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Design of an artificial knee was developed using computer 3-D modeling, the high flexion knee was obtained by using a multi-radii design pattern, The increase of final 20 degrees in flexion was obtained by increasing the condylar radii of curvature. The model of the high flexion knee was developed and one of the models was subjected to finite element modeling and analysis. The compositions of components in the artificial knee were, femoral component and the tibial component were metal, whereas the patellar component and the meniscal insert were made using polyethylene. The metal component used for the analysis in this study was Ti6Al4V and the polyethylene used was UHMWPE. Overall biomaterials chosen were: meniscus (UHMWPE, mass = 0.0183701 kg, volume = 1.97518e-005 m3), tibial component (Ti6Al4V, mass = 0.0584655 kg, volume = 1.32013e-005 m3), femoral component (Ti6Al4V, mass = 0.153122 kg, volume = 3.45742e-005 m3), total artificial assembly (mass = 0.229958 kg, volume = 6.75e-005m3). However, in this design the load had been taken to 10 times the body weight. The weight over single knee is only half the maximum load as the load is shared between the two knee joints. Following were the loading conditions, taking average body weight to be 70Kgs and taking extreme loading conditions of up to 10 times the body weight, i.e. 700Kgs on each of the leg performed the Finite Element Analysis (FEA) over the newly designed knee. The loading was done at an increment of 100 Kgs. The loading conditions and the meshing details for the analysis of the assembly were Jacobian check: 4 points, element size: 0.40735 cm, tolerance: 0.20367 cm, quality: high, number of elements: 80909, number of nodes: 126898. A maximum load of 600 Kgs is optimum for this model. The other components observed linear elastic behavior for the applied loads. Based on these results it was determined that the load bearing capacity of the model were well within the failure levels of the materials used for the analysis. A maximum load of 600 Kgs is optimum for this model. The other components observed linear elastic behavior for the applied loads. Based on these results it was determined that the load bearing capacity of the model were well within the failure levels of the materials used for the analysis. Conclusion drawn from this is that for the first time an innovative new design of an artificial knee joint to suite a segment of some religious population has been developed. This allows them to pray, bend in different positions and squat without too much difficulty.

A set of intervertebral pressure transducer (IVPT) and an intradiscal pressure transducer (IDPT) were developed to measure the pressures in the nucleus pulposus and around the annulus. Human lumbar spinal segments were loaded up to 2.0 kN and following parameters were recorded: applied compressive load as a function of time, intradiscal pressure as a function of time, intervertebral pressure as a function of time for anterior and lateral edges of the vertebra, strain as a function of time for anterior and lateral right and left sites of the vertebra, stress-relaxation of the complete segment as a function of time. All show very similar response to loading and stress-relaxation. However, annulus pressure did not respond to stress-relaxation. This was due to functional aspect of annulus.

Lumbar vertebrae are a heavily loaded component of human body. They are subjected to repetitive loading in daily activities. However, limited information on failure mechanism of lumbar vertebrae are available to date. Thus, the need to develop an analytical model to predict stress-fracture characteristics of vertebral body. A linear elastic fracture mechanics approach has been considered and a mathematical model has been proposed so that the predictions can be made more easily related to the occurrence of injury. Study reveals that for a person weighing 1334 N and lifting a weight of 345 kg during squat exercise causes a vertebral stress-fracture at 12 repetitive standing lifting. While same load at lowest position yields a stress-fracture at less than 3 lifting. Numerical study shows that for change of position from standing to lowest position resultant compressive force acting on spine increases by two times whereas the possibility of stress-fracture increases by five times. Similarly at dead lift exercise, lifting 325 kg from standing to lowest position increases resultant compressive forces on vertebrae by 2.5 times. However, stress-fracture ratio increases by six times. Study reveals that for a person weighing 800 N (height = 1.8 m) and lifting a weight of 900 N, vertebrae can be subjected to stress-fracture by three cyclic lifting. Rate of injury is dependent on flexion angle i.e. as flexion angle increases, so does rate of injury.Copyright © 2011 by ASME

