Cause. There are three predisposing factors: 1) congenital malformation the articular processes (rare); 2) spondylolysis (a defect in the pars interarticularis of the neural arch) and 3) osteoarthritis of the posterior (facet) joints.
Pathology. In the normal spine forward displacement of a vertebral joint is prevented by engagement of its articular processes with those of the segment next below it. In spondylolisthesis there is a failure of this check mechanism, and the attachments of the intervertebral disc alone are not strong enough to hold the vertebral bodies in alignment.
In the third type of spondylolisthesis, seen fairly commonly, the posterior intervertebral (facet) joints become unstable on account of osteoarthritis, with degeneration of the articular cartilage that is essential lo a snug fit of the joint surfaces. It may occur at any level in the lumbar spine most commonly between the fourth and fifth lumbar vertebrae. In this type the vertebral displacement is occasionally backwards rather than forwards but in either case displacement is never severe, neurological disturbance is the intervertebral disc at the site of vertebral slipping is inevitably Damaged and disc prolapse may occur
Clinical features. The clinical features of spondylolisthesis are inconsistent they depend to some extent upon the nature of the causative lesion and upon the degree of displacement. Thus in spondylolisthesis from under-development the articular processes and in that from a defect of the pars interarticularis the patient is usually an adolescent or a young adult. whereas displacement from degeneration of te facet joints in osteoarthritisis seen characteristically in patients beyond middle age. In some cases the deformity is entirely symptomless. When symptom occur they take the form of chronic backache, with or without sciatica. The back pain is worse on standing.
On examination there is often a visible or palpable ‘step’ above the sacral crest, due to the forward displacement of the spinal column; but this is obvious only when the displacement is severe. Spinal movements restricted only slightly, if at all. Abdomen: When displacement is severe spinal column is projected forwards and the lumbar vertebral bodies may palpable through the abdominal wall. Lower limbs Minor irritation of a sciatic root is often evidenced by impairment of straight leg raising, but severe neurological disturbance is seldom observed except in the rare cases in which congenital malformation of the articular process allows dislocation of the whole vertebra complete with its neural arch. Radiographic features. Radiographs show the displacement. The lateral and oblique views will demonstrate whether or not there is a defect of the neural arch.
Diagnosis. Spondylolisthesis is distinguished from other causes of back pain and sciatica by the radiographs.