bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hamstrings cocontraction reduces internal rotation, anterior translation, and anterior cruciate ligament load in weight‐bearing flexion
Authors: MacWilliams B. A. , Wilson D. R. , Desjardins J. D. , Romero J. , Chao E. Y. S. 
Published: February 2005

AbstractStrengthening of the hamstrings is often recommended following injury and reconstruction of the anterior cruciate ligament. It has been suggested that hamstrings activity stabilizes the knee and reduces anterior cruciate ligament load during weight‐bearing flexion; however, the effects of hamstrings cocontraction on the kinematics and mechanics of the normal knee have not been assessed at physiological load levels. The aim of this study was to determine whether the addition of hamstrings force affects knee rotations, translations, and joint and quadriceps force during flexion with loads at physiological levels applied to the muscles and joints. Eight cadaveric knee specimens were tested with a servohydraulic mechanism capable of applying controlled dynamic loads to simulate quadriceps and hamstrings muscle forces throughout a physiological range of motion. A constant vertical load of physiologic magnitude was applied to the hip, and quadriceps force was varied to maintain equilibrium throughout flexion. Two conditions were tested: no hamstrings force and a constant hamstrings force equivalent to the vertical load. Hamstrings fore significantly reduced internal rotation (p < 0.0001) and anterior translation (p < 0.0001), increased quadriceps force (p < 0.0001) and normal resultant force on the tibia (p < 0.0001), and reversed the direction of the shear force on the tibia (p < 0.0001). These results suggest that hamstrings strengthening following anterior cruciate ligament injury may benefit anterior cruciate ligament‐deficient and reconstructed knees by reducing the load in the ligament; however, they also imply that this comes at the expense of efficiency and higher patellofemoral and joint forces.
Down‐regulation of chondrocyte aggrecan and type‐II Collagen gene expression correlates with increases in static compression magnitude and duration
Authors: Ragan Paula M. , Badger Alison M. , Cook Michael , Chin Vicki I. , Gowen Maxine , Grodzinsky Alan J. , Lark Michael W. 
Published: February 2005

AbstractThe goal of this study was to examine the simultaneous effects of mechanical compression of chondrocytes on mRNA expression and macromolecular synthesis of aggrrecan and type‐II collagen. Bovine cartilage explants were exposed to different magnitudes and durations of applied mechanical compression, and levels of aggrecan and type‐IIa collagen mRNA normalized to glyceraldehyde‐3‐phosphate dehydrogenase were measured and quantified by Northern blot analysis. Synthesis of aggrecan and type‐II collagen protein was measured by radiolabel incorporation of [35S]sulfate and [3H]proline into macromolecules. The results showed a dose‐dependent decrease in mRNA levels for aggrecan and type‐II collagen, with increasing compression relative to physiological cut thickness applied for 24 hours. Radiolabel incorporation into glycosaminoglycans and collagen also decreased with increasing compression in a dose‐related manner similar to the changes seen in mRNA expression. The modulation of aggrecan and type‐II collagen mRNA and protein synthesis were dependent on the duration of the compression. Aggrecan and type‐II collagen mRNA expression increased during the initial 0.5 hours of static compression; however, 4‐24 hours after compression was applied total mRNA levels had significantly decreased. The synthesis of aggrecan and collagen protein decreased more rapidly than did mRNA levels after the application of a step compression. Together, these results suggest that mechanical compression rapidly alters chondrocyte aggrecan and type‐II collagen gene expression on application of load. However, our results indicate that the observed decreases in biosynthesis may not be related solely to changes in mRNA expression. The mechanisms by which mechanical forces affect different segments of the biosynthetic pathways remain to be determined.
Cytoindentation for obtaining cell biomechanical properties
Authors: Shin Daehwan , Athanasiou Kyriacos 
Published: February 2005

