>Jeff wrote:
>Looking at an average adult size calcaneus at my desk, I just measured the upper, symmetrical portion to be 13 millimeters and the total vertical height of the calcaneus to be 35 millimeters. When you palpate and bisect the upper portion of the heel, you should only have two to three line segments that represent the calcaneus. The remaining 2/3 of the bisection line is the result of an extension of the superior 1/3 line segment.
And this is one good reason for the high level of error.
You only need to displace one end of a 13 mm line by about 1 mm to cause an angular shift of about 5 degrees (same result by shifting the two end of the line by 0.5 mm in opposite directions). 1 mm shift at each end and you have a 9 or 10 degree shift!
Couple that simple piece of trigonometry with all of the other contributing factors (the positions of the previous skin marks, displacement of the skin, thickness of the pen lines themselves...) and its a marvel that anyone gets remotely close to agreement :-)!
Regards,
Stephen
Stephen Urry PhD
Lecturer
School of Public Health
Queensland University of Technology
Brisbane
4059
Australia
CRICOS No 00213J
-----------------------------------------------------------------
This message was distributed by the Podiatry JISCmail list server
All opinions and assertions contained in this message are those of
the original author. The listowner(s) and the JISCmail service take
no responsibility for the content.
to leave the Podiatry email list send a message containing the text
leave podiatry
to [log in to unmask]
Please visit http://www.jiscmail.ac.uk for any further information
-----------------------------------------------------------------
|