Effect of Calcar Screw Use in Surgical Neck Fractures of the Proximal Humerus With Unstable Medial Support: A Biomechanical Study.

OBJECTIVES

To evaluate the effect of calcar screw use in proximal humeral fractures with unstable medial support treated with locked plates.

METHODS

Standard osteotomies were performed in 36 cadaveric humeri to create a surgical neck fracture proximal humeral model. For static testing, 12 pairs of humeri were divided into 4 groups: normal alignment and varus deformity groups with and without 5-mm medial deficiencies. Calcar screw function was measured in each group by axial, shear, and torsion stiffness tests. Another 6 pairs of humeri with 5-mm medial deficiencies were subjected to cyclic loading tests in the normal alignment model with and without calcar screw application.

RESULTS

Calcar screws improved rotational stability in the normal alignment (P = 0.007) and varus (P = 0.002) groups. Calcar screws improved static and cyclic axial (P = 0.004) and shear (P = 0.017) stability in the normal alignment group with medial deficiency. In specimens with normal alignment and intact medial cortex, calcar screws provided no advantage in axial (P = 0.535) or shear (P = 0.537) stiffness. Calcar screws did not provide sufficient axial (P = 0.782) or shear (P = 0.772) stability to avoid reduction loss in humeri with varus malreduction.

CONCLUSIONS

In humeri with normal alignment, calcar screws can provide additional stability even when a medial deficiency exists. The use of calcar screws in humeri with varus deformity showed no biomechanical superiority.