Introduction
In our lifetime, spinal cord injury (SCI) has been transformed from an injury with nearly certain death shortly after the injury, to a disability in which nearly all people survive the injury process and then go on to active, productive lives.

Devivo, of National Spinal Cord Injury Database , Birmingham , Alabama presents a life expectancy for persons with SCI who survive at least 1 year following their initial injury. From his data, an individual who is age 20 at the onset of the SCI has a substantial life expectancy. ( See Table 1 below)

Table 1

With established survival following SCI, we now face the issue of many individuals growing older with SCI, adding to the normal aging process. A study done in 1988, commissioned by the Paralyzed Veterans of America indicated, of all SCI individuals in the United States, approximately 40% were over 45 years of age and 25% were over 20 years post injury.

Craig Hospital's SCI System was funded as a research and rehabilitation training center focusing on issues of the aging SCI patient from 1993 to 1997. During that time we undertook a series of studies to identify and understand the multiple issues of the aging process with SCI disability. From these studies, we have identified a model in which we describe 3 phases following the onset of SCI.

• Acute restoration
  The first phase is acute restoration, which occurs during the first 2 years following SCI. In acute restoration, a SCI individual develops close to 100% of the ability and function they have for their given neurologic injury. For a paraplegic this might involve gaiting or ambulating on long-leg braces and forearm crutches. For a paraplegic at a higher level, this might be complete independent living in a wheelchair. For a tetraplegia, it may involve attendant care for several hours a day. For a high level tetraplegia, it may involve being able to direct care givers in their care.
  
• Maintenance Phase
  After the acute restoration phase, a SCI individual enters into a steady state which we describe as the maintenance phase. This particular state lasts many years and is dependent in part upon the age of disability onset and a series of aging variables, such as family genetics, life style, adaptation to stress, sociologic role, and trauma. For a young individual this stable state may be 20 plus years, whereas if an individual who is elderly at onset, this state may last only several years. During the maintenance phase, there is an additive effect of the normal aging process and the superimposed additional stresses of SCI. Examples might be the overuse of arms for transfers and pushing wheelchairs or insensate skin break down that would not occur in a normal individual. This additive or cumulative aging effect creates an accelerated aging process. We perceive our SCI individuals as aging faster, that is, coming to the point in their life where they have to change the way in which they maintain themselves at a much earlier age than the general population.
  
• Phase of Decline
  The third and final phase of the SCI aging model is the phase of decline, which refers to the phase in which an individual has to start modifying how they live their life as a result of the aging process. This may involve changes, such as additional equipment (ie, power wheelchair when a person in the past only used a manual wheelchair), additional attendant care, and decrease in activity to mention a few.

We see the model of aging with SCI applying to other disabilities. In particular the polio population demonstrates the effect of decline and as a group, having all gone throughout the phase of acute restoration, maintenance, and are now solidly established in the decline phase. Whereas SCI individuals are well established in the maintenance phase, traumatic brain injury (TBI) systems of care are still working on trying to establish the optimal acute restoration and maintenance programs.

To understand the aging process, it is critical to know the age at onset of the disability. Because a normal aging process has occurred in an individual before the onset of the disability, the extent of the pre-injury aging process determines the ability to recover and adapt to the new SCI disability. We know that as a normal individual gets older, their ability to adapt to a new disability becomes less and as a result their outcomes or levels of function are lower than would be experienced by a younger person. Profiles of older individuals who sustained SCI have entirely different demographics than those of younger individuals and show much lower levels of independence and much greater likelihood of being discharged to institutions than younger individuals.

One of the significant issues identified in aging with a SCI disability is the problem of aging care givers. Just as the individual with SCI ages, the care giver, whether it be parents or spouses, all go through changes in which they become less able to provide the care that they have provided for many years following the onset of SCI. The problem of an aging caregiver presents an ethical dilemma in which the medical profession has focused their attention on the individual with the disability and therefore, often ignored the needs of the caregiver. It may also present as a medical crisis when the mother and father, or other loving family member, are no longer able to provide the quality of care in the home that has prevented illness and hospitalization. These changes often force the individual with disability to acquire new systems of care and/or move to new institutions where care can be provided. These dramatic changes often present emotional distress and require counseling and the development of new psychological skills in both the SCI individual and their care givers.

Quality of life is one parameter that has always been a pleasant surprise to investigators in the aging process. Despite what appears to be declining function, decreased activities, increased attendant care, and increasing equipment needs, individuals frequently report they have never felt better about themselves nor more whole at any point in their life since their SCI. This initially paradoxical finding can best be explained by the perception that aging involves multiple dimensions, one of which is physiologic, the second which is sociologic, and the third, spiritual or growth of the soul. As people get older, in both general populations and those with disability, there is a search for meaning in life, and for many, this meaning in life becomes more important than the various physiologic and sociologic changes or declines. Much remains to be understood of this process.

