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Spinal Instability and Spinal Fusion Surgery Workup

  • Author: Peyman Pakzaban, MD; Chief Editor: Brian H Kopell, MD  more...
Updated: Jan 14, 2016

Laboratory Studies

There are no laboratory studies that would assist in diagnosis of spinal instability. Laboratory studies can be helpful in diagnosing certain conditions that could result in spinal stability, such as spine infections (CBC, ESR, C-reactive protein, blood cultures), rheumatoid arthritis (rheumatoid factor), ankylosing spondylitis (HLA-B27), multiple myeloma (serum immunoelectrophoresis, urine Bence-Jones proteins), and others.

Laboratory studies are routinely performed as a part of preoperative preparation for spine surgery.


Imaging Studies

Spine MRI and plain x-ray films with flexion and extension are the most useful imaging studies for evaluation of spinal instability. In addition to demonstrating vertebral displacement, vertebral deformation and neural compression, MRI provides invaluable information about spinal cord injury, neoplastic and infectious processes, and ligamentous disruption. CT-myelography is used when MRI cannot be obtained or has not provided the resolution necessary to assess the extent of neural compression.

Plain CT is useful in assessing bone anatomy in the setting of vertebral fractures, spondylolysis, history of previous spine surgery, and congenital spine anomalies. CT may also be used to assess certain bony parameters (such as pedicle size in thoracolumbar spine, lateral mass anatomy in cervical spine, and vertebral artery anatomy in C1-2 region) in preparation for instrumentation of the spine.

To evaluate bone integrity prior to fusion when osteoporosis is suspected, a bone density scan is performed. Radionucleotide bone scans have been supplanted by high resolution CT for assessment of pseudarthrosis.


Other Tests

Electromyography (EMG) may be used to confirm nerve root compression but does not play a direct role in establishing the diagnosis of spinal instability.


Diagnostic Procedures

Selective nerve root injections can be used as a diagnostic tool to confirm that a particular nerve root is responsible for the pain syndrome. They are also used in a therapeutic capacity in nonsurgical management of spine disorders.

CT-guided biopsy/aspiration is used when tumor or infection is suspected and when the possibility of nonsurgical treatment is being entertained. When surgery has to be performed to decompress and/or stabilize the spine, the diagnosis can be obtained intraoperatively.

Substantial controversy exists regarding the value of discography in diagnosis of discogenic pain and in patient selection for fusion surgery. When performed, it should be accompanied by measurements of intradiscal pressure, documentation of severity and concordance of pain during injection, and postdiscography CT scan.


Histologic Findings

No histological findings are relevant to the diagnosis of spinal instability, except when a neoplasm is the source of instability.



Since spinal instability is a heterogenous disorder, no uniform staging/grading system exists that would be relevant to all forms of spinal instability.

Spondylolisthesis, defined as anterior translation of a vertebral body in relation to the adjacent caudal vertebral body, is graded according to the system in Table 3.

Table 3. Grading of Spondylolisthesis (Open Table in a new window)

Slip Distance/AP Diameter

of Vertebral Body

0-25% 1
25-50% 2
50-75% 3
75-100% 4
>100% Spondyloptosis


Grade 1 spondylolisthesis in neutral position prog Grade 1 spondylolisthesis in neutral position progresses to grade 2 with flexion, indicating overt instability in this case.

In the lumbar spine, spondylolisthesis is either isthmic, degenerative, or traumatic. Isthmic spondylolisthesis occurs because of a congenital weakness and subsequent fracture of pars interarticularis (usually of L5), resulting in uncoupling and glacial anterior translation of one vertebral body over another.

Grade I isthmic spondylolisthesis at L5-S1. Arrow Grade I isthmic spondylolisthesis at L5-S1. Arrow depicts the L5 pars fracture.

Degenerative spondylolisthesis occurs because of severe degeneration of facet joints and incompetence of facet capsules, which lose the capacity to resist the flexion moment, resulting in translation. Traumatic spondylolisthesis represents a fracture-dislocation of the spine.

Contributor Information and Disclosures

Peyman Pakzaban, MD Consulting Neurosurgeon, Houston MicroNeurosurgery; Chairman, Department of Surgery, Bayshore Medical Center

Peyman Pakzaban, MD is a member of the following medical societies: Alpha Omega Alpha, American Association of Neurological Surgeons, American Medical Association, Texas Medical Association, American Stroke Association, Congress of Neurological Surgeons, Harris County Medical Society

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Chief Editor

Brian H Kopell, MD Associate Professor, Department of Neurosurgery, Icahn School of Medicine at Mount Sinai

Brian H Kopell, MD is a member of the following medical societies: Alpha Omega Alpha, American Association of Neurological Surgeons, International Parkinson and Movement Disorder Society, Congress of Neurological Surgeons, American Society for Stereotactic and Functional Neurosurgery, North American Neuromodulation Society

Disclosure: Received consulting fee from Medtronic for consulting; Received consulting fee from St Jude Neuromodulation for consulting; Received consulting fee from MRI Interventions for consulting.

