Evaluation of the Aging Patient

Structural Changes in the Spine

The spinal unit is comprised of vertebral bodies, zygapophyseal joints, and intervertebral discs. A common pattern of degeneration of the joints, discs, and bone has been observed as patients age. This degenerative process is commonly associated with aging, although the process may occur in the young, as it is heavily modified by genetics and environment such as smoking. It represents a change in the homeostatic mechanism between the intradiscal environment and the vertebral end plate.

The disc is the biggest avascular structure in the human body, and cells in the center of an adult lumbar disc must survive at a distance of 6 to 8 mm from their nearest blood supply. The end plate is 40% porous in the central region, with sclerosis occurring over time. Nutrient supply is altered as the end plate changes. The degenerative process occurs as the end plate–disc interface becomes disrupted, leading to biomechanical and pressure changes within the disc, leading to further collapse of the disc. The cells of the disc are sensitive to mechanical stimuli. This leads to a loss of water and proteoglycans as the matrix within the nucleus changes. The rate of synthesis of proteoglycans decreases, as does the concentration of proteoglycans in the nucleus. The proteoglycans produced are smaller and less aggregated, and the concentration of chondroitin sulfate falls, resulting in a rise in the ratio of keratan sulfate to chondroitin sulfate. The collagen content of the nucleus increases, rendering the nucleus more fibrous and leaving fewer polar groups of the proteoglycans available to bind water.

As the aging process occurs, the boundary between the nucleus and the annulus becomes less distinct, with fissuring and tearing appearing in the third and fourth decade of life. Metalloproteinases are present, as are angiogenic and neurotrophic factors, leading to destruction and invasion of nociceptive fibers. The disc settles and flattens, leading to changes in the focal alignment of the spine, asymmetric loading of the facet joints, and bulging of disc material into the central canal. Settling also causes “up-down” foraminal stenosis, with the direct link between disc degeneration and radiculopathy established in the 1930s by Mixter and Barr.

Loss of focal alignment puts added stress on the supraadjacent levels and leads to a cascade of further degeneration. As the facet joints become asymmetrically loaded they subluxate over time, leading to destruction of articular cartilage and subarticular stenosis and changes in alignment. Schwab et al. demonstrated a 68% prevalence of degenerative scoliosis in healthy older volunteers. Furthermore, the ligamentum flavum goes through a degenerative process and thickens, with an increase in elastin leading to spinal stenosis. ^, Lumbar spinal stenosis is commonly identified (>38%) in patients older than 60 years of age compared with a younger population (16%).

Often older patients present with a constellation of pathologies in their cervical, thoracic, and lumbar spines, which contrasts with the younger patient who may present with discrete single-level pathology. Older patients often have multilevel disease with numerous pathologies. A patient presenting with lower back pain may have lumbar spinal stenosis, lumbar facet arthropathy, multilevel degenerative disc disease, lumbar scoliosis, thoracic kyphosis, and cervical myelopathy. It is common for older patients to have both lumbar spinal stenosis and cervical myelopathy. It is imperative to assess the cervical spine and to actively look for symptoms and signs of myelopathy. Patients will often present with a great deal of pain in their back and ignore signs of imbalance owing to myelopathy. Reflexes in the lower extremity may be blunted due to severe foraminal or central stenosis, and it is not until the upper extremities are tested is myelopathy revealed.

This is exemplified in Fig. 68.1 . A 74-year-old male presented to clinic with severe low back pain. His main reason for presenting to clinic was to have his low back fixed. Upon history and physical examination, it became apparent that he had difficulty walking, fell quite often, and had signs of myelopathy. Magnetic resonance imaging of the cervical spine and lumbar spine reveal severe spinal stenosis throughout both regions of the spine. Computed tomography (CT) scan of the lumbar spine demonstrated the advanced degenerative changes of the facet joints, discs and subsequent foraminal stenosis and scoliosis that also occurs.