Transplantation of engineered meniscus tissue to the intervertebral disc

[0001] This application is a continuation-in-part of U.S. patent application Ser. No. 09/688,716, filed Oct. 16, 2000, which claims priority from U.S. provisional patent application Serial No. 60/159,488, filed Oct. 14, 1999. The entire content of each application is incorporated herein by reference.

[0002] This invention relates generally to the treatment of diseased or traumatized intervertebral discs, and more particularly, to the use of engineered disc tissues in conjunction with such treatment.

[0003] Intervertebral discs provide mobility and a cushion between the vertebrae. At the center of the disc is the nucleus pulposus. The nucleus pulposus is surrounded by the annulus fibrosis, which is comprised of cells (fibrocyte-like and chondrocyte-like), collagen fibers, and non-fibrillar extracellular matrix. The components of the annulus are arranged in 15-25 lamellae around the nucleus pulposus. The fibers in the lamellae alternate their direction of orientation by 30 degrees between each band.

[0004] The annulus fibrosis has three important functions. First, the annulus contains the nucleus pulposus. Second, the annulus fibrosis, with other ligaments, connects the vertebrae of the spine. Lastly, the annulus fibrosis helps to control movement between the vertebrae.

[0005] The fibers of the annulus can tear causing pain and possible extrusion of the nucleus pulposus. Extrusion of the nucleus pulposus is known as a disc herniation. Disc herniations can compress nerves or the spinal cord resulting in arm or leg pain and dysfunction. Surgery to repair disc herniations leaves a hole in the annulus fibrosis. The hole in the annulus acts as a pathway for additional material to protrude into a nerve, resulting in a recurrence of the herniation.

[0006] To date, the treatment of tears or defects of the annulus fibrosis has relied for the most part on eliminating the defective disc or disc function. This may be accomplished by fusing the vertebra on either side of the disc. In terms of replacement, prior-art techniques replace either the nucleus or the nucleus and annulus functions. My co-pending U.S. patent application Ser. No. 09/322,516, and Patent Cooperation Treaty Application Serial No. PCT/US/14708 describe methods and devices to occlude annular defects.

[0007] Certain of my co-pending patent applications and issued patents referenced above recognize that the annulus fibrosis augmentation and/or transplantation techniques described therein are not limited to treatment of the intervertebral disc, and that such techniques may be used to treat other tissues of the body such as the meniscus of the knee. These previous disclosures teach that a meniscus may be removed from recently deceased humans and processed to kill the cells but preserve the extracellular matrix. Fibroctyes or chondrocytes are harvested and added to the meniscus extracellular matrix, as described in my pending U.S. patent application Ser. Nos. 09/639,309, 09/628,727, 09/638,726, and 09/638,242, all of which are incorporated herein by reference.

[0008] According to this invention, the transplanted meniscus is used to treat degenerative disc disease, disc herniation, or other pathologic conditions of the spine. Since the meniscus of the knee is capable of handling the high compression and shear loads placed on the meniscus by the bones of the knee, the mechanical properties of the meniscus make it an ideal tissue to transplant to other areas of the body, including the intervertebral disc.

[0009] In this embodiment, the harvested fibrocytes are added to a meniscus removed from a suitable donor, preferably a recently deceased human. The harvested meniscus could be processed to kill the cells but preserve the extracellular matrix. Killing the cells of the allograft meniscus minimizes the risk of disease transmission and graft refection. Fibrocytes or chondrocytes would be added to the harvested meniscus extracellular matrix prior to insertion of the engineered meniscus into a patient's spine. Alternatively, the cells could be added to the harvested meniscus during or after the meniscus is placed into a patient's spine.

[0010] Cells from the meniscus could be also be harvested from a patient's knee preferably using arthroscopic surgery or other minimally invasive procedure. For example, pieces of damaged meniscus removed by an arthroscopy, could be treated to harvest the cells of the meniscus. The cultured cells from a patient's meniscus are implanted into the allograft meniscus. The engineered meniscus is surgically implanted into a patient's spine at a second surgery.

