REAMING THE GLENOID SURFACE

Reaming the glenoid surface serves two purposes: first, it provides a congruent surface that matches the apposing surface of the implant by removing any remaining cartilage and smoothing the osseous surface, and second, it corrects any deformity caused by bony wear, as identified on preoperative imaging (Fig. 12-2). If no deformity is present, “light” reaming is performed. In patients with posterior glenoid wear, however, the anterior portion of the glenoid should be preferentially reamed to correct the deformity.

Figure 12-2 Example of identification of a biconcave glenoid deformity identified on preoperative imaging studies. This deformity should be corrected by eccentric reaming during the surgical procedure.

After humeral preparation and insertion of the humeral cut protector (Chapter 11), the humeral head retractor is replaced to retract the proximal humerus posteriorly and expose the glenoid (Fig. 12-3). It is helpful to mark the center point of the glenoid with an electrocautery. It is also important to realize that with severe deformity or biconcavity, the center point will change (the new center point is posterior to the original center point after “reaming away” a portion of the anterior glenoid) by preferentially reaming the anterior glenoid, and this should be considered when identifying the center point. A guide with a stop is used when drilling a pilot hole through the center point of the glenoid (Fig. 12-4). The tip of a reamer of the appropriate glenoid size (see the next section) is introduced into the pilot hole (Fig. 12-5). Introduction of the reamer is usually the most difficult part of glenoid resurfacing. A few techniques are helpful when performing this portion of the procedure in exceptionally stiff shoulders. We first confirm with the anesthesiologist that the patient is adequately relaxed with paralytic agents. We then determine which posterior glenoid retractor yields the best exposure. We start with the Trillat humeral head retractor. If this proves inadequate, we will also try a Fukada humeral head retractor, a large glenoid rim retractor, or one or more Hohmann retractors (these retractors are shown in Chapter 3). Many times it is necessary for the assistant retracting the humeral head to perform a maneuver with the humeral head retractor to facilitate insertion of the reamer. This is done by first forcefully retracting posteriorly and then relaxing the retractor to allow clearance of the posterior aspect of the reamer. The retractor can be left in place in a relaxed position during the actual reaming. This technique is illustrated in Figure 12-6. Rarely, despite the use of these techniques for exposure of the glenoid and insertion of the reamer, it may not be possible to insert the reamer tip into the pilot hole. In this scenario we remove the humeral head retractor completely and insert a laminar spreader between the glenoid and humerus. One limb of the laminar spreader is placed at the most superior aspect of the glenoid surface, and the other limb is placed on the cut surface of the proximal humerus. The laminar spreader is opened to distract the glenohumeral joint and retract the humerus laterally. This technique allows insertion of the glenoid reamer by eliminating obstruction of the reamer by the posterior humeral head retractor (Fig. 12-7). By using these techniques sequentially, we have yet to perform a shoulder arthroplasty in which we were unable to resurface the glenoid because of inadequate exposure.