Polyaxial Bone screw assembly with fixed retaining structure

• US 20100036433A1
• Filed: 10/09/2009
• Published: 02/11/2010
• Est. Priority Date: 07/14/2005
• Status: Active Grant

• Current Assignee: Roger P. Jackson
• Original Assignee: Roger P. Jackson
• Inventors: Jackson, Roger P.
• Granted Patent: US 11,234,745 B2
• Time in Patent Office: Days
• US Class Current: 606/302
• CPC Class Codes: A61B 17/7011 Longitudinal element being non-straight, e.g. curved, angled or branched adjustable length longitudinal elements A61B17/7014; A61B17/7019 takes precedence, e.g. coil springs
• CPC Class Codes: A61B 17/7032 Screws or hooks with U-shaped head or back through which longitudinal rods pass
• CPC Class Codes: A61B 17/7037 wherein pivoting is blocked when the rod is clamped
• CPC Class Codes: A61B 17/8605 Heads, i.e. proximal ends projecting from bone
• CPC Class Codes: A61B 17/863 with thread interrupted or changing its form along shank, other than constant taper
• CPC Class Codes: A61B 17/864 hollow, e.g. with socket or cannulated
• CPC Class Codes: A61B 2090/037 with a frangible part, e.g. by reduced diameter

Abstract

A polyaxial bone screw assembly includes a threaded shank body having an integral upper portion receivable in a receiver and retained within the receiver by a retaining structure in the form of an open ring. The retaining structure is compressible, having an opening with two ends that may be pressed toward one another. The receiver has a U-shaped cradle defining a channel for receiving a spinal fixation rod. The receiver channel communicates with a cavity partially defined by an upper spherical surface and a substantially cylindrical surface communicating with a bottom opening of the receiver that allows for bottom loading the shank upper portion and the compressed retaining structure into the receiver, but prevents passage of the retaining structure out of the receiver once the retaining structure expands to an original form thereof and thus retains the shank upper portion within the cavity. In some embodiments, the shank upper portion is designed to directly frictionally engage the spinal fixation rod when a closure structure operably urges the rod toward the upper portion, fixing the bone screw shank body in a selected angular orientation with respect to the receiver.

Claims

1. A polyaxial bone screw assembly comprising:

a) a bone screw shank having an upper portion with a capture structure having an outer, lower convex hemispherical first surface extending outwardly and upwardly and terminating in a substantially planar annular surface, and a convex hemispherical upper surface extending upwardly from the planar annular surface and includes a countersunk tool engagement formation with a plurality of apertures, the diameter of the first surface being greater than the diameter of the upper surface;

b) a receiver having a pair of arms forming a channel, the receiver also having a cavity with a concave partially spherically shaped second surface and an opening to an exterior of the receiver opposite the pair of arms, the cavity communicating with the channel, the bone screw upper portion being received in the cavity through the opening;

c) a retaining structure being receivable in the cavity and securable to the receiver in fixed relation thereto when the shank upper portion is in the receiver, the retaining structure having a third surface sized and shaped to receive a portion of the shank first surface, the retaining structure being sized and shaped to retain the shank upper portion within the receiver cavity, the shank upper portion sized and shaped to extend above the retaining structure and receive downward force from a rod when the shank upper portion is retained in the cavity by the retaining structure so as to lock the angular position of the receiver relative to the shank in a locked position, the assembly having an unlocked position wherein the shank upper portion is in sliding, pivotable relation with the retaining structure and a locked position wherein the shank first surface is in direct frictional engagement with the receiver second surface and the retaining structure third surface; and

d) the second surface of the receiver and the third surface of the retainer cooperating to receive the first surface of the shank capture structure to allow polyaxial rotation of the shank relative to the receiver in the unlocked configuration during assembly.

2. The assembly of claim 1 wherein the hemispherical upper surface extends into a rod-receiving channel in the receiver to directly engage a rod in the rod-receiving channel.

3. The assembly of claim 1 wherein the first surface of the shank upper portion slidably matingly engages the second surface of the receiver cavity in the unlocked position.

4. The assembly of claim 1 wherein the tool engagement formation is adapted for non-slip engagement by a tool for driving the bone screw shank into bone.

5. The assembly of claim 1 wherein the tool engagement formation includes at least two axially-offset, spaced apart apertures.

6. The assembly of claim 1 wherein the apertures have a profile selected from the group consisting of circles, polygons, multi-lobular stars, pie slices and combinations thereof.

