Isthmic spondylolisthesis is caused by a defect in the pars interarticularis that results in the anterior displacement of one vertebra on another. It commonly occurs at L5-S1 due to repetitive extension stresses. While often asymptomatic, it can cause back pain and radiculopathy. Diagnosis involves imaging like CT or MRI to view the pars defect. Treatment begins conservatively with rest, medication, and physical therapy. Surgery with fusion and instrumentation may be considered for persistent or progressive symptoms. Key factors like pelvic incidence correlate with severity and influence biomechanical stresses on the lumbar spine.

1. Adult Isthmic
Spondylolisthesis
Dr.Ponnilavan

2. Spondylolisthesis
- the ventral (or anterior) displacement of
one vertebra relative to the subjacent
vertebra.

3. Spondylolysis - considered to occur prior to appearance of
spondylolisthesis, as the anterior column of the vertebra is no longer in
continuity with the posterior column.

4. • Over time, vertebral body then displaces ventrally once disc &
supporting soft tissues are no longer able to maintain the structural
integrity & anatomic alignment of the vertebrae.

5. Spondylolisthesis Classification- Meyerding

6. Etiologic classification system was described by
Wiltse, which includes

9. • .
Children < 6 yrs- incidence - lumbar spondylolysis - 4.4% & spondylolisthesis-2.6%
At adulthood- L. spondylolysis - 5.4% & spondylolisthesis - 4%.
- reported pars defects did not typically heal & slippage occurred throughout f/u
period
Fredrickson et al..
prospective, pop-based
study of 500
schoolchildren from
northern Pennsylvania in
1950s

10. Fredrickson also reported that 2/3rd of spondylolysis cases were
males, & > 90% occurred at L5–S1.
Spondylolisthesis-found in 74% of pts with b/l pars defects at L5–S1,
but not in Pts with unilateral defects or pars defects at other levels.
Females - lower incidence of defects but higher rate of slip
progression.

11. • A more recent study by Urrutia et al. found a similar incidence of isthmic
spondylolisthesis in a non-US adult population of 3.8% (range, 1.7–6.8%).
• Incidence appeared not to change into adulthood, & authors concluded
spondylolysis is more likely an acquired disorder.

12. Pathophysiology
• Isthmic spondylolisthesis is a defect in pars interarticularis, a critical
structural component of posterior element of the vertebra.
• The pars is the intersection of the lamina, inferior and superior
articular processes, and pedicle.

14. • Etiologies for spondylolysis are numerous but many believe that the
vast majority are due to stress fractures of the pars interarticularis.
• Biomechanical studies have shown this region is exposed to the
highest extension forces in the lumbar spine.

15. It has also been suggested that this region of bone is the weakest
structural component of the posterior neural arch.
Repetitive lumbar extension loading appears to result in a
localized stress reaction in the vulnerable bone of the pars
region, and if the stress is sustained or excessive & if the bone is
unable to heal, then a spondylolysis develops.

16. Rosenberg et al. support this hypothesis, reporting their observation
that spondylolysis does not occur in nonambulatory individuals.
Additional support for the relationship b/w extension stress &
spondylolysis is the observation that a high incidence of pars defects
are observed in athletes such as wrestlers, football linemen, &
gymnasts—who frequently undergo repetitive hyperextension loads.

17. M/c level for spondylolysis is L5 &
- Isthmic spondylolisthesis at L5–S1 (90%)
- Due to previous data suggesting that sagittally oriented facet joints
predispose individuals to degenerative spondylolisthesis, they
analyzed facet joint orientation in an isthmic spondylolisthesis group.

18. • The group with isthmic spondylolisthesis had significantly more
coronal orientation of the facets of L3–L4 and L4–L5, that is, above
the affected level.
• They concluded that facet joints with more coronal—less sagittal—
orientation allow for less dorsal-ventral translation of cranial motion
segments, which leads to greater extension stresses on the L5 pars
and results in spondylolysis.

19. • Ward and Latimer evaluated the intrafacet distances of lumbar
vertebrae in individuals with & without spondylolysis & found an
increase in cranial-to-caudal intrafacet distance in nonaffected
individuals, which they concluded allowed for overlap of lamina
during lordosis.

20. potentially resulting in impingement of the L4 inferior articular process on the pars of L5.

