The Performance of Cemented Femoral Prosthesis Based on New Gel Materials

In view of the problems in hip replacement, a new gel material is developed and incorporated into cemented femoral prosthesis. The material precipitates hydroxyapatite (HA) onto silk fibroin (SF) by biomimetic method, namely silk fibroin hydroxyapatite (SF–HA). Through X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis, HA precipitates on SF. Taking the gel time as the standard, 5 groups of gel materials are selected. Through in vitro degradation experiments, the degradation rate of these materials is 45%∼55%. Cell experiments (mouse L929 cells, osteoblasts HO-F) show that these cells have no cytotoxicity and support the growth of osteoblasts. In addition, in the vivo experiment (two groups), one group was treated with gelatin materials and the other group is treated with bone cement prosthesis transplantation directly. Comparing the indexes before and after operation, it proves that the new gel material has great application value in hip replacement surgery.

Investigation of Mechanical Behaviour of the Bone Cement (PMMA) under Combined Shear and Compression Loading

Generally, implants fixations in orthopedic surgery are insured by bone cement; which is generated mainly from polymer polymethylmethacrylate (PMMA). Since, the cement is identified as the weakest part among bone-cement-prosthesis assembly. Hence, the characterization of mechanical behaviour is of a crucial requirement for orthopaedic surgeon’s success. In this study, we investigates the failure behaviour of bone cement, under combined shear and compression loading, for the aim to determine the strengths of bone cement for different mode loading conditions. Therefore, experimental cylindrical specimens has been tested to assess different shear-compression stresses. Based on the mechanical tests, a finite elements model of cylindrical specimens was developed to evaluate stresses distribution in the bone cement under compression, shear and combined shear-compression loading. Results show that, the load which leading to the failure of the cement decreased with increasing of the specimen angle inclination with respect of loading direction.

Direct Tensile Strength and Characteristics of Dentin Restored with All-Ceramic, Resin-Composite, and Cast Metal Prostheses Cemented with Resin Adhesives

A dentin-cement-prosthesis complex restored with either all-porcelain, cured resin-composite, or cast base metal alloy and cemented with either of the different resin cements was trimmed into a mini-dumbbell shape for tensile testing. The fractured surfaces and characterization of the dentin-cement interface of bonded specimens were investigated using a Scanning Electron Microscope. A significantly higher tensile strength of all-porcelain (12.5 ± 2.2 MPa) than that of cast metal (9.2 ± 3.5 MPa) restorations was revealed with cohesive failure in the cement and failure at the prosthesis-cement interface in Super-Bond C&B group. No significant difference in tensile strength was found among the types of restorations using the other three cements with adhesive failure on the dentin side and cohesive failure in the cured resin. SEM micrographs demonstrated the consistent hybridized dentin in Super-Bond C&B specimens that could resist degradation when immersed in hydrochloric acid followed by NaOCl solutions whereas a detached and degraded interfacial layer was found for the other cements. The results suggest that when complete hybridization of resin into dentin occurs tensile strength at the dentin-cement is higher than at the cement-prosthesis interfaces. The impermeable hybridized dentin can protect the underlying dentin and pulp from acid demineralization, even if detachment of the prosthesis has occurred.

The Cement Prosthesis-Like Spacer: An Intermediate Halt on the Road to Healing

Background. Periprosthetic infections remain a devastating problem in the field of joint arthroplasty. In the following study, the results of a two-stage treatment protocol for chronic periprosthetic infections using an intraoperatively molded cement prosthesis-like spacer (CPLS) are presented.Methods. Seventy-five patients with chronically infected knee prosthesis received a two-stage revision procedure with the newly developed CPLS between June 2006 and June 2011. Based on the microorganism involved, patients were grouped into either easy to treat (ETT) or difficult to treat (DTT) and treated accordingly. Range of motion (ROM) and the knee society score (KSS) were utilized for functional assessment.Results. Mean duration of the CPLS implant in the DTT group was 3.6 months (range 3–5 months) and in the ETT group 1.3 months (range 0.7–2.5 months). Reinfection rates of the final prosthesis were 9.6% in the ETT and 8.3% in the DTT group with no significant difference between both groups regarding ROM or KSS (, , resp.).Conclusion. The results show that ETT patients do not necessitate the same treatment protocol as DTT patients to achieve the same goal, emphasizing the need to differentiate between therapeutic regimes. We also highlight the feasibility of CLPS in two-stage protocols.

THE INFLUENCE OF SURFACE ROUGHNESS AND CEMENTING TECHNIQUE ON THE MICROSTRUCTURE AND MECHANICAL STRENGTH AT THE CEMENT-PROSTHESIS INTERFACE

It was generally considered that a femoral stem with a rough surface was not suitable for cemented fixation in total hip arthroplasty. The long-term follow-up studies on the cemented rough stems clearly revealed a significantly higher loosening and revision rate than those of polished stems. However, from a biomechanics point of view, a rough surface might result in stronger cement-prosthesis bonding because of micro-interlocking between the bone cement and the stem. This contradiction between biomechanical standpoint and clinical observation remains as a problem to be resolved. Thus, this study was designed to evaluate the effect of stem surface roughness and the cement pre-coating process on the bonding strength of the prosthesis-cement interface. A total of 48 Co-Cr rods with three different levels of surface roughness (polished, plasma-treated and bead-coated, 16 in each group) were enrolled in the study. All specimens were cylindrical in shape with lengths of 120 mm and 12 mm diameters. Sixteen specimens in each group were then treated with non-precoated or precoated cement fixation (8 in each group). After fixing the Co-Cr rod, the pushout test was carried out using a MTS testing machine, and the shear strength for each group was compared. An additional microscopic observation of the metal/cement interface was also performed. The results of the pushout test indicated that the shear strength increased with increasing implant surface roughness, regardless of whether or not the stem was treated with the cement precoating process. However, stem precoating did not statistically improve the bonding strength at each level of surface roughness. Microscopic observation of the stem-cement interfaces revealed that the bone cement significantly infiltrated the rough surface in both the precoated and non-precoated groups with stems with various levels of surface roughness. Surface roughness of the femoral stem significantly affected the stem/cement interface, improving shear strength significantly. Stem precoating did not statistically improve the shear strength using the present cementing technique with retrograde high-pressure injection. Although a high surface roughness of the femoral stem appears to be an effective choice to improve implant fixation in cemented THA, the longevity of the prostheses implanted with such a stem can only be determined from long-term clinical trials.