Proximal humerus fracture rotational stability after fixation using a locking plate or a fixed-angle locked nail: the role of implant stiffness.

BACKGROUND

Fixed-angle locked devices have been developed to improve internal fixation of proximal humerus fractures. Available low-profile precontoured locking plates and intramedullary nails with fixed-angle interlocks are currently favored by most surgeons in this setting. The aim of this study was to assess the relative stability of these two methods of fixation under torsion load.

METHODS

A surgical neck osteotomy was created in six pairs of embalmed humeri. In each pair, one specimen was secured with a titanium locking-compression plate, and the contralateral was secured with a titanium nail with a proximal locked spiral blade. The specimens were first tested cyclically in internal-external rotation for 10,000 cycles to evaluate interfragmentary motion (dynamic study). At the end of the cyclic testing, the specimens were loaded to failure in external rotation to measure torque to failure and construct stiffness (static study).

FINDINGS

There were no significant differences in interfragmentary motion between the two fixation devices in the dynamic study. When tested to failure, fixation with the locking plate tolerated on average 20 more degrees in torsion before failure, and demonstrated higher torsional load to failure and less torsional stiffness (P<0.05).

INTERPRETATION

Both locking plates and locked intramedullary nails may provide enough stability to avoid secondary displacement of proximal humerus fractures during early physical therapy. Locking plates demonstrated superior biomechanical properties under high rotational loads than locked intramedullary nails in a cadaveric proximal humerus two-part osteotomy model, and could provide more protection against unexpected high torsion loads.