Methods and Devices for Controlled Flexion Restriction of Spinal Segments

• US 20080319487A1
• Filed: 04/18/2008
• Published: 12/25/2008
• Est. Priority Date: 06/22/2007
• Status: Active Grant

• Current Assignee: Empirical Spine, Inc.
• Original Assignee: Simpirica Spine, Inc.
• Inventors: Bennett, Ian, Alamin, Todd, Kothari, Manish, Fielding, Louis, Litherland, Craig, Cahill, Colin, Malandain, Hugues
• Granted Patent: US 8,403,961 B2
• Time in Patent Office: Days
• US Class Current: 606/263
• CPC Class Codes: A61B 17/7053 with parts attached to bones or to each other by flexible wires, straps, sutures or cables
• CPC Class Codes: A61B 17/7062 Devices acting on, attached to, or simulating the effect of, vertebral processes, vertebral facets or ribs rib fixation devices A61B17/8076; Tools for such devices
• CPC Class Codes: A61B 17/7067 Devices bearing against one or more spinous processes and also attached to another part of the spine; Tools therefor
• CPC Class Codes: A61B 2090/064 for measuring force, pressure or mechanical tension

Abstract

A system for restricting spinal flexion includes superior and inferior tether structures joined by a pair of compliance members. Compliance members comprise tension members which apply a relatively low elastic tension on the tether structures. By placing the tether structures on or over adjacent spinous processes, flexion of a spinal segment can be controlled in order to reduce pain.

Claims

1. A method for restricting flexion of at least one spinal segment, said method comprising:

implanting a constraining structure having a superior end coupled to a superior spinous process and an inferior end coupled to an inferior spinous process or a sacrum;

wherein the constraining structure provides an elastic resistance to flexion beyond a neutral position of the spinal segment in the range from 7.5 N/mm to 20 N/mm.

2. A method as in claim 1, wherein the constraining structure provides a resistance to extension beyond the neutral position of the spinal segment below 3 N/mm.

3. A method as in claim 2, wherein the resistance to extension is below 0.5 N/mm.

4. A method as in claim 1, wherein implanting comprises placing a superior tether structure over or through the superior spinous process and placing an inferior tether structure over or through the inferior spinous process or sacrum, wherein the tether structures are substantially non-distensible and joined by at least one compliance member which provides the elastic resistance to flexion.

5. A method as in claim 4, wherein the tether structures are joined by at least two compliance members which are placed on the right and left sides of a midline of the spinal segment.

6. A method as in claim 1, wherein the constraining structure is tightened over the spinous processes to apply a force to the spinous processes in the range from 1N to 25N before flexion while the spinal segment remains at a neutral position.

7. A method as in claim 1, wherein the constraining structure is pre-tensioned to provide an initial static resistance in the range from 5N to 25N which must be overcome before initiating deformation.

8. A method as in claim 4, wherein the constraining structure elastically recovers its underformed position when the spinal segment returns to its neutral position.

9. A method as in claim 8, wherein the tethers of the constraining structure will experience a creep below 10% after one million cycles at typical physiologic loads.

10. A method as in claim 9, wherein the creep is below 5%.

11. A method as in claim 10, wherein the creep is below 1%.

12. A device for restricting flexion of at least one spinal segment, said structure comprising:

a constraint adapted to couple at least one superior spinous process and at least one inferior spinous process or sacrum,

wherein the constraint (1) has a dimension that is adjustable to allow tightening over the spinous processes or spinous process and sacrum when the spinal segment is in a neutral position and (2) provides an elastic resistance to flexion of the spinal segment beyond the neutral position in the range from 7.5 N/mm to 20 N/mm.

13. A device as in claim 12, wherein the constraint provides an elastic resistance to extension beyond the neutral position below 3 N/mm.

14. A device as in claim 13, wherein the resistance to extension is below 0.5 N/mm.

15. A device as in claim 12, wherein the constraint comprises a superior tether structure adapted to couple to the superior spinous process, an inferior tether structure adapted to couple to the inferior spinous process or sacrum, and at least one compliance member, wherein the tether structures are substantially non-distensible and the compliance member provides the resistance to flexion.

