1. Field of the Invention
The present invention relates to percutaneous dilators and more particularly to an apparatus and method for dilating the ligamentum flava and other soft tissue by the alternating insertion of expandable tubes.
2. Description of the Related Art
Electrical stimulation of electrically excitable tissue such as the brain and/or nerve tissue of the spinal cord or peripheral nerve is an increasingly popular technique for treatment of pain or treatment of neural disorders. For example, medical leads having electrode contacts have been implanted near the spinal cord of the human body to provide pain relief for chronic intractable pain. A current technique for implanting a medical lead into the epidural space of the spinal column is a laminotomy which is a highly invasive technique requiring the cutting of the skin, tissue, ligamentum flava, and bone surrounding the epidural space. A more desirable and less invasive technique is to percutaneously implant a medical lead in the epidural space. This technique involves piercing a needle through the skin and tissue to the targeted area, thereby creating an access hole for the insertion of the medical lead. It is often desirable to implant larger leads which are more stable when implanted in the epidural space and provide better nerve fiber coverage for more effective pain reduction. An example of such leads are paddle leads as disclosed in U.S. Pat. No. 5,417,719. These larger leads, however, require a larger access hole and presently, these leads have been implanted by a laminotomy. A more efficient and equally effective method of increasing the access hole to the targeted area is through the use of dilators or similar expansion tubes. By using a dilator, the surrounding skin and tissue is expanded, thereby enlarging the access hole without doing a laminotomy. A related patent includes U.S. Pat. No. 5,183,464 which describes an expandable dilator for forming and enlarging percutaneous penetrations into hollow body organs, tissues or cavities. This patent, however, requires several components to effect expansion including, for example, a pair of coaxial cylinders, an outer sheath, and an inner rod. This patent also does not provide for the anchoring of the dilator at the targeted penetration area. Other background patents include U.S. Pat. No. 5,320,611 which describes an expandable cannula, and U.S. Pat. No. 4,738,666 which describes an expandable catheter. These patents are incorporated herein by reference.