bluuebunny/crossref_metadata_2025 huggingface dataset:
Method for the measurement of friction between tendon and pulley
Authors: Uchiyama S. , Coert J. H. , Berglund L. , Amadio P. C. , An K.‐N.
Published: February 2005

An experimental system was developed that allows direct measurement of friction at the tendon‐pulley interface, and the results were interpreted by use of a theoretical model for friction of a cable around a fixed pulley. Validation experiments were conducted with a nylon cable around a nylon rod. One end of the cable was connected to an actuator via a load cell, and the other end was connected to a 4.9 N load via a similar load cell. The cable was passed around the nylon rod and then pulled toward the actuator. Tests were performed at five different arcs of contact. The friction forces, as measured by the difference between two load transducers, were compared with those determined for a theoretical model and were used for calculation of the friction coefficient. The measurement system then was used to study the friction force between the flexor digitorum profundus tendon and the A2 pulley on nine fresh frozen index digits. The method allows us to measure the direct interaction between the tendon and pulley and could be used to evaluate and compare procedures for tendon‐pulley and pulley repair and reconstruction, as well as for the study of tendon‐pulley friction in various pathological conditions.
Tibial intercalary allograft incorporation: Comparison of fixation with locked intramedullary nail and dynamic compression plate
Authors: Muir Peter , Johnson Kenneth A.
Published: February 2005

The healing and incorporation of intercalary cortical bone allografts stabilized with locked intramedullary nails was compared with that of allografts fixed with compression plates in a sheep model. Both techniques achieved healing of the allograft to host tibia, and there was no measurable difference in the area of callus or the quality of union histologically. Incorporation of the allograft as measured by fluorescent labeling was not different in the two groups.
Dimensional growth and extracellular matrix accumulation by neonatal rat mandibular condyles in long‐term culture
Authors: Garcia A. Minerva , Gray Martha L.
Published: February 2005

Mandibular condyles in organ culture commonly have been used as a model system for examination of the factors that influence skeletal growth and development. The work reported here complements previously published histological studies by providing quantitative temporal information on growth and matrix accumulation. Condyles maintained for as long as 5 weeks in serum‐free and 1% serum‐supplemented culture media were found to remain viable and metabolically active as demonstrated by continued dimensional growth as well as cell and matrix accumulation. Growth occurred by a combination of cell proliferation, matrix synthesis and accumulation, and cell hypertrophy (with the latter two mechanisms dominating). Increase in tissue volume correlated directly with increased glycosaminoglycan content; both increased 7‐fold over 5 weeks. In comparison with serum‐free culture, after 35 days in medium containing 1% serum, glycosaminoglycan content was 24% lower and collagen content was 36% higher, whereas dry weight, condyle length, and DNA content were not significantly different; in addition, histological observation suggested that, for samples cultured with serum, chondrogenic phenotype had been lost from some regions. The temporal behavior for all growth parameters exhibited a transient phase 1–2 weeks in duration followed by a steady‐state period in which dimenssions and tissue constituents or content increased at a constant or near constant rate. Comparison of the rates of incorporation of [35S]sulfate with glycosaminoglycan content in serum‐free cultures suggests that the loss of glycosaminoglycan occurs only initially or is negligible; therefore, under these baseline conditions, cartilage glycosaminoglycan content reflects the biosynthetic rate. The high degree of reproducibility seen during steady‐state growth suggests that these data provide reliable baseline information and further supports the notion that this model system is useful for investigation of the effects of specific physical factors on in vitro growth and development.
Texture correlation: A method for the measurement of detailed strain distributions within trabecular bone
Authors: Bay Brian K.
Published: February 2005

