CHAPTER 33 Humeral Surface Replacement
The advantage of complete surface replacement of the humeral head lies mainly in preservation of subchondral bone.1 In our practice, few situations exist in which complete surface replacement of the humeral head is more advantageous than conventional humeral head replacement with a stemmed implant. Additionally, use of these surface replacement implants hinders glenoid exposure and thus prevents implantation of a prosthetic glenoid implant in many cases.
INDICATIONS AND CONTRAINDICATIONS
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.
TECHNIQUE FOR PROSTHETIC RESURFACING
The operating room setup, anesthesia, patient positioning, skin preparation, surgical draping, and surgical approach are identical to that for humeral surface replacement and other shoulder arthroplasties (see Chapters 3, 4, and 8). The first difference in the technique involves handling of the anterior humeral circumflex vessels and subscapularis. When performing humeral surface replacement, we prefer to leave the anterior humeral circumflex vessels intact to maintain optimal blood flow to the humeral head. Consequently, after placing stay sutures in the subscapularis tendon as for unconstrained shoulder arthroplasty, we end our subscapularis tenotomy just superior to the anterior humeral circumflex vessels (Fig. 33-2). Subscapularis and capsular release is rarely necessary in patients undergoing humeral surface replacement. Next, the humeral head is dislocated by externally rotating and extending the arm. Hohmann retractors are placed circumferentially around the humeral head to complete the proximal humeral exposure (Fig. 33-3).
Figure 33-3 A and B, Completed proximal humeral exposure for surface replacement of the humeral head.
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
