Prosthetic ligament

#1. Field of the Invention

#The present invention relates generally to prosthetic devices and more particularly to a permanent prosthetic ligament.

#2. Description of the Prior Art

#The present invention can better be understood by reference to the drawings in which:

#FIG. 1 is a view of the preferred embodiment of the prosthetic ligament of the present invention joining the femur and tibia of a recipient.

#FIG. 2 is a view of a braided load bearing member of the present invention;

#FIGS. 1 through 5 illustrate the preferred embodiments of the prosthetic ligament 10 of the present invention. Although the prosthetic ligament 10 is shown as flexibly connecting the femur and tibia, it should be recognized that the prosthetic ligament 10 can be used to connect other skeletal members and, depending upon the means of attachment employed, to support soft tissue organs in place. For purposes of describing the preferred embodiment of the invention, however, the prosthetic ligament 10 is employed to permanently replace the natural cruciate ligament of the human knee.

#The prosthetic ligament 10 includes primarily a major load bearing member 20. A core 30 and sheath 40 may also be included. The load bearing member 20 is formed from a plurality of biocompatible polyolefin fibers 22 positioned at angles of from about 0.degree. to 55.degree. relative to the longitudinal axis 18 of the load bearing member 20, a range of about 110.degree. in all. The weave angle provides the load deformation characteristics of the prosthetic ligament 10. A weave angle greater than about 55.degree. relative to the longitudinal axis 18 has been found to elongate or stretch too much when the ligament 10 is under stress. Straight fibers will elongate much less. Angled fibers will elongate more and lower the stiffness in the ligament 10. It has been determined that, depending upon the desired stiffness (a natural cruciate ligament has a stiffness of about 180N/mm), the anatomical location of the prosthetic ligament 10, and the diameter and length of the prosthesis, the weave angle can vary between about 0.degree. and .+-.55.degree., inclusive, relative to the longitudinal axis 18. For example, in one embodiment, when the ligament 10 is made of polypropylene and replaces a cruciate ligament of the knee, the weave angle is between 40.degree. and 48.degree., inclusive. The preferred weave angle varies for different materials. A preferred embodiment is that of a braided member shown in FIG. 2. The braided construction allows utilization of the high-strength fibers as individual units while providing negligible bending resistance. Braiding also allows for the selection of a braiding angle which will result in the optimum load deformation characteristics.

#The fibers must be made of a biocompatible organic polymer, preferably polyolefins such as high strength polypropylene or ultrahigh molecular weight polyethylene. Kavesh et al. U.S. Pat. No. 4,413,110 describes a process for the production of ultrahigh molecular weight polypropylene and polyethylene fibers which have a high tenacity and a high tensile modulus. The commercial embodiments of the polyethylene fibers described in the Kavesh patent, have a tensile strength of about 375,000 psi per yarn. The density of each fiber is between 0.5-1.5 g/cc, preferably about 0.97. Each fiber is less than 100 microns in diameter. A plurality of such high strength polyolefin fibers, with each fiber having a tensile strength greater than or equal to about 50,000 psi, woven at the desired angle, provides a high strength load bearing member 10. Numerous fibers add to the life of the ligament 10 because there are numerous surfaces to tolerate the stress and to break in the event of excessive stress before the entire ligament 10 can fail.