View Full Version : Piriformis

William George Webright
03-09-1996, 11:44 PM
Following my inquiry regarding piriformis emg are the
responses. Thanks for the feedback.

My interest is in kinesiological emg of the piriformis.
Medline and biomch-l archive searches have not turned up any
information. I need your assistance with:

1. Any published or unpublished studies regarding piriformis
emg during gait (walking or running), manual muscle
testing, stair climbing, etc.

2. Recommendations for bipolar wire electrode and carrier
needle specifications for piriformis insertion: needle
gauge and length, wire diameter, wire type (metal alloy and
type of insulation), manufacturer/distributor.

Any other thoughts regarding piriformis function via emg and
kinematic investigation would be most welcome. All responses
will be posted. Thank you.

Bill Webright

Most gait labs don't routinely look at the Piriformis muscle.
However, I have
collected it on a few patients over the years. I use
"Anatomical Guide for
the Electromyographer" as my text for where to insert the
electrodes (ISBN #
0-398-5900-4). The text pp 218-219 says "Insert electrode deep
to bone at the
midpoint of a line between the posterior inferior iliac spine &
the posterior-
superior margin of the greater trochanter. The electrode will
travel through
the gluteus maximus muscle."

I use 27g 1 1/2 inch needles which may not be long enough in
obese people. I
also use 30g 1 inch needles when I can and occasionally use a 2
inch 25g if I
need the length. There is a big difference in the pain factor
from 25g - 30g.
I purchase my fine wire from California Fine Wire company in
Grover City, CA
93433 ((805) 489-5144). A 1000 ft roll of Stablohn 800-A with
H-Poly nylon
green insulation of size 0.00175 or 0.002 cost about $100/roll.
I use Basmajian's bipolar technique as described in J Applied
Physiology 17,
1962 to construct my electrodes. Please do not hesitate to
contact me should
you have any further questions.

Director, Gait & Biomechanics Lab

I don't have any specifics on EMG of the piriformis but I am
interested in the function of the SI joint during the walking
cycle. A
very good paper though it is only based on clinical
observations is Phil
Greenman's "Clinical aspects of the sacroiliac function in
Journal of Manual Medicine (1990) 5:125-130. I think this
provides an
excellent model to view piriformis function during gait and its
relationship to pelvic girdle mechanics. Good luck,

% Timothy W. Flynn, PT, MS, OCS %
% Center for Locomotion Studies %
% Room 10, Intramural Building %
% Pennsylvania State University %
% University Park, PA 16802 %
% (Lab) (814) 865-1972 FAX 863-4755 %
% (Home office) 867-5987 %
% Email- twf104@psu.edu


William G. Webright, MEd, PT, ATC wgw3a@curry.edschool.virginia.edu
PhD student Sports Medicine home: 804/293-4490
University of Virginia
Charlottesville, VA 22903