Flexible inter-vertebral stabilizer as well as process and apparatus for determining or verifying its tension before installation on the spinal column

• US 5,092,866 A
• Filed: 02/02/1990
• Issued: 03/03/1992
• Est. Priority Date: 02/03/1989
• Status: Expired

• Current Assignee: Francis H. Breard, Henry J.M. Graf
• Original Assignee: Francis H. Breard, Henry J.M. Graf
• Inventors: Graf, Henry J. M., Breard, Francis H.
• Primary Examiner(s): Green, Randall L.
• Assistant Examiner(s): Willse, David H.
• Application Number:
  US07/474,468
• Time in Patent Office: 760 Days
• Field of Search: 606/60, 606/61, 606/63, 128/69, 623/17, 623/13
• US Class Current: 606/54
• CPC Class Codes: A61B 17/7022 Tethers, i.e. longitudinal elements capable of transmitting tension only, e.g. straps, sutures or cables A61B17/702 takes precedence
• 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 17/842 Flexible wires, bands or straps A61B17/72, A61B17/82, A61B17/86 take precedence
• CPC Class Codes: A61B 2090/061 for measuring dimensions, e.g. length

Abstract

The present invention relates to an inter-vertebral stabilizer having one or more flexible ligaments. Each flexible ligament can be engaged with two respective vertebrae and/or associated with two retaining elements, such as screws, each of which is suitable for being implanted in a respective vertebra. The present invention also relates to a process, and the associated apparatus, for determining or verifying the tension of such an inter-vertebral stabilizer before it is put into place on the spinal column. This process includes implanting, in each of the vertebrae concerned, a corresponding rigid rod extending outside the patient'"'"'s body. The rods in each pair of adjacent rods are immobilized in an initial position. If the pain which is to be removed by the stabilizer persists, the process includes modifying the distance between the rods, then in immobilizing the rods in their new relative positions and in repeating the pain test. This cycle of operations is repeated, if necessary, until the pain disappears. The length to be allocated to the ligament is deduced from the distance then attained between the two rods.

Claims

1. An inter-vertebral stabilizer comprising at least one flexible ligament having an all-direction flexibility and at least two retaining elements, each retaining element having an implant portion configured to be implanted in a respective one of at least two successive vertebrae, a free head adjacent the implant portion for projecting from the respective vertebra when the implant portion is implanted in said verebra, and a lateral projection extending laterally from the head at a selected distance from the implant portion, said ligament being provided, at each end thereof, with a hanging means having a width less than the distance between the lateral projection and the implant portion for loose engagement around the free head of a respective one of the retaining elements, whereby the loose engagement of the ligament with the respective retaining element enables compensation for defects of a spine without hindering flexional and torsional movements thereof.

2. Inter-vertebral stabilizer according to claim 1, in which said at least one flexible ligament has the general form of a closed loop, the ends of which constitute said hanging means.

3. An inter-vertebral stabilizer according to claim 2 in which the lateral projection of each of the retaining elements is provided by a cap removably fitted on the head of the retaining element, said cap being radially over-dimensioned in relation to the head of the retaining element on which the cap is removably fitted, said cap preventing the ligament from slipping off the free head.

4. The Inter-vertebral stabilizer according to claim 2 in which the lateral projection of each retaining element for retaining the ligament in loose engagement on the retaining element is unitary with the head thereof.

5. Inter-vertebral stabilizer according to claim 1, in which said at least one flexible ligament is provided, at each end thereof, with a closed loop constituting said hanging means.

6. An inter-vertebral stabilizer according to claim 5 in which the lateral projection of each of the retaining elements is provided by a cap removably fitted on the head of the retaining element, said cap being radially over-dimensioned in relation to the head of the retaining element on which the cap is removably fitted, said cap preventing the ligament from slipping off the free head.

7. The inter-vertebral stabilizer according to claim 5 in which the lateral projection of each retaining element for retaining the ligament in loose engagement on the retaining element is unitary with the head thereof.

8. Inter-vertebral stabilizer according to claim 1, in which each of the retaining elements is provided with a removable cap radially over-dimensioned in relation to the head of the retaining element on which the cap can be fitted, the cap comprising the lateral projection of the retaining element.

9. Inter-vertebral stabilizer according to claim 1 in which the lateral projection for retaining the ligament in loose engagement on the retaining element is unitary with the head thereof.

