bluuebunny/crossref_metadata_2025_split huggingface dataset:
Computed tomography‐based finite element analysis predicts failure loads and fracture patterns for vertebral sections
Authors: Silva Matthew J. , Keaveny Tony M. , Hayes Wilson C. 
Published: February 2005

AbstractComputed tomography‐based finite element analysis represents a powerful research tool for investigating the mechanics of skeletal fractures. To provide evidence that this technique can be used to predict failure loads and fracture patterns for bone structures, we compared the observed and predicted failure behaviors of 18 midsagittal sections. 10 mm thick, cut from human vertebral bodies. The specimens were scanned by computed tomography, and finite element models were generated with use of empirically determined density‐property relations to assign element‐specific material properties. The specimens were loaded to failure in uniaxial compression, and the models were analyzed under matching conditions. The models provided predictions of yield load that were strongly correlated with experimentally measured values (r2 > 0.86) and were typically within 25% of measured values. Predicted stiffness values were moderately correlated with measured values, but large absolute differences existed between them. Comparisons between regions of observed fracture and of high predicted strain indicated that strain was an accurate indicator of the pattern of local fracture in more than two‐thirds of the bone specimens. In addition, strain contour plots provided better indicators of local fracture than did stress plots in these heterogeneous bone structures. We conclude that computed tomography‐based finite element analysis can be used successfully to predict both global and local failure behavior of simplified skeletal structures.
Surface stiffness affects impact force during a fall on the outstretched hand
Authors: Robinovitch Stephen N. , Chiu James 
Published: February 2005

AbstractFalls on the outstretched hand are among the most common causes of traumatic bone fracture. However, little is known regarding the biomechanical factors that affect the risk for injury during these events. In the present study, we explored how upper‐extremity impact forces during forward falls are affected by modification of surface stiffness, an intervention applicable to high‐risk environments such as nursing homes, playgrounds, and gymnasiums. Results from both experimental and linear biomechanical models suggest that during a fall onto an infinitely stiff surface, hand contact force is governed by a high‐frequency transient (having an associated peak force Fmax1), followed by a low‐frequency oscillation (having an associated lower magnitude peak force Fmax2). Practical decreases in surface stiffness attenuate Fmax1 but not Fmax2 or the magnitude of force transmitted to the shoulder. Model simulations reveal that this arises from the compliant surface's ability to decrease the velocity across the wrist damping elements at the moment of impact (which governs Fmax1) but inability to substantially reduce the peak deflection of the shoulder spring (which governs Fmax2). Comparison between model predictions and previous data on fracture force suggests that feasible compliant surface designs may prevent wrist injuries during falls from standing height or lower, because Fmax1 will be attenuated and Fmax2 will remain below injurious levels. However, such surfaces cannot prevent Fmax2 from exceeding injurious levels during falls from greater heights and therefore likely provide little protection against upper‐extremity injuries in these cases.
Blunt impact causes changes in bone and cartilage in a regularly exercised animal model
Authors: Newberry William N. , Mackenzie Charles D. , Haut Roger C. 
Published: February 2005

AbstractThe goal of this study was to document the effect of blunt‐impact trauma on the knee in a small animal model that incorporated a known level of physical exercise after impact. We hypothesized that a single blunt impact to the patellofemoral joint, of a magnitude comparable with our earlier studies, would result in degenerative changes to cartilage and to subchondral bone of the patella. Blunt impacts were delivered to rabbit patellofemoral joints without producing bone fracture, and biomechanical and histological analyses were performed on joint tissues at various times. At 12 months, the subchondral bone plate was thicker on the impacted side than on the unimpacted side and than that of the controls at comparable locations (near where surface fissures were found on the impacted side). The instantaneous modulus of cartilage was significantly less on the impacted side than that of controls at 3, 6, and 12 months after impact. The relaxed modulus of cartilage on the unimpacted side increased with time after impact and was significantly greater than that of controls at 12 months. These facts suggest that in this exercise model, the contralateral limb should not be considered a control. The retropatellar cartilage on the impacted side was significantly less thick than that of controls at 12 months, and histological analyses of the cartilage and bone indicated early‐stage osteoarthrosis in the impacted joint. Thus, in this animal model a single subfracture blunt impact produced degeneration of joint tissues.
Retinoic acid responsiveness of cells and tissues in developing fetal limbs evaluated in a RAREhsplacZ transgenic mouse model
Authors: Schroeder Herbert P. von , Heersche Johan N. M. 
Published: February 2005

