Spondylolytic spondylolysis is defined as a defect or fracture of the interarticular isthmus (pars interarticularis) of the vertebral arch. The vast majority of cases occur in the lower lumbar vertebrae (L5).  Spondylolisthesis is defined as the slow anterior sliding of a vertebra caused by spondylolysis.

Stress fractures are caused by repetitive loads on the back of the lumbar vertebrae, especially when the spine is in extension. In the spine, the vertebral body is designed to receive loads and the intervertebral disc to act as a shock absorber. The posterior unit of the vertebra is not designed to receive excessive loads, but to protect the spine. During extension, the centre of gravity is moved backwards. The facet joints must then bear a load for which they are not designed.

The lumbar spine is a lordosis and the facet joints are constantly receiving excessive weight due to the posterior shift of the center of gravity. Any situation that results in extension overload will eventually lead to deterioration of the cartilage surfaces and ultimately premature wear of the cartilage surfaces. Overloading of the facet joint, especially with repetitive or high intensity loads, can lead to the development of stress fractures. Stress fractures themselves produce pain, but they also create problems when they develop into spondylolisthesis.

  • In 25% of patients with spondylolysis, spondylolisthesis develops. Gymnasts have a fourfold increased risk of developing spondylolisthesis due to repetitive hyperflexion-hyperextension maneuvers such as flipping, jumping, straddling and backbending exercises.
  • Approximately 90% of spondylolisthesis occurs at L5, and the risk of slippage is at L5 – S1.
  • The hamstrings are usually contracted: The body reacts strongly to the forward vertebral shift by tilting the pelvis backwards and this with the help of the hamstring.
Diagram showing typical pain for a patient with spondylolisthesis, involving pain in the buttocks and posterior thigh.

What are the types of lumbar spondylolisthesis?

  1. Dysplastic: This type of spondylolisthesis is due to congenital abnormalities of the upper facets of the sacrum or the lower facets of the fifth lumbar vertebra, which allow L5 to slide over S1. There are no defects of the interarticular isthmus. The sacrum is not strong enough to support weight and effort. The isthmus and the lower facets of L5 are therefore deformed. If the isthmus elongates, it is impossible to distinguish this type from isthmic type II b) on radiographs. If the isthmus separates, it becomes impossible to distinguish this type from isthmic type II a) on radiographs. This type is also associated with defects of the sacrum and the vertebral arch. A familial tendency is observable.
  2. Spondylolytic (isthmic): This type is attributable to a defect in the interarticular isthmus that allows L5 to slide forward relative to S1. There are three subtypes of isthmic spondylolisthesis:
    1. A fatigue (stress) fracture of the interarticular isthmus – lytic. Attenuation of the pars
    2. An elongated but intact interarticular isthmus
    3. An acute fracture of the interarticular isthmus
  3. Degenerative: The lesion results from long-term intersegmental instability, followed by remodeling of the articular processes at the level of the injury. The presence of multiple small compression fractures on the lower articular process of the vertebra which slides forward has also been suggested as a possible cause. The articular processes change direction, taking a more horizontal position as the sliding increases. This lesion is four times more common in women than in men, and six times more likely to occur at the L4-5 level than at adjacent levels. This lesion is generally not seen in people younger than 40 years old.
  4. Traumatic: This type of spondylolisthesis follows fractures in the region of the bone hook, other than fractures of the interarticular isthmus, including the pedicle, blade or facet.
  5. Pathological: This type of spondylolisthesis results from localized or generalized osteopathy and fragility or weakness of the bone structure such as osteogenesis imperfecta.
Dysplastic spondylolisthesis with >75% slippage and rounding of the body of the sacrum due to an anomaly of the S1 facet.
Isthmic spondylolisthesis with a clearly visible pars defect (arrow)

What are the clinical signs of lumbar spondylolisthesis?

  • Age: dysplastic or isthmic types occur in childhood or adolescence, degenerative types occur in the elderly
  • Low back pain (LBP), especially in younger patients
  • Nerve root compression
  • Gait abnegation
  • Cyphosis
  • Palpable walking in the spine
  • Hamstring torsion
  • Scoliosis with or without spasm
  • Loss of lumbar lordosis

What causes lumbar spondylolisthesis?

  • Spondylolisthesis
    • most often caused by spondylolysis.
  • Spondylolysis
    • Genetic weakness of the isthmus interarticularis.
    • Repeated stress fractures caused by hyperextension of the back
      • gymnastic
      • Soccer
    • Degenerative arthritis.

Symptoms

The chief complaint of spondylolisthesis is back pain accompanied by pain referring to the sacroiliac joints. Pain can radiate to the hips, thighs and even feet (10%), but symptoms are usually in the lumbar region, with numbness or “pins and needles” in the legs.

  • In people with back pain, the presence of a crack (spondylolysis) and slippage (spondylolisthesis) on the x-ray image does not mean that this is the source of the symptoms.
  • Focal low back pain with radiation to the buttock or proximal lower extremity
    • Activity-related low back pain that often radiates distally to the buttock and/or thigh.
    • Radiation below the knee is rare and suggests a lower lumbar radiculopathy, which may occur with severe spondylolisthesis.
  • Symptoms are more common with slips greater than 50%.
    • Hamstring spasms/contractions are common and may result in limited forward flexion.
  • With higher grade injuries
    • neurological abnormalities may be seen, such as nerve root symptoms (radiculopathy) due to traction on the lower lumbar nerve roots, or bowel or bladder dysfunction (or symptoms of cauda equina syndrome) resulting from compression (or traction) of the component neuron.

One factor that further confuses the cause of pain in spondylolysis and spondylolisthesis is that the severity of symptoms does not necessarily correlate

Classifications

What are the differential diagnoses of lumbar spondylolisthesis?

  • Ankylosing spondylitis (HLA-B27 – positive sacroiliac joint changes)
  • Intervertebral disc lesion or herniation (radiculopathy occasionally present)
  • Osteoid osteoma (night pain, abnormal bone scan, pain relieved by aspirin)
  • Spinal cord tumor (sensory findings, upper motor neuron signs

 

X-ray

  • Oblique radiographs of the lumbosacral spine may show a break in the pars interarticularis which represents the break in the neck of the “Scottish Terrier (or Collared Scottish Terrier).”
Oblique view an interarticular isthmus fracture would be seen on radiograph as a fracture line and separation of the neck of the Terrier dog
Oblique radiograph shows a normal appearance of “Scottish Terrier Dog” in the area described.
  •  
Fracture of the right interarticular isthmus L5-S1

In the above vertebra, the Scotty dog has a “collar” (arrow), indicating the pars interarticularis defect of the spondylolysis
An AP radiograph below shows the “inverted Napoleon hat sign” indicating marked anterolisthesis of L5 over S1.Case courtesy of Dr. Matt A. Morgan, ref=”https://radiopaedia.org/cases/71470″>rID: 71470
The lateral radiograph shows a grade I spondylolisthesis (L5-S1). The arrow indicates the direction of the slip.
An AP radiograph below shows the “inverted Napoleon hat sign” which indicates the marked anterolisthesis of L5 on S1

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