Periprosthetic joint infections (PJI) are challenging complications following arthroplasty. Staphylococci are a frequent cause of PJI and known biofilm producers. Reoperations for PJI of the hip or knee between 2012 and 2015 performed at Sahlgrenska University Hospital were identified. Medical records were reviewed, and clinical parameters recorded for patients whose intraoperative bacterial isolates had been stored at the clinical laboratory. Staphylococcal strains isolated from reoperations due to first-time PJI were characterised by their ability to form biofilms using the microtiter plate test. The study group included 49 patients (70 bacterial strains) from first-time PJI, whereof 24 (49%) patients had recurrent infection. Strong biofilm production was significantly associated with recurrent infection. Patients infected with strong biofilm producers had a five-fold increased risk for recurrent infection. Strong biofilm production was significantly associated with increased antimicrobial resistance and PJI recurrence. This underscores the importance of determining biofilm production and susceptibility as part of routine diagnostics in PJI. Strong staphylococcal biofilm production may have implications on therapeutic choices and suggest more extensive surgery. Furthermore, despite the increased biofilm resistance to rifampicin, results from this study support its use in staphylococcal PJI.
Cortical bone is a complex composite material composed of an inorganic mineral phase and organic matrix of type I collagen and various non-collagenous proteins. The hierarchical organisation of bone results in a transversely isotropic material with the mechanical properties in the long-axis (z) being superior to the radial and circumferential axes which are equivalent. This directional dependence of bone has been well reported, whilst the mechanisms/anisotropy are more difficult to study. This study examined the anistropic nature of cortical bone and the influence of different sterilisation procedures. Ninety cortical bone cubes were prepared using established techniques (Walsh and Guzelsu) and randomly allocated to three treatments; control, 15 KGy, Super Critical Fluid (SCF) (n=30 per group). The ultrasonic moduli was examined using longitudinal sound waves at 5 MHz using a pulse receive technique. Unconfined compression was performed non-destructively in longitudinal (z), circumferential (ï±) and radial orientations (r). Samples were tested to failure in the z axis. A two-way analysis of variance (treatment and time) followed by a Games Howell post hoc test and covariate analysis was performed using SPSS for Windows. Data from this study revealed some interesting and intriguing results with respect to the effects of gamma irradiation and dense gas technology on the properties of cortical bone and load transmission. A statistical decrease in the compressive stiffness and strength was noted with 15 KGy of whilst SCF treatment did not alter the properties in the r or ï orientations. Similar results were found with respect to the ultrasonic moduli (data not shown). The pilot data confirmed the adverse effects of bone in compression following gamma irradiation as we found in our recently presented ORS work. However, the study in compression demonstrated that the directional dependence that makes cortical bone a transversely isotropic material is removed following gamma irradiation with SCF did not appear to have this effect. The effects of gamma irradiation on the mechanical performance of allografts in the long bone axis may play a role in their in vivo performance. The removal of the anisotropy following gamma irradiation provides insight into the relationship(s) between the mineral and organic constituents, which requires further study.
