bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential regulation of type‐II and type‐X collagen synthesis by parathyroid hormone‐related protein in chick growth‐plate chondrocytes
Authors: O'Keefe Regis J. , Loveys Luke S. , Hicks David G. , Reynolds Paul R. , Crabb Ian D. , Puzas J. Edward , Rosier Randy N.
Published: February 2005

Parathyroid hormone‐related protein is a critical autocrine regulator of endochondral ossification in the growth plate, as demonstrated by the severe disruption of growth‐plate structure and function in parathyroid hormone‐related protein‐deficient transgenic mice. In the present study, the effects of parathyroid hormonerelated protein on the synthesis of collagen mRNA and protein were studied in short‐term cultures of isolated chick growth‐plate chondrocytes. Parathyroid hormone‐related protein selectively inhibits type‐X collagen protein synthesis with no significant effect on type‐II collagen protein synthesis. These effects were present in all maturationally distinct populations of chondrocytes separated by countercurrent centrifugal elutriation. In cultures of resting chondrocytes, the onset of type‐X collagen expression was inhibited, while the synthesis of type‐X collagen was decreased in cultures of hypertrophic chondrocytes. Synthesis of type‐II and type‐X collagen mRNA was examined by nonradioactive in situ hybridization with synthetic oligonucleotide cDNA probes, and the level of expression was quantified using digital image analysis. Dose‐dependent suppression of type‐X collagen gene expression by parathyroid hormone‐related protein was observed, with no significant effect on type‐II collagen mRNA detected. The results were confirmed by analysis of Northern blots of total chondrocyte mRNA. These experiments demonstrated differential transcriptional regulation of type‐II and type‐X collagen, with selective suppression of type‐X collagen expression, by parathyroid hormone‐related protein in growth‐plate chondrocytes, In addition. Excellent agreement was found between traditional protein and mRNA analyses and microscopic digitial image analysis techniques, supporting the use of this convenient and sensitive assay method. Parathyroid hormone‐related protein inhibits chondrocyte maturation and is known to stimulate proliferation, suggesting that this autocrine factor may function to regulate premature hypertrophy in the growth plate.
Expression of parathyroid hormone‐related peptide in human osteoarthritis
Authors: Okano Kunihiko , Tsukazaki Tomoo , Ohtsuru Akira , Osaki Makoto , Yonekura Akihiko , Iwasaki Katsuro , Yamashita Shunichi
Published: February 2005

To evaluate the involvement of the expression of parathyroid hormone‐related peptide gene in human articular cartilage pathology, we performed immunohistochemical staining and in situ hybridization on specimens of femoral head cartilage obtained from 15 patients with osteoarthritis, 11 with rheumatoid arthritis, and 12 control subjects. Parathyroid hormone‐related peptide‐positive chondrocytes were observed predominantly in degenerated lesions of osteoarthritic tissue and were less evident in rheumatoid arthritic samples, while the normal cartilage expressed little parathyroid hormone‐related peptide. In addition, the level of parathyroid hormone‐related peptide expression was clearly dependent on the degree of cartilage degeneration; cartilage tissues with moderate degenerative changes contained more positive chondrocytes compared with mildly or severely degenerated cartilage. In situ hybridization confirmed the localization of parathyroid hormone‐related peptide protein and demonstrated intense expression of mRNA of the peptide in osteoarthritic samples. This is the first demonstration of parathyroid hormone‐related peptide expression in chondrocytes from pathologic articular cartilage of humans. Our results, suggest that parathyroid hormone‐related peptide may be involved in the pathophysiology of osteoarthritis.
Physical properties of rabbit articular cartilage after transection of the anterior cruciate ligament
Authors: Sah Robert L. , Yang Arlene S. , Chen Albert C. , Hant James J. , Halili Reynaldo B. , Yoshioka Makoto , Amiel David , Coutts Richard D.
Published: February 2005

The effect of unilateral transection of the anterior cruciate ligament on the confined compression and swelling properties of the distal femoral articular cartilage of skeletally mature rabbits at 9 weeks after surgery was determined. Gross morphological grading of the transected and contralateral control distal femora stained with India ink confirmed that cartilage degeneration had been induced by ligament transection. Osteochondral cores, 1.8 mm in diameter, were harvested from the medial femoral condyles. The modulus, permeability, and electrokinetic (streaming potential) coefficient of the articular cartilage of the osteochondral cores were assessed by confined compression creep experiments. The properties (mean ± SD) of control cartilage were: confined compression modulus, 0.75 ± 0.28 MPa; hydraulic permeability, 0.63 ± 0.28 × 10−15 m2/Pa*sec; and electrokinetic coefficient, 0.16 ± 0.31 ± 10−9 V/Pa. In transected knees, the modulus was reduced by 18% (p = 0.04), while the permeability and electrokinetic coefficient were not detectably altered. The change in modulus was accompanied by a trend (p = 0.07) toward a decrease (‐11%) in the glycosaminoglycan density within the tissue, a significant increase (p <0.001) in the water content of the cartilage after equilibration in 1 × phosphate buffered saline from 70.3 ± 4.1% in control knees to 75.2 ± 4.0% in transected knees, and little further swelling after tissue equilibration in hypotonic saline. The compressive modulus of the cartilage from both control and transected knees was positively correlated with the density of tissue glycosaminoglycan. The alterations in the physical properties of the articular cartilage after transection of the anterior cruciate ligament in the rabbit show trends similar to those observed in human and other animal models of osteoarthritis and provide further support for the use of this model in the study of cartilage degeneration.
Calcium‐mobilizing purine receptors on the surface of mammalian articular chondrocytes
Authors: Koolpe Mitchell , Benton Hilary P.
Published: February 2005

