Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Computer Peripherals”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 775 records · Page 43Linked to original sources
PubMed2005

High and low density in the same bone: a study on children and adolescents with mild osteogenesis imperfecta.

Children and adolescents with osteogenesis imperfecta (OI) generally have low bone mineral density (BMD) at the lumbar spine and hip. However, the effects of the disease on diaphyseal bone have not been well characterized, even though long-bone fractures are common in such patients. In this study on 42 fully mobile children and adolescents with mild OI (age 6-19 years; 17 girls), lumbar spine, radius (metaphysis and diaphysis) and second metacarpal (diaphysis) were analyzed using dual-energy X-ray absorptiometry, peripheral quantitative computed tomography and radiogrammetry, respectively. Bone mineral content at the lumbar spine, radial metaphysis and radial diaphysis was between 25% and 31% lower than in age-matched healthy children and adolescents. At the lumbar spine and radial metaphysis, bone size (as estimated from projection area and cross-sectional area, respectively) was normal or only slightly below the results expected for healthy individuals, whereas bone size was very small at the diaphyseal sites of the radius and the second metacarpal. Total volumetric BMD is defined as the ratio between bone mineral content and bone volume. Therefore, these differences in bone size between skeletal locations led to markedly discrepant results for total volumetric BMD. Total volumetric BMD was low at the lumbar spine (23% below result expected for healthy subjects of the same age) and the radial metaphysis (-15%) but elevated at the radial diaphysis (+25%; all differences to controls significant at P < 0.001). Despite high volumetric BMD, estimated bending strength at the radial diaphysis was very low. These results demonstrate that volumetric BMD can be abnormally high and low within the same bone in the same individual and highlight the fact that volumetric BMD at diaphyseal sites does not provide a good estimate of bone strength when bone size is abnormal.

Absorptiometry, Photon↗
PubMed2005

Regional distinctions in cortical bone mineral density measured by pQCT can predict alterations in material property at the tibial diaphysis of the Cynomolgus monkey.

We examined whether regional differences in cortical bone mineral density (Ct.BMD) measured by peripheral quantitative computed tomography is related to the heterogeneity of bone tissue and whether regional Ct.BMD is a better indicator of changes in bone material properties. Bilateral tibiae were obtained from 17 female adult Cynomolgus monkeys (Macaca fascicularis; mean age 16.8 years). After determining that Ct.BMD was similar between the right and left tibiae, the left tibiae were used for bone histomorphometry and the right for a three-point bending test. The Ct.BMD in the posterior quadrant was significantly higher than that in the anterior quadrant. In the bone histomorphometric analysis, all parameters (i.e., average osteonal area, average osteonal bone area, osteon population density, percent osteonal area [%On.Ar], percent osteonal bone area [%On.B.Ar], percent osteonal area of initial remodeling [%Il.On.Ar], percent osteonal area of secondary remodeling [%Sd.On.Ar], porosity, and percent osteoid area in the posterior region) were significantly lower than those in the anterior region. The results indicated that in the same cross-section, bone tissue structure was heterogeneous. Both total- and posterior-Ct.BMD were positively correlated with breaking stress and negatively correlated with toughness, whereas anterior-Ct.BMD was positively correlated with elastic modulus. Backward stepwise multiple regression analyses indicated that posterior-Ct.BMD and total-Ct.BMD were the best variables for predicting breaking stress and toughness, respectively, when age is taken into account. The %On.Ar, %On.B.Ar, and %Il.On.Ar in the posterior region were negatively correlated with elastic modulus. The %On.Ar, %On.B.Ar, and %Sd.On.Ar in the posterior region were positively correlated with toughness. These findings indicated that regional Ct.BMD measurement is useful to assess changes in the material properties of bone associated with the degree of mineralization. In particular, anterior-, posterior-, and total-Ct.BMD can be used separately to predict changes in the material properties of the tibial diaphysis.

Absorptiometry, Photon↗
PubMed2005

Side-to-side differences in cortical bone mineral density of tibiae in young male athletes.

