In general, a range-of-motion of a joint in the human body is the distance (e.g., linear or rotational) the joint can move in a certain direction. For example, movements of the shoulder joint (i.e., the glenohumeral joint) include flexion, extension, abduction, adduction, and internal and external rotation. Flexion of the shoulder joint involves rotational movement of the upper arm anteriorly, and extension involves rotational movement of the upper arm posteriorly. Abduction of the shoulder joint involves rotational movement of the upper arm laterally away from the midline of the body (e.g., upward), and adduction involves rotational movement of the upper arm medially toward the midline (e.g., downward). Internal (e.g., medial) rotation of the shoulder joint involves rotation of the upper arm about its longitudinal axis, toward the midline of the body, and external (e.g., lateral) rotation of the shoulder joint involves rotation of the upper arm about its longitudinal axis away from the midline. Internal (e.g., medial) rotation may involve inferior (e.g., downward) rotation of the forearm when the upper arm is abducted and the elbow is flexed 90 degrees, and external (e.g., lateral) rotation may involve superior (e.g., upward) rotation of the forearm when the upper arm is abducted and the elbow is flexed 90 degrees. Combinations of these shoulder joint movements are also possible, including transverse (e.g., horizontal) adduction (e.g., combining flexion and adduction), transverse (e.g., horizontal) abduction (e.g., combining extension and abduction), and circumduction (e.g., combining all directions of movement).
When a joint is injured, either by trauma or by surgery, scar tissue can form or tissue can contract and consequently limit the range-of-motion of the joint. For example, adhesions can form between tissues and the muscle can contract itself with permanent muscle contracture or tissue hypertrophy such as capsular tissue or skin tissue. Lost or limited range-of-motion may also result from trauma, such as excessive temperature (e.g., thermal or chemical burns), or surgical trauma, so that tissue planes which normally glide across each other may become adhered together, markedly restricting motion. The adhered tissues may result from chemical bonds, tissue hypertrophy, proteins such as Actin or Myosin in the tissue, or simply from bleeding and immobilization. It is often possible to mediate, and possibly even correct this condition by use of a range-of-motion (ROM) orthosis, but the longer the period of stiffness or loss of motion the greater the time interval and the force required to regain lost range-of-motion. Therefore, it is beneficial to treat the tissue or joint as early as possible. For example, a ROM orthosis may be applied immediately after surgery or as soon as the stiffness problem is diagnosed. ROM orthoses may also be used for tissue transport, bone lengthening, stretching of skin or other tissue, tissue fascia, and the like.