Patent Application
20110137417
1. Field of the Invention
The present invention relates to a bone allograft for implantation into a surgically altered area or site of a human, and more specifically, a bone allograft having a plurality of cortical bone and cancellous bone segments or wafers articulating with one another through a series of tabs and notches therein. A cortical pin is inserted through the widths of the respective bone wafers to form the allograft. The cortical pin is substantially cylindrically shaped, having thin diameter along its end portions and a thick middle diameter, thereby creating a shoulder to absorb stress placed on the allograft by insertion into the surgically altered site and to channel the stress throughout the cortical bone rather than the cancellous bone portion of the graft.
2. Description of the Related Art
A common problem many people encounter either as they get older or through injury is the collapsing of inter-vertebral discs. As the adjacent vertebrae collapse together, nerves are pinched causing further pain to the person as the vertebrae collapse upon one another. It is common to stabilize collapsing vertebrae by placing heterogeneous bone allografts from a human donor intervertebrally. Ideally, hard cortical bone would be retrieved from a donor and transplanted into a surgically altered site. Specifically, it would be optimal to insert hard cortical bone allografts between vertebrae to allow the cortical bone to fuse with the superior and inferior vertebrae to stabilize the vertebrae and provide relief to the patient.
However, because of limitations naturally placed on the tissue retrieving process by the human anatomy, and the eligible donor pool, the cortical bone segments of a donor which are desirable to retrieve for transplantation are fairly limited. The suitable cortical segments can only be retrieved from the shafts of the long bones of the human body, making it difficult if not impossible to retrieve a sufficient volume of single cortical bone segments or multiple segments from a donor of sufficient size and shape to insert inter-vertebrally or otherwise between bones or bone segments of a patient.
Moreover, the healing process wherein the heterogeneous cortical bone is incorporated into the native bone tissue makes it impractical to insert an allograft made completely of cortical bone. This is because fusion of cortical tissue to native bone of a patient occurs slowly over a long period of time by a reverse mechanism wherein osteoclasts break down portions of the implanted cortical tissue, creating canals through the cortical tissue to allow the body to vascularize the bone through the channels or canals and allow the native blood to supply rebuilding bone molecules to the cortical bone.
The cortical bone is initially weakened in this process, and is later strengthened as the heterogeneous cortical bone segment or segments are fused to the native bone of the patient. This process can take years to complete. Therefore, the stability ultimately provided by cortical bone segments is not provided in the interim between post-operation and substantial completion of the reverse mechanism healing process. Thus, a cortical bone implant cannot bear loads placed on it by the body by itself until it is stabilized within the surgically altered site by fusing to the native bone.
Cancellous bone fuses to native bone tissue much more quickly. Cancellous bone is very spongy, containing many vascularized canals. The patient's body sends native blood supply to the cancellous bone very quickly and allows the cancellous bone to vascularize and incorporate quickly into the native bone. However, cancellous bone is very weak, and cannot bear significant loads placed on it by the body by itself.
It is therefore desirable to construct a bone allograft having segments or wafers of cortical bone and segments or wafers of cancellous bone so that the allograft can initially fuse to native bone tissue via fusion with the cancellous wafers, thus providing initial stability to the allograft to allow the prolonged fusion of the cortical bone wafers to the native bone tissue. It is further desirable to construct the allograft in such a way that it absorbs forces placed on it during insertion into the surgically altered site without breaking apart. It is further desirable to construct the allograft in such a way as to allow interspersal of cortical bone and cancellous bone wafers adjacent one another so that larger bone allografts can be utilized in transplantation. It is further desirable to construct a cortical bone pin that can absorb insertion force during implantation of the allograft. It is further desirable to construct the allograft in such a way that it absorbs forces placed on it during the incorporation of the allograft into the recipient's anatomy.
There exists in the prior art bone allografts for insertion and/or fusion into the spinal column wherein the bone allograft has cortical bone wafers and cancellous bone wafers. However, bone allografts in the art suffer from several drawbacks. Some allografts do not utilize pins to hold the bone wafers together. Such allografts can easily break apart during insertion. Other allografts have pins inserted through the wafers of cortical and cancellous bone. However, in many instances the pins are not inserted completely through the allograft. Moreover, the pins are typically thin, cylindrical, straight, and of a uniform small diameter, lending to a tendency to be easily dislodged from the allograft if the allograft is jarred or encounters a blunt force such as the forces necessary to insert the allograft into the patient.
