1,721,081 research outputs found
Effect of long-term physiological activity on the long-term stem stability of cemented hip arthroplasty: in vitro comparison of three commercial bone cements
No full textLong-term endurance of the cement mantle is fundamental for the survival of cemented hip prostheses. Current protocols to characterize bone cements are unsuitable to predict the actual clinical outcome. The aim of this study was to assess if it is possible to rank cement types having diverse clinical outcome by using a simplified in vitro physiological test. Composite femurs were implanted with identical stems (Lubinus-SPII), using different commercial cement types: CMW1 to represent cement with poor clinical outcome; Simplex-P and Cemex-RX to represent cements with a positive clinical outcome. Implanted femurs were subjected to a validated protocol that simulated a demanding but physiological loading spectrum. Inducible micromotions and permanent migrations were recorded throughout the test. After test completion, the cement mantles were sectioned and inspected with dye penetrants to quantify the fatigue-induced cracks. Micromotions did not differ significantly between cement types (possibly because a successful prosthesis was chosen that is very stable in the host bone). Significant differences were observed in terms of cement cracks: CMW1 induced significantly more numerous and larger cracks than Simplex-P and Cemex-RX; no difference was observed between Simplex-P and Cemex-RX. This indicates that this protocol: (a) can discriminate between 'good' and 'bad' cements and (b) yields consistent results when comparable cements are tested. The proposed protocol overcomes the limitations of existing standardized material tests for bone cements. New cements can be assessed in comparison with other cements with known (positive/negative) clinical outcome, tested with the same protocol
Discussion on the design of a hip joint simulator
No full textHip joint simulators were developed for predicting, bu attempting to duplicate in vitro physiological loads and motion, the wear rate that total hip replacements are likely to show in vivo. From a theoretical point of view, loading and motion cycles of hip joints could be closely reproduced by three rotation actuators and three force actuators. However existing devices have been designed assuming that some of these degrees of freedom are negligible, in order to reduce the complexity of the equipment. The present study singles out some preliminary indication on the design choices regarding the spatial configuration of loading and motion actuators. The aim is to define theoretically a simplified simulator but still to apply the most physiologically realistic loading cycle to the specimen. Copyrigh
A pictographic atlas for classifying damage modes on polyethylene bearings
Full text linkEvaluation of medical devices retrieved after in vivo service provides unique evidence related to the physiological environment in which the biomaterials performed. This study implements a training procedure for evaluating polyethylene bearings of joint prostheses obtained after pre-clinical tests or explanted after in vivo function. A total of 161 damage regions on 45 bearings were evaluated by four observers. An illustrated Damage Mode Atlas was developed as a reference guide, inclusive of both photographs and concise written descriptions of 16 specific damage modes that are typical for polyethylene bearings. Utilizing the Damage Mode Atlas to train new researchers improved the damage pattern analysis, including more accurate identification of damage modes and improved inter-rater reliability. This Damage Mode Atlas is a useful supplementary tool for conducting Stage II non-destructive analysis of explanted polyethylene bearings used for joint replacement, in accordance with international guidelines for evaluating explanted medical devices
Automatic fracture reduction with a computer-controlled external fixator
No full textThe reduction of fractures by means of an Ilizarov's fixator is obtained by successively shortening or lengthening the rods. This entails that all reduction operations of the fracture stumps be performed with a series of empirical attempts, requiring great experience and manual dexterity in the surgeon. Moreover this process involves a long exposure of both physician and patient to potentially harmful radiation due to the continuous checking of the intermediate positions on the X-ray image intensifier. In order to overcome these limits a new device has been conceived, based on the application of three stepper-motors on three rods. Its basic principle is functionally very similar to Ilizarov's prototype. The relative motions between the two frames are carried out by controlling the three actuators with a computer, which processes the number of required steps on the basis of an algorithm, starting from a few inputs supplied by the surgeon. This article illustrates the functional kinematic study necessary for the complete automation of the reduction process. Also considered is the complex problem of the reduction trajectory definition, intended as a sequence of configurations of partial correction, obtained by formalizing in geometrical terms the empirical criterial followed by the orthopaedic surgeon in reducing fractures. Such a sequence is intended to be a suggestion for the surgeon who can visualize and possibly interact with the system to determine a trajectory harmless for the soft tissues surrounding the bone
Muscle discretization affects the loading transferred to bones in lower-limb musculoskeletal models.