An intradiscal pressure transducer (IDPT) and a set of intervertebral pressure transducer (IVPT) were developed to measure the pressures in the nucleus pulposus and around the annulus. Human lumbar spinal segments were loaded up to 2.0 kN and following parameters were recorded: applied compressive load as a function of time, intradiscal pressure as a function of time, intervertebral pressure as a function of time for anterior and lateral edges of the vertebra, strain as a function of time for anterior and lateral right and left sites of the vertebra, stress-relaxation of the complete segment as a function of time. All show very similar response to loading and stress-relaxation. However, annulus pressure did not respond to stress-relaxation. This was due to functional aspect of annulus.Copyright © 2010 by ASME

Low-back pain can affect almost anyone at any time. In the United States, 8–15 percent [Ranu, 1] of back injuries involve the spinal discs, which act as a cushion between each vertebra. When a human spinal disc slips or herniates, part or all of it bulges out from its usual setting between the vertebrae (Figure 1).

To gain further insight into the biomechanics of the human intervertebral disc and to determine a potential mechanism for causation and relief of symptoms related to a herniated disc, the pressure-volume relation was determined within the nucleus pulposus. Pressure was measured continuously within the nucleus pulposus in 17 intact lumbar discs from human cadavers by means of a miniature strain gauge at the tip of a size 4 French (1.3 mm) catheter inserted into the nucleus pulposus. The volume of the nucleus pulposus was increased at the slow, continuous rate of 0.034 ml/min by the pump regulated infusion of saline coloured with methylene blue. In 12 unloaded discs, nucleus pulposus pressure rose in a linear fashion (linear r = 0.96) from an initial mean pressure of 174 (SD 81) kPa. The mean rate of pressure rise was 327 (SD 109) kPa/ml volume increase. The peak pressure measured was 550 kPa; this was slightly higher than the capability of the transducer. Similar linear relations were obtained during infusion of saline into five vertically loaded discs fixed at the deformation produced by a 9.1 kg weight. The data define the pressure-volume relation within the disc and show that the nucleus pulposus, surrounded by the relatively inelastic annulus and the solid vertebral end plates, has the properties of a tight hydraulic space in which a large pressure rise will regularly result from a small increase in volume. Presumably the opposite is also true. The data may provide a biomechanical basis for the physiological variation in symptoms related to the disc, and for any benefits obtained from interventions designed to remove disc tissue.

A finite element model of a complete vertebra was formulated from a previously developed bilaterally symmetric model. This model was verified by comparing its results to those of the previous model and by ensuring that the output was bilaterally symmetric. The applied nodal loads were checked against experimentally measured pressures on the vertebral endplate. Simulations of complete and partial laminectomies on one side of a vertebra were performed. High tensile stresses occurred in the pedicle and in the region of the pars interarticularis as a result of surgery, particularly when the superior half of the lamina was removed.

In heme-deficient reticulocyte lysates a translational inhibitor which regulates protein synthesis is formed or activated. To define the mechanism of action of the translational inhibitor (RI), RI was partially purified. We have utilized the isolated RI to examine its relationship to the translational inhibitor formed in situ in heme-deficiency, some quantitative aspects of inhibition of protein synthesis, and the relationship of RI concentration to the initiation factor (IF-MP) which forms a ternary complex with Met-tRNAf and GTP (IF-MP-Met-tRNAf-GTP). The results demonstrate that the activity of isolated RI is related to the in situ heme-deficiency inhibitor by several criteria: (a) the biphasic kinetics of inhibition manifested by RI in lysates containing optimal levels of hemin are very similar to those observed in heme-deficiency, i.e., an initial period in which several rounds of protein synthesis proceed at the control rate followed by an abrupt decline in the rate of protein synthesis. (b) Both inhibitions are accompanied by the disaggreagation of polyribosomes with a concomitant increase in 80S ribosomes. (c) Both inhibitions are reversed by IF-MP. The isolated RI blocked protein synthesis in lysates at temperatures ranging from 15 degrees to 30 degrees. Although the rate of protein synthesis was a function of the temperature of incubation, the number of rounds of protein synthesis prior to shut-off was essentially the same at various temperatures. When RI was added to lysates, at increasing intervals after the start of incubation, the period of synthesis before shut-off (lag) progressively decreased. The inhibition of protein synthesis by RI was immediately reversed by the addition of IF-MP. The extent of reversal increased with increasing concentrations of IF-MP; at low levels of RI almost complete reversal of inhibition by IF-MP was obtained. However, at high levels of RI which did not appreciably increase the degree of inhibition of protein synthesis, equivalent amounts of IF-MP were less effective in reversing inhibition. These results suggest that the inhibition of protein synthesis by the isolated inhibitor involves the initiation factor IF-MP.