If we are to fully understand mechanisms of cartilage homeostasis, it is essential that we know the full catalogue of receptors present on the surface of a chondrocyte and the pathways regulated by ligands that bind to these receptors. In this study, we describe chondrocyte responses to adenosine 5′‐triphosphate and related molecules. Adenosine 5′‐triphosphate stimulated a statistically significant, dose‐dependent, transient rise in the concentration of calcium ions in Fura 2‐loaded, differentiated, primary chondrocytes. The increase occurred in the absence of extracellular calcium, indicating a mobilization from intracellular stores. The increase in concentration of cytoplasmic calcium ions induced by adenosine 5′‐triphosphate was mimicked by uridine 5′‐triphosphate but not by 2‐methylthioadenosine 5′‐triphosphate. Cytidine 5′‐triphosphate, or adenosine. Heteralogous desensitization experiments demonstrated that chondrocytes showed no subsequent response to uridirie 5′‐triphosphate after initial stimulation with adenosine 5′‐triphosphate nor did they respond to adenosine 5′triphosphate in inverse conditions, thereby indicating competition for the same receptor site. Together, these results are consistent with the presence of a P2U: receptor on the cell surface of chondrocytes. Purine‐induced calcium mobilization in passaged chondrocytes showed the same pharmacological profile with respect to aganist sensitivity, but responses were of greater magnitude than responses in primary differentiated chondrocytes, suggesting upregulation of the receptor with time in culture. Adenosine 5′‐triphosphate and uridine 5′‐triphosphate (1‐100 μM) did not alter cartilage matrix synthesis as measured by rate of incorporation of [35S]sulfate into glycosaminoglycan by cartilage explants or primary chondrocytes. Matrix degradation, measured by release of glycosaminoglycan from cartilage explants, was also unaltered by adenosine 5′‐triphosphate or uridine 5′‐triphosphate (1‐100 μM). Production of prostaglandin E2was upregulated by incubation with either adenosine 5′‐triphosphate or uridine 5′‐triphosphate. These data demonstrate the presence of a functional P2U,‐like purine receptor on the surface of primary articular chondrocytes and support the hypothesis that altered concentrations of extracellular purines may influence chondrocyte metabolism.
Glycosaminoglycans and proteoglycans from different zones of the porcine knee meniscus
Authors: Nakano Takuo , Dodd Carole M. , Scott Paul G.
Published: February 2005

Medial and lateral knee menisci were obtained from 20‐week‐old pigs, dissected into three zones of equal width, and analyzed for collagen and glycosaminoglycan content and for types of glycosaminoglycan and proteoglycan. The thin inner zones contained about 76% collagen and 8% glycosaminoglycan (by dry weight) and the ouer zones. 93% collagen and 2% glycosaminoglycan. The most abundant glycosaminoglycan in all zones was chondroitin sulphate, accounting for about 80% of total glycosaminoglycan in the inner zones and 50–56% in the outer zones, Dermatan sulphate was the second most abundant glycosaminoglycan, present relative to chondroitin sulphate in a ratio of about 1:5–6 in the inner zones and 1:1.5 in the outer zones. Hyaluronic acid accounted for 4–5% of total glycosaminoglycan content in the inner zones and 10% in the outer zones. All compositional parameters for the middle zones were between those for the inner and outer zones. There were no statistically significant differences in composition between medial and lateral menisci. Proteoglycans were extracted and separated into two groups (large and small proteoglycans) by gel chromatography and were further characterized by gel electrophoresis. The large proteoglycans stained with use of monoclonal antibodies to chondroitin sulphate and keratan sulphate. Biglycan and decorin, two related dermatan sulphate proteoglycans, were identified in the small proteoglycan pool by their behaviour on gel electrophoresis and by immunostaining with specific antibodies. In the middle and inner zones, biglycan predominated. The observed lower dectrophoretic mobilities of dermatan sulphate proteoglycans from the inner zone compared with those from the outer zone were explained by the discovery of longer dermatan sulphate chains on the former. Collectively, these results show that the extracellular matrix of knee meniscus varies continuously across its width in a manner consistent with increased compressive loading on the thinner, inside aspect of the structure.
Limb lengthening promotes muscle growth
Authors: Day Charles S. , Moreland Morey S. , Floyd S. Steven , Huard Johnny
Published: February 2005