AbstractA novel biomechanical testing methodology was developed to obtain the intrinsic material properties of an individual cell attached to a rigid substrate. With use of a newly designed cell‐indentation apparatus (cytoindenter), displacement‐controlled indentation tests were conducted on the surface of individual MG63 cells and the corresponding surface reaction force of each cell was measured. The cells were modeled with a linear elasticity solution of half‐space indentation and the linear biphasic theory on the assumption that the viscoelastic behavior of each cell was due to the interaction between the solid cytoskeletal matrix and the cytoplasmic fluid. To obtain the intrinsic material properties (aggregate modulus, Poisson's ratio, and permeability), the data for experimental surface reaction force and deformation were curve‐fitted with use of solutions predicted with a linear biphasic finite element code in conjunction with optimization routines. The MG63 osteoblast‐like cells had a compressive aggregate modulus of 2.05 ± 0.89 kPa, which is two to three orders of magnitude smaller than that of articular cartilage, six to seven orders smaller than that of compact bone, and quite similar to that of leukocytes. The peremeability was 1.18 ± 0.65 (×10‐10) m4/N‐s, which is four to six orders of magnitude larger than that of cartilage. The Poisson's ratio was 0.37 ± 0.03. The intrinsic material properties of the individual cell in this study can be useful in precisely quantifying mechanical stimuli acting on cells. This information is also needed for theories attempting to establish mechanotransductional relationships.
Inhibition of endochondral ossification during fracture repair in experimental hypothyroid rats
Authors: Urabe Ken , Hotokebuchi Takao , Oles Karl J. , Bronk James T. , Jingushi Seiya , Iwamoto Yukihide , Bolander Mark E. 
Published: February 2005

AbstractUsing a rat fracture model, we investigated the effects of a decrease in serum levels of thyroid hormone on the fracture‐repair process. Rats were divided into the following groups: (a) controls, (b) those treated with methimazole for the duration of the experiment, and (c) those treated with methimazole and L‐thyroxine, receiving both for the same duration. Three weeks after the initiation of pharmacologic treatment, closed femoral fractures were produced. The formation of cartilage tissue in the fracture callus in all rats was not obviously different on day 7 after fracture. In the rats treated with methimazole, differentiation from proliferating to hypertrophic chondrocytes in the fracture callus was less advanced and vascular invasion was clearly inhibited on day 12. Gene expression of alkaline phosphatase and osteocalcin in the callus was significantly lower in these rats than in the controls on days 10, 12, and 14. The mechanical properties of the fracture callus were also significantly weaker in these animals than in the controls on day 21, resulting in impaired fracture repair. These results demonstrate that hypothyroidism inhibits endochondral ossification, resulting in an impaired fracture‐repair process. L‐thyroxine replacement in the rats treated with methimazole caused the impaired repair process to revert to normal. These results indicate that thyroid hormone is one of the critical systemic factors for fracture repair.
Effect of age and sampling site on the chondro‐osteogenic potential of rabbit marrow‐derived mesenchymal progenitor cells
Authors: Huibregtse Barbara A. , Johnstone Brian , Goldberg Victor M. , Caplan Arnold I. 
Published: February 2005

AbstractFour sequential bone‐marrow aspirations from the ipsilateral tibia and iliac crest of New Zealand White rabbits, aged 4 months or 1, 2, or 3 years, were assayed in vitro and in vivo for their chondroosteogenic potential. Nonhematopoietic cells from the samples of bone marrow were isolated and expanded in culture: their colony‐forming efficiency was determined, and second‐passage marrow‐derived cells, referred to as mesenchymal progenitor cells, were loaded into porous calcium‐phosphate ceramic cubes as carrier vehicles for an in vivo cartilage and bone‐formation assay. The cubes were placed subcutaneously in nude BALB/C mice for 3 and 6 weeks. On histological examination, the cubes were scored for the presence of bone and cartilage in their pores, and average values for age groups and location were compared. At aspiration, the samples from the iliac crest exhibited an overall reduction in cell concentration with increasing age, and at the first harvest time, they showed a decrease in colony‐forming efficiency and cube score with increasing age. This study demonstrated that repeated bone‐marrow aspirations may be performed and may have an enhancing effect on the osteochondral progenitor cells of older animals.
Changes in bone mineral density at the proximal tibia after total knee arthroplasty: A 2‐year follow‐up of 28 knees using dual energy x‐ray absorptiometry
Authors: Li Ming G. , Nilsson Kjell G. 
Published: February 2005