[0011] Alternatively, allograft menisci could be transplanted to a patient's intervertebral disc without adding fibrocytes. In this second embodiment, one relies on the allograft donor cells that remain alive after tissue processing and the ingrowth of the patient's tissues and cells into the allograft meniscus.

[0012] One or more allograft menisci could be placed into the intervertebral disc. The menisci could be sewn or otherwise attached to the patient's annulus fibrosis. The allograft menisci could be prepared with sutures attached to the menisci to aid the surgeon in surgery. Alternatively, allograft menisci could be morselized and injected into a patient's disc. The morselized menisci could also be added to a bag like annular augmentation device described in my co-pending U.S. patent application Ser. No. 09/690,536, incorporated herein by reference in its entirety.

[0013] Broadly according to the invention, fibrocytes are harvested, cultured, added to annulus fibrosis extracellular matrix material, then sewn or otherwise placed relative to an injured or diseased disc. The annulus fibrosis cells and extracellular matrix are preferably harvested from a live human, though recently deceased human or animal donors may alternatively be used. Depending upon the extent of the harvest, the recipient may function at least in part as a donor, or the tissues from others, including fetal or embryo sources, may be used, preferably having a familial relationship to minimize or avoid the need for immunosuppressive substances. Guidelines for tissue procurement including surgical technique of removal, number of hours between death of the donor and tissue procurement, and testing of the donor for infectious disease, are well described.

[0014] Following annulus fibrosis harvest, the tissue is processed to kill the living cells. Care is taken to preserve the extracellular matrix. Guidelines for processing the harvested annulus fibrosis as described are well known to those skilled in the art. For example, the tissue could be frozen and thawed.

[0015] Fibrocytes are obtained from a tendon of the patient. For example, a palmaris longus tendon could be removed from one arm of the patient. The harvested fibrocytes are isolated and cultured using standard techniques. The harvested sterile tendon is morselized and washed with phosphate buffered saline. The cells are released from the extracellular matrix with 0.2% clostridial collagenase (Worthington CLS II, 140 u/mg) and agitated. See Klagsburn, Methods in Enzvmology, Vol. VII. The resulting suspension is filtered with 153.mu.g.nylon sieve (Tetko, Elmford, N.Y.).

[0016] The filtered solution is then centrifuged at 1800 rpm to remove the cells. The supernatant above the cells is removed with a micropipette until the cell concentration reaches 5.times.10.sup7 cells/cc. The harvested cells are grown in Hamm's F-12 culture media, 10% fetal calf serum, L-glutamine (292.mu.g/cc), penicillin (100 u/cc), streptomycin (100.mu.g/cc), and asorbic acid (5.mu.g/cc) at 37 C. The above method is described in U.S. Pat. No. 6,060,053, which is incorporated in its entirety herein by reference.

[0017] Precursor cells of the annulus fibrosis, annulus fibrosis cells, chondrocytes, or other living cells that could function like annulus fibrosis cells or that could differentiate into cells to build a functional annulus fibrosis may also be used.

[0018] The living cells from cell culture are implanted into the donor extracellular matrix to form a living annulus fibrosis. In the preferred embodiment, the cells are injected into small holes drilled into the donor extracellular matrix.

[0019] The living cells and extracellular matrix may be added to the patient's disc immediately after combination or after a period of time to allow attachment of the cells to the matrix. Naturally, in the delayed embodiment, the cells would preferably be supported with culture media.

[0020] The engineered annulus is added to the inside or the outside of a patient's annulus. Surgical procedures to access the inner or outer surface of the annulus fibrosis are well known to those skilled in the art. The engineered annulus could be sutured, placed against, or glued to the patient's annulus. Platelet rich plasma combined with calcium and thrombin or fibrin glue could be used to glue the annular tissues together.

