John Doe is a 60-year-old male who is evaluated in an outpatient physical therapy clinic. He reports dizziness that has worsened over the last three months and states that he “almost fell” several times at home. The patient’s insurance company has authorized five physical therapy visits.

In our current healthcare system, patients are admitted for therapy for shortened stays or a decreased number of therapy visits. This trend can be felt in the acute, long-term and outpatient healthcare sectors. While some patients may benefit from several therapy visits in a short time frame, other individuals may demonstrate greater therapeutic gains with fewer therapy visits over an extended time frame and active participation in a challenging home exercise program. With the first of the baby boomers reaching age 65 in 2011, healthcare practitioners can expect a greater number of older patients referred to therapy for dizziness, falls or fall-related injuries.

What Is a Fall?

Although the definition of a fall will vary at different facilities, a fall is often defined as an unexpected event in which the patient’s body comes to rest on the ground, floor or a lower level.¹ Recurrent falls may be defined as more than two falls in a six-month period.² Some healthcare organizations will document when a patient is lowered to the ground or seated by a staff member as a “near” or “assisted” fall.³ Near falls should be treated as actual falls by staff.4 Falls are the leading cause of morbidity and hospitalization in the United States and are the sixth leading cause of death in adults aged 65 years or older.⁵ More than one-third of community-dwelling older adults and 60% of nursing home residents fall annually.^2,6-8 Furthermore, more than 90% of hip fractures occur as a result of a fall.² This statistic is of particular importance because the mortality rate is 15% greater for adults in the year following a hip fracture. When completing healthcare screens, it is important for practitioners to identify patients with a history of falls or who are at risk for falls, because many of these “fallers” have experienced multiple fall episodes.

How can we predict patient falls? The strongest risk factors for patient falls are a history of previous falls, or strength, gait or balance impairments.⁹ In addition, the number of medications that a patient takes and the uses of specific classes of medications are considered to be strong risk factors.10 A patient’s balance confidence also influences the risk for falls. Fall risk factors can be divided into two different categories, including intrinsic factors (aspects of a patient’s medical history or complaints such as vestibular dysfunction) and extrinsic factors (focusing on the patient’s environment or medications).  Physical therapists should also be aware that certain types of medications can increase the risk of patient falls due to changes in a patient’s heart rate or blood pressure. In addition, specific diagnoses like cerebrovascular accidents, cardiovascular disease, depression, dementia, osteoarthritis, osteoporosis, Parkinson’s disease, seizure disorders^6,7,13,14 and limb loss increase the risk for falls. The likelihood of falling rises with an increasing number of risk factors. Physical therapists should also realize that a majority of patient falls occur in resident rooms around the bed¹⁵ or in the bathroom.¹⁶

Body Systems Involved in Falls

Balance is defined as the ability to control and maintain one’s center of mass within one’s base of support. Three major systems are involved in the control of balance: the somatosensory, visual and vestibular systems. Input from all of these systems is interpreted by the central nervous system, which uses the information to modulate balance appropriately. When one of these systems is impaired, the two remaining systems compensate to help control balance. However, if two systems are impaired, there is a greater risk of loss of balance and patient falls.

The first system to respond to a loss of balance is the somatosensory system, followed by feedback from the visual and vestibular systems. While the somatosensory system provides a majority of CNS feedback when a patient is standing on a supportive surface, the vestibular system provides greater feedback when the visual system is compromised or if the individual is on a less stable surface. However, even when the somatosensory and visual systems are intact, an impaired vestibular system can cause symptoms of dizziness, vertigo, dysequilibrium, oscillopsia (blurred vision), and diplopia (double vision), which can affect balance and interfere with a person’s daily function.

Have you ever wondered how a dancer can dance with his or her eyes closed and without bumping into other members of a dance troupe? This ability is attributed to proprioception. Proprioception is defined as “the perception of joint and body movement as well as position of the body, or body segments, in space.”¹⁷ Proprioception is the sensation of limb and body awareness and movement. To perform an activity or movement, awareness of the position of the limb is important. Specialized nerve endings originate in joints, muscles, tendons, ligaments, capsules and the periosteum of bone. Golgi tendon organs and muscle spindles are proprioceptors. With the change in deformation of tissues during movement, the afferent nerve endings originating from the proprioceptors relay information to the CNS at various levels.