AbstractThe change in bone mineral density at the proximal tibia during 2 years after total knee arthroplasty was studied in 28 knees (28 patients: 10 men and 18 women; median age: 71 years) with dual energy x‐ray absorptiometry. Bone mineral density was measured at the proximal tibia at nine regions of interest below the tibial component within 1 week after the operation (baseline); measurements were repeated at 3, 6, 12, and 24 months. All but one knee was malaligned before the operation, and all but three were corrected to within the normal range of alignment after it. The mean bone mineral density of all nine regions of interest at the proximal tibia temporarily decreased by 13% (p = 0.001) during the initial 3 months, probably due to a general metabolic reaction of the skeleton to the operative trauma combined with the effect of the postoperative immobilization, and then the initial level was regained for as long as 2 years. The overall changes in mean bone mineral density to 2 years were insignificant (p > 0.05); however, a great variation (43.9% decrease to 98.0% increase) was observed on an individual basis. This change over time was significantly associated (R2 = 0.36, p = 0.002) with the level of the baseline bone mineral density, which in turn was partly related (R2 = 0.24, p = 0.009) to the amount of malalignment of the knee before the operation. Knees with high baseline levels (n = 14: 11 with varus and three with valgus alignment) displayed a decrease of 10.0 ± 14.0% (mean ± SD, p > 0.05) for as long as 2 years, whereas those with low baseline levels (n = 14: seven with varus and six with valgus alignment and one neutrally alignment and one neutrally aligned) had an increase of 19.1 ± 38.2% (p = 0.038). In both groups, the mean bone mineral density converged to a level of 0.75–0.95 g/cm2 at 2 years.
Controlling the motion of total knee replacements using intercondylar guide surfaces
Authors: Walker Peter S. , Sathasivam Shivani 
Published: February 2005

AbstractTotal knee replacements using intercondylar cams, such as posterior stabilized types, have been in use for many years. In a previous study, software was written to analyze an alternative shape of the intercondylar cams. The goal of the current study was to investigate in a more general way the potential of intercondylar cams, or guide surfaces, for reproducing the anterior‐posterior motion of the natural knee throughout the flexion range. Typical sagittal outlines for the femoral and tibial bearing surfaces were defined, and a parametrized shape for the femoral guide surface was defined to produce a wide range of shapes. Software was written in which the femoral component was flexed in increments, with the posterior translation defined as a function of the flexion angle. The shape of the tibial guide surface was derived from the locus of the femoral guide surface at its multiple flexion positions. By iterating methodically through possible shapes of femoral guide surfaces, several types of total knee replacement components in common use today were identified, as well as other configurations of potential interest. For quantification of a given design, the software calculated the anterior and posterior laxity at each flexion angle. Laxity was defined as the motion before the femoral guide surface impacted the tibial guide surface or until the contact point of the bearing surfaces reached a specified slope. Convex femoral and concave saddle‐shaped tibial guide surfaces produced small laxities in both directions over most of the flexion range. A saddle design with small laxities in the first half of flexion, combined with a posterior stabilized feature, was an interesting combination. Potential improvements to the currently used designs were shown in this study and new shapes of intercondylar guide surfaces were derived that could be considered for application.
Hamstrings and iliotibial band forces affect knee kinematics and contact pattern
Authors: Kwak S. D. , Ahmad C. S. , Gardner T. R. , Grelsamer R. P. , Henry J. H. , Blankevoort L. , Ateshian G. A. , Mow V. C. 
Published: February 2005

