Metal on metal (MoM) bearings in hip surgery may result in increased blood levels of metal ions. The nature of the relationship between ion levels and failure is still not fully understood.

We compared three cohorts of resurfacing patients, grouped for brand and diameter of femoral component. We measured the blood level of Cobalt and Chromium ions at an average of 4 years postoperatively. The results were grouped as follows: Birmingham Hip Resurfacing ≥50 mm diameter, Durom resurfacing ≥50 mm diameter and Durom resurfacing <50 mm diameter.

120 patients were included in each group. There were significant differences in Cobalt levels between the groups. The median cobalt level for the BHR group was 8 nmol/L higher than the Durom ≥50 mm group (P<0.005). The Durom <50 mm group recorded cobalt levels 8.5 nmol/L higher than the Durom ≥50 mm group (P=0.0004). Revision rates were equal in the Large BHR's and Large Durom HRA (both 3.3%) however the small Durom HRA had a revision rate of 8.3%.

Elevated blood ion levels can indicate a failing MoM bearing. When similar ion levels were reported for BHR and small Durom the latter had significantly higher revision rates. The large BHR and large Durom HRA have similar revision rates yet the large Durom HRA had significantly lower metal ion levels. Only one of the patients having revision surgery (n=18) had metal ion levels above the MHRA threshold. This suggests ion levels do not absolutely predict the rate of HRA failure. Given similar revision rates with different ion levels between the large BHR and large Durom hips, mechanisms of failure leading to revision must be isolated from the release of metal ions. Therefore clinical and image based follow up are recommended in addition to ion level monitoring.

Prophylactic antibiotics administered prior to joint arthroplasty have become standard practice. Due to concern over the risk that 2nd generation cephalosporins posed to the elderly, as regards clostridium difficile associated infections the antimicrobial management team in our unit changed the protocol for prophylactic antibiotics. As of 1st September 2009, flucloxacillin and gentamicin were preferred over cefuroxime as the first choice of prophylactic antibiotic. However, it was noted that postoperatively patients were experiencing a decrease in renal function.

One hundred patients who underwent a total hip replacement following the policy change were randomly selected from the departmental joint arthroplasty database. This group was age and sex matched to 100 patients undergoing their surgery prior to the change. Data was collected on renal function, length of stay, antibiotic and age. Any change in renal function was categorised using the RIFLE criteria.

Exclusion secondary to variations from protocol or treatment for femoral neck fractures resulted in a total number of 156 patients with 78 in each arm. The average age for both groups was 64 years. Non-parametric analysis of preoperative and postoperative serum creatinine concentrations and Glomerular Filtration Rate (GFR) demonstrated a significant difference between the two groups, showing that GFR decreased (p=0.041) and serum creatinine concentration increased (p=0.037) in the cohort receiving gentamicin. Classing the impaired renal function as: risk, injury or failure (RIFLE criteria) demonstrated a statistically significant difference for any criterion positive (p=0.016) but no significant difference for the specific RIFLE groups (p=0.068).

Acknowledging the small numbers and potential confounders for renal impairment, this study was able to show a difference in renal function for patients receiving gentamicin over cefuroxime as prophylaxis for joint arthroplasty.

It is well established that cell behaviour is responsive to the surrounding environment. Chemistry, material stiffness and topography allow control of cell adhesion, proliferation, growth and differentiation. Biomimicry is playing a role in the next generation of biomaterials, surface engineering on orthopaedic implants may promote improved skeletal integration.

Human osteoblasts were cultured on engineered micro-topographical features with nanoscale depths, similar in scale to an osteoclast resorption pit. Three different micro-topographies were used (in addition to planar controls.) created on a hot moulded polymer. The cells were cultured in basal media on surfaces with 20, 30 and 40 micrometer circular pits, each with a depth of 400 nanometers. The cells were fixed at time points 3 days, 21 days and 28 days to allow assessment of cytoskeletal development, production of protein markers of bone production (osteopontin) and mineral deposition respectively.

At each time point greater indicators of cell activity and bone production were evident on the 30 and 40 micrometer structures as compared with the 20 micrometer structures and the planar controls. These positive results include increased focal adhesions, stronger expression of intracellular and extracellular osteopontin and more mature nodules of calcium formation.

This in vitro study demonstrates that micro and nanotopographies influence cell activity. Osteoblast response can be induced on the surface of a future generation of orthopaedic implants, lasting long after the effects chemical application have expired. Further research is required to assess the potential application to implant grade materials.

In recent years the majority of X-ray departments have moved to a digital format of recording and archiving radiographs. These digital images (as with previous ‘films’) have a built in magnification factor (variable with each patient), which, may cause errors in templating for joint replacement surgery. Placing a marker of known size at the same level as the joint in question allows calculation of the magnification. This may help to restore hip offset in total hip replacement.

To establish the magnification factor for digital radiographs taken in our unit.

To assess the usefulness of marker images in accurate preoperative templating. Preoperative marker radiographs were identified retrospectively. The apparent size of the marker was measured on digital image. This value was used to calculate the magnification of the image. The scaled X-ray was up loaded to a digital templating software programme. This software uses a ‘scaling tool’ to calculate the magnification of the image. The hip joint templating tool was the used to calculate the offset of the proximal femur, this was performed with the calculated magnification and also an assumed magnification of 120%. The recommended offset of Exeter V40 stem was noted for both values.

Images were identified for 40 patients with markers. The average magnification was 122% for both PACS and Orthoview with a range 113% – 129% and a standard deviation of 4%. The median value for magnification was 120%. The average change in offset between calculated and estimated magnification was 1.275mm with a maximum change of 3mm. In two cases this difference resulted in a change in the recommended offset (5%).

The use of marker radiographs is widely described. In this small series the magnification is the same as previously reported in other studies. The difference in offset between calculated and estimated magnification was relatively small and caused a change in the recommended offset in only two patients. Variation in the use of the templating tool in our software can produce a much greater change in offset. Marker radiographs will only be useful as part of a standardised method of pre-operative templating.