Compliant cervical screw locking mechanism

1. An orthopedic device comprising:

a screw assembly configured to be coupled to a bore of an implant member, said screw assembly including;

a bone screw having a head section, a thread section, and a central bore;

an expandable ring coupled to said head section; and

a pin at least partially disposed in said central bore; wherein

said pin includes a varying outer profile that engages said expandable ring to vary an outer diameter of said expandable ring to couple said screw assembly in said bore of said implant member; and

wherein said expandable ring comprises a continuous outer member.

2. The orthopedic device of claim 1 , wherein said expandable ring further comprises:

a generally circular perimeter; and

a plurality of recesses extending inwardly from said generally circular perimeter;

wherein said plurality of recesses define a plurality of flexural members in said expandable ring.

3. The orthopedic device of claim 2 , wherein said plurality of flexural members define a center orifice having a generally circular center with a plurality of extending channels;

said extending channels being configured to receive guide features on said orthopedic screw.

4. The orthopedic device of claim 3 , wherein said flexural members are configured to deflect in response to an insertion of said pin into said center orifice.

5. The orthopedic device of claim 4 , wherein said deflection of said flexural members in response to an advancement of said pin into said center orifice generates an increase in a diameter of said generally circular perimeter.

6. The orthopedic device of claim 5 , further comprising:

a plurality of driving features formed on said head section of said bone screw;

said driving features including a protruding inner edge, said edge defining an inner ring channel;

wherein said plurality of recess of said ring are configured to be moveably received said inner ring channel.

7. An orthopedic device comprising:

an implant member including a thru-bore having an entry diameter, an intermediate diameter, and an exit diameter, wherein said intermediate diameter is larger than said entry diameter and said exit diameter; and

a screw assembly including:

wherein said screw assembly further comprises:

a bone screw having a head section, a thread section, and a central bore;

an expandable ring coupled to said head section; and

a pin at least partially disposed in said central bore; wherein said pin includes a varying outer profile that engages said expandable ring to vary an outer diameter of said expandable ring to couple said screw assembly in said thru-bore of said implant member; and

wherein said expandable ring comprises a continuous outer member.

8. The orthopedic device of claim 7 , wherein said expandable ring further comprises:

a generally circular perimeter; and

a plurality of recesses extending inwardly from said generally circular perimeter; wherein

said plurality of recesses define a plurality of flexural members in said expandable ring.

9. The orthopedic device of claim 8 , wherein said plurality of flexural members define a center orifice having a generally circular center with a plurality of extending channels;

said extending channels being configured to receive guide features on said orthopedic screw.

10. The orthopedic device of claim 9 , wherein said flexural members are configured to deflect in response to an insertion of said pin into said center orifice, said deflection generating an increase in a diameter of said generally circular perimeter.

11. The orthopedic device of claim 10 , further comprising:

a plurality of driving features formed on said head section of said bone screw;

said driving features including a protruding inner edge, said edge defining an inner ring channel; wherein

said plurality of recess of said ring are configured to be moveably received said inner ring channel.

12. The orthopedic device of claim 9 , in which said pin is a substantially cylindrical member which further comprises:

a proximal end and a distal end, said distal end comprising as entry taper;

a retention cut-out portion comprising a small diameter surface which substantially corresponds to a diameter of said center orifice of said expandable ring;

an entry body disposed between said entry taper and said retention cut-out portion, said entry body being configured to a least slightly expand said center orifice of said expandable ring;

a locking surface configured to expand said expandable ring to frictionally engage said intermediate diameter of said thru-bore of said implant member; and

a graduated expansion surface disposed between said retention cut-out portion and said locking surface.