METHODS AND SYSTEMS FOR ENHANCING RADIOGRAPHIC IMAGES OF RADIOLUCENT IMPLANTS

Abstract

A radiolucent intervertebral prosthesis is implanted in an environment that has been prepared in a manner which enhances radiopacity of the prosthesis and/or the environment. A liquid, powder, or other fluid radiopaque (RO) material, such as iohexol, is introduced into an implantation site, either by directly introducing the material into the site and/or by applying the material to a surface of the implant. The presence of the RO material in the implantation site provides contrast with the material of radiolucent prosthesis while the implantation site is being radiographically imaged, e.g. during fluoroscopic visualization while the prosthesis is being implanted. During implantation, the RO material helps the physician view and manipulate the implant, and after the implantation is complete, the RO material will be resorbed or otherwise lost from the implantation site so that the area returns to a radiolucent condition to facilitate subsequent radiographic imaging when needed.

Claims

1. A prosthetic disc for insertion between adjacent vertebrae, the prosthetic disc comprising: upper and lower plates having outer surfaces locatable against the respective vertebrae and inner surfaces, wherein said inner surfaces are configured to allow relative articulation of the plates when the disc is implanted between adjacent vertebrae; wherein at least one of said upper and lower plates is at least partially formed from a radiolucent polymer; and wherein said at least one of said upper and lower plates has one or more collection features formed on a surface of the radiolucent polymer, said collection feature being configured to collect and retain fluoroscopic contrast medium to enhance radiographic imaging of the plate when being implanted in a patient in the presence of a fluid radiographic imaging medium.

2. A prosthetic disc as in claim 1, wherein the radiolucent polymer is polyaryletherketone (PAEK).

3. A prosthetic disc as in claim 2, wherein the PAEK comprises polyetheretherketone (PEEK).

4. A prosthetic disc as in claim 1, wherein the collection feature comprise comprises at least one of a hole, a trough or a capillary.

5. A prosthetic disc as in claim 1, wherein the collection feature is formed on at least an outer surface of one of the endplates.

6. A prosthetic disc as in claim 1, wherein the collection feature is formed on at least an inner surface of one of the endplates.

7. A prosthetic disc as in claim 1, wherein the collection feature is formed on at least a peripheral surface of one of the endplates.

8. A prosthetic disc as in claim 1, further comprising a mobile core disposed between inner surfaces of the upper and lower plates, the core arranged to slide and translate with respect to both the upper and lower plates when the prosthetic disc is implanted.

9. A prosthetic disc as in claim 8, further comprising a restraining structure on at least one of the plates configured to hold an outermost periphery of the core captive between the plates during sliding movement of the plates over the core when the prosthetic disc is implanted.

10. A prosthetic disc as in claim 8, wherein the core is formed of a ceramic.

11. A prosthetic disc as in claim 1, wherein the collection features are arranged in a pattern which is visible during implantation to facilitate observing the orientation of the implant as it is being implanted.

12. A prosthetic disc as in claim 1, wherein the radiolucent implant is coated with a fluoroscopic contrast medium.

13. A prosthetic disc as in claim 1, wherein the radiolucent implant is packaged with the liquid contrast medium.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:

[0022] FIG. 1 is in isometric view of an artificial disc having contrast medium collection features formed thereon in accordance with the principles of the present invention.

[0023] FIG. 2 is a bottom isometric view of a superior endplate of an artificial disc similar to that shown in FIG. 1 except that the contrast medium collection features are formed on a lower surface of the a superior endplate.

[0024] FIG. 3 is an isometric bottom view of a further alternative artificial disc design similar to that of FIG. 1 shown with a superior endplate having a single lateral contrast medium collection feature on an anterior face thereof.

[0025] FIGS. 4A through 4D illustrate a method performed in accordance with the principles of the present invention for implanting the artificial disc of FIG. 1 between superior and inferior vertebral bodies.

DETAILED DESCRIPTION OF THE INVENTION

[0026] As shown in FIG. 1, an artificial disc 10 constructed in accordance with the principles of the present invention includes a superior endplate 12 and an inferior endplate 14. The superior endplate and inferior endplate will be configured to articulate relative to each other so that they can act as an active replacement or artificial disc prosthesis when implanted between superior and inferior vertebral bodies in an implantation procedure as described herein below. In the embodiment of FIG. 1, articulation is provided by placing a mobile core 13 having spherical upper and lower surfaces between the endplates 12 and 14, where the core is received in a spherically concave receptacles 15, as shown for example in the lower surface of a superior endplate 12 in FIG. 2. The artificial disc 10 further includes a plurality of superior fins 16 and inferior fins 18 which are provided to stabilize the endplates after implantation, as described in more detail below.

[0027] Of particular interest in the present invention, the artificial disc 10 may include a variety of different collection features which are configured to collect and retain fluoroscopic contrast medium in order to enhance radiographic imaging of the artificial disc during implantation. As shown in FIG. 1, six vertical collection features 20 are formed on an anterior lateral surface of the superior endplate 12. During implantation, these collection features 20, which typically comprise shallow channels, troughs, grooves or capillaries, will temporarily collect and retain fluoroscopic contrast medium which is present at the implantation site during the implantation procedure. As the collection features 20 are spaced-apart at fixed distances and oriented vertically relative to the plate, it will be appreciated that viewing the image artifacts produced on the fluoroscopic display will assist the physician in properly positioning the artificial disc 10 as it is being implanted. The contrast medium will however, be absorbed by the surrounding tissue or otherwise lost from the contrast features 22 over time so that the implantation site of the artificial disc 10 will be generally free from radiopaque artifacts after the implantation is complete.

