Saturday, September 19, 2015

Shoulder arthroplasty - the stabilizing effect of the anteriorly offset humeral head component

Biomechanical benefits of anterior offsetting of humeral head component in posteriorly unstable total shoulder arthroplasty: A cadaveric study.

We first described our use of anteriorly offset humeral head components to manage posteriorly unstable shoulder arthroplasties in 2009 (Shoulder Rockwood and Matsen 4th edition p 1185-6). These authors have evaluated the biomechanical benefits of this technique in cadaveric specimens. They performed shoulder arthroplasty in 14 cadaveric shoulders from seven donors, creating either 10° or 20° glenoid retroversion by eccentric reaming. Two humeral head component offset positions were tested in each specimen: the anatomic and anteriorly offset.

They found that the the anteriorly offset humeral heads were significantly more stable against posteriorly directed loads.  The joint contact pressures were significantly shifted anteriorly, and the joint contact area significantly increased with the anteriorly eccentric humeral head in comparison to the anatomic head. Interesting, the stabilizing effect of the anteriorly eccentric head was greater in the more severely retroverted glenoids.

Posterior decentering of the humeral head is a common feature of glenohumeral osteoarthritis and capsulorrhaphy arthropathy; arthroplasties performed for these shoulders are technically challenging with poorer outcomes and component survivorship. Posterior humeral decentering may be recognized as ‘static posterior subluxation’ on preoperative imaging with the arm at the side, as functional decentering observed on imaging obtained with the arm elevated into a functional position, or as an intraoperative finding encountered in the conduct of a glenohumeral arthroplasty after surgical exposure, capsular release, and osteophyte resection.

Conventional approaches to shoulder arthroplasty may be insufficient to re-center a posteriorly unstable humeral head. Posterior capsular plication has been used in an attempt to achieve posterior stability, but this capsulorrhaphy has a tendency to stretch, allowing recurrence of the decentering. Posteriorly augmented glenoid components, posterior bone grafts and excessive anterior glenoid reaming can change glenoid version, but changing the direction that the glenoid faces does not assure that the humeral head will be reentered in it. 

The anteriorly eccentric humeral head is a simple modification that can be effective in centering the humeral component when posterior instability is noted intraoperatively.


Consultation for those who live a distance away from Seattle.

Check out the new Shoulder Arthritis Book - click here.

Click here to see the new Rotator Cuff Book

To see the topics covered in this Blog, click here

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and runreverse total shoulderCTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'