A1 Gait Disorders

Topic

Human gait follows a normal pattern that combines three references: the normal kinematic pattern, which describes how joints move throughout the gait cycle; normal joint power, which describes the force and mechanical work produced by each joint during that same cycle; and normal stability, which describes how the body maintains balance while walking. Together, the normal kinematic pattern, normal joint power, and normal stability determine what an unimpaired gait should look like and serve as the baseline against which any actual gait is compared.

Within this gait, the normal kinematic pattern establishes the angles, timing, and trajectories that joints should follow during each phase of the step. When a person's observed joint movement deviates from this normal kinematic pattern, the difference is recorded as a quantifiable kinematic deviation; the further the actual movement strays from expected values, the greater the recorded quantifiable kinematic deviation.

Alongside the normal kinematic pattern, normal joint power establishes the amount of force and mechanical work each joint should produce at various points in the gait cycle. When a person's measured joint power deviates from this normal joint power, a quantifiable joint power deviation occurs, increasing in magnitude as the actual power diverges from the normal joint power.

In addition to the normal kinematic pattern and normal joint power, normal stability dictates how the body controls its center of mass and avoids losing balance while moving forward. When observed balance control deviates from this normal stability, a quantifiable stability deviation arises; its magnitude depends on the extent to which the person's ability to remain stable during the step is compromised.

These three quantifiable deviations—kinematic deviation, joint power deviation, and stability deviation—do not in themselves constitute a disorder; they only do so when they exceed a significance threshold. As long as any of these deviations remain below that threshold, they are considered part of normal gait variation; As soon as a deviation crosses that threshold, it is no longer interpreted as a normal variation and instead constitutes a gait disorder.

Gait disorders are classified by combining two elements that depend directly on the previously described deviations: the type of alteration—determined by which of the three reference points (normal kinematic pattern, normal joint power, or normal stability) exhibits the significant deviation—and the magnitude of the alteration, which increases in proportion to the quantifiable deviation from the corresponding reference value. For instance, a disorder involving a large kinematic deviation is assigned a greater magnitude of alteration than one where the deviation barely crosses the significance threshold.

The type and magnitude of the alteration, in turn, determine the gait disorder's functional impact: the greater the magnitude of the alteration, the greater its functional impact on the individual's walking ability. This functional impact ultimately allows for a practical assessment of how the gait disorder affects the person's ability to walk, thereby linking the normal gait pattern described at the outset with the alteration that is ultimately classified.

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