Summary 80S ribosomes from skeletal muscle of diabetic rats were more susceptible than normal to dissociation by the initiation factor EIF-3; the increased sensitivity to dissociation was a property of the 60S subunit. Increased dissociation may be a reflection of the instability of diabetic 80S couples resulting from a change in the structure of the large subunit.

In the absence of added hemin, protein synthesis in rabbit reticulocyte lysates proceeds at maximal linear rates for several minutes and then ceases abruptly. Inhibition involves the action of a translational inhibitor whose formation is regulated by hemin. Addition of the isolated inhibitor to hemin-supplemented lysates produces an inhibition of protein chain initiation similar to that observed in heme-deficiency. The inhibitor has been purified over 300-fold and contains a protein kinase activity that copurifies with the inhibitory function. With calf thymus histone II as the phosphate receptor, the inhibitor-associated protein kinase requires ATP as the phosphorylating agent. Cycle AMP stimulates kinase activity 5- to 8-fold; the concentration of cycle AMP required for halfmaximal activity is 4 X 10-8 M. Preincubation of the inhibitor in the presence of cyclic AMP significantly reduces cyclic AMP-dependent phosphorylation and inhibitory activity. The corresponding protein kinase activity from hemin-supplemented lysates displays reduced cyclic AMP-dependency and little or no inhibitory activity. These findings suggest that the protein kinase activity associated with the purified translational inhibitor is involved in the mechanism of inhibition of initiation observed in hemedeficient reticulocyte lysates.

A finite element model of a complete vertebra has been formulated. It is used to simulate the laminectomy and Harrington rod procedures. The results indicate that high tensile stresses occurred on the affected side in the region of the pars interarticularis after laminectomy. High tensile stresses near the pars interarticularis and at the posterior junction of lamina and pedicles are predicted due to Harrington rod loading.

Man has recognized carbon as an implant material well tolerated by the body for many years. Indeed, carbon in an impure form (Indian ink) was first used in the making of tatoos. Most recently carbon has been used in a filamentous form of high strength. These carbon fibers are produced in long tows of 40,000 fibers, each with a cross sectional area of about 7μ (Figure 1), by heating acrylic fibers to high temperature. This causes the noncarbon components to be removed while maintaining the molecular structure (scaffold) of the acrylic. Fibers can be chopped into short lengths and used to reinforce polyethylenes (8, 11, 12). These reinforced plastics have-twice the strength and ten times the stiffness of their non-reinforced counterparts, but suffer only one tenth as much creep when subjected to a load (11). Long tows of carbon fibers are used in tendon and ligament replacement (1, 2, 4, 5, 6, 7, 9, 10). This application warrants further investigation because of the apparent ability of the carbon fibers to induce the formation of ligaments and tendons (3, 4, 5, 6, 7).

Protein chain initiation in reticulocyte lysates is inhibited by (a) heme-deficiency, (b) low levels of double-stranded RNA, and (c) a purified translational inhibitor isolated from heme-deficient lysates. Previous studies have shown that the inhibitions produced by heme-deficiency and double-stranded RNA are prevented by 3': 5'-cyclic AMP, and that GTP, but not ATP, prevents the inhibition of heme-deficiency. In view of the recent finding that the inhibitor purified from heme-deficient lysates is associated with a protein kinase which appears to be involved in the mechanism of inhibition, the effects of cyclic AMP, GTP, and ATP on the three modes of inhibition were examines. In all three types of inhibition, cyclic AMP or GTP (a) prevents the onset of inhibition when added at zero time, and (b) restores protein synthesis in inhibited lysates. In contrast to these effects, ATP potentiates each inhibition, and blocks reversal of inhibition by cyclic AMP or GTP. On the basis of these and earlier findings, we propose that (a) these inhibitions involve the phosphorylation by protein kinases of the Met-tRNAf binding factor and/or a related site(s) on the 40S ribosomal subunit; and (b) cyclic AMP, GTP, and ATP exert their effects by their actions on this phosphorylation mechanism.

