Reproducibility of techniques using Archimedes' principle in measuring cancellous bone volume by L. Zou, R. D. Bloebaum and K. N. Bachus.
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Animals↗
Biomedical subjects
R M Aspden
Publications and source records attributed to R M Aspden.
Significant antenatal factors in the development of lumbar spinal stenosis.
STUDY DESIGN: Adverse factors during pregnancy may permanently stunt the growth of the spinal canal. Subsequently, even in an optimal environment the canal cannot catch up in growth with the trunk and long bones because of its early maturation. The degree of retardation in canal size depends on the severity and timing of the adverse effect. The catch-up growth of the long bones mask the narrow canal, because the latter does not have growth potential, resulting in an adult of sufficient height and good proportions, but with a canal at risk for stenosis. OBJECTIVES: To investigate the influence of the antenatal environment on the growth of the lumber spinal canal. SUMMARY OF BACKGROUND DATA: To date, little is known about the effects of an adverse environment on the growth of the spinal canal, and no data have been reported on antenatal influencing factors. METHODS: Lumbar magnetic resonance imaging scans from 58 patients were examined. Dimensions of the central spinal canals were measured by computerized image analysis and compared with the subjects' obstetric data from their mothers' pregnancies. RESULTS: The L3 canal was found to be the most sensitive to the influence of the examined factors. Gestational age was the most significant factor; if short, it resulted in small adult canal. Small placental weight, greater maternal age, primiparity, low socioeconomic class, and low birth weight were also found to be significant in affecting the growth of the canal. CONCLUSIONS: An adverse antenatal environment does have a permanent, retarding effect on the growth of the lumbar spinal canal.
Adolescent↗
Matrix loss and synthesis following a single impact load on articular cartilage in vitro.
Articular cartilage biopsies were subjected to a single impact load and the metabolic response of the chondrocytes investigated using radiolabelled precursors for protein ([3H]leucine) and glycosaminoglycan ([35S]sulfate). The severity of the impact was controlled by using different masses and drop heights in a purpose built drop tower. Loss of matrix components was studied by prelabelling prior to loading, the possible repair response by pulse labelling at defined intervals after loading. There was an increase in the loss of both labels from the tissue with increasing severity of impact though the patterns of loss were different. Only 25%-40% of the sulfate was lost over a two week period and the loss increased with the severity of impact. This contrasted with 60% of the leucine being lost over the same period independently of loading. In addition to the loss of synthetic activity caused by cell death, there was a suppression of incorporation immediately following loading. This eventually recovered and increased above control values but the recovery time appeared to depend on the severity of the impact. These results provide preliminary evidence for a repair response.
Animals↗
An in vitro study of the biomechanical effects of flexible stabilization on the lumbar spine.
STUDY DESIGN: Lumbar motion segments were tested in vitro to examine biomechanical changes after posterior fixation by a flexible device. OBJECTIVES: To assess changes in load distribution and conformation of vertebral structures after a flexible stabilization. This should provide the foundations for a scientific understanding of the immediate effects of this surgical procedure. METHODS: Hooks were placed over the proximal spinous process and the distal laminas of a motion segment and connected by a polyester braid. Tension applied to the braid then generated a compression of the posterior elements. The force between the articular facets, the displacement of the posterior anulus fibrosus of the intervertebral disc, and the change in the relative position of the adjacent vertebrae were measured as the applied tension was increased. RESULTS: Facet joint force, disc bulge, and vertebral angulation increased with applied tension until a position of "locking" was achieved, apparently when the bony margin of the superior half of the facet joint contacted the inferior pars interarticularis. A tension of between 50 to 100 N in the braid was required for this. Facet joint force was less than 40% of this, and disc bulge was only 0.15 mm. The extension of the motion segment was between 2 degrees and 8 degrees. CONCLUSIONS: The results suggest that if such a system is applied surgically, stabilization is produced by compaction of the bony margins of the facet joints. Only a relatively small proportion of the posteriorly applied load is carried by the facet joints themselves, and little angulatory change is expected with minimal disc bulge.
Aged↗
Material properties of bone from the femoral neck and calcar femorale of patients with osteoporosis or osteoarthritis.