21. Biomechanics

22. Biomechanical environment at the lumbosacral
junction is a complex one that normally
functions as a harmonious linkage between the
trunk & pelvis.
During radiographic assessment of patients,
lumbar lordosis (LL), pelvic incidence (PI), sacral
slope (SS), and pelvic tilt (PT) are most
commonly measured.

23. Measurements
pelvic incidence
• correlates with severity of disease
pelvic incidence = pelvic tilt +
sacral slope

24. • pelvic tilt

25. • sacral slope

26. PI is considered a fixed anatomic measurement & does not change for
any given individual through adulthood.
LL, SS, and PT are measurements of the relative position of lumbosacral
spine
Sagittal spinopelvic parameters have been found to correlate significantly
with spondyloptosis as well as the severity of isthmic spondylolisthesis.

27. • Labelle et al. - 214 young adults
(ages 10–40 years) that PI is
significantly greater in
individuals with isthmic
spondylolisthesis and correlates
linearly with higher (Meyerding)
slip severities.

28. • They also showed that PI strongly correlates with the other
parameters:
• LL, SS, and PT they concluded that individuals with isthmic
spondylolisthesis stand with increased SS, PT, and LL.
• Moreover, these increased values—in particular, LL—are an
important factor in the amount of shear stress on the L5 lamina and
pars.

29. Diagnosis
• History
• Most individuals with spondylolysis are asymptomatic.
• While it is the most common cause of LBP in children, the same does
not hold true in the adult population.

30. • Andrade et al.recently reported a review of observational studies on
the association of spondylolysis and isthmic spondylolisthesis with
LBP.
• They reported that only 1 of 15 eligible studies found an association
and 11 did not.
• In fact, they found that LBP was significantly more prevalent in
individuals without spondylolysis/isthmic spondylolisthesis.

33. • Moller and Hedlund reported on 201 patients with isthmic
spondylolysis and found that their patients presented with
- back pain only in 27%,
- back pain and sciatica in 65%,
- and sciatica only in 8% of individuals.
• Back pain may be positional & may be worsened with standing and/or
lumbar extension maneuvers, while it may be relieved with forward
flexion or sitting.

34. • Lower extremity pain can be radicular in nature, as it is often caused
by impingement of the exiting L5 nerve root due to frequent
occurrence of associated foraminal stenosis at L5–S1.
• Pain in lower extremities can often be positional, similar to typical
LBP complaints.

35. Physical Examination
• There are no pathognomonic physical examination findings for
isthmic spondylolisthesis.
• Lumbar extension will often elicit LBP, lower extremity radicular
complaints, or both.
There can be a palpable or visible step-of in cases of highgrade slips.
The step-of occurs between the L4 and L5 spinous processes as the
posterior elements of L5 remain dorsal and in line with the S1 spinous
process

36. • Hamstring tightness is often described but difficult to assess
objectively.
• A positive straight-leg raise test will be present in approximately 50%
of patients.
• Sensory or motor abnormalities can be found due to associated
foraminal stenosis and exiting root compression.

37. Imaging
• Routine radiographic images can detect spondylolysis, especially if
spondylolisthesis is present, and slip severity can be measured on
lateral images.
• Additionally, standing images that include Flexion and extension
positioning should be evaluated.

38. • If spondylolysis is suspected but not visualized, oblique radiographic
images 45 degrees to the sagittal plane can be obtained that can
detect up to 96% of pars defects.
• Abnormalities in the “neck of the Scotty dog” is the hallmark
radiographic finding.

39. Complete defects are most common, but pars dysplasia & hypoplasia
can also be observed.
• Sagittal reformatted images best show the pars defect as being
distinct from facet joints and are the definitive finding in
spondylolysis.
• One limitation of CT is the lower sensitivity for soft tissue densities,
especially the internal anatomy of the neural foramen and the extent
of any associated nerve root compression.

40. - MRI is increasingly used as the primary imaging modality in patients
with LBP with or without radiculopathy.
• Sagittal T1-weighted images provide the greatest level of contrast
between hyperintense bone marrow and the signal void of bony
cortex at the pars defect.

41. • Single-photon emission computed tomography can be used in the
evaluation of suspected acute or impending spondylolysis.
• However, SPECT has been reported to have notable false-positive and
false-negative results in spondylolysis & thus should be used with
caution, although it may be of particular value in cases in which MRI
is contraindicated.