Studies of limb lengthening have demonstrated successful bone formation in the distraction gap. Failure of the muscle units to lengthen leads to many complications that significantly limit the success of this approach; it is, therefore, of paramount importance to characterize the behavior of the muscle during limb lengthening. In this study, tibiae of adult rabbits were lengthened for 10 days at a rate of 1 mm/day. The proliferative ability of the lengthened muscle was characterized using bromodeoxyuridine, a thymidine analogue that is incorporated during cell division, and desmin, a muscle‐specific marker. We observed a large number of proliferating cells, specifically in the lengthened muscle, that were co‐localized with many desmin‐positive cells. The presence of bromodeoxyuridine nuclei inside desminpositive muscle fibers suggests that limb lengthening promotes muscle growth by triggering myoblast proliferation and fusion into the lengthened muscle, Our findings are consistent with those of other studies in the reviewed literature, that also suggest that limb lengthening promotes muscle growth.
Topical application of nerve growth factor improves fracture healing in rats
Authors: Grills Brian L. , Schuijers Johannes A. , Ward Alex R.
Published: February 2005

The aim of the present study was to examine the effects of nerve growth factor on the healing of unsplinted fractured ribs. After fracture of a rib in male rats, nerve growth factor was delivered by a miniosmotic pump to the fracture site for 7 days at the rate of 1.4 μg/day. Callus catecholamine concentrations, hone callus size, histomorphometry, and biomechanical properties of the repairing rib were measured at 7,21, and 42 days after fracture. After 21 days, concentrations of norepinephrine and epinephrine were significantly increased in the group treated with nerve growth factor compared with those in the control group (211% norepinephrine and 322% epinephrine). Also, the midline longitudinal area of non osseous (fibrous tissue and cartilage) callus of the fracture was significantly smaller (54%) and had a higher proportion of cartilage in the treated group than in the controls. By 42 days, there was only bony callus between the fracture ends in both the control group and the treated group. The treated group, however, again showed significantly elevated concentrations of norepinephrine and epinephrine (286 and 382%, respectively) and significantly elevated breaking stress (50%) and Young's modulus (51%), together wilh a reduction in the transverse cross‐sectional area of the repair site (57%). The resultant increases in effectiveness and rate of repair of bone with administration of nerve growth factor suggest that it may play an important role in the healing processes of fractured bone.
Similar effects of recombinant human insulin‐like growth factor‐I and II on cellular activities in flexor tendons of young rabbits: Experimental studies in vitro
Authors: Abrahamsson Sven‐Olof
Published: February 2005

To improve the understanding of factors with the potential of affecting the healing of flexor tendons, this study compared the cellular effects of recombinant human insulin‐like growth factor‐II with those of recombinant human insulin‐like growth factor‐I in matched pairs of deep flexor tendons of young rabbits. Dose‐response effects on the synthesis of DNA and matrix proteins of either factor alone or in combination were investigated in short‐term culture, and effects on synthesis and turnover of matrix components were compared in long‐term culture. Both factors stimulated proteoglycan, collagen, noncollagen protein, and DNA synthesis in a dose‐dependent manner in the range of 10–500 ng/ml. Insulin‐like growth factor‐I increased proteoglycan synthesis to as much as six times that of controls but was less potent than insulin‐like growth factor‐II. Both factors stimulated increased cell proliferation by as much as five times compared with control values, but insulin‐like growth factor‐I was more potent than insulin‐like growth factor‐II. The two factors in combination did not enhance the synthesis of matrix proteins and DNA as compared with either factor alone. Insulin‐like growth factor‐I counteracted the decrease in collagen synthesis and stimulated protein synthesis to a higher degree than insulin‐like growth factor‐II in long‐term culture. Both factors had similar effects on matrix turnover, with estimated half times (t1/2) for elimination of newly labeled proteoglycans and proteins of 11 and 8 days, respectively. Insulin‐like growth factor‐II is capable of stimulating cell proliferation and matrix metabolism in tendon explants of young rabbits at levels similar to those of insulin‐like growth factor‐I; in combination, the two growth factors are unable to augment the stimulatory effects of either of the factors alone.
Migration and healing of ligament cells under inflammatory conditions
Authors: Witkowski Jeanine , Yang Li , Wood Douglas J. , Sung K‐L. Paul
Published: February 2005

It is well documented that the adult human medial collateral ligament has a functional healing response, whereas the anterior cruciate ligament does not. The differential healing responses of the medial collateral and anterior cruciate ligaments could be due to factors caused by different biological conditions and locations in vivo. In addition, different intrinsic properties of the constituent cells of these ligaments may contribute to their different healing abilities. Ligament healing follows an orderly process of hemorrhage, inflammation, proliferation, and remodeling. At the cellular level, healing involves a cell's detachment from and attachment to the matrix adjacent to the wound area, migration, and proliferation. This study sought to investigate whether, during migration, the responses of the medial collateral and anterior cruciate ligament fibroblasts are intrinsically different under the same inflammatory conditions. Human medial collateral arid anterior cruciate ligament fibroblast cells were cultured, and in vitro wounds were simulated by streaking the cells with an inoculating loop, creating a cell‐free area. The migration of the cells into this gap, thus filling the cell‐free area, was observed. Two sets of experiments were conducted; one varied the wound width and the, other added the inflammatory factors tumor necrosis factor‐a, complement C5a, and lipopolysaccharide the width of the wound increased, the rate of recovery decreased for both types of ligament cells (slope: anterior cruciate ligament, 0.13 hour/μm and medial collateral ligament, 0.10 hour/μm). Also, the three inflammatory factors used all inhibited the recovery rates of both ligaments to ones that were 1.4–2.3 times slower than controls. However, in both sets of experiments, the anterior cruciate ligament fibroblasts were more sensitive to inflammatory factors, and the medial collateral ligament fibroblasts had faster recovery rates (anterior cruciate ligament, 1.2–3.4 times slower than rates for medial collateral ligament fibroblasts, excluding those under lipopolysaccharide treatment). The results showed that medial collateral and anterior cruciate ligament fibroblasts responded differently under the same inflammatory conditions. This may suggest that these differences in intrinsic properties contribute to their different healing responses and abilities.
In situ forces in the anterior cruciate ligament and its bundles in response to anterior tibial loads
Authors: Sakane Masataka , Fox Ross J. , Glen Savio L‐Y. Woo , Livesay A. , Li Guoan , Fu Freddie H.
Published: February 2005

