Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2001-05-25
2004-03-30
Woo, Julian W. (Department: 3731)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S011110, C606S074000, C606S151000, C606S154000
Reexamination Certificate
active
06712851
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to implants for use in repairing various portions of the mammalian skeletal system and, more particularly, to implants for use in clinical procedures such as bone fracture repair, regeneration of bone loss, augmentation of deficient bone, and related procedures.
2. Description of Related Art
Various types of defects in the mammalian skeletal system can be treated by various surgical procedures. Defects in the mammalian skeletal system may include bone fracture, loss of bone occurring from traumatic, surgical, or infectious sources, and bone deficiencies stemming from conditions such as atrophy and congenital anomalies.
One procedure that is common in the prior art for treating bone defects involves the placement of additional bone into the bone defect area. This procedure, which is commonly referred to as bone grafting, is the second most frequently performed surgical grafting procedure, with skin grafting the most common surgical grafting procedure. Current bone grafting procedures include the use of vascularized or non-vascularized autografts and allografts.
A bone autograft is a portion of bone taken from another area of the skeletal system of the patient. A bone allograft, in contrast, involves a human donor source other than the recipient patient. Allogenic bone graft typically comprises bone harvested from cadavers, which is subsequently treated and stored in a bone bank and ultimately used as a bone graft implant. Allogenic bone graft is known to have osteoconductive and osteoinductive capabilities, although the osteoinductive properties are limited because of the necessary tissue sterilizing and cleaning procedures associated with harvesting these bone grafts. The term osteoconduction refers to a class of biomaterials which provide a three-dimensional porous framework to conduct the ingrowth of new living bone into this structure. The term osteoinduction refers to a class of materials having capabilities of recruiting mesenchymal stem cells of the patient and promoting their differentiation into osteoblasts, which are bone forming cells. An osteoinductive material will typically form bone if implanted into an area where bone would not normally grow. For example, the placement of bone morphogenic proteins into the muscle of a patient will result in ectopic (outside of bone) bone formation.
Both bone autografting procedures and bone allografting procedures are associated with shortcomings in the healing of bone defects within the mammalian skeletal system. Bone autografting procedures are typically associated with limitation of donor sites, bone quantity, and donor site morbidity (especially if multiple donor sites are required). Bone allografting procedures, to begin with, only have limited osteoinductive capabilities. In addition to the very limited osteoinduction properties of allogenic bone grafts, compared to autograft samples, allografts are immunogenic to a certain degree, bear the risk of disease transmission (e.g. HIV and Hepatitis), and, depending on the size of the allograft, require a long time for ingrowth and partial substitution with new bone. This long substitution process often requires a time duration of greater than one year before satisfactory clinical results are obtained. Additionally, pressure from the adjacent musculature may dislocate bone graft material. Bone grafts may re-fracture after fixator removal if bone ingrowth and substitution is inadequate.
As a substitute to actual bone grafts, which include autografts and allografts, various bone graft substitutes have been used by the prior art for treating bone defects in the mammalian skeletal system.
Porous ceramic bone graft substitutes, for instance, such as coralline hydroxyapatites, operate similarly to bone grafts by providing a three-dimensional structural framework. This framework conducts the regenerating bone of the patient into the porous matrix of the three-dimensional structural framework. This process of conducting the regenerating bone into the porous matrix is commonly referred to as osteoconduction, as opposed to osteoinduction discussed above. Permanent, non-resorbable, inorganic, ceramic implants have shortcomings such as inherent brittleness and large framework volume fractions. The framework volume fraction of a typical bone graft substitute comprises approximately 40 percent of the volume where new bone could otherwise grow. This 40 percent volume occupied by a bone graft substitute, consequently, cannot be occupied by the regenerating bone of the patient.
A process referred to as guided tissue regeneration is widely used by periodontists to regenerate bone and periodontal ligaments (ligaments between the tooth root and the bone) around dental implants, for example. This surgical procedure uses cell-occlusive (cells cannot pass through) but fluid-permeable membranes, which are otherwise known as semipermeable membranes, in order to cover and segregate a bone defect from the surrounding soft tissues. U.S. Pat. No. 3,962,153 discloses such a cell-occlusive, fluid-permeable membrane. Use of these cell-occlusive, fluid permeable membranes, has been predominantly developed and used by periodontists over the last decade, who worked in the mouth around teeth. The human body has many tissue types which originate from three primary germ layers of the embryo: the ectoderm, the mesoderm and the entoderm. From the ectoderm are derived the skin and its attached tissues, such as nails, hair and glands of the skin, the nervous system, external sense organs and the epithelial lining of the mouth and anus. From the mesoderm are derived the connective tissues, bone, cartilage, muscle, blood and blood vessels. From the entoderm are derived, among others, the digestive tract, bladder and urethra. The “precursor” cells of these layers are limited to only becoming cells of their respective tissue type. Bone, muscle, connective tissue, blood vessels and cartilage are of mesenchymal origin which means from the meshwork of embryonic connective tissue in the mesoderm, and are formed from versatile mesenchymal stem cells, whereas the lining of the mouth is of ectodermal origin and is formed of epithelial cells derived from the ectoderm. Ectodermal cells do not have the potential to become bone forming cells and, conversely, mesenchymal cells do not have the potential to form epithelium.
Epithelial cells are present in the mouth, but are not present in many other areas of the mammalian skeletal system, such as areas near long bones of the mammalian skeleton. The development of cell-occlusive, fluid permeable membranes was developed in the context of periodontal and oral applications, for the purpose of excluding the introduction of epithelial cells into the bone defect area of the patient because they are believed to hinder bone formation. Epithelial cells proliferate faster than bone cells and, therefore, the exclusion of these epithelial cells from the bone defect area has been considered to be essential for optimal bone and ligament regeneration in these periodontal and oral applications. Although cell-occlusive, fluid permeable membranes have been predominantly used in periodontal and oral applications, these cell-occlusive membranes have recently also been applied for tissue segregation in other defect sites in the mammalian skeletal system, such as long bone defects.
These cell-occlusive membranes of the prior art have a shortcoming of blocking blood vessels and mesenchymal cells from entering into the bone defect area. Thus, the advantage of precluding epithelial cells from the bone defect area in the oral cavity is achieved at the expense of also precluding entry of blood vessels and surrounding mesenchymal cells into the bone defect area, as well. In periodontal and oral applications, the advantage of precluding epithelial cells is believed to be worth the shortcoming of also precluding blood vessels and surrounding mesenchymal cells from the bone defect area. In other areas of the mammalian skeletal
Calhoun Christopher J.
Lemperle Stefan M.
MacroPore Biosurgery, Inc.
Stout, Uxa Buyan & Mullins, LLP
Woo Julian W.
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