Proprioception is assessed in two ways: measuring joint position sense and determining the sense of limb movement.¹⁷ When a therapist moves a patient’s extremity passively to a specific angle, the patient should be able to replicate the same joint angle on the unilateral and contralateral side. This is referred to as joint position sense.¹⁷ Proprioception is documented as intact or impaired. There are no scales available for therapists to determine or monitor meaningful proprioceptive change. Sense of limb movement, or joint kinesthesia, detects passive movement, including the direction and velocity of a limb.¹⁷ Both components of proprioception generate smooth and coordinated movement, maintain normal body posture, regulate balance and assist in motor learning.¹⁷ Without proprioception, there is a delay in the onset of movement and joint trajectory formation is both impaired and inaccurate.¹⁷

The somatosensory system contributes a great amount to balance control.¹⁷ One study found that participants, regardless of age, were more dependent on proprioception than on vision to maintain balance.¹⁸ Normal aging results in a decline of lower-limb proprioception at central and peripheral levels, resulting in impaired balance and a higher incidence of falls.¹⁷ Several studies conclude that a decline in proprioception in older adults is secondary to changes in muscle spindle function. Also, normal aging results in deficits in the processing of sensory input due to myelin abnormalities, axonal atrophy or a decline in nerve conduction velocity.¹⁷ In older adults, there are a fixed number of motor units, which are composed of both smaller and larger motor units, but with aging, motor unit reorganization may occur.¹⁷ The reorganized motor units have adverse effects on muscle force production and total muscle force, which affects proprioception. At the central processing level, aging results in a loss of dendrites in the motor cortex, loss of neurons and receptors, and neurochemical changes in the brain, which affect neural sensitivity.¹⁷ Studies indicate that older adults compensate for the decline in proprioception via peripheral inputs by increasing sensitivity of central input. This creates decreased perceptive errors during balance control.

Literature suggests that older adults who cannot recover from a trip in 145 milliseconds are more likely than other adults to lose balance, resulting in fall.¹⁹ Research also indicates that in older adults, predominant changes in proprioception occur from a distal to proximal direction; this is attributed to a reduction in the rate of axonal transport.²⁰ Thus, impaired proprioception in older adults results in a decrease in the detection of positional changes, which affects neuromuscular control and increases the incidence of falls.

The visual system is also responsible for balance control. This system provides cues related to body position and assists in perceiving motion. Errors in perception of these cues result in sensory conflict and impaired balance. When an individual’s eyes are closed, there is a significant increase in postural sway. Postural sway also increases when there are misleading visual cues due to moving visual fields. The fovea, which is the center of our visual field, helps us focus on specific objects within the field. The position of the fovea is important for maintaining balance.

This figure was published in Neuroscience Fundamentals of Rehabilitation, 2nd ed. Lundy-Ekman, Laurie. Figure 15-1 page 351. © Elsevier (2002). Reprinted with permission.

Six different muscles are attached to each eye and act as antagonists. The three most important oculomotor control systems of the eye musculature are the smooth pursuit system, the saccade system and the optokinetic system.

The smooth pursuit system keeps the fovea fixed on a moving object. It is responsible for calculating how fast an object is moving and then moving the eyes appropriately. The saccade system repositions the fovea from one object to another in the visual field. This involves fast, accurate and simultaneous movement of both eyes. The optokinetic system holds images stable during head or body rotation. A combination of smooth pursuit followed by fast, corrective saccades helps in maintaining visual field stability.

Older adults have decreased pupil size and receive approximately one-third of the light into the eye compared to younger adults. With normal aging, the photoreceptors may become abnormally oriented and disarranged, and therefore are less responsive to incoming light and more responsive to scattered light, which is perceived as glare. An example of age-related visual change is difficulty in discriminating colors, especially pastel shades. Impaired color discrimination affects contrast sensitivity, which makes it difficult to determine the boundaries of objects. Also, visual acuity is negatively affected with aging.

Cataracts, glaucoma and macular degeneration are examples of age-related disorders; however, diabetic retinopathy can be a consequence of diabetes at any age. Older adults may not be able to distinguish between age-related and disease-related impairments and may fail to seek appropriate healthcare follow-up. Visual system disorders adversely affect the information being sent to the CNS, resulting in dizziness, unsteadiness and an increased risk of falls.

In the United States, approximately 35% of people over the age of 40 with vestibular dysfunction and dizziness have an increased risk of falls by a factor of 12.²¹ In addition, patients with vertigo as a result of vestibular dysfunction report a greater level of handicap on the Dizziness Handicap Inventory compared to patients with vertigo of a nonvestibular cause.²² Therefore, it is important for physical therapists to try to determine the etiology behind complaints of dizziness in order to formulate the appropriate plan of care, as well as to differentiate between dizziness (a general feeling of disorientation or lightheadedness), vertigo (a feeling of spinning) and dysequilibrium (a feeling of imbalance).²³

The vestibular system and dysfunction can be daunting to understand, but given the growing wealth of evidence to support the use of vestibular rehabilitation, knowledge of basic concepts can aid in the treatment of patients with balance disorders due to vestibular dysfunction.