The importance of physical activity in the development and maintenance of bone mineral density (BMD) is widely accepted. However, the effects on cortical BMD have not been clarified in detail. The present study examined bilateral asymmetries in cortical BMD of the tibia using peripheral quantitative computed tomography. Subjects comprised 37 young male athletes and 57 controls (age range, 18-28 years). BMD and geometrical indices were determined in bilateral tibiae. Cortical and trabecular BMD were calculated at the diaphysis and distal metaphysis, respectively. Cortical width, periosteal cross-sectional area, and cross-sectional moment of inertia were calculated using tomographic data of the tibial diaphysis. In athletes, the non-dominant leg showed greater cortical BMD than the dominant leg (mean difference, 5.42%; P < 0.0001). Cortical width and moment of inertia were also greater in the non-dominant leg. Periosteal area displayed no significant difference between legs. The control group exhibited similar results except for cortical BMD. No differences in trabecular BMD were noted between legs in either athletes or controls. These results implies the existence of mechanisms for the mechanical adaptation of cortical BMD. Dominant leg is used for mobility or manipulation whereas the non-dominant leg contributes to support the actions of the dominant leg. Loading differences in bilateral legs in young athletes might affect the remodeling rate leading to the side-to-side differences in cortical BMD.

Adolescent↗
PubMed2005

Effect of protein supplementation during a 6-month strength and conditioning program on areal and volumetric bone parameters.

BACKGROUND: Skeletal loading and proper nutrition are necessary for optimal bone health. The appropriate amount of dietary protein to maximize skeletal health, however, is under constant debate. OBJECTIVE: To determine if 6 months of protein supplementation in conjunction with a strength and conditioning training program improves areal and volumetric bone mineral density (BMD). DESIGN: Fifty-two apparently healthy males and females ages 18-25 years were randomized to protein supplement (PRO, Myoplex, EAS, Inc. Golden CO) containing 280 kcal, 42 g protein, 21 g carbohydrate, and 1.5 g fat) or calorically equivalent carbohydrate control (CS). All subjects participated in a 5 sessions/week strength and conditioning program. Volumetric and areal BMD measurements were made by peripheral quantitative computed tomography (pQCT) of the tibia and whole body DXA. pSSI a measure of torsional bone strength, based on structural and material properties was obtained by pQCT. RESULTS: Measurements at the 20% tibia by pQCT revealed that overall there were significant increases in cortical vBMD (4.3 +/- 1.3 mg/cm(3)), cortical area (1.9 +/- 0.6 cm(2)), cortical thickness (0.05 +/- 0.02 mm) and pSSI (67 +/- 24 mm(3)), and a decrease in endosteal circumference (- 0.5 +/- 0.2 mm) over the intervention period (all, P < 0.05). None of the changes in DXA measures were found to differ by group or sex, there was a trend for a greater increase in whole body BMC among the carbohydrate compared to protein supplemented group and a greater increase among males (16 +/- 8 g) compared to females (-9 +/- 9 g) (P = 0.06). CONCLUSIONS: The results of this study indicate that the consumption of additional protein does not improve measurements of vBMD or bone size during a 6-month strength and conditioning program. Longer duration studies may be necessary to determine the influence of increased dietary protein on bone in young adults. Males and females may have different bone responses to increased protein intake while participating in a strength and conditioning program.

Absorptiometry, Photon↗
PubMed2005

The effects of first gestation and lactation on bone metabolism in dairy goats and milk sheep.

