Hollow, curved, superlastic medical needle

Details Hollow, curved, superlastic medical needle Hollow, curved, superlastic medical needle

1999-12-09

2003-07-15

Mendez, Manuel (Department: 3763)

Surgery

Means for introducing or removing material from body for...

Treating material introduced into or removed from body...

Reexamination Certificate

active

06592559

ABSTRACT:

TECHNICAL FIELD
This invention relates generally to medical devices and more particularly, to needles that are curved for indirect infusion access within the body.
BACKGROUND OF THE INVENTION
Medical procedures involving the vertebrae are typically complicated because of the preciseness required to avoid both neural damage and injury to major blood vessels, as well as the indirect path that is usually required to access the treatment site. This is certainly the case when performing a vertebroplasty, a procedure whereby bone cement, most commonly methyl methacrylate, is injected into a vertebral body to provide stabilization and/or pain relief in selected patients having a spinal condition such as osteolytic metastasis and myeloma, painful or aggressive hemangioma (benign lesions of the spine), or painful osteoporotic vertebral collapse. Standard treatment practice depends on the region of the spine being treated. For the cervical vertebrae, anterolateral access is used with a 15 gauge needle. The large vessels adjacent to the vertebra are laterally manipulated by the radiologist to provide an access site between the vessels and the pharyngolarynx. An upward access route is required because the needle must be introduced below the mandible. When accessing the thoracic or lumbar vertebrae, typically a large 10 gauge needle is used following a transpedicular or posterolateral approach. The transpedicular route is preferred to avoid spinal nerve injury and to decrease the probability of the cement leaking out into tissues adjacent to the vertebral body. To obtain a complete filling of a damaged vertebral body, it is often required that a second transpedicular access be made from the opposite side. A single infusion usually cannot fill the entire target area because the needle tip cannot be redirected from the original plane of entry. Continued infusion of cement from the first access site will usually not result in an adequate infusion due to the tendency of the material to set before it fills all of the affected area, thereby becoming a barrier to itself. Furthermore, the thick density of the marrow and structures, such as veins, usually acts to impede free flow of the cement within the vertebral body. Another concern during the procedure is accidental puncture of the these veins. Because vertebral veins lead directly to the lungs, there is a significant risk of pulmonary embolism if cement is accidentally introduced therein.
The inability to adequately maneuver the needle cannula tip within a body or around structures is a major limitation of the straight needle. Additional needle sticks to complete a medical procedure provide discomfort to the patient and additional risk of leakage and other complications. In order to sufficiently access a vertebral body for complete infusion of cement, the tip must be able to be deflected at significantly large angles from the original axis. This would require that the needle have a distal bend so that it could be rotated to selectively direct the material. Rigid curved needles are well known for suturing applications; however, adding anything more than a slight bend to an infusion needle limits its access path and ability to deeply penetrate tissue, especially bone. For example, a rigid curved needle would be unsuitable for use in a vertebroplasty procedure where the needle cannula must be driven through the bone and deep into the vertebral body using a relatively straight approach and maintained in place to avoid additional damage to the entry site. While the initial access must be done with a straight needle of sufficient strength to penetrate bone, the ideal approach would be to be able to direct a lateral infusion of cement following penetration, and then to withdraw the needle along its original path. Accomplishing this is problematic in that the density and resistance of the tissue at the treatment site can require that the inner infusion member be nearly as stiff as the outer piercing cannula. A certain degree of rigidity is required to be able to maneuver the inner member and accurately direct the flow of material. While stainless steel infusion needles having a slight distal bend are known, the amount of curvature necessary to provide adequate lateral infusion would not be possible in that the needle would be plastically deformed once inside the outer restraining cannula and be unable to resiliently return to its preformed shape. Thus, a second needle access would still be required to provide adequate filling.
Other medical procedures provide similar problems when a single straight needle is used. One example is tumor ablation where percutaneous ethanol injection is used to treat carcinoma of the liver and kidney. Originally introduced as a palliative treatment for inoperable hepatocellular carcinoma of the liver, ethanol injection has now been shown to have curative potential comparable to resection in many patients, especially for smaller tumors. Current practice has been to directly inject ethanol into masses using a straight needle and allow the ethanol to infuse from one or more side holes into the tissue. The problem is that the infusion may not penetrate any deeper than the needle tract and thus, portions of the tumor are not effectively treated. It is desired to provide a device for more effective infusion of ethanol into the tumor mass.
SUMMARY OF THE INVENTION
The foregoing problems are also solved and a technical advance is achieved in a curved member, such as a medical needle for use for example for infusion or aspiration, and made of a rigid superelastic material and having at least one preformed bend along the distal portion of its length. The needle is used coaxially with a second hollow cannula for restraining the needle in a substantially straight orientation during percutaneous introduction to the target site, whereby the needle is deployed to resiliently return to its preformed configuration. The ability of the preformed needle to deflect laterally upon exiting the restraining allows it to infuse or aspirate material at multiple points within different planes in the body by rotating the needle about its longitudinal axis. This is important in helping to reduce or eliminate the need for additional “sticks” with the outer cannula. It also allows the operator to make an entry from one direction, then to deploy the curved to reach a site that cannot be accessed directly, such as where another structure lies along the access path, thereby blocking the target site.
The preferred material for the needle is a superelastic, shape memory alloy such as nitinol (Ni—Ti); however, there are other non Ni—Ti alloys that may be used. A nitinol alloy is selected that has properties whereby the temperature at which the martensitic to austenitic phase change occurs is lower than the working temperature of the device (i.e., room temperature). As described by Jervis in U.S. Pat. No. 5,597,378 filed Oct. 2, 1992 and incorporated herein by reference, a permanent bend may be heat set in a superelastic nitinol cannula by maintaining the cannula in the desired final shape while subjecting it to a prescribed high temperature for a specific time period. The cannula can be elastically manipulated far beyond the point at which stainless steel or other metals would experience plastic deformation. Nitinol and other superelastic materials, when sufficiently deformed, undergo a local phase change at the point of stress to what is called “stress-induced martensite” (SIM). When the stress is released, the material resiliently returns to the austenitic state.
A second method of imparting a permanent bend to the material is by a process commonly known as cold working. Cold working involves mechanically overstressing or overbending the superelastic cannula. The material within the bending region undergoes a localized phase shift from austenite to martensite and does not fully return to its original shape. In the case of the cold-worked cannula, the result is a permanent curve about the bending zone which has been locked in to at least a partial martensit

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