AbstractLimb morphogenesis is a complex phenomenon in which retinoids play an important role. Abnormal maternal retinoid levels from high oral doses cause fetal malformations, including abnormalities of the musculoskeletal system. Our purpose was to identify the retinoid‐responsive cells in bone and cartilage during limb development by using a transgenic line of mice containing a reporter gene insert consisting of a retinoic acid response element linked to an Escherichia coli β‐galactosidase gene. Transgenic fetuses from day 11.5 after conception to birth (day 20) were analyzed histologically. Retinoid‐responsive cells and tissues were first seen in the limb bud at 12.5 days in the webs between the forming digits. The webs stained maximally at 14.5 days, after which staining intensity subsided. Staining in the muscles was detectable at 13.5 days, at a stage coinciding with myoblast fusion. Specific regions of perichondrium and periosteum also stained at this Stage. Occasional staining was observed in individual chondroblasts in all chondrogenic regions, including hypertrophic chondroblasts and certain articular surfaces of developing joints. Staining of these tissues decreased in intensity in subsequent stages. Osteoclasts started to express β‐galactosidase at 15.5 days and continued to stain into maturity. Our results indicate that specific subsets of cells respond to retinoids at specific stages in the course of normal limb development. In hypertrophic chondrocytes and cells in the webs and joints that display such a response, retinoid‐induced effects may be linked to cell death that occurs in these regions. Staining in muscle, perichondrium, and periosteum may reflect retinoid‐induced effects associated with cell differentiation and growth. These results suggest that retinoids play a role in a variety of tissues, including bone and cartilage, at specific stages during morphogenesis.
Analytic model to predict the strength of tendon repairs
Authors: Lotz Jeffrey C. , Hariharan Jayaram S. , Diao Edward 
Published: February 2005

AbstractWe developed an analytic model to predict suture load‐sharing immediately after flexor tendon repair in the hand. Tendon repair was mathematically modeled as two nonlinear springs in parallel, representing separate core and peripheral sutures that were in series with a third nonlinear spring representing the tendon. To serve as a basis for, and validation of, our analytic model, fresh human flexor digitorum profundus tendons were harvested and mechanically tested either intact or after surgical repair in a variety of ways: core suture alone, superficial peripheral suture alone, deep peripheral suture alone, core suture plus superficial peripheral suture, and core suture plus deep peripheral suture. The stiffness and strength of the composite repairs predicted with use of the analytic model were comparable with those determined experimentally. Furthermore, the model predicted inequities in suture load‐sharing, with 64% of the applied load carried by the peripheral suture when it was placed superficially, as compared with 77% when the peripheral suture was placed deep. Our results demonstrate a disparity in load‐sharing within composite suture systems, the rectification of which may lead to significant improvement in the repair strength. To this end, we expect that our analytic model will serve as a basis for the design of more efficient, and consequently stronger, suture techniques.
Collagen fiber sliding during ligament growth and contracture
Authors: Wood Mark L. , Lester Gayle E. , Dahners Laurence E. 
Published: February 2005

AbstractIt is hypothesized that the sliding of collagen fibers past one another plays an important role in changes of ligament length during growth or contracture. To explore this possibility, we used the fluorescent dye dichlorotriazinyl fluorescein to stain collagen fibers perpendicular to their orientation in a rat medial collateral ligament model. Growth, contracture, and control models (with rats weighing 50–75 g in the first and 500–600 g in the latter two groups) were studied. In the contracture model, the medial collateral ligament was transected distally. Marking sutures were used to verify the presence of growth or contracture in each medial collateral ligament. Fluorescence photomicrography after 2 weeks demonstrated stained collagen fibers protruding from either side of the original mark as one would expect, in either growth or contracture, if the fibers slid past one another and away from their initial location during changes in length. By measuring the initial and final widths of the growth and contracture model marks and correlating them to controls that had minimal growth (rats grow throughout their life) and were free of contracture, we have provided evidence that collagen sliding plays a significant role in changes in ligament length.
Longitudinal measurement of tibial motion relative to the femur during passive displacements in the cat before and after anterior cruciate ligament transection
Authors: Maitland Murray E. , Leonard Tim , Frank Cyril B. , Shrive Nigel G. , Herzog Walter 
Published: February 2005

