Compatibility of the totally replaced hip. Reduction of wear by amorphous diamond coating.

Particulate wear debris in totally replaced hips causes adverse local host reactions. The extreme form of such a reaction, aggressive granulomatosis, was found to be a distinct condition and different from simple aseptic loosening. Reactive and adaptive tissues around the totally replaced hip were made of proliferation of local fibroblast like cells and activated macrophages. Methylmethacrylate and high-molecular-weight polyethylene were shown to be essentially immunologically inert implant materials, but in small particulate form functioned as cellular irritants initiating local biological reactions leading to loosening of the implants. Chromium-cobalt-molybdenum is the most popular metallic implant material; it is hard and tough, and the bearings of this metal are partially self-polishing. In total hip implants, prerequisites for longevity of the replaced hip are good biocompatibility of the materials and sufficient tribological properties of the bearings. The third key issue is that the bearing must minimize frictional shear at the prosthetic bone-implant interface to be compatible with long-term survival. Some of the approaches to meet these demands are alumina-on-alumina and metal-on-metal designs, as well as the use of highly crosslinked polyethylene for the acetabular component. In order to avoid the wear-based deleterious properties of the conventional total hip prosthesis materials or coatings, the present work included biological and tribological testing of amorphous diamond. Previous experiments had demonstrated that a high adhesion of tetrahedral amorphous carbon coatings to a substrate can be achieved by using mixing layers or interlayers. Amorphous diamond was found to be biologically inert, and simulator testing indicated excellent wear properties for conventional total hip prostheses, in which either the ball or both bearing surfaces were coated with hydrogen-free tetrahedral amorphous diamond films. Simulator testing with such total hip prostheses showed no measurable wear or detectable delamination after 15,000,000 test cycles corresponding to 15 years of clinical use. The present work clearly shows that wear is one of the basic problems with totally replaced hips. Diamond coating of the bearing surfaces appears to be an attractive solution to improve longevity of the totally replaced hip.

Control of brittleness in butyl-methylmethacrylate resin embedding mixtures to facilitate their use in immunofluorescence microscopy.

Butyl-methylmethacrylate resin mixtures were tested for brittleness-inducing factors in polymerised resin using a rapid quantitative scoring technique. The major source of brittleness was identified as the reducing agent dithiothreitol, which is commonly included in resin mixtures at 10 mM, to protect against tissue oxidation. Lowering the dithiothreitol content to 5 mM substantially reduced brittleness. Changing the 4:1 ratio of butyl- to methylmethacrylate to 9:1 or 3:2, and reducing the concentration of the catalyst, benzoin ethyl ether, to 0.25% also reduced dithiothreitol-induced brittleness. Polymerisation at temperatures close to 0 degrees C increased dithiothreitol-induced brittleness, but this was controlled in the 4:1 and 9:1 resin mixtures by lowering the catalyst concentration from 0.5 to 0.25%. Degassing the resin mixture with nitrogen gas prior to polymerisation did not reduce brittleness. Immunolabelled onion roots which were embedded using the 3:2 resin mixture ratio, 5 mM dithiothreitol and the 0.25% catalyst concentration, showed excellent preservation of cortical microtubule arrays.

Integrated system for preparation of bone cement and effects on cement quality and environment.

We developed a prepacked mixing system for the preparation of bone cement. The system is based on mixing and collection of bone cement under a vacuum and serves as both the storage and mixing device for the cement components, thereby minimizing the exposure of the operating staff to the monomer and the risk for contamination of the cement during preparation. We evaluated the system using Palacos R and Simplex P. The cement produced was compared with cement obtained from a commercially available mixing system. Temperature evolution during curing, handling characteristics, density, and porosity of the cement obtained were analyzed. The results showed that the experimental system produces cement with physical properties (i.e., setting times and temperature, porosity, and density) equal to or better than those obtained with commercially available systems. Reducing the amount of monomer in the experimental system led to a reduction of the curing temperature without compromising the physical properties of the cements.

Intraocular lens durability after a mean of 10.9 years' implantation in humans.

AIMS/BACKGROUND: To clarify whether intraocular lens (IOL) implantation in the human eye affects the durability of polymethylmethacrylate over an average period of 10.9 years. METHODS: Shearing stress and extent of damage following neodymium (Nd):YAG laser application to 18 study and 12 control optics were examined. RESULTS: No significant difference was found between the study and the control IOLs in shearing stress and extent of damage following Nd:YAG. CONCLUSION: An average 10.9 years' implantation in humans does not affect either the shearing stress or extent of damage following Nd:YAG shots of polymethylmethacrylate.

BOP: biocompatible osteoconductive polymer: an experimental approach.

