Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2000-10-16
2002-02-19
Reip, David O. (Department: 3731)
Surgery
Instruments
Orthopedic instrumentation
C604S264000
Reexamination Certificate
active
06348055
ABSTRACT:
TECHNICAL FIELD
The present invention relates to systems for more accurately controlling the placement of implant materials percutaneously or otherwise under pressurized flow. Procedures for such placement include procedures for the repair of hard tissue by injection of hard tissue implant materials, such as in hip augmentation, mandible augmentation, and particularly vertebroplasty, among others. Procedures also include the placement of implant materials in soft tissues.
BACKGROUND ART
Polymethylmethacrylate (PMMA) has been used in anterior and posterior stabilization of the spine for metastatic disease, as described by Sundaresan et al., “Treatment of neoplastic epidural cord compression by vertebral body resection and stabilization.”
J Neurosurg
1985;63:676-684; Harrington, “Anterior decompression and stabilization of the spine as a treatment for vertebral collapse and spinal cord compression from metastatic malignancy.”
Clinical Orthodpaedics and Related Research
1988;233:177-197; and Cybulski, “Methods of surgical stabilization for metastatic disease of the spine.”
Neurosurgery
1989;25:240-252.
Deramond et al., “Percutaneous vertebroplasty with methyl-methacrylate: technique, method, results [abstract].”
Radiology
1990
;
117
(suppl):352; among others, have described the percutaneous injection of PMMA into vertebral compression fractures by the transpedicular or paravertebral approach under CT and/or fluoroscopic guidance. Percutaneous vertebroplasty is desirable from the standpoint that it is minimally invasive, compared to the alternative of surgically exposing the hard tissue site to be supplemented with PMMA or other filler.
A general procedure for performing percutaneous vertebroplasty involves placing a cannula with an internal stylet into the desired implantation site. The cannula and stylet are used in conjunction to pierce the cutaneous layers of a patient above the hard tissue to be supplemented, then to penetrate the hard cortical bone of the vertebra, and finally to traverse into the softer cancellous bone underlying the cortical bone. Once positioned in the cancellous bone, the stylet is then removed leaving the cannula in the appropriate position for delivery of a hard tissue implant material to reinforce and solidify the damaged hard tissue.
A syringe is next loaded with polymethyl methacrylate (PMMA) and connected to the end of the cannula that is external of the patient's body. Pressure is applied to the plunger of the syringe to deliver the PMMA to the site of damaged bone at the distal end of the cannula. Because in general, 10 cc syringes are only capable of generating pressures of about 100-150 psi, this places a limitation on the viscosity of the PMMA that can be effectively “pushed through” the syringe and cannula and fully delivered to the implant site. Of course, the use of a small barrel syringe, e.g., a 1 cc syringe enables the user to generate higher driving pressures. For example pressures of 800 psi and possibly as high as 1000-1200 psi (depending upon the strength of the user and the technique) may be generated using a 1 cc syringe. A serious limitation with the use of a 1 cc syringe, however, is that it will not hold a large enough volume to complete the procedure in one step or “load” and must be reloaded several times to complete the procedure, since, on average, about 3.5 cc of implant material per side of the vertebral body are required for an implantation procedure. This makes the procedure more complicated with more steps, and more risky in that the polymerization of the implant material causes it to become increasingly more viscous during the additional time required for reloading. Another problem with a 1 cc syringe is lack of control, as high pressures are generated in a “spike -like” response time and are not continuously controllable.
A viscous or syrupy consistency of PMMA is generally believed to be most advantageous for performing percutaneous vertebroplasty. Such a consistency insures that the implant material stays in place much better than a less viscous, more liquid material. Additionally, when PMMA is implanted percutaneously, the need to inject it through a relatively narrow needle or cannula also greatly increases the need for a high pressure driver. Still further, implantation of PMMA into a relatively closed implantation site (e.g., trabecular bone) further increases the resistance to flow of the PMMA, at the same time increasing the pressure requirements of the driver. Thus, a high pressure applicator that has enough storage capacity to perform a complete implantation procedure without having to reload the device in the midst of the procedure, and which is consistently controllable, for an even, constant application of pressure during delivery of the entirety of the implant material is preferred.
Attempts have been made to increase the ability to apply pressure to drive PMMA to the vertebral implant site by providing a smaller barrel syringe, but this holds less volume and must be refilled once or several times to deliver enough volume of PMMA to the site. Since there is a limited amount of time to work with PMMA before it begins to polymerize or set up, this type of procedure is more difficult to successfully complete within the allotted time, and thus poses an additional risk to the success of the operation. An improved high pressure applicator disclosed in U.S. application Ser. No. 09/053,108, has been developed for controllably applying higher pressures to a source of hard tissue implant material to successfully implant the material at the desired location in a single batch, for the performance of hard tissue implantation and particularly for percutaneous vertebroplasty. U.S. application Ser. No. 09/053,108 is hereby incorporated by reference in its entirety.
Leakage or seepage of PMMA from the vertebral implant site can cause a host of complications some of which can be very serious and even result in death. For example, Weil et al. reported cases of sciatica and difficulty in swallowing which were related to focal cement leakage,
Radiology
1996;Vol 199, No. 1,241-247. A leak toward the distal veins poses an even more serious risk, since this can cause a pulmonary embolism which is often fatal. In addition to misplacement of the cannula away from the intended implant site, leakage or seepage also may occur even when the cannula is properly placed. For example, overfilling of the intended implant site, under pressure, can result in seepage or leakage after removal of the cannula from the implant site.
Overfilling can occur simply by injecting a larger volume of implant material than the void to be filled at the implant site. Additionally, due to the high pressures involved in the implant procedure, compliance within the delivery system can act as a capacitance under pressure, thereby storing a volume of the implant material and energy under pressure. Upon release of the pressure at the pressure applicator end, the compliant portion of the system also releases its energy and consequently drives an additional amount of implant material into the implant site, thereby overfilling the intended implant site. Upon removal of the delivery system, a leakage or seepage problem ensues at the implant site as a result of the overfilling.
In a known arrangement disclosed by Tronzo in U.S. Pat. No. 4,653,489, a fenestrated hollow hip screw is adapted for delivery of bone cement to an osteoporitic hip fracture site in a femur. The screw is permanently fixed to the femur by screwing it thereto. Once the screw is mechanically fixed to the femur, bone cement is injected into the site by a 20 cc syringe through a standard intravenous (IV) extension tube which connects with a cannulation in the screw. In this situation, the cannulation is large and therefor a relatively lower driving pressure is required for delivery of the bone cement as compared to the situations described above. Additionally, the fact that the screw stays in place even after the injection of the bone cement helps to lessen the occurrence o
Becking Frank P.
Bozicevic Field & Francis LLP
Parallax Medical Inc.
Reip David O.
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