| CPC A61F 2/447 (2013.01) [A61F 2/442 (2013.01); A61F 2/28 (2013.01); A61F 2002/30579 (2013.01); A61F 2/4611 (2013.01)] | 15 Claims |

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1. An anti-loosening rotational drive mechanism for an expandable cage comprising:
a drive housing;
a drive screw rotatably coupled with the drive housing, the drive screw having a circumferential slot with a lower part that includes flat surfaces creating high flat surfaces and low flat surfaces;
one or more flexible retention pins positioned within retention pin holes in the drive housing configured to frictionally engage the high flat surfaces and low flat surfaces in the circumferential slot to resist drive screw rotation.
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