The goal of the present study was to compare mobilization rate of calcium (Ca) from bone in pregnant and lactating goats and sheep. Blood samples were collected from goats and sheep monthly during pregnancy and at 1, 2, and 4 weeks postpartum (pp) and monthly during lactation until 6 months after parturition. Total bone mineral content (BMC) and total bone mineral density (BMD) were quantified using peripheral quantitative computed tomography at the same intervals as the blood was taken. Bone resorption was assessed by immunoassays quantitating two epitopes of the carboxyterminal telopeptide of type I collagen (ICTP, CTX). Bone formation was estimated by quantifying serum osteocalcin (OC) and bone-specific alkaline phosphatase (bAP). In addition, Ca and 1,25-dihydroxy vitamin D (1,25-VITD) concentrations were determined in serum. Mean ICTP and CTX concentrations of both animal species increased the first week after parturition. By the second week pp, the concentrations of both markers had decreased toward early gestation levels. In contrast, mean OC concentrations continually decreased until the 1st week pp. By the 2nd week pp, the mean concentrations of OC started to increase again. Mean bAP activities decreased during gestation and reached a nadir in the first week pp in goats and 4 weeks pp in sheep. Afterwards, mean bAP activities increased again in goats and sheep. 1,25-VITD concentrations peaked the first week pp and returned to early gestation values thereafter. Total BMC and BMD decreased from the 4th month of pregnancy until the 1st week pp in both species. Afterwards, BMC increased throughout the first month pp in goats and the first 3 months pp in sheep. BMD levels of sheep and goats returned to prepartum levels during lactation. The resorptive phase of bone remodeling is accelerated at parturition and in early lactation and is uncoupled from the process of bone formation. This allows the animal to achieve Ca homeostasis at the expense of bone. Increased bone remodeling during lactation may represent physiological mechanisms to help replace the maternal skeleton lost as the animal adapted to enormously increased Ca losses to the fetus and milk in late gestation and early lactation.

Animal Feed↗
PubMed2006

Renal insufficiency-induced bone loss is associated with an increase in bone size and preservation of strength in rat proximal femur.

Chronic renal insufficiency (CRI) results in phosphate retention and secondary hyperparathyroidism, the treatment of which is largely based on the use of calcium salts as phosphate binders. Advanced CRI causes bone fragility, but information about bone geometry and strength in moderate CRI is scarce. We assigned 39 8-week-old male Sprague-Dawley rats to sham-operation (Sham) or 5/6 nephrectomy (NTX). Four weeks later, the rats were randomized to 0.3% calcium (Sham, NTX) or 3.0% calcium diet (Sham + Calcium, NTX + Calcium). After 8 weeks, the animals were sacrificed, plasma samples collected, and femora excised for neck and midshaft analyses: dual-energy X-ray absorptiometry, peripheral quantitative computed tomography, and biomechanical testing. The NTX increased plasma urea and PTH 1.6-fold and 3.6-fold, respectively, whereas high calcium intake suppressed PTH to 30% of controls. Total femoral bone mineral content decreased (-6.3%) in the NTX group, while this deleterious effect was reversed by high calcium diet. In the site-specific analysis of the femoral neck, the volumetric bone density (-6.5%) was decreased in the NTX group but not NTX + Calcium group. However, in the nephrectomized rats, there was also a concomitant increase in the cross-sectional area (+15%), and, despite the decrease in bone density, the mechanical strength of the femoral neck was maintained. In the midshaft, NTX decreased cortical volumetric bone density (-1.2%), but similar to the femoral neck, no differences were found in the mechanical strength. In conclusion, a decrease in bone mass in moderate experimental CRI was associated with a concomitant increase in bone size, and maintenance of mechanical competence. Although high calcium diet suppressed plasma PTH to under normal physiological levels, it prevented the CRI-induced loss of bone mass without an adverse influence on bone strength.

Absorptiometry, Photon↗
PubMed2006

Loading modalities and bone structures at nonweight-bearing upper extremity and weight-bearing lower extremity: a pQCT study of adult female athletes.

