Computerized Dynamic Posturography for Postural Control Assessment in Patients with Intermittent Claudication

The overall goal of this procedure is to assess a patient's balance objectively with the use of computerized dynamic posty through two diagnostic tests. This is accomplished by first ensuring the dual force plate support surface and visual surround are calibrated. The second step is to position the patient's feet correctly on the support surface and to secure the patient by attaching the safety harness to the safety bar.

Next, the sensory organization test and the motor control test are performed. The software automatically computes the patient's score and variables of interest relative to an age-matched normative data set. The final step is to assist the patient down from the platform and discuss their results.

Ultimately, computerized dynamic posty is used to identify possible deficits in the somatosensory visual or vestibular systems, and can also determine if a patient has a visual preference by relying on visual information even when it is inaccurate. The main advantage of this technique over existing methods is that computerized dynamic posty can measure balance objectively and it can quantify postural strategies in both static and dynamic conditions. It is intended to complement existing clinical outcome measures that categorize mechanisms of balanced disorders.

Visual demonstration of this method is critical because it is important for the investigator to understand the sequence of events. These include stable versus unstable support surfaces, static versus dynamic conditions, eyes open versus eyes closed, and conditions that are graded in magnitude. A PhD student from my laboratory, AMIA gang, will be demonstrating the protocol on the EQU test.

Ensure the area surrounding the EQU test is free of obstructions and remove any object from the dual force plates before turning on the EQU test system. Next, complete the dual force plate support surface and visual surround calibration. The dual force plates first rotate about the X axis so as to facilitate ankle dorsiflexion and plantar flexion at a maximum angular velocity of 50 degrees per second.

They then translate forwards and backwards about the Y axis, which is parallel to the floor at a maximum linear velocity of 15.24 centimeters per second. The visual surround tilts forward and backward about the x axis at a maximum angular velocity of 15 degrees per second across a range of plus or minus 10 degrees. Enter the participant information into the software program, indicate their age and height accurately.

The participant's results will be compared against an age matched normative data set. Choose whether to turn the display screen within the visual surround on or off. If the display screen is turned on, the participant will get real time visual biofeedback about their center of gravity movement.

This may be useful for practice sessions or when the operator wants the participant to see their score. Request that the participant wears comfortable loose clothing and removes their shoes for tests. On the EQU test, have the participant put on the safety harness while securing the long straps through their legs and fastening the waist buckle position the participant onto the dual force plates and clip the carabiner from the safety straps into the D-rings of the security harness.

The participant is now securely fixed to the safety bar, which will prevent them from actually falling should they lose their balance. During the testing center, the participant's feet on the support surface by positioning the medial malleolus of each foot over the black horizontal line so that the ankle joint is aligned with the transverse rotational axis. Position, the lateral side of the calcaneus according to the small, medium, or tall surface markings.

When the participant is standing with ankles over the black horizontal line and with feet equidistant laterally from the center line, according to the small, medium, or tall markings, their center of gravity should be located directly above the x and y axes intercept. This position acts as a reference point for the calculation of sway angles. Ask the participant to stand upright with their hands at their sides looking straight ahead at the visual surround request.

They refrain from moving their feet for the duration of the test. If the feet are correctly positioned. The center of gravity display should illustrate the stick figure at the intersection of the x and y axes.

However, if the stick figure is misaligned and the feet are correctly positioned, do not readjust the feet. The sensory organization test or SOT consists of six conditions, each comprised of three trials lasting 20 seconds each. The first three conditions are performed on a static support surface.

While the last three conditions use a dynamic support surface first complete condition, one where the participant stands quietly with eyes open, then complete condition two, where the participant stands quietly with eyes closed. Conditions one and two, establish weather sway increases when visual cues are removed and determines how effectively the participant makes use of somatosensory input. Interrupt any trial at any time if the participant looks like they require assistance.

Also allow the participant to rest in between trials if necessary and accurately reposition feet afterwards. Next, perform condition three where the participant stands with their eyes open. The visual surround is sway referenced and visual cues become inaccurate.

In condition four, the support surface is sway referenced. Thus somatosensory cues become inaccurate. Condition five is performed with eyes closed and a sway referenced support surface.