No full textModelling the mechanical effect of muscles is important in several research and clinical contexts. However, few studies have investigated the effect of different muscle discretizations from a mechanical standpoint. The present study evaluated the errors of a reduced discretization of the lower-limb muscles in reproducing the muscle loading transferred to bones. Skeletal geometries and a muscle data collection were derived from clinical images and dissection studies of two cadaver specimens. The guidelines of a general method previously proposed for a different anatomical district were followed. The data collection was used to calculate the mechanical effect of muscles, i.e. the generalized force vectors, and the errors between a large and a reduced discretization, in a reference skeletal pose and in the extreme poses of the range of motion of joints. The results showed that the errors committed using a reduced representation of muscles could be significant and higher than those reported for a different anatomical region. In particular, the calculated errors were found to be dependent on the individual anatomy and on the skeletal pose. Since different biomechanical applications may require different discretization levels, care is suggested in identifying the number of muscle lines of action to be used in musculoskeletal models
The effects of irradiation and EtO-treatment on ultrahigh molecular weight polyethylene acetabular cups following accelerated aging: degradation of mechanical properties and morphology changes during hip simulator tests.
No full textThe present study was aimed at investigating the effects of the sterilization method and accelerated aging on the wear and morphology of ultrahigh molecular weight polyethylene. In a first test, gamma- and EtO-sterilized acetabular cups were tested in a hip joint simulator for two million cycles. After the test, the cups underwent an accelerated aging treatment (80 °C, 4 weeks in air furnace) and were newly tested for another three million cycles. Wear was evaluated by gravimetric measurements, morphology by micro-Raman spectroscopy.
During the first test, the EtO-sterilized cups underwent a significantly higher wear than the gamma-sterilized ones (62 and 30 mg/million cycles, respectively). No significant crystallinity changes were observed. Upon accelerated aging, the crystallinity increase of the gamma-sterilized cups was more pronounced than for the EtO-sterilized cups, due to chain scission and oxygen incorporation. In the second test, the wear rate of EtO-sterilized cups decreased to 38 mg/million cycles, while for gamma-irradiated cups it increased to 84 mg/million cycles. At the same time, the latter cups underwent significant increases in temperature and crystallinity, due to the higher friction. For the EtO-sterilized cups a significant decrease in crystallinity was observed, due to the occurrence of an orthorhombic → monoclinic phase transformation
The human proximal femur behaves linearly elastic up to failure under physiological loading conditions
Full text linkIt has not been demonstrated whether the human proximal femur behaves linearly elastic when loaded to failure. In the present study we tested to failure 12 cadaveric femurs. Strain was measured (at 5000 Hz) on the bone surface with triaxial strain gages (up to 18 on each femur). High-speed videos (up to 18,000 frames/s) were taken during the destructive test. To assess the effect of tissue preservation, both fresh-frozen and formalin-fixed specimens were tested. Tests were carried out at two strain-rates covering the physiological range experienced during daily motor tasks. All specimens were broken in only two pieces, with a single fracture surface. The high-speed videos showed that failure occurred as a single abrupt event in less than 0.25 ms. In all specimens, fracture started on the lateral side of the neck (tensile stress). The fractured specimens did not show any sign of permanent deformation. The force– displacement curves were highly linear (R2 4 0.98) up to 99% of the fracture force. When the last 1% of the force–displacement curve was included, linearity slightly decreased (minimum R2 1⁄4 0.96). Similarly, all force–strain curves were highly linear (R240.98 up to 99% of the fracture force). The slope of the first part of the force–displacement curve (up to 70% fracture force) differed from the last part of the curve (from 70% to 100% of the fracture force) by less than 17%. Such a difference was comparable to the fluctuations observed between different parts of the curve. Therefore, it can be concluded that the proximal femur has a linear-elastic behavior up to fracture, for physiological strain-rates
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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