A new technique, termed texture correlation, is described for the measurement of displacement and strain patterns within samples of trabecular bone. Texture correlation is a modification of digital image correlation, a method for analysis of deformation in objects marked with random surface speckle. Instead of surface speckle, the trabecular pattern itself is used as a basis for correlation. Digitized contact radiographs of samples in unloaded and loaded states are compared by computer to determine displacements of a grid of points. Displacements are filtered with Savitsky‐Golay polynomial‐convolution filters to reduce noise, and then strain is calculated with finite element techniques. The method is conceptually similar to the manual measurement of surface markers but has numerous advantages: no marking of the sample is required, displacements are measured automatically by computer, measurement of thousands of displacements is practical, and filtering allows calculation of strain over small regions of the sample. The validity of the technique is demonstrated by comparison of strain patterns measured by texture correlation at low resolution with the same patterns measured by a surface marker technique in six samples of trabecular bone from a human femoral head. The results of texture correlation at full resolution then are presented to demonstrate the capabilities of the method.
Elastase activity, uninhibited by α1‐antitrypsin, in the periprosthetic connective matrix around loose total hip prostheses
Authors: Takagi Michiaki , Konttinen Yrjö T. , Santavirta Seppo , Kangaspunta Petri , Sorsa Timo , Yamakawa Mitsunori , Suda Akio
Published: February 2005

To clarify the proteolytic cascade in the loosening of total hip prostheses, the presence, tissue localization, and content of the serine proteinase, elastase, and its endogenous inhibitor, α1‐antitrypsin, were studied in perioprosthetic tissues around 12 loose hip prostheses by immunohistochemistry, spectrophotometric enzyme assay, and immunoblot analysis, and the results were compared with those in control synovial tissue samples from eight knees. Increased numbers of elastase‐immunoreactive cells and elevated elastase activity, inhibited by the addition of native α1‐antitrypsin, were observed both in the interface tissues between the bone and implants and in the pseudocapsular tissues from around loose hip prostheses. Elevated elastase activity, uninhibited by α1‐antitrypsin in situ and inhibited by the addition of native inhibitor, suggests a proteinase‐inhibitor imbalance that contributes to the weakening of periprosthetic tissues and thus causes the loosening of hip prostheses.
In vitro evaluation of bonding of the cement‐metal interface of a total hip femoral component using ultrasound
Authors: Davies Jeff P. , Tse M‐K. , Harris W. H.
Published: February 2005

Debonding of the cement‐metal interface of a cemented femoral component is one mechanism associated with loosening of total hip replacement. An ultrasonic pulse‐echo technique was developed to determine, nondestructively, the integrity of the cement‐metal interface in vitro. The characteristics of the ultrasonic reflections of bonded and debonded interfaces were obtained by using a physical model that consisted of a flat slab of cement and a flat cobalt alloy plate with known conditions of bonded and debonded interfaces. The same model was used to establish that the ultrasonic technique could distinguish between two surfaces that were in direct apposition but not bonded and those that were actually bonded. This technique then was shown to be useful in nondestructively detecting bonded and debonded cement‐metal interfaces of femoral prostheses cemented into fiberglass femurs and femurs from human cadavera.
Femoral component migration in total knee arthroplasty: Randomized study comparing cemented and uncemented fixation of the Miller‐Galante I design
Authors: Nilsson Kjell G. , Kärrholm Johan , Linder Lars
Published: February 2005

The Miller‐Galante I knee replacement was inserted in 25 women and three men (33 knees) with osteoarthrosis. All patients received a TiAIV femoral component with a commercially pure titanium fibermesh undersurface. Cemented or cementless fixation was used based on a randomization protocol. Micromotions of the femoral components were recorded with roentgen stereophotogrammetric analysis during the first 2 postoperative years. The magnitude of migration did not differ between cemented and uncemented fixation. The number of nonmigrating prostheses decreased from 21 (12 cemented and nine uncemented) at 3 months to six (three cemented and three uncemented) at 24 months. In both groups, the magnitude of prosthetic tilting about the longitudinal axis (internal‐external rotation) was as large as that about the transverse axis (flexion‐extension). Rotation into extension was as common as rotation into flexion. The largest translations were recorded at either of the posterior condyles. In 10 uncemented components, radiolucent lines were seen at the distal interface postoperatively. Proximal migration of the femoral component was recorded in these knees, and the width of the lines decreased or the lines disappeared totally at 24 months. After 2 years, lines were noted around four cemented and four uncemented replacements, mainly anteriorly or distally. All of these prostheses migrated. One prosthesis, revised because of malalignment, displayed pronounced migration after an initial period of stability. Bone ingrowth was observed anteriorly and anterodistally despite the presence of motions of 1 mm or more.
Reperfusion injury in vascularized bone allografts
Authors: Moran Christopher G. , McGrory Brian J. , Bronk James T. , Wood Michael B.
Published: February 2005