Patients with osteoarthritis (OA) rarely fracture the neck of the femur whereas this is common in patients with osteoporosis (OP). The reasons for this are not clear. In this study, cores of trabecular bone and thin slices of bone from the calcar were obtained from the femoral neck of patients with OA or OP following hip arthroplasty and a normal group post mortem. The mechanical properties, densities and material composition were measured. The aim was to determine whether differences in these properties could explain why osteoarthritic patients did not suffer from fractured neck of femur. No difference was found in the density or stiffness of the calcar between the groups, though there appeared to be a small increase in mineralization in the OA bone compared with the OP. However, there was a 72% increase in the volume of trabecular bone in the OA group compared with a loss of about 20% in the OP group. This increased apparent density of the OA trabecular bone resulted in a greater stiffness, yield strength and energy absorbed to yield, whereas the same properties of OP bone were not significantly lower than normal. These marked changes in the OA bone could result in a redistribution of stresses due to loads caused by falling, thereby absorbing the energy of impact and preventing the formation of a fracture surface.
Aged↗
Mechanical and material properties of the subchondral bone plate from the femoral head of patients with osteoarthritis or osteoporosis.
OBJECTIVE: To determine the material properties of the subchondral bone plate in patients with osteoarthritis or osteoporosis. METHODS: Femoral heads were obtained after surgical removal from age and sex matched groups of patients with either osteoporosis (OP), after a fractured neck of femur, or osteoarthritis (OA) and compared with a normal group. The mechanical stiffness, density, and composition of the subchondral bone plate from sites selected to represent areas of heavy, intermittent, and light loading were measured. RESULTS: Overall, OP bone was the least stiff and dense, followed by OA bone; normal bone was stiffer and more dense (p < 0.05). Though OP bone contained less mineral, the organic and water contents were increased in proportion suggesting no change in the relative amount of organic matrix. OA bone was also hypomineralised (p < 0.05) but had different organic and water fractions suggesting a defect in the matrix. Site variation of most properties was small, though across all the groups the superior region was significantly stiffer than the inferior. CONCLUSION: This study shows that subchondral bone plate is less stiff than normal in both OP and OA and so cannot, by itself, explain the preserving of the overlying cartilage in OP while aiding its destruction in OA. However, the subchondral bone plate is only one part of the bony structure of the femoral head and changes in the cancellous bone need to be considered. The generalised changes in bone composition found in patients with OA support the hypothesis that the disease could involve the bone in the primary pathogenesis.
Aged↗
Composition and mechanical properties of cancellous bone from the femoral head of patients with osteoporosis or osteoarthritis.
The material properties of cancellous bone from patients with osteoporosis (OP) or osteoarthritis (OA) were determined and compared with normal controls. Samples were selected from defined sites in human femoral heads which are subjected to different loads in vivo. Overall, OP bone had the lowest stiffness and OA the highest, and this same order was reflected in the apparent densities of the bone, with OA being the most dense and OP the least. Normal and OP bone were found to have very similar stiffness-density relationships and composition. However, OA bone differed significantly from normal. The stiffness of OA bone increased more slowly with apparent density and its material density was significantly reduced. These findings were due to an altered composition of the bone in which the mass fraction of mineral is 12% less than normal. There was also greater site variation of both apparent and material density, suggesting an altered sensitivity to applied load. These results support the concept that osteoporosis is a loss of normal bone. They also provide evidence for the hypothesis that osteoarthritis is, at least partly, a bone disease in which proliferation of defective bone results in an increase in bone stiffness.
Biomechanical Phenomena↗
Euler buckling as a model for the curvature and flexion of the human lumbar spine.
The upright thoraco-lumbar spine resembles an Euler column buckled in the second mode (n = 2) when viewed in the sagittal plane. An advantage of n = 2 buckling is that further load can be carried without adopting a stooped posture. Flexion of the spine is considered as the first quarter cycle of an Euler pendulum. This is possible if the antagonistic muscles which control movement increase the bending stiffness, EI, to a value of about 15 N m2. If the muscles are incapable of increasing EI sufficiently to support the weight of the body, or any excess load, the spine will be dynamically unstable. This conclusion is consistent with a static model which considers spinal instability as 'loss of stiffness' and a dynamic model which suggests that it arises from ineffective adaptive control. The flexed spine resembles an n = 1 buckled column.
Humans↗
A comparison of methods for measuring trunk list. A simple plumbline is the best.
