Spondylolysis is a unilateral or bilateral defect of the pars inter-articularis affecting one or more of the lumbar vertebrae. Spondylolysis is also known as ‘pars defect”. It should not be confused with the term ‘spondylosis’, which refers to changes that are predominantly genetically and age dependent and are referred to incorrectly as degenerative changes.These are all primarily radiological findings, which may or may not be associated with clinical symptoms.

Spondylolisthesis refers to the slipping forward of one vertebra on an adjacent vertebra. It occurs most commonly in combination with a spondylolysis, but also occurs in later life in association with local wear and tear changes, in which case it is called a degenerative spondylolisthesis.

Spondylolysis and spondylolisthesis are both radiological diagnoses. Their presence in a person presenting with back pain, referred pain or radicular pain (sciatica) does not imply that the defects either cause or contribute to the pain. These defects occur commonly in people who have not or do not have pain derived from the low back.

Spondylolysis is a unilateral or bilateral defect of the pars inter-articularis that can affect one or more vertebrae. Spondylolysis is frequently present in the people who have never had any back problem, and its presence does not mean that it is the cause of back pain The majority of adolescents with spondylolysis do not have symptoms, or their symptoms are mild and possibly unrelated to the defect in any case. In a population of people 50 years of age or older with or without back pain, spondylolysis has a higher prevalence in symptomatic people (odds ratio 5.06; 95% CI, 1.65-15.53).It is therefore a radiological diagnosis. Spondylolysis occurs in about 6-11% of people attending medical clinics for non-back related problems.3-5 It is more common in males (3:1).It most frequently arises in the second decade of life.

Spondylolysis occurs secondary to strain on the part of the vertebra known as the pars. Genetic and mechanical factors pre-dispose the pars to fracture. Simple spondylolysis does not occur before a human walks. It is not a ‘congenital’ abnormality.

Genetic factors refer to the inherent strength of the pars. A possible pre-disposition to the development of a spondylolysis is a small cross-sectional area of the pars. Another is the morphology of the lumbar spine and sacrum, and, in particular, the sacral table angle (STA) is more relevant than the pelvic incidence (PI). Genetically homogeneous groups with a lower STA in normal specimens have an increased occurrence rate of spondylolysis.

Mechanical factors relate to the vertical load on the spine, the activity of the muscles on the trunk, and the effects of movement. People who participate in high-risk sports are more likely to develop a spondylolysis as the increased repetitive forces across the pars can be significant enough to fracture it. Consistent with the concept of contributory mechanical factors, there is a mild increase in the prevalence of spondylosis in elite athletics (8%).In some sports where the loads are obviously greater across the pars, the prevalence is markedly increased. Reported prevalence rates in individual sports include: sports involving rowing (17%), throwing (27%), gymnastics (10-40%), diving (43-85%), wrestling (30%), cricket fast bowlers (55%) and weightlifting (15-45%).

Is the spondylolysis the cause of back pain?

If a spondylolysis is considered to be the cause of pain it is said to be an active spondylolysis. Spondylolysis is one type of stress fracture that can occur in a lumbar vertebra. Other sites can also be exposed to loads, and be subject to stress fracture.

The clinical features that should suggest the possibility of an active spondylolysis (stress fracture) include:

On History

• Back pain with or without referred pain: the pain should be maximal in the back. It is frequently unilateral, but bilateral stress fractures can occur, and it is also possible to have two pathologies, for example, a symptomatic stress fracture on one side, and a facet joint origin pain on the other.

• The pain can come on slowly in association with a repetitive aspect of a sport: it can also occur in association with a traumatic event in sport.

• Pain aggravated by weight bearing.

• Pain aggravated by a component of sport. It is unlikely for a spondylolysis to be the cause of symptoms in a person who gets back pain on sitting yet who can play sport and feel better for it.

On Examination

• Pain aggravated by some movements. Most typically, the quadrant movement (bending backwards while twisting to one side) is restricted and painful.

• Another provocation test that might suggest an active spondylolysis is pain induced by bending backwards when standing on one leg.

• Very well localised tenderness.

On Special Tests

• Plain x-rays are unhelpful in determining whether or not a spondylosis is painful. Plain x-rays do often demonstrate the defect (but not always). Note also that the pars inter-articularis can be painful in the phase before it frankly fractures. Such a ‘bone bruise’ can produce back pain, but it will generally not be apparent on plain x-ray.

• CT Scan: again this will show the architecture of the fracture, but it is not helpful with the determination of whether or not the fracture is likely to be the cause of the presenting symptom (such as back pain).

• SPECT bone scan and/or MRI: in order to determine whether a spondylolysis is active or inactive, a SPECT bone scan or MRI is needed:

  • If active, the SPECT scan shows uptake, and the MRI scan shows bone marrow oedema adjacent to the pars defect

  • If there are no indications of activity with the pars defect, then the spondylolysis is considered inactive and any low back pain the patient is experiencing is almost certainly not caused by a stress fracture.

