Aging is a “natural, inevitable, physiological change that leads to compromises in physical, mental and functional abilities” and represents a decreased capacity for regeneration and repair.1 Currently, the global population is experiencing a shift in its age structure due to decreasing fertility rates and increasing longevity.2-4 Worldwide birth rates have declined from 5.0 births per woman in the 1950s to 2.5 in the 2000s and are expected to further decrease over time.5 On the other hand, life expectancy at birth has increased from 46.5 years in 1950 to 66.0 years in 2000.3 This estimate is projected to reach 76 years by 2045.
Approximately 75% and 33% of individuals born between 2000 and 2005 are expected to survive to ages 60 and 80 years, respectively.3 It is projected that a larger proportion of newborns will live to older ages in 2045 to 2050: 88% to age 60 and greater than 50% to age 80. Life expectancy at age 60 is also anticipated to increase from 18.8 years in 2000 to 22.2 years in 2045 and from 7.2 to 8.8 years at age 80.3 In addition, there is a significant increase in the speed and acceleration at which the population is aging.6 In 1950, 205 million people were ≥60 years and only 3 countries had >10 million individuals in this age bracket (China, the United States, and India).3 In 2000, this figure nearly tripled to 606 million and 12 countries had >10 million people over the age of 60 years. In the first 50 years of the 21st century, the population over 60 years of age is projected to rise to approximately 2 billion.3 Furthermore, the growth rate of the older population is expected to increase to 3.5 times the speed of growth of the total population.
Other indicators of aging include average age, median age, proportion of the population over the age of 60 years, and the population average of remaining years. In 2000, the average and median age of the world population was 29.7 and 26.6 years, respectively.4 Ten percent of the population was over the age of 60 and the average of remaining years was 43.8 years.4 In 2050, the mean age is expected to rise to 38.8 years and to 45.5 years by 2100.4 The proportion of the population over the age of 60 is also anticipated to increase to 22% in 2050 and 32% in 2100.4 There is no significant predicted change in the average remaining years between 2000 and 2100, indicating an overall upward shift in the age structure of the global population.
Older populations are also aging. In 1950, 1 in every 15 people over the age of 60 was also over 80 years.3 This ratio increased to 1 in 9 in 2000 and is projected to further increase to 1 in 5 in 2050. Further, the number of people over 80 years of age in 2050 is expected to be 379 million, a figure significantly larger than the 69 million estimated in 2000.3 The number of centenarians is projected to be 3.2 million and significantly higher than the estimated 180 000 in 2000.
THE EPIDEMIOLOGICAL TRANSITION
As a result of the aging of the population, there is a current shift in the cause of disease and mortality. This is referred to as the “epidemiological transition” and reflects the evolution from infections, parasitic and nutritional deficiency diseases, to chronic and degenerative diseases.5,7 Over the next decade, there will be increased disability and a greater number of deaths from noncommunicable diseases such as heart disease, cancer, and diabetes mellitus than from communicable diseases. In 2008, the World Health Organization published that major chronic disorders accounted for 60% of all deaths worldwide and 43% of the global burden of disease.5 This impact is expected to rise to 73% of all deaths and 60% of the global burden by 2020. Furthermore, the proportion of the population living with chronic conditions is projected to increase; currently, 80% of people in the United States aged >65 years have at least 1 chronic condition and 50% have 2.8
In a study by Denton and Spencer,9 the prevalence rates of various chronic diseases in Canada were reported for age groups 12 to 29, 30 to 49, 50 to 64, 65 to 79, and >80 years. The prevalence of certain conditions increases with age, including Alzheimer disease or other dementia, neurodegenerative disease, cataracts, glaucoma, heart disease, stroke, chronic obstructive pulmonary disease, emphysema, urinary incontinence, cancer, high blood pressure, diabetes mellitus, thyroid problems, and chronic bronchitis. For example, the rates of arthritis or rheumatism increase from 27.3% in patients aged 50 to 64 years to 44.3% and 51.6% in those aged 65 to 79 years and >80 years, respectively. In general, the overall prevalence of chronic conditions rises from 79.3% in the 50 to 64 age group to 90.0% in the 65 to 79 age group. As the population ages, the prevalence rates of chronic conditions are projected to increase by 4.7% in a 25-year period between 2005 and 2030.9 Similar figures and estimates of chronic disease prevalence have been reported in the United States.10
THE AGING OF THE SPINE
With the aging of the global population, clinicians worldwide will be required to manage an increasing number of spinal disorders specific to the elderly and the aging of the spine. The elderly population poses a unique challenge to health care systems and spinal physicians, because this age group is associated with multiple medical comorbidities, reduced bone mass density and osteoporosis, decreased mobility, spinal degeneration and deformities, poor balance, and a greater propensity to falls. Clinicians must consider all of these factors when designing and implementing therapeutic strategies to ensure adequate patient support, optimize outcomes, and prevent catastrophic events. Common age-related disorders of the spine are presented in Figure 1.
