Thermal damage done to bone by burring and sawing with and without irrigation in knee arthroplasty

Heat from bone resecting tools used in knee surgery can induce thermal osteonecrosis, potentially causing aseptic implant loosening. This study compared oscillating saws to burrs in terms of temperature generation and histologic damage. Use of irrigation to reduce bone temperature was also investigated. Temperatures were recorded during sawing and burring with or without irrigation (uncooled or cooled). Histologic analyses were then carried out. Differences between groups were tested statistically (α = 0.05). On average, burring produced higher temperatures than sawing (P < .001). When uncooled irrigation was used, bone temperatures were significantly lower in sawed bone than in burred bone (P < .001). Irrigation lowered temperatures and thermal damage depths and increased osteocyte viability (P < .001). These results suggest that irrigating bone during resection could prevent osteonecrosis onset

Confined compression of collagen hydrogels

Reconstituted collagen hydrogels are often used for in vitro studies of cell-matrix interaction and as scaffolds for tissue engineering. Understanding the mechanical and transport behaviours of collagen hydrogels is therefore extremely important, albeit difficult due to their very high water content (typically > 99.5%). In the present study the mechanical behaviour of collagen hydrogels in confined compression was investigated using biphasic theory (J. Biomech. Eng. 102 (1980) 73), to ascertain whether the technique is sufficiently sensitive to determine differences in the characteristics of hydrogels of between 0.2% and 0.4% collagen. Peak stress, equilibrium stress, aggregate modulus and hydraulic permeability of the hydrogels exhibited sensitivity to collagen content, demonstrating that the technique is clearly able to discriminate between hydrogels with small differences in collagen content and may also be sensitive to factors that affect matrix remodelling. The results also offer additional insight into the deformation-dependent permeability of collagen hydrogels. This study suggests that confined compression, together with biphasic theory, is a suitable technique for assessing the mechanical properties of collagen hydrogels

Sensitivity analysis of permeability parameters of bovine nucleus pulposus obtained through inverse fitting of the nonlinear biphasic equation : effect of sampling strategy

Permeability controls the fluid flow into and out of soft tissue, and plays an important role in maintaining the health status of such tissue. Accurate determination of the parameters that define permeability is important for the interpretation of models that incorporate such processes. This paper describes the determination of strain-dependent permeability parameters from the nonlinear biphasic equation from experimental data of different sampling frequencies using the Nelder–Mead simplex method. The ability of this method to determine the global optimum was assessed by constructing the whole manifold arising from possible parameter combinations. Many parameter combinations yielded similar fits with the Nelder–Mead algorithm able to identify the global maximum within the resolution of the manifold. Furthermore, the sampling strategy affected the optimum values of the permeability parameters. Therefore, permeability parameter estimations arising from inverse methods should be utilised with the knowledge that they come with large confidence intervals

Delivery of an injectable biomaterial to the striatum- a computational analysis

The delivery of a cell-embedded hydrogel to the striatum is a promising strategy for Parkinson’s disease.In this study, a computational model of the intrastriatal injection was used to analyze the delivery process

Flow simulation of a natural polymer in a syringe-needle delivery device

Neurodegenerative diseases, such as Parkinson's disease, affect a large num- ber of the erderly population and still remain untreated. In recent years, cell therapy has emerged as a promising therapeutic strategy. To increase cell viability, biomaterials are of- ten used as scaffolds and facilitate cell deposition, through injection, to the site of interest. However, fluid forces acting on the cells during injection may lead to their disruption or death. This study aims to develop a novel device for the delivery of a cell-embedded, in situ forming, collagen hydrogel. A preliminary simulation study on constricted channels rep- resenting the syringe was performed to gain insight into the effect of needle diameter and syringe geometry. Straight needles emanating co-axially from syringes of various geome- tries were computationally modelled in the two-dimensional space, using OpenFOAMⓇ. The natural collagen solution was modelled as a continuum medium, without cells, and the flow was assumed incompressible, with non-Newtonian fluid constitutive behaviour. The effects of needle diameter and syringe geometry on velocity and shear stresses were examined. The results highlight the importance of geometric characteristics on the design of new cell delivery devices. If cells pass from the syringe barrel to the needle, the pressure drop and the increased velocity could damage them. This is more likely to occur using higher Gauge needles. Further analysis is required including simulations of cells during injection and analysis of their deformation