7. The assembly of claim 1 wherein the tool engagement formation includes four equally spaced apart apertures, each aperture having a pie slice-shaped profile.

8. The assembly of claim 1 wherein the retaining structure further comprises first and second spaced ends, the retaining structure being compressible and expandable with the first and second ends being movable toward and away from one another.

9. The assembly of claim 1 wherein the retaining structure is bottom-loadable into the receiver.

10. The assembly of claim 1 wherein the bone screw shank has a body for fixation to bone, the shank body being integral with the shank upper portion.

11. The assembly of claim 1 wherein the bone screw shank is cannulated.

12. The assembly of claim 1 further comprising a closure structure insertable into the receiver, the closure structure for operably urging the bone screw shank in a direction to frictionally lock the position of the shank upper portion with respect to the retaining structure and the receiver, thereby locking the shank in a selected angle with respect to the receiver.

13. The assembly of claim 12 wherein:

(a) the receiver arms each have a guide and advancement structure on inside surfaces thereof; and

(b) the closure structure is sized and shaped to be positionable between the arms for closing the channel, the closure structure having a splay-resistant guide and advancement structure for rotatably mating with the guide and advancement structures on the arms, biasing the closure structure upon advancement rotation against a rod disposed in the channel.

14. The assembly of claim 12 wherein the closure structure is adapted to operably urge the rod against the shank upper portion upon the closure structure being positioned in the receiver.

15. The assembly of claim 1 wherein the receiver defines a recess for receiving and retaining the retaining structure within the receiver cavity.

16. The assembly of claim 15 wherein the recess is a circumferential groove.

17. A medical implant comprising:

a) a receiver having a lower portion with a lower opening and an upper portion with a rod-receiving channel;

b) a bone screw shank having an upper portion structured for up-loading through the receiver lower opening, the shank upper portion including an upper convex partially spherically shaped surface that is sized and positioned such that when the shank is assembled in the receiver and a rod is received in the rod-receiving channel, the upper convex partially spherically shaped surface engages the rod, the upper convex partially spherically shaped surface including a tool engagement formation having a plurality of spaced apart apertures;

c) a retaining member securable to the receiver at a lower end of the shank upper portion and sized and shaped for preventing the shank upper portion from passing out of the receiver through the lower opening; and

d) a rod positionable within the rod receiving channel, the rod directly contacting and compressing on the shank upper portion for locking the shank in a position relative to the receiver.

18. The assembly according to claim 17 wherein:

a) the shank upper portion including a lower convex partially spherically shaped surface that is sized and positioned such that, when the shank is assembled in the receiver, the shank upper portion pivots within the retaining structure when the assembly is in a positioning configuration and frictionally engages the retaining structure when the assembly is in a locking configuration.

19. The assembly according to claim 17 wherein:

a) the upper convex partially spherically shaped surface extends into a rod-receiving channel in the receiver so as to receive downward force directly from the rod.

20. The assembly of claim 17 wherein the tool engagement formation includes at least two axially-offset, spaced apart apertures.

21. The assembly of claim 17 wherein the apertures have a profile selected from the group consisting of circles, polygons, multi-lobular stars, pie slices and combinations thereof.

22. The assembly of claim 17 wherein the tool engagement formation includes four equally spaced apart apertures, each aperture having a pie slice-shaped profile.

23. A polyaxial bone screw assembly comprising:

a) a bone screw shank having an upper portion with a capture structure having an outer convex substantially spherical first surface extending upwardly and terminating in a substantially planar annular surface, the planar annular surface being substantially perpendicular to a longitudinal axis of the shank and including a countersunk tool engagement formation;

b) a receiver having a pair of arms forming a channel, the receiver also having a cavity with a concave partially spherically shaped second surface and an opening to an exterior of the receiver opposite the pair of arms, the cavity communicating with the channel, the bone screw upper portion being received in the cavity through the opening;

c) a retaining structure being receivable in the cavity and securable to the receiver in fixed relation thereto when the shank upper portion is in the receiver, the retaining structure having a third surface sized and shaped to receive a portion of the shank first surface, the retaining structure being sized and shaped to retain the shank upper portion within the receiver cavity, the shank upper portion sized and shaped to extend above the retaining structure and receive a downward force from a rod when the shank upper portion is retained in the cavity by the retaining structure so as to lock an angular position of the receiver relative to the shank in a locked position, the assembly having an unlocked position wherein the shank upper portion is in sliding, pivotable relation with the retaining structure and a locked position wherein the shank first surface is in direct frictional engagement with the receiver second surface and the retaining structure third surface;

d) the second surface of the receiver and the third surface of the retainer cooperating to receive the first surface of the shank capture structure to allow polyaxial rotation of the shank relative to the receiver in the unlocked configuration during assembly; and

e) a compression insert being receivable in the receiver above the cavity and including a body and a pair of upstanding spaced apart arms forming an elongate member receiving channel.

