An assessment of worker exposure to respirable dust and crystalline silica in workshops fabricating engineered stone.

There is a significant silicosis risk for workers fabricating engineered stone (ES) products containing crystalline silica. The aims of this study by SafeWork NSW were to: (i) assess current worker exposure to respirable dust (RD) and respirable crystalline silica (RCS) following a 5-y awareness and compliance program of inspections in ES workshops and (ii) to identify improvements in work practices from the available evidence base to further reduce exposures. One hundred and twenty-three personal full shift samples taken on as many workers and 34 static samples across 27 workshops fabricating ES were included in the final assessment. The exposure assessment was conducted using Casella Higgins-Dewell cyclones (Casella TSI) placed in the breathing zone of workers attached to SKC Air Check XR 5000 or SKC Chek TOUCH sampling pumps. Sample filters were sent to an ISO (2017) 17025:2017 accredited laboratory for gravimetric analysis for RD and X-Ray Diffraction (XRD) analysis to determine the amount of deposited RCS i.e. alpha-quartz and cristobalite. All workshops used wet methods of fabrication. The geometric mean (GM) of the pooled result for respirable dust (RD) was 0.09 mg/m3 TWA-8 h and 0.034 mg/m3 TWA-8 h for RCS. The highest exposed workers with a GM RCS of 0.062 mg/m3 TWA-8 h were those using pneumatic hand tools for cutting or grinding combined with polishing tasks. Workers operating semiautomated routers and edge polishers had the lowest GM RCS exposures of 0.022 mg/m3 TWA-8 h and 0.018 mg/m3 TWA-8 h respectively. Although ES workers remain exposed to RCS above the workplace exposure limit (WEL) of 0.05 mg/m 3 TWA-8 h, these results point to a very substantial reduction in exposures compared to poorly controlled dry methods of fabrication. Therefore, the wearing of respiratory protection by workers remains necessary until further control measures are more widely adopted across the entire industry e.g. reduction in the crystalline silica content of ES.

PEEK Versus Ti Interbody Fusion Devices: Resultant Fusion, Bone Apposition, Initial and 26-Week Biomechanics.

STUDY DESIGN: Comparative evaluation of in vitro and in vivo biomechanics, resulting fusion and histomorphometric aspects of polyetheretherketone (PEEK) versus titanium (Ti) interbody fusion devices in an animal model with similar volumes of bone graft. OBJECTIVE: Identify differences in the characteristics of fusion and biomechanics immediately following implantation (time 0) and at 26 weeks with each interbody implant. SUMMARY OF BACKGROUND DATA: PEEK has been well accepted in spinal surgery, it provides a closer match to the mechanical properties of bone than metallic implants such as Ti. This is thought to reduce graft stress shielding and subsidence of interbody fusion devices. There remains controversy as to the overall influence of this as a factor influencing resultant fusion and initial stability. Although material modulus is 1 factor of importance, other design factors are likely to play a large role determining overall performance of an interbody implant. METHODS: A Ti and PEEK device of similar size with a central void to accommodate graft material were compared. The PEEK device had a ridged surface on the caudal and cephalad surfaces, whereas Ti device allowed axial compliance and had bone ingrowth endplates and polished internal surfaces. A 2-level ALIF was performed in 9 sheep and fusion, biomechanics, and bone apposition were evaluated at 26 weeks. Time 0 in vitro biomechanical tests were performed to establish initial stability immediately after implantation. RESULTS: No differences were detected in the biomechanical measures of each of the devices in in vitro time 0 tests. All levels were fused by 26 weeks with considerably lower range of motion when compared with in vitro tests. Range of motion in all modes of bending was reduced by over 70% when compared with intact values for axial rotation (Ti-74%, PEEK-71%), lateral bending (Ti-90%, PEEK-88%), and flexion/extension (Ti-92%, PEEK-91%). Mechanical properties of fusions formed with each implant did not differ; however, bone apposition was variable with polished internal Ti surfaces being lower than PEEK and treated Ti endplates showing the greatest levels. Graft material displayed axial trabecular alignment with both implants. CONCLUSIONS: Although material properties and surface characteristics resulted in differing amounts of biological integration from the host, both implants were capable of producing excellent fusion results using similar volumes of bone graft.

Influence of electron beam melting manufactured implants on ingrowth and shear strength in an ovine model.

