Monday, January 21, 2013

The humeral head component selection in shoulder arthroplasty

The role of eccentric and offset humeral head variations in total shoulder arthroplasty

The authors report that of one hundred sixty primary total shoulder arthroplasties performed for osteoarthritis the humeral head selection was standard in 52, eccentric in 60 and offset (extended neck) in 48. Head geometry was selected intraoperatively based on achieving a complementary relationship to the glenoid. At a minimum of 2 year followup, there was no difference among head configurations was found for any of these outcomes.

In contrast to some, we are less concerned about achieve an 'anatomic' reconstruction of the arthritic joint, in that putting metal and plastic in the 'normal' configuration does not always restore stability and mobility. 

Step 1 - select the glenoid size to optimally cover the available glenoid bone 
Step 2 - select the humeral stem that can be insterted without reaming the endosteal surface of the diaphysis (knowing that fixation can be achieved by impaction grafting).
Step 3 - select the humeral head diameter of curvature that matches that of the glenoid selected in step 1
Step 4 - select the humeral head prosthesis with a neck thickness that provides 45 - 60 degrees of internal rotation in abduction and approximately 50% posterior translation.
Step 5 - position the humeral trail so that the head is centered on the glenoid (proper register)
Step 6 - check for posterior subluxation (drop back) when the arm is elevated, if this occurs consider anteriorly eccentric humeral head and possibly a rotator interval plication, just as we've described for the ream and run.

See this example below

We also use eccentric heads occasionally to adjust the superior/inferior register for example in this case of posttraumatic arthritis treated with a ream and run - the intramedullary scarred bone made it difficult to put the humeral component down to the ideal location so we compensated with the eccentric head and achieved ideal register.

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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.