrosus. Most commonly disc slip is caused by degenerative changes and traumatic insults to the spine. Although, disc herniation can occur in any part of the vertebral column but lumbar disc slips are far more common than disc herniations in other parts of the spine. Males, obese, smokers and heavy weight lifters are at increased risk of developing disk slip. Clinical features of the disk slip vary depending upon the location and presence or absence of nerve impingement. Common clinical features include back pain, pain radiating to upper or lower extremity, motor weakness, numbness or tingling, absent deep tendon reflexes. MRI and CT scan have excellent sensitivity in diagnosing intervertebral disc slip. Conservative management starts with lifestyle modifications and medical therapy. Most of the patients get pain relief with conservative management. For severe or persistent cases surgical management can be used.

# Historical Perspective
- Intervertebral disc slip was first described by Virchow, a german physician, in  in his publication related to disc pathologies. 
- In , the first laminectomy was done by William MacEwen and Victor Horsely to treat lumbar disc slip. The first discectomy was done by surgeon Fedor Krause in 1908.  

# Classification
- Intervertebral disc slip may be classified according to the extent of displacement of nucleus pulposus into 4 subtypes:
- Bulging: Disc margins extend beyond vertebral endplate margins.
- Protrusion: Nucleus pulposus impinges on annulus fibrosus, posterior longitudinal ligament stays intact.
- Extrusion: Nucleus pulposus extrudes through the annulus fibrosus, posterior longitudinal ligament stays intact.
- Sequestration: Posterior longitudinal ligament is compromised. Nucleus pulposus extrudes through the annulus fibrosus and posterior longitudinal ligament into epidural space.

# Pathophysiology
- The pathogenesis of disc slip is characterized by bulging of nucleus pulposus of the disk through the annulus pulposus. Nucleus pulposus is the central part of the intervertebral disc that contains proteoglycans. Proteoglycans cause water retention, thus nucleus pulposus is responsible for providing cushioning effect to vertebrae. Annulus fibrosis is the peripheral ring surrounding nucleus pulposus that is responsible for keeping nucleus pulposus in the center of the disk. Displaced fragments of nucleus pulposus can then compress the nerve roots passing behind the intervertebral disk space. Disc degeneration is the most common preceding factor in the development of disk slip. Several underlying changes have been implicated in the development of slipped discs including decreased water content in nucleus pulposus, increased activity of degradative processes including inflammatory mediators, apoptosis, and matrix metalloproteinase enzyme leading to degeneration of intervertebral discs. Role of multiple genes has also been implicated in intervertebral disc degeneration and consequent herniation. It is also documented that axial overburdening of vertebral column may cause disc slip. 
- Genes responsible for disc slip include genes coding for matrix metalloproteinases, structural proteins, Vitamin D receptor, apoptosis factors, growth factors, collagen type I and IX, interleukin 1, interleukin 6, asporin, aggrecan. 

# Causes
Disc slip may be caused by age-related degenerative changes, systemic inflammatory processes, vertebral trauma, sudden vertebral strain, twisted movement of the spine, connective tissue disorders.  

# Differentiating intervertebral disc slip from other Diseases
- Disc slip must be differentiated from other diseases that cause radicular pain, sensory deficits, and motor weakness, such as :
- Spinal tumors
- Spinal abscess
- Spinal fractures
- Spinal stenosis
- Arthritis
- Spinal cysts
- Epidural hematoma

# Epidemiology and Demographics
- The incidence of intervertebral disc slip is estimated to be  cases per 1000 individuals annually. In case of lumbar disc slips, 95% of the herniations in patients aged between 25 to 55 occur at L4-L5 or L5-S1 level. In case of cervical spine, C6-C7 disc is most commonly herniated. 

## Age
- Intervertebral disc slip is more commonly observed among patients aged 30 to 50 years old.

## Gender
- Males are more commonly affected with intervertebral disc slip than females.

## Race
- There is no racial predilection for intervertebral disc slip.

# Risk Factors
- Common risk factors in the development of intervertebral disc slip are  male gender, excessive body weight, smoking, sedentary life style, abrupt increase in physical activity, heavy weight lifting, poor posture, poor nutrition.  

# Natural History, Complications and Prognosis
- Two-third of patients with lumbar disc herniation improve within 6 months as herniated disk tends to regress over time. After 6 weeks, only around 10% of the patients have persistent pain to consider surgery. 
- If left untreated, patients with intervertebral disc slip may develop chronic back pain, permanent nerve damage, persistent motor weakness, persistent sensory deficits, Cauda equina syndrome.  