24. The assembly of claim 23 wherein the planar annular surface engages a lower surface of the compression insert.

25. The assembly of claim 23 wherein the first surface of the shank upper portion slidably matingly engages the second surface of the receiver cavity in the unlocked position.

26. The assembly of claim 23 wherein the compression insert includes a bore adapted for passage of a tool therethrough.

27. The assembly of claim 23 wherein the tool engagement formation is adapted for non-slip engagement by a tool for driving the bone screw shank into bone.

28. The assembly of claim 23 wherein the retaining structure further comprises first and second spaced ends, the retaining structure being compressible and expandable with the first and second ends being movable toward and away from one another.

29. The assembly of claim 23 wherein the retaining structure is bottom-loadable into the receiver.

30. The assembly of claim 23 wherein the bone screw shank has a body for fixation to bone, the shank body being integral with the shank upper portion.

31. The assembly of claim 23 wherein the bone screw shank is cannulated.

32. The assembly of claim 23 further comprising a closure structure insertable into the receiver, the closure structure for operably urging the bone screw shank in a direction to frictionally lock the position of the shank upper portion with respect to the retaining structure and the receiver, thereby locking the shank in a selected angle with respect to the receiver.

33. The assembly of claim 32 wherein:

(a) the receiver arms each have a guide and advancement structure on inside surfaces thereof; and

(b) the closure structure is sized and shaped to be positionable between the arms for closing the channel, the closure structure having a splay-resistant guide and advancement structure for rotatably mating with the guide and advancement structures on the arms, biasing the closure structure upon advancement rotation against an elongate member disposed in the channel.

34. The assembly of claim 32 wherein the closure structure is adapted to operably urge the elongate member against the compression insert and the compression insert against the shank upper portion upon the closure structure being positioned in the receiver.

35. The assembly of claim 23 wherein the receiver defines a recess for receiving and retaining the retaining structure within the receiver cavity.

36. The assembly of claim 35 wherein the recess is a circumferential groove.

37. A medical implant comprising:

a) a receiver having a lower portion with a lower opening and an upper portion with a rod-receiving channel;

b) a bone screw shank having an upper portion structured for up-loading through the receiver lower opening, the shank upper portion including a convex substantially spherical outer surface with a top surface including a countersunk tool engagement formation;

c) a retaining member securable to the receiver at a lower end of the shank upper portion and sized and shaped for preventing the shank upper portion from passing out of the receiver through the lower opening;

d) a compression insert being receivable in the receiver between the rod-receiving channel and the shank surface; and

e) a rod positionable within the rod receiving channel, the rod directly contacting and compressing on the compression insert for locking the shank in a position relative to the receiver.

38. The assembly according to claim 37 wherein:

a) the convex substantially spherical surface being sized and positioned such that, when the shank is assembled in the receiver, the shank upper portion pivots within the retaining structure when the assembly is in a positioning configuration and frictionally engages the retaining structure when the assembly is in a locking configuration.

39. The assembly according to claim 37 wherein:

a) the planar annular surface engages a lower surface of the compression insert.

40. The assembly of claim 37 wherein the tool engagement formation includes at hexagonal profile.

41. The assembly of claim 37 wherein the tool engagement formation includes an aperture have a profile selected from the group consisting of circles, polygons, multi-lobular stars, pie slices and combinations thereof.

42. A polyaxial bone screw assembly comprising:

a) a bone screw shank having an upper portion with an outer convex substantially spherical first surface and a top surface including a countersunk tool engagement formation;

b) a receiver having a pair of arms forming a channel, the receiver also having a cavity with a concave partially spherically shaped second surface and an opening to an exterior of the receiver opposite the pair of arms, the cavity communicating with the channel, the bone screw upper portion being received in the cavity through the opening;

