Biomedical Engineering Reference
In-Depth Information
protocols for the use of the equipment continue to develop. The validity of these protocols
and associated models and the care with which they are applied ultimately dictate the
meaning and quality of the resulting data provided for interpretation. This is one area in
which engineers in collaboration with their clinical partners can have a significant impact
on the clinical gait analysis process.
Generally, data collection for clinical gait analysis involves the placement of highly
reflective markers on the surface of the patient's skin. These external markers reflect light
to an array of video-based motion cameras that surround the measurement volume. The
instantaneous location of each of these markers can then be determined stereometrically
based on the images obtained simultaneously from two or more cameras. Other aspects
of gait can be monitored as well, including ground reactions via force platforms embedded
in the walkway and muscle activity via electromyography with either surface or intramus-
cular fine wire electrodes, depending on the location of the particular muscle.
In keeping with the other material presented in this chapter, the focus of this section will
pertain to the biomechanical aspects of clinical gait analysis and includes an outline of the
computation of segmental and joint kinematics and joint kinetics, and a brief illustration of
how the data are interpreted.
4.6.1 The Clinical Gait Model
The gait model is the algorithm that transforms the data collected during walking trials into
the information required for clinical interpretation. For example, the gait model uses the data
associated with the three-dimensional displacement of markers on the patient to compute
the angles that describe how the patient's body segment and lower-extremity joints are
moving. The design of the gait model is predicated on a clear understanding of the needs of
the clinical interpretation team—for example, the specific aspects of gait dynamics of interest.
To meet these clinical specifications, gait model development is constrained both by the tech-
nical limitations of the measurement system and by the broad goal of developing protocols that
may be appropriate for a wide range of patient populations that vary in age, gait abnormality,
walking ability, and so on. An acceptable model must be sufficiently general to be used for
many different types of patients (e.g., adults and children with varying physical and cognitive
involvement), be sufficiently sophisticated to allow detailed biomechanical questions to be
addressed, and be based on repeatable protocols that are feasible in a clinical setting.
4.6.2 Kinematic Data Analysis
Reflective markers placed on the surface of the patient's skin are monitored or tracked in
space and time by a system of video-based cameras. These marker trajectories are used to
compute coordinate systems that are anatomically aligned and embedded in each body seg-
ment under analysis. These anatomical coordinate systems provide the basis for computing
the absolute spatial orientation, or attitude, of the body segment or the angular displace-
ment of one segment relative to another, such as joint angles. For this analysis, at least three
noncollinear markers or points of reference must be placed on or identified for each body
segment included in the analysis. These markers form a plane from which a segmentally
fixed coordinate system may be derived. Any three markers will allow the segment motion
to be monitored, but unless these markers are referenced to the subject's anatomy, such
