Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-01-29
2001-09-18
Schaetzle, Kennedy (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S075000
Reexamination Certificate
active
06292699
ABSTRACT:
BACKGROUND OF THE INVENTION
This application relates generally to spinal fusion devices and methods and, more particularly, to spinal fusion devices and methods employing direct current (DC) bone growth stimulation as an adjunct to interbody fusion.
Approximately 100,000 lumbar spine fusion surgeries are performed annually in the U.S. on patients with lower back pain due to degenerative disc disease or spondylolisthesis. Adjacent vertebrae are fused together in such surgical procedures, thereby eliminating motion among the spine levels and significantly reducing lower back pain in most patients. Known spinal fusion methods include posterolateral fusion, also known as inter-transverse process fusion because it involves fusion of the transverse processes of adjacent vertebrae, and interbody fusion, which involves fusion of the bodies of adjacent vertebrae. Traditional interbody fusion involves insertion of autograft or allograft (bone graft from the patient's own body or from another body, respectively) into the intervertebral disc space as a spacer.
Interbody fusion is gaining popularity as an alternative to posterolateral fusion. The introduction of threaded titanium interbody fusion cages has made this technique simpler and more common among orthopedists and neurosurgeons. Such a cage is typically a rigid, hollow cylinder with a pattern of holes through its sidewall to allow bone growth into and through the cage. The cage is typically filled with morselized bone to facilitate fusion by bone growth through the cage, which thereby promotes interbody fusion. A number of interbody fusion devices and techniques have been proposed, as exemplified by those described in the following patents:
Patent No.
Inventor
Issue Date
4,501,269
Bagby
February 26, 1985
4,961,740
Ray
October 9, 1990
5,015,247
Michelson
May 14, 1991
5,489,307
Kuslich et al.
February 6, 1996
5,489,308
Kuslich et al.
February 6, 1996
Fusion success rates greater than 85% at 1-2 year follow-ups have been reported for titanium interbody fusion cages in one-level fusions, whereas the success rates for such cages in two-level fusions have been reported to be approximately 70-80%. Fusion success rates as low as 70% present a serious and expensive problem, since a large portion of patients require revision surgery, which is costly, painful, and disabling. One proposed solution to the problem is to pack interbody fusion cages with synthetic bone growth factors, particularly bone morphogenic proteins, which exhibit the ability to induce bone and/or cartilage formation. There is a safety concern over the potential formation of ectopic bone on or near the spinal cord with the use of potent growth factor products. It is also believed that bone growth factors remain at the fusion site for only hours or at most a few days before diffusing away.
Implantable direct current bone growth stimulation has been established as a useful adjunct for posterolateral fusion as well as for the traditional type of interbody fusion involving bone graft alone as the interbody spacer. Spinal fusion stimulators with titanium cathodes are available from Electro-Biology, Inc., the assignee of the present invention, and have been employed with the titanium cathodes placed in contact with bone graft material and the decorticated spine to deliver direct current to the fusion site. A small direct current (typically 20 or 40 &mgr;A divided among multiple cathodes) is delivered constantly for six months to enhance bone fusion. However, physicians are cautioned not to allow any metallic part of the stimulator to contact any metal internal fixation device. Bone graft is packed in and around the cathodes to form a fusion mass in which the cathodes are completely embedded.
In spite of all known adjuncts for interbody fusion, there remains a need for devices and methods for speeding interbody fusion and increasing fusion success rates.
SUMMARY OF THE INVENTION
The present invention meets this need and provides significant advantages over prior art devices and methods with a spinal fusion stimulator adapted to supply a constant DC current directly to an interbody fixation device adapted to be implanted in the intervertebral disc space of a patient's spine. The interbody fixation device functions as the electronegative cathode in addition to providing immediate stabilization and weight-bearing capability. DC current is supplied at a current level effective to produce a surface current density in said interbody fixation device that is effective to enhance osteogenesis. According to one aspect of this invention, a current density of at least 1 &mgr;A/cm
2
is produced in the interbody fixation device when implanted.
