Looking for Better Balance Outcomes? Don’t Forget Your Patient’s “Sensory Side”

By Joseph Koley, PT, MPT
Physical Therapist

Students and newly graduated clinicians often tend to focus on their patient’s condition of muscle weakness in their plans of care. Rehabilitation professionals identify more with the role of helping their patients “get stronger” than they do with the “weak” patient who arrived on the first day. This can lead to a POC mainly focused on overcoming strength deficits in order to achieve improved function. Clinicians, especially PTs, can be indoctrinated in school to focus on the motor system. When asked “What does a PT know?” the answer is usually “movement,”

Strength is necessary, but not sufficient, for movement. Coordinated movement is only achieved with adequate sensory input. Think of a circle, with sensory input being used to drive motor output. The movement then changes the sensory environment. The new sensory input then drives continued motor output…on and on and on in a circle of a performance task over a measure of time.

This collaboration of sensory and motor is evident in human upright postural control or, more simply put, “standing balance.” The brain acquires sensory input through the three peripheral end-organ systems of vision, vestibular, and somatosensory. As a central processor of information, the brain combines, compares, and analyzes the input received. What results then, ideally, is an organized motor output to allow the person to maintain their balance, complete a task, or respond to a challenging environmental situation.

Digging Deeper into the Sensory Side of the Balance Equation

Consider the example of two people standing and maintaining their balance in the dramatically different situations described:

Two friends are at a lake. One friend is standing on a pier and the other friend is standing on a boat in the water at the end of the pier.

How does each person maintain their balance? Let’s start by assessing each person’s sensory input. The friend on the pier is standing on a flat, dry, smooth, wooden surface. His visual system sees several objects on the pier with him including a trash can and a light pole. These objects are static in comparison to him. But if he does sway forward briefly, he sees the trash can get visually closer to him. This reverses as he sways back away from it. His vestibular system also tells his brain he is not accelerating or decelerating in a straight line or rotation. Finally, his somatosensory system tells him that his feet are on a flat surface where he uses an ankle strategy (without even thinking about it!) to gently allow his center of gravity to move forward and backward, left and right on the surface of the pier.

His friend on the boat has a different experience. The boat is rocking up and down as the waves roll into the pier. She is on a flat surface, but it is wet. There is little visual feedback for her as she looks out over the water. The visual feedback she has of the boat is in symmetry with her own movement. Her vestibular system is noting the acceleration up, rest, then acceleration down as the boat moves up and down from the waves. Since the up and down movement is constantly changing, this is taking up most of her attention in maintaining her balance. Her feet also feel the boat push up against the plantar surface of her feet and then drop away with every wave big and small.

A third observer looking at each friend from a distance would see the friend on the dock very comfortable with keeping his balance and able to pay attention to other things — like trying to find his friend. The friend on the boat is in quite a different situation. She can stand and keep her balance, stepping every once in a while to maintain her posture. This keeps most of her attention, though. She can also grab onto the rail on the side of the boat. By holding the rail, she appears much more comfortable with her balance and can attend to looking for her friend on the pier.

In the example, each friend was able to maintain their balance regardless of the “sensory environment” they found themselves encountering. A clinician could draw the conclusion that each of their sensory systems of balance is intact. However, what if a clinician is asked to objectively test each system? What would be their approach?

How Physical Therapists Can Objectively Test the Sensory Side of Balance

Visual System

This test is the most straightforward. Everyone has experienced a visual acuity test with a Snellen chart at the doctor’s office. Clinicians usually ask patients about their vision: can you read the paper? Can you see the TV? And, maybe, when was the last time you had an eye exam? Although too detailed for this discussion, overuse of visual cues is actually an abnormal way a patient can keep their balance.

Vestibular System

This can be the least understood sensory input and, at times, most difficult to test clinically. Initially, a subjective vestibular assessment can be much less stressful for a patient. Questions like: “Do you ever feel yourself spinning when you are in bed or at the hairdresser?” can be a good lead-in to performing (or not performing-at least on the first visit) the Dix-Hallpike test.

“Have you ever been really ‘dizzy’ for an entire day? Were you so dizzy you couldn’t even get out of bed?” can be a good guide if you need to perform a head-thrust or DVA (Dynamic Visual Acuity) test.

Remember that you as the clinician do not have to fully understand the patient’s dysfunctions in one evaluation session. A practice pattern of stating “It doesn’t sound like you have trouble with your inner ear, but next time I will check to make sure” is a good strategy. Patients and families can be shown YouTube videos of Dix-Hallpike and Epley maneuvers to get them prepared for the next visit. Another consideration is that a positive vestibular test is usually a good sign that you have a patient condition that can be treated and improved!

Somatosensory System

This is possibly the most important of the three sensory systems. Consider the thought experiment of a theoretical patient without either a visual, vestibular, or somatosensory system. The patient without vision is “blind” but still able to balance in standing. The patient without the vestibular system may fall under certain conditions and may have needed to compensate for this over time but otherwise can be functional.

The patient with absent somatosensation (specifically in their lower extremities) is more than likely in a wheelchair. This is due to the fact that even when all three sensory systems are available, humans mainly rely on somatosensation for balance. Another way of saying this is that given all three inputs, the brain (central processor) mainly uses somatosensory cues to drive the motor system and to successfully maintain a person’s balance.

The somatosensory system is very susceptible to disease processes that impair its ability to function normally. Damage to this system is usually seen in degrees of clinical presentation and functional impairment. A patient with mild diabetic neuropathy may still “feel” some sensation in their feet as opposed to the severe neuropathy with “socks” distribution in bilateral insensate feet. Testing can be completed in several ways to assess for the absence or presence of clinical symptoms of pathophysiology and then to assess for the degree of impairment. Semmes-Weinstein monofilament testing, a tuning fork, or specific joint proprioception are all valid examples of these types of tests. With all of this testing involving the foot and ankle, it could be argued that a complete professional rehabilitation assessment always involves looking at your patient’s feet!

Don’t Forget to Assess Sensory Systems

In summary, when assessing a patient with reported falls, balance, or gait problems, be sure to fully assess the contribution of their sensory systems to their functional deficits. Familiarity and confidence with clinical tests such as Dix-Hallpike, DVA (dynamic visual acuity), and Semmes-Weinstein Monofilament will allow for the clinically excellent individual to more fully understand patient sensory impairments and drive a focused plan of care.