Extension drive mechanism for intramedullary extension nails

An extension drive mechanism for causing an intramedullary nail to extend or to retract in an application area so as to enable a bone to extend or to retract in a controlled manner, the extension drive mechanism comprising:

• a direction control part having direction control pins on a bottom surface thereof, said direction control part being rotatable;
• a bearing housing positioned on the bottom surface of said direction control part, said bearing housing having movement surfaces on an interior thereof;
• a plurality of needle bearings positioned within each of the movement surfaces in said bearing housing, said plurality of needle bearings being arranged in at least pairs and having respective axes that are changeable by the direction control pins;
• a plurality of bearing springs positioned respectively between said plurality of needle bearings, said plurality of bearing springs separating respectively said plurality of needle bearings by urging against a side surface of the needle bearing;
• a drive shaft positioned between said plurality of needle bearings from a lower end of said bearing housing, said plurality of needle bearings causing said drive shaft to rotate either clockwise or counterclockwise by said plurality of needle bearings;
• and
• a gear motor engaged with an upper end of said direction control part, said gear motor cooperative with said direction control part so as to cause said direction control part to be driven in said desired rotational direction for rotating said drive shaft.