Fracture of the fibrous networks of normal and irradiated rat dermis have been studied using the SEM. The implications of these observations are discussed with regard to the mechanical behaviour of the tissue in the living animal. It is shown that after radiation the normal fibrous structure of collagen is replaced by a solid mat which is ill adapted to support stress, so that rupture at low stress levels is inevitable.

To define the mechanism of regulation of the protein kinase that is activated in heme deficiency and that inhibits initiation of protein synthesis, we have isolated and purified the heme-reversible form of the protein kinase from rabbit reticulocytes. The inhibitory activity is found in a single band after polyacrylamide gel electrophoresis under nondenaturing conditions. It migrates as a 95,000-dalton polypeptide in 15% sodium dodecyl sulfate/polyacrylamide gels. This purified inhibitor becomes self-phosphorylated in the presence of ATP; the phosphorylated protein and the inhibitory activity copurify. The inhibitor produces characteristic biphasic kinetics of inhibition in reticulocyte lysates and phosphorylates the 38,000-dalton subunit of eukaryotic initiation factor 2 (eIF-2); the inhibition is reversed by added eIF-2. In contrast to the heme-irreversible inhibitor, this heme-reversible inhibitor is no longer inhibitory after incubation with 20 micron hemin. Incubation with hemin also inhibits self-phosphorylation. Preincubation of the heme-reversible inhibitor in the presence of ATP potentiates the inhibition of protein synthesis in the subsequent incubation, as does treatment with N-ethylmaleimide. Phosphorylation of the heme-reversible inhibitor and inhibition of protein synthesis in the lysate due to phosphorylation of eIF-2 appear to be related. These findings suggest that hemin acts directly on the heme-reversible inhibitor.

In vitro thermal properties of human cortical bone have been measured using a specially developed technique. The technique enables accurate measurement of the coefficient of thermal expansion and contraction and the average values have been measured to be 27.5 ± 3.9 × 10−6 mm/°C for expansion and 27.2 ± 5.2 × 10−6 mm/°C for contraction.

Pressures in the nucleus pulposus and under the annulus fibrosus have been measured, using the specially developed miniature pressure transducers, when the vertebral segment was subjected to physiological loading. Strain data and stress-relaxation were also measured. Results show that pressures are linear with loading. Pressure variations within the nucleus are due to disc degeneration.

Protein synthesis in rabbit reticulocytes and their lysates is regulated by heme. In heme-deficient reticulocyte lysates, protein synthesis proceeds at the initial rate for several minutes and then declines abruptly. Inhibition of protein synthesis is due to the activation of a heme-regulated translational inhibitor (HRI) which blocks the initiation of protein synthesis. Addition of the isolated HRI to hemin-supplemented lysates causes inhibition of initiation similar to that observed in heme-deficiency. HRI has been shown to be a protein kinase that specifically phosphorylates the Met-tRNA f binding factor (eIF-2). We have isolated an inhibitor (LI) of protein chain initiation from rat liver which displays properties similar to those of HRI: ( i ) the chromatographic behavior of LI on DEAE-Sephadex, DEAE-cellulose, and phosphocellulose is similar to that of HRI; ( ii ) both LI and HRI inhibit protein chain initiation in rabbit reticulocyte lysates with the same kinetics of inhibition—i.e., an initial period of synthesis for several minutes at the control rate followed by an abrupt decline in the rate of initiation; ( iii ) both inhibitions are prevented or reversed by eIF-2; ( iv ) GTP (2 mM) prevents, and ATP (2 mM) potentiates, the inhibition of protein synthesis induced by either inhibitor; ( v ) LI is associated with a protein kinase that also phosphorylates the 38,000-dalton subunit of elF-2. These findings indicate that a mechanism for the regulation of protein synthesis similar to that found in rabbit reticulocytes may be present in rat liver.