Traditionally, we have evaluated an individual with SCI by their impairment. An example using the American Spinal Injury Associations ( ASIA ) standard medical classification of SCI would be to describe an individual as having tetraplegia C6 last preserved segment ASI Impairment A. That means this individual has wrist extensor muscle function last preserved and complete loss of sensation and movement below the C6 neurologic level. As we get into research on the aging process, it's important to expand our understanding beyond that of impairment. The impact of loss of function resulting from the impairment is described as the disability, which means because this individual has only wrist extensor function, they are unable to do a variety of things, such as their bowel and bladder care, dressing, etc. Measurement of those loses or disabilities is done through an instrument called the Functional Independence Measurement (FIM), which is now widely used in all medical centers for monitoring and evaluating change in function of an individual. The FIM measures the amount of assistance a SCI individual needs to maintain their daily routine function.

A new element is the concept of handicap. Handicap is described as the loss of abilities to function in a community as a result of the disability, which is the loss of function resulting from the impairment. Examples of handicap would be the inability to get around a community in a wheelchair because it may not be wheelchair accessible or because there is inadequate transportation to accommodate an individual in a wheelchair. Another example would be the inability to earn an adequate wage because of the loss of function. At Craig Hospital , we have developed an instrument for measuring and monitoring the effects of handicap. This instrument is the Craig Hospital Assessment and Reporting Technique. In this instrument, a series of questions are developed relating to physical independence, mobility, occupation, social integration, economic self sufficiency, in which graded responses are tallied and a score is developed indicating the extent the individual has been integrated into the community. It will be important in the years ahead to understand the effects of aging as it is measured by handicapped scores (ie. integration in the community).

Physiologic Changes
In SCI, we see specific physiologic consequences of the aging process, particularly in the urologic system, the gastrointestinal system, the musculoskeletal system, and the neurologic system. The urologic system, in particular, is affected in most SCI. We have identified that the presence of a neurologic bladder diagnosis, regardless of the technique of management, increases the risk for development of cancer of the bladder. In a recent study of Craig Hospital patients, we found that the general population has an instance of bladder cancer that is less than 0.1 percent. Individuals with SCI appear to have an incidence of bladder cancer that gradually increases from 0.2% in the first 10 years following SCI to 9% after 30 years. This creates specific concerns in follow-up that we need to be doing cystoscopic examinations of the bladder more frequently as an individual gets older to make sure that we see and identify precancerous and/or early cancerous changes so that we can initiate timely treatment and changes.

Another specific area of concern is the gastrointestinal tract in which control of bowel evacuation is lost following SCI. Studies done in Veterans Administration has shown that there is a significant increase in all gastrointestinal pathology in all individuals with SCI. This ranges from an increase incidence of gastric paresis and gall bladder disease, to severe constipation and increased rectal pathology. In the area of musculoskeletal system, it is well documented that there are increased incidences of shoulder pain and pathology resulting from the use of the upper extremities to perform body manipulations and maneuvers for transfers, getting in and out of the wheelchairs, etc., that would normally be performed by lower extremities.

Another significant problem in the musculoskeletal system is the general loss of strength associated with normal aging. This gradual loss of strength means that an individual who uses all of their strength following their SCI to attain a certain degree of independence may very well lose that function and independence as their muscles get weaker with age. Another musculoskeletal concern, but poorly understood, is the risk of osteoporosis and fractures, which results from accelerated osteoporosis following the onset of SCI.

In the area of neurologic function, we now know that approximately 15% of individuals with SCI will have additional neurologic loss or pathology after the initial recovery following SCI. This comes in many forms, such as loss of strength and sensation, increased sweating and spasticity, onset of pain, and usually occurs from cystic myelopathy and/or tethering of the spinal cord. There is also increased risk of peripheral nerve injury, such as median and ulnar nerve pathology at the wrist or elbow resulting from trauma on the elbows and hands from the abnormal use of upper extremities for mobility and function.

Conclusion
We have found that aging with SCI is not something to be taken lightly. It needs to be addressed through education and development of interventions that can be used to modify the aging process, and hopefully delay the onset of decline phase of the aging model. To best deal with the multiple issues of the aging process, a SCI individual needs to be followed in a system of SCI care, which is familiar with the aging process and has the appropriate surveillance methodology, educational resources, and interventions to deal with the aging process.