Reducing Postoperative Fracture Displacement After Locked Plating of Proximal Humerus Fractures: Current Concepts

Others have successfully used cancellous allograft to fill humeral head bone defects.^29,32,47-49 Duralde and Leddy⁴⁷ reported 100% radiographic union and 81% good to excellent results in cases treated with a locking plate and morselized cancellous allograft to fill bone voids. Varus collapse and screw cutout did not occur, but there were 2 cases of AVN. Ricchetti and colleagues²⁹ reviewed 54 cases treated with a locking plate and rotator cuff suture construct. Allograft cancellous chips and demineralized bone matrix were used in 3- and 4-part fractures (70% of cases) along with shorter screws in the humeral head. Major complications included AVN (1), fixation failure (3), and varus malunion (5). Others investigators have had less favorable results with use of cancellous bone graft. Schliemann and colleagues¹⁹ reported on 27 patients who were older than 65 years when they underwent ORIF with rotator cuff sutures to stabilize the tuberosities and either cancellous graft or a synthetic bone substitute in patients with massive metaphyseal defects. Patient-reported outcomes were superior to Constant scores. Complications included screw penetration (22.2%), reduction loss (44.4%), implant failure (3.7%), and AVN (29.6%).

Autograft. Autograft has both osteoconductive and osteoinductive properties and has been successfully used for metaphyseal defects.^32,50 Kim and colleagues⁵⁰ reported on patients with 4-part proximal humerus fractures treated with a locking plate and autologous iliac graft. All cases achieved union and had good or excellent outcomes. There were no cases of AVN, varus collapse, or hardware-related complications.

Bone Cement. Calcium phosphate cement has osteoconductive properties and enhances screw purchase in cancellous bone (Figures 2A–2F). It can be injected or molded into bone voids to provide improved compressive strength. It is resorbed through cell-mediated processes resembling bone remodeling and does not disappear until new bone forms. (Calcium sulfate cement, on the other hand, resorbs through a chemical process independent of new bone formation.⁵¹) Egol and colleagues⁵² reviewed the cases of 92 patients (mean age, 61 years) with 2-, 3-, and 4-part proximal humerus fractures treated with locked plate fixation. Metaphyseal defects were treated with no augmentation, augmentation with cancellous chips, or augmentation with calcium phosphate cement. Adding calcium phosphate cement was associated with lower incidence of intra-articular screw penetration and humeral head settling. In a recent cadaveric biomechanical study using 2-part proximal humerus fractures with metaphyseal comminution, the group augmented with calcium phosphate cement had enhanced axial stiffness and load to failure with reduced screw penetration.⁵³ Other biomechanical studies have found increased screw pullout strength⁵⁴ and decreased interfragmentary motion when specimens were augmented with calcium phosphate cement.⁵⁵

Similar good clinical and radiographic outcomes have been observed with use of calcium sulfate cement.^56,57 Somasundaram and colleagues⁵⁶ reported good clinical outcomes in 82% of patients treated with locking plates and calcium sulfate cement used to fill metaphyseal voids. All fractures united without infection, fixation failure, subsequent malunion, tuberosity failure, or AVN. Lee and Shin⁵⁷ compared outcomes of 14 patients who received calcium sulfate augmentation with outcomes of patients who did not receive this augmentation. Overall, 89% of patients had good or excellent results. Calcium sulfate cement did not affect the reduction failure rate or clinical outcomes in cases in which medial cortical reduction was achieved. However, postoperative displacement caused by lack of medial support was associated with poor outcomes.

Screw Placement

Screws optimally should be placed in the posterior-medial-inferior aspect of the humeral head to provide medial support for the fracture and mechanical stability.⁵⁸ Cadaveric studies have shown the highest cancellous bone density in the proximal, posterior, and medial portions of the humeral head.^59-63 Similarly, in a cadaveric study, Liew and colleagues⁶¹ found greater screw purchase and higher pullout strength when the screw was placed in the center of the humeral head, within subchondral bone; fixation was poorest when the screw was placed in the anterosuperior region of the humeral head. Tingart and colleagues⁶² reported that humeral head trabecular density significantly affected pullout strength of cancellous screws. In addition, the most pullout strength was at the center of the head, and the least within the anterosuperior head. Trabecular density was higher in the inferior and posterior regions than in the superior and anterior regions.

Most locking plate designs allow screws to be placed at the level of the medial calcar—the goal being to provide medial column support (Table 2). Zhang and colleagues⁵⁸ treated 2-, 3-, and 4-part fractures with a locking plate and randomized them into receiving the plate with or without medial support screws. For 3- and 4-part fractures, the group with these screws had a significantly greater final neck-shaft angle and smaller angulation loss compared with the group without screws. No additional benefit was found for 2-part fractures. Erhardt and colleagues⁶³ simulated unstable proximal humerus fractures using cadavers and testing different fixation methods using a polyaxial locking plate. They found that 5 screws in the head fragment and an inferomedial support screw significantly reduced the risk of screw perforation. Other authors have concluded that placing 1 or more inferomedial screws is important in cases of medial comminution or medial column malreduction.²⁶ Interestingly, compared with use of a polyaxial implant, which allows for adjustment of screw direction, use of a monoaxial locking plate did not lead to a clinically different outcome or complication profile.⁶⁴