Unconstrained Humeral Stem

In cases in which we are going to implant an unconstrained proximal humeral stem, we prefer to implant a stem with geometry designed originally for use in proximal humeral fractures. This cemented stem design allows a good fit into the humeral metaphysis and comes in a variety of lengths. This allows the surgeon to treat periprosthetic fractures or bypass the distal aspect of a humeral diaphyseal osteotomy used for extraction of the humeral stem (Fig. 39-1).

Figure 39-1 Unconstrained stems used in revision shoulder arthroplasty.

For this revision stem, no metaphyseal broaching is necessary. The diaphysis is progressively reamed with the hand reamers provided (Fig. 39-2). Frequently, after removing an uncemented humeral stem, a small pedestal of bone exists in the intramedullary canal at the level just distal to the tip of the original humeral stem (Fig. 39-3). It is easy to tap the smallest diaphyseal reamer through this osseous pedestal. Subsequent reamers pass through this area without difficulty.

Figure 39-2 A and B, Diaphyseal reaming.

Figure 39-3 Pedestal of intramedullary cortical bone (arrows) distal to the tip of an uncemented humeral stem.

Once a humeral stem diameter of appropriate size is selected, the trial humeral stem is inserted by impacting the stem into the proximal humerus (Fig. 39-4). Effort is made to impact the stem laterally into the tuberosities (Fig. 39-5). It is not necessary to broach the humeral metaphysis because the bone in this area is relatively soft and compresses sufficiently to allow full seating of the implant. On occasion, the metaphyseal bone will be moderately to severely osteopenic, and the trial humeral stem will fall into the medial portion of the metaphysis (Fig. 39-6). This “loose fit” hinders testing of the trial implant. The trial may be stabilized within the proximal humerus in this scenario by wrapping a sterile sponge (or portion of a sterile sponge) around the metaphyseal portion of the trial implant before placing it in the humeral canal (Fig. 39-7).

Figure 39-4 A and B, Impaction of the trial humeral stem into the proximal humerus.

Figure 39-5 A and B, The trial humeral stem is impacted laterally into the greater tuberosity.

Figure 39-6 A to C, Humeral stem poorly filling the proximal humerus.

Figure 39-7 A to E, Use of a gauze sponge around the metaphyseal portion of the trial humeral stem to allow easier trial insertion of the revision implants.

Once the trial humeral stem is securely placed in the proximal humerus, a humeral head implant of appropriate size is selected. 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. 39-8). Once 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. 39-9). 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. 39-10). 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.

Figure 39-8 A and B, Selection of the offset of the trial humeral head.

Figure 39-9 A to D, Judgment of humeral version during revision shoulder arthroplasty by ensuring that the prosthetic head is centered in the glenoid with the arm in neutral rotation.

Figure 39-10 A and B, Judgment of humeral version during revision shoulder arthroplasty by placing the humeral stem in 30 degrees of retroversion relative to the long axis of the forearm. This technique is used in patients with nonconcentric glenoid wear or in those with glenoid osseous deficiency.

Reverse-Design Humeral Stem

In cases in which a reverse-design humeral implant is to be used as the revision humeral stem and the osseous proximal humerus is relatively preserved, the epiphysis, metaphysis, and diaphysis are prepared in much the same way as for insertion of a reverse prosthesis as a primary implant. The epiphyseal reamer is first used to create a place for the proximal portion of the humeral implant (Fig. 39-11), after which the metaphyseal hand reamer is used (Fig. 39-12). Progressive diaphyseal reaming is then performed, with penetration of any osseous pedestal present in the humeral canal (Fig. 39-13). The trial humeral stem is assembled by using an implant diameter corresponding to the largest-diameter diaphyseal reamer that was used. The trial humeral implant is placed in approximately 10 degrees of humeral retroversion by using the forearm referencing insertion instrument and is fully impacted (Fig. 39-14). The position of the fin is marked on the proximal humerus with the electrocautery (Fig. 39-15).

Figure 39-11 A and B, Epiphyseal reaming for a reverse prosthesis during revision shoulder arthroplasty.

Figure 39-12 A and B, Metaphyseal reaming for a reverse prosthesis during revision shoulder arthroplasty.

Figure 39-13 A and B, Diaphyseal reaming for a reverse prosthesis during revision shoulder arthroplasty.

Figure 39-14 A and B, Insertion of the trial humeral component during revision shoulder arthroplasty with a reverse prosthesis.

Figure 39-15 A and B, Marking retroversion of the humeral component during revision shoulder arthroplasty with a reverse prosthesis.

