Displacement of disc material is common, and occurs across a spectrum of severity. Least severe is a disc bulge, in which displacement affects more than 50% of the disc circumference, and usually extends less than 3 mm beyond the bony margin.¹⁰ A disc bulge is a normal finding, and its identification on imaging does not allow any inference to be drawn as to the source of pain.

A disc prolapse is any displacement more severe than a disc bulge. Prolapse thus defines a broad category of changes to the disc, which are further sub-classified according to severity and morphology. In disc prolapse, the nucleus pulposus, anulus fibrosus, end-plate cartilage and fragmented vertebral bone may all be displaced. A disc may compress and/or contribute to inflammation of the spinal nerve roots, spinal dura, cauda equina; however, it not invariably prolapses without consequence.  

Prolapse compressing the nerve root is a very common finding, observed in 70% of the asymptomatic population.²⁵ The factors that cause pain in a minority of such prolapses are not well understood, though inflammation is thought to play a key role. Disc prolapse accounts for 5% of low back disorders, and is one of the commonest reasons that patients undergo surgery.¹²

Cervical radicular pain can be one of the most painful presentations in clinical practice. It is not easy to diagnose it based on pain alone, as there are features in the pain that could implicate somatic and neurological structures. The condition has a good prognosis. Interventions such as epidural injection and surgery should only be contemplated when the pain is uncontrollable despite conservative measures, and/or, neurological loss is progressive and severe.

Spondylolysis is a unilateral or bilateral stress fracture of the pars inter-articularis, affecting one or more lumbar vertebrae. Repeated flexion, extension, rotation, and torsion, particularly in combination, are thought to be associated with the highest prevalence of spondylolysis.

Lumbar spondylolysis occurs in 6-8% of the general population, and is usually asymptomatic.⁴ The condition is two to three times more common in males than it is in females, and arises most frequently in late childhood or adolescence. ⁵ It is rare for spondylolysis to arise after the age of 20.¹

Spondylolisthesis refers to the anterior slippage of one vertebra on the adjacent caudal vertebra. The majority of spondylolistheses are exclusively attributable to an abnormality of the pars inter-articularis, such as spondylolysis.⁴ 15% of those with spondylolysis progress to spondylolisthesis.⁵ Spondylolisthesis is also produced by pathology such as facet joint incompetence.⁴

Spondylolysis and spondylolisthesis are radiological diagnoses, and both are common in the asymptomatic population. The prevalence of back pain is no higher among adults with spondylolysis and low grade spondylolisthesis,⁴ implying that an observation of either defect does not allow any inference to be drawn as to the source of a patients back pain. The first part of this article addresses spondylolysis, and the second addresses spondylolisthesis.

Spondylolysis is a unilateral or bilateral stress fracture of the pars inter-articularis, affecting one or more lumbar vertebrae. Repeated flexion, extension, rotation, and torsion, particularly in combination, are thought to be associated with the highest prevalence of spondylolysis.

Lumbar spondylolysis occurs in 6-8% of the general population, and is usually asymptomatic.⁷ The condition is two to three times more common in males than it is in females, and arises most frequently in late childhood or adolescence. ⁸ It is rare for spondylolysis to arise after the age of 20.¹

Spondylolisthesis refers to the anterior slippage of one vertebra on the adjacent caudal vertebra. The majority of spondylolistheses are exclusively attributable to an abnormality of the pars inter-articularis, such as spondylolysis.⁷ 15% of those with spondylolysis progress to spondylolisthesis.⁸ Spondylolisthesis is also produced by pathology such as facet joint incompetence.⁷

Spondylolysis and spondylolisthesis are radiological diagnoses, and both are common in the asymptomatic population. The prevalence of back pain is no higher among adults with spondylolysis and low grade spondylolisthesis,⁷ implying that an observation of either defect does not allow any inference to be drawn as to the source of a patients back pain. The first part of this article addresses spondylolysis, and the second addresses spondylolisthesis. 

Prevalence 

Note that this information is quoted from a book chapter: Vivian D, Verrills P. Pathophysiology of painful cervical spine disorders.  In: DePalma M. eds. iSpine: Interventional Spine Care. 2011. Demos Medical

Neck pain is extremely common, particularly in women, having a lifetime prevalence of 70%, a one year prevalence of 40% and a point prevalence of 10-20%. In working populations it is very common, to the point where it can be considered almost normal! For example, in a study of 495 female kitchen workers the 3-month prevalence of any musculoskeletal pain was 87%, the most common sites being the neck (71%), low back (50%) and forearms/hands (49%). Multiple pain sites was the norm, as about 73% of the subjects had pain in at least two sites, 36% in four or more, and 10% in 6-7.  In another study on office workers, the 1-year prevalence of neck pain was 45.5%, with additional demographic findings revealing that women have an almost two-fold risk compared with men, that persons older than 30 years have 2.6 times more chance of having neck pain than younger individuals, and that being physically active decreases the likelihood of having neck pain. Pain of any description is common in the workplace: in a study of 4006 workers from industrial and service companies, only 7.7% were free of regional pain of any description. 

Neck pain also occurs in children, and it can be persistent. When 1756 9-12-year-old schoolchildren were followed over a 4-year period and questioned about the occurrence of neck pain, 24% reported no neck pain in that period, 71% had fluctuating neck pain and 5% persistent weekly neck pain. There was a trend to weekly pain in children with other musculoskeletal and/or other physical and psychological stress symptoms at baseline. Another survey of 643 adolescents (54.6% female) reported at the 14-year follow-up that females had a higher prevalence of lifetime, 1-month and chronic neck/shoulder pain than males (50.9 versus 41.7%, 34.1 vs 23.5%, and 9.2 vs 6.2% respectively), and that there was no relationship between neck pain and the level or intensity of physical activity or the type of sedentary activity.

Low back pain (LBP) is a big problem for health systems especially in industrialized countries,¹⁶ affecting approximately 60-80% of the adult population at some stage^14;24;39 and about 6% of people each day.²⁴ LBP affects up to 80% of the working population during their lifetime and is the second most common reason for physician visits,²⁵ and for work disability.³⁸ Although LBP is typically self-limiting,³⁷ it is still associated with substantial health care costs and absenteeism from work.^16;27;35

LBP is often associated with pain in other sites. For example, in a study of kitchen-hand workers, generalized musculoskeletal pain was present in 87%; including neck pain in 71%, LBP in 50% and forearm/hand pain in 49%.²¹ Also, 73% had pain in at least two sites, 36% in four or more, and 10% in 6-7.²¹ In another study of 4006 workers only 7.7% were free of regional pain of any description.²

In Australia, back problems are the most frequently seen musculoskeletal condition in general practice and the seventh most common reason for seeking care.³ In Australia, a 2001 survey found the point prevalence of LBP to be 26%, the 12-month prevalence 68% and lifetime prevalence 79%.³⁹ Only about 50% of the adult population experience low-intensity pain and low disability from it and another 11% experience high intensity-pain but still low disability in any 6-month period.³⁹ However, about 11% of the population experience high-disability LBP,^36;39 and it is to this group that most resources are presumably directed.