# Diagnosis

## Diagnostic Criteria
There are no specific diagnostic criteria for intervertebral disc slip.

## History and Symptoms
- Symptoms of Intervertebral disc slip depend upon the site and extent of the slipped disc and are present in the are supplied by the compressed nerve. They may include the following:

### Lumbar disc slip
- Lower back pain
- electric shock like or sharp pain radiating from buttock to leg(sciatica)
- numbness or tingling in one leg
- lower extremity weakness
- loss of bowel or bladder control
- pain aggravation with walking, standing or sitting

### Cervical or thoracic disc slip
- Neck pain
- pain between shoulder girdles
- pain radiating down the arm to the hand or fingers
- numbness/tingling in the forearm, arm or shoulder
- increase in pain with neck movements.
- weakness in the muscles of hand or forearm

## Physical Examination
- Physical examination findings depend upon the nerve root compressed and maybe remarkable for:
- C5 nerve: numbness in lateral arm, weakened shoulder abduction, external rotation, forearm supination and elbow flexion, abnormal biceps reflex and brachioradialis reflex.
- C6 nerve: numbness in thumb, index finger, lateral foream, weakened shoulder abduction, external rotation, forearm supination, forearm pronation and elbow flexion, abnormal biceps reflex and brachioradialis reflex.
- C7 nerve: numbness in palm, index and middle fingers, weakened wrist flexion, radial extension, and forearm pronation, abnormal triceps reflex.
- C8 nerve: numbness in medial forearm and hand, weakened distal finger flexion, extension, abduction, adduction, distal thumb flexion and wrist extension. Normal reflexes
- T1 nerve: numbness in anterior and medial forearm, weakened finger adduction, abduction, thumb abduction and distal thumb flexion. Normal deep tendon reflexes
- L1 nerve: altered sensation in inguinal region, weakened hip flexion.
- L2,L3,L4 nerves: altered sensation in medial leg and anterior thigh, weakened hip fexion, adduction, knee extension, abnormal patellar reflex.
- L5 nerve: altered sensation in lateral calf, dorsal for and space between 1st and 2nd toe, weakened hip abduction, knee flexion, foot dorsiflexion, toe flexion and extension, foot eversion and inversion. Abnormal semitendinosus or semimembranosus reflex.
- S1 nerve: altered sensation on posterior calf, lateral or plantar foot, weakened hip extension, knee flexion, foot plantar flexion, loss of bowel or bladder control, sexual dysfunction.
- S2-S4 nerves: altered sensation on medial side of buttock, perianal and perineal region, absence of wink and bulbocavernosus reflex.
- positive straight leg raise test in lumbar radiculopathy.

## Laboratory Findings
- There are no specific laboratory findings associated with intervertebral disc slip.

## Electrocardiogram
There are no ECG findings associated with intervertebral disc slip.

## X-ray
There are no x-ray findings associated with intervertebral disc slip. However, an x-ray may be helpful in detecting other etiologies causing similar symptoms like fractures, abscesses, tumors, bony spurs etc.

## Echocardiography or Ultrasound
There are no echocardiography/ultrasound  findings associated with intervertebral disc slip.

## CT scan
CT scan may be helpful in the diagnosis of intervertebral disc slip. Like MRI, CT scan also provides a detailed view of the spinal canal and its contents, thus it can detect disc slip along with its extent and location.Findings on CT scan suggestive of intervertebral disc slip include bulging of intervertebral disc, nerve root compression, and spinal cord compression.  

## MRI
MRI may be helpful in the diagnosis of intervertebral disc slip, as it is considered the gold standard for the diagnosis of this disorder. MRI has an excellent capacity to visualize all the soft tissues including the spinal cord, and nerve roots thus it can easily detect bulging intervertebral disc and also if there is any compression of nerve root or spinal cord. MRI is also very helpful in ruling out other differentials.

## Other Imaging Findings
Myelogram may be helpful in the diagnosis of intervertebral disc slip. It is a modified x-ray technique in which the spinal canal is visualized after injection of a contrast material. It can show if a slipped disk is compressing a nerve root or spinal cord

## Other Diagnostic Studies
Electromyogram and nerve conduction studies may be helpful in the diagnosis of intervertebral disc slip. These tests assess the response of nerve or muscle to electric stimulation. They can reveal if there is any nerve damage or compression as a consequence of slipped disk.

# Treatment
Certain non-pharmacologic treatments and lifestyle modifications can be used before any pharmacologic treatment is done. They include maintenance of activity level that is painless, physiotherapy, avoidance of any activity that incites pain, avoidance from lifting heavy weights, weight control, use of spinal support, spinal massage, spinal manipulation, spinal traction, heat or ice application.  

## Medical Therapy
- The medical treatment options for pain relief in intervertebral disc slip are analgesic medications like NSAIDS or acetaminophen, muscle relaxants, steroids and anti depressants. A steroid injection in the epidural space may also be administered to provide pain relief. 

## Surgery
- Discectomy can be performed for patients with intervertebral disc slip who do not improve with medical management and lifestyle modifications. It can also be performed in patients with persistent or progressive neurologic deficit due to nerve compression. Discectomy is of 2 types. Microsurgical discectomy involves a small incision in the center of the back followed by microdissection to reach the herniated disk. Then the part of the disk impinging on the nerve root is removed. Microendoscopic discectomy involves an incision at the back. In order to reach the vertebra, dilators are used. Then an endoscope is used to access and remove the herniated disk. Microendoscopic discectomy causes lesser tissue damage than microsurgical discectomy. Other options like laser discectomy are also available but their efficacy is not fully proven. In selective cases, discectomy can be combined with laminectomy and spinal fusion 

## Prevention
- Effective measures for the primary prevention of intervertebral disc slip include maintaining a normal body weight, regular exercise, smoking cessation and good posture.