AbstractPassive anterior‐posterior displacement and medial‐lateral rotation of the tibia on the femur in the feline knee were assessed before transection of the anterior cruciate ligament, immediately after transection, and 2 and 4 months after transection. Four anaesthetized experimental and three sham‐operated control animals were positioned in a stereotaxic frame. Motions of the tibia relative to the femur were measured with use of 60‐Hz video motion analysis, while a strain‐gauged system allowed measurement of forces and moments applied to the tibia. Displacement at 15 N of anterior force and 30° of knee flexion increased by an average of 6 mm following transection, and stiffness decreased by an average of 6 N/mm. At 2 and 4 months following transection, there were statistically significant reductions in this abnormal displacement. Stiffness during anterior displacement of the tibia at 30° increased significantly from immediately after transection to 4 months. At 90°, mean anterior displacement decreased from 5.1 mm immediately after transection to 2.9 mm at 4 months. Media rotation at 30° of knee flexion was significantly decreased from a mean of 16.5° after transection to a mean of 10.7° at 4 months. Changes in medial rotation at 90°, lateral rotation at 90°, and lateral rotation at 30° were not statistically significant. These results indicate a significant change in secondary constraints to tibial motion in response to knee instability.
Nonlinear dependence of loading intensity and cycle number in the maintenance of bone mass and morphology
Authors: Qin Yi‐Xian , Rubin Clinton T. , McLeod Kenneth J. 
Published: February 2005

AbstractThe daily stress stimulus theory of bone adaptation was formulated to describe the loading conditions necessary to maintain bone mass. This theory identifies stress/strain magnitude and loading cycle number as sufficient to define an appropriate maintenance loading signal. Here, we extend the range over which loading cycle number has been evaluated to determine whether the daily stress stimulus theory can be applied to conditions of very high numbers of loading cycles at very low strain magnitudes. The ability of a relatively high‐frequency (30‐Hz) and moderate‐duration (60‐minute) loading regimen to maintain bone mass in a turkey ulna model of disuse osteopenia was evaluated by correlating the applied strain distributions to site‐specific remodeling activity. Changes in morphology were investigated following 8 weeks of disuse compared with disuse plus daily exposure to 108,000 applied loading cycles sufficient to induce peak strains of approximately 100 microstrain. A strong correlation was observed between the preservation of bone mass and longitudinal normal strain (R = 0.91) (p < 0.01). The results confirm the strong antiresorptive influence of mechanical loading and identify a threshold near 70 microstrain for a daily loading cycle regimen of approximately 100,000 strain cycles. These results are not consistent with the daily stress stimulus theory and suggest that the frequency or strain rate associated with the loading stimulus must also play a critical role in the mechanism by which bone responds to mechanical strain.
Cultured human ankle and knee cartilage differ in susceptibility to damage mediated by fibronectin fragments
Authors: Kang Yong , Koepp Holger , Cole Ada A. , Kuettner Klaus E. , Homandberg Gene A. 
Published: February 2005