The vestibular system consists of three major components: the peripheral sensory apparatus in the inner ear, the central processing system in the vestibular nuclei in the brainstem and cerebellum, and the motor output system. The primary function of the peripheral vestibular system is to detect head position and movement and to send the information to the CNS via the vestibular nerve. The vestibular nuclei process incoming sensory signals and outgoing motor signals. Information is also processed by the cerebellum, which monitors performance and makes modifications. The cerebellum is responsible for maintaining vestibular ocular reflex gain (the ratio of eye movement to head movement during rotation of the head while the eyes maintain a fixed gaze on an object), adjusting duration of VOR and controlling the vestibulospinal reflex. The motor output system is comprised of the VOR and VSR. The VOR maintains gaze stability during movement of the head. The peripheral sensory apparatus senses rotation of the head in one direction and send signals to the vestibular nuclei, which then relay information to the ocular motor nuclei. The ocular motor nuclei send signals to the ocular muscles via cranial nerves III, IV and VI to elicit the appropriate eye movement. In normal conditions, the VOR gain is equal to 1.0, meaning that, with head rotation in one direction, the same degree of eye movement should occur in the opposite direction when maintaining a fixed gaze on a target. The purpose of the VSR is to maintain posture and balance. The peripheral sensory apparatus detects changes in position and sends the information to the central vestibular system, which then sends motor output signals to the anterior horn cells of the spinal cord via the medial and lateral vestibulospinal tract to activate or inhibit appropriate extensor muscles.²³ For example, when the peripheral sensory apparatus detects head tilting to the right, the VSR causes the trunk extensor musculature on the right to activate and the flexor musculature to activate on the left in order to maintain postural stability.

Vestibular Dysfunction

Disorders of the vestibular system can occur in the peripheral vestibular system or in the central vestibular system. Vestibular dysfunction can also occur unilaterally or bilaterally. Peripheral disorders can be further classified according to type of dysfunction.²⁴ Vestibular hypofunction or reduced vestibular function occurs when the sensitivity of the peripheral sensory apparatus is impaired. A peripheral sensory apparatus is located in each ear and is responsible for detecting linear acceleration and angular velocity of the head, in addition to orienting the head in relation to gravity. Each peripheral sensory apparatus is composed of a membranous labyrinth within a bony labyrinth in the temporal bone of the skull. The membranous labyrinth consists of five sensory organs: the three semicircular canals and the two otoliths.²³ The semicircular canals are arranged at right angles to each other and are named for their orientation in relation to the head: anterior, posterior and lateral (or horizontal). The anterior canal sits 45° anterior to the sagittal plane, the posterior canal sits 45° posterior to the sagittal plane, and the lateral canal sits 30° tilted upward from the transverse plane. Due to their orientation, the function of the semicircular canals is to detect angular velocity of the head. Hair cells in the sensory organs are displaced during head movement, causing transduction of a signal that produces neural firing of the vestibular nerve, thus sending an afferent signal to the CNS.²⁵ The otoliths are comprised of the saccule and the utricle. They are responsible for detecting linear acceleration of the head, as well as static tilting of the head in relation to gravity. The saccule detects vertical acceleration and the utricle detects horizontal acceleration. Otoconia are calcium carbonate crystals that are embedded in the otolithic membrane, which overlie in the walls of the otoliths. The otoconia provide mass to the otoliths, thus making the otoliths sensitive to gravity and linear acceleration.²⁶

The asymmetry of signals produced by the peripheral sensory system with a unilateral peripheral vestibular hypofunction can produce vertigo, impaired gaze stability and dysequilibrium. Specific etiologies include acoustic neuroma, labyrinthitis, vestibular neuronitis, vascular ischemia, trauma, hair cell damage cause by ototoxic drugs (e.g., various chemotherapy drugs) and age-related hair cell degeneration. Symptoms of bilateral peripheral vestibular hypofunction include marked dysequilibrium, ataxia and oscillopsia. Because vertigo is a result of asymmetry of signals, it is not usually present in bilateral dysfunction. Dysequilibrium is typically more severe in bilateral dysfunction because of the lack of peripheral input, resulting in an inability to compensate.²³