[0028] The collection features may be located in a variety of other positions and orientations on the superior endplate, the inferior endplate, and/or the core. As shown in FIG. 2, a series of three small holes, dimples or divots 22 are formed in the lower face of the superior endplate 12. These collection features 22 will also temporarily collect contrast medium to enhance visibility of the otherwise radiolucent artificial disc during implantation. As shown in FIG. 3, a collection feature 24 is shown as a horizontal or lateral groove, channel or recess in a side surface of the endplate. The horizontal collection feature 24 is formed on the anterior surface of a superior endplate 12.

[0029] Although a three piece disc design of a prosthetic disc with a mobile core 13 has been illustrated, the method may also be used with ball and socket and other disc designs. The method is also useful for other spinal implants and orthopedic implants formed of a radiolucent material including poly(aryl-ether-ether-ketone), commonly abbreviated as PEEK, and PEEK composites to improve radiographic imaging of these implants. Implants may include fusion spacers, nucleus replacement devices, fracture fixation devices, joint replacements, such as hips and knees, balls, stems, plates, rods and screws.

[0030] Referring now to FIGS. 4A-4D, a method for implanting the artificial disc 10 is described. Initially, a discectomy is performed to remove the native disc D, as shown in FIG. 4A. After the disc D is removed leaving the lateral ligaments LL in place, a pair of grooves or notches G are formed in the lower face of the superior vertebral body SV and the upper surface of the inferior vertebral body IV, as shown in FIG. 4B. The groves G are sized and shaped to accommodate the fins 16 and 18 and the grooves may be omitted if an implant without fins is to be used. Alternatively, an implant with multiple fins on the superior and inferior endplates would require multiple grooves to be cut in the vertebral bodies. The artificial disc 10 may then be inserted into the space between the superior vertebral body SV and the inferior vertebral body IV as shown in FIG. 4C. Of particular interest to the present invention, a fluoroscopic contrast medium will be present in the implantation site between the superior and inferior vertebral bodies, as shown by a darkened cloud around the artificial disc 10 in FIG. 4C. It will be appreciated that the artificial disc 10 itself remains radiolucent, but the disc will occupy a region or volume within the cloud of fluoroscopic contrast medium, thus allowing the peripheral or the outline of the artificial disc to be viewed under fluoroscopic imaging. By providing vertical or other collection features, such as the collection features 20, on the anterior face of the superior endplace 12, the orientation of the disc may be viewed with reference to the accumulation of the contrast medium within these collection features, which accumulations will appear more clearly on the fluoroscopic image.

[0031] After the implantation is complete, typically over a period of hours or days, the contrast medium (CM) will disappear from the implantation site between the superior vertebral body SV and the inferior vertebral body IV, as shown in FIG. 4D. Once the contrast medium has disappeared, typically by resorption, the region of the spine wherein the artificial disc is implanted may be imaged under various radiographic imaging technologies with minimal interference from the radiolucent disc 10. The time frame for disappearance of the CM may be increased by irrigation or other means. On one example, the contrast medium is no longer visible under fluoroscopy within 1 hour, within 2 hours, within 5 hours, or within 12 hours of insertion of the implant.

[0032] Contrast medium can include any of the contrast medium known to be used in the fields of angiography including coronary, pulmonary, interventional, renal or cerebral angiography. Contrast media generally include iodine. They are water soluble, chemically and heat stable, biologically inert and safe. Although for many angiography applications including coronary contrast media would have a low viscosity, such as less than 15 centipoise or less than 10 centipoise at 37 degrees C., contrast media used in this method can have a higher viscosity, such as greater than 10 centipoise or greater than 15 centipoise at 37 degrees C., to remain in the collection features.

[0033] The fluoroscopic contrast medium may be injected before, during or after insertion of the radiolucent implant. The injection of the contrast medium may be a one time, multiple time or continuous injection by syringe, catheter, or other injection means.

[0034] In an alternative embodiment, the implant may be dipped into the contrast medium before the implant is inserted into the implantation site in the patient. The implant may be coated with the contrast medium in the operating room by one or more of dipping, spraying, or painting. The contrast medium will pool in the collection features and be retained in the collection features by surface tension and/or capillary action. For the dipping method, a higher viscosity contrast medium can be used.

[0035] In another alternative embodiment, the implant is coated with the contrast medium or packaged with the liquid contrast medium to provide a combined ready to use implant with contrast.

[0036] Examples of contrast agents include iohexol, iopromide, iopromide, and diatrizoate both with and without salt. Agents are available commercially under the brand names Ultravist, Ominipaque, Isovue and Visiopaque. Contrast agents come in different iodine concentrations including high concentrations of 30% iodine or above and low concentrations of less than 30% of iodine. Contrast agent may be in a liquid, gel, and/or powder form.

[0037] While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.