Sunday, August 23, 2015

Shoulder motion in three dimensions

Three-dimensional analysis versus goniometric measurement of total active elevation in normal subjects.

These authors advocate measuring humeroscapular elevation in a plane of reference that is perpendicular to the plane of motion. They found that subjects consistently moved toward scaption as the extremity moved above 90° of elevation, regardless of the initial plane of motion.

Comment: Back in 1994, we published a book entitled Practical Evaluation and Management of the Shoulder in which we examined the planes of elevation in detail using position sensors attached to pins drilled into our humerus and scapula in reference to a transmitter on our thorax. In that the book is now out of print, many have asked how they might get a copy. Recently, the publisher has kindly allowed us to offer a PDF of the book this link. We were interested not only in the plane of maximal motion, but also the planes of motion used in activities of daily living as reflected by the Simple Shoulder Test (SST).

The planes of motion can be easily defined in reference to the plane of the body as shown below.

Each shoulder motion can be characterized in terms of the plan in which the motion takes place and the angle of elevation in that plane. The table below shows these planes and angles for selected activities of daily living. Note that planes with a + sign are anterior to the plane of the body and those with a - sign are posterior to the plane of the body. In these subjects maximal elevation took place in the 55 degree anterior plane. The term 'scaption', while often used actually is inappropriate in that the scapula moves on the chest wall during these movements so the clinical examiner does not know the relationship of the motion of the humerus to the plane of the scapula. (N.B. if one reads further in the Practical Evaluation and Management of the Shoulder , the reader can see an analysis of humeral motions with respect to the plane of the scapula).

We found that these data could be nicely represented in global diagrams in which the range of maximal humerothoracic elevation in different planes is shown by the connected white dots and the positions used for the activities of daily living are shown by the black dots.

In describing shoulder motion we need to be precise with respect to whether we are talking about the motion of the humerus in respect to the scapula or the thorax as well as the plane and angle of elevation.


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