AbstractMany clinical studies have emphasized the role of the hamstrings and the iliotibial band on knee mechanics, although few biomechanical studies have investigated it. This study therefore examined two hypotheses: (a) with loading of the hamstrings, the tibia translates posteriorly and rotates externally and the tibial contact pattern shifts anteriorly; furthermore, the changes in tibial kinematics alter patellar kinematics and contact; and (b) loading the iliotibial band alters the kinematics and contact pattern of the tibiofemoral joint similarly to loading the hamstrings, and loading the iliotibial band laterally translates the patella and its contact location. Five cadaveric knee specimens were tested with a specially designed knee‐joint testing machine in an open‐chain configuration. At various flexion angles, the knees were tested always with a quadriceps force but with and without a hamstrings force and with and without an iliotibial band force. The results support the first hypothesis. Hence, the hamstrings may be important anterior and rotational stabilizers of the tibia, a role similar to that of the anterior cruciate ligament. The results also support the second hypothesis, although the iliotibial band force had a smaller effect on the tibia than did the hamstrings force. Both forces also changed patellar kinematics and contact, demonstrating that these structures should also be considered during the clinical management of patellar disorders.
Importance of the medial meniscus in the anterior cruciate ligament‐deficient knee
Authors: Allen Christina R. , Wong Eric K. , Livesay Glen A. , Sakane Masataka , Fu Freddie H. , Woo Savio L‐Y. 
Published: February 2005

AbstractThe incidence of meniscal tears in the chronically anterior cruciate ligament‐deficient knee is increased, particularly in the medial menicus because it performs an important function in limiting knee motion. We evaluated the role of the medial meniscus in stabilizing the anterior cruciate ligament‐deficient knee and hypothesized that the resultant force in the meniscus is significantly elevated in the anterior cruciate ligament‐deficient knee. To test this hypothesis, we employed a robotic/universal force‐moment sensor testing system to determine the increase in the resultant force in the human medial meniscus in response to an anterior tibial load following transection of the anterior cruciate ligament. We also measured changes in the kinematics of the knee in multiple degrees of freedom following medial meniscectomy in the anterior cruciate ligament‐deficient knee. In response to a 134‐N anterior tibial load, the resultant force in the medial meniscus of the anterior cruciate ligament‐deficient knee increased significantly compared with that in the meniscus of the intact knee: it increased by a minimum of 10.1 N (52%) at full knee extension to a maximum of 50.2 N (197%) at 60° of flexion. Medial meniscectomy in the anterior cruciate ligament‐deficient knee also caused a significant increase in anterior tibial translation in response to the anterior tibial load, ranging from an increase of 2.2 mm at full knee extension to 5.8 mm at 60° of flexion. Conversely, coupled internal tibial rotation in response to the load decreased significantly, ranging from a decrease of 2.5° at 15° of knee flexion to 4.7° at 60° of flexion. Our data confirm the hypothesis that the resultant force in the medial meniscus is significantly greater in the anterior cruciate ligament‐deficient knee than in the intact knee when the knee is subjected to anterior tibial loads. This indicates that the demand on the medial meniscus in resisting anterior tibial loads is increased in the anterior cruciate ligament‐deficient knee compared with in the intact knee, suggesting a mechanism for the increased incidence of medial meniscal tears observed in chronically anterior cruciate ligament‐deficient patients. The large changes in kinematics due to medial meniscectomy in the anterior cruciate ligament‐deficient knee confirm the important role of the medial meniscus in controlling knee stability. These findings suggest that the reduction of resultant force in the meniscus may be a further motive for reconstructing the anterior cruciate ligament, with the goal of preserving meniscal integrity.
Osteogenic growth peptide normally stimulated by blood loss and marrow ablation has local and systemic effects on fracture healing in rats
Authors: Brager Michael A. , Patterson Michael J. , Connolly John F. , Nevo Zvi 
Published: February 2005