c) a retaining structure being receivable in the cavity and securable to the receiver in fixed relation thereto when the shank upper portion is in the receiver, the retaining structure having a third surface sized and shaped to receive a portion of the shank first surface, the retaining structure being sized and shaped to retain the shank upper portion within the receiver cavity, the shank upper portion being sized and shaped to extend above the retaining structure and receive a downward force from a rod when the shank upper portion is retained in the cavity by the retaining structure so as to lock an angular position of the receiver relative to the shank in a locked position, the assembly having an unlocked position wherein the shank upper portion is in sliding, pivotable relation with the retaining structure and a locked position wherein the shank first surface is in direct frictional engagement with the receiver second surface and the retaining structure third surface;

d) the second surface of the receiver and the third surface of the retainer cooperating to receive the shank first surface to allow polyaxial rotation of the shank relative to the receiver in the unlocked configuration during assembly; and

e) a compression insert being receivable in the receiver above the cavity and including a body with an upper surface to engage a rod and a lower surface to engage said shank surface.

43. A polyaxial bone screw assembly comprising:

a) a bone screw shank having an upper portion with an outer convex-shaped first surface and a top including a countersunk tool engagement formation;

b) a receiver having an upper portion with a pair of arms forming a channel, the receiver also having a lower portion with a cavity having an inner concave-shaped second surface spaced above an opening to an exterior of the receiver opposite the pair of arms, the cavity communicating with the channel, the bone screw upper portion being received in the cavity through the opening;

c) a retaining structure being receivable in the cavity and securable to the receiver in fixed relation thereto when the shank upper portion is in the receiver, the retaining structure having a third surface sized and shaped to engage a portion of the shank first surface, the retaining structure being sized and shaped to retain the shank upper portion within the receiver cavity, the shank upper portion being sized and shaped to extend above the retaining structure and receive a downward force from a rod when the shank upper portion is retained in the cavity by the retaining structure so as to lock an angular position of the receiver relative to the shank in a locked position, the assembly having an unlocked position wherein the shank convex upper portion first surface is in sliding, pivotable relation with the receiver retaining structure concave second surface and the third surface and a locked position wherein the shank first surface is in direct frictional engagement with the retaining structure third surface; and

d) a compression insert being receivable in the receiver above the cavity and including a body with an upper fourth surface to engage a rod and a lower fifth surface to engage said shank first surface and through which said downward force is transmitted.

44. A polyaxial bone screw assembly comprising:

a) a bone screw shank having an upper portion with a capture structure having an outer convex-shaped first surface extending upwardly and terminating with a top including a countersunk tool engagement formation;

b) a receiver having a pair of arms forming a channel, the receiver also having a cavity with a concave-shaped second surface and an opening to an exterior of the receiver opposite the pair of arms, the cavity communicating with the channel, the bone screw upper portion being received in the cavity through the opening;

c) a retaining structure being receivable in the cavity and securable to the receiver in fixed relation thereto when the shank upper portion is in the receiver, the retaining structure having a third surface sized and shaped to receive a portion of the shank first surface, the retaining structure being sized and shaped to retain the shank upper portion within the receiver cavity, the shank upper portion sized and shaped to extend above the retaining structure and receive a downward force from a rod when the shank upper portion is retained in the cavity by the retaining structure so as to lock an angular position of the receiver relative to the shank in a locked position, the assembly having an unlocked position wherein the shank upper portion is in sliding, pivotable relation with the retaining structure and a locked position wherein the shank first surface is in direct frictional engagement with the retaining structure third surface;

d) the second surface of the receiver and the third surface of the retainer cooperating to receive the first surface of the shank capture structure to allow polyaxial rotation of the shank relative to the receiver in the unlocked configuration during assembly; and

e) a compression insert being receivable in the receiver above the cavity and including a body with an upper surface to engage the rod and lower surface to engage the shank upper portion.

45. A medical implant comprising:

a) a receiver having a lower portion with a cavity having an inner concave surface and a lower opening and an upper portion with a rod-receiving channel;

b) a bone screw shank having an upper portion structured for up-loading through the receiver lower opening, the shank upper portion including a convex-shaped outer surface with a top surface including a countersunk tool engagement formation;

c) a retaining member securable to the receiver in the receiver lower portion and sized and shaped for preventing the shank upper portion from passing out of the receiver through the lower opening;

d) a compression insert being receivable in the receiver between the rod-receiving channel and the shank surface; and

e) a rod positionable within the rod receiving channel, the rod directly contacting and compressing on the compression insert for locking the shank in a position relative to the receiver, wherein the convex surface is in frictional engagement against the concave surface of the receiver cavity.

