Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2000-02-29
2001-06-12
Philogene, Pedro (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S023450
Reexamination Certificate
active
06245112
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to artificial joints and the structure by which they are secured in the natural bone of the host or patient.
BACKGROUND
The connection by which the artificial joint is held in the host bone is of critical importance to the long term success of any joint replacement surgery. The characteristics of the artificial joint must be matched with the characteristics of the naturally occurring host bone to prevent undue stress resulting in trauma to the natural bone and pain to the host.
Bone prosthesis are either secured in the host with bone cement or without the use of cement. While initially providing a useful connection between the prosthesis and the bone, the earlier cements tended to degrade over time with deleterious results. One approach to overcome this degradation problem was to not use cement at all. This invention relates to installing joint prosthesis without the use of bone cement.
When no cement is used, the connection or fit of the prosthesis within the intramedullary canal of the natural bone becomes more critical. Without the cushioning effect of cement surrounding the intramedullary insert of the prosthesis, there is a requirement for a more accurate matching of the prosthesis insert with the host bone. The prosthesis must, not only, conform to the size of the intramedullary canal of the host bone but to the inherent strength and flexibility or brittleness of the cancellous bone surrounding the intramedullary canal.
These different criteria can create mutually exclusive design requirements, for example, a large insert that must be very flexible because the characteristics of the host bone or a small insert that must be very stiff.
There are various patents and publications directed to the implantation of bone prosthesis without the use of cement each citing the attendant advantages of such procedures. Several patents are directed to the flexibility of joint prosthesis.
U. S. Pat. No. 5,549,702 to Ries et al discloses a one piece or two piece prosthesis in which one end or one portion of the prosthesis is inserted into the intramedullary canal of the host bone. The intramedullary insert of Ries et al has various modifications to achieve a specific flexibility. The insert may be a solid bar or it may be partially tubular. Among the modifications are spiral slots of varying depth. The slots may extend partially through the insert or may extend from a central bore through the entire thickness of the insert forming a coil structure. Other modifications include varying the thickness of the insert along the longitudinal axis. Once each of these variations is manufactured, the flexibility of the insert is permanently set.
U.S. Pat. No. 4,997,444 to Farling discloses a joint prosthesis in which the modulus of elasticity of the intramedullary insert may be varied along the length. The variation results from stacking disks having different characteristics upon a central strut or struts. Farling states that the disks and struts are connected together mechanically or metallurgically bonded together. This indicates that these devices are manufactured with various degrees of stiffness throughout their length and the resulting device cannot or should not be changed thereafter.
U.S. Pat. No. 5,062,851 to Branemark discloses a joint mechanism to be used in smaller bones. The tubular anchoring element has external screw threads for bone contact and a tapering wall thickness. The end portions of the tubular element have longitudinal slits and the wall thickness decreases toward the slit portion. The combination of the slits and thinner walls produce a more flexible end portion of the device.
These references are merely illustrative of the prior art and are not to be considered to be an exhaustive listing.
SUMMARY OF THE INVENTION
The instant invention is a joint prosthesis having an intramedullary insert. The intramedullary insert has an elongated body with an attached or integrated spring like helical construct having a continuous spiraling recess, that is, a coil spring like endpiece. For ease of explanation, the helical construct with recess will be referred to as a coil spring throughout this disclosure. The coil spring provides variable flexibility at different locations along the spring. A control rod is inserted through the coil spring and attached thereto further allows for the flexibility of the coil spring. The shape of the control rod may be varied throughout its length producing different flexibility. The instant invention allows the surgeon to match the stiffness of a particular prosthesis to the strength of the host bone by selecting certain combinations of interchangeable elements of the artificial joint. These elements are then assembled forming an artificial joint having the desired features for use in a particular host. The selection of a particular coil spring and a particular control rod allows joint prosthesis having varying flexibility.
Accordingly, it is an objective of the instant invention to provide a joint prosthesis which can be matched to the natural bone of a particular host.
It is a further objective of the instant invention to provide a joint prosthesis with an intramedullary insert which has a coil structure of particular flexibility. The flexibility results from the properties of the coil, such as the material from which the component is made, the helical slot width, helical slot pitch, cross sectional area of the coil, including outside diameter, inside diameter and width of the coil.
It is yet another objective of the instant invention to provide a control rod inserted through the coil which varies the flex through the shape of the rod. This also allows for differing amounts of flexibility at different points along the length of the intramedullary insert.
It is a still further objective of the invention to provide a plurality of prosthesis elements having differing structural characteristics in a kit. This allows the surgeon to custom build a joint prosthesis to fit the needs of the patient.
While the invention is directed to the major joints of the body, such as the hip, shoulder, elbow and knee, the same principles can be applied to artificial joints between the smaller bones.
Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.
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Doubler Robert L.
Hammill, Sr. John E.
Hammill Manufacturing Co.
McHale & Slavin
Philogene Pedro
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