BOP (biocompatible osteoconductive polymer) is a material proposed for osteosyntheses and for filling of bone defects in orthopaedics, neurosurgery and stomatology. It is a composite made of a copolymer of N-vinylpyrrolidone and methylmethacrylate, of polyamide-6 fibers and of calcium gluconate. The histological investigation includes the study of 30 intact rabbit femurs instrumented with a BOP rod, as well as the study of organs of the reticuloendothelial system. The currently available results show the absence of toxicity on hematopoietic tissue. Zones of osteoblastic activity surround the rods, coupled with an osteoclastic reaction which may result in the partial fragmentation of the polyamide fibers and its incorporation in the newly formed bone. We also observed the encapsulation of the material. The biomechanical approach investigated the mechanical properties of the material in bending and in shear. The radiological aspects of the investigation consisted of computerized axial tomography of the implanted femurs to measure density at the bone-implant interface.

Influence of haptic materials on the adherence of staphylococci to intraocular lenses.

A recent case-control study indicated that the insertion of an intraocular lens with polypropylene (Prolene) haptic materials was a significant risk factor for postoperative endophthalmitis (odds ratio = 4.5, P < .01). In the present study, we used quantitative techniques to evaluate adherence of Staphylococcus epidermidis to two intraocular lens types--lenses with polypropylene haptic materials and all-polymethyl methacrylate optic and three-piece all-polymethyl methacrylate lenses--using a quantitative culture method, a radioisotope technique, and scanning electron microscopy. All three methods demonstrated approximately twice as many bacteria adherent to lenses with polypropylene haptic materials as to all-polymethyl methacrylate lenses. Scanning electron microscopy showed preferential bacterial adherence to the polypropylene haptic materials. These data provide a pathogenic mechanism to explain our epidemiologic findings of an increased risk of postoperative endophthalmitis associated with implantation of intraocular lenses with polypropylene haptic materials.

Injectable soft tissue substitutes.

Historical and modern advances in the development of an injectable soft tissue substitute are reviewed. Nonbiologic alloplastic and biologic injectables are described. The authors' experiences, as well as those of others, employing presently available materials in terms of specific indications and special techniques are delineated. The search for a safe, effective, easy-to-use, and long-lasting soft tissue substitute continues.

Additional mechanical tests of bone cements.

A revision of the ISO-standard for bone cement testing has been proposed to include compressive strength after 24 hours in air and 4-point bending testing after 50 hours in a 37 degrees water bath. Nine commercially available bone cements were tested in accordance with the new program. Compressive strength varied from 78 to 100 MPa, bending strength from 48 to 74 MPa and bending modulus from 2.2 to 2.8 GPa. The highest strengths, but also the highest stiffness, were encountered with Simplex brands and low-viscosity cements.

Vancomycin vs tobramycin elution from polymethylmethacrylate: an in vitro study.

We fabricated batches of cement containing 0.5 gm, 1.0 gm, and 2.0 gm vancomycin and one with 1.0 gm tobramycin and shaped them into cylinders. They were immersed into 0.5 L of normal saline and the fluid volume was changed daily. Samples of fluid were obtained on days 1, 2, 3, 5, 7, 14, and 28. All fluid samples had antibiotic assays performed to quantitate the amount of elution for vancomycin or tobramycin. Vancomycin elution from PMMA occurred under our study conditions in similar quantities to that measured for tobramycin controls. Vancomycin-loaded PMMA cement may have a clinical role in the treatment of musculoskeletal sepsis caused by gram-positive bacteria, particularly if organisms resistant to the usual antibiotic agents are identified.

High vacuum as a method of reducing porosity of polymethylmethacrylate.

In total hip arthroplasty, fracture and subsequent premature loosening are directly related to the strength of the cement mantle serving as an interface between bone and prosthesis. The cement has been shown to be weakened by its porosity, which enhances the formation of microfractures that contribute to crack propagation. By means of a vacuum mixing method for preparing the cement, nearly all the porosity can be removed and cement strength enhanced by about 17%.

Consideration of physical parameters to predict thermal necrosis in acrylic cement implants at the site of giant cell tumors of bone.

In the previous paper we had developed a general thermodynamic equation describing a polymethylmethacrylate implant at the site of giant cell tumors. In this paper we consider various characteristics of bone and methylmethacrylate crucial to the analysis such as thermal conductivity, specific heat, density, and heat generation. Also, an estimation of the temperature at which adjacent cells die is analyzed from literature. Finally, using the physical constants measured in laboratory situations a temperature profile is developed at various depths of bone that could facilitate predicting the zone of necrosis. These analyses show the maximum temperature attained in the acrylic cement-bone system depends primarily on the volume of the implant, the relative proportion of polymerization of the monomer, the temperature at which the monomer and polymer are mixed together, and the time lapse between the beginning of polymerization and implantation into the bone cavity. The temperature profile is shown to be relatively insensitive to the geometry of the system, greatly simplifying the analysis.

Strength of polymethylmethacrylate increased by vacuum mixing.

The mechanical strength of high and low viscosity gentamicin-containing cement was analysed using three different mixing procedures: hand, vibration, and vacuum stirring. Vacuum mixing improved the flexural and compression strength and the modulus of elasticity by 15-30 per cent, especially for high viscosity cement.