A vascularized allograft canine tibia was used to evaluate the preservation of the osseous microcirculation. Six pairs of adult tibiae were harvested, and a vascular washout was performed with mannitol solution. The bones then were perfused continuously (0.03 ml/min at 5°C) for 20 hours with University of Wisconsin solution. Following storage, each pair of bones was transplanted, by microvasacular anastomosis, to a recipient dog, and bone blood flow was estimated using the radiolabeled microsphere method. Adreno‐receptor control mechanisms were evaluated in one specimen, and endothelial function was evaluated in the contralateral specimen. Alpha1‐adrenoreceptor blockade produced a significant increase (89 ± 80%) in bone blood flow (p < 0.05). A further increase (99 ± 56%) was observed with the addition of alpha2‐blockade (p < 0.01). Acetylcholine produced a decrease (65 ± 65%) in blo od flow (p < 0.1). This effect was inhibited by L‐NG‐monomethyl‐arginine, which resulted in an increase (53 ± 47%) in bone blood flow (p < 0.05). The no‐reflow phenomenon was observed in two vascularized allografts. These results demonstrate that smooth muscle adrenoreceptors were preserved successfully for 24 hours. In contrast, endothelial function was abnormal. There was no evidence that the endothelium was producing endothelium‐derived relaxing factor, and the results suggest that an endothelium‐derived constricting factor dependent on L‐arginine was produced during reperfusion. It is concluded that University of Wisconsin solution does not preserve normal endothelial function in the microcirculation of bone.
Cartilage oligomeric matrix protein: Isolation and characterization from human articular cartilage
Authors: DiCesare Paul E. , Mörgelin Matthias , Carlson Cathy S. , Pasumarti Subhalakshmi , Paulsson Mats
Published: February 2005

Cartilage oligomeric matrix protein was purified in a native form from normal adult human articular cartilage. The key steps in the purification scheme were selective extraction with buffer containing EDTA, wheat germ agglutinin affinity chromatography, and removal of the related protein thrombospondin by heparin affinity chromatography. Particles of cartilage oligomeric matrix protein viewed by electron microscopy after rotary shadowing revealed structures similar to the prototype molecule purified from Swarm rat chondrosarcoma. The protein demonstrated a bouquet‐like five‐armed structure, with peripheral globular domains connected by thin flexible strands to a central assembly domain. Immunohistochemistry revealed age‐dependent differences in the protein's distribution in cartilage. In normal human adult articular cartilage, there was a relatively uniform distribution throughout the interterritorial extracellular matrix, whereas in fetal articular cartilage, immunostaining was localized to the extracellular matrix directly adjacent to the chondrocytes. The isolation and characterization of human cartilage oligomeric matrix protein will facilitate its study in pathological conditions of human cartilage.
Use of a guanidine extract of demineralized bone in the treatment of osteochondral defects of articular cartilage
Authors: Tanaka Takaaki , Fujii Katsuyuki , Ohta Mitsunobu , Soshi Shigeru , Kitamura Atsushi , Murota Kagehisa
Published: February 2005

In order to evaluate the ability of a guanidine extract of demineralized bone to repair osteochondral defects in articular cartilage, plugs made of this extract were implanted into defects in rabbit knees. The repair tissue was examined macroscopically, histologically, and immunohistochemically at 4, 8, 12 and 30 weeks. Controls (defects that were left empty) showed no cartilage formation. Four weeks after implantation of a guanidine extract plug, histological examination showed a nonhomogeneous metachromatically stained region extending from the surface of the repair tissue down to cancellous bone. This region also was labeled by an anti‐type‐II collagen antibody, indicating that cartilage‐like tissue had been induced. At 8 weeks, the newly formed cartilage in the subchondral and cancellous bone had been partially replaced by bone. At 12 weeks, the thickness of the newly formed cartilage layer had decreased, and most of the newly formed cartilage in the subchondral and cancellous bone had been replaced by bone. In addition, a tidemark was observed. At 30 weeks, the repair tissue was a mixture of cartilage and fibrocartilage, and there was severe degeneration of the cartilage surrounding the repaired defects. These findings indicate that osteochondral defects of articular cartilage can be partially repaired by the implantation of a guanidine extract and that the newly formed cartilage‐like tissue is not permanent.
Structure and histopathology of the insertional region of the human achilles tendon
Authors: Rufai A. , Ralphs J. R. , Benjamin M.
Published: February 2005