The anterior cruciate ligament has a complex fiber anatomy and is not considered to be a uniform structure. Current anterior cruciate ligament reconstructions succeed in stabilizing the knee, but they neither fully restore normal knee kinematics nor reproduce normal ligament, function. To improve the outcome of the reconstruction, it may be necessary to reproduce the complex function of the intact anterior cruciate ligament in the replacement graft. We examined the in situ forces in nine human anterior cruciate ligaments as well as the force distribution between the anteromedial and posterolateral bundles of the ligament in response to applied anterioi tibial loads ranging from 22 to 110 N at knee flexion angles of 0–90°. The analysis was performed using a robotic manipulator in conjunction with a universal force‐moment sensor. The in situ forces were determined with no device attached to the ligament, while the knee was permitted to move freely in response to the applied loads. We found that the in situ forces in the anterior cruciate ligament ranged from 12.8 ± 7.3 N under 22 N of anterior tibial load applied at 90° of knee flexion to 110.6 ± 14.8 N under 110 N of applied load at 15° of flexion. The magnitude of the in situ force in the posterolateral bundle was larger than that in the anteromedial bundle at knee flexion angles between 0 and 45°, reaching a maximum of 75.2 ± 18.3 N at 15° of knee flexion under an anterior tibial load of 110 N. The magnitude of the in situ force in the posterolateral bundle was significantly affected by knee flexion angle and anterior tibial load in a fashion remarkably similar to that seen in the anterior cruciate ligament. The magnitude of the in situ force in the anteromedial bundle, in contrast, remained relatively constant, not changing with flexion angle. Significant differences in the direction of the in situ force between the anteromedial bundle and the posterolateral bundle were found only at flexion angles of 0 and 60° and only under applied anterior tibial loads greater than 66 N. We have demonstrated the nonuniformity of the anterior cruciate ligament under unconstrained anterior tibial loads. Our data further suggest that in order for the anterior cruciate ligament replacement graft to reproduce the in situ forces of the normal anterior cruciate ligament, reconstruction techniques should take into account the role of the posterolateral bundle in addition to that of the anteromedial bundle.
Changes in the flexibility characteristics of the ankle complex due to damage to the lateral collateral ligaments: An in vitro and in vivo study
Authors: Lapointe Stephan J. , Siegler Sorin , Hillstrom Howard , Nobilini Robert R. , Mlodzienski Alan , Techner Lee
Published: February 2005

This study was part of a long‐term effort to develop a reliable diagnostic procedure for ankle ligament injuries. Earlier efforts led to the development and validation of a six‐degrees‐of‐freedom instrumented linkage capable of measuring the flexibility characteristics of the ankle complex in vitro and in vivo. The major goal of the present study was to determine if these flexibility measurements are sufficiently sensitive to detect the presence of damage to the lateral collateral ligaments of the ankle joint both in vitro and in vivo. The in vitro testing was conducted on the legs from six fresh cadavers before and after serial sectioning of the anterior talofibular ligament and the calcaneofibular ligament. The flexibility in inversion‐eversion, anterior drawer, and internal‐external rotation was measured before and after resection of the ligaments. The in vivo testing was conducted on five patients with unilateral injuries to the ankle ligament. The flexibility evaluation used for in vitro specimens was also performed on both the injured and the intact ankles. For the in vitro testing, the data analysis was based on comparison of flexibility values before and after resection of the ligaments, whereas the data analysis for the in vivo testing was based on comparison of the flexibility of the injured joint with that of the intact contralateral joint. The results of the in vitro study indicated that both an isolated rupture of the anterior talofibular ligament and combined damage of the anterior talofibular and calcaneofibular ligaments produce statistically significant changes in flexibility. Furthermore, the most sensitive parameters to the presence of ligament injuries were found to be early flexibility in anterior drawer, early flexibility in inversion, and the amount of coupling between internal rotation and inversion. These parameters provided a basis for differentiating between an isolated injury to the anterior talofibular ligament and a combined anterior talofibular and calcaneofibular ligament injury. For an isolated anterior talofibular ligament injury, a significant increase in flexibility in anterior drawer was present, whereas the increase in inversion flexibility or in the amount of coupling was insignificant. However, the increases in inversion flexibility and the amount of coupling became significant when both ligaments were involved. The results of the in vivo study indicated that significant changes in flexibility can be detected in patients with lateral ankle injuries. Finally, both the in vitro and in vivo results suggest that development of a reliable diagnostic test for ankle ligament injury based on changes in passive flexibility may be possible.
Effects of continuous distraction on cartilage in a moving joint: An investigation on adult rabbits
Authors: Hung Shih‐Chieh , Nakamura Kozo , Shiro Ryoji , Tanaka Kiyokazu , Kawahara Hazime , Kurokawa Takahide
Published: February 2005

