Optical and Electromagnetic Shape-Capturing Systems for Limb Anthropometrics
5.7 Practical Methods and Techniques
One of the advantages of digital shape capture of limb anthropometrics is the portability of digital fi les. With the traditional method described in Fig. 5.1 , the only complete record of limb shape and volume is the physical positive model. If the limb shape has been digitized, complete shape informa- tion is contained in a single computer fi le.
This portability has expanded the practicality of central fabrication in prosthetics and orthotics (Smith and Burgess 2001 ) . In this model, practitioners see patients at a different facility from the one in which components are fabricated. There are multiple potential benefi ts to a central fabrica- tion approach. Facility overhead is reduced, enabling the establishment of smaller offi ces in more locations, possibly reducing expense. However, the model does require close communication between practitioner and fabricator. In particular, anthropometric defi nitions must be clearly defi ned. A variable such as “residual limb length” is highly dependent on measurement technique.
Even if the proximal location from which length is measured is clearly specifi ed, results can vary widely. If the length is measured on the limb or on a positive model, one practitioner might align the caliper parallel to the long axis of the limb. Another might keep the caliper close to the surface
Fig. 5.7 Digital calipers. Confi guration of a magnetic fi eld contact scanner as digital calipers. The model reference sensor is used as an additional stylus. The system provides real-time feedback of the distance between the two sensors, and the dimension can be recorded by the system (following software modifi cation) by clicking the button marked with the black triangle on the stylus
125 5 Optical and Electromagnetic Shape-Capturing Systems for Limb Anthropometrics
of the limb. Still another might use a tape measure. If the same measurement is determined from a digitized model using anthropometric software, it is important to understand the technique employed by the software.
The portability of shape capture equipment has also found application in the developing world, where patient care is challenged by distance. With fewer fabrication facilities and increased diffi culty for patients to reach those facilities, portable anthropometric measurement can be the only feasible patient care solution. Because digital shape capture devices can be carried by the practitioner to remote locations and because they produce computer fi les that can be easily transferred to distant fabrication facilities, they provide a practical solution to challenging patient care.
Summary Points
Tools for digital capture of limb shapes have developed specifi cally for clinical use in prosthetics
•
and orthotics
Prosthetists and orthotists have need for measurements of limb length, circumferences at certain
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levels, and anterior–posterior and medial–lateral limb diameters Limb volume is important but not routinely quantifi ed
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Two primary technologies are used for digital shape capture: optical scanners and electromag-
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netic fi eld scanners
Accuracy of these devices has been independently assessed in the literature
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Magnetic fi eld-based systems have a potential application in clinical gait analysis for the routine
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recording of body segment parameters
Digitization of the limbs has advanced the concept of centralized fabrication of prosthetic and
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orthotic components
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Table 5.3 Key features of limb digitzation systems
Time for capture Digitization occurs in real time. Optical systems can capture a limb shape in less than 1 s. Contact scanners require contact with the entire limb surface area, which can take 2–3 min.
Landmarks and modifi cation
Optical systems automatically identify landmarks, which are in some cases special marks affi xed to the limb prior to digitization. Contact systems allow marker identifi cation using the stylus. Modifi cation can occur on the limb with contact scanners and in post-processing with both systems.
Patient involvement The limb must be held relatively still and extended with both technologies. A reference sensor in magnetic fi eld systems permits some patient movement within the magnetic fi eld. Most systems can be used with the limb in a variety of orientations.
Portability Both systems are portable enough to take to remote locations and can be carried by one person along with a laptop computer. This portability has permitted the use of limb digitizers in developing countries to treat patients who do not have local facilities and cannot travel.
This table lists the key features of limb digitization systems, including their practical use in the clinic
126 M.D. Geil
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© Springer Science+Business Media, LLC 2012
Abstract Malnutrition is a serious problem in many developing countries. It is one of the main causes of child morbidity and contributes signifi cantly to premature mortality. This chapter discusses the design and use of an alternative indicator of malnutrition – the composite index of anthropometric failure (CIAF). It argues the three most commonly used anthropometric indicators of stunting, wasting and underweight, while providing valuable information about distinct biological processes, are indi- vidually unable to provide a comprehensive picture of the overall burden of malnutrition among young children in a population. They are frequently used to predict health and mortality risk, but provide quite limited information on the relationship between malnutrition and disease. The CIAF, however, can also be used to predict morbidity risk, and in its disaggregated form provides a more useful picture of the relationship between ill health and malnutrition. It can also be used to examine the relationship between different forms of malnutrition and poverty.
Using the new World Health Organization (WHO) reference population norms and recent anthro- pometric data on 45,377 Indian children aged under 5 years, the prevalence of stunting, wasting and underweight are calculated and compared to prevalence estimates by the CIAF. Age adjusted logistic regression is used to see how well different indicators predict morbidity risk. Analysis of variance is used to see the relationship between groups of anthropometric failure and poverty. This chapter also provides information on how reliable, nationally representative anthropometric data from household surveys can be freely accessed by researchers to pursue their own study.
Abbreviations
ARI Acute Respiratory Infection
CIAF Composite Index of Anthropometric Failure DHS Demographic and Health Survey
HTA Height for Age
LSMS Living Standards Measurement Study MDGs Millennium Development Goals MICS Multiple Indicator Cluster Surveys NCHS National Center for Health Statistics