The Achilles tendon inserts onto the calcaneus, and the retrocalcaneal bursa intervenes between it and the bone immediately proximal to the enthesis. The enthesis, the bursa, and the bursal walls form a complex insertional region protecting against wear and tear. We examined the structure and histopathology of the insertional region in 50 tendons from cadavers (age at time of death, 57‐96 years). The enthesis contained fibrocartilage typical of attachment sites. In specimens with a prominent superior tuberosity (the majority), the walls of the bursa also were fibrocartilaginous. On the anterior wall, fibrocartilage replaced the calcaneal periosteum; on the posterior wall, there was a sesamoid fibrocartilage in the deep part of the tendon. When the tuberosity was not prominent, the bursal fibrocartilages were absent. Histopathological features were observed in 31 entheses. Bone spurs extended from the calcaneus into the tendon and probably formed by endochondral ossification of enthesial fibrocartilage. Longitudinal fissures were splits in the fibrocartilage along the lines of the endotenon, and small transverse tears occurred at the tendon‐bone junction. Longitudinal fissures showed evidence of repair; they were filled with amorphous material and surrounded by clusters of cells. In the bursal walls, calcification or degeneration, or both, were observed in 37 specimens and usually involved both sesamoid and periosteal fibrocartilages. These fibrocartilages could therefore be implicated in retrocalcaneal bursitis.
Increased expression of the β1, α5 and αv integrin adhesion receptor subunits occurs coincident with remodeling of stress‐deprived rabbit anterior cruciate and medial collateral ligaments
Authors: AbiEzzi Salwan S. , Gesink Dirk S. , Schreck Paul J. , Amiel David , Akeson Wayne H. , Woods Virgil L.
Published: February 2005

The biomechanical, biochemical, and morphological properties of the anterior cruciate and medial collateral ligaments are dramatically altered in response to deprivation of normal physical forces and joint motion. Integrin adhesion receptors are known to play important roles in the tissue remodeling that occurs in the course of normal wound repair. We propose that integrins play a similar role in the remodeling of the extracellular matrix in stress‐deprived periarticular ligaments. This study tests the hypothesis that altered expression of integrins on ligament fibroblasts accompanies this remodeling. The left knees of 15 New Zealand White rabbits were surgically immobilized in acute flexion and the right knees served as controls (no operation). The anterior cruciate and medial collateral ligaments were harvested at 1, 3, 5, 9, or 12 weeks after immobilization. Sections from the ligaments were immunostained with monoclonal antibodies specific for the integrin subunits β1, α5, α6, and αv, as well as with a negative control antibody. Fibroblasts within both the stress‐deprived anterior cruciate and medial collateral ligaments demonstrated markedly increased staining for the β1, α5, and αv subunits, as compared with the controls. The increased staining was greatest at 9 weeks in the anterior cruciate ligament and at 12 weeks in the medial collateral ligament. Western blot study of ligament proteins extracted with sodium dodecyl sulfate demonstrated an increased amount of β1 subunit protein in both ligaments from knees that were stress deprived for 9 and 12 weeks, as compared with the control ligaments. These studies establish that stress deprivation in this animal model is accompanied by increased expression of integrin cell‐surface receptors containing the β1, α5, and αv subunits on anterior cruciate and medial collateral ligament fibroblasts, with a time course similar to that previously reported for indices of extracellular matrix remodeling induced by stress deprivation. This outcome suggests an important role for these integrins in the remodeling of stress‐deprived ligaments.
Three‐dimensional geometric and structural symmetry of the turkey ulna
Authors: Adams Douglas J. , Pedersen Douglas R. , Brand Richard A. , Rubin Clinton T. , Brown Thomas D.
Published: February 2005

