Posturography is a clinical technique used to objectively assess and quantify a person’s ability to maintain balance and postural stability in an upright stance. This method transforms the often subjective experience of dizziness or unsteadiness into measurable data. Maintaining balance is a complex process that relies on the central nervous system integrating signals from three main sensory systems: vision, the inner ear’s vestibular system, and proprioception (the body’s sense of position). Posturography evaluates the body’s control mechanisms by measuring its response to various controlled challenges.
The Underlying Science of Measuring Balance
Posturography tracks the subtle, continuous movement of the body. When a person stands still, the body constantly sways in small, involuntary movements as muscles make micro-adjustments to maintain equilibrium. Posturography measures this balancing act by focusing on the relationship between the Center of Gravity (COG) and the Center of Pressure (COP). The COG represents the body’s theoretical balance point, while the COP is the point on the support surface where the total force of the body is applied. During upright stance, the nervous system keeps the COG aligned over the base of support, and the COP moves actively under the feet to correct for COG displacement.
The data collected is quantified to provide clinical insight into balance control. Measures include the total area covered by the COP’s movement, the distance of the COP from the COG, and the velocity of the sway. A larger sway area or a higher sway velocity indicates poorer postural control, as the individual is making larger or more frequent corrective movements.
Standard Techniques Used in Posturography
Posturography employs techniques to stress the balance system and isolate the sensory components responsible for stability. The most fundamental method is Static Posturography, which involves the patient standing quietly on a force plate. Testing typically involves conditions like standing with eyes open versus eyes closed on a firm surface, which highlights the importance of visual input for maintaining stability.
Computerized Dynamic Posturography (CDP) systematically challenges the patient’s balance by manipulating the sensory environment. The most common CDP protocol is the Sensory Organization Test (SOT), which uses a movable platform and a surrounding visual enclosure. The SOT consists of six standardized conditions that selectively make one or two of the three main sensory inputs—visual, vestibular, or somatosensory (proprioception)—unreliable or conflicting.
For example, the platform can be “sway-referenced,” meaning it tilts in response to the patient’s sway, which effectively cancels out reliable feedback from the somatosensory system. The visual surround can also be made to move, providing misleading visual information. By measuring the patient’s sway under these progressively challenging conditions, the SOT determines how effectively the patient can use and switch between their visual, vestibular, and somatosensory inputs to maintain an upright posture.
Clinical Relevance and Diagnostic Interpretation
Posturography provides data that clinicians use to diagnose and manage a variety of balance disorders. Physicians may order the test for patients complaining of dizziness, vertigo, or unsteadiness, or to evaluate fall risk in older adults. The test is also used to assess recovery from concussions, monitor the progression of neurological conditions like Parkinson’s disease, and evaluate the effectiveness of rehabilitation programs.
The results from the Sensory Organization Test are analyzed to produce a sensory analysis ratio, which identifies which sensory system the patient is over-relying on or failing to use effectively. For instance, a patient who performs poorly only when the somatosensory input is inaccurate but the visual and vestibular inputs are available may have a proprioceptive deficit. Conversely, a patient who shows poor balance when both somatosensory and visual inputs are inaccurate is likely struggling with a vestibular issue, as they cannot rely on their inner ear for balance. The objective scores offer a baseline for treatment and a quantitative means to track a patient’s improvement over time.