| abstract |
A prosthetic stem insertable in an intramedullary cavity to support an articulation component includes a proximal neck portion and a distal root portion. The proximal neck is solid metal and extends for a length effective to reach into the cavity and couple to surrounding bone for load bearing engagement therewith, while the distal root portion includes a stranded cable which fills the bone cavity but flexes to avoid significant transfer of bending stresses. The cable is tightly bunched at its junction with the neck, providing a transitional degree of stiffness to its distal part which is significantly more flexible and bends to accommodate natural displacement of the surrounding bone. The prosthesis may be formed of a compatible metal such as titanium, cobalt chromium, stainless steel or the like. The prosthesis has a section modulus characterized by three distinct regions. The proximal end region has the largest cross section and presents a stiff modulus of solid material, while the distal region is composed of strands and presents a flexible bending stiffness. An intermediate region of relatively short length where the cable attaches to the upper portion has a bending modulus that changes quickly from fairly stiff to flexible. The location of this portion may be varied by changing the relative lengths of the proximal solid and distal cable portions thus determining or limiting to a small local region the area of bone which may experience any stress shielding. The stiffness of the cable may also be varied by use of different gauge wires or the addition of welds or circumferential bands. In various embodiments, the cable may be entirely enclosed within a surrounding shell, may have its distal end crimped within a surrounding ring or cup, or may have its filaments welded or otherwise fused or bonded together at one or more regions. In one embodiment the cable is formed of asymmetric fibers which run parallel to each other to provide a bending modulus that is stiffer in one plane than in the transverse direction. |