46. A polyaxial bone screw assembly comprising:

a) a bone screw shank having an upper portion with an outer convex-shaped first surface and a top surface including a countersunk tool engagement formation;

b) a receiver having an upper portion with a pair of arms forming a channel, the receiver also having a lower portion with a cavity having a concave-shaped second surface and an opening to an exterior of the receiver opposite the pair of arms, the cavity communicating with the channel, the bone screw upper portion being received in the cavity through the opening;

c) a retaining structure being receivable in the cavity and securable to the receiver in fixed relation thereto when the shank upper portion is in the receiver, the retaining structure having a third surface sized and shaped to engage a portion of the shank first surface, the retaining structure being sized and shaped to retain the shank upper portion within the receiver cavity, the shank upper portion being sized and shaped to extend above the retaining structure and receive a downward force from a rod when the shank upper portion is retained in the cavity by the retaining structure so as to lock an angular position of the receiver relative to the shank in a locked position, the assembly having an unlocked position wherein the shank upper portion is in sliding, pivotable relation with the receiver and retaining structure and a locked position wherein the shank first surface is in direct frictional engagement with the retaining structure third surface;

d) the second surface of the receiver and the third surface of the retainer cooperating with the shank first surface to allow polyaxial motion of the shank relative to the receiver in the unlocked configuration; and

e) a compression insert being receivable in the receiver above the cavity and including a body with an upper surface to engage a rod and a lower surface to engage said shank surface, wherein a downward force from the insert locks a position of the shank with respect to the receiver.

47. A polyaxial bone screw assembly comprising:

a) a bone screw shank having an upper portion with an outer convex-shaped first surface and a top surface including a countersunk tool engagement formation;

b) a receiver having an upper portion with a pair of arms forming a channel, the receiver also having a lower portion with a cavity having a concave-shaped second surface and an opening to an exterior of the receiver opposite the pair of arms, the cavity communicating with the channel, the bone screw upper portion being received in the cavity through the opening;

c) a retaining structure being receivable in the cavity and securable to the receiver in fixed relation thereto when the shank upper portion is in the receiver, the retaining structure having a third surface sized and shaped to engage a portion of the shank first surface, the retaining structure being sized and shaped to retain the shank upper portion within the receiver cavity, the shank upper portion being sized and shaped to extend above the retaining structure and directly receive a downward force when the shank upper portion is retained in the cavity by the retaining structure so as to lock an angular position of the receiver relative to the shank in a locked position, the assembly having an unlocked position wherein the shank upper portion is in sliding, pivotable relation with the receiver and retaining structure and a locked position wherein the shank first surface is in direct frictional engagement with the retaining structure third surface;

d) the second surface of the receiver and the third surface of the retainer cooperating with the shank first surface to allow polyaxial motion of the shank relative to the receiver in the unlocked configuration, wherein the shank first convex surface is opposed to the receiver second concave surface; and

e) a compression insert being receivable in the receiver above the cavity and including a body with an upper surface to engage a rod and a lower surface to engage said shank first convex surface, wherein a downward force from the insert locks a position of the shank with respect to the receiver and the retainer.

48. A polyaxial bone screw assembly comprising:

a) a bone screw shank having a top surface and an upper end portion with a convex first surface;

b) a receiver having an upper portion with a pair of arms forming a channel, the receiver also having a lower portion with a cavity having a concave-shaped second surface shaped to match the convex first surface and an opening to an exterior of the receiver opposite the pair of arms, the cavity communicating with the channel, the bone screw upper portion being received in the cavity through the opening, wherein the upper end portion is uploadable into the cavity such that the convex first surface engages the matching concave surface of the cavity and can go no further, such that the top surface extends into a bottom of the channel;

c) a retaining structure being uploadably receivable in the cavity and securable to the receiver in fixed relation thereto when the shank upper portion is in the receiver, the retaining structure having a third surface sized and shaped to engage a portion of the shank first surface, the retaining structure being sized and shaped to retain the shank upper portion within the receiver cavity, the shank upper portion being sized and shaped to extend above the retaining structure and receive a downward force from a rod when the shank upper portion is retained in the cavity by the retaining structure so as to lock an angular position of the receiver relative to the shank in a locked position, the assembly having an unlocked position wherein the shank upper portion is in sliding, pivotable relation with the receiver and retaining structure and a locked position wherein the shank first surface is in direct frictional engagement with the retaining structure third surface; and

d) the second surface of the receiver and the third surface of the retainer cooperating with the shank first surface to allow polyaxial motion of the shank relative to the receiver in the unlocked configuration.