The natural aging process affects all elements of the spine including the intervertebral discs, facet joints, vertebral bodies, and supporting muscles and ligaments. Aging initially leads to biochemical and biomechanical alterations of the spine which can progress to micro- and gross-structural changes to its anatomic components.11 This degenerative cycle is associated with spinal instability, disrupted homeostasis, and various clinical manifestations, such as diverse neurological syndromes and pain.12 Although the majority of the elderly will exhibit some radiological evidence of these degenerative changes, many will be symptom-free.13,14
The degenerative process of the spine starts at the level of the intervertebral discs. Early modifications of an aging disc include a loss of aggrecan and water, fragmentation of type I and type II collagen fibers, reduction of disc height, and an increase in proteases responsible for the enzymatic degradation process.1 Advancing age decreases the permeability of the end plates. The limited diffusion across the end plates results in a reduction in the nutrient supply to the intervertebral disc and ultimately leads to tissue breakdown.12 The normally avascular discs compensate for this nutrient insufficiency by forming a capillary network at the periphery of the annulus fibrosus, causing microedema and exposing the disc to the cells of the immune system.1 Moreover, a loss of proteoglycans, which are major drivers of the osmotic pressure within the intervertebral discs, results in progressive disc dehydration. A decrease in turgor and nutrition favor the formation of radial and concentric fissures that eventually enlarge and migrate posterolaterally.1,11
Disc degeneration and resultant loss of intervertebral space ultimately alters the load-bearing function of the intervertebral joint and places increased stress on the facet joints.15 This initially creates synovial inflammation and joint space narrowing and eventually leads to facet hypertrophy, apophyseal malalignment, subluxation, and osteophyte formation.1 In addition, destabilization of the intervertebral and facet joints results in instabilities of the spine, which translate clinically into cases of degenerative spondylolisthesis and scoliosis.11 The elderly also experience changes in sagittal alignment, including decreased lumbar lordosis, increased thoracic kyphosis, and anterior advancement of the C7 plumb line.16-18
Aging of the vertebral body results in sclerosis of the end plates, osteophyte spurring, and bone remodeling. Bone mass and mineral density also decrease with increasing age. After the age of 16 to 25 years, bone mass gradually and continually decreases at a rate of 0.3% per year in men and 0.5% per year in women (5%-6% per year during menopause).11,19 Elderly men can lose up to 30% and elderly women up to 50% of their total bone mass density. Osteoporosis results from a combination of hormonal and lifestyle changes and external mechanical loads: (1) a decrease in nutrient absorption, such as vitamin D and calcium; (2) a decrease in the production of hormones responsible for bone formation, including parathyroid hormone and estrogen; (3) an increase in chemokines that enhance osteoclastic activity; (4) a decrease in physical activity and exercise; and (5) suppression of appetite.1,11 There is also a change in the internal scaffolding of the vertebral bodies due to a greater loss of horizontal compared to vertical trabeculae.