Data

In USA college footballers, the prevalence of spondylolysis in players with persistent LBP in one study was 21%, but there was no difference in terms of time lost from games and sport practice between those with or without spondylolysis, indicating that there was no clinical significance to the finding of the spondylolysis.

In the Framingham Heart Study with 3529 participants, 188 individuals were consecutively enrolled in this study to assess radiographic features potentially associated with LBP. Of these, 21 (11.2%) had CT detected spondylolysis, and 38 (20.4%) reported significant LBP. However, statistical analysis did not reveal a significant association between the observation of spondylolysis on CT and the occurrence of LBP, suggesting that the condition does not seem to represent a major cause of LBP in the general population, and that the spondylolysis is irrelevant.

In a study of parachuting, which places enormous stresses on the human spine, spondylolysis of L5-S1 and L3-L4 segments were observed in 12.2% and 1.4% percent respectively. No correlation was found between the severity of radiographic changes, including spondylolysis, and either the prevalence or the severity of low back pain.

Even when the spondylolysis appears active, with diagnosis by both planar and single-photon-emission computed tomographic (SPECT) bone scintigraphy and computed tomographic (CT) scan, and the fracture is treated with bracing, the outcome in terms of sports resumption is good and the result seems independent of the degree of fracture healing. That is, even non-union does not seem to compromise the overall outcome or sports resumption in the short term. Osseous healing is most likely to occur in unilateral active spondylolysis.Chances of bony healing diminish when the fracture is bilateral, and diminish even further when it is pseudo-bilateral.

A systematic review concluded that the finding of spondylolysis and spondylolisthesis in an adult patient is usually incidental and not likely to be a direct source of pain unless there is concurrent instability.

Spondylolisthesis refers to the slipping forward of one vertebra on an adjacent caudal vertebra. Spondylolisthesis most typically results from spondylolysis or degeneration. Spondylolisthesis occurs most commonly at the lowest vertebral joint (L5/S1). Spondylolythesis occurs in about 3% of people attending medical clinics for non-back related problems.

Classification

Dysplastic (‘birth defect’): This is a congenital defect and is probably related to genetic factors. The dysplasia affects the neural arch of L5 or the upper sacrum resulting in a slip of the L5 vertebra on S1.

Isthmic: This is when the slip is due only to an abnormality of the pars. This is the most common type of spondylolisthesis. These are of three types: 1) lytic–a true separation in the pars resulting from a stress fracture; 2) elongation–elongation of the pars without separation; or 3) acute fracture–always secondary to severe trauma.

Degenerative: This is when the slip is secondary to severe degenerative remodelling of a vertebral joint. It is typical for there to be severe disc space narrowing and facet joint degeneration. This type of spondylolisthesis is relatively common in the elderly population.

Traumatic: Secondary to acute trauma that fractures a part of the arch other than the pars (lamina, facet joint and pedicle).

Pathologic: A generalized or focal bone disease that results in interruption of the neural arch. This occurs particularly in diseases that result in loss of calcium (osteoporosis).

Is the spondylolisthesis the cause of back pain?

Spondylolisthesis can cause or contribute to both local/referred back pain and to sciatica. In low back pain with or without referred pain the presence of spondylolisthesis is not relevant for the determination of the cause of pain. It may, however, be a significant pre-disposing factor in the development of pain derived from one of the local structures. It is important for the practitioner dealing with back pain and spondylolisthesis not to be trapped into the mistake of ascribing the pain to a radiological condition.

Spondylolisthesis causes narrowing of the spinal canal. If the narrowing relates to the neural foraminae, through which the radicular nerves travel, nerve compression is more likely to occur either as a result of the narrowing itself or as a result of other pathology such as disc prolapse, which in turn is more likely to cause symptoms because the available space for the nerve is reduced.

Treatment of significantly significant degenerative spondylolisthesis with spinal stenosis (the older patient)

When symptomatic, surgery is more effective than conservative management. In a multicentre randomised cohort or observational cohort study, patients with at least 12 weeks of neurogenic claudication (leg pain on walking derived from the spine) or radicular leg pain with imaging studies revealing spinal stenosis due to degenerative spondylolisthesis were followed for two years.17 Surgical treatment was standard posterior decompression laminectomy, with or without fusion. Conservative care included physical therapy, analgesics, and epidural steroid injections. Although the intention-to-treat groups were similar at 4 years, the extent of crossover from conservative to surgical treatment was substantial, and the as-treated surgical group had significantly better outcomes at 4 years.

Other points of interest included:

a) Neurogenic claudication had the best outcome with surgery

b) Neurological deficit was not a factor in outcome

c) Re-operation rate was 15% by 4 years

d) Complications were rare

e) Mortality in both groups was lower than expected with actuarial predictions.

It should be noted that most spine interventions decrease pain but rarely do they totally eliminate it.