Additional Contributors

Paul L Penar, MD, FACS Professor, Department of Surgery, Division of Neurosurgery, Director, Functional Neurosurgery and Radiosurgery Programs, University of Vermont College of Medicine

Paul L Penar, MD, FACS is a member of the following medical societies: Alpha Omega Alpha, American Association of Neurological Surgeons, World Society for Stereotactic and Functional Neurosurgery, Congress of Neurological Surgeons

Disclosure: Nothing to disclose.


Images 5, 12, 15, 20, 22, 23, 24, and 28 are protected by copyright under Synthes, Inc. or its affiliates; West Chester, Pennsylvania. The efforts of Mr. Jamison Wolocko and Ms. Cynthia Ryen in securing and providing these illustrations for this article are gratefully acknowledged.

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Bilateral jumped facet syndrome is an example of overt spinal instability due to trauma. Notice the grossly abnormal displacement of C5 relative to C6 with neck flexion.
Example of anticipated instability: Figure A shows a large mass affecting right C3-4 facet joint and lateral masses in a patient with severe right-sided neck and shoulder pain; Figures B and C show complete resection of the tumor and simultaneous C3-4 anterior fusion to circumvent the anticipated iatrogenic stability produced by radical resection of facet and lateral masses.
Spinal stenosis with fixed degenerative spondylolisthesis in an elderly patient is a common example of covert instability. Acceptable surgical treatment options include decompression alone vs decompression with fusion.
A. Compression fracture; B. Burst fracture; C. Hyperextension injury to lamina and facets; D. Flexion-distraction (seatbelt) ligamentous injury and Chance fracture; E. Shear fracture-dislocations.
Example of application of biomechanical principles to spine surgery. Insertion of special pedicle screws (Schanz screws) pivoting on a rod transfers the instantaneous axis of rotation (IAR) to the screw/rod interface. Compression of the proximal end of the screws produces distraction-reduction of the vertebral burst fracture. If the posterior longitudinal ligament is intact, retropulsion is corrected by ligament taxis. Image courtesy of Synthes, Inc.
Comparison of vertebral anatomy in cervical, thoracic, and lumbar spine. Note the variation in anatomy and size of pedicles.
Loosening of this infected pedicle screw is evidenced by a radiolucent halo (arrows) surrounding the screw.
In this patient with T7-8 discitis, vertebral enhancement on MRI persisted 8 weeks after clinical and microbiological cure.
Grade 1 spondylolisthesis in neutral position progresses to grade 2 with flexion, indicating overt instability in this case.
Grade I isthmic spondylolisthesis at L5-S1. Arrow depicts the L5 pars fracture.
C1-2 fusion with cable fixation (Gallie technique). In this case, the fusion is supplemented with transarticular screws.
C1-2 fusion and cable fixation (Brooks technique). Image courtesy of Synthes, Inc.
C1-2 fusion with cable fixation (Sonntag technique): coronal (left) and sagittal (right) CT reconstructions.
C1-2 transarticular screw. Notice the proximity of vertebral artery to the typical screw trajectory.
Anterior cervical plate, applied in this case after 2-level anterior cervical discectomy and fusion. Image courtesy of Synthes, Inc.
Large central disc herniations (A and B) and cervical spondylotic myelopathy with kyphosis (C) are two common indications for anterior cervical discectomy and fusion.
C5-6 bilateral jumped facets associated with disc herniation (left) was treated with C6 anterior cervical decompression and fusion (right).
Anterior cervical discectomy and fusion: A. Disc removed and interspace prepared to receive graft; B. Iliac crest bone graft harvested; C. Bone graft; D. Graft inserted into disc space; E. Plate screwed to anterior surface of vertebral bodies.
Intraoperative fluoroscopy for pedicle screw insertion.
Pedicle screw fixation of lumbar spine. Image courtesy of Synthes, Inc.
Combined interbody and posterolateral lumbar fusion with pedicle screws: coronal (left) and sagittal (right) CT reconstructions.
Anterolateral lumbar corpectomy followed by reconstruction with a fixed-height cage and a dynamic rod system that allows compression across the cage. Image courtesy of Synthes, Inc.
A modular posterior thoracolumbar instrumentation system, which is attached to the spine by a combination of screws and hooks, in turn attached to long rods. In this case, it is used for correction of scoliosis, using 3-point bending biomechanical principles. Image courtesy of Synthes, Inc.
Anterolateral thoracic corpectomy followed by reconstruction with an expandable cage and a fixed plate/screw system. Image courtesy of Synthes, Inc.
Anteroposterior and lateral radiographs of anterior thoracic corpectomy and reconstruction for pathological fracture due to vertebral osteomyelitis.
Modern operating room setup for spine surgery with fluoroscopy unit, neurophysiological monitoring equipment, operating microscope, and digital radiology monitors.
Transition level syndrome: C6-7 disc herniation developed 6 years after C4-5 and C5-6 anterior cervical discectomy and fusion.
Artificial lumbar disc. Image courtesy of Synthes, Inc.
Table 1. Traumatic Instability of Cervical Spine


