Musculoskeletal Imaging

Spondylolisthesis

an alignment abnormality of the spine in which one vertebra is displaced with respect to another ( Fig.1) (Fig.2). This condition may occur in isolation, in association with spondylolysis, or in degenerative diseases. Severe spondylolisthesis may occur in patients with Ehlers Danlos syndrome.

An anterior degenerative spondylolisthesis occurs in some elderly persons, being noted most commonly at the interspace between the fourth and fifth lumbar vertebrae in older women. In this condition, the vertebral facets at the L4 -  L5 level are orientated more sagittally than those at the L5 - S1 level, thus allowing anterior movement. Owing to degenerative joint changes, the inferior facets of the fourth lumbar vertebra gradually erode between the superior facets of the fifth lumbar vertebra, producing forward displacement of L4. Patients may have backache with or without leg pain, sciatica with or without backache but with signs of nerve root compression, and intermittent claudication of the cauda equina. On radiographs osteoarthritis of apophyseal joints (articular space narrowing, sclerosis and osteophytes), forward slipping of the superior vertebra on the inferior one and, in some instances, intervertebral (osteo)chondrosis (vacuum phenomenon, disc space narrowing, vertebral body sclerosis) may be evident.

Another pattern of degenerative spondylolisthesis without spondylolysis, termed degenerative retrolisthesis, involves posterior displacement of one vertebral body on the subjacent vertebral body. Degenerative retrolisthesis is associated with intervertebral osteo chondrosis and occurs most frequently in the cervical and lumbar spine. On radiographs a vacuum phenomenon, disc space loss, vertebral body marginal sclerosis, small osteophytes, and apophyseal joint instability and subluxation may be observed. Patients may experience pain, rigidity and neurologic abnormalities resulting from spinal cord compression.

In the lumbar spine five types of spondylolisthesis may be recognized: dysplastic, isthmic, degenerative, traumatic and pathologic. Usually it is difficult to predict which patients with spondylolysis will develop spondylolisthesis.

Traumatic spondylolisthesis of the axis occurs after a fracture of the cervical spine. This injury is also known as hangmans fracture because it mimics the injury sustained in hanging. Causes include motor vehicle accidents, falls or other injuries leading to hyperextension or vertical compression of the neck. The odontoid process remains intact, but the neural arches are separated from the vertebral body. The injury is unstable but serious neurologic damage is not common.

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Fig.1

Lateral radiograph of the lumbar spine demonstrates bilateral spondylolysis (arrow) involving the L4 vertebra with resultant spondylolisthesis and degenerative disc disease at the L4 L5 level.
Spondylolisthesis, Fig.1
Spondylolisthesis, Fig.2 (a)
Spondylolisthesis, Fig.2 (b)