Distorted vestibular function occurs when there is an inaccurate detection of sensory stimuli, usually due to a mechanical disruption caused by dislodged otoconia from the otoliths, which occurs in benign positional paroxysmal vertigo (BPPV). Two types of BPPV can occur: cupulolithiasis and canalithiasis. At the end of each semicircular canal is an area with a widened diameter called the ampulla. Within each ampulla, the hair cells rest on tissue called the crista. A flexible membrane called the cupula overlies the crista and closes off the ampulla from the vestibule. In normal conditions, the cupulae and the semicircular canals are not gravity sensitive.²⁷ In cupulolithiasis, the otoconia get displaced into either the cupula or one of the semicircular canals, causing signals to be inaccurately transduced in response to gravity. In canalithiasis, the dislodged otoconia become free-floating in the endolymphatic fluid.²⁸ Canalithiasis is much more common than cupulolithiasis.

Fluctuating vestibular function occurs during occasional disruptions in function in the peripheral sensory apparatus. Common etiologies include endolymphatic hydrops (Meniere’s disease), in which there are fluctuations in fluid and electrolytes, and perilymphatic fistula, in which there are fluctuations in pressure caused by an opening in the round or oval windows. Symptoms are episodic and can include vertigo or generalized dizziness, tinnitus and dysequilibrium.²³

Central vestibular disorders can occur with a lesion to the vestibular nuclei in the pons and the medulla, the cerebellum or any of the vestibular pathways. This type of lesion can occur in ischemic or hemorrhagic cerebrovascular accidents, vascular occlusions or dissections of the basilar or vertebral arteries, tumors and demyelinating disease such as multiple sclerosis.²⁹ Symptoms can include vertigo, nausea, severe dysequilibrium, multidirectional nystagmus and ataxia, as well as other neurological signs such as hearing loss, tinnitus, visual field deficits, diplopia, oscillopsia, impaired smooth pursuit eye movements, impaired VOR cancellation, impaired sensation and hemiplegia.^23,29

The Limits of Stability and Compensatory Strategies

All individuals have a limit of stability, which is the maximum distance persons can shift their weight around their center of gravity without leaning over, taking a step or losing their balance. The body uses three strategies to maintain balance: ankle strategy, hip strategy and stepping strategy. An ankle strategy is used for slow, small center-of-gravity displacements, where the feet remain planted on the ground and the body rotates around the ankle in order to reestablish balance. The distal muscles should be activated before the proximal musculature. A hip strategy — where the proximal muscles are activated before the distal muscles — is employed for faster, larger perturbations or when the individual is standing in a narrower base of support. A stepping strategy is reserved for large perturbations where the ankle or hip strategies would be ineffective in maintaining standing balance. These strategies are automatic and usually occur 85 to 90 milliseconds after the body recognizes the instability. In addition, a suspensory strategy is when an individual lowers his or her center of gravity during standing or ambulation to better control the center of gravity. This strategy consists of an anterior trunk bend with hip and knee flexion, which may progress to the individual assuming a squatting position in order to recover balance. In older adults, strategies may be ineffective and lead to falls secondary to age-related or pathological changes. Furthermore, the direction of the perturbation will influence which strategy the body employs.

Age-related and pathological changes affect a person’s limits of stability and ability to recover balance. These changes may include a delay in amplitude of muscle response to a perturbation, a reverse in the sequence of muscle activation, co-contraction of agonist and antagonist muscle groups, weakness in the distal musculature of the lower extremities and sensory cue alteration. Therapists may notice that older adults activate their hip musculature before their plantarflexors and dorsiflexors during an ankle strategy or that they activate their distal muscles before their hip muscles during a hip strategy. When completing evaluations, therapists should be sensitive to patient impairments that will influence balance, such as decreased strength, decreased range of muscle, poor coordination, altered proprioception and impaired sensation. There are helpful mnemonics that may assist practitioners in recalling and assessing risk factors.

Conclusion

It is important for physical therapists to understand the importance of patient falls, be able to identify fall risk factors and realize that several etiologies may account for patient complaints of dizziness. Therapists should be attentive to inquiring and documenting these factors when completing medical screens or evaluations. Furthermore, an understanding of the anatomy of the somatosensory, visual and vestibular systems can aid therapists in determining if dysfunction is present. This dysfunction may be due to normal, age-related physiological change, or due to pathology.

Part II of this module will emphasize evidence-based assessment tools for the evaluation of dizziness, vestibular dysfunction and falls. In addition, the module will review existing fall prevention guidelines and therapy interventions to improve balance and decrease the risk of patient falls.

Gannett Education guarantees this educational activity is free from bias.