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Measurements and errors at orthopaedic workshops
The everyday work at an orthopaedic workshop is highly dependent on qualitative and subjective judgements and the experience of the individual CPO. The experience of examination of patients and production of prostheses and orthoses is hard to communicate to less experienced colleges. This has resulted in a practice at the orthopaedic workshops where the novices can get advice from the more experienced CPOs, but have to learn very much through trial-and-error. The disadvantage of trial-and-error is that it is very time consuming and many patients are bound to get a suboptimal treatment meanwhile.Standardisation and mechanisation of methods are important to reduce the errors due to the observer, that is, the CPO taking the measures, doing the casting or the rectification, et cetera. The measuring instruments should also be improved to reduce errors. For example may different measuring-tapes give different results. CAD/CAM systems using a laser beam to scan stumps are examples of mechanisation of the casting process, which normally is highly subjective. When the process is less bound to specific persons and instruments, persons and instruments can be exchanged, which makes the process more flexible. For example can another person than the specific CPO does the rectification of the limb model after measurements taken in a standardised manner. Today, measures taken on the patient are so highly influenced by the CPO (and maybe the measuring-tape) that it may be hard for other persons to use them in the production, in case the CPO gets ill, is on holiday, et cetera. Less personal and instrumental influence also makes it possible to localise the whole production somewhere else (central production). A more mechanised procedure is also easier to learn to perform to the inexperienced CPO. The success of the work is then less dependent on gained experience. The trail-and-error period may then be reduced and fewer patients get a unsatisfactory treatment caused by the inexperience of the CPO. Further, if errors of measurement are evaluated for the standardised methods the material in the CPOs’ journals can be used in scientific studies. Today, many of the measurements performed at orthopaedic workshops have not been evaluated when it comes to errors of measurements, or at least the results are unknown among CPOs.The crucial question is how the experience and qualitative knowledge of the clinically active CPOs can be transformed into more standardised, mechanised, and quantifiable methods. This development work should preferable be performed by persons with technical knowledge and insight in errors of measurement in cooperation with experienced CPOs.The focus in this thesis is the quantification of the volume changes after an amputation.Although several factors influence the decision of when to fit with definitive prosthesis, the quantification of volume would at least make the “volume factor” less subjective. Before the method to assess stump volume can be recommended for clinical use it is necessary to evaluate its errors of measurement.
AIM
The aim of the present study was to evaluate accuracy and intra- and interrater precision of a method to assess residual limb volume from circumferential measurements when used on transtibial stumps.
INTRODUCTION
THEORY
Measurements
Classification of measurements
Scales of measurement
Errors of measurement
The infinite experiment and systematic and random errors
Propagation of error
Direct measurements
Indirect measurements
Simultaneous and combined measurements
Determination and correction of errors
More about accuracy and precision
Measurements and errors in orthopaedic workshops
MATERIAL AND METHODS
Study design
Volume determination
Determination of volume using circumferential measurements
Determination of volume using CAPOD
Accuracy
Theoretical accuracy of tip volume
Theoretical accuracy of stump volume
Practical accuracy of stump volume
Precision and sources of error
Measuring procedure
Intrarater precision
Interrater precision
Sources of error
Subjects
Statistical methods
RESULTS
Accuracy
Theoretical accuracy of tip volume
Theoretical accuracy of stump volume
Practical accuracy of stump volume
Precision
Intrarater precision
Interrater precision
Sources of error
DISCUSSION
Main results
Accuracy
Theoretical accuracy of tip volume
Theoretical accuracy of stump volume
Practical accuracy of stump volume
Precision
Intrarater precision
Interrater precision
Sources of error
Clinical implications
Methodological considerations and limitations of the study
External accuracy
Internal accuracy
Other methodological considerations
Future studies
CONCLUSIONS
ACKNOWLEDGEMENTS
REFERENCES
APPENDIX I, INSTRUCTIONS FOR THE MEASUREMENTS
APPENDIX II, MEASURING FORM
APPENDIX III, CALCULATIONS
Error limits for cut cone
Error limits for sphere segment
