Manual impaction, with a mallet and introducer, remains the standard method of installing cementless acetabular cups during total hip arthroplasty (THA). This study aims to quantify the accuracy and precision of manual impaction strikes during the seating of an acetabular component. This understanding aims to help improve impaction surgical techniques and inform the development of future technologies. Posterior approach THAs were carried out on three cadavers by an expert orthopaedic surgeon. An instrumented mallet and introducer were used to insert cementless acetabular cups. The motion of the mallet, relative to the introducer, was analyzed for a total of 110 strikes split into low-, medium-, and high-effort strikes. Three parameters were extracted from these data: strike vector, strike offset, and mallet face alignment.Aims
Methods
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
With information about a patient's bone mechanical properties orthopaedic operations could be optimised to reduce intra- and post-operative complications. However, there is currently no reliable method of measuring a patient's bone mechanical properties in vivo. We have previously investigated microindentation, using a 1.5mm diameter spherical indenter tip, and found no correlation between these measurements and compression testing measurements. We hypothesised that by using a larger diameter indenter tip we would closer match bone millimetre-scale mechanical properties. 20 bone samples were taken from 20 patients undergoing hip replacement surgery. The samples were machined from the femoral neck calcar cortical bone into 6×3×3mm parallelepiped specimens, aligned with the osteons along the long axis. The samples were micro-computed tomography (CT) scanned to calculate porosity. Microindentation was performed using a 6mm diameter, sapphire, spherical indenter tip. 12 indentations were performed in a grid and the reduced moduli were calculated using the Oliver-Pharr method. Compression testing was then performed to failure and the apparent elastic modulus was calculated for each sample. A moderate correlation was found between the indentation reduced moduli and compression testing elastic moduli (r=0.52, r2=0.275, p=0.018). In addition, a moderate correlation was found between the indentation reduced moduli and CT-measured porosity (r=0.5, r2=0.251, p=0.025) and a strong correlation was found between compression testing moduli and porosity (r=0.75, r2=0.568, p<0.001). Using large-tip spherical microindentation, indentation reduced moduli correlated significantly with compression testing apparent elastic moduli in these 20 cortical bone specimens. Microindentation using a large, spherical indenter tip may predict the mechanical properties of bone at the millimetre length scale and shows promise as a potential future clinical decision aid in surgery.
The ability to determine human bone stiffness is of clinical relevance in many fields, including bone quality assessment and orthopaedic prosthesis design. Stiffness can be measured using compression testing, an experimental technique commonly used to test bone specimens A keyword search of all English language articles up until December 2017 of compression testing of bone was undertaken in Medline, Embase, PubMed, and Scopus databases. Studies using bulk tissue, animal tissue, whole bone, or testing techniques other than compression testing were excluded.Objectives
Methods
Microindentation has the potential to measure the stiffness of an individual patient’s bone. Bone stiffness plays a crucial role in the press-fit stability of orthopaedic implants. Arming surgeons with accurate bone stiffness information may reduce surgical complications including periprosthetic fractures. The question addressed with this systematic review is whether microindentation can accurately measure cortical bone stiffness. A systematic review of all English language articles using a keyword search was undertaken using Medline, Embase, PubMed, Scopus and Cochrane databases. Studies that only used nanoindentation, cancellous bone or animal tissue were excluded.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.
Osteoporosis is a global health issue with 200 million people suffering worldwide and it is a common condition in the elderly. Bisphosphonates including alendronate and risendronate are considered as the first line treatment for osteoporosis. However, there is increasing evidence that bisphosphonate (BP) therapy is associated with atypical fractures. Animal studies have reported a dose-dependent association between the duration of BP therapy and the accumulation of micro-damage. We tested the hypothesis that hip fracture patients treated with BP exhibited greater micro-damage density than untreated fracture and ‘healthy’ aging non-fracture controls. Trabecular bone cores from patients treated with BP were compared with patients who had not received any treatment for bone metabolic disease (ethics reference: R13004). Non-fractured cadaveric femora from individuals with no history of bone metabolic disease were used as controls. Cores were imaged in high spatial resolution (∼1.3µm) using Synchrotron X-ray tomography (Diamond Light Source Ltd.) 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. Our findings show that the BP group had the highest micro-damage density across all groups. The BP group (7.7/mm3) also exhibited greater micro-crack density than the fracture (4.3/mm3) and non-fracture (4.1/mm3) controls. Furthermore, the BP group (1.9/mm3) demonstrated increased diffuse damage when compared to the fracture (0.3/mm3) and non-fracture (0.8/mm3) controls. In contrast, the BP group (1.9mm3) had fewer perforations than fracture (3.0/mm3) and non-fracture controls (3.9/mm3). BP inhibits bone remodelling, thereby reducing the number of perforated trabeculae, but over-suppression leads to micro-damage accumulation. Accumulated damage could weaken the trabecular bone in the femoral head and neck, increasing the risk of a fracture during a trip or fall.
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 are therefore investigating whether microindentation can accurately 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. Micro-indentation testing was performed in the direction of loading of the bone using a MicroMaterials indenter. 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. To assess which microindentation machine settings most precisely calculate the elastic modulus we varied the loading and unloading rates, load and indenter tip shape. The most precise results were obtained by using a spherical indenter tip (rather than Berkovich tip), high load (10N), a loading rate of 100 mN/s and unloading rate of 300 mN/s with a pause of 60 seconds at maximum load and multiple load cycles with constant loads. Using these settings the mean elastic modulus over 12 cycles of testing was 13.0 GPa (+/- 2.47). By using a spherical indenter tip and fast unloading it was possible to get precise apparent modulus values. By unloading as fast as possible the effects of bone viscoelastic properties are minimised. By using a spherical indenter tip, plastic deformation at the tip is minimised (compared to the Berkovich tip). We are performing further standard compression tests on the samples to verify the accuracy of the indentation tests.