An animal model, using distraction force on adult rabbits, was developed to study the effects of nonweight‐bearing on articular cartilage in a moving joint. Histologic evaluation was used to compare the morphology of chondrocytes, safranin O intensity, cartilage thickness, and structural changes between the test and contralateral joints. At 3 and 6 weeks, the chondrocytes in superficial and intermediate zones were round, with an increase in cellular volume density and mean cell volume and with less metachromasia; the safranin O intensity and cartilage thickness were the same as in the controls. In cartilage of the 9‐week group, mean cell volume decreased with cell cloning in the superficial zone, while numerical density increased and mean matrix volume per cell decreased in the superficial and intermediate zones. The cartilage, with a 34% reduction in thickness and a 53–72% decrease in safranin O intensity from the superficial to the deep zone, had superficial fibrotic proliferation, suface erosion or depression, ard tidemark irregularity. Continuous distraction in a moving joint caused morphological changes in chondrocytes prior to degeneration of cartilage. These results support the hypothesis that the forces perceived by cells may dictate their shape and then stimulate alterations in cellular biochemistry and matrix metabolism.
Comparison of the tissue response to absorbable self‐reinforced polylactide screws and metallic screws in the fixation of cancellous bone osteotomies: An experimental study on the rabbit distal femur
Authors: Viljanen Janne T. , Pihlajamäki Harri K. , Törmälä Pertti O. , Rokkanen Pentti U.
Published: February 2005

The availability of absorbable fracture‐fixation devices for clinical use calls for better knowledge of the reaction of bone tissue to absorbable polyester implants as compared with similar metallic devices. To examine and compare the tissue response to biodegradable and metallic screws within cancellous bone, a transverse transcondylar osteotomy of the distal femur was fixed with absorbable self‐reinforced polylevolactide screws in 35 rabbits and with stainless‐steel screws in 35 rabbits. New bone formation and consolidation of the osteotomy were examined histologically, histomorphometrically, and microradiographically within standardized sample fields 1,3,6,12,24,36, and 48 weeks postoperatively. The intact contralateral femur served as the control. A vigorous osteoconductive response to the polylevolactide screws was observed at 3 weeks postoperatively, and the osteoid surface fraction was significantly higher in all follow‐ups than in the contralateral femora. In the femora with metallic screws, new bone formation was seen 3,6, and 12 weeks postoperatively, but at 24,36, and 48 weeks the osteoid surface fraction did not differ significantly from that of the intact control femora. The total bone area was significantly larger in the femora with self‐reinforced polylevolactide screws than in the control bone 6‐48 weeks postoperatively; in the femora with metallic screws, this was found only at 6 and 12 weeks. After 48 weeks, the femora fixed with metallic screws had statistically smaller total bone area than the intact control femora. Solid bone union was seen in 84% of the osteotomies in the self‐reinforced polylevolactide group and in 76% of those in the metallic group after 3 weeks or more. No signs, of degradation of the self‐reinforced polylevolactide implant and only a mild foreign‐body reaction with no accumulations of inflammatory cells to either self‐reinforced polylevolactide or metallic screws were observed during the follow‐up period. Both types of screws seemed to induce an osteostimulatory response around their threads. This phenomenon was transient for metallic screws but lasted for at least 48 weeks for self‐reinforced polylevolactide screws. The polylevolactide screw does not seem to cause osteopenia at the implantation site. The fixation properties of both self‐reinforced polylevolactide screws and metallic screws appear to be sufficient for the fixation of small fragments of cancellous bone.
Subfracture insult to a knee joint causes alterations in the bone and in the functional stiffness of overlying cartilage
Authors: Newberry William N. , Zukosky Derek K. , Haut Roger C.
Published: February 2005

The current criteria used by the automotive industry for predicting joint injury are based on fracture of bone, but clinical studies suggest that chronic diseases such as osteoarthrosis can occur from a single blunt insult without bone fracture. In the current study, blunt insults were delivered to the patellofemoral joints of rabbits without producing bone fractures. Biomechanical and histological studies were performed on joint tissues at various times after insult. The functional integrity of the retropatellar cartilage on the lateral facet was measured with mechanical indentation experiments, and the thickness of the subchondral bone was measured from histological sections. Impacts produced surface lesions on the retropatellar cartilage. The thickness of the subchondral bone in representative animals tended to increase with time after insult, and the bone exhibited significant thickening at 12 months. The overlying cartilage showed signs of degeneration. However, the mechanical stiffness of the cartilage did not change until 12 months after the insult.
Extracellular collagen modulates the regulation of chondrocytes by transforming growth factor‐β1
Authors: Qi Wen‐Ning , Scully Sean P.
Published: February 2005

