Surgery – Instruments – Blunt dissectors
Reexamination Certificate
2000-11-13
2003-07-22
Reip, David O. (Department: 3731)
Surgery
Instruments
Blunt dissectors
C606S064000, C606S096000, C604S164010
Reexamination Certificate
active
06596008
ABSTRACT:
SUMMARY OF THE INVENTION
This invention relates generally to surgery, and more particularly to methods and instrumentation having their principal utility in spinal surgery.
My U.S. Pat. Nos. 5,242,443, dated Sep. 7, 1993 and 5,480,440, dated Jan. 2, 1996, the disclosures of which are here incorporated by reference, describe a surgical technique for percutaneous fixation of two or more adjacent vertebrae by means of screws inserted percutaneously into the pedicles of the vertebrae and secured together by links located just under the skin of the patient's back. The technique avoids the many difficulties encountered in conventional internal and external vertebral fixation.
In vertebral fixation according to the methods described in my prior patents, a cannulated tubular guide is maneuvered into alignment with the pedicle. A pin is introduced through the guide and tapped with a mallet so that it enters the cortical bone at the junction of the base of the transverse process and the proximal articular process. The guide is then removed and a cannulated obturator is placed over the pin. An access cannula is then placed over the obturator and advanced to the pedicle. The obturator is then removed from the access cannula and a cannulated drill is advanced over the pin and operated to form an entrance into the medullary canal of the pedicle. A probe is then advanced into the medullary canal to create a bore into the vertebral body. The bore may then be tapped to form threads engageable by a pedicle screw, or alternatively a self-tapping pedicle screw can be inserted. With pedicle screws threaded into pedicles of adjacent vertebrae, adapters of the appropriate length are selected and secured to the proximal ends of the screws. The screws, with the adapters attached to them, are connected by links located just underneath the patient's skin. The procedure is much less invasive than conventional internal fixation, minimizes damage to muscle tissue and ligaments, reduces recovery and rehabilitation time, and simplifies removal of the fixation appliances. The procedure also reduces the infection risks, and avoids the physical limitations, imposed on the patient by external fixation.
The placement of a plate or rod under the skin, following commonly practiced open spinal fusion and pedicular screw insertion, facilitates subsequent retrieval of the hardware when the fusion and stabilization are accomplished. This eliminates the need for a second operation for access to, and retrieval of, the deeply positioned hardware.
The internal diameter of the medullary canal of the lumbar pedicles is typically only about 7 to 8 mm. The small size of the medullary canal mandates precise positioning of screws in the pedicle. To achieve proper alignment of the cannulated tubular guide with the axis of the pedicle, the guide is visualized fluoroscopically as it is being inserted. When properly aligned, the guide appears as an opaque circle in the center of the pedicle. A similar fluoroscopic method is used for alignment of the screw with the pedicle, the screw appearing as a dot in the center of the pedicle when properly aligned. This method is referred to as the “bulls-eye” method.
Conventional bulls-eye alignment has proven to be less than entirely reliable for proper positioning of percutaneously inserted guides and screws for several reasons. First, the operation is carried out using a radiolucent table and a C-arm fluoroscope. To allow better visualization of the pedicles the table is tilted away from the C-arm, or alternatively, the C-arm is tilted relative to the table. The angle of tilt of the C-arm fluoroscope relative to the operating table affects the angle of the guide or screw. Therefore, accurate measurement of the necessary tilt of the C-arm to accommodate the desired angle of insertion of the guide or screw is necessary. A second deficiency of the conventional bulls-eye alignment method arises because the skin entry point plays a significant role in the proper positioning of the guide at the center of the pedicle and the insertion of the probe into the vertebral body. A third deficiency of the bullseye method is that the distance between the guide and the x-ray tube can have an effect on the position of the guide relative to the pedicle. If the x-ray tube is too close to the patient and the angle of the tilt of the C-arm has not been predetermined and measured, the peripheral x-ray beams may present a distorted view of the position of the guide. A fourth deficiency of the bulls-eye method is that, when the C-arm is tilted by 20° to 30°, clear visualization of the boundaries of the pedicles is difficult.
Similar difficulties are encountered in positioning a biopsy cannula for taking a vertebral biopsy. An important object of this invention, therefore, is to provide a more accurate and reliable method for establishing an insertion point for a percutaneously inserted instrument for spinal surgery.
A method for determining the point for insertion of an instrument in a percutaneous spinal procedure in accordance with the invention, comprises the following steps. The patient is scanned by computed tomography, and an image is produced of an axial plane through the patient, i.e. a plane perpendicular to the long axis of the patient's body. On that image, a desired path for insertion of a guide pin is determined, and the lateral distance from the patient's midline to the point at which said path intersects the skin of the patient's back is determined. By viewing the patient's spine radiographically in the anterior-posterior direction, the skin of the patient's back is marked directly over the midline, and marking the skin of the patient's back is also marked with a line extending transverse to the patient's midline in a plane corresponding to the transverse plane in which the computed tomography scan was taken. Thereafter, an insertion point is established on the patient's back, on the transverse line, at a distance equal to the lateral distance measured on the image.
Another important object of this invention, therefore, is to provide an more accurate and reliable method for placement of a guide in the center of a pedicle in preparation for the insertion of a pedicle screw or biopsy cannula.
In accordance with the invention, the insertion points and insertion angles for the guide pins are established by a technique using a combination of computed tomography and conventional radiographic visualization. CT scans of the patient are taken in axial planes through the pedicles of two or more vertebrae to be fixated. Using the CT images, a desired path for insertion of a guide pin into each of these vertebrae is established. The angle of the path relative to the median plane is measured on the CT image for each of the vertebrae. Also, for each of these vertebrae, a measurement is made, on the CT image thereof, of the lateral distance from the patient's midline to the point at which the insertion path intersects the skin of the patient's back. By viewing the patient's spine radiographically in the anterior-posterior direction, a marking is made on the skin of the patient's back directly over the midline, and a transverse line is drawn for each of the vertebrae to be fixated over the centers of a pedicle thereof. Then, for each of the vertebrae to be fixated, an insertion point is established on the patient's back, on the corresponding transverse line, at a distance equal to the lateral distance measured on the CT image thereof. Thereafter a guide pin is inserted through the patient's back, and into a pedicle of each of the vertebrae to be fixated, through the insertion point established therefor and at the angle measured therefor.
Another problem with the method of percutaneous fixation as described in my prior patents is that the adapters that are attached to the proximal ends of the pedicle screws need to be available in a variety of sizes so that, during surgery, pedicle screws of the appropriate lengths can be selected to posi
Howson & Howson
Reip David O.
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