A8 Functional limitations of the ROM

Topic

The available range of joint motion is reduced by physical factors when something inside or around the joint physically prevents it from reaching the angle it should. This reduction in the range of joint motion can stem from four distinct mechanisms.

The first mechanism is increased tissue stiffness: when the tissue surrounding the joint becomes stiffer than normal, it offers greater resistance to movement and reduces the available range of joint motion.

The second mechanism is capsular contracture: when the capsule enveloping the joint shortens and loses elasticity, the contracted capsule physically limits the joint's displacement and—like tissue stiffness—reduces the available range of joint motion.

The third mechanism involves adhesions: when structures that should glide freely against one another become stuck together by scar tissue, these adhesions prevent the structures from sliding enough for the joint to achieve its full range of motion.

The fourth mechanism is muscle retraction: when a muscle crossing the joint permanently shortens, the retracted muscle resists joint movement in the direction where it should be lengthening, thereby reducing the available range of joint motion.

These four mechanisms—tissue stiffness, capsular contracture, adhesions, and muscle retraction—produce a kinematic limitation on the range of joint motion: a physical inability to reach the angle, distinct from the limitation imposed by musculoskeletal pain. While musculoskeletal pain halts movement before the potential angle is reached because continuing would be painful, these four mechanisms prevent that angle from being reached even in the absence of pain.

To distinguish whether the reduction in the range of joint motion arises from these four physical mechanisms or from a different cause, the model compares passive range of motion—the range achieved when another person moves the joint without muscle contraction—with active range of motion—the range the individual achieves by contracting their own muscle. When the gap between passive and active ranges of motion is small, the deficit is tissue-related and corresponds to one of the four mechanisms previously described; when that gap is large, the deficit is muscular, because the tissue allows the angle to be reached, but the muscle fails to generate the movement to that point on its own.

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