Finding Comfortable Routes for Ambulance Transfers of Newborn Infants.

Early inter-hospital ambulance transport of premature babies is associated with more severe brain injury. The mechanism is unclear, but they are exposed to excessive noise and vibration. Smart-routing may help minimise these exposure levels and potentially improve outcomes.An app for Android smartphones was developed to collect vibration, noise and location data during ambulance journeys. Four smartphones, with the app installed, were provided to the local neonatal transport group to attach to their incubator trolleys. An example of route comparison was performed on the roads used between Nottingham City Hospital (NCH) and Leicester Royal Infirmary (LRI).Almost 1,700 journeys were recorded over the space of a year. 39 of these journeys travelled from NCH to LRI, comprising of 9 different routes. Analysis was performed on all recorded data which travelled along each road. For routes from NCH to LRI, the route with least vibration was also the quickest. Noise levels, however, were found to increase with vehicle speed. Ambulance drivers in the study did not tend to take the quickest, smoothest or quietest route.Android smartphones are a practical method of gathering information about the in-ambulance environment. Routes were found to vary in vibration, noise and speed, suggesting these could be minimised. The next step is to combine recorded and clinical data to try and define an ideal neonatal comfort metric which can then be fed into the routing. Roll-out of the app around the UK is also planned.Clinical relevance-Transferring preterm neonatal infants to specialist units lead to worse outcomes. By reducing the levels of vibration and noise the infants are exposed to during transport, we hope to improve outcomes.

Finite element investigation of the effect of a bifid arch on loading of the vertebral isthmus.

BACKGROUND: The biomechanical effect of a bifid arch as seen in spina bifida occulta and following a midline laminectomy is poorly understood. PURPOSE: To test the hypothesis that fatigue failure limits will be exceeded in the case of a bifid arch, but not in the intact case, when the segment is subjected to complex loading corresponding to normal sporting activities. STUDY DESIGN: Finite element analysis. METHODS: Finite element model of an intact L4-S1 human lumbar motion segment including ligaments was used. A section of the L5 vertebral arch and spinous process was removed to create the model with a midline defect. The models were loaded axially to 1 kN and then combined with axial rotation of 3°. Bilateral stresses, alternating stresses, and shear fatigue failure on both models were assessed and compared. RESULTS: Under 1 kN axial load, the von Mises stresses observed in midline defect case and in the intact case were very similar (differences <5 MPa) having a maximum at the ventral end of the isthmus that decreases monotonically to the dorsal end. However, under 1 kN axial load and rotation, the maximum von Mises stresses observed in the ipsilateral L5 isthmus in the midline defect case (31 MPa) was much higher than the intact case (24.2 MPa), indicating a lack of load sharing across the vertebral arch in the midline defect case. When assessing the equivalent alternating shear stress amplitude, this was found to be 22.6 MPa for the midline defect case and 13.6 MPa for the intact case. From this, it is estimated that shear fatigue failure will occur in less than 70,000 cycles, under repetitive axial load and rotation conditions in the midline defect case, whereas for the intact case, fatigue failure will occur only after more than 10 million cycles. CONCLUSIONS: A bifid arch predisposes the isthmus to early fatigue fracture by generating increased stresses across the inferior isthmus of the inferior articular process, specifically in combined axial rotation and anteroposterior shear.

2009 ISSLS Prize Winner: What influence does sustained mechanical load have on diffusion in the human intervertebral disc?: an in vivo study using serial postcontrast magnetic resonance imaging.

STUDY DESIGN: An in vivo study of the effects of mechanical loading on transport of small solutes into normal human lumbar intervertebral discs (IVD) using serial postcontrast magnetic resonance imaging (MRI). OBJECTIVE: To investigate the influence of a sustained mechanical load on diffusion of small solutes in and out of the normal IVD. SUMMARY OF BACKGROUND DATA: Diffusion is an important source of disc nutrition and the in vivo effects of load on diffusion in human IVD remains unknown. METHODS: Forty normal lumbar discs (on MRI) in 8 healthy volunteers were subjected to serial post contrast (Gadoteridol) 3 Tesla MRI in 2 phases. In phase 1 (control), volunteers were scanned at different time points--precontrast and 1.5, 3, 4.5, 6, and 7.5 hours postcontrast injection. In phase 2, 1 month later, the same volunteers were subjected to sustained supine loading for 4.5 hours. MRI scans were performed precontrast (preload) and postcontrast (postloading) at 1.5, 3, and 4.5 hours. Their spines were then unloaded and recovery scans performed at 6 and 7.5 hours postcontrast. In house software was used to analyze images. RESULTS: Repeated-measures ANOVA and pairwise comparisons at different time points in the central region of the loaded disc (LD) compared to the unloaded discs (UD) revealed significantly lower signal intensity ratios (P1.5h:P3h:P4.5h<0.001:<0.001:<0.002) indicating reduction in transport rates for the LDs. Signal intensity ratios continued to rise in LD for 3 hours into recovery phase,whereas UD at the same time point showed a decrease (mean +/- SD = 0.08 +/- 0.08 vs. -0.21 +/- 0.03). CONCLUSION: Sustained supine creep loading (50% body weight) for 4.5 hours retards transport of small solutes into the center of human IVD and it required 3 hours of accelerated diffusion in recovery state for LD to catch-up with diffusion in UD. The study supports the theory that sustained mechanical loading impairs diffusion of nutrients entering the disc and quite possibly accelerates disc degeneration.

The internal mechanical functioning of intervertebral discs and articular cartilage, and its relevance to matrix biology.

