Spondylolisthesis
Definition
Gk spondylos which means vertebra and olisthesis which means to slip or slide down a slippery incline.
History
First recognized in 1782 by the Belgian obstetrician Herbiniaux.
Term spondylolisthesis first used in 1854 by Kilian.
Classification
Wiltse classification of spondylolisthesis
i. Congenital
a. Dysplastic posterior elements and articular processes at the level of slippage, frequently associated with spina bifida.
b. Dysplastic articular processes with sagittal orientation of the facet joints resulting in instability primarily at L5-S1.
c. Other congenital anomalies, such as congenital kyphosis, that produce slippage
ii. Isthmic
a. Lytic, presumed to be a stress fracture of the pars
b. Elongated but intact pars interarticularis secondary to a healed type ii.a.
c. Acute pars fracture
iii. Degenerative
iv. Post-traumatic: acute fracture and or ligamentous injury in an area other than the pars interarticularis that results in spondylolisthesis
v. Pathologic: generalized or localized bone disease that produces degeneration of posterior elements and allows slippage of one vertebra on another
a. Subtype A: Generalized. Widespread generalized bony changes allow the slip to occur, as in osteoporosis, osteogenesis imperfecta, arthrogryposis and syphilis
b. Subtype B: Localized. Due to localized bone destruction such as tumour or infection
vi. Postsurgical: result of partial or complete loss of posterior elements secondary to surgery
Congenital
Type
i.a. is caused by a failure of proper formation of the posterior column of the spine.
i. There is always dysplasia of the articular processes
ii. The pars interarticularis may be intact, elongated or discontinuous
i. If the pars is intact it is uncommon for the slip to be greater than 50%
ii. If there is greater slippage with an intact pars then a cauda equina syndrome may result
iii. Associated bony abnormalities include spina bifida occulta of the upper sacrum and dysplasia of the superior surface of the body of S1
Type i.b. is caused by dysplasia of the posterior elements with a more sagittal orientation of the facet joint
1. There can be instability on flexion/extension views
Degenerative
The frequent presence of degenerative spondylolisthesis at the L4/L5 level is thought to be the result of the restraining effect of the iliolumbar ligaments on the fifth lumbar vertebra, which allows subluxation and increased motion at the next level.
Degenerative spondylolisthesis tend not to progress past 30% subluxation without a laminectomy.
Iatrogenic spondylolisthesis
Unilateral facetectomy, or excision of more than 50% of both facets can directly cause iatrogenic instability (Abumi and Panjabi).
Indirect postsurgical spondylolisthesis occurs as a result of increased stress at the motion segments on either side of a fused motion segment. This is also known as the transition syndrome.
Isthmic spondylolisthesis
Isthmic spondylolisthesis occurs in the presence of a spondylolysis (lytic).
Commonly L5-S1
Incidence
Most common type in children.
Probably starts to occur as a stress fracture in genetically predisposed children undergoing stressful lumbar extension exercises, and then persists as these children grow into adults- most present as adults age 20 years.
Twice as common in males but women have higher grade slips
Has only been found once in all of the literature in stillborn infants.
5% in children 5-7 years of age
6-7% by age 18 (Wiltse)
Around 7% in adults and varies with race.
Twice as common in whites and occurs in 50% of Eskimos
Associated with vigorous exercise and thoracolumbar Scheuermann’s disease.
Aetiology Combination of genetic and environmental factors, especially repetitive extension exercises eg gymnastics.
Family members have a reported incidence of 28-69%.
May be hereditary weakness of the pars interarticularis.
Genetic predisposition is coupled with stress imposed by bipedal posture and extension loading with repetitive microfractures. The erect posture throws constant downward and forward thrust on the lower lumbar vertebrae.
Spondylolisthesis has never been reported in quadrupeds.
Symptoms
Spondylolisthesis is often asymptomatic and picked up on examinations for other complaints.
1. Pain
a. Typically begins with adolescent growth spurt
b. Most common cause of low back pain in children and adolescents
c. Most common pain pattern is a dull aching pain in the back, buttocks and posterior thigh, which is mechanical and relieved by activity modification and NSAIDs.
