Monday, January 23, 2017

Managing posterior instability with an anteriorly eccentric humeral head component

Effects of Anterior Offsetting of Humeral Head Component in Posteriorly Unstable Total Shoulder Arthroplasty: Finite Element Modeling of Cadaver Specimens

The technique of using anteriorly eccentric humeral head components to manage intraoperative posterior instability was published in a 2009 Journal of Bone and Joint Surgery article "Current Technique for the Ream-and-Run Arthroplasty for Glenohumeral Osteoarthritis" and the clinical utility of this method in a more recent publication "Management of intraoperative posterior decentering in shoulder arthroplasty using anteriorly eccentric humeral head components."

The authors of this article sought to characterize the changes in joint mechanics associated with anterior offsetting with various amounts of glenoid retroversion using cadaver specimen-specific 3-dimensional finite element models. They developed specimen specific computational finite element models by importing digitized locations of six musculotendinous units of the rotator cuff and deltoid muscles based off three cadaveric shoulder specimens implanted with total shoulder arthroplasty in either anatomic or anterior humeral head offset. 

In this model, anterior offsetting was associated with significant anterior shift of center of pressure and humeral head displacement upon muscle loading (p<0.05).

The authors concluded that the use of an anteriorly eccentric humeral head may contribute to joint stability in posteriorly unstable shoulder arthroplasty and may reduce eccentric loading on glenoid components although the long term clinical results are yet to be investigated in future.

Comment: We use anteriorly eccentric humeral heads without or with rotator interval plication routinely to optimize the centering of the humeral head on the glenoid. This approach enables posterior stability without specifically attempting to change glenoid retroversion.

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.


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