Accurate and precise acetabular reaming is a requirement for the press-fit stability of cementless acetabular hip replacement components. The accuracy of reaming depends on the reamer, the reaming technique and the bone quality. Conventional reamers wear with use resulting in inaccurate reaming diameters, whilst the theoretical beneficial effect of ‘whirlwind’ reaming over straight reaming has not previously been documented. Our aim was to compare the accuracy and precision of single use additively-manufactured reamers with new conventional reamers and to compare the effect of different acetabular reaming techniques. Forty composite bone models, half high-density and half low-density, were reamed with a new 61 mm conventional acetabular reamer using either straight or ‘whirlwind’ reaming techniques. This was repeated with a 61 mm single use additively-manufactured reamer. Reamed cavities were scanned using a 3D laser scanner with mean diameters of reamed cavities compared using the Mann-Whitney U test to determine any statistically significant differences between groups (p<0.05) [Fig. 1).Aims
Materials and Methods
For patients with Developmental Dysplasia of the Hip (DDH) who progress to needing total joint arthroplasty it is important to understand the morphology of the femur when planning for and undertaking the surgery, as the surgery is often technically more challenging in patients with DDH on both the femoral and acetabular parts of the procedure1. The largest number of male DDH patients with degenerative joint disease previously assessed in a morphological study was 122. In this computed tomography (CT) based morphological study we aimed to assess whether there were any differences in femoral morphology between male and female patients with developmental dysplasia undergoing total hip arthroplasty (THA) in a cohort of 49 male patients, matched to 49 female patients. This was a retrospective study of the pre-operative CT scans of all male patients with DDH who underwent THA at two hospitals in Japan between 2006–2017. Propensity score matching was used to match these patients with female patients in our database who had undergone THA during the same period, resulting in 49 male and 49 female patients being matched on age and Crowe classification. The femoral length, anteversion, neck-shaft angle, offset, canal-calcar ratio, canal flare index, lateral centre-edge angle, alpha angle and pelvic incidence were measured for each patient on their pre-operative CT scans.Objectives
Methods
The increase in revision joint replacement surgery and fractures of bone around orthopaedic implants may be partly addressed by keeping bone healthy around orthopaedic implants by inserting implants with mechanical properties closer to the patient's bone properties. We do not currently have an accurate way of calculating a patient's bone mechanical properties. We therefore posed a simple question: can data derived from a micro-indenter be used to calculate bone stiffness? We received ethical approval to retrieve femoral heads and necks from patients undergoing hip replacement surgery for research. Cortical bone from the medial calcar region of the femoral neck was cut into 3×3×6mm cuboid specimens using a diamond wafering blade. Micro-indentation testing was performed in the direction of loading of the bone using a MicroMaterials (MicroMaterials, UK) indenter, using the high load micro-indentation stage (see Figure 1). To simulate in vivo testing, the samples were kept hydrated and were not fixed or polished. From the unloading curve after indentation, the elastic modulus was calculated, using the Oliver-Pharr method using the indentation machine software. To assess which microindentation machine settings most precisely calculate the elastic modulus we varied the loading and unloading rates, load and indenter tip shape (diamond Berkovich tip, 1mm diameter Zirconia spherical tip and 1.5mm diameter ruby spherical tip). Following this, for 11 patients' bone, we performed compression testing of the same samples after they were indented with the 1.5mm diameter ruby spherical tip to assess if there was a correlation between indentation values of apparent elastic modulus and apparent modulus values calculated by compression testing (see Figure 2). Platens compression testing was performed using an Instron 5565 (Instron, USA) materials testing machine. Bluehill compliance correction software (Instron, USA) was used to correct for machine compliance. The strain rate was set at 0.03mm/s. The apparent elastic modulus was calculated from the slope of the elastic region of the stress-strain graph. The correlation between values of apparent modulus from compression testing and indentation were analyzed using IBM SPSS Statistics 22.Introduction
Methods
Bisphosphonates (BP) are the first-line therapy for preventing osteoporotic fragility fractures. However, concern regarding their efficacy is growing because bisphosphonate use is associated with over-suppression of remodeling. Animal studies have reported that BP therapy is associated with accumulation of micro-cracks (Fig. 1) and a reduction in bone mechanical properties, but the effect on humans has not been investigated. Therefore, our aim was to quantify the mechanical strength of bone treated with BP, and correlate this with the microarchitecture and density of micro-damage in comparison with untreated osteoporotic hip-fractured and non-fractured elderly controls. Trabecular bone cores from patients treated with BP were compared with patients who had not received any treatment for bone osteoporotic disease. Non-fractured cadaveric femora from individuals with no history of bone metabolic disease were also used as controls. Cores were imaged in high resolution (∼1.3µm) using Synchrotron X-ray tomography (Diamond Light Source Ltd.) The scans were used for structural and material analysis, then the cores were mechanically tested in compression. A novel classification system was devised to characterise features of micro-damage in the Synchrotron images: micro-cracks, diffuse damage and perforations. Synchrotron micro-CT stacks were visualised and analysed using ImageJ, Avizo and VGStudio MAX.Introduction
Methods
Appropriate seating of acetabular and femoral components during total hip arthroplasty (THA) surgery is essential for implant longevity. Additionally, the appropriate assembly of components is essential for proper function, for example to prevent taper corrosion or acetabular component disassembly. However the current understanding of the forces and energies imparted during surgery is sparse. Perhaps more importantly, there exists a risk that much of the preclinical testing performed to develop implants and surgical techniques do not apply the appropriate boundary conditions to surgical impaction and component assembly, leading to the possibility of huge overestimations in impaction force. This in-vitro study examines the influence of mechanical boundary condition parameters that affect the forces imparted to implant and patient during THA surgery; including the attenuation of two common types of acetabular cup introducer and the hard tissue (pelvic) boundary conditions. A drop tower test-rig that allows full customisation of impaction and implantation parameters was built, with pelvis boundary conditions simulated with silicone cylinders using adjustable geometry to vary stiffness and damping. The least stiff setup represented a large, unbolstered patient on the operating table. A medium stiffness setup represented a slim, well bolstered patient. An extremely stiff, metal boundary was selected to replicate the pre-clinical testing conditions usually employed in implant or instrument testing, where impact testing takes place in a vice, or metal test frame. For each of these stiffness scenarios, piezo-load cells and LVDTs were used to measure forces and displacement of the pelvis model. We also investigated the use of two common implant introducers; a straight and a bent introducer. The latter is often used for large patients or for specific approaches (e.g. direct anterior). In total, 180 drop weight tests and 120 strikes by an orthopaedic surgeon were measured. For the drop weight testing the peak force measured varied between 7.6kN and 0.4kN for stiffest and softest support conditions respectively. When the surgeon applied the impact strike manually, the range was between 13.2kN and 0.8kN for the stiffest and softest support conditions respectively (Figure 1). Using the bent introducer attenuated the load by between 13.0% and 115% compared to the straight introducer (Figure 1). Pelvic boundary conditions are overlooked in much of the literature on implant seating or assembly in THA surgery. In laboratory settings with impaction performed on a workbench or frame of a materials testing machine, high forces may be sufficient to seat or assemble implants. However our data show that these high forces will not be replicated in vivo, and this could be a causative factor in poor assembly of acetabular components or femoral head/stem tapers, which can lead to clinical problems like disassembly or crevice corrosion. We found the geometry of the introducer and the stiffness of the pelvis support had significant attenuating influence. We also found that the surgeon does not compensate for these differences, resulting in vast differences in the delivered strike force. It is recommended these factors are carefully considered when designing surgical tools and in particular conducting pre-clinical testing.