AbstractAccording to numerous cadaveric, radiographic, and clinical studies, ankle and knee joints differ in susceptibility to osteoarthritis. To test for biochemical differences in susceptibility to damage, a chondrocytic chondrolysis system has been utilized. In this system, fibronectin fragments are added to cultured cartilage explants, resulting in enhanced release of catabolic cytokines. induction of matrix metalloproteinases, temporary suppression of proteoglycan synthesis, and consequently, severe loss of cartilage proteoglycan. We found that the addition of an amino‐terminal thrombin‐generated 29‐kDa fibronectin fragment to cultured knee cartilage from 14 donors (average age: 53 years) usually caused a 30–50% decrease in proteoglycan content by day 7. However, of the ankle cartilage specimens examined from 21 donors (average age: 50 years), only three showed damage by, day 7. one by day 14, and six by day 21. and 11 were not damaged until day 28. For eight of the donors (average age: 44 years), both knee and ankle cartilages were obtained; this allowed comparison between tissues from the same donor. The analysis showed that the ankle cartilage was much more refractory to damage than was the knee cartilage from the same donor. These data clearly show differences between ankle and knee cartilage in susceptibility to the fibronectin fragments and suggest the feasibility of use of these fragments for discerning differences in homeostasis of the ankle and knee cartilage.
Distal radius fractures: Mechanisms of injury and strength prediction by bone mineral assessment
Authors: Augat Peter , Iida Hiroyuki , Jiang Yebin , Diao Edward , Genant Harry K. 
Published: February 2005

AbstractThe strength of the radius depends on the mechanical properties of cancellous and cortical bone. By assessing both compartments quantitatively with bone densitometry. we tried to identify the specificity of each in predicting the load at which the distal raius will fracture. Twenty human cadaver forearms were scanned for bone mineral and geometric properties with quantitative computed tomography and dual x‐ray absorptiometry. In both a neutral loading situation and one in which the wrist was extended 45°, the load distribution was determined with pressure‐sensitive films, and a fracture simulating a fall on the hand was produced with a material testing machine. Fractures that occur with the wrist in extension were produced by a central impact of the scaphoid onto the radiocarpal joint, and those that occur under neutral loading conditions were produced by a more commonly distributed loading pattern. The load at fracture was most specifically predicted (r2 = 0.74) by bone mineral and geometric measures of the cortex at the shaft of the radius. Bone mineral density measures of trabecular (r2 = 0.64) and total (r2 = 0.66) bone were less successful in predicting the fracture load. After adjustment for bone size, the geometric and density measures revealed similar specificity. Cortical bone, therefore, contributes significantly to the strength of the distal radius and may play an important role in the prediction of osteoporotic wrist fractures.
In situ forces in the posterolateral structures of the knee under posterior tibial loading in the intact and posterior cruciate ligament‐deficient knee
Authors: Höher Jürgen , Harner Christopher D. , Vogrin Tracy M. , Baek Goo Hyun , Carlin Gregory J. , Woo Savio L‐Y. 
Published: February 2005

AbstractThe posterolateral structures of the knee consist of a complex anatomical architecture that includes several components with both static and dynamic functions. Injuries of the posterolateral structures occur frequently in conjunction with ruptures of the posterior cruciate ligament. To investigate the role of the posterolateral structures in maintaining posterior knee stability, we measured the in situ forces in the posterolateral structures and the distribution of force within the structures major components, i.e., the popliteus complex and the lateral collateral ligament, in response to a posterior tibial load. Eight cadaveric knees were tested. With use of a robotic/universal force‐moment sensor testing system, a posterior tibial load of 110 N was applied to the knee, and the resulting five‐degree‐of‐freedom kinematics were measured at flexion angles of 0, 30, 60, 75, and 90°. The knees were tested first in the intact state and then after the posterior cruciate ligament had been resected. These tests were also performed with an additional load of 44 N applied at the aponeurosis to simulate contraction of the popliteus muscle. In the intact knee, the in situ forces in the posterolateral structures were found to decrease with increasing knee flexion. After the posterior cruciate ligament was sectioned, these forces increased significantly at all angles of flexion. With no load applied to the popliteus muscle, the in situ forces in the popliteus complex were similar to those in the lateral collateral ligament. However, with a load of 44 N applied to the popliteus muscle, in situ forces in the popliteus complex were three to five, times higher than those in the lateral collateral ligament. These results reveal that in response to posterior tibial loads, the posterolateral structures play an important role at full extension in intact knees and at all angles of flexion in posterior cruciate ligament‐deficient knees. The popliteus muscle appears to be a major stabilizer under this loading condition; thus, the inability to restore its function may be a cause of unsatisfactory results in reconstructive procedures of the posterolateral structures of the knee.
Immobilization increases the vulnerability of rabbit medial collateral ligament autografts to creep
Authors: Boorman Richard S. , Shrive Nigel G. , Frank Cyril B. 
Published: February 2005

