Adult Spinal Deformity - Spine

summary
- Adult Spinal Deformity is an idiopathic or degenerative condition of the adult spine leading to a deformity in the coronal or sagittal plane.
- Diagnosis is made with full-length spine radiographs.
- Treatment is a trial of nonoperative management with NSAIDs and physical therapy. Surgical deformity corrected is indicated for progressive disabling pain that has failed nonoperative management, and/or progressive neurological deficits.

Epidemiology
- Demographics
  - mean age is 60 years
  - males and females equally affected
- Anatomic location
  - idiopathic scoliosis is more common in the thoracic spine
  - degenerative scoliosis occurs more commonly in the lumbar spine.

Etiology
- Types
  - coronal plane imbalance
    
    defined as lateral deviation of the normal vertical line of the spine > 10 degrees
  - sagittal plane imbalance
    
    defined as radiographic sagittal imbalance of >5cm
- Pathoanatomy
  - degenerative scoliosis results from the asymmetric degeneration of disc space and/or facet joints in the spine.
  - may occur in the coronal plane (scoliosis) or the sagittal plane (kyphosis/lordosis)
  - factors contributing to loss of sagittal plane balance
    
    osteoporosis
    
    preexisting scoliosis
    
    iatrogenic instability
    
    degenerative disc disease

                        Classification
                    
                        Coronal deformity can be broken down into
                    
                        idiopathic (residual) ASD
                    
                        the result of untreated adolescent idiopathic scoliosis in the adult
                    
                        degenerative (de novo)  ASD
                    
                        defined as a progressive deformity in the adult caused by
                    
                        degenerative changes
                    
                        iatrogenic
                    
                        paralytic
                    
                        Difference between Idiopathic (residual) and Degenerative (de novo) ASD
                    
                        Idiopathic (residual)
                    
                        Degenerative (de novo)
                    
                        Curve pattern
                    
                        Follows classic curve patterns
                    
                        Lack classic curve patterns
                    
                        Vertebral segments
                    
                        Involves more vertebral segments
                    
                        Involves fewer vertebral segments
                    
                        Curve location
                    
                        Thoracic spine
                    
                        Lumbar spine
                    
                        Curve magnitude
                    
                        Larger curves
                    
                        Smaller curve magnitude

Presentation
- Symptoms
  - low back pain (40-90%)
    
    commonest symptom is low back pain
    
    caused by spondylosis, micro/macro instability, and discogenic pain
    
    more severe and recurrent than general population
  - neurogenic claudication
    
    pain in lower extremities and buttocks
    
    unlike classic claudication, patients with scoliosis + stenosis do not obtain relief with sitting / forward flexion
    
    caused by spinal stenosis
    
    stenosis is located on the concave side of the curve
  - radicular leg pain and weakness
    
    caused by foraminal and lateral recess stenosis
    
    worse in concavity of the deformity where there is vertebral body rotation and translation
- Physical exam
  - deformity with thoracic prominence seen with forward bending
  - muscle weakness

Imaging
- Radiographs
  - recommended views
    
    full length long 36-inch cassette standing scoliosis xrays in coronal (AP radiograph) and sagittal plane (lateral radiograph), with right and left bending films
    
    bending films help assess curve flexibility and possibility of correction with surgical intervention
  - measurements
    
    AP radiograph
    
    Cobb angle
    
    coronal balance
    
    using C7 plumb line (C7PL) and center sacral vertical line (CSVL)
    
    lateral radiograph
    
    sagittal balance
    
    using C7 plumb line (C7PL)
    
    pelvic incidence
    
    pelvic incidence (PI) = sacral slope (SS) + pelvic tilt (PT)
- CT scan
  - will help identify bony deformity such as facet arthrosis
- CT myelogram
  - most useful for assessing stenosis and bony anatomy as rotation makes interpretation of MRI difficult
  - better appreciation of bony anatomy and rotational deformity than MRI
- MRI
  - indicated when lower extremity pain is present
  - can identify
    
    central canal stenosis
    
    facet hypertrophy
    
    pedicular enlargement
    
    foraminal encroachment
    
    disc degeneration
- DEXA scan
  - important to determine bone density for surgical planning

