8.3 Proprioceptive, Balance, and Sensorimotor Re-education

Proprioceptive, Balance, and Sensorimotor Re-education

Postural control uses sensory information and coordinated movement to stabilize the body during standing and functional tasks. In quiet stance, control relates the center of mass to the base of support. During movement, momentum and the ability to change the base by stepping also matter.

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The Sensorimotor Triad

The central nervous system relies on sensory input from three distinct afferent systems to maintain equilibrium and coordinate postural adjustments:

1. The Somatosensory System

• Mechanoreceptive Input: Provides information regarding body position, movement, and joint orientation relative to the supporting surface.
  • Muscle spindles signal muscle length and change in length. Group Ia primary afferents are sensitive to changes in length and also carry length information. Group II secondary afferents contribute especially to sustained length information.
  • Golgi tendon organs send force-related feedback through group Ib afferents. Their influence on motor output depends on the task and other inputs to the spinal circuit.
  • Joint afferents provide information about mechanical loading and movement in joint tissues, with some responding near the limits of motion.
  • Plantar skin afferents include fast- and slow-adapting receptors. They signal contact and pressure changes as the foot interacts with the support surface.
• Dominance: When the support is stable, surface and joint cues can provide a strong reference. Their relative weighting can change with the task and surface.

2. The Visual System

• Spatial orientation: Visual landmarks and optic flow contribute information about body motion and the environment. Vision also helps identify obstacles before movement.
• Contribution: Visual cues can receive greater weight when surface cues become less reliable. A moving or misleading scene can also disturb balance.

3. The Vestibular System

• Gravitational Reference Frame: Provides information about head rotation, translation and orientation in gravity for integration with other sensory cues.
  • Semicircular Canals (Horizontal, Anterior, Posterior): Endolymph motion during head rotation deflects the cupula. The three canal planes are approximately perpendicular.
  • Otolith Organs (Utricle and Saccule): Calcium carbonate otoconia load the sensory membrane, allowing the otolith organs to respond to linear acceleration and gravity. With the head upright the utricle is particularly responsive to horizontal acceleration and the saccule to vertical acceleration.
• Contribution: Vestibular information becomes especially important when vision and reliable surface cues are limited. Performance still depends on the overall postural control system.

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Clinical Assessment: The CTSIB / "Foam and Dome" Test

The original Clinical Test of Sensory Interaction on Balance (CTSIB) compares timed standing across six combinations of surface and vision. A visual conflict dome changes the visual reference, and foam changes the reliability of surface cues. Guard the patient and record stance position, surface, time and reason for ending a trial. Foot position and foam characteristics can affect performance.

The modified CTSIB (mCTSIB) uses firm eyes open, firm eyes closed, foam eyes open and foam eyes closed, in that order. Foam with eyes closed is condition 5 on the full test and condition 4 on the modified version.

A patient who stands steadily on firm ground and on foam with eyes open but steps or needs support on foam with eyes closed has difficulty under that combination. It raises the demand on vestibular input, while somatosensory function, strength, stance and other factors can affect performance. Compare the other conditions and the history before choosing further balance, neurologic or vestibular testing.

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Automatic Postural Control Strategies

Horak and Nashner observed characteristic responses to platform translations. The available support affected the movement pattern. Distinguish the direction the platform carries the feet from the direction the body initially sways relative to the feet.

Classic ankle-dominant responses on a firm, long platform
Platform moves backward → initial forward sway  → posterior muscle sequence
Platform moves forward  → initial backward sway → anterior muscle sequence

Patients can combine ankle and hip motion, and activation timing varies with the perturbation and the individual. A compensatory step can begin while the center of mass is still within the original base. Active knee and hip flexion can also lower the body when a task calls for a crouched position.

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Sensorimotor Rehabilitation Progression

Select the task and support based on the patient's impairments, symptoms, fall risk and goals. Guard the patient and provide a handhold or other support when appropriate. Adjust one challenge at a time so the reason for a change in performance is clear.

1. Base and reaching: Start with a stance the patient can control. Narrow the base, reach within it, or practice stepping as tolerated.
2. Surface and sensory cues: Move from a firm surface to a compliant one if it serves the goal. Briefly reduce vision or add head turns when appropriate. Use a safe setup and watch symptoms.
3. Anticipatory and reactive balance: Practice self-initiated reaching or stepping. Add controlled external perturbations with appropriate protection when reactive stepping is a goal.
4. Dual-task practice: Add a functional task such as turning while carrying an object or walking while talking. Compare both task performances with single-task performance and adapt if safety declines.

For a patient with chronic ankle instability who wants to manage uneven ground, begin with supported single-leg stance and a short reach if tolerated. Progress to a step and controlled landing when the patient can perform the simpler task safely. Reassess the original activity goal alongside the balance task.

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Stages of Motor Learning (Fitts & Posner)

Motor learning refers to a relatively durable change in skill from practice. Use a later retention trial and, when useful, a related task to assess transfer. The Fitts and Posner stages describe changes in attention and execution as a person becomes more skilled.

A patient may be at different stages for different tasks. In early practice after knee arthroplasty, first check pain, quadriceps activation and any operative restrictions. If the patient is cleared and has adequate strength but is working out an unfamiliar movement, demonstrate it and simplify the initial practice.

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Augmented Feedback Schedules and the Guidance Hypothesis

Intrinsic feedback is sensory information from the movement itself. Augmented feedback is information supplied by a clinician, device or other external source.

• Knowledge of results (KR) describes the outcome, such as how far a step landed from the target.
• Knowledge of performance (KP) describes the movement, such as how the knee moved during landing.

Frequent cues can help the patient understand a new movement or practice safely. In some experiments, less frequent feedback supported performance at delayed retention tests. The guidance hypothesis proposes that some feedback schedules can encourage reliance on external cues. Match the schedule to the task and the patient and check performance again with fewer cues.

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Practice Organization and Scheduling

Blocked practice repeats the same task before moving on, such as three reaches to one shelf height followed by three to another. Random practice mixes the order of several tasks or variants. In classic experiments, interleaving made practice more challenging and improved some later retention and transfer outcomes. A stroke study found better retention for one practiced upper-limb sequence under random practice. Choose the order according to task difficulty, patient capacity and the goal. Check later performance rather than inferring learning from accuracy during practice.

Massed and distributed practice differ in the amount of rest relative to practice. Choose rest intervals to preserve safe, useful repetitions. A patient who loses movement quality with fatigue may benefit from shorter bouts with rest.

Part and whole practice differ in how much of the task the patient performs at once. A patient may rehearse positioning a wheelchair before attempting a whole transfer. When components depend strongly on one another, practice a safe version of the whole task to preserve coordination and timing.