AbstractRehabilitation after soft‐tissue autograft reconstructions is controversial because there is indirect evidence that some grafts fail by creeping over time. The vulnerability of soft‐tissue grafts to creep over healing time and the effects of the load environment during healing on this vulnerability have never been studied specifically. We hypothesized that immobilization would decrease the magnitude of the vulnerability of ligament grafts to creep. Thirty‐nine skeletally mature New Zealand White rabbits underwent a standardized medial collateral ligament autograft procedure to the right hindlimb, and 19 of the rabbits also had the limb rigidly pinned into flexion. Subgroups were killed at 3 or 8 weeks, and all isolated tibia/medial collateral ligament/femur complexes were tested for creep at 4.1 MPa under a standardized protocol. Eight normal medial collateral ligament controls were tested similarly. Results showed that all grafts were quantitatively more susceptible to cyclic and static creep than were normal medial collateral ligament controls (p < 0.05). By 3 weeks of healing, immobilization significantly increased the magnitude of the vulnerability of the grafts to cyclic, static, and total creep (all: p < 0.05). Furthermore, the grafts had more unrecovered creep strain than did the controls following a 20‐minute recovery period. Contrary to our hypothesis, immobilization resulted in increased vulnerability of these ligament autografts to creep even with this relatively nonprovocative test of short duration and low stress. We postulate that following immobilization, this increase in the magnitude of susceptibility of the grafts to creep will result in functionally significant elongation of the graft if it is exposed to higher loads and over longer periods of time in vivo.
In vitro strength comparison of hydroxyapatite cement and polymethylmethacrylate in subchondral defects in caprine femora
Authors: Crawford Kevin , Berrey B. Hudson , Pierce William A. , Welch Robert D. 
Published: February 2005

AbstractHydroxyapatite cement was investigated in situ for the reconstruction of juxta‐articular defects. Polymethylmethacrylate is currently the most commonly used material for the reconstruction of bone defects following the exteriorization and curettage of aggressive benign tumors. In vitro, we compared the effects of hydroxyapatite cement and polymethylmethacrylate in restoring the stiffness of the subchondral plate in a caprine femoral defect model, fen matched pairs of caprine femora underwent nondestructive compression testing normal to the load‐bearing surface. A standardized subchondral defect 12 mm in diameter was created in the medial femoral condyle. Compression testing was repeated to determine the reduction in stiffness caused by the defect. Each femur from each pair was randomly assigned to one of two groups (n = 9), and the defects were augmented with either polymethylmethacrylate or hydroxyapatite cement. After 12 hours, compression tcsting/vas repeated to determine the subchondral stiffness after augmentation. Compared with intact femora, the defect specimens that were later treated with either polymethylmethacrylate or hydroxy‐npatite cement exhibited stiffness values of 70 (386 ± 107 N/mm) and 59% (343 ± 94 N/mm) respectively, which represented a significant reduction in stiffness (p = 0.05). Augmentation with polymethylmethacrylate or hydroxyapatite cement restored stiffness by 81 (450 111 N/mm) and 71% (413 ± 115 N/mm), respectively, of tile values of intact specimens. Hydroxyapatite cement restored stiffness significantly (p = 0.05) over the stiffness of the nonaugmented defect compared with the stiffness after augmentation with polymethylmethacrylate (p = 0.12). Neither polymethylmethacrylate nor hydroxyapatite cement restored stiffness to that of intact femora (p = 0.05). In the current defect model, hydroxyapatite cement was comparable with poly‐moihylmethacrylate in restoring subchondral stiffness. Unlike polymethylmethacrylate, however, hydroxy‐apalile cement has the following advantages: it is osteoconductive, is replaced by host bone, and avoids the potential for thermal necrosis. Hydroxyapatite cement may therefore provide a viable alternative to poly‐methylmethacrylate lor augmentation of juxta‐articular and other bone defects.