Surgery – Instruments – Electrical application
Reexamination Certificate
2001-04-09
2003-05-13
Peffley, Michael (Department: 3739)
Surgery
Instruments
Electrical application
C607S117000, C606S046000
Reexamination Certificate
active
06562033
ABSTRACT:
TECHNICAL FIELD
The invention relates to an intradiscal lesioning apparatus for treating intervertebral disc disorders, such as localized tears or fissures in the annulus fibrosus, localized disc herniations, and circumferential bulging of discs.
BACKGROUND OF THE ART
Lower back injuries and chronic back pain are a major health problem resulting not only in a debilitating condition for the patient, but consuming a large proportion of funds allocated for health care, social assistance and disability programs. However, there is no consensus among medical researchers on the mechanism of the disorder despite extensive experimentation and clinical testing on the subject. Disc abnormalities may result from trauma, repetitive use in the workplace for example, metabolic disorders or aging.
Each intervertebral disc is composed of a central, gel-like nucleus pulposus surrounded by a tough fibrous semielastic annulus fibrosus. Common disorders include localized tears or fissures in the annulus fibrosus; localized disc herniations with contained or escaped extrusions of the nucleus pulposus; and chronic circumferential bulging of discs. For most patients, however, a well-defined abnormality cannot be found to solely explain the cause of the low back pain, making treatment and pain management very difficult. Isolated cases where a specific anatomic disorder can be diagnosed are the exception. Regrettably, most patients are merely treated symptomatically to reduce pain, rather than to eliminate the root cause of the condition.
The intervertebral discs form about one-quarter the length of the vertebral column in a healthy adult human. Discs are thickest in the cervical and lumbar regions, where the movements of the vertebral column are greatest. With age the vertebral column, including the intervertebral discs, undergo various morphological and biochemical changes such as dehydration of the discs and concaving vertebral bodies. As a result, the size and configuration of the disc components vary considerably from person to person.
The annulus fibrosus is composed of concentric layers of fibrocartilage, in which the collagen fibers are arranged in parallel strands running obliquely between vertebral bodies. The inclination is reversed in alternate layers thereby crossing over each other obliquely. In children and adolescents, the nucleus pulposus is an amorphous colloidal mass of gelatinous material containing glycosaminoglycans, collagen fibrils, mineral salt, water and cellular elements. The nucleus pulposus is normally under pressure and is contained within an ovoid cavity formed laterally by the annulus fibrosus and bounded by thin plates of hyaline cartilage covering the adjacent vertebrae. The annulus fibrosus is thinner nearer to the posterior than to the anterior margin of the disc, and many disc ruptures occur in the posterior region thereby exerting pressure on the adjacent nerve fibers.
Increasingly however, evidence suggests that the source of back pain in many patients are nerves within the degenerated disc itself, rather than the exertion of pressure on adjacent spinal nerves by a damaged disc. For example, as documented by Jonathan C. Houpt, B A, Edison S. Conner, M D, and Eric W. McFarland in “Experimental Study of Temperature Distributions and Thermal Transport During Radiofrequency Current Therapy of the Intervertebral Disc”, Spine. 1996;21(15), 1808-1813, afferent innervation of the outer half of the annulus fibrosus has been established whereas the nucleus pulposus contains no nerves or blood vessels. Pain response has been widely reported in response to specific stimulation of the outer layers of the annulus fibrosus. In another study documented by A. J. Freemont, “Nerve ingrowth into diseased intervertebral disc in chronic back pain”, The Lancet. 1997; 350, 178-181, nociceptive nerves were found ingrown deeper into the disc, as far as the nucleus pulposus, in association with disc degeneration.
Where patients are diagnosed with clear discogenic pain (i.e. pain originating from a disc), complete surgical removal of the intervertebral disc and fusion of the adjacent vertebrae is often carried out with success rates over 80% in measurable pain reduction after surgery. Such major surgical procedures are invasive, expensive and involve significant risk. To alleviate some of the disadvantages of diskectomy, U.S. Pat. No. 5,201,729 to Hertzmann et al describes a percutaneous method of diskectomy.
Due to the pain reduction success of surgical diskectomy, less drastic means of denervating rather than surgically removing the disc are of significant interest. Denervating the disc is less invasive, less costly, simpler to administer and does not require the fusing of adjacent vertebrae thereby better preserving the patient's freedom of movement.
To destroy nerve cells in the annulus fibrosus, the prior art includes probes that emit various forms of energy from within the nucleus pulposus such as, radio frequency electric current, microwave or thermal energy. It appears that the surface of the disc is devoid of temperature sensing neurological structures, probably since the disc is at core body temperature, and only mechanical and chemical stimulus-sensing nociceptors exist in the annulus fibrosus.
U.S. Pat. No. 5,433,739 to Sluijter et al describes a method of relieving back pain through percutaneous insertion of a needle or electrode into the intervertebral disc under fluoroscopy or other imaging control. Radio frequency electrodes of the same type are commonly used in neurosurgery, anesthesiology and cardiology to lesion neural tissue including an insulated shaft with an exposed tip conducting radio frequency current. A second dispersive electrode with large surface area is placed elsewhere on the patient's body to complete the circuit. The intensity of radio frequency current at the exposed tip causes heating of the adjacent tissue and when the temperature increases sufficiently, the neural tissue is coagulated. The mechanism is direct interruption of the nerves by formation of a lesion and thus the transmissions of pain signals are blocked.
It is well known to those skilled in the art that percutaneous access to the disc is by placing a needle or tube into the disc from the posterior lateral approach, but the limited access does not allow much room to manoeuvre. Once the tube pierces the tough annulus fibrosus, the tube is fixed and has very little freedom of movement. Thus, with a simple needle or electrode, access to only small portions of the central and anterior nucleus pulposus is available.
To permit percutaneous access to the posterior half of the nucleus or to the posterior wall of the disc, U.S. Pat. Nos. 6,007,570; 6,073,051; 6,122,549 and 6,126,682 to Sharkey et al describe a flexible heating element that is inserted into the nucleus pulposus through a hollow tube that has been pierced through the annulus fibrosus. The flexible heating element has sufficient rigidity to be advanced longitudinally under force through the nucleus pulposus while having flexibility to be compliant to the inner wall of the annulus fibrosus. The heating element is guided by sliding contact with the inner wall and ideally should not puncture or damage the annulus fibrosus during positioning.
The shape, size and configuration of the nucleus pulposus may vary considerably and obstacles such as a radial fissure or a fibrous lump, commonly existing in degenerated discs, may impede sliding contact of the heating element. As a person ages, the border between the nucleus pulposus and the annulus fibrosus becomes less distinguished, beginning when a person is about 30 years old. The transition zone is made of both fibrous material of the annulus fibrosus and gelatinous material of the nucleus pulposus. However, the Sharkey heating element relies on sliding contact with the inner wall of the annulus fibrosus to guide it into position and to bend the element into a configuration that closely engages the inner wall of the annulus fibrosus. As a result, the accuracy with which the Sharkey heat
Baylis Frank Headley
Leung Mark
Shah Krishan
(Ogilvy Renault)
Baylis Medical Co.
Peffley Michael
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