This determines how the participant makes use of vestibular cues when visual cues are removed and somatosensory cues are inaccurate. Finally, perform condition six where the visual surround and support surface are both sway referenced. This condition identifies if the participant relies on visual cues, even when they're inaccurate.

Evaluate the score After each trial. A green or red bar will appear displaying the participant's equilibrium score relative to the age-matched normative dataset. Green bars indicate the participant performed better than the age-matched normative data while red bars indicate their performance was worse.

Mark any trial where the participant takes a step touches the visual surround or starts to fall as a loss of balance, complete all six protocols on the motor control test or MCT, including three forwards and three backwards translations that are graded in magnitude as small, medium, and large ensure the feet are positioned precisely on the support surface. The MCT automatically starts with three small backwards translations during which time the support surface will translate backwards only minimally. The next series of translations become progressively greater so as to generate a maximal response during the large translations.

Each translation occurs at a constant velocity and therefore transfers constant forward or backward angular momentum to the patient's body, assist the participant down from the platform. Following the completion of the SOT and MCT finally discuss the implications of the findings by explaining how they performed overall on the SOT and MCT. A typical interpretation of the equilibrium score, sensory and strategy analysis and center of gravity alignment from the SOT for one single participant is illustrated here.

The green bars indicate the participant performed better than the age matched normative dataset on conditions one through four. The participant scored worse than the normative dataset in the last trial for condition five and the first trial in condition six. However, the composite score indicated the participant had a normal equilibrium score.

Overall, the sensory analysis results are shown here. The green bars indicate the participant did not have any deficits in the somatosensory visual or vestibular systems, and thus was able to make use of these sensory references adequately. The participant was able to discern between accurate and inaccurate visual information and scored better than normative scores on visual preference.

Strategy analysis results are presented here where each condition is indicated as a symbol. Large values indicated the participant used a predominant ankle strategy to maintain balance in those conditions. An ankle strategy is appropriate in response to small perturbations when corrective postural adjustments can be made by generating a small torque about the ankle joint to realign the center of gravity.

Conversely, small values indicated the participant relied on a hip strategy for that condition. A hip strategy is necessary to generate a larger torque about the hip joint to reposition the center of gravity in response to larger perturbations. Whilst a stepping strategy quickly realigns the base of support to the rapidly changing center of gravity.

For example, this participant primarily used in ankle strategy in conditions one through three and a combination of ankle and hip strategies in conditions four through six, but the low strategy analysis score for one trial in conditions five and six indicated the participant's center of gravity was approaching their limits of stability as they were relying on a hip strategy to generate larger and faster postural corrections about the hip joint. The XY plot of the center of gravity alignment prior to the onset of the SOT condition is represented by various symbols here. Those outside of the white box are considered off-center and indicate under which conditions the participant is more likely to lose their balance if the postural disturbance is in the same direction as the alignment offset.

The results for the motor control test are presented here. Weight symmetry values during graded backwards and forwards translations reveal this participant have their weight relatively centered between the left and right legs prior to the onset of the support surface translation. This is evident as a score of 100 indicates perfect between limb symmetry.

The time lapse between perturbation onset and postural correction is presented in milliseconds.Here. In this case, the participant did not generate a sufficiently quick active force response with the left leg when subjected to medium and large translations in the backward direction, which explains the presence of the red bars. The four at the bottom of each bar specifies the reliability of the latency score.

In this case, four algorithms agreed on the same takeoff point. The data are considered highly reliable. Amplitude scaling or response strength reflects the participant's ability to generate a response that is in proportion to the perturbation.

It is scored in units of angular momentum and normalized to body height and weight. This participant exhibited good symmetry for both legs in the backwards direction, but the response strength was weaker for medium and large translations in the forward direction indicating the participant may be less effective at responding quickly to forwards perturbations Depending on the patient's physical ability and function. Once this technique is mastered, the sensory organization test should take approximately 15 minutes and the motor control test protocol should take approximately five to 10 minutes to complete.

This is if the patient doesn't rest in between the conditions and all the conditions are performed properly. Don't forget that when working with patients with balance impairments or suspected underlying medical conditions, it is important to establish a good rapport and to continuously monitor their physical ability and wellbeing. It is important to prevent an actual trip or stumble from occurring during testing.

Always assist your patient when stepping up onto and stepping down from the support surface.