Synthesis of a Lubricant to Mimic the Biorheological Behavior of Osteoarthritic and Revision Synovial Fluid

The rheological properties of synovial fluid (SF) are essential for the friction behavior and wear performance of total joint replacements. Standardized in vitro wear tests for endoprosthesis recommend diluted calf serum, which exhibits substantial different rheological properties compared to SF. Therefore, the in vitro test conditions do not mimic the in vivo conditions. SF samples from osteoarthritis knee patients and patients undergoing knee endoprosthesis revision surgery were compared biochemically and rheologically. The flow properties of SF samples were compared to synthetic fluid constituents, such as bovine serum albumin (BSA) and hyaluronic acid (HA). Interestingly, HA was identified as a significant contributor to shear-thinning. Using the acquired data and mathematical modelling, the flow behavior of human SF was modelled reliably by an adapted adjustment of biorelevant fluid components. Friction tests in a hard/soft bearing (ceramic/UHMWPE) demonstrated that, in contrast to serum, the synthetic model fluids generate a more realistic friction condition. The developed model for an SF mimicking lubricant is recommended for in vitro wear tests of endoprostheses. Furthermore, the results highlight that simulator tests should be performed with a modified lubricant considering an addition of HA for clinically relevant lubrication conditions.

Influence of Exogenous Variables on Intrusion Depth of PMMA Bone Cement: Revision of ISO 5833 Standard

Background: Poly (methyl methacrylate) (PMMA) bone cement is widely used to anchor total joint replacements to the contiguous bone. Among the clinically-relevant properties of this material is its intrusion depth (ID) because it indicates the potential for interdigitation of the curing cement into the interstices of the cancellous bone. ID is determined using procedures stipulated in ISO 5833. There is only one study in which ISO 5833 was examined critically, but only one exogenous variable was considered. Purpose: We carried out an extensive critical analysis of the ISO 5833 Standard with a view to making recommendations for revising it. Materials and Methods: 7 approved PMMA bone cement brands (covering low-, medium-, and high-viscosity brands) were used in two series of tests. In the first series, the influence of time at which ID was determined (relative to achievement of cement doughing time (DT)) was delineated. In the second series, the influence of three clinically-relevant variables on ID for each of these brands was determined and, then, response surface methodology was used to analyze the results. Results: ID results are given for both series of tests. Over the range of the variables used, the optimum IDs for a low-, medium-, and high-viscosity brand were computed to be 5.7 mm, 3.1 mm, and 2.4 mm, respectively. Conclusion: The findings allowed us to recommend that the following revisions be made to stipulations in ISO 5833 for determining ID: prior to running the ID test, store the cement unit at 1°C; 60 minutes after removing the cement unit from the storage medium, mix the cement powder and liquid, in a vacuum chamber, at 120 rpm; and determine ID 3 minutes after DT is achieved.

An Antibiotic-Releasing Bone Void Filling (ABVF) Putty for the Treatment of Osteomyelitis

The number of total joint replacements (TJR) is on the rise with a corresponding increase in the number of infected TJR, which necessitates revision surgeries. Current treatments with either non-biodegradable, antibiotic-releasing polymethylmethacrylate (PMMA) based bone cement, or systemic antibiotic after surgical debridement do not provide effective treatment due to fluctuating antibiotic levels at the site of infection. Here, we report a biodegradable, easy-to-use “press-fitting” antibiotic-releasing bone void filling (ABVF) putty that not only provides efficient antibiotic release kinetics at the site of infection but also allows efficient osseointegration. The ABVF formulation was prepared using poly (D,L-lactide-co-glycolide) (PLGA), polyethylene glycol (PEG), and polycaprolactone (PCL) as the polymer matrix, antibiotic vancomycin, and osseointegrating synthetic bone PRO OSTEON for bone-growth support. ABVF was homogenous, had a porous structure, was moldable, and showed putty-like mechanical properties. The ABVF putty released vancomycin for 6 weeks at therapeutic level. Furthermore, the released vancomycin showed in vitro antibacterial activity against Staphylococcus aureus for 6 weeks. Vancomycin was not toxic to osteoblasts. Finally, ABVF was biodegradable in vivo and showed an effective infection control with the treatment group showing significantly higher bone growth (p < 0.001) compared to the control group. The potential of infection treatment and osseointegration makes the ABVF putty a promising treatment option for osteomyelitis after TJR.

Elective interventions

This chapter provides an overview of common elective interventions used in the specialty of orthopaedics. Evidence-based concise information is provided regarding total joint replacements and revision of joint replacements including preoperative preparation. Other procedures such as osteotomy, arthrodesis, and arthroscopic surgery are also explained. Common procedures used for correction of deformity of hands and feet are also explained with an emphasis on good pain management and a holistic approach to supporting patients before and following these procedures.

Acrylic Bone Cements Modified with Graphene Oxide: Mechanical, Physical, and Antibacterial Properties

Bacterial infections are a common complication after total joint replacements (TJRs), the treatment of which is usually based on the application of antibiotic-loaded cements; however, owing to the increase in antibiotic-resistant microorganisms, the possibility of studying new antibacterial agents in acrylic bone cements (ABCs) is open. In this study, the antibacterial effect of formulations of ABCs loaded with graphene oxide (GO) between 0 and 0.5 wt.% was evaluated against Gram-positive bacteria: Bacillus cereus and Staphylococcus aureus, and Gram-negative ones: Salmonella enterica and Escherichia coli. It was found that the effect of GO was dependent on the concentration and type of bacteria: GO loadings ≥0.2 wt.% presented total inhibition of Gram-negative bacteria, while GO loadings ≥0.3 wt.% was necessary to achieve the same effect with Gram-positives bacteria. Additionally, the evaluation of some physical and mechanical properties showed that the presence of GO in cement formulations increased wettability by 17%, reduced maximum temperature during polymerization by 19%, increased setting time by 40%, and increased compressive and flexural mechanical properties by up to 17%, all of which are desirable behaviors in ABCs. The formulation of ABC loading with 0.3 wt.% GO showed great potential for use as a bone cement with antibacterial properties.