Another problem associated with allografts in the art using the slender cylindrical pins is that such allografts are inserted into the surgically altered area such that the length of the pin bears the insertion load asserted on the allograft by a surgical mallet or other surgical device typically used to insert a bone allograft inter-vertebrally or otherwise between bone wafers. In other words, the bone pin is exposed across, or perpendicular to the insertion plane as opposed to with, or parallel to the plane of insertion.
By inserting the allograft such that the pin is perpendicular to the plane of insertion, each individual bone wafer of the allograft is likewise perpendicular to the plane of insertion. By exposing the allograft in such a way, the insertion force is asserted not only across the length of the bone pin, but also directly upon each bone wafer. Therefore, each strike of the mallet or other surgical tool must be sustained substantially equally by each cortical and cancellous bone wafer in order to keep the bone pin from breaking and the allograft from coming apart. This is nearly impossible to accomplish, and it is therefore common for such allografts to fall apart during or shortly after insertion. This problem is exasperated by the fact that the bone pins—if used at all by the prior art—are thin, straight cylindrical rods, resembling a straight pin. The construction of these pins does not allow the pin to successfully absorb the force of insertion asserted on the pin by a mallet or other surgical instrument. Thus, the pins break and the allograft comes apart.
The present invention is different than the prior art. The bone allograft of the present invention is held together by a bone pin made of cortical bone. The cortical pin is made of a single piece of cortical bone and is substantially cylindrical, and shaped similar to a rolling pin. The cortical pin has a thick middle diameter which corresponds to and is inserted within canals in the inner bone wafers of the allograft. The cortical pin has diameters smaller than the middle diameter along its end portions.
The smaller diameter end portions of the cortical pin correspond to and are inserted within the end cortical bone wafers of the allograft. The junctions of the small end portions of the cortical pin with the thick middle diameter of the cortical pin create a shoulder on each side of the thick middle diameter. The shoulders aid in absorbing the brunt of the force asserted on the allograft by a surgical mallet or other appropriate medical device during insertion of the allograft.
The allograft is comprised of two end cortical bone segments or wafers. The cortical end wafers have at least one hole or tubular canal extending through the width of the wafers. The canal is of a diameter sufficient to receive the end portions of the cortical pin snugly, but too small in diameter to receive the thick middle diameter of the cortical pin. At least one cancellous bone wafer is disposed adjacently between the cortical end wafers. Where a small bone allograft is desired, as few as one cancellous bone wafer may be disposed adjacently between the cortical end wafers. The size of the allograft desired can be accommodated by either adding cancellous bone wafers adjacent one another between the cortical end wafers, or cutting wider cancellous wafers and inserting them between the end cortical wafers.
However, if too many cancellous bone wafers are placed adjacent one another such that the width of the adjacent cancellous segments become too wide, or if a single cancellous bone member is created too wide, the cancellous wafer or wafers will simply collapse or crush between the cortical end wafers during insertion of the allograft and/or during remodeling or incorporation of the allograft. It is therefore desirable—especially where larger allografts are required—to have inner cortical bone wafers interspersed between adjacent cancellous bone wafers to add structural integrity and additional load-bearing support to the inner portion of the allograft to prevent such crushing.
In fact, it is desirable to have each cancellous bone member created to be approximately eight millimeters wide or less to reduce the risk of crushing or collapsing during insertion or the pending remodeling. Alternatively, if multiple thinner cancellous wafers are placed adjacent one another in the allograft, it is desirable to have a cortical wafer interposed between such multiple thinner cancellous wafers such that the total width of the cancellous wafers adjacent one another is approximately eight millimeters or less. Each wafer disposed between the end cortical wafers has one or more tubular canal(s) disposed through the wafer across the width thereof. The canal is of sufficient size to snugly receive the middle diameter of the cortical pin.
In one aspect of the invention, all of the wafers are disposed side by side such that sides of the wafers which are adjacent one another are substantially flat. However, in another aspect of the present invention, the wafers comprise a trough and shelf, or tab and groove configuration to interlock adjacent wafers. This incorporated feature serves two purposes. First it aids is absorbing insertion forces associated with surgically placing the allograft. Second, it provides additional strength to the composite allograft to decrease the likelihood of the allograft fracturing during the remodeling process. One of the end cortical wafers has a tab along the side of the cortical wafer that is disposed on the internal side of the allograft. A groove is disposed along the adjacent side of an adjacent cancellous wafer. The groove is formed to snugly receive the tab of the end cortical wafer. On the side of the cancellous wafer opposite the groove is a tab substantially the same as the tab on the end cortical wafer.