Type/Issue Treatment
C1 Jefferson fracture

(axial loading)

1. Isolated -->

2. With transverse ligament rupture -->

3. Widely diastatic -->

4. With odontoid fracture -->

1. Hard collar

2. Halo

3. Consider occiput-C2 fusion

4. Treat according to odontoid fx

C1-2 Rotatory subluxation

(twisting moment)

1. Children, URI -->

2. Adults, tumor, trauma, infection -->

1. Bedrest, analgesics, halter traction, soft collar

2. Traction, hard collar, halo, or C1-2 fusion depending on cause and duration

Odontoid fracture

(flexion in young, extension in old)

1. Type 1 -->

2. Type 2, < 6 mm displaced -->

3. Type 2, >6 mm displaced or chronic or type 2A -->

4. Type 3 -->

1. If no atlanto-occipital instability, collar x 3 mo

2. Halo x 3-6 mo

3. C1-2 fusion or odontoid screw

4. Halo x 6 mo

C2 Hangman fracture


1. Pars approximated->

2. Pars separated, reducible -->

3. Pars separated, not reducible -->

1. Hard collar x 3 mo

2. Reduce in extension, then halo x 3 mo

3. C2-3 fusion

Unilateral jumped facet

(flexion + rotation)

1. Reducible -->

2. Not reducible -->

3. With facet fracture -->

4. With disc herniation-->

1. Reduce and halo x 3 mo

2. Open reduction and posterior fusion

3. Open reduction and posterior fusion

4. Anterior decompression, open reduction, and anterior fusion

Bilateral jumped facet


1. Reducible, without disc herniation -->

2. Not Reducible, without disc herniation-->

3. With disc herniation-->

1. Closed reduction, then posterior fusion

2. Open anterior or posterior reduction and fusion

3. Anterior discectomy, reduction and fusion

Subaxial spine axial loading injuries

(axial +/- flexion)

1. Simple compression fracture -->

2. Burst fracture +/- tear drop fx -->

3. Burst + posterior column fracture -->

1. Hard collar

2. Anterior corpectomy and fusion

3. Anterior corpectomy and fusion

(+/- posterior fusion)

Clay shoveler fracture


Always stable Soft collar and analgesics
Anterior avulsion fracture


Always stable Soft collar and analgesics
Table 2. Traumatic Instability of Thoracic and Lumbar Spine
Fracture Denis Columns Involved Treatment
Compression fracture Anterior column Bracing (note that >50% vertebral body height loss or Cobb angle >30 degrees predict worsening of kyphosis)
Compression fracture with splaying of spinous processes Anterior and posterior columns Posterior instrumented fusion
Stable burst fracture

(preserved posterior longitudinal ligament)

Anterior column and part of middle column If no neural compromise, treat with TLSO brace

If canal stenosis present, retropulsed fragment may be reduced by ligamentous taxis in distraction

with posterior instrumented fusion

Unstable burst fracture Anterior and middle columns with significant retropulsion,

or all 3 columns

Anterior decompression and instrumented fusion
Flexion-distraction seat belt injury (ligamentous) Middle and posterior columns Posterior reduction and instrumented fusion
Chance fracture (osseous) 2 or 3 columns but with good bone contact TLSO brace
Shear fracture dislocation 3 columns Instrumented fusion, anterior, posterior, or both
Table 3. Grading of Spondylolisthesis
Slip Distance/AP Diameter

of Vertebral Body

0-25% 1
25-50% 2
50-75% 3
75-100% 4
>100% Spondyloptosis
Table 4. Odontoid Fracture Classification
Type Fracture Anatomy
1 Fracture through the odontoid tip (rare)
2 Fracture across the base of the odontoid process (most common)
2A As in type 2, except with comminution of fracture line, reducing the possibility of healing of fracture in halo or with odontoid screw
3 Fracture extension into C2 vertebral body; because of larger bone contact area, fracture usually heals well in a halo
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