Nearly one in five Americans report a disability, a proportion that increases with age, low literacy, and low education level, according to the Centers for Disease Control and Prevention. Mobility problems related to arthritis, back, or spine problems are the most prevalent causes of self-reported disability in the United States. A growing public health concern with the aging US population, disability-related health care costs exceed $400 billion per year. More than 7 million disability assessments are made each year in the United States, many of which are made by physicians in the field of pain medicine.

Regardless of training, background, or specialty, physicians are asked for assessments, opinions, and expertise regarding disability or impairment in their patients. The process of disability assessment can be fraught with subjective bias, and the role of determining disability can pose ethical issues for treating physicians. As “healers,” physicians aim to maximize the health, well-being, and functional potential of patients, but in disability determination, physicians become advocates for patients’ financial interests and health care resources, the role which can conflict with the “healer” role. For some physicians, disability determination causes discomfort or unease, especially when opinions between physician and patient differ or when litigation is involved.

Disability determination is not typically a part of medical education, and in most states, no formal training or certification is required for physicians to make these assessments. In turn, many physicians lack experience or training in the methods of assessing disability, how to perform an independent medical evaluation (IME), how to assess a patient’s ability to return to work, or how to assess what activities a patient is capable of performing. In theory, disability determination should be a transparent, unprejudiced, and objective process, and impairments, functional limitations, and work restrictions should be associated with objective evidence for tissue damage, organ dysfunction, or cognitive dysfunction. Furthermore, this evidence should be reproducible with high interrater agreement. Knowledge of basic terminology in disability determination is important to the pain specialist.

Disability is an alteration in one’s physical or cognitive capacity to perform a specific task, function, or activity and is highly dependent on individuality and context. Disability is greatly influenced by education, age, and social and cultural factors, as well as vocational opportunities and training and is therefore contextual and subjective. There is no universally accepted method for the assessment of disability. In fact, the definition of disability varies widely among government entitlement programs, private disability insurers, state Workers’ Compensation Boards, and others.

In contrast, impairment is an objective term that defines the loss or loss of use of, or derangement of any body part, organ function or organ system, or cognitive and psychological functioning. Impairment can be temporary or permanent, and can be reproducibly measured through testing or physician assessment. Handicap is the legal or social policy term used to describe a disability.

An impairment rating or whole person impairment rating is an objective assessment of a patient’s disablement and should reflect the severity of a particular medical condition and the way one’s activities of daily living or vocation are affected. For example, the accidental amputation of a finger in a concert pianist creates a much greater impairment than the same injury in a truck driver. Validated, evidence-based methods for calculating these impairments are important.

Impairment ratings can be calculated using the American Medical Association’s (AMA) Guides to the Evaluation of Permanent Impairment, currently in its sixth edition. Previously faulted for lack of validity and reliability, the Guides in its current iteration is meant to be a more accurate tool to measure functional loss as an integral part of the impairment rating and provide a more standardized assessment of activities of daily living and functional limitations from a particular injury or disease process. Overall, the impairment rating defines the impact of injury or disease on one’s ability to perform self-care, manual tasks, maintain home and health, manage in an emergency, care for one’s children or dependents and to communicate, function independently, travel, and work. The more serious the injury and the more impactful the impairment for an individual, the larger the whole person impairment rating will be. In most cases, impairment is considered permanent if there is no significant change in the condition over a 12-month period. The calculation of impairment ratings using the Guides remains a complicated process when injury or disease severity is high or when multiple injuries or diseases are involved.

This system is meant to be logical, systematic, and fair. In contrast to prior editions of the Guides that used a “tables method” and “range-of-motion method” for calculating impairment rating based on anatomic loss or damage assessed with physical examination or diagnostic findings, the new Guides uses a “diagnosis based impairment model” to provide a more individualized assessment of impairment with a multidimensional approach.

In general, an impairment class for any injury or disease is defined on a scale of 0–4, shown in Table 10.1 , and an impairment rating or percentage is calculated (no impairment, minimal impairment, moderate impairment, severe impairment, very severe impairment) using categories or scores defined by a patient’s history, clinical presentation, physical examination findings, diagnostic or objective test results, functional history, and burden of treatment compliance. For each organ system or body region, the Guides provide clinical examples and calculations for the clinician to follow.

For example, a 20-year-old female with a low back injury incurred while lifting a toddler while working in a day care center, who responds to conservative therapy over the course of 3 weeks but still complains of mild nonradiating low back pain with heavy lifting, and on physical examination has only normal findings, radiographs are normal. Her impairment rating is calculated a 0 because she experienced a minor injury, had a short period of treatment, has no physical examination findings, and demonstrates full physical function because she can still work and take care of herself with complete independence.

In contrast, one with more complicated and serious pain, physical examination findings, and long-term limitations would have a much higher impairment rating. For instance, a 52-year-old male chauffeur is a restrained driver in an auto accident, wherein his car collides with a retaining wall. He suffers L4-5 and L5-S1 disc herniations that required laminectomies at two levels and a two-level posterior spine fusion with implanted hardware. At maximal medical improvement (MMI) 1 year later, he has a foot drop on examination and loss of sensation in the right L4, L5 and S1 dermatomes, and right L5 and S1 radiculopathies are confirmed on electromyelography. Pain and function do not improve with rehabilitation and strength training and after a year of treatment, and he takes multiple medications to control pain at rest and with any activity. He must use an orthotic on the left ankle in addition to a cane to ambulate and he cannot drive a car due to his right leg and foot weakness. A Pain Disability Questionnaire confirms that his function is extremely limited in several domains. Using this patient information and the charts, tables, and equations in The Spine and Pelvis chapter of the Guides, his impairment rating is noted within the class 4 range, which translates to 25%–33% whole person impairment. This impairment rating is then modified with a grade (A, B, C, D, or E; A being the lowest grade, and E being the most severe grade) by considering the functional impairments, physical examination findings, and objective findings in this particular case, within an impairment class. In this case, a net adjustment of 2 is calculated when considering the high severity in the listed domains, which translates to a grade E.

Note that the Pain Disability Questionnaire is used more in research studies. Other questionnaires used in back disability and functional impairments include the Pain Disability Index, Oswestry Low Back Pain Questionnaire, the Roland-Morris Low Back Pain and Disability Questionnaire, Quebec Back pain Disability Scale, and the Waddell Disability Index. Although the different questionnaires have been compared, it is beyond the scope of this chapter to detail these comparisons.

The Guides outlines a systematic approach to this rating system, which is increasingly complicated with more impactful injuries and disease processes. In addition, impairments from multiple organ systems or body regions are accounted for by adding impairment values together; however, the complexity of this process is beyond the scope of this chapter. Although the Guides was redeveloped to be accurate, reliable, unbiased, and reproducible, this modification of impairment rating has not been tested or validated in rigorous trials but because it is the only evidence-based and peer-reviewed impairment assessment tool available in the United States, the Guides may be the best reference for calculating impairment ratings.

Impairment ratings are used in calculating damage awards and other monetary compensation packages. It is important to note that an impairment rating should not be assessed until the patient has reached MMI, the state at which all potential healing, repair, and treatment has been completed, and the impairment is permanent and unlikely to change significantly within the ensuing 1-year period.