MODES OF FIXATION FAILURE IN PROXIMAL HUMERUS FRACTURES

Abstract

To identify mechanisms of failure in plate and nail fixation in proximal humerus fractures. 5% of the proximal humerus fractures need surgical fixation, which is carried out, principally, by open reduction and internal fixation or closed reduction and intramedullary nailing. Fixation failure remains a problem. This study answers the mode of failure of these implants regardless of the fracture personality. In-vitro testing of proximal humerus fixation devices was undertaken in 30 simulated osteoporotic bone models. Fracture-line was created at the surgical neck of humerus in all samples and fixed with five fixation devices; three plating and two nailing devices. The samples were subjected to failure under compression and torque. Failure was achieved in all models. Three failure patterns were observed in torque testing:

1. The two conventional plates Cloverleaf and T-plate behaved similarly, failing due to screw pull-out from both the proximal and distal fragment with a deformed plate.

2. The PHILOS plate failed by avulsion of a wedge just distal to the fracture site with screws remaining embedded in the bone.

3. Both the nailing systems, Polaris and European humeral nail, failed by a spiral fracture starting at the distal locking screw. In compression testing the modes of failure were:

4. The Clover-leaf and T-plate failed by plastic deformation of plate, backing out of the screw in the proximal fragment followed by fracture of the distal fragment.

5. The PHILOS failed by plastic deformation of plate and fracture of the distal fragment distal to the last locking screws.

6. In both the nails, the proximal fragment screws failed.

The failure mode is dependent on implant properties as well, independent of the fracture personality. It is important to recognise the potential points of failure (proximal or distal fragment) when making the choice of implant to avoid fixation failure.