44. Differential Diagnosis
• The differential diagnoses for isthmic spondylolisthesis are those of its
clinical presentations: LBP and sciatica.
• First, spinal trauma, tumors & infections should be ruled out.
• Next, degenerative disc disease, spondylosis, spinal stenosis, or disc
herniation should be considered.

45. • Other causes include systemic diagnose-
- rheumatoid arthritis &
- spondyloarthropathies, and other
- nonspinal,
- musculoskeletal etiologies, such as sacroiliac joint arthrosis,
hip arthritis, & more.
Finally, abdominal/visceral considerations would include renal,
gastrointestinal, and vascular disorders.

46. Treatment
• Nonoperative Treatment
• Initial Rx for patients presenting with acute LBP should be
nonoperative.
• The mainstays are patient education, activity modification, and
medications - NSAIDS
• The addition of physical therapy and exercise can be considered when
early treatments fail and LBP becomes more long-standing.
• Other alternative pain management modalities—such as chiropractic
care, acupuncture, and massage—have been widely utilized, with
reported improvements in pain and function.

47. • Short-term use of narcotic analgesics should be considered with
caution.
• A minor neurologic deficit, such as radicular numbness or
paresthesias, but excluding severe motor weakness, can also be
managed nonoperatively but may benefit from corticosteroid
injection via injection therapies, such as Fluoroscopically guided
selective nerve root blocks.

48. Operative Treatment
• Indications-
• Severe, persistent back
• &/or lower extremity pain that is associated with functional
limitations or that significantly impacts quality of life—with or
without flexion–extension instability on radiographs, progressive
motor weakness, or cauda equina syndrome—are all generally
accepted indications for operative intervention.
• Patients should complete a rigorous course of nonoperative
treatment prior to considering surgery unless a signiicant neurologic
deficit exists.

49. Surgery
• Goals of operative intervention in isthmic spondylolisthesis are to
decompress neural elements & stabilize the affected motion segment.
• Uncommonly, decompression alone can be performed in certain
circumstances when fusion is not necessary.
• More typically, surgery involves stabilization traditionally performed
with posterior in situ fusion techniques with or without pedicle screw
instrumentation and sometimes without decompression.

50. • Supplemental anterior column support using interbody fusion
techniques approached posteriorly (posterior lumbar interbody
fusion [PLIF]) or anteriorly (anterior lumbar interbody fusion) has
been recently popularized and may currently represent the most
popular form of surgical treatment in the United States.

51. Decompression
• Decompression without fusion can be performed on individuals who
have only radicular symptoms & stable spondylolisthesis on dynamic
radiographs or a bony fusion seen on CT scans.
• Low-demand individuals or those with significant medical
comorbidities may be reasonable candidates.
• Gill laminectomy entails removal of the entire posterior arch and the
hypertrophied fibrocartilaginous tissue at the pars, as well as partial
facetectomies to decompress the nerve root.
• Long-term results of laminectomy alone have not been favorable,
leading most experts to believe that addition of fusion is required in
most cases to obtain good clinical outcomes.

52. • Direct Pars Repair
• Fusion

53. PEARLS
Isthmic spondylolisthesis are rarely symptomatic, but those who do
develop severe back pain, radiculopathy, or both can be effectively
treated without surgery.
Significant evidence exists that isthmic spondylolisthesis develops in
adolescence as a result of an extension stress injury.
Spondylolisthesis develops as the soft tissues around the vertebral
motion segment become incompetent.
Symptomatic individuals who fail nonoperative treatment is commonly
treated with a spinal fusion.
Ideal treatment technique has not been agreed upon and often involves
use of pedicle screw instrumentation and interbody techniques.

54. PITFALLS
1. Failure to identify spondylolysis on imaging studies is common; if
high suspicion exists, further imaging should be considered.
2. Because spinal fusion is the mainstay of treatment, individuals
with high risk of nonunion should be approached with caution.
3. Decompression alone should be reserved in individuals who are
low demand and poor operative candidates.
4. Nerve root involvement occurs at the level of the foramen and
should correlate with clinical symptoms at presentation.
5. Reduction of high-grade slips can increase risk of nerve injuries.

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