This remodeling and alteration in bone architecture, along with a decrease in bone mass density, increases the risk of fractures in the vertebral bodies. These fractures can occur from a single traumatic event or from the accumulation of microfractures due to repetitive loading that fatigues the cancellous bone. Osteoporotic vertebral fractures have a 39% prevalence in patients over the age of 65 years.11 They typically result in a reduction of height of the anterior aspect of the vertebral body, causing local kyphosis which may progress to a more severe kyphotic deformity following fracture of adjacent vertebrae.11
Spinal ligaments and supporting muscles are also subjected to degenerative changes. Ligaments may experience alterations in their elastin and collagen content, fiber organization, and fiber cross-linking that reduce their tensile strength and impair their stabilizing function.11,20 The ligamentum flavum may thicken and buckle and the posterior longitudinal ligament may ossify.21 On the other hand, muscle degeneration or degenerative myopathy can result in reduced strength of paraspinal and truncal muscles, compromise spinal dynamics, destabilize the spine, and exacerbate degeneration.11
Degenerative changes of the intervertebral discs, facet joints and supporting ligaments narrow the spinal canal, decreasing the flow of cerebrospinal fluid and increasing venous pressure. These elements together may compromise the neural and vascular structures of the spinal cord and/or nerve roots. Spinal stenosis can lead to signs and symptoms of myelopathy in the cervical spine, and to radiculopathy and neurogenic claudication in the lumbar segment. In addition, these degenerative changes reduce muscular support, increase stiffness of the cervical spine, and predispose the elderly to central cord syndrome following a hyperextension injury such as a fall.
The spinal cord also experiences age-related alterations to its composition. In a human autopsy study, Terao et al,22 (1994) demonstrated that advancing age is significantly correlated with a decreased density of small myelinated fibers in the corticospinal tract. Furthermore, aging is associated with a reduced number of small neurons in the intermediate zone of the ventral horn as well as of large α- and medium-sized υ-motorneurons.23 These physiological changes to the spinal cord should be taken into account when managing patients with age-related spinal disorders.
OVERVIEW OF FOCUS ISSUE
In anticipation of the aging of the population, we undertook this project to heighten physicians' awareness of common age-related spinal disorders, including geriatric odontoid fractures, central cord syndrome, osteoporotic compression fractures, degenerative cervical myelopathy, lumbar spinal stenosis, and degenerative spinal deformity. This focus issue provides an overview of the epidemiology, natural history, diagnosis, and risk factors of these spinal disorders; summarizes the cost burden of disease management and the cost-effectiveness of surgical intervention; highlights the trends for spine surgery in the elderly; and discusses techniques and important considerations for treating the aging of the spine. We expect this focus issue will appropriately convey the impact of the aging population on global health care systems and hope clinicians worldwide will use these reviews and recommendations as an aid to facilitate diagnosis, monitor their high-risk patients, implement preventative strategies, and design appropriate treatment programs.
This focus issue consists of 16 articles developed to address key questions surrounding the epidemiology, pathophysiology, natural history, diagnosis, clinical and radiographic presentation, and treatment strategies of a wide range of age-related spinal disorders. Of these, some are narrative reviews and others are systematic reviews or primary research studies. The first introductory article defines the societal burden of spinal disorders in the elderly and emphasizes the need to optimize the value of care through reducing costs and improving the durability of treatment. After this article, the focus issue is divided by topic into five comprehensive sections.
Section 1 discusses spine trauma in the elderly by summarizing the current knowledge on geriatric odontoid fractures, vertebral compression fractures, and traumatic central cord syndrome. This section proposes specific recommendations for the management of spinal fractures and addresses areas of controversy, including optimal timing of surgical intervention (early vs delayed) for central cord syndrome and appropriate treatment strategies for osteoporotic and odontoid fractures. The first article is a systematic review that compares short- and long-term mortality rates between nonoperative and operative treatment for patients >60 years with a type II odontoid fracture. The second study presents differences in neurological outcomes, complications, and lengths of intensive care unit and hospital stay in patients treated early vs delayed for central cord syndrome. The final article in this section discusses the epidemiology, morbidity and mortality, and economic burden of vertebral compression fractures and summarizes evidence surrounding the effectiveness of percutaneous vertebral augmentation (kyphoplasty and vertebroplasty).