Treatment
- Nonoperative
  - observation with nonoperative modalities
    
    indications
    
    coronal curves < 30 degrees rarely progress
    
    modalities
    
    oral medications
    
    NSAIDS
    
    tricyclic antidepressants help with sleep disturbance
    
    physical therapy
    
    includes core strengthening (walking, cycling, swimming, selected weight lifting)
    
    corticosteroid injections and nerve root blocks
    
    diagnostic and therapeutic
    
    bracing
    
    may slow progression and increase comfort
- Operative
  - surgical curve correction with instrumented fusion
    
    general indications
    
    curve > 50 degrees of the following type
    
    sagittal imbalance
    
    curve progression
    
    intractable back pain or radicular pain that has failed nonsurgical efforts
    
    cosmesis (controversial)
    
    cardiopulmonary decline
    
    thoracic curves >60deg affect pulmonary function tests
    
    thoracic curves >90deg affect mortality
    
    technique
    
    posterior only curve correction and instrumented fusion
    
    indications
    
    thoracic curves > 50 degrees
    
    most double structural curves > 50 degrees
    
    selecting technique is patient and surgeon specific
    
    combined anterior/posterior curve correction with instrumented fusion
    
    indications
    
    isolated thoracolumbar
    
    isolated lumbar curves
    
    extremely rigid curves requiring anterior release

Techniques
- General
  - goals of surgery
    
    restore spinal balance
    
    sagittal plane balance is the most reliable predictor of clinical symptoms postoperatively
    
    can be measured by C7 plumb line (C7 sagittal vertical axis)
    
    correction of sagittal plane deformity requires intense preoperative planning
    
    correct lumbar lordosis to normal anatomic range:
    
    PI = LL+/- 9°
    
    LL ≤ 45° - TK - PI
    
    most predictive of sagittal plane correction maintenance
    
    relieve pain
    
    obtain solid fusion
  - Worse outcomes associated with:
    
    Baseline depression
    
    Obesity
- Selecting Proximal and Distal fusion level
  - proximal extension
    
    extend to a neutral and horizontal vertebra above the main curve
  - extend fusion to L5
    
    indications
    
    only indicated if no pathology at L5/S1
    
    patients with normal C7 plumb line and normal sacral inclination have lowest risk of future L5-S1 disc degeneration
    
    outcomes
    
    high failure rate if instrumentation does not extend to the sacrum if pathology at L5/S1
  - extend fusion to sacrum (S1)
    
    indications
    
    extend to sacrum if any pathology at L5-S1 including
    
    L5-S1 spondylolisthesis
    
    L5-S1 spondylolysis
    
    L5-S1 facet arthrosis
    
    prior laminectomy
    
    technique
    
    may require concomitant anterior release and anterior column support (through anterior approach) for better deformity correction
    
    outcomes
    
    advantages
    
    increased stability of long fusion construct
    
    constructs less likely to fail if instrumentation extends to sacrum
    
    disadvantages
    
    increased risk of pseudoarthrosis
    
    increased surgical time
    
    increased reoperation rate
    
    increased risk of sacral insufficiency fractures
    
    altered gait postoperatively
  - extend fusion to ilium (sacropelvic fusion)
    
    indications
    
    consider this if sacrum is included in fusion involving >3 levels
    
    technique
    
    using iliac screws or bolts
    
    outcomes
    
    advantage
    
    increased stability of long fusion construct
    
    increases success of lumbosacral fusion
    
    disadvantage
    
    prominent hardware
  - cement augmentation
    
    indications
    
    osteoporotic patients
    
    technique
    
    cement injection through fenestrated tap at the end vertebra followed by pedicle screw insertion
    
    outcomes
    
    increased fusion rates
    
    decreased deformity correction loss
    
    increased screw pull-out stregnth
    
    no added complications
- Osteotomies
  - overview
    
    useful to regain sagittal balance in severe angulation deformities
    
    30deg or more correction can be obtained through Smith-Petersen or pedicle subtraction osteotomies
    
    intraoperative neuromonitoring preferred
  - Smith-Petersen osteotomy (SPO)
    
    indications
    
    mild-moderate sagittal imbalance
    
    requiring correction of up to 10deg (per level of osteotomy)
    
    prerequisites
    
    no anterior fusion at the level of osteotomy
    
    adequate correction requires adequate disc height and mobility (correction is at the level of the disc)
    
    more correction in the lumbar spine (greater disc height and mobility)
    
    less correction in the thoracic spine (lesser disc height and mobility)
  - pedicle subtraction osteotomy (PSO)
    
