Instrumented Gait Analysis

Original Editor - Mariam Hashem

Top Contributors - Mariam Hashem, Jess Bell, Aminat Abolade, Kim Jackson, Tony Lowe and Tarina van der Stockt

What is Normal Gait?

Normal gait is a range of typical gait patterns, found in a healthy population, presenting similar characteristics. People present a certain degree of variability that is called inter-subject variability and is due to differences in age, gender, muscular strength and anatomical differences.

For example. if we are to assess the gait of an 80-year-old man and a 20-year-old woman, both without any pathologies affecting gait. They might present completely different gait patterns. However, they will both be considered physiological or normal because their gait patterns will be within the range of normality corresponding to their own population. So when assessing the gait of a patient in physiotherapy, the idea is to confront the gait parameters we find with our own patient against the range of normality established for the corresponding population.

Visual Gait Analysis

A commonly used method by physiotherapists to investigate gait problems with their patients using a smartphone or any video recording instrument.

Pros:

• Allows peer-reviewing, by showing your colleagues the videos and discussing the presented case
• Reproducible, by taking multiple videos you can track your patient's progression
• Allows observing the gait from multiple angles to detect deviations in multiple plans

Cons:

• Has poor reliability
• It doesn't allow observing high-velocity events, force in moments during walking.
• Subjective, It depends on the observer therefore prone to error

Instrumented Gait Analysis

Refers to the collection of quantitative data related to the gait of our patients, such as videography, kinematics, kinetics, oxygen consumption, and electromyography.

Literature suggests that instrumented gait analysis is a valuable tool in clinical practice for the diagnosis, the assessment, and the management of patients affected by conditions altering gait. And in the research field, instrumented gait analysis is often used to evaluate the effectiveness of treatments such as foot orthoses and to explore the consequences of pathologies related to gait, like Rheumatoid Arthritis.

• To apply to clinical practice
• To get familiar with the terminology that is often used in research publications and scientific articles

To ensure the reliability of the results, which refers to the consistency of the results across multiple repetitions and within a cohort of subjects that present with similar characteristics the following must be considered:

• Inter-subject variability
• Within-subject variability, which refers to the possibility of obtaining slightly different results with the gait parameters on two different trials, with the same person. This can be caused by small changes in one person's gait from one trial to another due to, for example, stress or apprehension or the desire of the patient to do his best performance. Also, it can be caused by the measurement techniques which give slightly different results under the same conditions

Reliability is very important when it comes to gait analysis to ensure that the results of either clinical or research analysis can be generalized to other conditions.

Electromyography

Electromyography (EMG) refers to the measurement of the electrical activity of a contracting muscle. It measures the electrical, but not mechanical information. Electromyography does not give information about:

• The type of contraction (concentric, eccentric or isometric)
• The force produced by the muscle during this contraction.

However, EMG facilitates the understanding of the onset of contractions. This is made by recording the signal's magnitude and frequency of the muscles and refers to the amount of electrical activity during the contraction and the range of firing rates of the bar units that are being recorded.

Methods used to record muscle activity:

1. Invasive methods with a fine wire and needle, but are not really appropriate for gait analysis.
2. Surface EMG, which is the most commonly used method to record muscle activity during gait. Surface EMG is a non-invasive method, so it's really well tolerated by patients. It can be wireless, and there are various protocols that describe the correct placement of the electrodes to record the muscle activity of muscle groups. So it's a little less precise than other methods, but usually plenty sufficient for gait analysis.

?guidelines describe clearly the different steps to get reliable measurements of electromyography such as electrode shape, type, size, placement and the different processing of the initial signal that you have to do before being able to interpret data.

Prior to the gait analysis, begin by recording maximal voluntary contraction. This allows you to normalize the data in percentage to this electrical activity obtained with a maximum voluntary contraction. Once recorded the electrical activity is also normalized to a full gait cycle from zero to 100%. And sometimes it can be normalized to only the stance phase, the time that the patient has his foot on the ground.

So once you have your data normalized to the maximal voluntary contraction and presented from zero to 100% of the gait cycle, you can see if the muscle you've been recording is active or not throughout the gait and at selected moments/phases of the gait cycle, or not. For example, some research suggests that patients with Rheumatoid Arthritis and pes planovalgus or flatfoot, have increased activation in Tibialis Posterior during the stance phase, and this muscle is known to be physiologically maintaining the longitudinal medial arch of the foot during stance phase. The over-activation of this muscle could be compensation, done unconsciously by the patient, to prevent the sagging of the arch during weight-bearing in the stance phase.

Kinematics

Kinematics refers to the characterization of the movement of the different body parts, usually the legs. We also use a representation in segments. such as foot, knee, hips, and trunk.

For the purpose of recording gait kinematics, we place different markers on the patient's body. These markers are reflective, meaning that the position and the timing of walking are recorded by different cameras that are placed all over the laboratory. Then the position of the markers is integrated into a computer, which allows a 3D representation of the patient's walking, as well as the velocity and the acceleration of different body parts.

The kinematic data provides realtime precise information on the position of the joints during gait. For example, patients with Rheumatoid Arthritis have shown flat feet, excessive dorsal flexion of the ankle, as well as increased valgus of the ankle in the frontal plane during the stance phase. With kinematic data, It is also possible to obtain a level of precision up to one degree for a joint's range of motion or one millimeter for example, like a marker placed on a bony reference.

kinetic data

This refers to the characterizations of forces and moments applied to the patient while walking. For example, the ground force reaction or plantar pressure.

Kinetic data can be recorded with different methods:

The forced platform, which is usually used to characterize the different components of the ground force reaction. Special pressure sensitive insoles that can be used to calculate plantar pressures. For each studied reaction, it is possible to isolate values that have a clinical meaning. For example, when recording plantar pressure, it is possible to isolate values like the peak pressure or the time during the peak pressure is applied. The literature has shown an association of the development of ulcers, with people with certain values that are quite high.

The integration of kinetic, kinematic data as well as anthropometric values using a computer model that calculates the different moments and power produced and applied during gait. For example, researchers have been able to demonstrate that below-knee amputees using a ..... foot with a classic prosthetic leg, have a decrease in 50% in ankle power generation at the toe-off moment in the walking cycle.

Energy Expenditure

And the literature suggests that the best way to calculate energy expenditure is by calculating the oxygen uptake and carbon dioxide production as they reflect the patient's metabolism chemistry.

To obtain this, the patient wears a face mask, usually very uncomfortable, and they are asked to walk around while wearing the mask, The consumed oxygen and produced carbon dioxide are then calculated.

Conclusion

Instrumented gait analysis can be a valuable tool to quantify gait parameters. It is true that it is mostly applied in the research field to date, but we can hope, with the simplification of technology, it will be more available to a large number of physiotherapists in their day to day practice. As an alternative to instrumented gait analysis, visual analysis supported by video recording is a valuable tool to assess our patient's gait. And even better if we can include a validated tool like the gait deviation index that allows more reproducibility and are less observer-dependent.