Complete Surface Replacement

We rarely perform complete surface replacement of the humeral head in our practice. As detailed in Chapter 6, we perform glenoid resurfacing in most shoulder arthroplasty candidates with an indication other than acute fracture. The most common indication for which we will use a complete humeral surface replacement is early-stage humeral head osteonecrosis in an active patient younger than 50 years in whom the segment of necrotic bone is sufficiently small that it will not jeopardize implant fixation, typically less than 25% of the humeral head. An additional indication is an exceptionally young, otherwise healthy patient who is a candidate for shoulder arthroplasty. Most of our patients falling into this category have chondrolysis of the glenohumeral joint after an arthroscopic instability procedure. In these cases we will consider use of a complete humeral head surface replacement combined with biologic resurfacing of the glenoid (see Chapter 34).

In addition to the standard contraindications to unconstrained shoulder arthroplasty (see Chapter 6), any condition jeopardizing implant fixation is a contraindication to humeral head surface replacement (i.e., proximal humeral fracture, extensive proximal humeral osteonecrosis). Moreover, insertion of a standard polyethylene glenoid component is a relative contraindication to use of a humeral head surface replacement, and in the vast majority of cases a conventional stemmed humeral implant should be used instead. As detailed in Chapter 10, glenoid exposure is the most important portion of prosthetic glenoid resurfacing, and preservation of a portion of the humeral head should never be favored over optimal glenoid exposure. Conversely, biologic resurfacing typically does not involve correction of glenoid deformity and does not entail the use of a pegged or keeled glenoid component. These concessions usually make biologic glenoid resurfacing possible with the more limited glenoid exposure available during humeral head resurfacing.

Partial Surface Replacement

Partial surface replacement is indicated in patients with localized full-thickness defects of the articular cartilage of the humeral head who have failed other treatments. When patients with full-thickness articular cartilage lesions of the humeral head are seen in our practice, we initially treat them nonoperatively with nonsteroidal anti-inflammatory medications, selective rest, and activity modification for a period of 6 to 12 weeks. If such treatment proves unsuccessful, we offer arthroscopic treatment of the lesion with débridement and drilling of subchondral bone to stimulate the formation of fibrocartilage. If patients remain symptomatic 6 months after arthroscopic treatment, we will offer them partial surface replacement. In patients older than 30 years, we opt for prosthetic replacement with a metallic device (Hemicap, Arthrosurface, Inc., Franklin, MA). In younger patients, we opt for matched osteochondral allograft replacement. In our experience, it is rare for a patient to fail arthroscopic treatment of these localized articular cartilage lesions, thus minimizing the indications for partial surface replacement.

Contraindications specific to partial surface replacement include cartilaginous lesions larger than 35 mm in diameter (the diameter of the largest implant available), the presence of nonlocalized disease (Fig. 33-1), and the absence of sufficient bone quality to support the implant.

Figure 33-1 A and B, Radiographs of a patient who had undergone partial resurfacing of the humeral head for primary osteoarthritis. The patient never improved after surgery, and revision to a standard unconstrained total shoulder arthroplasty was eventually performed.

Complete Surface Replacement

For complete surface replacement, we use a system (Tornier, Inc., Stafford, TX) that allows the same 12 different humeral head sizes available for stemmed unconstrained arthroplasty. We believe that selection of the appropriate humeral head size is no less important in humeral surface replacement than in stemmed humeral arthroplasty. After exposure of the humeral head is complete and peripheral humeral osteophytes are removed, the size of the humeral head is determined with the sizing guides (Fig. 33-4). If the native humeral head is between two sizes, the smaller size is selected. The pin guide corresponding to the selected humeral head size is centered over the humeral articular surface (Fig. 33-5). The guide pin is drilled into the proximal humerus through the cannulated pin guide until it engages the lateral humeral cortex (Fig. 33-6). The pin guide is removed and the guide pin left in place (Fig. 33-7). A reamer of the appropriate size is advanced over the guide pin, and the humerus is reamed until the leading edge of the reamer is in contact with the humeral anatomic neck (Fig. 33-8). The reamer is removed and a trial head gauge is inserted over the guide pin to ensure that the reamed humeral surface conforms to the back surface of the implant by looking through fenestrations in the trial head gauge (Fig. 33-9). The trial head gauge is removed, and a cannulated stem compactor of appropriate size is advanced over the guide pin until the collar is flush with the humeral surface (Fig. 33-10). The cannulated stem compactor is removed with the guide pin. The final humeral implant is oriented in the stem hole and impacted into place with the smooth compactor (Fig. 33-11). The glenohumeral joint is reduced.

