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A screw system includes a screw and a washer assembly captive to the screw. The washer assembly is polyaxially pivotable relative to the screw. The screw may be freely rotated in one direction relative to the washer assembly, but frictionally binds with the washer assembly when rotated in a second d

A screw system includes a screw and a washer assembly captive to the screw. The washer assembly is polyaxially pivotable relative to the screw. The screw may be freely rotated in one direction relative to the washer assembly, but frictionally binds with the washer assembly when rotated in a second direction.

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1. A system, comprising: a screw, wherein the screw comprises a spherical head; anda washer assembly around the head, wherein the washer assembly comprises: a washer, wherein the washer comprises a socket and a ramp, wherein the socket receives the head to form a ball-and-socket joint, wherein the r

1. A system, comprising: a screw, wherein the screw comprises a spherical head; anda washer assembly around the head, wherein the washer assembly comprises: a washer, wherein the washer comprises a socket and a ramp, wherein the socket receives the head to form a ball-and-socket joint, wherein the ramp extends partially around the socket between a first end which is outwardly displaced from the socket and a second end which is tangential to the socket, and wherein the ramp comprises a semicircularly dished face,a cap secured to the washer, wherein the cap comprises a ring, wherein an inner diameter of the ring is smaller than an equatorial diameter of the spherical head, and wherein the spherical head is interposed between the ring and the socket, anda ball, wherein the ball is positioned between the face and the head, wherein rotation of the head in a first direction urges the ball along the face toward the first end so that the ball fits loosely between the face and the head so that the screw is freely rotatable relative to the washer assembly, wherein rotation of the head in a second direction urges the ball along the face toward the second end until the ball binds between the face and the head so that the screw and the washer assembly are locked together, wherein the second direction is opposite the first direction. 2. The system of claim 1, wherein the washer assembly is captive to the head. 3. The system of claim 1, wherein the ball is continuously biased toward the second end, wherein rotation of the head in the first direction temporarily overcomes the bias to urge the ball toward the first end. 4. The system of claim 1, wherein, when the ball binds between the face and the head, the ball deforms against the head. 5. The system of claim 1, wherein the cap comprises: a cantilever beam, wherein the beam extends between a fixed end of the beam and a free end of the beam, wherein the fixed end is connected to the ring, wherein the free end continuously spring biases the ball toward the second end, wherein rotation of the head in the first direction deflects the beam to temporarily overcome the bias. 6. The system of claim 1, wherein the screw comprises a shaft extending from the head through the washer assembly, wherein the washer assembly comprises a spike pointing along the shaft away from the head. 7. A system, comprising: a screw, wherein the screw comprises a spherical head; anda washer assembly captive to the head, wherein the washer assembly comprises: a washer, wherein the washer comprises a socket and a ramp, wherein the socket receives the head, wherein the ramp extends between a first end which is outwardly displaced from the socket and a second end which is tangential to the socket, and wherein the ramp comprises a semicircularly dished face,a cap secured to the washer, wherein the cap comprises a ring, wherein an inner diameter of the ring is smaller than an equatorial diameter of the head, and wherein the head is interposed between the ring and the socket, anda ball positioned between the face and the head, wherein rotation of the head in a first direction urges the ball along the face toward the first end so that the ball fits loosely between the face and the head, wherein rotation of the head in a second direction urges the ball along the face toward the second end until the ball binds between the face and the head so that the screw and the washer assembly are locked together, and wherein the second direction is opposite the first direction. 8. The system of claim 7, wherein the socket is spherical, wherein the socket is complementary to the head. 9. The system of claim 7, wherein the ball is continuously biased toward the second end, wherein rotation of the head in the first direction temporarily overcomes the bias to urge the ball toward the first end. 10. The system of claim 7, wherein, when the ball binds between the face and the head, the ball deforms against the head. 11. The system of claim 7, wherein the cap comprises: a cantilever beam, wherein the beam extends between a fixed end of the beam and a free end of the beam, wherein the fixed end is connected to the ring, wherein the free end continuously biases the ball toward the second end, wherein rotation of the head in the first direction deflects the beam to temporarily overcome the bias. 12. The system of claim 7, wherein the screw comprises a shaft extending from the head through the washer assembly, wherein the washer assembly comprises a spike pointing along the shaft away from the head. 13. A system, comprising: