Bone and joint infections cause significant morbidity, often requiring combination medical and surgical treatment. The presence of foreign material reduces the number of organisms required to cause an infection. The aim of this study was to assess whether there was a difference in the species of organism identified on culture in osteomyelitis compared to prosthetic joint infection. This was a retrospective observational cohort study of patients that had surgical intervention for prosthetic joint infection or osteomyelitis with positive microbial culture between 2019 and 2022. Data including patient demographics, site of injury, BACH score for osteomyelitis and JS-BACH score for prosthetic joint infection, organism classification and antibiotic resistance to vancomycin and gentamicin were extracted from the medical record. Logistic and multiple regressions were used to adjust for potential confounding variables.Aims
Method
Local antibiotics, delivered to the site of infection, achieve high tissue concentrations and are used as an adjunct to systemic therapy. Local gentamicin provides levels well above the minimum inhibitory concentration and may be sufficient on its own, however, the efficacy of single or combination local antibiotics has not been studied. This retrospective study evaluated the effect of combination aminoglycoside and vancomycin local antibiotic treatment compared to aminoglycoside alone in the surgical management of bone infection. We studied patients with microbiologically confirmed osteomyelitis and fracture-related infection, who had implantation of antibiotic carriers as part of their surgical management. Data including patient demographics, type of surgery, microbiological characteristics, BACH score, duration of antibiotic treatment and clinical outcomes were collected. Failure of therapy was a composite of recurrence of infection, continued or new antimicrobial therapy, or reoperation with suspected or confirmed infection at one year after index surgery.Aim
Method
Investigation of how natural joints functioned seemed closely dependent on the lubrication mechanisms involved. This was equally relevant to artificial joints where, if fluid-film lubrication could be generated, the rubbing surfaces would be completely separated by the liquid film which would have the advantage of reducing friction, since this depends only on the shearing of the lubricant film, and reducing wear since the two surfaces would not be touching. In 1969 when I first entered this research area, hip joints were mainly small diameter (<32mm) made from ultra high molecular polyethylene (UHMWPE) rubbing against stainless steel or cobalt chromium molybdenum alloy (CoCrMo), metal-on-metal joints and alumina-on-alumina joints. A few calculations showed that the small diameter metal-on-metal hips and the UHMWPE acetabular components in combination with any type of head material were unable to produce fluid-film lubrication. Insufficient film-thicknesses could be generated to separate the rough surfaces of the joints so surface-to-surface contact prevented full separation. Ceramic-on-ceramic was different. This could be polished very smoothly and was hydrophilic so it could draw the water based lubricants (synovial fluid), into the contact region, which in turn generated fluid-films. This meant that with alumina-on alumina, wear was not a problem-but fracture was in some circumstances. As more was learned about lubrication, large diameter CoCrMo hip resurfacing devices became possible. Whilst small diameter metal-on-metal hip joints were unable to generate fluid-film lubrication, larger diameter hips could, provided the lubricant contained serum (similar to synovial fluid). This was interesting since water based lubricants of similar rheology to synovial fluid (carboxy methyl cellulose, CMC) could not produce fluid-films (Figure 1) even though theory suggested that they should. Thus it was assumed that the proteins present in the natural lubricant were important, but the reason was unknown. Returning to the original assumptions of Osborne Reynolds in deriving the theory of hydrodynamic lubrication, we see that in order to draw fluid into the contact area, the fluid adjacent to the solid boundary was assumed to be travelling at the same speed as the boundary itself. To do this the lubricant must ‘wet’ the surface or attach to it- but what if the surfaces are hydrophobic? The speed of drawing the fluid into the contact will be lower than the surface speed and so less fluid will be drawn in and the pressure generated will be lower than predicted by theory. So a simple experiment was tried using a large diameter CoCrMo alloy hip resurfacing device where a water-based lubricant (CMC) first had bovine serum added, then a simple detergent to reduce the surface tension. Figure 1 shows clearly that the lubrication improves markedly with the detergent – even more so than the bovine serum. This suggests that the wettability of the surfaces is important. Another approach to enhancing fluid-film lubrication stems from the concept of elasto-hydrodynamic theory. Here, lower modulus, more compliant surfaces, produce thicker fluid-films for similar entraining velocities and applied loads. Thus we developed compliant hip and knee joints using hydrophilic poly carbonate urethane (PCU) acetabulae against metals or ceramics. These produced phenomenally low coefficients of friction (circa 0.001) and in the knee, wear rates of only 0.06 mm3/million cycles (two orders of magnitude lower than metal on UHMWPE). Another interesting biomaterial is carbon-fibre reinforced poly-ether-ether-ketone (CFR-PEEK). Very long term hip simulator wear experiments (25 million cycles), showed wear rates which were lower than cross-linked polyethylene (circa 1.5 mm3/million cycles), yet friction was very high (µ=0.2–0.3). Clearly this was not fluid-film lubrication but improvements are being investigated.
Recent concerns over adverse effects of metal ion release, have led to the development of alternative hip joint replacements. This study reports the performance of new hemispherical MOTIS® (milled pitch-carbon fibre reinforced polyetheretherketone) acetabular cups articulating against Biolox Delta® femoral heads with the aim of producing lower wear and more biologically compatible bearings. The wear performance of 40mm hemispherical MOTIS® cups articulating against Biolox Delta® heads has been investigated. The diametral clearance was 322±15.3nm (mean ± standard deviation). Wear tests were carried out on the Simplified Mark II Durham Hip Wear Simulator to 8 million cycles. New born bovine calf serum was used as the lubricant, diluted to give a protein content of 17g/l. Friction tests were carried out on the unworn joints and worn joints after 7.5 million cycles using lubricants containing protein (bovine serum based carboxymethyl cellulose (CMC) fluids) and without protein (water based CMC fluids). Temperature measured near every hip joint over a continuous wear testing period of 0.5 million cycles was recorded using PICO TC-08 data logger. One K-type thermocouple was placed carefully and consistently in each wear station and two were used to record the ambient room temperature. After stopping the wear test, the data logger continued recording the temperature for a further ten hours to indicate the cooling period. Additionally surface analyses were undertaken before and after wear testing using a non-contacting profilometer and atomic force (AFM) microscope.Introduction
Materials and Methods
