Surfactant-stabilized emulsion increases gentamicin elution from bone cement.

BACKGROUND: Liquid antimicrobial use for antimicrobial-loaded bone cement is limited because of decreased strength and small volume that can be loaded. Emulsifying the liquid antimicrobial into the monomer may address both issues. QUESTIONS/PURPOSES: We determined the effect of using a surfactant-stabilized emulsion on antimicrobial release, compressive strength, and porosity. METHODS: We made 144 standardized test cylinders from emulsified antimicrobial-loaded bone cement (three batches, 72 cylinders) and control antimicrobial-loaded bone cement made with antimicrobial powder (three batches, 72 cylinders). For each formulation, five specimens per batch (n = 15) were eluted in infinite sink conditions over 30 days for gentamicin delivery; five specimens per batch were axially compressed to failure after elution of 0, 1, and 30 days (n = 45); and two noneluted specimens and two gentamicin delivery specimens from each batch (n = 12) were examined under scanning electron microscopy for porosity. Antimicrobial release and compressive strength were compared across cement type and time using repeated-measures ANOVA. RESULTS: Emulsified antimicrobial-loaded bone cement released four times more antimicrobial than control. Compressive strength of emulsified antimicrobial-loaded bone cement was less than control before elution (58.1 versus 81.3 MPa) but did not decrease over time in elution. Compressive strength of control antimicrobial-loaded bone cement decreased over 30 days in elution (81.3 versus 73.9 MPa) but remained stronger than emulsified antimicrobial-loaded bone cement. Porosity was homogeneous, with pores ranging around 50 µm. CONCLUSIONS: Emulsified antimicrobial-loaded bone cement has homogeneous porosity with increased drug release but a large loss of strength. CLINICAL RELEVANCE: Liquid antimicrobials are released from emulsified antimicrobial-loaded bone cement, but increased strength is needed before this method can be used for implant fixation.

Modelo de interfaz cemento-vástago en artroplastias totales de cadera. Estudio de la superficie con elementos finitos / Cement-femoral stem interface model in total hip prosthesis: study of the surface with finite element

Introducción. La separación entre el cemento y el implante femoral se relaciona con los aflojamientos asépticos y con la supervivencia de los implantes. El objetivo del trabajo es el desarrollo de un modelo de daño que simule la degradación del cemento y el aflojamiento del implante, con dos acabados superficiales del vástago. Material y método. Aplicamos un modelo axisimétrico de elementos finitos de un vástago rodeado por una capa de cemento. La carga de compresión aplicada al vástago varía de 0 a 7 kN con frecuencia de 1 Hz durante 1,7 millones de ciclos. Una vez que se soltó la interfaz se incorporó rozamiento entre ambas superficies. Resultados. En los vástagos lisos el daño estimado en el cemento estaba más distribuido, siendo el daño global menor. En los rugosos hay mayor concentración del daño y mayor degradación del cemento en la zona distal, continuándose por la zona proximal. Conclusión. La simulación con elementos finitos permite predecir el comportamiento de los implantes relacionando macrogeometría y superficie. En nuestro modelo se demuestra la influencia del acabado superficial del vástago en la localización e intensidad del daño en el cemento y en la interfaz (AU)

Introduction. Debonding of the stem-cement interface is one of the most important causes aseptic loosening of the femoral stem, and it is related with the implant survival. The main goal of this study is the development of a damage model, in order to simulate the cement degradation and the debonding process of the stem-cement interface, respectively. We would consider two different surfaced finishing of the stem. Materials and methods. An axisymetric finite element model of a stem and the surrounding cement mantle was developed. The cement damage model was also implemented to simulate its degradation. The stem was gradually compressed in the cement by a dynamic, sinusoidal axial force, cycling between 0 and 7 kN for 1.7 million cycles at a frequency of 1 Hz. When the interface is completely debonded, contact friction is incorporated between both surfaces. Results. Subsidence is higher in the polished stems because the stem-cement interface is completely debonded. Cement damage in the polished stem is more distributed and quantitatively is lower than for the rough stems, where cement damage is more concentrated distally. Conclusion. Finite element models are able to predict the behaviour of implants relating the stem geometry with its surface finished. The influence of the surface finished on the cement damage and debonding process of the stem-cement interface have been demonstrated with the model proposed (AU)

Orthopedic devices; classification for the resorbable calcium salt bone void filler device. Final rule.

