Type I. Dysplastic: This type results from congenital abnormalities of the upper sacral facets or inferior facets of the fifth lumbar vertebra that allow slipping of L5 on S1. There is no pars interarticularis defect in this type. The sacrum is not strong enough to withstand the weight and stress. Thus, the pars and inferior facets of L5 are deformed. If the pars elongates, it is impossible to differentiate it by x-ray from the isthmic (type II b) Spondylolisthesis. If the pars separates, it becomes impossible to differentiate it by x-ray from the isthmic lytic (type II a) Spondylolisthesis. This type is also associated with sacral and neural arch deficiencies. It has a familial tendency.
The lytic (subtype a) results from the separation or dissolution of the pars. The incidence of this type of Spondylolisthesis increases from less than 1 percent in children 5 years of age to 4.5 percent in children 7 years of age. The remaining 0.8 to 1 percent increase occurs between the ages of 11 to 16 years, presumably because of stress fractures caused by athletic activity. Extension movements of the spine, with lateral flexion, can increase the shearing stress at the pars interarticularis and result in Spondylolysis.
For posterior spinal decompression surgery to aggravate Spondylolysis or Spondylolisthesis, signs/symptoms of Spondylolysis or Spondylolisthesis should occur within 10 years of the surgery.
Severe trauma to the lumbar spine means a major, high impact, direct injury to the lumbar spine which produces immediate lumbar pain and precludes unaided ambulation for a period of at least 2 weeks, and is associated with other fractures and/or significant soft tissue injuries. Examples are as follows:
Signs/symptoms of Spondylolisthesis and/or Spondylolysis at the time of the repetitive trauma, or within 2 to 3 days of cessation of the trauma;
Dysplastic Spondylolisthesis results from congenital abnormalities of the upper sacral facets or inferior facets of the fifth lumbar vertebra that allow slipping of L5 on S1.
There may be no objective signs in Spondylolysis, or in first or second degree Spondylolisthesis. The finding of Spondylolysis on x-ray in an adult is likely to be incidental, and not the cause of back pain if that pain did not commence in childhood or adolescence. Tightened hamstrings are present in the majority of those who are symptomatic. Tenderness and spasms of the paravertebral muscles may be present at the level of the vertebral defect and surrounding segments. Pain may be induced and increased by certain movements.
In Spondylolysis, symptoms are often absent. Defects are then discovered only incidentally on x-ray made for other purposes. In Spondylolisthesis, injury may aggravate (permanently worsen) any symptoms, but rarely does a single injury cause symptoms in a person who previously had none. Symptoms generally begin insidiously during the second or third decade as an intermittent dull ache in the lower back, present with increasing frequency during walking and standing. Later, pain may develop in the buttocks and thighs, and still later unilateral sciatica may develop.
Spondylolysis and Spondylolisthesis usually cause no symptoms in children; however, many seek medical evaluation because of a postural deformity or gait abnormality. Pain most often occurs during the adolescent growth spurt and is predominantly backache, with only occasional leg pain. Symptoms are exacerbated by high activity levels or competitive sports and are diminished by activity restriction and rest. The back pain probably results from instability of the affected segment, and the leg pain is usually related to irritation of the L5 nerve root.
Although this subtype has a strong hereditary tendency, it makes up only half of the dysplastic group. The elongated pars (subtype b) is believed to result from micro fractures that heal with an elongated pars rather than from a lytic lesion. Acute pars fractures (subtype c) always result from significant trauma; these are rare and most frequently occur with Spondylolysis rather than with Spondylolisthesis.
Spondylolisthesis has been classified into grades I, II, III, IV and V depending on the severity of the displacement of the vertebra above on the vertebra below. In severe cases involving the lumbar spine, cauda equina syndrome can occur.
Spondylolisthesis by its nature causes instability of the spine. This instability has an adverse effect on the disc immediately below the displaced vertebra and can influence the development of degenerative changes to a moderate to severe degree.
Most spondylolytic defects and cases of Spondylolisthesis are congenital. The prevalence of Spondylolisthesis in the general population is about 5% and is about equal in men and women. Spondylolysis and Spondylolisthesis most frequently involve L5, although L4 can also be affected and, rarely, more proximal levels.