Arthroplasty has evolved with the application of electron beam melting (EBM) in the manufacture of porous mediums for uncemented fixation. Osseointegration of EBM and plasma-sprayed titanium (Ti PS) implant dowels in adult sheep was assessed in graduated cancellous defects and under line-to-line fit in cortical bone. Shear strength and bony ingrowth (EBM) and ongrowth (Ti PS) were assessed after 4 and 12 weeks. Shear strength of EBM exceeded that for Ti PS at 12 weeks (P = .030). Ongrowth achieved by Ti PS in graduated cancellous defects followed a distinctive pattern that correlated to progressively decreasing radial distances between defect and implant, whereas cancellous ingrowth values at 12 weeks for the EBM were not different. Osteoconductive porous structures manufactured using EBM present a viable alternative to traditional surface treatments.

Osseointegration of porous titanium implants with and without electrochemically deposited DCPD coating in an ovine model.

BACKGROUND: Uncemented fixation of components in joint arthroplasty is achieved primarily through de novo bone formation at the bone-implant interface and establishment of a biological and mechanical interlock. In order to enhance bone-implant integration osteoconductive coatings and the methods of application thereof are continuously being developed and applied to highly porous and roughened implant substrates. In this study the effects of an electrochemically-deposited dicalcium phosphate dihydrate (DCPD) coating of a porous substrate on implant osseointegration was assessed using a standard uncemented implant fixation model in sheep. METHODS: Plasma sprayed titanium implants with and without a DCPD coating were inserted into defects drilled into the cancellous and cortical sites of the femur and tibia. Cancellous implants were inserted in a press-fit scenario whilst cortical implants were inserted in a line-to-line fit. Specimens were retrieved at 1, 2, 4, 8 and 12 weeks postoperatively. Interfacial shear-strength of the cortical sites was assessed using a push-out test, whilst bone ingrowth, ongrowth and remodelling were investigated using histologic and histomorphometric endpoints. RESULTS: DCPD coating significantly improved cancellous bone ingrowth at 4 weeks but had no significant effect on mechanical stability in cortical bone up to 12 weeks postoperatively. Whilst a significant reduction in cancellous bone ongrowth was observed from 4 to 12 weeks for the DCPD coating, no other statistically significant differences in ongrowth or ingrowth in either the cancellous or cortical sites were observed between TiPS and DCPD groups. CONCLUSION: The application of a DCPD coating to porous titanium substrates may improve the extent of cancellous bone ingrowth in the early postoperative phase following uncemented arthroplasty.

The relationship between gap formation and grip-to-grip displacement during cyclic testing of repaired flexor tendons.

The assessment of repair site gap formation during cyclic loading of reconstructed flexor tendons provides important data on the performance of repair techniques in the early postoperative period. This study describes our cyclic testing protocol and evaluates the relationship between changes in optical gap and grip-to-grip displacement. Sixteen sheep hind limb deep flexor tendons were randomized into four repair groups (n=4 per group): a 2-strand repair (modified Kessler) and 4-strand repair (Adelaide), both with and without a simple running peripheral suture. Repaired tendons were cycled for 1000 cycles at appropriate rehabilitation loads for the reconstruction. Tendons were paused at 18 pre-determined cycle points to measure gap and displacement. A strong positively linear relationship between gap and displacement was demonstrated for all repair groups (R²>0.90). An initial non-linear region during the first 10 cycles was noted with some combined core and peripheral repairs. Although trends in displacement after 10 cycles can be used to reflect gapping behaviour, direct optical measurement of gap remains preferable. We hypothesized that the adjustment of suture strands and equilibration of forces within the reconstruction occurs mostly during the initial 10 cycles. Gap-cycle curves provide a good illustration of dynamic changes at the repair site, and should be added more frequently to cyclic testing studies.

Pore distribution and material properties of bone cement cured at different temperatures.

Implant heating has been advocated as a means to alter the porosity of the bone cement/implant interface; however, little is known about the influence on cement properties. This study investigates the mechanical properties and pore distribution of 10 commercially available cements cured in molds at 20, 37, 40 and 50 degrees Celsius. Although each cement reacted differently to the curing environments, the most prevalent trend was increased mechanical properties when cured at 50 degrees Celsius vs. room temperature. Pores were shown to gather near the surface of cooler molds and near the center in warmer molds for all cement brands. Pore size was also influenced. Small pores were more often present in cements cured at cooler temperatures, with higher-temperature molds producing more large pores. The mechanical properties of all cements were above the minimum regulatory standards. This work shows the influence of curing temperature on cement properties and porosity characteristics, and supports the practice of heating cemented implants to influence interfacial porosity.