INTRODUCTION

Deformation of modular acetabular press-fit shells is of much interest for surgeons and manufacturers. Initial fixation is achieved through press-fit between shell and acetabulum with the shell mechanically deforming upon insertion. Shell deformation may disrupt the assembly process of modular systems and may adversely affect integrity and durability of the components and tribology of the bearing. The aim of the study was to show shell deformation as a function of bone and shell stiffness.

Purpose. Alpine skiing is associated with large skeletal loads with distinct patterns of loading rate and direction, and alpine skiers were previously found to have a robust bone structure compared to normally active controls. However, it is not known whether the mechanical stimuli experienced by skiers are also associated with enhanced bone microarchitecture and strength. Thus, the purpose of this study was to use high-resolution peripheral quantitative computed tomography (HR-pQCT) to compare bone macro- and microarchitecture and bone strength between elite alpine skiers and normally active controls. Method. Participants included 7 female and 12 male members of the Canadian Alpine Ski Team, and 10 female and 16 male normally active control subjects. A whole body dual energy X-ray absorptiometry (DXA) scan was performed to measure lean mass and percent body fat. HR-pQCT (XtremeCT, Scanco) was used to assess bone macro- and microarchitecture including total, cortical and trabecular bone area, total and cortical bone mineral density (BMD), and bone volume ratio (BV/TV) of the dominant distal tibia and radius. Finite element analysis was applied to the HR-pQCT scans to estimate bone strength (failure load, N). Analysis of covariance (ANCOVA) was used to compare outcomes between groups adjusting for body weight (tibia) and height (tibia and radius). Results. Bone area of the distal radius was significantly greater in female (30%, p<.001) and male (21%, p=.003) skiers compared with controls. Similarly, distal radius failure load was greater in female (37%, p=.001) and male (42%, p<.001) skiers. Higher BV/TV was apparent in the distal tibia of the male (18%, p=.005) and female skiers (19%, p=.012) and at the radius for the male skiers (19%, p=.02) compared with controls. High BV/TV is associated with a higher trabecular area at the distal tibia for the female athletes (14%, p=.06) and the distal radius for male athletes (32%, p=.002). Distal tibia failure load was higher in male (18%, p<.001) and female skiers (22%, p=.012) compared with controls. Distal tibia failure load remained significantly higher for the male athletes even after adjusting for lean mass. Conclusion. Compared to controls, skiers have larger bone areas at the radius in men and women, and at the tibia in women. Trabecular bone volume is augmented in skiers compared with controls, even after adjusting for height and weight. After adjusting for lean mass, group differences in bone strength were still apparent at the distal tibia in men, suggesting that direct mechanical input associated with alpine skiing affects bone microarchitecture. In conclusion a larger bone size and greater trabecular bone volume may represent skeletal adaptations to the extreme mechanical environment experienced during competitive skiing, and likely contribute to the greater bone strength observed in skiers compared with controls at both skeletal sites

In cases of poor bone quality intraoperative torque measurement might be an alternative to preoperative dual energy x-ray absorptiometry (DXA) to assess bone quality in Total Hip Arthroplasty (THA). 14 paired fresh frozen human femurs were included for trabecular peak torque measurement. We evaluated an existing intraoperative torque measurement method to assess bone quality and bone strength. We modified the approach to use this method in total hip arthroplasty (THA), which has not been published before. Since there are several approaches used in THA to exposure the hip joint, we decided to prefer the measurement in the femoral head which allows every surgeon to perform this measurement. Here a 6.5 × 23 mm blade was inserted into the proximal femur without harming the lateral cortical bone (figure 1). Further tests of the proximal femur evaluated the results of this new method: DXA, micro-computed tomography (μCT) and biomechanical load tests. Basic statistical analyses and multiple regressions were done. In the femoral head mean trabecular peak torque was 4.38 ± 1.86 Nm. These values showed a strong correlation with the values of the DXA, the μCT and the biomechanical load test. In comparison to the bone mineral density captured by DXA, the results of the intraoperative torque measurement showed a superior correlation with high sensitive bone quality evaluating methods (mechanical load tests and micro-computed tomography). Hence, the use of this intraoperative torque measurement seems to be more accurate in evaluating bone strength and bone quality than DXA during THA. The torque measurement provides sensitive information about the bone strength, which may affect the choice of implant in cases of poor bone stock and osteoporosis. In clinical use the surgeon may alter the prosthesis if the device indicates poor bone quality. Furthermore, we assume that the disadvantages associated with DXA scans like radiation exposure or errors caused by potential extraosteal sclerosis and interindividual soft-tissue artifacts could be excluded