Degeneration of intervertebral discs and articular cartilage can cause pain and disability. Risk factors include genetic inheritance and age, but mechanical loading also is important. Its influence has been investigated using miniature pressure transducers to measure the distribution of compressive stress (force per unit area) within loaded tissue. The technique quantifies stress concentrations, and detects regions that behave in a fluid-like manner. Intervertebral discs demonstrate a central fluid-like region which normally extends beyond the anatomical nucleus pulposus so that the whole disc functions like a "water bed". With increasing age, the fluid region shrinks and pressure within it falls. Stress concentrations appear in the surrounding anulus fibrosus, with location depending on posture. Stress concentrations become large in degenerated discs, and are intensified by sustained loading or injury. Articular cartilage never exhibits an internal fluid pressure: stress gradients and concentrations normally occur within it, and are intensified by sustained loading. Excessive matrix stresses can cause pain and progressive damage. They also inhibit matrix synthesis and stimulate production of matrix-degrading enzymes. In this way, injury to chondroid tissues can initiate a 'vicious circle' of abnormal matrix stresses, abnormal metabolism, weakened matrix, and further injury, which explains many features of their degeneration.

High pressures and asymmetrical stresses in the scoliotic disc in the absence of muscle loading.

BACKGROUND: Loads acting on scoliotic spines are thought to be asymmetric and involved in progression of the scoliotic deformity; abnormal loading patterns lead to changes in bone and disc cell activity and hence to vertebral body and disc wedging. At present however there are no direct measurements of intradiscal stresses or pressures in scoliotic spines. The aim of this study was to obtain quantitative measurements of the intradiscal stress environment in scoliotic intervertebral discs and to determine if loads acting across the scoliotic spine are asymmetric. We performed in vivo measurements of stresses across the intervertebral disc in patients with scoliosis, both parallel (termed horizontal) and perpendicular (termed vertical) to the end plate, using a side mounted pressure transducer (stress profilometry) METHODS: Stress profilometry was used to measure horizontal and vertical stresses at 5 mm intervals across 25 intervertebral discs of 7 scoliotic patients during anterior reconstructive surgery. A state of hydrostatic pressure was defined by identical horizontal and vertical stresses for at least two consecutive readings. Results were compared with similar stress profiles measured during surgery across 10 discs of 4 spines with no lateral curvature and with data from the literature. RESULTS: Profiles across scoliotic discs were very different from those of normal, young, healthy discs of equivalent age previously presented in the literature. Hydrostatic pressure regions were only seen in 14/25 discs, extended only over a short distance. Non-scoliotic discs of equivalent age would be expected to show large centrally placed hydrostatic nuclear regions in all discs. Mean pressures were significantly greater (0.25 MPa) than those measured in other anaesthetised patients (<0.07 MPa). A stress peak was seen in the concave annulus in 13/25 discs. Stresses in the concave annulus were greater than in the convex annulus indicating asymmetric loading in these anaesthetised, recumbent patients. CONCLUSION: Intradiscal pressures and stresses in scoliotic discs are abnormal, asymmetrical and high in magnitude even in the absence of significant applied muscle loading. The origin of these abnormal stresses is unclear.

The objectives for the mechanical evaluation of spinal instrumentation have changed.

The objectives for the mechanical evaluation of spinal implants have changed because many modern devices are designed to modify the mechanics of the disc rather than to simply fix the segment. This means that a biomechanical objective must be decided, a priori, for a particular device. It is then relatively straightforward to design a biomechanical evaluation protocol that can either test whether this objective is fulfilled, or optimise the device in the context of the objective. Because 'soft stabilisation' systems are soft, their performance is affected by the magnitude of the loading sustained by the bridged segment. This means that is vital to reproduce a realistic loading regime for the biomechanical evaluation, if its results are to be relevant to a clinical problem. Similarly, the condition of the segment in terms of disc degeneration, facet joint condition, etc. affect the mechanical performance of the segment and must be relevant to the performance objectives set for the device. Loading protocols for testing short and long segments are discussed. Since the aim of many spinal devices is to modify the loading of the intervertebral disc, it is important to quantify their effect in terms of how both the internal loads and deformations are changed. A number of different technologies for quantifying both loads and deformations in intact discs are described and discussed.

The angular distribution of vertebral trabeculae in modern humans, chimpanzees and the Kebara 2 Neanderthal.

Bone is known to remodel to optimize its structure according to its mechanical environment. In particular trabecular arcades are thought to align with the orientations of components of principal strain. This paper presents the application of a novel method for quantifying trabecular orientation to test the hypothesis that hominoid posture and locomotion are reflected in trabecular architecture. Lateral radiographs were taken of vertebrae from the entire thoracolumbar spines of eight modern humans, seven Pan troglodytes and one Neanderthal. The radiographs were digitized and a square region of interest located at the centre of each vertebral body selected. Fourier transforms of the regions of interest were performed and the relative magnitude of the transform in each of 16 angular segments calculated. The simple indices of external vertebral body morphology, wedge angle and aspect ratio, were also calculated from the radiographs. All three species exhibit the same pattern, with the majority of trabeculae oriented either axially or dorsoventrally. This suggests that vertebral mechanical loading is similar in chimpanzees and humans, despite their apparent postural and locomotor differences. Significant differences between the magnitudes of the Fourier transform in the 78.75 degrees and 135 degrees orientations of chimpanzee and human vertebrae were observed in all but the upper thoracic spine. As the magnitudes at these orientations in the Neanderthal correspond more closely to that in the human and the orientational features were unrelated to the external vertebral morphology, the difference between the two magnitudes may well prove to be a useful parameter in future phylogenetic analysis. Modern human spines were found to show a greater variation in the proportions of axial and dorsoventral trabeculae with spinal level than chimpanzees, with the greatest differences observed in the upper thoracic spine and thoracolumbar junction, suggesting an association with postural spinal curves.