There are currently no standard examination positions for the shoulder. During movements of the gleno-humeral joint there are always relative movements within the scapulo-thoracic junction. These are usually described as fitting a set of established normal patterns. These must be considered when testing the shoulder. When testing or exercising the shoulder it is vital that the patient has sufficient warm-up before performing any movements.
Abduction/Adduction
Standing
When the movement is performed in the standing position (as seen below however, the subject would normally face the dynamometer) stabilization is almost impossible but the subject can hold the seat (if available and remember consistency during testing).
The axis of rotation is commonly set to a point roughly 2-3 cms below the inferior lip of the acromial arch (the right acromial arch is demonstrated in the anatomical model above). But it has been shown by Walmsley (1993) that the gleno-humeral joint as a whole (never mind its instantaneous axis of rotation) moves by an average of 8cm through range so the need for accuracy must be questioned.
Seated
Alignment is commonly achieved by positioning the actuator axis roughly 2-3 cms below the inferior lip of the acromial arch (as above but remember it has been shown by Walmsley 1993 that the gleno-humeral joint as a whole (never mind its instantaneous axis of rotation) moves by an average of 8 cm through range so the need for accuracy must be questioned).
In this position there is the increased innate thoracic stability (little rotation occurs) but adduction is severely limited as the subjects body stops the movement at anatomical zero. In this position the thoracic belts should be utilized to prevent upper body movements.
Seated Horizontal
Horizontal abduction/adduction (if of interest) offers full available shoulder ROM. The alignment of the instantaneous axis of rotation is approximately 1cm away from the mid line above the acromial process when the humerous is at a right angle to the body and the scapula is angled at 90degrees (see below). Stabilization is achieved with thoracic strapping usually).
As velocities in some sports (any involving throwing an object) are known to reach thousands of degrees/second (Pappas et al., 1985) testing using a dynamometer will never be functional. (Even if this speed could be achieved it is over such a small arc that the results gained would be fruitless.) Generally it is accepted that speeds of 60 degrees/second and multiples of this should be used. Speeds over 300 degrees/second have been found to be difficult to achieve by even baseball pitchers (Cook et al., 1987).
