Northwestern University

Jeremy L Gilbert

Eugene P Lautenschlager

Richard L Wixson

Steven J Duray

Peter Monaghan

Orthopedic bone cements of low porosity, prepared by mixing together at least two liquid components under conditions that allow only minimal exposure to air, are disclosed. In a preferred system, each liquid component consists essentially of a solution of a linear (non-crosslinked) polymer or copolymer of methyl methacrylate (PMMA) dissolved in a non-crosslinking methyl methacrylate (MMA) monomer, with one such solution also containing an activator and a polymerization inhibitor and a second solution containing an initiator as well as a polymerization inhibitor. No reinforcing fillers are present, although a small amount (no more than 12% by weight of the total cement composition) of a radiopacifier may be included in the composition. Since polymerization is initiated by mixing together two or more liquid solutions, and such mixing may be performed in a mixing chamber in which no air is required or is introduced during the mixing operation, prior problems of cement porosity and weakness resulting from air entrapment are avoided or greatly reduced while the reliability and reproducibility of the mixing operation are greatly improved.

Bone cement and method of preparation

Self-reinforced composites of amorphous thermoplastic materials such as poly(methylmethacrylate), polycarbonate and polysulfone are made by melt-extruding and simultaneously drawing and cooling the material to produce fibers with longitudinally-oriented molecular chains, then arranging the fibers in a preform, such as a mat, rod, plate or other useful shape, in which adjacent fibers are in contact with each other, and thereafter heating the preform with fiber constraint to a temperature above the glass transition temperature and below the degradation temperature of the thermoplastic, and applying pressure, to soften and fuse together the outer surfaces of the fibers without completely eliminating the longitudinal orientation of the molecules within the fibers. Where the amorphous thermoplastic is poly(methylmethacrylate), the preform may be wrapped about the bone-implantable element of a joint prosthesis to provide a high-strength integrated mantle of connected, contracted, and oriented fibers. Upon implantation of the element in the intramedullary cavity of a bone, the surface of the self-reinforced mantle of sintered fibers may then bond chemically with a grouting of conventional poly(methylmethacrylate) bone cement.

Methods of making self-reinforced composition of amorphous thermoplastics

An orthopedic implant, such as the bone-implantable portion of a joint prosthesis, in which a rigid stem is dimensioned to be received in the intramedullary canal of a bone, and in which the stem has at least a portion of its length encased in a preformed mantle consisting of a self-reinforced poly(methylmethacrylate) fiber composition where the fibers are oriented in predetermined directions with respect to the axis of the stem, are of a diameter within the range of about 5 to 500 microns (.mu.m), and have aligned molecular chains that provide such fibers with longitudinal heat relaxation ratios of no less than about 6 to 1 is disclosed. Also disclosed are the methods for making such an implant and for securing it in an intramedullary canal.

Growing community of inventors

Downers Grove, IL, United States of America

Jeremy L Gilbert