Purpose. Stress fractures (SFs) are highly prevalent in female athletes, especially runners (1337%), and result in pain and lost training time. There are numerous risk factors for SFs in athletes; however, the role of bone quality in the etiology of SFs is currently unknown. Therefore, our primary objective was to examine whether there are characteristic differences in bone quality and bone strength in female athletes with lower limb SFs using high-resolution peripheral quantitative computed tomography (HR-pQCT). A secondary objective was to compare muscle strength between SF subjects and controls. Method. Female athletes with (n=19) and without (n=19) lower limb SFs were recruited from the local community. All SFs were medically confirmed by a physician and subjects were assessed within 1–47 weeks (12.7 13.7) of diagnosis. Controls were age-, training volume- and sport-matched to SF athletes. Bone density and microarchitectural bone parameters such as cortical thickness and porosity, as well as trabecular thickness, separation and number of all subjects were assessed using HR-pQCT at two distal tibia scanning sites (distal, ultra-distal). Finite element (FE) analysis was employed to estimate bone strength and load sharing of cortical and trabecular bone from the HR-pQCT scans. Regional analysis was applied to the HR-pQCT scans to investigate site-specific bone differences between groups. Muscle torque was measured by a Biodex dynamometer as a surrogate of muscle strength. Independent sample t-tests and Mann-Whitney U-tests were used for statistical analyses (p < 0.05). Results. Significant differences and trends indicated compromised trabecular bone and slightly thicker cortices with fewer pores in SF subjects compared with controls. This was most pronounced in the posterior region of the distal tibia, which is the site of highest tensile stresses during running and a common SF site. FE analysis indicated significantly higher cortical loads (median 4.2% higher; p=0.03) in the distal tibia site (but not ultra-distal site) of SF subjects compared to controls. The SF group exhibited significantly reduced knee extension strength (median 18.3% lower; p=0.03) and a trend towards reduced plantarflexion (median 17.3% lower; p=0.24) and eversion strength (median 9.6% lower; p=0.49) compared to controls. Conclusion. This is the first study to compare bone microarchitectural quality and lower-limb muscle strength between female athletes with SFs and health controls. A reduced trabecular bone quality in SF subjects may result in an insufficient ability to absorb and distribute tibial loads. This, in turn, may lead to higher stresses in the cortex and a higher risk for SFs. Low muscle strength may increase SF risk by providing insufficient muscular support to counteract shear stresses associated with reaction forces during running. Further study is needed to determine whether a resistance-training program can improve bone quality and in turn, reduce SF risk

INTRODUCTION. Deformation of modular acetabular press-fit shells is a topic of much interest for surgeons and manufacturer. Such modular components utilise a titanium shell with a liner manufactured from metal, polyethylene or ceramic. Initial fixation is achieved through a press-fit between shell and acetabulum with the shell mechanically deforming upon insertion. Shell deformation may disrupt the assembly process of inserting the bearing liner into the acetabular shell for modular systems. This may adversely affect the integrity and durability of the components and the tribology of the bearing. OBJECTIVE. Most clinically relevant data to quantify and understand such shell deformation can be achieved by cadaver measurements. ATOS Triple Scan III was identified as a measurement system with the potential to perform those measurements. The study aim was to validate an ATOS Triple Scan III optical measurement system against a co-ordinate measuring machine (CMM) using in-vitro testing and to check capability/ repeatability under cadaver lab conditions. METHODS. Two sizes of custom-made acetabular shells were deformed using a uniaxial/ two-point loading frame and measured repeatedly at different loads. Roundness measurements were performed using both the ATOS Triple Scan III optical system and a co-ordinate measuring machine and then compared. The repeatability was also tested by measuring shells pre and post insertion in a cadaver lab multiple times. RESULTS. The in-vitro comparison with CMM demonstrated a maximum difference of 5 µm at the rim and 9 µm at the measurement point closest to the pole of the shell. Deviation between the two systems increased towards the pole for the in-vitro measurements. However as press fit shells are designed to be loaded at the rim, this is likely where the maximum deflection will occur as a result of the highest force. Therefore, the increased difference between the systems towards the pole is of less importance compared with accuracy at the rim. Maximum repeatability was below 1 µm for the CMM and 3 µm for the ATOS Triple Scan III optical system. Repeatability of the ATOS Triple Scan III optical system was comparable between pre insertion (below 2 µm) and post insertion (below 3 µm) measurements in the cadaver lab. In addition these values were comparable to the repeatability measured during the in-vitro validation study (below 3 µm). This proves high repeatability not only for in-vitro conditions, but also for the cadaver lab as well. CONCLUSIONS. This study supports the view that the ATOS Triple Scan III optical system fulfils the necessary requirements to accurately measure shell deformation in cadavers. As a result, the authors propose further studies using cadavers to identify the impact of other factors upon shell deformation. Other factors to be measured include bone strength, shell diameter, under reaming and wall thickness

