Humerus

The most common humeral complication is iatrogenic fracture, which usually results from performing an overly aggressive dislocation maneuver without previous adequate soft tissue release. Many patients undergoing reverse shoulder arthroplasty have moderate to severe osteopenia, thus placing them at increased risk for this complication. Intraoperative tuberosity fractures during glenohumeral dislocation are less common during reverse shoulder arthroplasty than during unconstrained shoulder arthroplasty because of the lack of a rotator cuff attaching to the tuberosities, which could otherwise contribute to fracture during a dislocation maneuver. Fractures involving the humeral diaphysis should be reduced and a long-stem humeral implant placed. Allograft struts and cerclage cables may be added in patients with severe osteopenia (Fig. 32-1).

Figure 32-1 Patient with an intraoperative humeral diaphyseal fracture treated by placement of a long-stem humeral component and allograft struts fixed with cerclage cables.

Intraoperative fractures involving the greater or lesser tuberosities (or both) are usually nondisplaced. Many of these fractures are stable or become stable once the humeral implant is inserted (Fig. 32-2). If a greater tuberosity fracture fragment that has maintained attachment of a substantial portion of the posterior rotator cuff is not satisfactorily stable, suture fixation of the tuberosity is performed and the postoperative rehabilitation adjusted accordingly to allow healing of the tuberosity. A greater tuberosity fracture fragment that is devoid of rotator cuff attachment and is unstable may simply be excised.

Figure 32-2 Postoperative radiograph of a patient with a nondisplaced lesser tuberosity fracture without any specific treatment.

Intraoperative lesser tuberosity fractures commonly occur during retraction of the proximal humerus in the course of glenoid preparation and insertion. The thin anterior cortex of the humeral metaphysis, including the lesser tuberosity, may be crushed by the humeral retractor (Fig. 32-3). Creation of this fracture is often necessary to obtain adequate glenoid exposure during insertion of the reverse prosthesis through a deltopectoral approach. This fracture is without clinical consequence and can largely be ignored.

Figure 32-3 Fracture (arrows) of the lesser tuberosity caused by proximal humeral retraction during implantation of a reverse-prosthesis glenoid component.

Glenoid

Intraoperative glenoid fractures are more detrimental than humeral injury. Frequently, surgeons who are beginning their experience in reverse shoulder arthroplasty do not have much proficiency in glenoid preparation because they have previously performed hemiarthroplasty for most cases in which shoulder arthroplasty is indicated. Many surgeons initially attempt to ream the glenoid as though it were an acetabulum (i.e., overaggressively), which often leads to obliteration of the glenoid bone, to glenoid fracture, or both. Patients undergoing reverse shoulder arthroplasty are at particular risk for intraoperative glenoid fracture because they tend to have more osteopenia than patients undergoing unconstrained arthroplasty for nonfracture conditions. Fractures may involve only the peripheral glenoid rim or may extend significantly into the central portion of the glenoid. Adequate capsular release helps minimize the risk for glenoid fracture. Additionally, a motorized reamer (not a drill, because the speed and torque are different) should be used for preparation of the glenoid surface. The reamer should be started before the surgeon applies force to engage the reamer onto the glenoid face. This avoids having the reamer “catch” an edge of the glenoid, which may cause a fracture.

Fractures that involve only a small portion of the peripheral rim generally require no treatment, and the glenoid component can be inserted as planned. Glenoid fractures that extend into the central portion of the glenoid should be bone-grafted with the humeral head. The reverse glenoid component can be inserted to help secure the bone graft and internally fix the fracture. If the central post of the reverse component is firmly seated within native glenoid bone, consideration can be given to placing the humeral component in the same surgical setting. If the glenoid component does not seem secure or the central post of the glenoid base plate is not firmly seated in unfractured native glenoid bone, the humeral component should be initially omitted for 6 months to allow the fracture to heal. After 6 months a humeral component can be placed as the second part of a two-stage procedure (Fig. 32-4). Alternatively, if an intraoperative glenoid fracture occurs, the fracture can be bone-grafted and the humeral stem plus a hemiarthroplasty adapter placed (Fig. 32-5). After the fracture has healed and remodeled (around 6 months after the index attempt at reverse shoulder arthroplasty), the second stage of the procedure, consisting of implantation of the glenoid component, may be performed (Fig. 32-6).

Figure 32-4 Case in which an intraoperative fracture of the glenoid was treated by bone grafting from the humeral head and placement of the glenoid component. Placement of the humeral component was delayed 6 months until the fracture had healed and remodeled.

Figure 32-5 Intraoperative glenoid fracture treated by bone grafting from the humeral head and placement of the reverse stem and hemiarthroplasty adapter.

Figure 32-6 Placement of the glenoid component is performed 6 months after bone grafting of the glenoid and placement of the reverse stem and hemiarthroplasty adapter. At the time of the second stage, the hemiarthroplasty adapter is simply removed and a polyethylene insert is placed, thereby eliminating the need for exchange of the humeral stem.

Rotator Cuff

With proper exposure, intraoperative injury to the rotator cuff is rare. Although patients undergoing reverse shoulder arthroplasty have a compromised rotator cuff, every effort should be made to preserve any rotator cuff function that remains, both anteriorly and posteriorly. Repair of the subscapularis tendon after reverse shoulder arthroplasty helps prevent postoperative dislocation. Preservation of the posterior rotator cuff improves outcomes by allowing active external rotation postoperatively. If the rotator cuff is adequately visualized, inadvertent damage to the rotator cuff during reverse shoulder arthroplasty can be avoided.

Neurovascular Structures

Catastrophic injury to the neurovascular structures around the shoulder is exceedingly rare during reverse shoulder arthroplasty. The neural structures most at risk during reverse shoulder arthroplasty are the axillary and musculocutaneous nerves. These nerves should not be at risk for transection during primary arthroplasty using accepted operative technique. Neuropraxic injury caused by stretch most commonly involves the axillary nerve, but any nerves within the brachial plexus can be affected. Care should be taken when positioning the patient to maintain the cervical spine in neutral alignment to avoid a stretch injury to the brachial plexus. We have yet to establish risk factors for neuropraxic injury to the axillary nerve. Logic would suggest that patients with the most stiffness creating difficulty in glenoid exposure would be at the highest risk for this type of complication. Our clinical experience has not borne this out, however, and we are currently unable to predict which patients are most likely to suffer this complication. Patient education preoperatively is of paramount importance in dealing with neuropraxia inasmuch as patients are much more accepting if they have heard about the possibility of this complication before surgery. Axillary nerve (and other nerve) neuropraxia is treated by observation, with most patients recovering by 3 to 4 months postoperatively.

Although tearing of the cephalic vein is common and largely without consequence, significant arterial and venous injuries occurring during primary reverse shoulder arthroplasty performed for nonfracture indications are exceptionally rare. Injury to the major upper extremity vessels is usually caused by overzealous medial dissection, which is not needed during shoulder arthroplasty. Should one of these injuries occur, after cross-clamping of the injured vessel, emergency intraoperative consultation with a vascular surgeon is required.