STUDY DESIGN: Trunk list was measured using three different techniques to compare accuracy, precision, and ease of use. OBJECTIVE: To obtain a reproducible technique for further studies of the nature, cause, and clinical relevance of trunk list. SUMMARY OF BACKGROUND DATA: Gravity-induced trunk list is a clinical sign that is frequently observed in patients with low back pain and has been associated with intervertebral disc lesions. METHODS: Patients with trunk list participated in a comparison of three techniques to determine list magnitude and direction. Paired measurements of trunk list were obtained from each patient using three techniques: a plumbline, a projected shadow, and the 3SPACE Isotrak (McDonnell Douglas Electronics Company, Colchester, VT). In addition, intra- and interobserver reliability of list measurement was assessed by comparison of paired measurements by each of two observers. RESULTS: List measurements assessed by the plumbline and the projected shadow techniques were not significantly different, but the Isotrak produced data that differed significantly (P < 0.05) from both of these techniques. Comparison of intra- and interobserver repeatability of list measurement using the plumbline technique indicated no significant difference between repeated measures by each observer or between two observers. CONCLUSIONS: A plumbline is the most useful instrument for measuring static trunk list, but its limitations and the need for standardization of measurement technique must be recognized.
Adult↗
Matrix damage and chondrocyte viability following a single impact load on articular cartilage.
An impact load was applied to full-depth circular samples of articular cartilage in vitro and the effects of impact energy and velocity on matrix integrity and chondrocyte viability were studied. Following a severe impact, calculated to correspond to the energy density over the cartilage surface that might be expected in a man jumping off a 1-m-high wall, the tissue was grossly disrupted. It became elliptical, fissured, and flattened. Cartilage samples remaining attached to the underlying bone showed less damage at similar drop masses and heights. Chondrocyte viability was found to decrease linearly with increasing impact energy. Cartilage biopsies maintained in culture for up to 15 days following impact gained mass over the first 3 days which they did not subsequently lose. The gain in mass increased with the severity of impact and was due to an increased hydration of the tissue. Scanning electron microscopy and light microscopy showed fissures penetrating the tissue but which were never found to pass through the full depth. They were commonly oriented at about 45 degrees to the plane of the surface and gave the appearance of being deflected parallel to the surface on reaching the transition zone. This produced a "delaminating" effect where the surface zone was separating from the deep zone.
Animals↗
Stiffening effects of cortical bone on vertebral cancellous bone in situ.
STUDY DESIGN: This study tested a theory about vertebral cancellous bone stiffness by performing experimental tests and comparing the results with the theoretical predictions. OBJECTIVES: To test experimentally a theoretical prediction that vertebral cancellous bone appears stiffer than would be expected from isolated tests because of the constraining effects of the cortical bone, to measure the magnitude of this strengthening effect and its dependency on tissue composition and density. SUMMARY OF BACKGROUND DATA: Vertebral bodies are composed mainly of cancellous bone surrounded by a thin shell of much stronger cortical bone. Little is known of the ways in which these two materials function synergistically to produce strong but light structures and why sometimes extensive damage to the cancellous bone has apparently little outward effect on vertebral body strength. METHODS: Cancellous bone from 45 lumbar vertebrae from a homogeneous group of pigs was tested in compression both in situ in the vertebral body and as an excised cylinder. The density and composition of the bone were then measured and correlation tested with both of the stiffness measurements. RESULTS: The cancellous bone in situ appears much stiffer than when isolated by a factor of about 4 (range, 1.6-12). No correlation was found between stiffness, either in situ or in isolation, and density, although density is predicted entirely by the volume fractions of water, organic, and mineral phases. CONCLUSIONS: Combining low density cancellous bone with stiffer, more dense cortical bone leads to a lightweight structure that is much stronger than might be expected from the isolated properties of its components.
Animals↗
Trefoil configuration and developmental stenosis of the lumbar vertebral canal.
The midsagittal and interpedicular diameters and the trefoil shape of lumbar vertebrae of known age at death were measured in skeletons from a population aged between 1 and 70 years. All the trefoil configurations were at L5 with the exception of one at L4. The overall prevalence was 25%, but this shape was not generally apparent until adulthood. The midsagittal diameter in the trefoil canals was found to be significantly smaller than that in the unaffected canals. This did not change significantly after six years of age indicating that the cause of the trefoil configuration is probably present early in life. The trefoil shape was no more common in the spines of the elderly subjects. Our findings indicate that the trefoil configuration of the lumbar vertebral canal has a developmental origin and is not a consequence of degenerative processes.
Adult↗
The growth of the lumbar vertebral canal.
