Causes and mechanisms of development
Spondylolisthesis is categorized into 6 types based on the etiology:
- Congenital dysplasia of the articular processes.
- Defect of the pars interarticularis (pars articularis).
- Degenerative changes of the facet joints.
- Fracture of the vertebral arch.
- Pathological weakening of the arch associated with bone diseases.
- Iatrogenic factor (excessive bone resection during surgery).
Degenerative spondylolisthesis is the most common type, predominantly affecting individuals over 50 years of age (especially women). Osteoarthritis of the facet joints serves as its primary underlying factor. In this case, the vertebral arch remains intact, but the joints acquire a sagittal orientation. Consequently, even a minimal increase in the degree of displacement can provoke cauda equina syndrome.
Clinical manifestations
Patient complaints are directly related to the narrowing of the spaces through which neural structures pass (stenosis of the central canal, lateral recesses, and intervertebral foramina).
The symptom complex includes:
- Pain syndrome: pain localized in the lower back with radiation to the lower extremities.
- Radiculopathy: signs of exiting nerve root compression.
- Neurogenic claudication: appears as central spinal canal stenosis progresses.
Interestingly, the risk of developing spondylolisthesis at the L4–L5 level increases fourfold if the patient presents with sacralization of the fifth lumbar vertebra.
Diagnostic radiology
To confirm the diagnosis and evaluate associated changes, a combination of imaging modalities is employed:
- Radiography (lateral view): allows visualization of anterior vertebral displacement, disc height loss, and facet joint degeneration. A characteristic sign of degenerative listhesis is the anterior displacement of the spinous process relative to the spinous process of the inferior vertebra (which helps differentiate it from the isthmic variant).
- CT and MRI: provide a detailed depiction of facet joint osteoarthritis, disc herniation/bulging, and stenosis. Sagittal MRI slices clearly demonstrate narrowing of the intervertebral foramina and lateral recesses, as well as compression of the cauda equina.
- Bone marrow MRI: nonspecific changes—such as a reaction to segmental instability—may be detected within the pedicles (roots of the arches).
Posterior element pathology and stenosis
Spondylolisthesis is closely associated with a complex of changes in the posterior spinal structures. Degeneration of the facet joints, which are richly innervated, serves as a potent source of pain. Enlargement of the articular process (hypertrophy) and thickening of the ligamentum flavum (ligamentum flavum) further narrow the spinal canal.
Occasionally, Baastrup's disease (phenomenon) occurs secondary to degeneration—characterized by the close apposition of adjacent spinous processes ("kissing spines"), which also provokes lower back pain. Juxta-facet cysts may form in the region of the facet joints and are capable of compressing nerves.
Briefly: answers to topical questions
What are the classic neurological syndromes and complications of lumbar spondylolisthesis?
The classic neurological manifestations and complications of lumbar spondylolisthesis include nerve root compression, neurogenic claudication, and cauda equina syndrome.
- Nerve root compression — occurs due to lateral recess stenosis (recessus lateralis) and foraminal stenosis, manifesting as lower back and leg pain.
- Neurogenic claudication — develops as the disease progresses secondary to central canal stenosis.
- Cauda equina syndrome (cauda equina syndrome) — a severe complication that can be triggered even by a minor progression of vertebral displacement with an intact neural arch.
Which anatomical structures of the posterior support complex of the spine are involved in the pathological process of spondylolisthesis?
The pathological process in spondylolisthesis involves the facet joints, vertebral arches, spinous and articular processes, and the ligamentous apparatus.
- Facet joints — undergo degenerative changes and osteoarthritis, which is the primary cause of degenerative spondylolisthesis.
- Pars interarticularis (pars articularis) and vertebral arch — defects, fractures, or weakening of these structures lead to displacement.
- Spinous processes — their alignment is disrupted, and impingement may occur due to degeneration (Baastrup's phenomenon).
- Ligamentum flavum (ligamentum flavum) — its concurrent thickening and hypertrophy exacerbate spinal canal stenosis.
Class and exam questions
How is the severity of vertebral displacement assessed?
The Meyerding classification is utilized. The anteroposterior dimension of the superior endplate of the inferior vertebra is divided into four equal parts; the grade (1 to 4) is assigned based on the number of quarters the superior vertebra has displaced.
How to differentiate degenerative listhesis from isthmic listhesis on radiographs?
In the degenerative type, the spinous process of the displaced vertebra is also displaced anteriorly relative to the inferior vertebra. This indicates that the vertebral arch (including the pars interarticularis) has remained intact.
What is Baastrup's phenomenon?
This refers to the impingement or "kissing" of the spinous processes of adjacent vertebrae, which occurs in the setting of marked degenerative changes.
What else to study on this topic
- Cauda equina syndrome: clinical presentation and emergency management
- Radiographic signs of isthmic spondylolisthesis
- Classification of spinal canal stenosis (central, foraminal)
- Myelographic "string of pearls" appearance in multilevel stenosis
- Juxta-facet cysts: etiology and imaging
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