3.1.3. Sizing

The preparation of the metaphysis for modern components that rely on peripheral fixation typically aims to place the component "bowl" so that it will leave 2–4 mm of cancellous bone between the component and the cortical rim of the metaphysis (Figure 8). A wider distance may be advantageous in patients with a stronger bone that does not require maximizing peripheral fixation. The guide pin for the reaming of the metaphysis may be centered using a trial humeral head or sizing discs.

**Figure 7.** Use of an extramedullary cutting guide may facilitate predictable osteotomy of the humerus in a specific degree of inclination.

**Figure 8.** Primary component stability may be optimized by the implant fit at the periphery of the proximal humerus, within 2–4 mm of the cortical rim. (**A**), Sizing disk; (**B**), Trial; (**C**), Humeral component.

#### 3.1.4. Humeral Preparation and Implantation

Since short and stemless humeral components do not provide selfaligning features, surgeons must be extremely careful at the time of compactor preparation and component implantation to replicate the desired alignment based on the preoperative planning and the osteotomy performed. The most common pitfall is to place the component in an excessive varus. As such, an effort must be made to use the compactor/inserter handle when pushing into the varus.

#### 3.1.5. Humeral Head Selection

The resected humeral head provides a grea<sup>t</sup> reference for the selection of the correct diameter and also for the thickness. The geometry of the humeral head can be perfectly replicated by selecting the right combination of diameter, thickness, and eccentricity. In shoulders with a severe preoperative soft tissue imbalance, changes in the humeral head thickness or in diameter may be needed. As mentioned previously, arthritic shoulders with a severe posterior subluxation may require the use of a thicker humeral head to properly tension the posterior capsule and cuff. In shoulders with avascular necrosis, it may be wise to downsize the humeral head since there is a higher risk of stiffness. Intraoperative testing may be used to confirm an adequate soft tissue balance in anatomic shoulder arthroplasty (Table 2).

**Table 2.** Intraoperative assessment of the soft tissue balance in anatomic shoulder arthroplasty.

