Bony structures and ligamentous apparatus of the lumbar spine
The stability and mobility of the lumbar segment rely on a complex anatomical structure. The structure of a typical lumbar vertebra includes a massive body (corpus vertebrae) and the intervertebral disc (discus intervertebralis) located between adjacent vertebral bodies. The central canal, forming vertebral canal (canalis vertebralis), accommodates the spinal cord and cauda equina roots. The vertebral arch connects to the body via pedicle (pediculus arcus vertebrae), and its posterior part is represented by lamina (lamina arcus vertebrae), transitioning into the unpaired spinous process (processus spinosus). Paired processes extend laterally ( transverse processes (processus transversi), while superior articular processes (processus articulares superiores) participate in the formation of zygapophyseal (facet) joints.
Longitudinal and transverse stability is provided by the ligaments:
- Anterior and posterior longitudinal ligaments (ligamentum longitudinale anterius et posterius) — run along the anterior and posterior surfaces of the vertebral bodies, respectively (the posterior lines the anterior wall of the canal).
- Ligamentum flavum (ligamentum flavum) — connects the laminae of the arches in the posterior part of the canal.
- Interspinous and supraspinous ligaments (ligamenta interspinalia et supraspinale) — fix the spinous processes.
- Capsular ligaments — reinforce the facet joints.
Pathophysiology of degenerative changes and sources of compression
Compression of the spinal canal contents or intervertebral foramina (foramina intervertebralia) causes nerve root compression. The main "culprits" are:
- Ligamentum flavum (its hypertrophy).
- Intervertebral disc (herniations and protrusions).
- Bony elements (osteophytes, articular process hypertrophy).
- Posterior longitudinal ligament (hypertrophy or ossification).
The degenerative cascade begins with disc flattening, which narrows the foraminal opening and alters the geometry of the facet joints, causing their osteoarthritis. This stimulates the growth of osteophytes, which can grow into the canal (causing central or lateral stenosis) or into the foramen itself.
Loss of stability leads to spondylolisthesis (vertebral slippage). It is important to distinguish its types:
- Degenerative: the pars interarticularis of the arch (pars interarticularis) is intact, displacement is usually up to 25% (rarely up to 50%).
- Isthmic: there is a defect of the pars interarticularis, displacement often exceeds 50%.
Clinical presentation and differential diagnosis of claudication
Without stenosis, patients are often asymptomatic or complain of pain upon bending. In lumbar stenosis, compression of the cauda equina (cauda equina) occurs, resulting in pain, paresthesias, leg and pelvic weakness. Pain in spondylosis is "mechanical" in nature (depends on movement), but due to compensatory muscle spasm, it may persist at rest.
The key symptom is intermittent claudication. It is necessary to differentiate its two types caused by ischemia of different structures:
Neurogenic claudication (in lumbar stenosis):
- Occurs due to ischemia of the spinal nerve roots.
- Localized proximally (buttocks, posterior thigh).
- Posture-dependent: pain subsides with spinal flexion (forward bending maximally expands the canal). Walking with a shopping cart or riding a bicycle is easily tolerated.
- Pulses in the leg arteries are preserved, skin is unchanged.
Vascular claudication (in arterial insufficiency):
- Caused by ischemia of the leg muscles.
- Localized distally (in the calf muscles).
- Activity-dependent: increases with exertion and resolves at rest (crescendo/decrescendo pattern).
- Pulses are diminished or absent, skin is cool, shiny, and fragile.
Objective findings and imaging
Laboratory tests are not indicated for degenerative diseases and are ordered only to rule out infections or tumors.
The basis of instrumental diagnostics consists of:
- Electromyography (EMG): helps distinguish radiculopathy in the setting of stenosis from peripheral neuropathy (e.g., diabetic).
- Radiography: reveals disc space narrowing, facet joint hypertrophy, endplate sclerosis, osteophytosis, and spondylolisthesis. A classic example of pathology on a lateral radiograph is degenerative narrowing of the disc space at the L5/S1 level against the background of preserved height of the superior discs.
Briefly: answers to topical questions
Which processes extend from the arch of a typical lumbar vertebra?
The following processes extend from the arch of a typical lumbar vertebra:
- Superior articular processes (processus articulares superiores) — form the anterior part of the zygapophyseal (facet) joints.
- Spinous process (processus spinosus) — an unpaired process directed posteriorly.
- Transverse processes (processus transversi) — paired processes directed laterally.
What instrumental methods are used to diagnose degenerative spine diseases?
The following instrumental methods are used to diagnose degenerative spine diseases:
- Radiography — plain (in two projections) and functional (in maximal flexion and extension positions).
- Magnetic resonance imaging (MRI) — including contrast-enhanced studies (gadolinium).
- Computed tomography (CT).
- Contrast studies — CT myelography, myelography, and discography.
- Electrodiagnostic studies — electromyography (EMG) with nerve conduction velocity testing.
What types of surgical interventions are indicated for degenerative lumbar spinal stenosis?
The following surgical interventions are used for degenerative lumbar spinal stenosis:
- Laminectomy (laminectomy) is the surgical removal of the vertebral lamina.
- Extended decompression involves the resection of the articular processes (facet joints); the absence of facet joints leads to instability and requires supplementary surgical fusion.
- Laminotomy (laminotomy) is the removal of a small portion of the vertebral lamina.
- Foraminotomy (foraminotomy) is decompression at the level of the intervertebral foramen.
- Interspinous distraction (interspinous distraction) is the placement of an implant between the spinous processes.
- Spinal fusion (fusion) is used to stabilize the spine.
The "shopping cart sign" helps distinguish neurogenic claudication: patients with neurogenic claudication (stenosis) find it much easier to walk while leaning on a shopping cart (flexing the spine forward), whereas in vascular claudication, trunk flexion does not relieve muscle ischemia.
Class and exam questions
Why does forward bending reduce pain in neurogenic claudication?
Spinal flexion anatomically widens the spinal canal and intervertebral foramina, reducing pressure on the ischemic cauda equina nerve roots. Conversely, an upright posture (extension) narrows the canal.
What is the difference between degenerative and isthmic spondylolisthesis?
In degenerative spondylolisthesis, the pars interarticularis remains intact, and displacement occurs due to joint and disc instability. In isthmic spondylolisthesis, there is an anatomical defect in this part of the lamina.
Can facet joint arthritis cause pain at rest?
Osteoarthritis itself causes pain with movement. However, vertebral instability can trigger persistent muscle spasm, which causes pain even at rest.
What else to study on this topic
- Mechanisms of formation and compensation of muscle spasms in spinal instability.
- Anatomical features of pars interarticularis defects in isthmic spondylolisthesis.
- The role of the ligamentum flavum in the development of lateral stenosis.
- Changes in facet joint biomechanics during intervertebral disc flattening.
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