Common post-operative problems in shoulder arthroplasty such as glenoid loosening and joint instability can be reduced by improvements in glenoid design shape, material choice and fixation method [1]. Innovation in shoulder replacement is usually carried out by introducing incremental changes to functioning implants [2], possibly overlooking other successful design combinations. We propose an automated framework for parametric analysis of implant design in order to efficiently assess different possible glenoid configurations. Parametric variations of reference geometries of a glenoid implant were automatically generated in SolidWorks. The different implants were aligned and implanted with repeatability using Rhino. The glenoid-bone models were meshed in Abaqus, and boundary conditions and loading applied via a custom-made Python script. Finally, another MATLAB script integrated and automated the different steps, extracted and analysed the results. This study compared the influence of reference shape (keel vs. 2-pegged) and material on the von Mises stresses and tensile and compressive strains of glenoid components with bearing surface thickness and fixation feature width of 3, 4, 5 or 6 mm. A total of 96 different glenoid geometries were implanted into a bone cube (E = 300 MPa, ν = 0.3). Fixed boundary conditions were applied at the distal surface of the cube and a contact force of 1000 N was distributed between the central nodes on the bearing surface. The implants were assigned UHMWPE (E = 1 GPa, ν = 0.46), Vitamin E PE (E = 800 MPa, ν = 0.46), CFR-PEEK (E = 18 GPa, ν = 0.41) or PCU (E = 2 GPa, ν = 0.38) material properties and the bone-implant surface was tied (Figure 1). The von Mises stresses, compressive and tensile strains for the different models were extracted. The influence of design parameters in the mechanical environment of the implant could be assessed. In this particular example, the 95. th. percentile values of the tensile and compressive strains induced by modifications in reference shape could be evaluated for all the different geometries simultaneously in form of radar plots. 2-pegged geometries (green) consistently produced lower tensile and compressive strains than the keeled (blue) configurations (Figure 2). Vitamin E PE and PCU glenoids also produced lower maximum von Mises stresses values than CFR-PEEK and UHMWPE designs (Figure 3). The developed method allows for simple, direct, rapid and repeatable comparison of different design features, material choices or fixation methods by analysing how they influence the mechanical environment of the bone surrounding the implant. Such tool can provide invaluable insight in implant design optimisation by screening through multiple potential design modifications at an early design evaluation stage and highlighting the best performing combinations. Future work will introduce physiological bone geometries and loading, a wider variety of reference geometries and fixation features, and look at bone/interface strength and osteointegration predictions

Objectives

There remains conflicting evidence regarding cortical bone strength following bisphosphonate therapy. As part of a study to assess the effects of bisphosphonate treatment on the healing of rat tibial fractures, the mechanical properties and radiological density of the uninjured contralateral tibia was assessed.

Construction of a functional skeleton is accomplished through co-ordination of the developmental processes of chondrogenesis, osteogenesis, and synovial joint formation. Infants whose movement in utero is reduced or restricted and who subsequently suffer from joint dysplasia (including joint contractures) and thin hypo-mineralised bones, demonstrate that embryonic movement is crucial for appropriate skeletogenesis. This has been confirmed in mouse, chick, and zebrafish animal models, where reduced or eliminated movement consistently yields similar malformations and which provide the possibility of experimentation to uncover the precise disturbances and the mechanisms by which movement impacts molecular regulation. Molecular genetic studies have shown the important roles played by cell communication signalling pathways, namely Wnt, Hedgehog, and transforming growth factor-beta/bone morphogenetic protein. These pathways regulate cell behaviours such as proliferation and differentiation to control maturation of the skeletal elements, and are affected when movement is altered. Cell contacts to the extra-cellular matrix as well as the cytoskeleton offer a means of mechanotransduction which could integrate mechanical cues with genetic regulation. Indeed, expression of cytoskeletal genes has been shown to be affected by immobilisation. In addition to furthering our understanding of a fundamental aspect of cell control and differentiation during development, research in this area is applicable to the engineering of stable skeletal tissues from stem cells, which relies on an understanding of developmental mechanisms including genetic and physical criteria. A deeper understanding of how movement affects skeletogenesis therefore has broader implications for regenerative therapeutics for injury or disease, as well as for optimisation of physical therapy regimes for individuals affected by skeletal abnormalities.

Cite this article: Bone Joint Res 2015;4:105–116

Osteoporosis is common and the health and financial cost of fragility fractures is considerable. The burden of cardiovascular disease has been reduced dramatically by identifying and targeting those most at risk. A similar approach is potentially possible in the context of fragility fractures. The World Health Organization created and endorsed the use of FRAX, a fracture risk assessment tool, which uses selected risk factors to calculate a quantitative, patient-specific, ten-year risk of sustaining a fragility fracture. Treatment can thus be based on this as well as on measured bone mineral density. It may also be used to determine at-risk individuals, who should undergo bone densitometry. FRAX has been incorporated into the national osteoporosis guidelines of countries in the Americas, Europe, the Far East and Australasia. The United Kingdom National Institute for Health and Clinical Excellence also advocates its use in their guidance on the assessment of the risk of fragility fracture, and it may become an important tool to combat the health challenges posed by fragility fractures.