Saturday, January 21, 2017

Arthritic glenohumeral pathoanatomy, B3 or not to be.

Characterization of the Walch B3 glenoid in primary osteoarthritis

These authors suggest that a biconcave arthritic glenoid can progress to a uniconcave glenoid through additional wear. They define a "B3" glenoid as one with a single concavity and over 15 degrees of retroversion. This is in apparent contrast to an "A2" glenoid which has a single concavity and less than 15 degrees of retroversion.

They conducted 3-dimensional analysis of CT data on 52 patients with B3 glenoids. In these shoulders the mean retroversion was 24±7 degrees, superior inclination 8±6 degrees, and medialization 14±4 mm.

The position of the humeral head relative to the plane of the scapula was, as would be expected, significantly correlated with the amount of glenoid retroversion. As also would be expected from the definition, in these cases the humeral head was not decentered with respect to the face of the glenoid: i.e. the humeral head remained concentric to the erosion. 

Comment: This article prompts us to consider the surgical management of the retroverted glenoid with a centered humeral head. In our practice shoulders with osteoarthritis or capsulorrhaphy arthropathy often have glenoid version in excess of 15 degrees. Our surgical goal is not primarily to change glenoid version, but rather to stably center the humeral head in a glenoid with a single concavity.

If after insertion of the glenoid component, there is excessive posterior translation of the trial humeral head, we use an anteriorly eccentric humeral head prosthesis

without or with a rotator interval plication.

The issue of categorizing the highly variable glenohumeral pathoanatomy into types has been discussed in a previous post.

A modification to the Walch classification of the glenoid in primary glenohumeral osteoarthritis using three-dimensional imaging.

These authors proposed several modifications to the Walch classification for arthritic glenohumeral pathoanatomy.

They define a B3 glenoid as being monoconcave and worn preferentially in its posterior aspect, leading to pathologic retroversion of at least 15° or "subluxation" of 70%, or both. 

They define a D glenoid as glenoid anteversion or anterior humeral head subluxation. 

They redefine a A2 glenoid as having a line connecting the anterior and posterior native glenoid rims that transects the humeral head. 

As pointed out in prior posts (see link), there many arthritic forms that lie between and among the classically described glenoid types, so that a categorical system has difficulty capturing them all. 

For example in the proposed system, the difference between an 

and a

is based on whether or not the retroversion is greater or less than an arbitrarily selected level of 15 degrees.

In addition there is confusion when the term 'subluxation' - which should be used to describe the relationship of the humeral and glenoid articular surfaces - is used to describe the relationship of the humeral head to the scapular plane (see the discussion in this link). The B3
as described does not show the separation of the the humeral and glenoid joint surfaces that characterizes 'subluxation' in the usual sense of the word.

By contrast the B2, B1, and D meet the usual definition of subluxation - "incomplete or partial dislocation of a joint "


An alternative approach can be based on three parametric measurements:

(1) The percent of the glenoid surface that has a pathologic biconcavity (33% posterior in the example below).

 (2) The angle of retroversion of the glenoid face (G) in relation to the scapular body (S)

(3) The centering of the humeral head with respect to the glenoid  (the distance between the anterior glenoid lip and the center of glenohumeral contact (C) divided by the distance between the anterior and posterior glenoid lips (G)).  0.5 indicates a centered humeral head.
Using this system, 
the example "D" glenoid below would be 50% anterior biconcavity, 10 degree retroversion, and decentering of .25 (subluxation).

the example "B3" glenoid below would be 0 biconcavity, 40 degree retroversion, and centering of .5. 

the example "A2" glenoid below would be 0 biconcavity, 15 degree retroversion, and centering of .5. 

Such a system can provide the information necessary for characterizing the pathology and for planning treatment.


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