The objective of section 2 is to explore various degenerative diseases of the spine in the elderly, including degenerative cervical myelopathy, lumbar spinal stenosis, and spinal deformity. The first article promotes the adoption of a new term “degenerative cervical myelopathy” to comprise both osteoarthritic changes to the spine, including disc herniation, spondylosis and facet arthropathy (collectively referred to as cervical spondylotic myelopathy), as well as ligamentous aberrations such as ossification of the posterior longitudinal ligament. The first and third study of this section provide overviews of the epidemiology, natural history, diagnosis, and impact of degenerative cervical myelopathy and spinal deformity and recommend optimal management strategies for these disorders. The second article examines the evidence supporting surgical intervention for the management of symptomatic lumbar spinal stenosis in the elderly.
Techniques for handling the aging spine are presented in section 3. Specifically, this section discusses the evolution of medical management of osteoporosis, surgical treatment of spinal conditions in the osteoporotic spine, and the role of minimally invasive spine surgery in the elderly. The first article of this section discusses various treatment options for osteoporosis, including bisphosphonates, parathyroid hormone injections, and surgical intervention, and emphasizes the importance of optimization pre and postoperatively. The second article addresses the role of adjacent segment vertebral augmentation in preventing adjacent segment failure and discusses various methods related to increasing stability of spinal fixation in osteoporosis. Finally, in the third article, a systematic review was conducted to summarize literature surrounding the effectiveness and safety of minimally invasive surgery in the elderly, including lumbar decompression, lumbar decompression and interbody fusion, and lumbar spinal deformity surgery.
Section 4 provides an economic perspective in relation to outcomes of surgery for spinal disorders in the elderly. In the United States, recent legislative developments have prescribed value-based purchasing and pay-per-performance models. There is, therefore, an increasing need to prove that surgery is cost-effective in the elderly and that it results in favorable outcomes with respect to pain, disability, quality of life, and functional status. The first 2 studies in this section focus on comparing the cost per quality-adjusted life-years and various outcomes between an elderly (≥70 years) and young (<70 years) cohort of patients treated for various lumbar pathologies. The final article of this section discusses current trends in relation to spine surgery for the elderly and summarizes the implications of increased rates on access to health care in North America.
The final section of this focus issue discusses spinal deformity in the elderly, a scenario that presents a unique challenge to the spine surgeon. Surgery to correct deformity is typically extensive and, in older persons, a careful risk-benefit assessment must be undertaken. The first article in this section discusses when it is appropriate to perform limited surgery (simple decompression or short-segment fusion) in the setting of spinal deformity. This is contrasted with indications for more extensive long-segment fusion to address the deformity itself. The second article discusses the pathogenesis of thoracic hyperkyphosis in the context of normal changes associated with aging. The management of hyperkyphosis and important surgical considerations are detailed. The final article presents an overview of the association between movement disorders and spinal deformity. This article delineates both the unique deformities associated with specific movement disorders and the impact of movement disorders on adult spinal deformity in general.
By way of this focus issue, we have summarized current knowledge gaps and limitations in the evidence to provide direction for future research and investigation. As the global population ages, clinicians must be aware that there will be a shift in the type of spinal disorders they manage: (1) there will be an increase in nontraumatic spinal cord injuries, including degenerative cervical myelopathy and lumbar stenosis; (2) the most common form of traumatic spinal cord injury will be central cord syndrome caused by neck hyperextension during a fall; and (3) osteoporosis and spinal deformity will be more prevalent. Furthermore, spinal physicians must take into account that the elderly may have multiple medical comorbidities, decreased physiological reserves, and age-related changes to the spinal cord. All of these factors must be considered when developing and implementing appropriate treatment strategies.
Dr Smith: Biomet, consultant, honorarium, royalties; Nuvasive, consultant, honorarium; Cerapedics, consultant; K2M, honorarium. Dr Harrop: consultant, Depuy Scientific; advisor, Tejin, Bioventus, Asterias. The other authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.
The authors thank Christina Goldstein for providing relevant images for our summary figure.
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