Structural models of long‐bone preparations usually assume left‐right symmetry of contralateral bones under normal (baseline) conditions. To obtain insight on how this assumption affects the detection of subtle changes (as from functional adaptation), we formally examined the three‐dimensional geometric and structural symmetry of paired long bones, using contemporary image reconstruction and stress analysis techniques. Nine pairs of ulnae from normal male turkeys were reconstructed computationally from serial transverse images obtained by either (a) mechanical sectioning and digital photographic imaging or (b) computed tomography. Computed tomography scans allowed greater precision in reconstruction than did digitally imaged photographs. Left‐right comparisons of parameters of geometric symmetry (from computed tomography reconstructions) revealed average differences in whole bone volume and whole bone principal moments of inertia of 3.6 and 3.0%, respectively. Differences in bone curvature were indexed as noncolinearity of left compared with (mirrored) right centroidal axes, giving a disparity of 0.7 ± 0.3 mm. Within the longitudinal central 20% of the diaphysis (the customary region for histomorphometry), average left‐right differences in cross‐sectional area and area principal moments of inertia for computed tomography images were 4.7 and 5.0%, respectively. The overlap of longitudinally paired cross sections of the mid‐diaphysis, aligned at common centroids and oriented in the respective principal inertial directions, was greatest (as much as 95%) in the central 20% of the diaphysis. Paired three‐dimensional finite element models demonstrated nearly identical left and right stress/strain fields throughout the ulnar diaphyses for both compressive and torsional loading. Our data suggest that the assumption of contralateral geometric symmetry in long bones should be judged in the context of the specific attribute of symmetry under consideration; however, we conclude that for purposes of finite element modeling the assumption of symmetry is reasonable.
Correlation between synthetic activity and glycosaminoglycan concentration in epiphyseal cartilage raises questions about the regulatory role of interstitial pH
Authors: Boustany Nada N. , Gray Martha L. , Black Ann C. , Hunziker Ernst B.
Published: February 2005

Current data provide compelling evidence that the pH of the interstitial fluid of cartilage is an important determinant of the metabolic activity of chondrocytes, and this has served as the basis for a mechanistic proposal whereby chondrocytes could sense mechanical compression. The objective of the current study was to test this hypothesis further by examining biosynthetic activity in cartilage as a function of glycosaminoglycan content, which is the major determinant of interstitial pH. On the basis of previous data, increased biosynthetic activity would be anticipated to correlate with a decreased glycosaminoglycan content and an elevated interstitial pH. In contrast to our expectations, we found that the biosynthetic activity (monitored by measurement of incorporation of sulfate and proline) was positively correlated with the glycosaminoglycan content of tissue. These results raise doubt as to whether interstitial pH provides a dominant mechanism for controlling the metabolism of chondrocytes.
Transforming growth factor‐β1 and fibroblast growth factors in rat growth plate
Authors: Jingushi S. , Scully S. P. , Joyce M. E. , Sugioka Y. , Bolander M. E.
Published: February 2005

Chondrocytes in the growth plate progress in an orderly fashion from resting through proliferating to hypertrophic cells. In the region of hypertrophic chondrocytes, the cartilage is invaded by capillary loops and endochondral ossification is initiated. It is currently believed that growth factors may regulate the proliferation and maturation of chondrocytes and the synthesis of extracellular matrix in the growth plate. The ordered sequence of proliferation and differentiation observed in the growth plate provides a unique opportunity to study the role of acidic fibroblast growth factor, basic fibroblast growth factor, and transforming growth factor‐β1 in the regulation of these processes. In this study, expression of the mRNA of these growth factors was examined using total RNA extracted from the physis and epiphysis of rat tibias. Transforming growth factor‐β1 mRNA was detected by Northern hybridization. Expression of the genes encoding acidic and basic fibroblast growth factors was demonstrated by polymerase chain reaction amplification. In addition, using polyclonal antibodies against these growth factors, we localized them by immunohistochemical analysis. Strong intracellular staining with a predominantly nuclear pattern was observed in chondrocytes from the proliferating and upper hypertrophic zones. In contrast, chondrocytes in the resting zone stained only faintly for the presence of these growth factors. Some chondrocytes in the resting zone adjacent to the proliferating zone stained with these antibodies, and the antibodies also stained cells in the zone of Ranvier, which regulates latitudinal bone growth. Lastly, the location of transforming growth factor‐β1 was examined further with use of a polyclonal antipeptide antibody specific for its extracellular epitope. Interestingly, extracellular staining for transforming growth factor‐β1 was observed only around chondrocytes in the hypertrophic zone. These results suggest a role for these growth factors in the regulation of proliferation and maturation of chondrocytes and in endochondral ossification.
Frozen storage increases the ultimate compressive load of porcine vertebrae
Authors: Callaghan Jack P. , McGill Stuart M.
Published: February 2005