a screw, wherein the screw comprises a spherical head;a washer encircling the head, wherein the washer comprises an aperture extending through the washer from a first side of the washer to a second side of the washer opposite the first side, wherein the head is positioned within the aperture, wherein the washer comprises a side wall encircling the aperture, wherein the side wall comprises a groove extending at least partially around the side wall, wherein the groove extends between a shallow end of the groove and a deep end of the groove;a cap secured to the washer, wherein the cap comprises a ring, wherein an inner diameter of the ring is smaller than an equatorial diameter of the head, wherein the head is interposed between the ring and the aperture; anda ball positioned between the side wall and the head, wherein the ball travels along the groove in response to rotation of the head relative to the washer;wherein, when the head rotates in a first direction, the ball travels along the groove to the deep end where the ball is loose between the deep end and the head so that the head rotates freely relative to the washer;wherein, when the head rotates in a second direction opposite the first direction, the ball travels along the groove to the shallow end where the ball jams between the shallow end and the head so that the screw, washer, and ball are frictionally locked together. 14. The system of claim 13, wherein the washer is captive to the head. 15. The system of claim 13, wherein the aperture comprises a spherical socket complementary to the head, wherein the washer is polyaxially pivotable about the head. 16. The system of claim 13, wherein the ball is continuously biased toward the shallow end, wherein rotation of the head in the first direction temporarily overcomes the bias to urge the ball toward the deep end. 17. The system of claim 13, wherein, when the ball jams between the shallow end and the head, the ball deforms against the head. 18. The system of claim 13, wherein the cap comprises: a cantilever beam, wherein the beam extends between a fixed end of the beam and a free end of the beam, wherein the fixed end is connected to the ring, wherein the free end continuously biases the ball toward the shallow end, wherein rotation of the head in the first direction deflects the beam to temporarily overcome the bias. 19. The system of claim 13, wherein the screw comprises a shaft extending from the head through the washer, wherein the washer comprises a spike pointing along the shaft away from the head. 20. A system, comprising: a screw, wherein the screw comprises a head;a washer assembly encircling at least a portion of the head, wherein the washer assembly comprises: a washer body encircling at least a portion of the head,a ring encircling at least a portion of the head,a tapered surface with a cross section comprising an arc of a circle, anda sphere, wherein the sphere is between the head and at least a portion of the washer body, wherein the sphere is interposed between the ring and the washer body,wherein, when the ring rotates relative to the head, the sphere moves along the tapered surface between a first position and a second position;wherein the washer body is locked to the head when the sphere is in the first position;wherein the washer body is unlocked and freely polyaxially rotatable relative to the head when the sphere is in the second position;wherein the washer body locks and unlocks in response to movement of the sphere along the tapered surface. 21. The system of claim 20, wherein, when the ring rotates relative to the head in a first direction, the sphere moves along the tapered surface toward the first position; wherein, when the ring rotates relative to the head in a second direction, the sphere moves along the tapered surface toward the second position, wherein the second direction is opposite the first direction;wherein the sphere is wedged against the washer body when the sphere is in the first position; andwherein the washer assembly is captive to the head. 22. A system, comprising: a screw, wherein the screw comprises a spherical head; anda washer assembly around the head, wherein the washer assembly comprises: a washer, wherein the washer comprises a socket and a ramp, wherein the socket receives the head to form a ball-and-socket joint, wherein the ramp extends partially around the socket between a first end which is outwardly displaced from the socket and a second end which is tangential to the socket and wherein the ramp comprises a semicircularly dished face,a cap, wherein the cap comprises a ring and a cantilever beam, wherein the ring is secured to the washer, wherein the beam extends between a fixed end of the beam and a free end of the beam, and wherein the fixed end is connected to the ring; anda ball, wherein the ball is positioned between the face and the head, wherein rotation of the head in a first direction urges the ball along the face toward the first end so that the ball fits loosely between the face and the head so that the screw is freely rotatable relative to the washer assembly, wherein rotation of the head in a second direction urges the ball along the face toward the second end until the ball binds between the face and the head so that the screw and the washer assembly are locked together, wherein the second direction is opposite the first direction, wherein the free end continuously spring biases the ball toward the second end, and wherein rotation of the head in the first direction deflects the beam to temporarily overcome the bias.