This cross-sectional study of adult female athletes assessed whether the apparent loading-related differences in bone structure are primarily associated with the loading type or the muscle performance-related joint moments. Several structural variables at shaft sites of the tibia, radius and humerus, and distal sites of the tibia and radius were measured with peripheral quantitative computed tomography (pQCT) among 113 female national level athletes (representing hurdling, volleyball, soccer, racket-sports and swimming) and their 30 nonathletic referents. For the weight-bearing lower extremities, the loading modalities of the above sports were classified into high-impact (hurdling, volleyball), odd-impact (soccer, racket-sports) and repetitive, nonimpact (swimming) loadings; and for the nonweight-bearing upper extremities into high magnitude (functional weightlifting in hurdling and soccer), impact (volleyball, racket-sports) and repetitive, nonimpact (swimming) loadings. As expected, athletes' bone mass was substantially higher at loaded bone sites compared with the nonathletic referents, but more pertinently to the locomotive perspective, the loading-induced additional bone mass seemed to be used to build mechanically strong and appropriate bone structures. Compared with controls, the weight-bearing bone structures of female athletes (swimmers excluded) were characterized by larger diaphysis, thicker cortices and somewhat denser trabecular bone. The athletes' bones at the nonweight-bearing upper extremity were generally larger in cross-sectional area. The estimated indices of joint moment (muscle force x estimated lever arm) were explained from 29% to 50%, and the loading modalities from 8% to 25%, of the variance in most bone variables (P < 0.05) of the tibia (shaft and distal site). In contrast to the weight-bearing tibia, only the estimated joint moment was positively associated (P < 0.05) with the structural characteristics of the radius and humerus, accounting for 6% to 26% of the variance in bone variables of the shafts of these bones. Such association was not observed at the distal radius. In conclusion, at the weight-bearing lower extremity, the strong bone structure of the female athletes was attributable to muscle performance-related estimated joint moments and impact loading modality. At the shaft sites of the nonweight-bearing upper extremity, the strong bone structure was mainly attributable to the estimated joint moments. Thus, different loading history and other features of loading seemed to govern the skeletal adaptation at the upper and lower extremity.

Absorptiometry, Photon↗
PubMed2006

A single intravenous administration of zoledronic acid prevents the bone loss and mechanical compromise induced by aromatase inhibition in rats.

Recent evidence has demonstrated that long-term estrogen deprivation using aromatase inhibitor therapy in postmenopausal women with breast cancer results in bone loss and increased fracture risk. Bisphosphonates are potent inhibitors of bone resorption and have demonstrated efficacy in preventing bone loss in postmenopausal women with low bone mineral density (BMD) and in patients with breast cancer receiving estrogen deprivation therapy. Therefore, this study investigated the effects of the bisphosphonate zoledronic acid on BMD and bone strength in rats treated with the aromatase inhibitor, letrozole. Peripheral quantitative computed tomography demonstrated that treatment of rats with daily oral letrozole (1 mg/kg) induced significant bone loss and cortical thinning compared with control animals (P < 0.01). A single prior intravenous dose of zoledronic acid dose dependently protected against letrozole-induced bone loss and cortical thinning, with the highest evaluated dose (20 microg/kg) resulting in BMD values that were not significantly different from controls over the 24 weeks of letrozole treatment. Furthermore, biomechanical testing of the distal femoral metaphysis demonstrated that zoledronic acid (20 microg/kg) significantly prevented the decrease in stiffness and elastic modulus induced by letrozole treatment. Taken together, these data support the use of zoledronic acid for the prevention of bone loss in women with breast cancer receiving aromatase inhibitor therapy.

Animals↗
PubMed2006

Detrimental effect of oral contraceptives on parameters of bone mass and geometry in a cohort of 248 young women.

The aim of this cross-sectional analysis was to examine the skeletal effects of low-dose monophasic oral contraceptive (OC) use in a cohort of 248 young Caucasian women aged 18-24 years. Areal bone mineral density (BMD) of the femoral neck and lumbar spine was evaluated by dual-energy X-ray absorptiometry. Volumetric BMD, bone mineral content (BMC), and bone geometry were assessed in the tibia by peripheral quantitative computed tomography (pQCT). The women were allocated into ever or never OC users, and also into 5 different OC groups according to duration and time of initiation of OC use. Women with >2 years of OC use and OC initiation within 3 years after menarche were characterized by 10% lower femoral neck areal BMD (P<0.001), 5% lower spine areal BMD (not significant, P=0.101), 7% lower distal tibial total BMC (P<0.05), and 6% lower total BMC at the tibial shaft (P<0.05) relative to never users. In addition, women who had ever used OCs had lower bone mass at the femoral neck and tibial shaft, despite similar age, height, weight, BMI, hours of exercise, and calcium intake compared with never users. At the tibial shaft, OC users showed reduced total cross-sectional area, and increased cortical BMD. In conclusion, our data suggest that OC use is associated with a detrimental effect on bone mass in young women, and provide further insight into the pathophysiological mechanisms involved.

