Cephalasporin antibiotics have been commonly used for prophylaxis against surgical site infection. To prevent Clostridium difficile, the preferential use of agents such as flucloxacillin and gentamicin has been recommended. The aim of this study was to investigate the bone penetration of these antibiotics during hip and knee arthroplasty, and their efficacy against Staphylococcus aureus and S. epidermidis.

Bone samples were collected from 21 patients undergoing total knee arthroplasty (TKA) and 18 patients undergoing total hip replacement (THA). The concentration of both antibiotics was analysed using high performance liquid chromatography. Penetration was expressed as a percentage of venous blood concentration. The efficacy against common infecting organisms was measured using the epidemiological cut-off value for resistance (ECOFF).

The bone penetration of gentamicin was higher than flucloxacillin. The concentration of both antibiotics was higher in the acetabulum than the femoral head or neck (p=0.007 flucloxacillin; p=0.021 gentamicin). Flucloxacillin concentrations were effective against S. aureus and S. epidermis in all THAs and 20 (95%) TKAs. Gentamicin concentrations were effective against S.epidermis in all bone samples. Gentamicin was effective against S. aureus in 11 (89%) femoral samples. Effective concentrations of gentamicin against S. aureus were only achieved in 4 (19%) femoral and 6 (29%) tibial samples in TKA.

Flucloxacillin and gentamicin was found to effectively penetrate bone during arthroplasty. Gentamicin was effective against S. epidermidis in both THA and TKA, while it was found to be less effective against S. aureus during TKA. Bone penetration of both antibiotics was less in TKA than THA.

It is widely accepted that a tip apex distance of greater than 25mm is associated with dynamic hip screw (DHS) failure and cut-out. The aim was to devise an accurate and easy method for calculation of DHS tip apex distance (TAD) from intraoperative imaging using the tools available on Kodac Picture Archiving and Communications System. This method was applied to all patients treated with a DHS for intertrochanteric hip fracture during a six month period. Any subsequent radiographs were assessed for evidence of failure within 18 months.

The TAD was calculated using a modification of a previously described method using a similar imaging system (Johnston et al, Injury 2008) which has been shown to be accurate and reproducible. Scaling was based on the 12.5mm thread diameter of all Synthes (Switzerland) DHS screws.

60 patients underwent a DHS during the study. Nine patients were excluded who had an additional method of fixation or an intracapsular fracture. Four patients had insufficient xrays for analysis. Data was gathered for 47 patients and showed a mean TAD of 17mm (range 8.2–30.6mm). Three patients had a TAD greater than 25mm. 22 patients had a post-operative xray within 18 months. There were two cut-outs identified and both were from patients with a TAD of greater than 25mm (25.7 and 30.6mm). No incidences of implant failure or complications were identified for patients with acceptable TADs.

93.6% of screws were therefore inserted satisfactorily. Two out of the three patients with a TAD greater than 25mm had xray evidence of screw cut-out. This study supports previous evidence that a DHS lag screw should be positioned with a TAD within 25mm and a distance greater than this is associated with screw cut-out. TAD can be easily calculated using intraoperative xrays and scaled using the screw itself.

Digital radiographs are routinely used for preoperative planning, both in trauma and elective patients; particularly in preoperative templating for total hip replacement. Traditional wisdom holds that radiographs are oversized, though the degree to which this occurs is unclear. Although digital templating systems offer the use of calibration markers, this option is not always availed. We aimed to ascertain the typical magnification in departmental xrays of the hip, both to determine the typical degree of magnification as well as ascertain its consistency.

All patients undergoing dynamic hip screw fixation (DHS) in our unit over the past 12 months were identified. Using the PACS system, subsequent xrays of the patient with the implant in situ were identified; both anteroposterior abdominal and pelvic films were used. The width of a standard DHS screw (12.5 mm) was compared with the width measured on the xrays to determine a magnification factor. 164 patients were identified, of these 39 had undergone DHS fixation with subsequent xrays. 3 films were focused on the abdomen but provided good coverage of the hip also. 2 xrays were excluded – both due to limited quality. The average magnification was 26.4% (range 15.5%–42%). There was limited consistency between images.

Radiographs are a core investigation in the assessment of the orthopaedic patient. The advent of picture archiving and communications systems (PACS) has allowed the enterprising surgeon to pre-emptively plan their surgical technique and implant use. However, the utility of non-calibrated images in planning implant size is limited by variation in magnification. Surgeons should be cautious in using such images to guide their implant usage.

Osteogenesis is key to fracture healing and osteointegration of implanted material. Modification of surfaces on a nanoscale has been shown to affect cell interaction with the material and can lead to preferential osteogenesis. We hypothesised that osteogenesis could be induced in a heterogeneous population of osteoprogenitor cells by circular nanopits on a material surface. Furthermore, we intended to assess any correlation between nanopit depth and osteoinductive potential.

The desired topographies were embossed onto polycaprolactone (PCL) discs using pre-fabricated nickel shims. All pits had a diameter of 30μm and investigated pit depths were 80nm, 220nm and 333nm. Scanning electron microscopy confirmed successful embossing and planar controls were shown to be flat. A bone marrow aspirate was obtained from the femoral neck of a healthy adult undergoing a hip replacement. After establishing a culture, cells were seeded onto the PCL discs, suspended in basal media and incubated. Samples were fixed and stained after three and 28 days.

Cells were stained for the adhesion molecule vinculin after three days. Lowest concentrations of vinculin were seen in the planar control group. Osteoprogenitor cells on the shallowest pits, 80nm, had larger and brighter adhesion complexes. After 28 days, osteocalcin and osteopontin expression were used as markers of cell differentiation into an osteoblastic phenotype. 220nm deep pits consistently produced cells with the highest concentrations of osteopontin (p = 0.017) with a similar trend of osteocalcin expression. Cells on all topographies had higher expression levels than the planar controls.

We demonstrated stimulation of osteogenesis in a heterogeneous population of osteoprogenitor cells. This cell mix is similar to that present in fracture healing and after reaming for intramedullary devices or uncemented implants. All nanopit depths gave promising results with an optimum depth of 220nm after 28 days.