16. A device as in claim 15, comprising at least two compliance members arranged to lie on either side of a midline when the tether structures are placed over the spinous processes or spinous process and sacrum.

17. A device as in claim 13, wherein the constraint is pre-tensioned to provide an initial resistive force to flexion which must be overcome prior to initiating deformation.

18. A device as in claim 17, wherein the initial resistive force is in the range from 5N to 25N.

19. A system for restricting flexion of at least one spinal segment, said system comprising:

a superior tether structure adapted to couple to a superior spinous process and having a right connecting segment and a left connecting segment;

an inferior tether structure adapted to couple to an inferior spinous process or a sacrum and having a right connecting segment and a left connecting segment;

a right compliance member including a tension element having an upper end connectable to the right connecting segment of the superior tether structure and a lower end connectable to the right connecting segment of the inferior tether structure; and

a left compliance member including a tension element having an upper end connectable to the left connecting segment of the superior tether structure and a lower end connectable to the left connecting segment of the inferior tether structure.

20. A system as in claim 19, wherein the superior and inferior tether structures are substantially non-distensible.

21. A system as in claim 20, wherein the tether structures comprise elongate bands adapted to be placed over the superior and inferior surfaces of adjacent superior and inferior spinous processes.

22. A system as in claim 21, wherein the connecting segment of each tether structure is connected to the tension member near a center of the end of the compliance member to minimize off-axis loading.

23. A system as in claim 19, wherein one connecting segment of the superior tether structure is attached to one compliance member before implantation and one connecting segment of the inferior tether structure is attached to the other compliance member before implantation.

24. A system as in claim 19, wherein the compliance members each further comprise a sheath over the tension element.

25. A system as in claim 19, wherein the compliance members each further comprise an element that limits elongation.

26. A system as in claim 25, wherein the elongation limit prevents elongation of the tension element beyond 20 mm.

27. A system as in claim 19, wherein the tension elements each comprise a coil spring having a superior tether connector and an inferior tether connector.

28. A system as in claim 27, wherein one of the tether connectors is adapted for adjustable attachment and the other is adapted for fixed attachment.

29. A system as in claim 27, wherein the coil spring and tether connectors are formed from a single piece of material.

30. A system as in claim 27, wherein the coil spring and tether connectors are cast, machined, or cut from a metal blank.

31. A system as in claim 27, wherein the coil spring and tether connectors are molded, machined, or cut from a polymer material.

32. A system as in claim 27, wherein the tension element comprises machined or laser cut titanium stock having features formed at superior and inferior ends to define the tether connectors.

33. A system as in claim 32, wherein one feature comprises a transverse hole having a rotatable roller for adjustably receiving a connecting segment of one tether structure.

34. A system as in claim 33, wherein the other feature comprises a transverse hole having a pin for fixedly receiving a connecting segment of the other tether structure.

35. A system as in claim 27, wherein the tension elements each have a spring constant in the range from 3.75 N/mm to 8.75 N/mm.

36. A system as in claim 19, wherein the tension elements each comprise an elastomeric body having a superior tether connector and an inferior tether connector.

37. A system as in claim 36, wherein the elastomeric body comprises a beam having discrete superior and inferior passages which define the tether connectors.

38. A system as in claim 36, wherein the elastomeric body comprises a ring having a central opening which defines the tether connectors.

39. A system as in claim 36, wherein the elastomeric body comprises a body having upper and lower end caps.

40. A system as in claim 36, wherein the elastomeric body comprises silicone rubber.

41. A system as in claim 40, wherein the elastomeric body is pre-cycled in tension to stabilize stiffness value.

42. A system as in claim 40, wherein the elastomeric body has a stiffness value in the range from 3.75 N/mm to 8.75 N/mm.

43. A system as in claim 36, further comprising cords adjustably connected to one end of each elastomeric body, wherein the cords attach to the tether structures to permit constriction adjustment.

44. A system as in claim 36, wherein the superior and inferior tether each comprise a braided tube, wherein the elastomeric body is secured in one end of the tube.