Disability is a moral and global issue that affects over 1 billion people, one in seven individuals, or roughly 15% of the global population.¹ The World Health Organization (WHO) has recognized that global disability adversely affects human rights and basic public health (Fig. 1–1). Based upon data from the WHO, disability disproportionately affects individuals who suffer from poverty, and may decrease access to health care, education, and employment.² Those who suffer from disability are more likely to have had a violation of basic human rights; be abused; and suffer discrimination, violence, and loss of autonomy.

Unlike classic medical models, which are either provider- or disease-centric, the modern rehabilitation model is patient-centric. In this model a group of health care providers, family members, and other caregivers collaborate to care for and restore function of an individual suffering from disability.

The specialty also addresses the complex interplay of social circumstances of patients with impairments and disability. These include the home environment (e.g., numbers of steps to enter; location of kitchen, bedroom, and bathroom; accessibility of spaces) and assessments of activities of daily living, occupation, vocation, health insurance status, presence of family caregivers, and hobbies.

The rehabilitation model is further unique, as functional goals are defined by the team and require patient participation. The goals often include the diminution of impairment, disability, and the patient’s handicap—ultimately the restoration of function. These goals are achieved through the utilization of medications, interventions, therapies, modalities, patient education, and lifestyle and workplace modifications. Oftentimes caregivers are included as part of the rehabilitative team.

The primary objective of the field of rehabilitation medicine is to achieve the maximal functional restoration of an individual suffering from impairment, disability, and ensuing handicap. Impairment is defined as the loss or diminution of psychologic, cognitive, physiologic, or anatomic function. Examples of impairment may include the loss of a limb, diminished motor strength, or a cognitive deficit. Disability is described as the diminished ability to perform a task or activity that would generally be considered normal for a person within their societal context. The loss of the ability to perform activities of daily living (e.g., dressing, grooming, and cooking) is an example of disability. The overall societal disadvantage that an individual may have in which an impairment causes disability is further defined as their handicap.

The American Board of Physical Medicine and Rehabilitation has defined the goal of the specialty as “[t]o restore function, reduce pain and improve quality of life.”³ The definition is further expanded to “caring for the whole person.” Not surprisingly, the definition of rehabilitation is different in different parts of the world and often reflects regional conditions. The United Nations has defined rehabilitation more broadly: “Rehabilitation and habilitation go far beyond the health field and [embrace] a wide range of issues including education, social counseling, vocational training, transportation, accessibility and assistive technology …. For most people with disabilities, access to adequate (re)habilitation is a condition for integration into society and participation in the communities in which they live.”⁴ The WHO defines rehabilitation as “a set of measures that assist individuals who experience, or are likely to experience, disability to achieve and maintain optimal functioning in interaction with their environments.”⁵ Furthermore, the organization affirms that rehabilitation provides aid throughout the entire continuum of care, improves health outcomes, reduces costs by decreasing length of in-patient stay, reduces disability, and improves quality of life.^6–12 Rehabilitation medicine is defined as “improving functioning through the diagnosis and treatment of health conditions, reducing impairments, and preventing or treating complications.”¹³

Recognizing that rehabilitation has lacked a basic unifying framework, the WHO published The International Classification of Functioning, Disability and Health (ICF) in its World Report in 2011.¹⁴ The ICF is a classification system of disability that provides a framework for measuring disability and health both at an individual and global level, and is operationalized through the WHO Disability Assessment Schedule (WHODAS 2.0).¹⁵

The concepts of disability and functional restoration have been recorded since ancient times. One of the earliest records of an assistive device was discovered in a cave drawing from ancient Egypt dating to 2830 BC¹⁶ Interestingly, computed tomography (CT) scans of an Egyptian mummy dating to the 21st Dynasty (1085–950 BC) revealed a prosthetic toe¹⁷ (Fig. 1–2).

A second prosthetic toe was discovered still attached to the mummy; careful analysis suggested that it was composed of a wood resin with signs of wear, held in place by woven textile (Fig. 1–3).

In ancient Greece, individuals afflicted with functional impairments and disabilities were at times shunned from society. As disability was seen as a punishment for sin, great impetus was placed upon functional restoration so that the individual could once again be accepted by society.¹⁸ Individuals who made a functional recovery were thought to have been blessed by deities. A paradigm shift in the view of disability occurred shortly after Hippocrates described disease and its sequelae as a natural process of aging rather than punishment for sin.¹⁹

Interestingly, rehabilitation has been intertwined with war from early times. In the second century, Galen (a physician of the Roman emperor) prescribed particular forms of exercise for therapy in soldiers with war-related injuries.²⁰ Herodicus, an ancient Greek physician, later described a series of exercises in the fifth century for management and prevention of disease.²¹ The sentiments toward those suffering from disability shifted after the spread of Christianity. Those who suffered common impairments (e.g., blindness, hearing loss, leprosy) were viewed in a more sympathetic light.

Concepts of modern rehabilitation were born during the Renaissance period when physicians made great progress in the study of human anatomy, the kinetic chain, and their relation to function. Most notable was the Italian anatomist Andreas Vesalius (1514–1564), who published the textbook “De humani corporis fabrica” (On the Fabric of the Human Body)²² (Fig. 1–4). Subsequently, the French physician Andry de Bois-Regard (1658–1742) wrote “Traité d’orthopédie” (Treatise on Orthopaedics) in 1741, in which he described a causal relationship between exercise and functional restoration.²³ Building on this work, the Swiss physician Joseph Clément Tissot (1747–1826) published “Gymnastique Médicinale et Chirurgicale” (Medical and Surgical Gymnastics) in 1780. Tissot was the first to describe the benefits of early mobilization and exercise in those suffering from illness and postsurgical patients—concepts that were far ahead of their time.²⁴