10. A process for stabilizing a length of the spinal column comprising at least two successive vertebrae, said process comprising the steps of;

a) providing at least one flexible ligament having an all-direction flexibility and provided at each end with hanging means for loosely hanging the flexible ligament,

b) providing at least two retaining elements, each of which has a free head and an implantation end,

c) making a surgical incision in the patient'"'"'s body in front of each vertebra of said length of the spinal column,

d) implanting the implantation end of each retaining element in a respective one of said successive vertebrae, with said free head projecting from the vertebra after said retaining element has been implanted,

e) installing said at least one flexible ligament on two respective successive retaining elements by passing the hanging means of each ligament end around the projecting free head of a respective one of said two successive retaining elements, so that said ligament end at least partly loosely encircles the free head of said retaining element thus permitting a movement of the ligament with respect to the retaining elements during selected flexional movements of the spinal column, said at least one ligament forming an inter-vertebral stabilizer together with the associated retaining elements.

11. The process of claim 10, in which said inter-vertebral stabilizer comprises a plurality of ligaments chained along the spinal column by means of the same plurality, plus one, of retaining elements.

12. The process of claim 10, further comprising the step of implanting at least one additional inter-vertebral stabilizer on the back face of said vertebrae, each of said stabilizers being placed on one respective side of the spine along the length of the spinal column to be stabilized.

13. The process of claim 10 comprising additional steps for determining the length at rest of said at least one ligament, said additional steps being performed between steps c) and d) and comprising successively:

implanting a rigid rod in each of the vertebrae concerned and at the point for implantation of the corresponding retaining element, with said rod extending out of the patient'"'"'s body.

immobilizing the two rods of each pair of adjacent rods at a predetermined distance from one another,

performing a pain test by permitting a selected amount of time to elapse and determining whether a pain to be removed by the stabilizer persists, and

in the event where the pain, the cause of which is to be removed by the stabilizer is persisting after the selected time has elapsed, modifying the distance between the rods by a selected pitch, immobilizing the rods in their new relative positions and carrying out the pain test again, by allowing the time to elapse and determining whether the pain persists, the steps of modifying the distance, immobilizing and testing for pain being repeated, if necessary until the pain disappears, the length at rest to be given to the ligament then being deduced from the value of the distance then attained between the two rods.

14. Apparatus for implement the process according to claim 13, characterized in that the apparatus comprises a set of at least two rods (11,12) each having an implantation end (2,3) for implanting in the respective vertebra (V1, V2), the rods being associated with at least one rigid link (15) of adjustable length for joining the rods at a point remote from their implantation ends.

15. Apparatus according to claim 14, characterized in that the implantation end of each rod is constituted by the corresponding retaining element (2,3) of the ligament of the said stabilizer and each of the rods (11,12) further comprises a removable extension piece (13) fitting onto the head (4) of said retaining element.

16. Apparatus according to claim 15, characterized in that the said length-adjustable rigid link (15) comprises a thin bar (16) and two collars (17,18) that can be fitted respectively on the two rods (11,12) and are provided with means (20) for supporting the bar slidingly between them, an element (19) for locking the bar (16) being provided on each collar.

17. Apparatus according to claim 14, characterized in that it comprises an instrument (24) for determining the length at rest of the ligament, which is formed by two crossed legs (25,26) articulated on one another at their middle, the ends of the legs located on the same side of the articulation (27) each having a substantially semi-circular contacting portion (28,29).

18. An inter-vertebral stabilizer comprising at least one flexible ligament having an all-direction flexibility and at least two retaining elements, each retaining element having an implantation end implantable in a respective one of two successive vertebrae and a projecting free head, said ligament being provided at each end thereof with a hanging means for loosely engaging around the free head of a respective one of the retaining elements, at least two rods each having an end for temporary implantation in the respective vertebra, the rods being associated with at least one rigid link of adjustable length for joining the rods at a point remote from their implantation ends, whereby the rods and the link are employed for determining a proper relative position for stabilizing the vertebrae, and whereby the retaining elements and the ligament are employed for stabilizing the vertebrae in the relative position determined with the rods and the rigid link of adjustable length.

19. A stabilizer as in claim 18 wherein the implantation end of each said rod is defined by a corresponding one of the retaining elements, the rods being selectively removable from the retaining elements after determining the preferred relative position for stabilizing the vertebrae.

20. A stabilizer according to claim 18 wherein the rigid link of adjustable length comprises a pair of collars slidably engaged on the respective rods and a bar adjustably engagable by the collars for locking the rods in selected positions relative to one another.

21. A stabilizer according to claim 18 further comprising an instrument for determining the length at rest of the ligament, the instrument comprising a pair of crossed legs articulated to one another at their middle, the ends of the legs each having a substantially semi-circular contacting portion for engaging the rods at locations thereon generally adjacent the respective vertebrae.