Coronal deformities of the spine larger than 10 degrees are called scoliosis. When diagnosed in adults and associated with degenerative changes, the deformity is called Adult Degenerative Scoliosis (ADS). ADS negatively affects quality of life in the elderly population that suffer from it, as has been measured by public health outcome tools such as Disability Adjusted Life Years (DALYs) and Quality Adjusted Life Years (QALYs). Although common to find degenerative changes in the spine of the elder, degenerative changes are not strictly related to age and can be seen in the relatively young.
The initial change of the degenerative spine is the injury and degeneration of the intervertebral disc. Several molecular and cellular processes at the disc are caused by repetitive stress, mechanical overload, cell senescence and apoptosis and genetic predisposition leading to dehydration, derangement of the annulus fibrosus and its collagen fibres, increased catabolism of the extracellular matrix due pro-inflammatory cytokines and impaired nutrition. These events are the beginning of disc degeneration.
ADS is the culmination of complex underlying aging and/or degenerative changes that lead to numerous alteration to the spinal structure. These include tears in the annulus fibrosus that may cause disc herniations. Subsequent osteophyte formation, arthritis of the facet joints, redundant, hypertrophic and incompetent ligaments of the posterior elements of the spine then lead to vertebral rotatory subluxation, olisthesis and associated weakness of the pelvic, abdominal and back muscles, among others. Hence the word scoliosis in ADS under-represents the complex structural end-changes.
ADS is usually diagnosed in the 6th decade of life. Spinal stenosis symptoms, radicular pain, decreased height, altered posture, low back pain and neurological claudication are common findings of ADS.
Radiographic evaluation of ADS includes standing AP and lateral x-rays of the complete spine, bending and/or traction films, CT, MRI, sagital balance assessment and spino-pelvic parameters measurement. The commonest curve seen is a lumbar single curve, followed by double curves (thoracic and lumbar).
Curve progression of ADS is directly related to the magnitude of the curve (scoliosis with Cobb measurements bigger than 30 degrees tend to progress more swiftly than those smaller than 30 degrees), superior L4 endplate angulation, lateral olisthesis of more than 6 mm, axial rotation of the apical vertebrae (Moe and Nash grade II or more) and an intercrest line that crosses L5. Age, sex, sacral slope, pelvic incidence do not affect the appearance or the progression of ADS.