Absorptiometry, Photon↗
PubMed2007

Long-bone changes after pamidronate discontinuation in children and adolescents with osteogenesis imperfecta.

Cyclical intravenous pamidronate is a widely used symptomatic therapy in moderate to severe osteogenesis imperfecta (OI). The effects of treatment discontinuation on long bone development have not been characterized. In this observational study we used peripheral quantitative computed tomography to assess the radius at the distal metaphysis and at the diaphysis in 23 young OI patients (11 female) who had received pamidronate for at least 3 years. Measurements were performed twice, at the time of treatment discontinuation (when the age of the patients ranged from 5.9 to 21.3 years) and at an average of 1.9 years (range 1.5 to 2.4 years) later. At the time of pamidronate discontinuation, all but one of the patients who were below 15 years of age (n=14) had a positive age- and sex-specific z-score for bone mineral content (BMC) at the metaphysis, resulting in a mean z-score of +2.0 (SD=1.0) for this subgroup. In contrast, patients aged 15 years or older (n=9) had an average metaphyseal BMC z-score of -1.5 (SD=1.5). After pamidronate discontinuation, metaphyseal BMC z-score decreased by an average of 2.4 (SD=2.0) in the whole group. The change in BMC z-score was growth-dependent, as BMC z-scores decreased by about 2 or more in all patients in whom distal radius growth plates were open when pamidronate was discontinued. In contrast, none of the 11 patients with closed distal radius growth plates experienced a decrease in metaphyseal BMC z-score by more than 2. At the diaphysis, the average BMC z-score was low at the time of the last pamidronate infusion [z-score -1.7 (SD=1.4)]. After pamidronate discontinuation, the average diaphyseal BMC z-score decreased by only 0.3 (SD=0.4). In summary, this study shows that the effect of pamidronate discontinuation is much larger at the radial metaphysis than at the diaphysis and is dependent on growth. Metaphyseal bone tissue added by longitudinal growth after treatment discontinuation has a lower density than tissue created during treatment. It is possible that this produces zones of localized bone fragility after pamidronate treatment is stopped in growing children.

Adolescent↗
PubMed2005

Subclinical hypervitaminosis A in rat: measurements of bone mineral density (BMD) do not reveal adverse skeletal changes.

We have previously shown that subclinical hypervitaminosis A in rats causes fragile bones. To begin to investigate possible mechanisms for Vitamin A action we extended our previous study. Forty-five mature female Sprague-Dawley rats were divided into three groups, each with 15 animals. They were fed a standard diet containing 12IU Vitamin A per g pellet (control, C), or a standard diet supplemented with 120 IU ("10xC") or 600 IU ("50xC") Vitamin A/g pellet for 12 weeks. At the end of the study, serum retinyl esters were elevated 4- and 20-fold. Although neither average food intake nor final body weights were significantly different between groups, a dose-dependent reduction in serum levels of Vitamin D and E, but not Vitamin K, was found. In the 50xC-group the length of the humerus was the same as in controls, but the diameter was reduced (-4.1%, p<0.05). Peripheral quantitative computed tomography (pQCT) at the diaphysis showed that bone mineral density (BMD) was unchanged and that periosteal circumference had decreased significantly (-3.7%, p<0.05). Ash weight of the humerus was not affected, but since bone volume decreased, volumetric BMD, as measured by the bone ash method, even increased (+2.5%, p<0.05). In conclusion, interference with other fat-soluble Vitamins is a possible indirect mechanism of Vitamin A action. Moreover, BMD measurements do not reveal early adverse skeletal changes induced by moderate excesses of Vitamin A in rats. Since the WHO criterium for osteoporosis is based on BMD, further studies are warranted to examine whether this is also true in humans.

25-Hydroxyvitamin D 2↗
PubMed2006

Comparison of the skeletal effects of the progestogens desogestrel and levonorgestrel in oral contraceptive preparations in young women: controlled, open, partly randomized investigation over 13 cycles.