The wafer adjacent the cancellous wafer—whether cancellous or cortical—has a groove to receive the tab of the cancellous wafer, and a tab on the side opposite the groove which will be inserted into a groove of an adjacent wafer. Each internal wafer has the tab and groove configuration such that each groove receives the tab of the adjacent wafer. The other end cortical wafer has a groove for receiving the tab of an adjacent cancellous wafer.
The allograft of the present invention is inserted into the surgically altered area of the patient with its assembled sections laying perpendicular to the way the other allografts in the art are inserted. Specifically, the allograft is inserted such that the cortical pin runs with, or parallel to the plane of insertion as opposed to perpendicular to the plane of insertion. By inserting the allograft parallel to the plane of insertion, one end cortical wafer is receiving the direct impact from the surgical mallet or other insertion device, and the other end cortical wafer is receiving the transferred impact from the cortical pin. Moreover, insertion of the allograft parallel to the plane of insertion aids in preventing fracturing and reducing stress placed on the allograft during the remodeling process.
The tab and groove configuration of the wafers allows the wafers to interlock with one another to add stability of the allograft during insertion and especially during remodeling. Furthermore, the tab of the end cortical wafer provides an elevated shelf which is adjacent the shoulder formed by the junction of the end portion and the middle diameter of the pin. As the wafer is impacted by the mallet during insertion, the energy is transferred through the allograft by the cortical pin and is absorbed by the end cortical wafer and the end portion of the cortical pin disposed therein.
Specifically, the configuration of the cortical pin allows the energy from the mallet to be transferred from the thin end portion disposed within the end cortical wafer that receives the direct impact from the surgical mallet to the thick middle diameter of the cortical pin. The energy is then displaced through middle diameter of the bone pin to the tab of the opposite end cortical wafer, where the shoulder formed by the junction of the end portion and middle diameter of the cortical pin abuts the opposite end cortical wafer. Thus, the construction of the cortical pin and the allograft, in addition to the alignment of the allograft in relation to the plane of insertion allow for optimal energy transfer and displacement through the allograft to minimize the risks of the cortical pin breaking and/or the allograft otherwise coming apart.
Referring to
Each cortical wafer 14 and cancellous wafer 12 has at least one canal 14a and 12a, respectively. The canals 14a and 12a are all substantially aligned with one another such that cortical pin 10 is inserted through the canals 14a and 12a of the cortical wafers 14 and cancellous wafers 12, respectively, to form the allograft 8. Cortical pin 10 is preferably made of cortical bone, and is constructed of a single piece of cortical bone. However, it should be understood that alternatively all cortical pins 10, 20, 30, 38 and 40 can be made of multiple pieces and may constitute any combination of cortical and cancellous bone. Moreover, while shown in
As shown in
Referring to
Each cortical wafer 14, 14b and cancellous wafer 12 has at least one canal 14a and 12a, respectively. The canals 14a and 12a are all substantially aligned with one another such that cortical pin 10 is inserted through the canals 14a and 12a of the cortical wafers 14, 14b and cancellous wafers 12, respectively, to form the allograft 8. Cortical pin 10 is preferably made of cortical bone, and is constructed of a single piece of cortical bone. However, it should be understood that alternatively all cortical pins 10, 20, 30, 38 and 40 can be made of multiple pieces and may constitute any combination or cortical and cancellous bone.
As shown in
The wafers 14, 14b and 12 in
Referring now to
Adjacent cortical wafer 24 is a cancellous wafer 22. Along the side adjacent tab 42 is a corresponding groove 44. The groove 44 extends the length of the cancellous wafer 22. The groove 44 is sized to snugly receive the tab 42, thereby allowing cortical wafer 24 to interlock with cancellous wafer 22. On the side of cancellous wafer 22 directly opposite the groove 44 is a tab 46 which extends the length of cancellous wafer 22. Tab 46 is substantially the same size and shape as tab 42, although some variation of size and shape of the tabs of the wafers discussed herein is acceptable so long as the groove of the adjacent wafer is sized and shaped appropriately to snugly receive the tab 46. Cancellous wafer 22 has a canal 22a. The canal 22a is of sufficient size to snugly receive the middle diameter 20b of cortical pin 20.
Adjacent cancellous wafer 22 is an end cortical wafer 26. Cortical wafer 26 has a groove 48 corresponding to tab 46 of cancellous wafer 22. The groove 48 extends the length of the cortical wafer 26, and is sized to snugly receive the tab 46 of the cancellous wafer 22, thereby allowing cortical wafer 26 and cancellous wafer 22 to interlock. Cortical wafer 26 has a canal 26a which is substantially the same as canal 24a. Canal 26a snugly receives the other end portion 20a of cortical pin 20, but is too small to receive middle diameter 20b.