This article describes the modulation, by extracellular collagen, of DNA and proteoglycan synthesis in articular chondrocytes stimulated with transforming growth factor‐β1, Type‐I and type‐II collagen, heat denatured type‐II collagen, and bovine serum albumin were each incorporated into alginate in increasing concentrations. Bovine articular chondrocytes were isolated and were resuspended in the alginate, yielding alginate beads with final extracellular protein concentrations of 0‐1.5% (wt/vol) for the collagens and 0‐2.5% (wt/vol) for bovine serum albumin. Cultures of beads were maintained for 7 days in basal Dulbecco's modified Eagle medium or in medium supplemented with 10 ng/ml transforming growth factor‐β1. Subsequently, the synthesis of DNA and proteoglycan was measured by radiolabel‐incorporation methods with [35S]sulfate and [3H]thymidine, and the values were normalized to the DNA content. Transforming growth factor‐β1 stimulated the synthesis of both DNA and proteoglycan in a bimodal fashion. The presence of extracellular type‐II collagen increased the rate of DNA and proteoglycan synthesis in a dose‐dependent fashion in cultures stimulated by transforming growth factor‐β1, whereas heat‐inactivated type‐II collagen abrogated the effects observed with type‐II collagen for synthesis of both DNA and proteoglycan. In contrast, the presence of extracellular type‐I collagen caused a dose‐dependent inhibition of synthesis of both DNA and proteoglycan in cultures stimulated with transforming growth factor‐β1. Extracellular bovine serum albumin brought about a limited increase in synthesis rates, presumably by blocking nonspecific cytokine binding. These results suggest that type‐II collagen has a specific role in chondrocyte regulation and serves to mediate the response of chondrocytes to transforming growth factor‐β1.
Forearm muscle oxygenation decreases with low levels of voluntary contraction
Authors: Murthy Gita , Kahan Norman J. , Hargens Alan R. , Rempel David M.
Published: February 2005

The purpose of our investigation was to determine if the near infrared spectroscopy technique was sensitive to changes in tissue oxygenation at low levels of isometric contraction in the extensor carpi radialis brevis muscle. Nine subjects were seated with the right arm abducted to 45°, elbow flexed to 85°, forearm pronated 45°, and wrist and forearm supported on an armrest throughout the protocol. Altered tissue oxygenation was measured noninvasively with near infrared spectroscopy. The near infrared spectroscopy probe was placed over the extensor carpi radialis brevis of the subject's right forearm and secured with an elastic wrap. After 1 minute of baseline measurements taken with the muscle relaxed, four different loads were applied just proximal to the metacarpophalangeal joint such that the subjects isometrically contracted the extensor carpi radialis brevis at 5, 10, 15, and 50% of the maximum voluntary contraction for 1 minute each. A 3‐minute recovery period followed each level of contraction. At the end of the protocol, with the probe still in place, a value for ischemic tissue oxygenation was obtained for each subject. This value was considered the physiological zero and hence 0% tissue oxygenation. Mean tissue oxygenation (±SE) decreased from resting baseline (100% tissue oxygenation) to 89 ± 4, 81 ± 8, 78 ± 8, and 47 ± 8% at 5, 10, 15, and 50% of the maximum voluntary contraction, respectively. Tissue oxygenation levels at 10, 15, and 50% of the maximum voluntary contraction were significantly lower (p < 0.05) than the baseline value. Our results indicate that tissue oxygenation significantly decreases during brief, low levels of static muscle contraction and that near infrared spectroscopy is a sensitive technique for detecting deoxygenation noninvasively at low levels of forearm muscle contraction. Our findings have important implications in occupational medicine because oxygen depletion induced by low levels of muscle contraction may be directly linked to muscle fatigue.
Effect of low dietary calcium on bone metabolism in the SENCAR mouse
Authors: Murray Elsa J. Brochmann , Murray Samuel S. , Grisanti Mario , Duarte Maria Eugenia L. , Urist Marshall R.
Published: February 2005

The SENCAR (sensitive to carcinogenesis) mouse is a unique tool for investigating the interaction between a specific defect in intracellular signaling, dietary calcium, and metabolic bone disease. The SENCAR mouse was developed by selective breeding for enhanced sensitivity to two‐stage carcinogenesis. Its major genetic defect, which renders it exquisitely sensitive to stimulation with diacylglycerol or phorbol esters, is in the regulatory domain of protein kinase C, one of the primary intracellular mediators of hormonal effects. At sexual maturity, SENCAR mice are large and have big bones, but our previous pharmacokinetic studies showed that they accumulate lesscalcium under normal conditions and lose more calcium under adverse conditions than do other, standard strains of mice. To histologically define the effect of low dietary calcium on bone metabolism, we performed histomorphometric analysis of tetracycline‐labeled sections of femoral bone from male SENCAR mice maintained on calcium‐sufficient and calcium‐deficient diets during the critical period from 10 to 14 weeks of age. The bone volume, absolute osteoid volume, and mineral apposition rate were lower at 14 than at 10 weeks of age in SENCAR mice fed 0.02 or 0.6% calcium diets. Calcium deficiency increased the architectural disarray and the probability of observing focal discontinuities in the growth plate. Thus, characteristic features of impaired bone metabolism (low bone volume and apposition rate) develop early in SENCAR mice and are exacerbated by low dietary calcium. Detailed examinations of the histology and biochemistry of SENCAR mouse bone will provide insights into the mechanisms by which specific defects in the signal transduction of protein kinase C contribute to impaired bone metabolism.
Surface remodeling of trabecular bone using a tissue level model
Authors: Smith Tait S. , Martin R. Bruce , Hubbard Mont , Bay Brian K.
Published: February 2005

