Intervertebral implant having back-out prevention feature
View Patent ↗A spinal implant for implantation in an intervertebral space is provided, such that the implant may provide a back-out prevention feature and may also provide a visual indication of whether the back-out prevention feature is engaged. The visual indication may be a contrast between a circular visible shape of the screw head and a non-circular visible shape of the screw head. The back-out prevention feature may provide engagement of a tapered thread in the screw head with an internal thread of the implant. A hard stop may also be provided. Such back-out prevention feature may also provide a torque-based indication of engagement or non-engagement of the back-out prevention feature. The implant may possess a polymeric posterior body joined to a metallic anterior body.
1. A spinal surgical device, comprising:
an implant suitable to fit in an intervertebral space between adjacent vertebrae, said implant comprising a hole therethrough suitable to accept a screw; and
wherein said hole comprises an interior envelope that is non-circular, and wherein at least a portion of said hole having an internal helical thread,
in combination with a screw, wherein said screw has a first threaded region in a side surface of a head of said screw and has a second threaded region along a shaft of said screw,
wherein when said screw head is screwed into said internal helical thread in said hole to a torque corresponding to full insertion, a top surface of said head of said screw is within a region of said hole that has said internal helical thread.
2. The apparatus of claim 1 , wherein said interior envelope of said hole comprises, dispersed around its perimeter, a first perimeter region and a second perimeter region, wherein said first perimeter region is recessed to a greater radial dimension than a radial dimension of said second perimeter region, wherein said first perimeter region intersects said internal helical thread.
3. The apparatus of claim 1 , wherein said hole further comprises an entry region adjacent to said internal helical thread, said entry region being unthreaded.
4. The apparatus of claim 1 , wherein said internal helical thread is of uniform pitch and uniform major diameter everywhere that it exists.
5. The apparatus of claim 1 , wherein said first perimeter region is recessed such that in said first perimeter region some of said internal helical thread remains.
6. The apparatus of claim 1 , wherein said first perimeter region is recessed such that in said first perimeter region none of said internal helical thread remains.
7. The apparatus of claim 1 , wherein said implant comprises a posterior body and an anterior body joined to said posterior body, and said hole passes at least through said anterior body.
8. The apparatus of claim 7 , wherein said joining of said posterior body and said anterior body comprises a dowel pin that is an interference fit in one of said posterior body and said anterior body and is a clearance fit in the other of said posterior body and said anterior body.
9. The apparatus of claim 1 , wherein said implant comprises an open space therethrough suitable to contain bone graft material.
10. The apparatus of claim 1 , wherein said first threaded region has a tapered thread.
11. The apparatus of claim 1 , wherein said first threaded region has a first threaded region thread pitch and said internal helical thread has an internal helical thread pitch equal to said first threaded region thread pitch.
12. The apparatus of claim 1 , wherein said first threaded region has a first threaded region thread pitch and said second threaded region has a second threaded region thread pitch, and said first threaded region thread pitch and said second threaded region thread pitch are different from each other.
13. A spinal surgical device, comprising:
an implant suitable to fit in an intervertebral space between adjacent vertebrae, said implant comprising a hole therethrough;
said hole comprising a hole internal thread; and
a screw comprising a screw head and a screw shaft that is suitable to pass through said hole; and
wherein an interaction between said screw and said implant provides a back-out prevention feature for prevention of back-out of said screw from said implant; and
wherein said interaction of said screw and said implant provides a visual indication of engagement of said back-out prevention feature, said visual indication comprising a change in a shape of a visible portion of said screw head when said back-out prevention feature is engaged as compared to a shape of a visible portion of said screw head when said back-out prevention feature is not engaged.
14. The device of claim 13 , wherein during non-engagement of said back-out prevention feature, said screw head is visible as a circular shape, and during engagement of said back-out prevention feature, said screw head is visible as a non-circular shape.
15. The device of claim 14 , wherein during non-engagement of said back-out prevention feature, said screw head is visible as a full shape of said screw head, and during engagement of said back-out prevention feature, said screw head is visible as a non-circular shape.
16. The device of claim 14 , wherein said non-circular shape comprises a more-compact region and a more-expanded region.
17. The device of claim 14 , wherein said non-circular shape has a perimeter that comprises a convex portion and a concave portion.
18. The device of claim 13 , wherein during non-engagement of said back-out prevention feature, said screw head is visible as a full shape of said screw head, said full shape being non-circular, and during engagement of said back-out prevention feature, said screw head is visible as a circular shape.
19. The spinal surgical device of claim 13 , wherein during non-engagement of said back-out prevention feature, said visible portion of said screw head comprises at least one circular arc and at least one indentation along a periphery of said screw head.
20. The device of claim 19 , wherein said indentation has a minimum radial position that is at a greater radius than a radius of a crest of said hole internal thread.
21. A spinal surgical device, comprising:
an implant suitable to fit in an intervertebral space between adjacent vertebrae, said implant comprising a hole therethrough, said hole having a hole internal thread; and
a screw comprising a screw head and a screw shaft suitable to pass through said hole; and
wherein a combination of said implant and said screw provides a back-out prevention feature for prevention of back-out of said screw from said implant,
wherein said back-out prevention feature provides both a visual indication of engagement of said back-out prevention feature and a torque indication of engagement of said back-out prevention feature;
wherein said visual indication comprising a change of a visible shape of the screw head; and
wherein said torque indication comprising a change in an amount of torque needed to advance said screw.
22. The device of claim 21 , wherein said hole has an internal helical thread, and wherein said hole comprises, dispersed around its perimeter, a first perimeter region and a second perimeter region, wherein said second perimeter region is recessed to a greater radial dimension than a radial dimension of said first perimeter region.