View Full Version : Wrist Extension

Timothy B F Woodfield
06-13-1996, 02:13 PM
Greetings Biomch-L members,

My name is Tim Woodfield and I am a final year Mechanical Engineering
student at Canterbury University, Christchurch, New Zealand. Recently
I designed and built a device (called the Troidometer) which measures
the isometric torque (in Nm) developed about the elbow. It was
specifically designed to test post operative triceps strength in
tetraplegics (C5, C6) who have had posterior deltoid to triceps transfer
surgery. This device was presented at the International Medical
Society of Paraplegia conference (IMSOP) in Feb '96.
Using a similar setup, I am now investigating methods for measuring
STRENGTH of wrist extension and flexion (again in Nm). Strength is
important for wrist tendon transfer surgery to provide pinch grip and
palmer grip.
For the elbow I built a transducer capable of sensing the often
small loads applied, using a lever arm distance to get torque and
hence a comparison between patients.
Elbow rotation is relatively simple, but for the wrist, texts state
that about 60% of flexion occurs at the midcarpal joint and 67% of
extension occurs at the radiocarpal joint, thus finding an
approximate centre of rotation to set the lever arm difficult.
Using EMG negates this problem, but as I found out recently on
Biomch-L, electrode placement, electrode spacing, skin moisture.....
affect readings making comparisons difficult and don't give readings
in the desired Nm standard units.

This rather long winded introduction prompts the following
questions :
1. If a transducer is used, is there an accepted point of rotation or
bony landmark on the ulnar / radius to aid obtaining a lever arm for
each patient?
2. Are there cunning methods for improving inter-patient comparisons
using EMG?
3. Am I going about this wrong? (bearing in mind I have mostly an
engineering point of view to the problem as opposed to a
biomechanical one).

Thanks in advance for any input. Any comments from those more
involved than I in this area would be much appreciated.

Tim Woodfield
University of Canterbury
Mechanical Eng Dept
New Zealand
email: woodfitb@cad.canterbury.ac.nz