Referring to
As the allograft 8 is inserted into the surgically altered site of the patient (not shown) in the plane of insertion I, a surgical mallet (not shown) or other appropriate medical/surgical device (not shown) is used to strike the allograft 8 in the direction of the plane of insertion I. Cortical wafer 26 and the end portion 20a of cortical pin 20 disposed within cortical wafer 26 absorb the initial energy imparted on the allograft 8. The energy imparted on the end portion 20a of the cortical pin 20 is transferred through shoulder 20d, which is surrounded by the stronger cortical bone tissue of cortical wafer 26, and into middle diameter 20b. From middle diameter 20b, the energy is transferred through the shoulder 20c of the cortical pin 20, which is abutted against the hard cortical tab 42 of cortical member 24, thereby transferring the energy from cortical pin 20 to cortical wafer 24 and the end portion 20a of cortical pin 20 disposed within cortical wafer 24.
Referring to
Referring to
As the allograft 8 is inserted into the surgically altered site of the patient in the plane of insertion I, the surgical mallet or other appropriate medical/surgical device is used to strike the allograft 8 in the direction of the plane of insertion I. Cortical wafer 26 and the end portion 40a of cortical pin 40 disposed within cortical wafer 26 absorb the initial energy imparted on the allograft 8. The energy imparted on the end portion 40a of the cortical pin 40 is transferred through shoulder 40d, which is surrounded by the stronger cortical bone tissue of cortical wafer 26, and into middle diameter 40b. From middle diameter 40b, the energy is transferred through the shoulder 40c of cortical pin 40, which is abutted against the hard cortical tab 42 of cortical member 24, thereby transferring the energy from cortical pin 40 to cortical wafer 24 and the end portion 40a of cortical pin 40 disposed within cortical wafer 24.
Referring to
Referring to
As the allograft 8 is inserted into the surgically altered site of the patient in the plane of insertion I, the surgical mallet or other appropriate medical/surgical device is used to strike the allograft 8 in the direction of the plane of insertion I. Cortical wafer 26 and the end portion 30a of cortical pin 30 disposed within cortical wafer 26 absorb the initial energy imparted on the allograft 8. The energy imparted on the end portion 30a of the cortical pin 30 is transferred through shoulder 30d, which is surrounded by the stronger cortical bone tissue of cortical wafer 26, and into middle diameter 30b. From middle diameter 40b, the energy is transferred through the shoulder 30c of cortical pin 30, which is abutted against the hard cortical tab 42 of cortical member 24, thereby transferring the energy from cortical pin 30 to cortical wafer 24 and the end portion 30a of cortical pin 30 disposed within cortical wafer 24.
Referring to
Cortical pins 38 attach the two halves 36a and 36b to the cancellous spacers 34. The cortical pins 38 are shaped substantially similar to the rolling pin configuration of the cortical pins 20, 30 and 40 discussed hereinabove. Upon insertion of the allograft 82, the ends 38a of the cortical pins 38 receive the energy transferred from the strike of the surgical mallet on half 36b of femoral ring 36. The energy is transferred through shoulder 38d into middle diameter 38b, and onto shoulder 38c. Shoulder 38c abuts against half 36a of femoral ring 36. Therefore, the energy is transferred from shoulder 38c onto half 36a. The advantage of the cancellous spacers 34 and ball 32 is that it allows the allograft 82 made of the femoral ring 36 to be expanded such that larger allografts 82 can be assembled than is otherwise anatomically possible simply from retrieving a femoral ring 36 from a donor.
The allografts 8 of the present invention provide advantages not previously available in the art. Although the allografts 8 of the present invention have been described with reference to specific embodiments, this description is not meant to be construed in a limited sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention will become apparent to persons skilled in the art upon the reference to the description of the invention. For instance, it should be understood in the art that more than one cortical pin 20, 30, 40 could be inserted into the allografts 8 shown in
Moreover, although described as three, four or five-wafer allografts 8, it should readily be understood that the allografts 8 of the present invention could have any number, composition and arrangement of cortical and cancellous wafers. In fact, it will be readily understood that the allografts 8 of the present invention can easily be sized by adding or removing internal cortical and/or cancellous wafers, or by increasing or decreasing the width of the wafers used in the allograft 8. It is furthermore desirable to insert an internal cortical wafer, such as that shown as cortical wafer 80 in
Furthermore, although described as being able to be inserted into the spinal column, or intervertebrally into a patient, the allografts 8 of the present invention can be inserted on or between any bone or bone segments where stabilization is required or desired. In light of the detailed description above, it is contemplated that the appended claims will cover such modifications that fall within the scope of the invention.