AIM: This 12-month study was conducted to evaluate the skeletal effects of two monophasic oral contraceptives containing 20 mug of ethinylestradiol and 100 mug of levonorgestrel (LEVO) or 150 mug of desogestrel (DESO). METHODS: Fifty-two women (18-24 years) were randomized into the DESO group or the LEVO group; 36 women served as controls. The areal bone mineral density (aBMD) of the femoral neck and the lumbar spine was evaluated by DXA, and parameters of bone geometry and volumetric bone mineral density (vBMD) were assessed by peripheral quantitative computed tomography at the distal radius and the tibia. RESULTS: The LEVO group did not lose vertebral aBMD, whereas women in the DESO group lost 1.5%. At the distal radius and the tibia (shank level, 14%), LEVO induced an increase in total cross-sectional area, indicating increased periosteal bone formation. Radial trabecular vBMD declined by 1.4+/-1.8% in the DESO group, while it remained unchanged in the LEVO group. CONCLUSION: Our study suggests that the skeletal effects of OC preparations may be influenced by progestogenic components in young women.

Absorptiometry, Photon↗
PubMed2004

Experimental and finite element analysis of the rat ulnar loading model-correlations between strain and bone formation following fatigue loading.

The rat forelimb compression model has been used widely to study bone response to mechanical loading. We used strain gages to assess load sharing between the ulna and radius in the forelimb of adult Fisher rats. We used histology and peripheral quantitative computed tomography (pQCT) to quantify ulnar bone formation 12 days after in vivo fatigue loading. Lastly, we developed a finite element model of the ulna to predict the pattern of surface strains during compression. Our findings indicate that at the mid-shaft the ulna carries 65% of the applied compressive force on the forelimb. We observed large variations in fatigue-induced bone formation over the circumference and length of the ulna. Bone formation was greatest 1-2 mm distal to the mid-shaft. At the mid-shaft, we observed woven bone formation that was greatest medially. Finite element analysis indicated a strain pattern consistent with a compression-bending loading mode, with the greatest strains occurring in compression on the medial surface and lesser tensile strains occurring laterally. A peak strain of -5190 microepsilon (for 13.3N forelimb compression) occurred 1-2 mm distal to the mid-shaft. The pattern of bone formation in the longitudinal direction was highly correlated to the predicted peak compressive axial strains at seven cross-sections (r2 = 0.89, p = 0.014). The in-plane pattern of bone formation was poorly correlated to the predicted magnitude of axial strain at 51 periosteal locations (r2 = 0.21, p < 0.001), because the least bone formation was observed where tensile strains were highest. These findings indicate that the magnitude of bone formation after fatigue loading is greatest in regions of high compressive strain.

Animals↗
PubMed2004

Determination of mechanical stiffness of bone by pQCT measurements: correlation with non-destructive mechanical four-point bending test data.

Mechanical tests of bone provide valuable information about material and structural properties important for understanding bone pathology in both clinical and research settings, but no previous studies have produced applicable non-invasive, quantitative estimates of bending stiffness. The goal of this study was to evaluate the effectiveness of using peripheral quantitative computed tomography (pQCT) data to accurately compute the bending stiffness of bone. Normal rabbit humeri (N=8) were scanned at their mid-diaphyses using pQCT. The average bone mineral densities and the cross-sectional moments of inertia were computed from the pQCT cross-sections. Bending stiffness was determined as a function of the elastic modulus of compact bone (based on the local bone mineral density), cross-sectional moment of inertia, and simulated quasistatic strain rate. The actual bending stiffness of the bones was determined using four-point bending tests. Comparison of the bending stiffness estimated from the pQCT data and the mechanical bending stiffness revealed excellent correlation (R2=0.96). The bending stiffness from the pQCT data was on average 103% of that obtained from the four-point bending tests. The results indicate that pQCT data can be used to accurately determine the bending stiffness of normal bone. Possible applications include temporal quantification of fracture healing and risk management of osteoporosis or other bone pathologies.

Animals↗
PubMed2004

Finger joint impedance during tapping on a computer keyswitch.