Revision cases with proximal humeral insufficiency may require proximal humeral osseous reconstruction with a bone graft. In general, in any case in which the rotator cuff insertion is compromised and glenoid bone stock allows, we will use a reverse prosthesis for revision arthroplasty. In cases of proximal humeral insufficiency limited to the proximal humeral metaphysis, no bone graft is indicated because the reverse prosthesis can be implanted into the intact humeral diaphysis (Fig. 39-16). In cases in which proximal humeral bone loss extends distally and compromises the proximal humeral diaphysis, bone graft reconstruction of the proximal humeral diaphysis is indicated (Fig. 39-17). In many cases, only a portion of the proximal humeral diaphysis is deficient (anterior or posterior). For this reason we prefer to reconstruct only the portion that is deficient and leave any native bone intact. Fresh frozen cortical strips of allograft tibia are used for the reconstruction (Fig. 39-18). The residual diaphysis is reamed with the hand reamers.

Figure 39-16 Patient with proximal humeral bone loss that did not require proximal humeral bone graft reconstruction before (A) and after (B) revision arthroplasty with a reverse prosthesis.

Figure 39-17 Patient with severe proximal humeral bone loss that required proximal humeral bone graft reconstruction before (A) and after (B) revision arthroplasty with a reverse prosthesis.

Figure 39-18 Fresh frozen allograft tibial strips used in proximal humeral reconstruction.

Depending on the length of the humeral defect, we place two or three cables composed of a nylon monofilament core wrapped in a braided ultrahigh-molecular-weight polyethylene (Kinamed, Inc., Camarillo, CA) subperiosteally around the residual native humerus with the cable-passing instrumentation provided (Fig. 39-19). One or two allograft strips are trimmed to fit the diaphyseal defect and placed in the defect. The trial humeral stem is placed in the humeral diaphysis, and the allograft is placed in the diaphyseal defect (Fig. 39-20). The cables are tightened in a distal-to-proximal direction with the tensioning device (Fig. 39-21). The humeral stem is removed while leaving the reconstructed proximal humerus, and attention is turned to the glenoid, if indicated (Fig. 39-22).

Figure 39-19 A and B, Passage of fixation cables to secure the allograft during proximal humeral reconstruction.

Figure 39-20 A and B, Placement of the allograft strip over the diaphyseal defect during proximal humeral reconstruction.

Figure 39-21 A and B, Tensioning of fixation cables during proximal humeral reconstruction.

Figure 39-22 A and B, The trial humeral stem is removed while leaving the reconstructed proximal humerus.

In cases in which a proximal humeral osteotomy has been performed for removal of the humeral stem, the cerclage cables are secured before removal of the trial humeral stem (see Chapter 38). In cases in which the native humeral cortex is excessively thin, fresh frozen allograft cortical struts are placed around the native humerus beneath the cables before tightening them to provide additional support for the proximal humerus, as shown in Chapter 38. The trial humeral stem is removed and attention is turned to the glenoid, if indicated.

Periprosthetic Fracture

In cases of periprosthetic fracture, the fracture must be reduced before placement of the revision humeral stem. The fracture and associated structures (i.e., the radial nerve) are exposed as detailed in Chapter 37. The humerus distal to the fracture site is reamed with the diaphyseal reamers introduced at the fracture site (Fig. 39-30). The humerus proximal to the fracture site is prepared with the instrumentation provided for the selected humeral stem. It is often helpful to stabilize the proximal humeral fragment with a bone clamp during preparation of the proximal humerus (Fig. 39-31).

Figure 39-30 A and B, The humerus distal to the fracture site is reamed with diaphyseal reamers introduced at the fracture site.

Figure 39-31 A and B, The humerus proximal to the fracture site is prepared with the instrumentation provided for the selected humeral stem.

Once the proximal humerus has been prepared, the fracture is reduced and the trial humeral stem is placed. A humeral stem that bypasses the distal extent of the fracture by a minimum of two cortical diameters is selected (Fig. 39-32).¹ The position of the humeral stem within the humerus is noted after trial reduction and stability testing, as previously described. Fresh frozen cortical strips of allograft tibia are used on each side of the humerus and centered at the fracture site. We place two or four cables composed of a nylon monofilament core wrapped in a braided ultrahigh-molecular-weight polyethylene (Kinamed Inc., Camarillo, CA) subperiosteally around the residual native humerus with the cable-passing instrumentation provided while taking care to avoid the radial nerve posteriorly (Fig. 39-33). The cables are tightened with the tensioning device, the humeral stem is removed, and the periprosthetic fracture is left reduced (Fig. 39-34). The humeral canal is irrigated with sterile saline and dried with suction and gauze sponges. The final humeral implant is cemented into place with antibiotic-impregnated cement via the technique previously described in this chapter (Fig. 39-35). The cement is allowed to cure before reducing the glenohumeral joint.

Figure 39-32 A, Preoperative radiograph. B, The humeral stem selected should bypass the distal extent of the fracture by a minimum of two cortical diameters.

Figure 39-33 A and B, Cables placed for fixation of a cortical strip allograft during treatment of a periprosthetic humeral fracture by revision arthroplasty.

Figure 39-34 A and B, The humeral stem is removed, leaving the periprosthetic fracture reduced.

Figure 39-35 A and B, The final humeral implant is cemented into place with antibiotic-impregnated cement.