STUDY DESIGN: This study examines the growth and development of the lumbar spinal canal with emphasis on early life. OBJECTIVE: Changes in dimensions of the canal were investigated throughout life. SUMMARY OF BACKGROUND DATA: Seven hundred and fifteen lumbar vertebrae were examined from the Spitalfield Collection of Skeletons at the Natural History Museum, London. METHODS: Unmagnified silhouette pictures were taken of the canals with a specially designed photographic box. Computerized image analysis provided the accurate measurements. RESULTS: Regarding the midsagittal diameter and the cross-sectional area, the cranial four lumbar vertebrae were already fully matured in infants. At L5 there was significant increase up to 4 years of age when the midsagittal diameter was even larger than in the adult. The interpedicular diameter significantly increased at L1 until 10 years of age, at the other levels until adulthood, as did the perimeter at L4 and L5 until 14 years of age. The shape of the canal was assessed by measuring the circularity, the 'trefoilness' and the situation of the centroid. The first measurement significantly decreased with age, the trefoilness increased until adulthood, and the centroid of the canal approached the vertebral body. In spines with spina bifida occulta, the lumbar canal was significantly larger proximal to the lesion than in the unaffected spines. CONCLUSION: The lumbar spinal canal exhausts its growth potential by infancy as regards the midsagittal diameter and the cross-sectional area. Thus, in the case of delayed development, it is not capable of catch-up growth.
Adolescent↗
Fibre reinforcing by collagen in cartilage and soft connective tissues.
Mechanical support in animals is performed by connective tissues. The soft tissues consist of collagen fibres embedded in a highly hydrated proteoglycan gel. By considering them as fibrous composite materials, a unifying theme can be found to explain their mechanical behaviour in terms of their structure and composition. Interactions between fibres and matrix are essential to their functioning in this way. Calculations are made of the maximum stress transfer per D-period required to enable collagen fibres of a given axial ratio to provide effective reinforcing. Weak non-specific interactions are shown to be sufficient. A mechanical function is proposed for type X collagen in the epiphyseal growth plate on the basis that it modifies and supplements the properties of the type II fibrils. This provides extra reinforcing and, hence, a greater stiffness to the cartilage to compensate for the reduced amount of extracellular matrix.
Animals↗
Collagen organization in the crural interosseous membrane and its relationship to fibular osteotomy.
The organization of collagen fibres in the crural interosseous membrane was measured using X-ray diffraction. The fibres were found to be highly aligned and steeply angled in a distal direction from tibia to fibula with a mean angle of 13 degrees. This organization will lead to a very stiff, ligament-like structure which will transmit forces to the tibia generated by the muscles attached to the fibula. It also suggests an optimum site for a fibular osteotomy about 4 cm distal to the tibial fracture site.
Aged↗
Nerve traction during correction of knee flexion deformity. A case report and calculation.
We report the case of a child with cerebral palsy and spastic diplegia treated for bilateral fixed flexion of the knee by bilateral hamstring lengthening. An attempt to straighten the legs from 90 degrees to 20 degrees flexion damaged the sciatic nerve. There are no objective means of estimating how much deformity can be reduced safely. We present a method of calculating the extra strain in the sciatic nerve produced by reducing a flexion deformity. The result, combined with clinical judgement, provides guidelines for safe corrective surgery.
Cerebral Palsy↗
Breast compression: a preliminary study.
X-Ray mammography is the technique employed to image breast tumours; it is the gold standard for both diagnosis and screening. To increase the sensitivity of the test and to reduce the dose of X-radiation, breast compression is used. The effect of squeezing a simple model of a breast in which there is an idealized spherical tumour volume is investigated; the cases where the lesion has both a smaller, and a larger compressibility than the surrounding tissues are considered. Surface strain is computed as a function of the deformation of the lesion from its spherical shape. Evidence from earlier studies is adduced to show that when the lesion is malignant care should be exercised to avoid the possibility of disseminating cancer cells by the application of compressive forces.
Breast Neoplasms↗
Measurement of vertebral foraminal dimensions using three-dimensional computerized tomography.
The dimensions of lumbar intervertebral foramina were measured in cadaveric spines using three-dimensional computerized tomography. Six different image reconstruction protocols were used. The results were compared with measurements of the same foramina using calipers after dissection. All the three-dimensional computerized tomographic measurements underestimated the true foraminal dimensions. The best agreement, as well as the best images, were obtained using 4/3 slices and a reconstruction threshold of 300 Hounsfield Units. This method is not recommended for measurement of foraminal dimensions. However, there may be a use in assessment and planning surgical management.
Aged↗