Humeral component - Clinical Tree

Reconstruction of the proximal humerus can be a very difficult aspect of revision shoulder arthroplasty. During extraction of the previous humeral stem, every effort should be made to preserve as much native proximal humeral bone as possible (see Chapter 38 ). The overall condition of the proximal humerus and rotator cuff plays a significant role in determining the type of implant to be used in revision surgery (unconstrained vs. semiconstrained). In cases in which the rotator cuff is largely functional, preservation of the greater and lesser tuberosities helps to dictate which type of revision implant to use during revision surgery. After the type of revision implant to be used is selected, preparation of the proximal humerus and implantation of the humeral component proceed just as for primary arthroplasty. This chapter details our techniques for reconstruction and preparation of the proximal humerus and implantation of the humeral component in revision shoulder arthroplasty.

Technique for Preparation of the Proximal Humerus

Preparation of the proximal humerus is largely dependent on the residual osseous anatomy of the proximal humerus after the previously placed humeral stem has been extracted. In cases in which extraction of the previous humeral stem was relatively uncomplicated, with minimal compromise of the proximal humeral metaphysis and tuberosities, preparation of the proximal humerus can be straightforward and similar to proximal humeral preparation for primary shoulder arthroplasty. In cases in which the proximal humeral osseous anatomy has been compromised either before or during extraction of the humeral stem, preparation of the proximal humerus becomes substantially more complicated.

When proximal humeral osseous anatomy is well preserved, proximal humeral preparation for either an unconstrained stem or a reverse stem is performed similar to cases of primary arthroplasty.

Unconstrained Humeral Stem

In revision cases in which we are going to implant an unconstrained proximal humeral stem, we prefer to implant a cementless short stem whenever possible. If fixation into the metaphysis seems compromised, we will opt for a slightly longer stem ( Fig. 39.1 ). Only in cases of periprosthetic fracture or when we have to bypass a humeral diaphyseal osteotomy used for stem extraction do we opt for a long-stem humeral component ( Fig. 39.2 ). Only if press fit of the humeral component is deemed inadequate do we consider cementing the humeral component.

FIGURE 39.1, Unconstrained stems used in revision shoulder arthroplasty.

$FIGURE 39.2, Long-stem unconstrained humeral implants used in the treatment of a periprosthetic fracture or when a diaphyseal humeral osteotomy has been required for stem removal.$

When using a short stem for revision, the humeral diaphysis is sounded just as in primary unconstrained arthroplasty ( Fig. 39.3 ; see Chapter 11 ). The proximal humerus is then prepared using broaches for the standard short stem or the slightly longer stem, depending on the quality of the proximal humeral bone ( Fig. 39.4 ).

FIGURE 39.3, (A and B) The humeral canal is sounded to determine appropriate size of the humeral component.

FIGURE 39.4, (A and B) Broaching of the proximal humerus.

After a humeral stem of appropriate size is selected, the proximal humerus can be planed, if necessary, to match the inclination of the humeral implant ( Fig. 39.5 ). The appropriate size trial humeral head is then placed on the final humeral broach. The prosthetic head should provide adequate coverage of the proximal humeral metaphysis but not overhang the humerus at any portion. The system that we use allows variable medial-to-lateral and anterior-to-posterior offset. The prosthetic humeral head is placed on the trial humeral stem at the various offset positions to allow selection of the best offset index ( Fig. 39.6 ). After the proper index has been selected, the glenohumeral joint is reduced and humeral version is judged. With the arm in neutral rotation, the center of the prosthetic humeral head should align with the center of the glenoid, provided that osseous glenoid morphology is intact and does not demonstrate a nonconcentric wear pattern ( Fig. 39.7 ). In cases with nonconcentric glenoid morphology or cases in which the osseous glenoid is compromised, we judge humeral version by placing the prosthesis in approximately 30 degrees of retroversion relative to the long axis of the forearm ( Fig. 39.8 ). The humeral stem retroversion can also be determined by using the version rod on the insertion handle relative to the forearm. If the version of the trial humeral stem is unacceptable, the humeral trial is removed and humeral version changed by revising the original plane of humeral head resection by way of a revision humeral cut to introduce more retroversion or anteversion, as deemed appropriate by the trial glenohumeral reduction. The trial humeral implant is reinserted and the trial reduction repeated to ensure that humeral version has been corrected acceptably.