In recent years,the incidence of joint diseases has increased year by year,and the number of orthopedic implants used for joint replacement has increased year by year(10).But inadequate cement technology can affect the prosthetic retention rate and other complications(11).Aseptic loosening is one of the leading causes of implant failure,with approximately 18% of implant failures due to aseptic loosening (12).Since the fixation strength of bone cement is an important reason for the aseptic loosening of the prosthesis,our results showed that the fixation strength of the femoral prosthesis is higher than that of the tibial plateau prosthesis,and increasing the temperature of the prosthesis before bonding can improve the fixation strength of the bone cement,and prosthesis fixation strength is positively correlated with temperature,and the aim of this study was to provide some information that might reduce the incidence of tibial component loosening.
Polymethyl methacrylate (PMMA) cement has the advantages of excellent biocompatibility,good in situ formability and sufficient strength,so it is widely used in bone cement joint replacement surgery and is a successful biomaterial in orthopedic surgery(13–15).In vivo experiments have shown that porous PMMA has a good effect on soft tissue coverage.In contrast to dense PMMA,porous PMMA creates a temporary gap that provides a platform for soft tissue regeneration and lays the foundation for eventual repair of bone tissue,which is beneficial for postoperative recovery and complications(16).However,long-term clinical observations show that PMMA cement also has some disadvantages.The most common complications of PMMA in orthopaedic applications are aseptic loosening,prosthesis infection and thermal necrosis of surrounding tissues,especially aseptic loosening accounts for almost half of revision knee arthroplasty(17,18) .The main cause of aseptic loosening is the lack of desirable biological and mechanical properties of PMMA cement,resulting in a weak PMMA-bone interface.X-ray photoelectron spectroscopy (XPS) and wettability studies have shown that PMMA aging increases the hydrophilicity of bone cement.A.Bettencourt et al suggested that this phenomenon may affect the bone/biomaterial interface at the cellular level,leading to aseptic loosening of the implant(17).This study investigated the fixation strength between PMMA cement and a polypropylene base during joint prosthesis fixation by means of an out-of-the-box experiment.We found that the fixation strength of the tibial plateau prosthesis was lower than that of the femoral prosthesis under the same conditions (P < 0.05).Because we control for other variables.Therefore,the consideration may be related to the larger amount of cement in the femoral prosthesis,the larger base area of the prosthesis and the more curvature of the femoral condyle.The specific mechanism remains to be discussed in the future.Terrier et al calculated an optimal cement sheath thickness of 1.0-1.5 mm for the glenoid.In the same study,thicker cement sheaths were found to transfer excessive stress to the cement-bone interface(19).The good ductility of bone cement makes us worry about whether the potential influencing factor of bone cement thickness between each group can be agreed,but each group was fixed with a constant force of 100N for 10min.Studies have shown that reducing porosity can prolong fatigue life.Preheating the stem in the hip joint experiment reverses the direction of curing in the bone cement and reduces the generation of pores associated with the shrinkage process,thereby reducing bone cement porosity and increasing bone cement fatigue life(20) (21).The bone cement completely covers all contact points of the prosthesis and the base and the thickness of the bone cement is basically the same.In addition,we found that increasing the temperature of tibial plateau component and femoral component prior to fixation increased the fixation strength of bone cement (P < 0.05).Hip-related studies have shown that preheating the stem reverses the direction of aggregation and greatly reduces the formation of micropores at the stem-cement interface.The smaller the void volume in the bone cement,the better the compressive and flexural properties and the higher the strength of the bone cement(22).This coincides with our findings, which also found that increased temperature reduces the pore space of bone cement.There are also studies showing that preheating the CoCrMo alloy rod before inserting the bone cement can improve its ultimate push-out load and surface shear strength(23),which is consistent with our findings.Therefore,we believe that high temperature will reduce the porosity of the micro-interface of bone cement.
A common operational and controversial variable affecting the handling of PMMA bone cement during polymerization is ambient temperature.The higher the temperature during mixing,the faster the polymerization rate,the shorter the working time and the setting time,but has no effect on the peak temperature.These effects have led to the popularity of pre-cooling high-viscosity cements to slow down polymerization.However,the problem with this treatment is the increased porosity due to prolonged working time,which eventually leads to a decrease in the strength of the PMMA bone cement (24).Studies have shown that increased bone cement thickness is also accompanied by increased heat production,which increases the risk of thermal necrosis of the surrounding bone,and some studies using standard surgical techniques have shown temperatures > 50°C for 1 minute,considered the temperature necessary for osteonecrosis and exposure time,which may lead to prosthesis loosening (25,26).Furthermore,in vitro measurements of temperatures have shown that preheating of the stem results in a negligible increase in bone temperature (27).Taking this into account,in our experimental design,the endpoint temperature in the variable was set at 45°C.For the effect of polymerization temperature,chitosan (Cs) was used as an additive for PMMA,and Shi et al.(28) added chitosan (Cs) nanoparticles to bone cement.It has significant antibacterial activity against Staphylococcus aureus and Staphylococcus epidermidis,while these nanoparticles have no effect on the mechanical strength of bone cement,and through the complexation of Cs and PMMA,the polymerization temperature of the cement is significantly reduced,reducing the risk of osteonecrosis.However,we knew little about how to improve the fixation strength of bone cement,so we thought of a new angle and took the prosthesis temperature as the study variable,and found that increasing the temperature of tibial plateau prosthesis and femoral prosthesis fixation can improve the fixation strength of bone cement (P < 0.05).
Although this study focused on the fixation strength 24 hours after bone cement fixation,the long-term effects were not described in detail.We controlled the endpoint temperature at 45°C to avoid inducing osteonecrosis,but we did not conduct in-depth studies on whether the increase in prosthesis temperature and the temperature generated by bone cement polymerization induce osteonecrosis.Looking forward to more in-depth studies and related clinical trials with larger samples,although our study does not fully reproduce the in vivo environment around the prosthesis,it contributes to understanding the changes in the bone cement surface that modulate the patient's response to the prosthesis.We believed that preheating the prosthesis temperature in advance before surgical placement of the prosthesis can improve the fixation strength of the implants and may reduce the occurrence of aseptic loosening.