AbstractOsteogenic growth peptide, a histone H4‐related, 14‐amino‐acid peptide, is an active mediator of local, as well as systemic, osteogenic activity in response to marrow ablation, trauma, and blood loss. In this study, the effect of exogenous osteogenic growth peptide on the healing of femoral fractures in rats was investigated. A fracture at the midshaft of the femur was created in 50 rats. Half of the rats were injected subcutaneously with 25 ng of osteogenic growth peptide per rat per day for the first 7 days after fracture. Radiographs were taken each week, and the diameter of the callus was measured. The femurs of four animals from each group were harvested 1, 2, 3, and 4 weeks after fracture. Two femurs from each group were sectioned for histologic examination, and two were sectioned for measurement of density and mineral content. Marrow was aspirated from the contralateral femurs to establish adhering cell cultures, which were examined for osteogenicity. At 2 weeks, a large increase in mitogenicity and osteogenicity was seen in the marrow‐derived cultures from the rats treated with osteogenic growth peptide; this increase was sustained through 4 weeks. Extraction of RNA from the contralateral marrow (systemic expression) and callus (local expression) for amplification with reverse transcription‐polymerase chain reaction revealed greater systemic expression of transforming growth factors β1, β2, and β3, fibroblast growth factor‐2, insulin‐like growth factor‐1, and aggrecan throughout the 4 weeks after fracture, whereas types IIA and IIB collagen, link protein, and fibroblast growth factor receptor‐3 had a greater local expression. The specimens treated with osteogenic growth peptide had a stronger expression of transforming growth factor‐β1, both locally and systemically. The average diameter of the callus was greater for the treated rats at all time intervals, and peak diameters were 7.58 mm at 3 weeks for the treated rats and 6.64 mm at 2 weeks and 6.63 mm at 3 weeks for the controls. Histological study revealed an earlier organization and faster healing of the treated fractures, as evidenced by the larger, earlier appearance of cartilaginous soft callus and the more rapid organizaton of bridging trabecular bone. No statistical significance was obtained when these comparisons were made between the groups. These results suggest that osteogenic growth peptide can be used to promote earlier proliferation and differentiation of osteogenic cells in marrow and bone‐repair callus, possibly through its effect on the transforming growth factor‐β family.
Changes in conduction, blood flow, histology, and neurological status following acute nerve‐stretch injury induced by femoral lengthening
Authors: Jou I‐Ming , Lai Kuo‐An , Shen Chin‐Liang , Yamano Yoshiki 
Published: February 2005

AbstractThe effects of an acute stretch on evoked potential, blood flow, histological change, and clinical neurological state were studied in a rat model of acute nerve stretch induced by femoral lengthening. The purposes of this study were to assess, in a model of acute limb lengthening, the safe limits of nerve stretch for nerve function, the pathogenesis of nerve dysfunction, the sensitivity of spinal somatosensory evoked potential, and one of the proposed criteria for irreversible compromise of the sciatic nerve. Thirty‐two rats were assigned to one of four groups defined by the degree of acute femoral lengthening (8, 16, 24, and 32%). Spinal somatosensory evoked potential at L5/6 following stimulation of the sciatic nerve was recorded before, immediately after, and 30 minutes after lengthening. Sciatic nerve blood flow was measured by laser Doppler flowmetry at the stretched site before and after lengthening. One week after the operation and without further lengthening, clinical neurological status was evaluated by the functional index of the sciatic nerve and histological examination was performed. At the measurement immediately after the procedure, amplitude changed significantly in all groups except for the group with 8% lengthening. In all groups, sciatic nerve blood flow also dropped significantly compared with values for the control side. Moreover, a greater percentage increase in acute lengthening corresponded with more marked changes in spinal somatosensory evoked potential and sciatic nerve blood flow. The groups that underwent acute lengthening of 24 and 32% had significant neurological deficits and histological changes and demonstrated a significant and profound (50%) drop in amplitude and blood flow. We concluded that spinal somatosensory evoked potential is very sensitive and may serve as an effective tool for the early detection of impending acute nerve‐stretch injury and that a 50% reduction in amplitude indicates irreversible damage.