[0021] Additional therapeutic substances could be added to the transplanted annulus. For example, resorbable culture medium, tissue growth or differentiation factors (recombinant generated morphogenetic proteins, PDGF, TGF-, EGF/TGF-, IGF-I, FGF), hydrogels, absorbable or nonresorbable synthetic or natural polymers (collagen, fibrin, polyglycolic acid, polylactic acid, polytetrafluoroethylene, etc.), antibiotics, anti-inflammatory medication, immunosuppressive medications, etc. may be used.

[0022] In an alternative embodiment, living cells are not added to the harvested annulus fibrosis. The harvested annulus fibrosis is processed as described above to kill the living host annulus cells.

[0023] Although annulus fibrosis augmentation and/or transplantation is being described herein in detail, the invention is not limited to treatment of the intervertebral disc. For example, the invention could also be used to treat other tissues of the body such as the meniscus of the knee. In such cases, a meniscus would be removed from recently deceased humans. The harvested meniscus would be processed to kill the cells but preserve the extracellular matrix. Fibroctyes harvested as described above would then be added to the extracellular matrix prior to insertion of the engineered meniscus into a patient's knee. Similarly, chondrocytes could be harvested and added to the meniscus extracellular matrix as described in my pending U.S. patent Ser. Nos. 09/639,309, 09/628,727, 09/638,726, and 09/638,242.

[0024] In addition, since the meniscus of the knee is capable of handling the high compression and shear loads placed on the meniscus by the bones of the knee, the mechanical properties of the meniscus make it an ideal tissue to transplant to other areas of the body, including the intervertebral disc. The transplanted meniscus may be used in accordance with this invention to treat degenerative disc disease, disc herniation, or other pathologic conditions of the spine. Biologic tissues such as a transplanted meniscus have important advantages over disc replacement with synthetic materials. As a biologic tissue, the transplanted tissue is capable of repair. Cells that are added to the engineered meniscus, or cells that invade the meniscus after transplantation are capable of repairing and producing extracellular matrix. Artificial disc replacements made of synthetic materials are not capable of repairing themselves. Furthermore, the particles from wear of synthetic materials may promote loosening of the artificial disc. Prosthetic knees and hips often loosen as the result of particles of polyethelene that are released into the surrounding tissues.

[0025] In this embodiment, fibrocytes harvested as described herein are added to a meniscus removed from a suitable donor, preferably a recently deceased human. The harvested meniscus could be processed to kill the cells but preserve the extracellular matrix. Killing the cells of the allograft meniscus minimizes the risk of disease transmission and graft refection. Fibrocytes or chondrocytes would be added to the harvested meniscus extracellular matrix prior to insertion of the engineered meniscus into a patient's spine. Alternatively, the cells could be added to the harvested meniscus during or after the meniscus is placed into a patient's spine.

[0026] Cells from the meniscus could be also be harvested from a patient's knee preferably using arthroscopic surgery or other minimally invasive procedure. For example, pieces of damaged meniscus removed by an arthroscopy, could be treated to harvest the cells of the meniscus. The cultured cells from a patient's meniscus are implanted into the allograft meniscus. The engineered meniscus is surgically implanted into a patient's spine at a second surgery.

[0027] Alternatively, allograft menisci could be transplanted to a patient's intervertebral disc without adding fibrocytes. In this second embodiment, one relies on the allograft donor cells that remain alive after tissue processing and the ingrowth of the patient's tissues and cells into the allograft meniscus.

[0028] One or more allograft menisci could be placed into the intervertebral disc. The menisci could be sewn or otherwise attached to the patient's annulus fibrosis. The allograft menisci could be prepared with sutures attached to the menisci to aid the surgeon in surgery. Alternatively, allograft menisci could be morselized and injected into a patient's disc. The morselized menisci could also be added to a bag like annular augmentation device described in my co-pending U.S. patent application Ser. No. 09/690,536, incorporated herein by reference in its entirety.