2. Neurological symptoms are rare
a. Weakness of EHL (L5).
b. Bowel and bladder symptoms
c. Paraesthesias in L5.
Signs
1. Palpation at the spinous process above the level of slip may produce localized or radicular pain
2. May be a palpable step
3. May be weakness
4. May be spasm of the hamstrings; the typical posture with severe hamstring spasm is flexion of the hips and knees, backwards tilting of the pelvis, and flattening of the normal lumbar lordosis
5. With high grade slips there may be loss of the waist, with the ribs abutting the pelvis
6. May develop heart shaped buttocks.
Imaging
Plain X-rays
1. AP and lateral of the lumbosacral spine may not show spondylolysis and if this is suspected then oblique views are required.
2. To adequately document the full extent of a slip standing lateral X-rays are required.
3. The “reverse Napoleon hat sign” is found on the AP of the lumbar spine and represents the L5 vertebra viewed end on through the sacrum.
Radiographic measurements 1. Meyerding grading
a. The AP diameter of the first sacral vertebra is divided into quarters and assigned grades of I, II, III and IV to slips of one, two, three or four quarters.
2. Taillard’s method
a. Describes the degree of slip as a percentage of the AP diameter of the top of the S1 or L5 vertebra
3. Slip angle
a. A line is drawn along the posterior cortexes of the S1 and S2 vertebrae.
b. A second line is drawn perpendicular to this
c. A third line is drawn along the superior cortex of the slipped vertebra and the angle of intersection with the second line is the slip angle.
The slip angle is the most sensitive measure of the likelihood of progression.
4. Sacral inclination
a. This measures the increasingly vertical orientation of the sacrum as the grade of spondylolisthesis increases.
5. The sagittal pelvic tilt index is correlated with increased likelihood of progression
a. A horizontal line is drawn from the centre of S2, and this meets a vertical line from the centre of the femoral head.
b. A vertical line is then dropped from the centre of L5, and this should be close to in line with the line from the femoral head. If it is less than 70% of the distance along the line, this correlates with increased likelihood of progression.
6. Lumbar index: the ratio of the posterior to anterior height of the body of L5.
CT scan and MRI scan
1. Useful for detecting disc herniation prior to surgery
Bone scan
1. May be useful when the patient is first seen:
a. If spondylolysis is suspected but not seen on X-ray then a positive bone scan may warrant casting
b. If the bone scan is negative but the lysis is seen on X-ray then the injury is chronic and casting will not be of benefit
Natural History
83% of patients with low back pain because of a isthmic spondylolisthesis treated non-operatively rated themselves as good to excellent at 7 years follow-up.
Slips can be asymptomatic, therefore before embarking on treatment, it is vital to exclude other possible causes of pain.
Treatment
Non-operative
Wiltse’s guidelines for continued evaluation of young patients with spondylolisthesis or lysis are:
1. Pars defect discovered under 10: radiographs every 4 months initially; later, semiannually to 15 years of age; then at 1-2 years until growth ceases
2. Up to 25% isthmic spondylolisthesis in an asymptomatic child: no limitation of activity; recommend an occupation avoiding heavy labour
3. Up to 50% slip in an asymptomatic child: recommend activity modification and avoidance of contact sports and an occupation avoiding heavy labour
4. Up to 50% slip in a symptomatic patient: initiate conservative therapy (exercises, corset, brace, limitation of activities) and avoid heavy labour.
5. Greater than 50% slip – consider surgery.
Operative
Indications for surgery
1. Persistence or recurrence of major symptoms for at least one year despite activity modification and physical therapy (most common reason for surgery).
2. Tight hamstrings, persistently abnormal gait, or postural deformities unrelieved by physical therapy
3. Sciatic scoliosis
4. Progressive neurological deficit
5. Progressive slipping beyond 50% even when asymptomatic
6. A high slip angle (40-50 degrees) in a growing child
Goals of surgery
1. Reduction of back and leg pain
2. Prevention of further slip
3. Stabilization of the unstable segment
4. Reversal of the neurological deficit
5. Restoration of normal spine mechanics, posture and gait
Operative options
1. Pars defect repair
2. Decompression
3. In situ fusion
4. Reduction and fusion
