Shoulder arthroplasty - centering the humeral head in the glenoid

Management of intraoperative posterior decentering in shoulder arthroplasty using anteriorly eccentric humeral head components

These authors report the use of anteriorly-eccentric humeral head components to manage posterior instability recognized at shoulder arthroplasty when standard trial components are in place. Radiographic centering was characterized before surgery and at follow-up on standardized axillary radiographs with the arm held in a position of functional elevation. Preoperative posterior humeral head decentering did not correlate with preoperative glenoid version.

In 33 shoulder arthroplasties with 2-year outcomes the preoperative radiographic humeral decentering was reduced from 10.4% ± 7.9% to 0.9% ± 2.3% postoperatively (P < .001). SST scores improved from 4.8 ± 2.3 to 10.0 ± 2.3 (P < .001).  Glenoid retroversion was 19.8° ± 8.9° preoperatively and 15.5° ± 7.5° postoperatively. Rotator interval plication was performed in 16 cases as an adjunctive stabilizing procedure.

Comment: Posterior instability after a shoulder arthroplasty can result in pain, functional loss and rocking horse loosening or rim wear of a glenoid component.

While posterior decentering can be identified before surgery by the 'truth' view (an axillary taken with the arm in a functional position of elevation in the plane of the scapula) as shown below

often this preoperative posterior instability will respond to soft tissue balancing and use of standard humeral components. In other cases, the posterior instability persists at surgery, being manifest by a posterior 'drop back' when the arm is elevated. 

Not infrequently a shoulder without apparent posterior instability before surgery becomes posteriorly unstable at surgery after osteophyte resection and soft tissue releases. 

In cases where posterior instability is identified at surgery when trial components are in place, centering of the humeral head can usually be established through the use of an anteriorly eccentric humeral head without or with a rotator interval plication.

resulting in a stabilized head without needing to change glenoid version. Below is the postoperative view of the case shown in the earlier x-ray in which these methods were used.

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