Interlocking spinal inserts

Details Interlocking spinal inserts Interlocking spinal inserts

1999-05-26

2001-06-26

Willse, David H. (Department: 3738)

Prosthesis (i.e., artificial body members), parts thereof, or ai

Implantable prosthesis

Bone

C623S017110

Reexamination Certificate

active

06251140

ABSTRACT:

TECHNICAL FIELD
The present invention relates to intervertebral spinal inserts.
BACKGROUND OF THE INVENTION
Intervertebral spinal inserts are used to provide support and maintain normal distance between adjacent vertebrae in cases where a patient's vertebral discs have degenerated. Such degeneration can occur as a result of aging or trauma and typically results in pinched or damaged nerves between or proximal to the adjacent vertebrae. Moreover, such discal degeneration causes shifting of the loading along the patient's spinal column, which in turn further accelerates the vertebral degeneration.
Intervertebral inserts are typically used to reestablish normal intervertebral spacing and to cause fusion between adjacent vertebral bodies.
A common problem with the existing intervertebral spinal inserts is that they do not provide stabilization in two perpendicular directions in the plane of the patient's intervertebral space.
Another disadvantage is that, during such major surgery, the actual insertion of the intervertebral insert requires distraction of the adjacent vertebrae to first open a sufficiently large passage for the insertion of the insert therebetween. Such distraction is typically performed by dedicated instrumentation and invasive tools which must first enter the intervertebral space and then grip and hold apart the adjacent vertebrae.
Moreover, the shape of current inserts does not take advantage of the natural contoured shape of the adjacent vertebral surfaces such that an intervertebral insert can be provided which supports itself flush against the contour of the vertebral surfaces with the vertebrae being supported at a proper lordotic angle.
SUMMARY OF THE INVENTION
In a preferred aspect of the present invention, first and second intervertebral inserts are positioned in a patient's intervertebral space between adjacent vertebrae. The inserts are positioned parallel to the vertebrae with their central longitudinally extending axes disposed at an angle to one another. Preferably, the angle between central longitudinally extending axes of the inserts ranges from 70° to 135° and is most preferably about 90°. Due to the fact that the inserts have their central longitudinally extending axes oriented generally perpendicular to one another, increased vertebral stability is provided. An advantage of such increased stability is that the potential for vertebral fusion is increased.
In addition, the inserts are interlocked together with one another, enhancing their stability. Preferably, the inserts are each sequentially rotated about their respective central longitudinally extending axes into an anchored position between the adjacent vertebrae such that teeth on each of the inserts penetrates into the surfaces of the vertebrae, securing the inserts into position. In preferred aspects of the invention, the rotation of the inserts causes the inserts to become interlocked together, such that relative motion therebetween is prevented.
In preferred aspects of the invention, each of the first and second interlocking inserts have opposite outwardly facing convexly curved camming surfaces thereon, which act to cam apart the adjacent vertebrae when the inserts are rotated into an anchored position. Specifically, the outwardly facing convexly curved camming surfaces are adapted to engage, and to separate by camming action, the opposed adjacent vertebrae when the insert is initially placed between the vertebrae and then subsequently rotated by 90°. An illustration of employing such outwardly facing convexly curved camming surfaces to cam apart the adjacent vertebrae is provided in provisional patent applications Ser. No. 60/086,945 filed May 27, 1998; No. 60/113,651 filed Dec. 23, 1998; and No. 60/120,663 filed Feb. 19, 1999; incorporated herein by reference in their entirety. After the inserts are rotated into position, they support the spinal load, thereby easing pressure on the vertebral disc and surrounding tissue. As such, prior distraction of the adjacent vertebrae with dedicated instrumentation is either not required, or is substantially minimized.
In preferred aspects of the invention, the first and second inserts are each positioned within the patient's intervertebral space by separate cannulae entering the patient in opposite posterolateral approaches. Preferably, the cannulae are introduced percutaneously through the patient's back at generally right angles to one another. The inserts are preferably advanced through the respective cannulae into the intervertebral area in a fluoroscopically guided approach. Since the first and second inserts are inserted and anchored into position by the present method with only two percutaneous cannulae being required, a very minimally invasive surgical technique is provided.
This minimally invasive approach offers the benefit of introducing each insert while avoiding damage to the anterior and posterior longitudinal ligaments, interspinous ligaments and the facet joint capsules, while enabling the positioning of the inserts at generally right angles to one another with each insert being at an angle of about 45° to the sagittal plane of the patient.
In further preferred aspects of the method, the cannulae have an oval, racetrack, or other non-symmetric cross-section such that the cross-sectional area is substantially reduced from that of a generally circular cross-sectional cannula, reducing patient trauma and facilitating accurate placement fully into the patient's intervertebral space when the cannula is received into the patient.
In a preferred aspect, the size and shape of the insert creates a proper lordotic angle between the adjacent vertebrae. Specifically, in a preferred aspect, the insert has opposite, flattened vertebral support surfaces which taper inwardly towards the rotational axis at the posterior end of the insert. Optionally, the vertebral support surfaces can also be angled with respect to one another across the insert in a direction perpendicular to the central longitudinal axis of the insert. This tapering and angling of the vertebral support surfaces permits the insert to provide the required lordosis angle along the anterior-posterior contour of the opposite adjacent vertebrae.
In another aspect of the present invention, the insert is fabricated from a bio-absorbable material such that it will eventually be absorbed into the patient's body over time. For example, in a preferred aspect, the material used would be poly-L-lactic acid, polyglycolic acid, collagen, calcium phosphates, bioabsorbable ceramics, or any combination thereof which imparts sufficient initial implant strength to distract the vertebral bodies, to maintain a preferred vertebral spacing for a period of time, and which would be resorbed thereafter to promote natural disc healing. By varying the composition of the bio-absorbable material, the speed of bio-absorption can be adjusted per the desired use of the insert.


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