The Food and Drug Administration (FDA) is classifying the resorbable calcium salt bone void filler device intended to fill bony voids or gaps of the extremities, spine, and pelvis that are caused by trauma or surgery and are not intrinsic to the stability of the bony structure into class II (special controls). Elsewhere in this issue of the Federal Register, FDA is announcing the availability of a class II special controls guidance entitled "Class II Special Controls Guidance Document: Resorbable Calcium Salt Bone Void Filler Device; Guidance for Industry and FDA." This action is being undertaken based on new information submitted in a classification proposal from Wright Medical Technology under the Federal Food, Drug, and Cosmetic Act as amended by the Medical Device Amendments of 1976, the Safe Medical Devices Act of 1990, and the Food and Drug Administration Modernization Act of 1997.

PMMA-based bioactive cement: effect of CaF2 on osteoconductivity and histological change with time.

A new bioactive bone cement (designated GBC), which is a polymethyl methacrylate- (PMMA-) based composite consisting of bioactive glass beads as an inorganic filler and high-molecular-weight PMMA (hPMMA) as an organic matrix, has been developed. The bioactive glass beads consist of MgO-CaO-SiO(2)-P(2)O(5)-CaF(2) glass. The purpose of the present study was to evaluate the effect of CaF(2) on osteoconductivity and to evaluate the degree of cement degradation with time. Three different types of cement were prepared. GBC(F +), which has been previously described, consisted of CaF(2)-containing bioactive glass beads and hPMMA. GBC(F -) consisted of CaF(2)-free bioactive glass beads and hPMMA. The third cement was hPMMA itself (as a reference material). These three types of cement were packed into the intramedullary canals of rat tibiae to evaluate osteoconductivity, as determined by an affinity index calculated as the length of bone in direct contact with the cement surface expressed as a percentage of the total length of the cement surface. Rats were killed at 4, 8, 25, and 52 weeks after implantation, and the affinity index was calculated for each type of cement at each time point. Histologically, new bone had formed along the surface of both GBC(F +) and GBC(F -) within 4 weeks, whereas hPMMA had little contact with bone, and an intervening soft tissue layer between bone and cement was detected. No significant difference in affinity index was found between GBC(F +) and GBC(F -) at any of the time points studied, although GBC(F -) showed higher affinity indices than GBC(F +) at 8, 25, and 52 weeks. The affinity indices for GBC(F +) and GBC(F -) were significantly higher than those for hPMMA at all time points. With GBC(F +) and GBC(F -), significant increases in the affinity indices were found as the implantation period increased, and the affinity index values at 52 weeks reached more than 70%. In hPMMA, no significant increase in affinity index was observed up to 52 weeks, and the value at 52 weeks was less than 30%. Although no significant difference in affinity index was found between GBC(F +) and GBC(F -), GBC(F -) is conclusively better than GBC(F +) because diseases such as chronic fluorosis might be caused by CaF(2)-containing glass beads. Regarding the cement degradation of both GBC(F +) and GBC(F -), the degree of the degradation at 25 weeks was the same as that at 52 weeks. Therefore, the cement degradation does not appear to proceed rapidly. Further studies are needed to better understand the degradation process.

Medical devices; reclassification of polymethylmethacrylate (PMMA) bone cement. Final rule.

The Food and Drug Administration (FDA) is announcing that it has reclassified the polymethylmethacrylate (PMMA) bone cement intended for use in arthroplastic procedures of the hip, knee, and other joints for the fixation of polymer or metallic prosthetic implants to living bone from class III to class II (special controls). The agency is also announcing that it has issued an order in the form of a letter to the Orthopedic Surgical Manufacturers Association (OSMA) reclassifying the device. The special control for the device is a guidance document entitled "Class II Special Controls Guidance Document: Polymethylmethacrylate (PMMA) Bone Cement." The agency is reclassifying this device into class II because special controls, in addition to general controls, would provide reasonable assurance of the safety and effectiveness of the device, and there is sufficient information to establish special controls.