Tensile properties of the transverse carpal ligament and carpal tunnel complex

A new sophisticated method that uses video analysis techniques together with a Maillon Rapide Delta to determine the tensile properties of the transverse carpal ligament–carpal tunnel complex has been developed. Six embalmed cadaveric specimens amputated at the mid-forearm and aged (mean (SD)): 82 (6.29) years were tested. The six hands were from three males (four hands) and one female (two hands). Using trigonometry and geometry the elongation and strain of the transverse carpal ligament and carpal arch were calculated. The cross-sectional area of the transverse carpal ligament was determined. Tensile properties of the transverse carpal ligament–carpal tunnel complex and Load–Displacement data were also obtained. Descriptive statistics, one-way ANOVA together with a post-hoc analysis (Tukey) and t-tests were incorporated. A transverse carpal ligament–carpal tunnel complex novel testing method has been developed. The results suggest that there were no significant differences between the original transverse carpal ligament width and transverse carpal ligament at peak elongation (P= 0.108). There were significant differences between the original carpal arch width and carpal arch width at peak elongation (P=0.002). The transverse carpal ligament failed either at the mid-substance or at their bony attachments. At maximum deformation the peak load and maximum transverse carpal ligament displacements ranged from 285.74 N to 1369.66 N and 7.09 mm to 18.55 mm respectively. The transverse carpal ligament cross-sectional area mean (SD) was 27.21 (3.41)mm2. Using this method the results provide useful biomechanical information and data about the tensile properties of the transverse carpal ligament–carpal tunnel complex

Non-invasive computer-assisted measurement of knee alignment

The quantification of knee alignment is a routine part of orthopaedic practice and is important for monitoring disease progression, planning interventional strategies, and follow-up of patients. Currently available technologies such as radiographic measurements have a number of drawbacks. The aim of this study was to validate a potentially improved technique for measuring knee alignment under different conditions. An image-free navigation system was adapted for non-invasive use through the development of external infrared tracker mountings. Stability was assessed by comparing the variance (F-test) of repeated mechanical femoro-tibial (MFT) angle measurements for a volunteer and a leg model. MFT angles were then measured supine, standing and with varus-valgus stress in asymptomatic volunteers who each underwent two separate registrations and repeated measurements for each condition. The mean difference and 95% limits of agreement were used to assess intra-registration and inter-registration repeatability. For multiple registrations the range of measurements for the external mountings was 1° larger than for the rigid model with statistically similar variance (p=0.34). Thirty volunteers were assessed (19 males, 11 females) with a mean age of 41 years (range: 20-65) and a mean BMI of 26 (range: 19-34). For intra-registration repeatability, consecutive coronal alignment readings agreed to almost ±1°, with up to ±0.5° loss of repeatability for coronal alignment measured before and after stress maneuvers, and a ±0.2° loss following stance trials. Sagittal alignment measurements were less repeatable overall by an approximate factor of two. Inter-registration agreement limits for coronal and sagittal supine MFT angles were ±1.6° and ±2.3°, respectively. Varus and valgus stress measurements agreed to within ±1.3° and ±1.1°, respectively. Agreement limits for standing MFT angles were ±2.9° (coronal) and ±5.0° (sagittal), which may have reflected a variation in stance between measurements. The system provided repeatable, real-time measurements of coronal and sagittal knee alignment under a number of dynamic, real-time conditions, offering a potential alternative to radiographs

The assessment of instability in the osteoarthritic knee

• Patient-reported instability is a common complaint amongst those with knee arthritis • Much research has examined the assessment of self-reported instability in the knee, however no definitive quantitative measure of instability has been developed • This review focuses on the current literature investigating the nature of self-reported instability in the arthritic knee, and discusses the possibilities of further investigatio

Paradoxical size effects in composite laminates and other heterogeneous materials

Size effects in which there is an apparent increase in stiffness with reducing size scale are forecast in those heterogeneous materials that have constitutive behaviour described by more generalized continuum theories such as couple stress, micropolar or micromorphic elasticity. This short paper considers possibly the simplest heterogeneous material exhibiting such size effects, a two phase composite laminate consisting of alternating layers of stiff and compliant material, and shows that when loaded in bending the nature of the size effect actually depends on the composition of the sample surfaces. The laminate material is apparently capable of exhibiting a diversity of size effects some of which are compatible with the predictions of generalized continuum theories while others are contradictory. Another heterogeneous material consisting of a periodic or regular array of voids within a classically elastic matrix is then considered. Detailed finite element analysis shows that the diversity of size effects encountered in the laminate material may also be observed in this more representative material thereby providing some insight into the contradictory size effects that have sometimes been reported elsewhere in the literature

Towards an effective, needle-based delivery device for Parkinson's disease : a simulation study on the impact of needle diameter

Recently, several therapies have emerged for Parkinson’s disease, a challenging neurodegenerative disorder. However, clinical translation is restricted, partially due to limitations in delivering therapeutics to the Central Nervous System (CNS)which cannot be reached by systemic administration. An alternative method, that bypasses the blood brain barrier and offers high-concentrated deposition in the diseased region, is intrastriatal delivery of a cell-loaded in situ forming collagen hydrogel. However, this strategy has disadvantages, including neuroimmune response and haemorrhage. To minimize these responses, an optimised medical device should be designed. Of main consideration is the volume dispensed and the needle dimensions. Current approaches use 18-20-Gaugediameter needles and multiple cranial penetrations [1]. Additionally, fluid forces acting on cells may lead to cell disruption and death [2]. This study aims to develop a novel device for the effective delivery of a cell-loaded in situ forming collagen hydrogel to the CNS. A simulation study on constricted channels representing the needle was performed to gain insight into the optimal needle diameter