Postural Instability: Definition and Clinical Significance
Postural instability is an impairment in the ability to maintain balance and postural control, resulting from dysfunction in the integration of sensory inputs (visual, vestibular, and somatosensory systems) and the motor output needed to respond to postural disturbances. 1
Core Pathophysiology
Postural instability occurs when the nervous system cannot properly:
- Integrate sensory information from visual, vestibular, and somatosensory systems 1
- Generate appropriate anticipatory postural reactions during functional behaviors 1
- Produce reactive motor responses to postural disturbances 1
The condition affects one or more sensory and motor networks, making it difficult to safely complete activities of daily living, move about the home and community, and live independently 1.
Clinical Manifestations
Primary Symptoms
- Impaired balance control during standing and movement 1
- Difficulty maintaining upright posture without support 2, 3
- Increased mediolateral sway and sway area, particularly with eyes closed 4
- Forward shift of center of pressure, reflecting flexed posture 4
- Reduced ability to respond to balance challenges in various directions 3
Associated Features
- Abnormal motion sensitivities not associated with nystagmus 1
- Sense of disorientation in space 1
- Feeling unstable or losing balance with position changes 1
Clinical Consequences and Morbidity
Fall Risk and Injury
Postural instability directly increases fall risk and associated morbidity. 1
- Patients with stroke and postural instability who fall are twice as likely to sustain hip fractures compared to those who fall without stroke 1
- Large percentages of affected individuals report falling at least once within the first 6 months after neurological injury 1
- Patients with vestibular disorders and postural instability face significantly higher risk of falls and fall-related injuries 1
Functional Impact
- Low balance confidence develops, which further reduces activity levels 1
- Loss of independence in daily activities 2
- Difficulty with mobility in home and community settings 1
- If left undetected or untreated, postural instability results in a cascade of serious, undesirable, and expensive events 1
Disease-Specific Patterns
Parkinson's Disease
- One of the cardinal signs of Parkinson's disease 2
- Can be present even at diagnosis but becomes more prevalent and worsens with disease progression 2
- Represents one of the most disabling symptoms in advanced stages 2, 5
- Forward-backward decline occurs earliest, with more severe impairment in these directions 3
- Postural abnormalities can occur at early stages (Hoehn and Yahr stage II) 3
Stroke
- Common after stroke because stroke can affect one or more sensory and motor networks 1
- Balance impairment is inclusive of postural control impairment 1
Vestibular Disorders
- BPPV can result in definable abnormal postural control with heightened fall risk even after successful treatment of positional nystagmus 1
- Statistically significant increased risk for persistent postural abnormalities in the elderly where multifactorial comorbid impairments may be present 1
- Can manifest as isolated sense of instability brought on by position changes such as sitting up, looking up, bending over, and reaching 1
Clinical Assessment
Evaluation of balance abilities and postural control is considered part of routine clinical practice in individuals with neurological conditions affecting balance 1. Standardized tests challenge different aspects of postural control, including anticipatory postural reactions during functional behaviors 1.
Key Assessment Measures
- Mediolateral sway and sway area with eyes closed serve as potential discriminators for increased fall risk 4
- Limit of stability testing in multiple directions (forward, backward, right, left, and diagonal directions) reflects dynamic evolution of postural instability 3
- Specific balance limitations identified during evaluation help determine fall risk and guide intervention selection 1