Biomechanical parameters of the BPenriched bone c

Authors: Łukasz Matuszewski Grażyna Olchowik Tomasz Mazurkiewicz Bartłomiej Kowalczyk Agata Zdrojewska Anna Matuszewska Andrzej Ciszewski Małgorzata Gospodarek Iwona Morawik

Publish Date: 2013/05/14

Volume: 24, Issue: 4, Pages: 435-441

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Abstract

Bisphosphonates BPs are wellknown substances with very efficient antiresorptive properties Their beneficial actions are useful not only in achieving better bone mineral density but also in improving bone microarchitecture strength and consequently its quality Surgical cement being a polymer composite is required to be highly biocompatible and biotolerant The goal of the presented study was to assess whether the enrichment of cement with pamidronate has changed its biomechanical properties We compared the biomechanical parameters of clean bone cement and BPenriched bone cement which were both used formerly in our rat models Biomechanical properties of BPenriched bone cement are defined by two basic terms stress and strain which are caused by the influence of external force In the investigatory process of the bone’s biomechanical parameters the compressive test and the threepoint flexural tests were used During the threepoint flexural investigation the sample was supported at both ends and loaded in the middle resulting in a flexure After a specific range of flexure the sample was fractured In obtained results there were no significant differences in the values of the stress determined at the point of maximal load and the energy stored in the samples for proportional stress–strain limit elastic region There were also no significant differences in the density of the samples The study shows that the enrichment of bisphosphonates causes yielding of the bone cement material In the presented data we conclude that use of pamidronate implanted in bone cement did not have a detrimental effect on its biomechanical properties Therefore the obtained results encouraged us to perform further in vivo experiments which assess the biomechanical properties of bones implanted with BPenriched bone cementBisphosphonates BPs are wellknown substances with very efficient antiresorptive properties 1 2 Therefore BPs have important effects on bone turnover and are widely used to treat a variety of diseases such as osteoporosis bone metastasis hypercalcemia of malignancy Paget’s disease osteogenesis imperfecta or fibrous dysplasia of bone 3 4 Their beneficial actions not only aid in the achievement of better bone mineral density also are useful in the improvement in bone microarchitecture strength and consequently its quality 5 6 BPs regulate osteoblastic functions such as proliferation and differentiation prevent osteoblast apoptosis modulate osteoblastic production of extracellular matrix proteins and regulate osteoblastic expression and secretion of various growth factors and cytokines 7 8 9 Recent studies indicate that the most promising roles for the BPs are the prevention of bone collapse following osteonecrosis and the enhancement of implant fixation Such combination therapies that have both bone antiresorptive and anabolic agents appear to be of great promise for other further orthopedic applications 3Modern generation of cementing techniques has really affected the survivorship of the use of orthopedic implants Despite the optimization of cement preparation and proper initial cementing technique the biomechanical properties of the bone cement used seem to be very important in preventing the further aseptic loosening of the implant 10 Nowadays PMMAbased bone cement methyl polymethacrylate seems to be most effective in total joint replacements implants The first use of PMMA in a hip joint alloplasty was in the early 1960s when Charnley anchored the hip joint endoprosthesis inside the femur Surgical cement being a polymer composite sets using an elemental bonding prosthesis with bone and thus it is required to be highly biocompatible and biotolerant Many kinds of cements either as pure polymer or with admixtures of different substances are used Application of fillers is of great significance to the mechanical properties of the PMMA Specificity of the working conditions forces the necessity of transition of extremely complex loading resulting from human motor activity Working environment of the bone cement is highly aggressive which dramatically increases the aging rate and causes higher enucleating of the cement weakening the bone–cement–implant system This phenomenon can lead to endoprosthesis loosening and to the necessity of a reimplantation procedure 11 The most important mechanical properties of PMMA cement are tensile compressive shear and fracture toughness The variation in these properties is related to differences in composition mixing methods aging temperature and viscosity during application Such biomechanical parameters are mostly responsible for dynamic and static loads PMMA is a very specific material of high modulus and low ductility 10 Therefore a high degree of stiffness of the bone cement is very important The lack of this stiffness is responsible for the creep deformation which is the tendency of a solid material to move slowly or deform permanently over the time under the influence of stresses 12 However creep deformation can be influenced by such factors as porosity cement composition or molecular weight 13The goal of the presented study was to assess whether the enrichment of bone cement with pamidronate has changed its biomechanical properties We compared the biomechanical parameters of clean bone cement and BPenriched bone cement which were both used in our former rat modelOur previous animal studies demonstrated that local treatment with BPs can affect the level of bone turnover markers in blood serum 14 We also proved that there are significant changes in the microarchitectural bone structure during the local use of pamidronate Therefore BPenriched bone cement used in rat models had a positive effect on bone formation 15Bisphosphonate pamidronate Pamifos 60 was purchased from Vipharm Warsaw Poland Bone cement was purchased from CMW 1 DePuy International Ltd England Research was performed on probes of BPenriched bone cement where 40 g of cement was mixed with 60 mg pamidronate by using a vacuum mixer Then it was compared with probes of clean bone cementBiomechanical properties of the material are defined by two basic terms stress and strain which are caused by the influence of external force applied to a solid In the investigatory process of the bone’s biomechanical parameters the compressive test and the threepoint flexural tests were used During the threepoint flexural investigation the sample was supported at both ends and loaded in the middle resulting in a flexure After a specific range of flexure the sample was fractured

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