What is Involved in a Clinical Gait Analysis Test? That is, How is it Performed?
As indicated above, clinical gait analysis involves the measurement of the patient's gait pattern with specialized technology. But pertinent medical history and physical presentation is documented as well. This collection of information provides the basis upon which treatment decisions are made.
Among the first "examinations" of the patient in the Gait Analysis Laboratory is the careful observation by the clinician (and simultaneous video recording from the side and front) of the patient, barefoot and, perhaps, in orthoses, as she/he walks along a smooth, level pathway. Videotape records provide a qualitative documentation of how a person walks, affording an opportunity to evaluate the "smoothness" or "fluidity" of a gait pattern. The ability to obtain close-up views of a specific motion and the use of slow motion greatly enhance the observer's ability to evaluate the patient's walking pattern. For example, close-up views of the feet provide a means to evaluate hind foot position and motion.
This initial videotape session is followed by an extensive physical examination of the patient's status at rest. The specific measurements depend somewhat on the pathology being evaluated. These measures may include the passive lower extremity joint motion, joint and muscular contracture, muscle strength and tone, bony deformity, and neurological assessment. This information may then be correlated with gait data to help determine the potential causes of the patient's gait deviations. However, the standard clinical examination used in isolation is limited in its capacity to offer diagnostic information because the effects of body position, gravity, and walking result in changes in functional demands that cannot be fully appreciated in a manual examination.
Motion and Muscle Assessment
Consequently, central to clinical gait analysis are the additional quantitative measurements of the patient's walking pattern provided from several different technologies.
1. Passive reflective markers are placed on the surface of the patient's skin and aligned with specific bony landmarks and joint axes. As the patient walks along a straight pathway in the laboratory (shown in Video 1 and illustrated in Figure 1), the locations of these markers are monitored with a three-dimensional motion data capture system comprising five or six special video cameras, all interfaced to a central controlling computer. Each of these cameras is equipped with a cluster of light emitting diodes (tiny light bulbs) that strobe the pathway with infrared light. The infrared light, which cannot be seen by the patient (and therefore does not distract the patient), is reflected by the markers back to the cameras. Computer programs allow the determination of the three-dimensional locations of the markers in space to within several millimeters based on the images of each pair of cameras, analogous to the way depth is perceived in human vision with two eyes. Marker position data allows for the mathematical computation of the angular orientation of particular body segments as well as the angles between segments (ie, joint angles), collectively referred to as "kinematics."
A depiction of the basic configuration of a quantitative gait analysis laboratory with passive reflective markers placed on patient walking along a straight pathway. Patient is monitored by force platforms mounted in the walkway and by an array of specialized video cameras that strobe infrared light (refer also to Video 1).
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Video 1. An example of motion data collection for a 35-year-old patient with Charcot-Marie Tooth. Issues concerning foot and orthotic wear were being addressed to improve the patient's stability in gait. Patient is walking with passive reflective markers along a straight pathway and is being monitored by specialized video cameras and force platforms mounted in the walkway (see also Figure 1).
2. Multi-component force platforms imbedded in the walkway provide a measure of the net reactions between the foot and the ground as the patient walks along the pathway (Video 1, Figure 1). These data may be assessed directly or used to calculate loads found in and across the joints of the lower extremity. These joint loads (referred to as "kinetics") are computed analytically from relationships drawn from physics that combine the simultaneously acquired kinematic information and estimates of limb mass and inertial properties.
3. Electrodes placed on the surface of the skin or inserted as fine wires (smaller in diameter than human hair) into specific muscles allow muscle activity (expressed as action potentials) to be monitored, again, as the patient walks along the laboratory pathway (Video 2) through an approach referred to as dynamic electromyography, or EMG. The EMG signal gives information concerning the "on-off" activity of a muscle. This information can be used with joint kinematic and kinetic results to better understand the patient's neuromuscular abnormalities.[1,4]
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Video 2. An example of electromyographic data collection for a 9-year-old patient with cerebral palsy spastic diplegia. This patient was referred to the gait laboratory for orthopedic surgical decision-making. Patient is walking while instrumented with surface electrodes to monitor muscle activity (dynamic electromyography).
Foot switches that indicate when the patient's foot is in contact with the floor may be incorporated into this process and used to identify the timing of the gait cycle. Other instruments such as plantar pressure measurement systems (pedobarographs) may be used in conjunction with the equipment listed above to gain a more complete understanding of the loading to the plantar surface of the foot during gait. Also, metabolic energy measurement systems are sometimes used to determine the energy consumption of the patient while walking.
A typical gait analysis test can take from two to four hours, depending on the particular evaluations performed and on the cooperation, behavior, and gait complexity (ie, involvement) of the patient. Usually a physical therapist or kinesiologist works directly with the patient and a more technically oriented person such as an engineer or technician manages the computer and measurement system operation during the test.
It should be noted that not all clinical gait laboratories operate in this fashion. Some do not have the technology to provide three-dimensional body marker data and analytical processes that produce three-dimensional joint rotations (flexion-extension, abduction-adduction, and internal-external rotation) for interpretation. These clinical gait analysis laboratories use less sophisticated technology that collects and processes motion data based on the assumption that all of the rotations occur in the sagittal plane of the body. This assumes that all motions associated with gait can be appreciated from a side view of the patient. While this might not be unreasonable in the analysis of normal ambulators (except perhaps for ankle/foot motion), it is clearly ill-advised for clinical decision-making in cases of pathological gait where three-dimensional motion is commonplace.
Moreover, at other facilities, a clinical gait analysis might be limited to a video recording and the measurement of certain gait stride and temporal parameters such as velocity, cadence, stride length, step length and percentage of stance/swing. While the video record is a useful tool in developing and substantiating visual impressions, it is inappropriate to "measure" joint and segment gait kinematics directly from the videotape or monitor, even though some commercially available hardware and software products do this. With respect to stride and temporal parameters, these are "outcome" measures and provide an indication of the level of function when compared to normal values. They do not, however, give an indication of the cause of the gait abnormality and are, consequently, of limited value in clinical decision-making.
Cite this: Clinical Gait Analysis and Its Role in Treatment Decision-Making - Medscape - Sep 01, 1999.