Another aspect of the invention is a method of stimulating spinal fusion that includes implanting an interbody fixation device in the intervertebral disc space of a patient's spine, and supplying a constant DC current to the interbody fixation device at a level based on the exposed electrically conductive surface area of the interbody fixation device and a predetermined desired surface current density.
A general object of the present invention is to provide an improved method and apparatus for promoting osteogenesis in interbody fusion.
Another object of the present invention is to employ direct current bone growth stimulation with a direct connection to an interbody fixation device with sufficient surface current density to significantly improve the efficacy of the interbody fusion.
These and other objects and advantages of the present invention will be more apparent upon reading the following detailed description in conjunction with the accompanying drawings.
REFERENCES:
patent: 3783880 (1974-01-01), Kraus
patent: 3918440 (1975-11-01), Kraus
patent: 4175565 (1979-11-01), Chiarenza et al.
patent: 4306564 (1981-12-01), Kraus
patent: 4421115 (1983-12-01), Kraus
patent: 4430999 (1984-02-01), Brighton et al.
patent: 4501269 (1985-02-01), Bagby
patent: 4506674 (1985-03-01), Brighton et al.
patent: 4558701 (1985-12-01), Spalten
patent: 4781591 (1988-11-01), Allen
patent: 4889111 (1989-12-01), Ben-Dov
patent: 5015247 (1991-05-01), Michelson
patent: 5030236 (1991-07-01), Dean
patent: 5304210 (1994-04-01), Crook
patent: 5489307 (1996-02-01), Kuslich et al.
patent: 5489308 (1996-02-01), Kuslich et al.
patent: 5738521 (1998-04-01), Dugot
patent: WO 95/32673 (1995-12-01), None
Spadaro, Joseph A., “Bioelectrochemistry Studies of Implantable Bone Stimulation Electrodes,”Bioelectrochemistry and Bioenergetics5, pp. 232-258 (1978).
Salman, N.N. et al., “The Effect of Direct Electrical Current Stimulation on the Bone/Porous Metallic Implant Interface,” Apr. 28, 1980.
Brighton, Carl T. et al., “Electrically Induced Osteogenesis: Relationship between Charge, Current Density, and the Amount of Bone Formed: Introduction of a New Cathode Concept,” inClinical Orthopaedics and Related Research, pp. 122-132, 1981.
Brighton, C.T., “Present and Future of Electrically Induced Osteogenesis,” inClinical Trends in Orthopaedics, Ed. L.R. Straub et al., pp. 1-15, 1981.
Colella, S.M. et al, “Fixation of Porous Titanium Implants in Cortical Bone Enhanced by Electrical Stimulation,”Journal of Biomedical Materials Research, vol. 15, pp. 37-46, 1981.
Black, J. et al., “The Role of Electrode Material and Current Density in Electrical Stimulation of Osteogenesis,” Paper presented at 2ndAnnual BRAGS, Oxford, U.K., Sep. 20-22, 1982.
Spadaro, J.A. et al., “Electrically Enhanced Osteogenesis at Various Metal Cathodes,”Journal of Biomedical Materials Research, vol. 16, No. 6, pp. 861-873, 1982.
Buch, F. et al., “The Bone Growth Chamber for Qunatification of Electrically Induced Osteogenesis,”Journal of Orthopaedic Research, vol. 4, pp. 194-203, 1986.
Meril, Allen J., “Direct Current Stimulation of Allograft in Anterior and Posterior Lumbar Interbody Fusions,”Spine, vol. 19, No. 21, pp. 2393-2398, 1994.
Black Jonathan, et al., “Mechanisms of Stimulation of Osteogenesis by Direct Current,” inElectrical Properties of Bone and Cartilage—Experimental Effects and Clinical Application,Br
Schwardt Jeffrey D.
Simon Bruce J.
Electro-Biology, Inc.
Schaetzle Kennedy
Woodard Emhardt Naughton Moriarty & McNett
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