We studied the dynamic behavior of finger joints during the contact period of tapping on a computer keyswitch, to characterize and parameterize joint function with a lumped-parameter impedance model. We tested the hypothesis that the metacarpophalangeal (MCP) and interphalangeal (IP) joints act similarly in terms of kinematics, torque, and energy production when tapping. Fifteen human subjects tapped with the index finger of the right hand on a computer keyswitch mounted on a two-axis force sensor, which measured forces in the vertical and sagittal planes. Miniature fiber-optic goniometers mounted across the dorsal side of each joint measured joint kinematics. Joint torques were calculated from endpoint forces and joint kinematics using an inverse dynamic algorithm. For each joint, a linear spring and damper model was fitted to joint torque, position, and velocity during the contact period of each tap (22 per subject on average). The spring-damper model could account for over 90% of the variance in torque when loading and unloading portions of the contact were separated, with model parameters comparable to those previously measured during isometric loading of the finger. The finger joints functioned differently, as illustrated by energy production during the contact period. During the loading phase of contact the MCP joint flexed and produced energy, whereas the proximal and distal IP joints extended and absorbed energy. These results suggest that the MCP joint does work on the interphalangeal joints as well as on the keyswitch.

Adult↗
PubMed2005

Finger joint coordination during tapping.

We investigated finger joint coordination during tapping by characterizing joint kinematics and torques in terms of muscle activation patterns and energy profiles. Six subjects tapped with their index finger on a computer keyswitch as if they were typing on the middle row of a keyboard. Fingertip force, keyswitch position, kinematics of the metacarpophalangeal (MCP) and the proximal and distal interphalangeal (IP) joints, and intramuscular electromyography of intrinsic and extrinsic finger muscles were measured simultaneously. Finger joint torques were calculated based on a closed-form Newton-Euler inverse dynamic model of the finger. During the keystroke, the MCP joint flexed and the IP joints extended before and throughout the loading phase of the contact period, creating a closing reciprocal motion of the finger joints. As the finger lifted, the MCP joint extended and the interphalangeal (IP) joints flexed, creating an opening reciprocal motion. Intrinsic finger muscle and extrinsic flexor activities both began after the initiation of the downward finger movement. The intrinsic finger muscle activity preceded both the IP joint extension and the onset of extrinsic muscle activity. Only extrinsic extensor activity was present as the finger was lifted. While both potential energy and kinetic energy are present and large enough to overcome the work necessary to press the keyswitch, the motor control strategies utilize the muscle forces and joint torques to ensure a successful keystroke.

Adult↗
PubMed2006

Apparent Young's modulus of human radius using inverse finite-element method.

The ability to assess the elastic and failure properties of cortical bone at the radial diaphysis has a clinical importance. A new generation of quantitative ultrasound (QUS) devices and peripheral quantitative computed tomography (p-QCT) has been developed to assess non-invasively bone material and structural properties at the distal radius. This anatomical site is characterized by a thin cortical thickness that complicates traditional mechanical testing methods on specimens. Until now, mechanical properties of cortical bone at distal radius (e.g., elastic modulus, yield stress and strain) remain rarely studied probably due to experimental difficulties. The present study introduces an inverse finite-element method strategy to measure the elastic modulus and yield properties of human cortical specimens of the radial diaphysis. Twenty millimeter-thick portions of diaphysis were cut from 40 human radii (ages 45-90) for biomechanical test. Subsequently the same portion was modeled in order to obtain a specimen-specific three dimensional finite-element model (3D-FEM). Longitudinal elastic constants at the apparent level and stress characterizations were performed by coupling mechanical parameters with isotropic linear-elastic simulations. The results indicated that the mean apparent Young's modulus for radial cortical bone was 16 GPa (SD 1.8) and the yield stress was 153 MPa (SD 33). Breaking load was 12,946 N (SD 3644), cortical thickness 2.9 mm (SD 0.6), structural effective strain at the yield (epsilon(y)=0.0097) and failure (epsilon(u)=0.0154) load were also calculated. The 3D-FEM strategy described here may help to investigate bone mechanical properties when some difficulties arise from machining mechanical sample.

Aged↗