Saturday, April 30, 2016

Shoulder osteoarthritis - scapulohumeral relationships with the arm at the side

A three-dimensional comparative study on the scapulohumeral relationship in normal and osteoarthritic shoulders.

These authors studied three-dimensional reconstructions of computed tomography scans of 151 nonpathologic shoulders (control group) and 110 shoulders with primary glenohumeral arthritis (OA group). Subjects were positioned in the CT gantry in a supine position while holding a cushion on the abdomen, which was fixed with a strap around the cushion and the torso. Both arms were adducted to the trunk, the elbows were at right angles, and the forearms were positioned in the anterior  direction with neutral rotation.

They analyzed the anterior-posterior, inferior-superior, and medial-lateral position of the humeral head in relation to the scapula. Shoulders were classified as centered (type A) or posteriorly subluxed (type B) according to the Walch classification of glenoid morphology. 

Both type A and type B shoulders showed significant posterior translation of the humeral head (P <.001). Type B shoulders had significantly more posterior translation than type A shoulders (P <.001). 

Comment: This article gives opportunity to make some observations on the assessment of glenohumeral arthritic pathoanatomy. These authors pointed out that their 'centered' type A glenoids were associated with posterior humeral translation. We note that part of the issue lies in the fact that the glenoid types so nicely described by Gilles Walch and his colleagues do not always capture what is actually a continuum ranging from a typical type A2:

to a typical type B2 glenoid.

In practice we recognize that the categories of A1, A2, B1, B2 and C do not recognize intermediate pathologies, such as that between A1 and B1, or that between A2 and B2 as shown below

The second issue is that CT scans taken with the arm at the side may not reflect the glenohumeral relationship when the arm is in the functional position of elevation in the plane of the scapula.  The change in position of the humeral head when the arm is placed in a functional position is known as functional decentering (see this link). This relationship is better revealed by an axillary view taken with the arm in the functional position, as shown below. This is explained in greater detail in a prior post (see this link).

Studies of glenohumeral pathoanatomy need to specify the position of the arm when the images are taken and to characterize the glenoid version and the degree of decentering of the humeral head on the glenoid when the arm is in a functional position.

Shown below is a simple method for measuring glenoid version (left) and the point of glenhumeral contact (right) on the axillary view.

These views enable the comparison of the glenohumeral relationships before and after surgery



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