Design of a retractable intramedullary nail for the humerus.

This paper describes the design of a retractable intramedullary nail for the humerus that does not require inter-locking screws. The developed nail has a series of fins which open out from the casing to grip the medullary canal of the bone, thus securing it in position. Prototypes of the nail have been mechanically tested using static compression, dynamic compression and static torsion tests. During the compression tests no nails were found to fail. Statically a mean force of 809 N was withstood. During dynamic testing all the nails survived 1 million cycles, with a maximum applied load of 400 N. In torsion the two nails failed at 1.0 and 2.2 N m. Based on the mechanical testing, the retractable intramedullary nail would appear strong enough to withstand the expected loading conditions in the human body.