Figure 33-4 A and B, Determination of the proper humeral head implant diameter.

Figure 33-5 A and B, The pin guide is centered over the articular surface of the humeral head.

Figure 33-6 A and B, Placement of the guide pin with the pin guide.

Figure 33-7 A and B, Final position of the guide pin.

Figure 33-8 A and B, Reaming of the articular surface of the humeral head.

Figure 33-9 A and B, Placement of the trial head gauge to ensure that the implant will fully seat.

Figure 33-10 A and B, Insertion of the cannulated stem impactor.

Figure 33-11 A and B, Insertion of the final humeral implant.

The subscapularis is closed with interrupted no. 2 braided permanent tendon-to-tendon suture. The closure is reinforced with a running no. 1 braided absorbable suture. The wound is then closed as for other cases of shoulder arthroplasty.

Partial Surface Replacement

A drill guide just large enough to circumscribe the articular cartilage lesion is selected (Fig. 33-12). Available sizes are 25, 30, and 35 mm. A guide pin is inserted to the level of the laser mark by using the drill guide centered in the articular cartilage defect (Fig. 33-13). The drill guide is removed and a cannulated drill is passed over the guide pin until it is flush with the humeral head articular surface (Fig. 33-14). A tap is advanced over the guide pin and removed (Fig. 33-15). The central screw is advanced over the guide pin until the laser mark on the screw driver is flush with the articular surface of the humeral head (Fig. 33-16). The guide pin is removed and the central hole of the screw is cleaned with the taper cleaner (Fig. 33-17). A trial cap is inserted and should be at or below the level of the articular cartilage (Fig. 33-18). If the trial cap is prominent, it is removed, the screw is advanced half a revolution, and the position of the trial cap is rechecked. The centering shaft is placed in the central hole of the screw, and measurements are made with the specially designed measurement contact probe at the superior, inferior, medial, and lateral margins (Fig. 33-19) and recorded on the sizing card (Fig. 33-20). Selection of implant diameter is based on the measurements recorded on the sizing card, and the maximal measurement recorded is used. An example is shown in Figure 33-21. The centering shaft is removed and a guide pin is replaced in the central hole of the screw.

Figure 33-12 A and B, Drill guide used for partial humeral head resurfacing.

Figure 33-13 A and B, Insertion of the guide pin used in partial humeral head resurfacing.

Figure 33-14 A and B, Drilling the hole for the central screw used in partial humeral head resurfacing.

Figure 33-15 A and B, Tapping the screw hole.

Figure 33-16 A and B, Placement of the central screw.

Figure 33-17 A and B, Cleaning the central screw with the taper cleaner.

Figure 33-18 A and B, The trial cap is inserted to ensure that the central screw has been advanced sufficiently.

Figure 33-19 A to C, Each quadrant of the humeral head is measured with the contact probe placed over the centering shaft.

Figure 33-20 Measurements are recorded on the sizing card.

Figure 33-21 Example of implant size selection based on information recorded on the sizing card.

A surface reamer appropriate for the implant chosen is selected and used for reaming until it contacts the screw (Fig. 33-22). The reamer and guide pin are removed, and the central screw hole is cleaned with the taper cleaner. The appropriate sizing trial is placed in the central screw hole to ensure that the final implant will not be prominent (Fig. 33-23). The edges of the trial implant should be flush or slightly recessed with respect to the surrounding intact articular surface. The trial is removed and the central screw hole cleaned with the taper cleaner. The final implant is placed onto the central screw with the suction inserter (Fig. 33-24). The inserter is removed by disconnecting the suction, and the implant is impacted into place with the impactor provided (Fig. 33-25). The glenohumeral joint is reduced.

Figure 33-22 A and B, Reaming with a surface reamer corresponding to the selected implant size.

Figure 33-23 A and B, Placement of the sizing trial to ensure that the final implant will not be prominent.

Figure 33-24 A and B, Placement of the final implant onto the central screw with the suction inserter.

Figure 33-25 A and B, Impaction of the surface component of the final implant.

The subscapularis is closed with interrupted no. 2 braided permanent tendon-to-tendon suture. The closure is reinforced with running no. 1 braided absorbable suture. The wound is then closed as for other cases of shoulder arthroplasty.