We propose a two‐dimensional mathematical model of trabecular bone remodeling that simulates the surface‐based addition and removal of material in the actual physiological process. The model is based on a finite element representation of individual trabecular struts in which the material properties of the subtrabecular elements are constant. The remodeling stimulus is strain energy density, sensed and communicated through the osteocytic network as proposed by Mullender et al. We propose a modified osteocyte communication scheme that incorporates bone‐lining cells and examines the implications of set point locations in one or the other of these two cell types. This model produces trabecular struts that align with its general loading direction. Placing the set point in the bone‐lining cells rather than in the osteocytes makes the model more sensitive to changes in the other biological parameters. Introduction of a dead zone causes the model to reach a less oscillatory equilibrium in fewer iterations and produces better in‐filling of trabecular strut intersections. The model gravitates to equilibrium states in which the average strain energy density is inversely proportional to the bone volume fraction to the 3.2 power.
Bone maintenance and remodeling: A control system based on fatigue damage
Authors: Taylor David
Published: February 2005

This paper explores the relationship between damage, repair, and remodeling in compact bone. A model of microcrack growth is developed that takes account of recent findings on the behaviour of small fatigue cracks in other materials. This is combined with a simple model of a repair process, envisaged as a constant rate of decrease in crack length. The system that results is capable of achieving a stable and precise control of crack length without the need to measure it. This is very useful because it implies that bone does not require the complexities of crack‐measuring, transducers or active decision‐making processes. A simple explanation is suggested for the presence of a “lazy zone” of remodeling equilibrium strains, and the limits of this zone are quantified. The model is developed through a necessarily simplified geometry and loading scheme but can be extended to provide a general solution applicable to in vivo conditions.
Model of flexural fatigue damage accumulation for cortical bone
Authors: Griffin L. V. , Gibeling J. C. , Martin R. B. , Gibson V. A. , Stover S. M.
Published: February 2005

Analytical models that predict modulus degradation in cortical bone subjected to uniaxial fatigue loading in tension and compression are presented. On the basis of experimental observations, damage was modeled as self‐limiting for tension but not for compression. These mechanistic uniaxial damage models were then developed into a model for flexural fatigue of cortical bone based on laminated beam theory. The unknown coefficients in the uniaxial damage models were obtained by successfully fitting the resulting equations to uniaxial fatigue data from the literature on human cortical bone in tension and compression. Then, the predictions of the flexural model for the behavior of human cortical bone were compared with experimental results from a small but independent set of specimens tested at three different ranges of load in our laboratory. The behavior of the modulus degradation curves and the flexural fatigue lives of the specimens were in excellent agreement with the predictions of the model.
Gait compensations in patients with osteoarthritis of the hip and their relationship to pain and passive hip motion
Authors: Hurwitz D. E. , Hulet C. H. , Andriacchi T. P. , Rosenberg A. G. , Galante J. O.
Published: February 2005

This study related mechanisms of gait compensations to the level of pain and to limitations in passive motion in patients with osteoarthritis of the hip. Joint motion, moments, and intersegmental forces were calculated for 19 patients with unilateral osteoarthritis of the hip (12 men and seven women) and for a group of normal subjects (12 men and seven women) with a similar age distribution. The patients who had osteoarthritis walked with a decreased dynamic range of motion (17 ± 4°) of the hip and with a hesitation or reversal in the direction of the sagittal plane motion as they extended the hip. The patients with a hesitation or reversal in motion had a greater loss in the range of motion of the hip during gait (p < 0.004) and a greater passive flexion contracture (p < 0.022) than those with a smooth pattern of hip motion. This alteration in the pattern of motion was interpreted as a mechanism to increase effective extension of the hip during stance through increased anterior pelvic tilt and lumbar lordosis. The patients who had osteoarthritis of the hip walked with significantly decreased external extension, adduction, and internal and external rotation moments (p < 0.008). The decreased extension moment was significantly correlated with an increased level of pain (R = 0.78; p < 0.001). This finding suggests that decreasing muscle forces (hip flexors) may be one mechapism used to adapt to pain.
Ligament creep cannot be predicted from stress relaxation at low stress: A biomechanical study of the rabbit medial collateral ligament
Authors: Thornton G. M. , Oliynyk A. , Frank C. B. , Shrive N. G.
Published: February 2005

