Intramedullary nailing in humeral shaft fractures. Mechanical behavior in vitro after osteosynthesis with three different intramedullary nails.

The aim of this in vitro study was to compare the mechanical behavior of fixation by the Russell-Taylor nail with the more recent Polarus nail. Fixation with an experimental nail made from polyacetal polymer was also included in the study. Thirty humeri were fractured and randomized to receive one of the three nail types. A four-point nondestructive bending test was performed, as well as torsional testing to failure. The torsional test was designed to record the amount of 'play' (uncontrolled rotation) in the bone/implant construct. The Polarus nail gave higher rigidity of the nail/bone construct than the two other types. The Russell-Taylor nailing exhibited a high degree of 'play' (uncontrolled rotation). The polyacetal nails allowed a large elastic deformation before failure.