    indications
    
    severe sagittal imbalance >12cm
    
    requiring correction of 30-35deg in the lumbar spine, and 25deg in the thoracic spine
    
    where anterior fusion is present (correction is at the level of the vertebral body and not at the disc)
  - vertebral column resection
    
    indications
    
    severe sagittal imbalance (provides more correction than PSO)
    
    requiring correction of up to 45deg
    
    rigid angular thoracic spine kyphosis, such as associated with tumor, fracture or infection
    
    severe rigid scoliosis
    
    congenital kyphosis
    
    hemivertebrae resection in thoracic/lumbar spines
- Anterior Procedures
  - indications
    
    large curves >70deg
    
    rigid curves (no flexibility on side bending films)
    
    isolated lumbar or thoracolumbar curves
    
    anterior interbody fusion at L5/S1 when fusing to sacrum
  - technique
    
    anterior release and fusion usually combined with posterior instrumentation and fusion
    
    staged or same day
  - outcomes
    
    disadvantages
    
    longer surgeries (if performed on the same day)
    
    higher complication rates
    
    more medically stressful
    
    advantage
    
    increases stability of L5-S1 long fusion constructs
    
    helps restore and maintain sagittal and coronal balance

Complications (surgical)
- Overall
  - overall complication rate ~13.5%
  - 10% major complications which often irreversibly affect long term health of patient
  - complication rate is significantly higher when osteotomies, revision procedures, and combined anterior/posterior approaches
  - venous thromboembolism is most likely to result in poor clinical outcome following adult spinal deformity surgery
- Pseudoarthrosis
  - incidence (~5-25%)
  - most common surgical technique resulting in pseudoarthrosis is posterior only fusion (15%)
  - commonest locations
    
    L5-S1
    
    thoracolumbar junction
  - risks
    
    age>55
    
    kyphosis >20 degrees
    
    positive sagittal balance >5cm
    
    hip arthritis
    
    smoking
    
    thoracoabdominal approach
    
    incomplete lumbopelvic fixation
- Dural tear (~2.9%)
- Infection
  - deep wound infection (~1.5%)
  - superficial wound infection (~0.9%)
  - increased risk with diabetes, smoking, increasing age, and revision surgery
- Implant complication
  - instrumentation failure more likely in bone with lowest ratio of cortical to cancellous bone (sacrum
  - most common cause of reoperation, related to pseduoarthrosis
  - lower rates of mechanical complications with GAP scores <3
- Neurologic deficits
  - acute neurological deficits (~1.0%)
    
    can occur intraoperatively after deformity correction maneuver
    
    if identified on neurophysiologic monitoring, should remove instrumentation and consider wake-up test
  - delayed neurological deficits (~0.5%)
  - acute neurological deficits following PSO (18%)
    
    nerve root injury
    
    screw malposition
    
    corrective maneuver
- Epidural hematoma (~0.2%)
- Pulmonary embolus (~0.2%)
- Deep venous thrombosis (~0.2%).
- Deaths (~0.3%)

Prognosis
- Worse prognosis with
  - if symptoms progress to the side of curve convexity
  - sagittal plane imbalance
    
    sagittal plane balance is the most reliable predictor of clinical symptoms in adults with spinal deformity
- Progression
  - depends on curve type
    
    thoracic > lumbar > thoracolumbar > double major
    
    right thoracic curves (1 degree per year)
    
    right lumbar curves (0.5 degree per year)
    
    thoracolumbar curves (0.25 degree per year)
  - depends on curve magnitude
    
    curves <30 deg rarely progress
    
    curves >50 deg commonly progress
  - additional risk factors for progression
    
    increased risk when intercrestal line is below L4-5
    
    preexisting rotational changes exist

Action	Numeric Key	Letter Key	Function Key
Show Bullets		S	Enter (frontside only)
20%	1	N
40%	2	H
60%	3	F	Enter (backside only)
80%	4	E
100%	5	M
Toss	0	T

Difference between Idiopathic (residual) and Degenerative (de novo) ASD
	Idiopathic (residual)	Degenerative (de novo)
Curve pattern	Follows classic curve patterns	Lack classic curve patterns
Vertebral segments	Involves more vertebral segments	Involves fewer vertebral segments
Curve location	Thoracic spine	Lumbar spine
Curve magnitude	Larger curves	Smaller curve magnitude