BRIEF DESCRIPTION OF THE DRAWINGS
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
FIG. 1 is a side elevational view of a pedicle screw distractor instrument according to one embodiment of this invention;
FIG. 2 is a rear elevational view of the instrument of FIG. 1;
FIG. 3 is an enlarged view of the head of the instrument in encircled area 3 of FIG. 2;
FIG. 4 is a cross-sectional view of the instrument head taken along line 4-4 of FIG. 3;
FIG. 5 is a side elevational view of another component of one embodiment of this invention mounted in a spinal instrument;
FIG. 6 is a perspective view of the pedicle screw distractor and companion instruments according to one embodiment of this invention in use on a patient's spine; and
FIG. 7 is an enlarged side elevational view of a portion of the instruments shown in FIG. 6.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1, one embodiment of a pedicle screw distractor 10 according to this invention is shown. The distractor 10 includes a head 12 adapted to receive a convex-shaped head 14 of a pedicle screw 16 (FIG. 6). The head 12 is joined to a lever 18 of the pedicle screw distractor 10. A handle 20 of the distractor 10 projects from a fulcrum arrangement 22 positioned at a juncture between the handle 20 and the lever 18. A saddle 24 is formed at the fulcrum 22 between the lever 18 and the handle 20 and includes a pair of spaced flanges 26 forming a channel 28 there between as shown in FIG. 2. While a variety of orientations and configurations of the pedicle screw distractor 10 are available according to this invention, a longitudinal axis of the handle 20 in one embodiment forms approximately an 138° angle with respect to a longitudinal axis of the lever 18.
The head 12 of the distractor 10 is shown in more detail in FIGS. 2-4 and includes a bifurcated yoke 30 with a pair of spaced prongs 32 extending distally from the head 12. The spaced prongs 32 form an arcuate-shaped clearance notch 34 there between which is adapted to conveniently receive the head 14 of the pedicle screw 16 during the distraction process. The head 12 includes an arcuate-shaped forward rim 36 along a leading edge thereof. Each prong 32 includes a generally planar sill 38 in which the clearance notch 34 is formed and a midline bulk head or wall 40 is formed between the sill 38 and the forward rim 36. On a rear face of the head 12, a concave brace 42 is formed adjacent to a concave screw head seat 44. A rearward ledge 46 is formed distally from the concave seat 44 on each prong 32.
The pedicle screw distractor 10 as shown and described herein is useful in distracting the pedicle screw 16 inserted into a vertebrae 48 in a patient's spine 50 as shown in FIGS. 6 and 7. The pedicle screw 16 is part of a spinal fixation system 52 which in one embodiment is a dynamic stabilization system having a generally cylindrical spacer 54 with a central lumen 56 there through seated between adjacent pedicle screws 16 and having a cord 58 passing through the spacer 54 and the pedicle screw heads 14. According to one embodiment of such a dynamic stabilization system 52 as provided by the assignee of this invention, the spacer 54 may be a polycarbonate material and the cord 58 a polyethylene-terephalate material. The cord 58 is tensioned during the installation process between the pedicle screws 16 and secured in the tensioned orientation by a set screw 60 in each pedicle screw head 14. Each pedicle screw head 14 includes a bore 62 through which the cord 58 passes. The set screw 60 when fastened secures the tensioned cord 58 in the bore 62.
The installation procedure for the dynamic stabilization system 52 utilizes various known and existing instruments. The pedicle screw distractor 10 may be used in conjunction with a companion instrument 64 such as a DYNESYS® cord guide instrument as shown in FIGS. 6 and 7. The cord guide instrument 64 is useful to tension the cord 58 during the stabilization system 52 installation. The cord guide instrument 64 is seated on an adjacent pedicle screw 16 in the patient's spine 50 and includes an elongate shaft 66 and operates in conjunction with a cord tensioning instrument 68 for installation of the cord 58. The cord tensioning instrument 68 includes a tensioning operator 70 to be grasped by the surgeon. An arm 72 projects from the upper end of the shaft 66. A handle extension 74 may be added to the upper shaft 66 of the companion instrument 64 to provide for more convenient and stable distraction. The handle extension 74 includes an upper grip 76 and a lower post 78 which may be seated longitudinally in the shaft 66 of the instrument 64 as shown in FIG. 5.
Other companion instruments such as an anti-torque tool or the like may also be utilized in conjunction with the pedicle screw distractor 10 of this invention. Since existing instrumentation 64 is utilized in conjunction with the pedicle screw distractor 10, the companion instrument 64 such as the cord guide, anti-torque or other instrument includes a head 80 mounted on the adjacent pedicle screw 16 as shown in FIGS. 6 and 7. During the installation of the cord 58 and spacer 54, distraction of the adjacent pedicle screws 16 is advantageously accomplished with the pedicle screw distractor 10 according to this invention to facilitate the minimally invasive installation of the system 52. The concave screw head seat 44 is mounted on the pedicle screw head 14 and allows for use of the pedicle screw distractor 10 with screws 16 that are implanted in non-parallel orientations or off-axis configurations. The clearance notch 34 and screw head seat 44 provide a stable mounting of the pedicle screw distractor 10 on the pedicle screw 16. The bifurcated arrangement of the prongs 32 permits the spacer 54 to be seated against the pedicle screw 14 as well as allowing the cord 58 to pass through the screw head bore 62 without interference when the distractor 10 is seated on the screw 16. The spacer 54 sits against the sill 38 after installation and proper clearance is provided for seating of the spacer 54.
The saddle 24 is seated on the shaft 66 of the companion instrument 64 such as the cord guide, anti-torque or other tool mounted on the adjacent pedicle screw 16. Since these companion tools 64 are fixed in orientation to the pedicle screw 16 on which they are mounted, the pedicle screw distractor 10 accommodates any misalignment between the instruments 10, 64 in the saggital plane. The clearance notch 34 on the head 12 of the pedicle screw distractor 10 accommodates a range of orientations for such a purpose.
Once the pedicle screw distractor head 12 is seated on the pedicle screw 16 and the saddle 24 against the shaft 66 of the companion instrument 64, the surgeon may squeeze the handle 20 toward the companion instrument 64 in the direction of arrow A (FIG. 6) thereby distracting the pedicle screw 16 through the fulcrum arrangement 22 at the saddle 24. Once the pedicle screw distraction process is accomplished, the cord 58 may be pulled taught between the pedicle screws 16 thereby seating the spacer 54 there between. Once the spacer 54 is seated between the screws 16, the distractor 10 is removed and the pedicle screws 16 are allowed to return to their normal position for secure installation of the remainder of the spinal stabilization system 52.
From the above disclosure of the general principles of the this invention and the preceding detailed description of at least one embodiment, those skilled in the art will readily comprehend the various modifications to which this invention is susceptible. Therefore, we desire to be limited only by the scope of the following claims and equivalents thereof.
Patent Application
20080009863