In normal daily activity, ligaments are probably subjected to repeated loading rather than to repeated deformation. The viscoelastic response to repeated loading is creep; this effect has significance for ligament reconstructions, which potentially “stretch out” over time. However, most experimental studies have examined the viscoelastic response to repeated deformation, stress relaxation. We hypothesized that the creep of a ligament could be predicted from its stress‐relaxation behaviour. Left and right medial collateral ligaments of eight skeletally mature rabbits were subjected to either creep or stress‐relaxation testing under comparable conditions. The time‐dependent increase in strain (creep) and reduction in load (relaxation) from the tests were modelled with use of the quasilinear viscoelastic theory and generalized standard linear solid modelling. Ligaments were found to creep distinctly less than would be predicted from relaxation tests. Although the reason for this behaviour remains unknown, we speculate that it is due to the progressive recruitment of collagen fibres during creep.
Hyperpolarisation of cultured human chondrocytes following cyclical pressure‐induced strain: Evidence of a role for α5β1 integrin as a chondrocyte mechanoreceptor
Authors: Wright M. O. , Nishida K. , Bavington C. , Godolphin J. L. , Dunne E. , Walmsley S. , Jobanputra P. , Nuki G. , Salter D. M.
Published: February 2005

Mechanical stimuli influence chondrocyte metabolism, inducing changes in intracellular cyclic adenosine monophosphate and proteoglycan production. We have previously demonstrated that primary monolaycr cultures of human chondrocyles have an electropysiological response after intermittent pressure‐induced strain characterised by a membrane hyperpolarisation of approximately 40%. The mechanisms responsible for these changes are not fully understood but potentially involve signalling molecules such as integrins that link extracellular matrix with cytoplasmic components. The results reported in this paper demonstrate that the transduction pathways involved in the hyperpolarisation response of human articular chondrocytes in vitro after cyclical pressure‐induced strain involve α5β1 integrin. We have demonstrated, using pharmacological inhibitors of a variety of intracellular signalling pathways, that the actin cytoskeleton, the phospholipase C calmodulin pathway, and both tyrosine protein kinase and protein kinase C activities are important in the transduction of the electrophysiological response. These results suggest that α5β1 is an important chondrocyte mechanoreceptor and a potential regulator of chondrocyte function.
Improved osteoinduction of cortical bone allografts: A study of the effects of laser perforation and partial demineralization
Authors: Lewandrowski Kai‐Uwe , Tomford William W. , Schomacker Kevin T. , Deutsch Thomas F. , Mankin Henry J.
Published: February 2005

Massive cortical bone allografts have been found to incorporate slowly into host bone and thus are subject to complications such as nonunion, fatigue fracture, and infection. To better understand and improve the process of osteoinduction in these types of bone grafts, a new experimental model was developed with use of diaphyseal cortical bone grafts from rat tibiae that were prepared by partial mineralization and drilling of 0.33 mm diameter holes with a pulsed, 2.94 μm wavelength, erbiunr:yttrium‐aluminum‐garnet laser. Six types of grafts were analyzed: untreated (Type I), demineralized 25 μm deep (Type II), demineralized 150 μm deep (Type III), laser perforated (Type V), laser perforated and then demineralized 25 μm deep (Type V), and laser perforated and then demineralized 150 μm deep (Type VI). The graft was orthotopically transplanted in the tibia of an adult Sprague‐Dawley rat and followed for as long as 4 months. Histologic evaluation at 1 and 4 months postoperatively with use of hematoxylin and eosin staining confirmed that there was new bone growth in Types II, III, V, and VI grafts. The amount of growth was estimated by comparing bone mineral density before implantation with values obtained after retrieval of the graft. These measurements were correlated to histomorphometric analysis of graft incorporation. The results show that the processes of partial demineralization (p < 0.000001) and laser perforation with partial demineralization (p < 0.000001) were both significant in enhancing bone growth in this model. New bone growth was significantly increased when the grafts were prepared with extensive demineralization (p < 0.015). This study demonstrates that osteogenesis in cortical bone grafts can be fostered through the process of partial demineralization and laser perforation. To the extent that minimal partial demineralization and laser perforation allow maintenance of Structural integrity while altering the osteoinductive properties in such a way as to promote ingrowth of new bone, this experimental model represents an advance in understanding how osteogenesis in cortical bone grafts may be improved.
Assessment of cell proliferation in regenerating bone during distraction osteogenesis at different distraction rates
Authors: Li G. , Simpson A. H. R. W. , Kenwright J. , Triffitt J. T.
Published: February 2005

An experimental model of lengthening of the lower limb was used to study the morphology and cellular proliferation of regenerating bone tissue after 20% lengthening at four rates of distraction. Groups of rabbits were killed at different times 1‐8 weeks after surgery. The regenerated area was divided into three zones: fibrous, primary mineralization front, and new bone. As the rate of distraction increased, the size of the fibrous zone increased and that of Ihe new bone. one decreased. Necrosis, formation of cysts, and cartilage were found in the regenerated area at the higher distraction rates. Cell proliferation was assessed by in vivo labelling with' bromodeoxyuridine and the positive staining index for anti‐bromodeoxyuridine antibody was calculated in the zones of the regenerated tissue, The index values for the fibrous zones and the new bone zones did not differ significantly in any of Ihe groups, The value increased significantly (p < 0,05) in the primary mineralization front as the rate of distraction increased from 0.3 to 0.7 mm/day, but there was no further significant increase at higher distraction rates. In conclusion, cell proliferation was increased at all of the higher rates (more than 0.3 mm/day) of distraction studied. Higher rates of distraction caused tissue damage. A distraction rate of 0.7 mm/day appeared optimal for cell proliferation and histological characteristics.