The use of freezing as a method of storage is commonplace in mechanical testing of biological tissues. The effects of freezing on tissues that comprise spinal segments have been examined separately, but little work has been done on intact specimens. We examined the effect of freezing on the structural properties of porcine cervical spines. The intact cervical spines of seven pigs (a total of 14 specimens–seven of C2–C4 and seven of C5–C7) were stored frozen (−20°C) for 1 month. The ultimate compressive load, displacement, stiffness, and energy absorbed were obtained using a monotonic compressive load applied at 3,000 N/sec. The structural properties were compared with those of another 14 porcine cervical specimens (control group, matched for age and weight) that were tested in a fresh state. The frozen storage of the vertebral specimens significantly increased the ultimate compressive load (24%) and energy absorbed to failure (33%). The stiffness and displacement at failure were not affected. We concluded that the use of freezing as a storage medium should be of concern when the resulting measures are used to quantify the ultimate compressive load of the spinal motion segments.
Regulation of chondrocyte maturation by fibroblast growth factor‐2 and parathyroid hormone
Authors: Iwamoto Masahiro , Shimazu Atsushi , Pacifici Maurizio
Published: February 2005

Fibroblast growth factor‐2 and parathyroid hormone are strong modulators of the maturation process of chondrocytes during endochondral ossification. To clarify whether and how these agents may exert stage‐specific effects during this process, we analyzed the responsiveness and phenotypic consequences of treatment with fibroblast growth factor‐2 or parathyroid hormone on chondrocytes at different stages of maturation. Populations of immature lower sternal, maturing upper sternal, and hypertrophic tibial growth plate chondrocytes were isolated from day 18–20 chick embryos and were allowed to resume the maturation process by growth in standard monolayer cultures. Treatment of immature lower sternal cultures with as little as 0.1 ng/ml of fibroblast growth factor‐2 or 10−10 M parathyroid hormone prevented both the emergence of mature type‐X collagen‐synthesizing chondrocytes and the ensuing enlargement of cells that occurred in control (untreated) cultures. Similarly, the treatment of cultured early maturing upper sternal cells with these factors severely reduced the synthesis of type‐X collagen and alkaline phosphatase activity and the levels of their respective mRNAs. In sharp contrast, when the cultured upper sternal cells were allowed to grow and mature further before treatment, the responsiveness to fibroblast growth factor‐2 was markedly reduced and the responsiveness to parathyroid hormone remained strong and largely unchanged. Cultures of hypertrophic tibial growth plate cells displayed a similar reduced sensitivity to fibroblast growth factor‐2, as also indicated by the lack of mitogenic effects, and strong sensitivity to parathyroid hormone. The phenotypic changes induced by treatment with either of these factors were fully reversible when cultures that had been treated were placed in control medium. The results demonstrate that fibroblast growth factor‐2 and parathyroid hormone are equally potent in affecting the early stages of maturation but exert differential effects as the cells progress along the maturation pathway. The factors appear to be part of sequentially acting mechanisms to ensure normal progression of chondrocyte maturation during endochondral ossification.
Fatigue behavior of the equine third metacarpus: Mechanical property analysis
Authors: Gibson V. A. , Stover S. M. , Martin R. B. , Gibeling J. C. , Willits N. H. , Gustafson M. B. , Griffin L. V.
Published: February 2005

This is the first in a series of experiments to study the fatigue properties of equine cannon (third metacarpal) bone specimens from Throughbred racehorses. Monotonic and fatigue tests to failure were performed in four‐point bending on diaphyseal specimens in a 37°C saline bath to answer three initial questions. (a) Will a linear variable differential transducer yield the same elastic modulus as strain gauges? (b) Will fatigue results depend on whether the periosteal or endosteal side of the beam is in tension? (c) Are there regional variations in the monotonic and fatigue properties of the cannon bone midshaft? Eighteen left‐right pairs of specimens from six horses were used. One beam of each pair was fitted with strain gauges. Fatigue tests were conducted on 24 specimens under load control at 2 Hz; an initial range of 0‐10,000 microstrain was used so as to produce failure in a reasonable period of time. There were no left‐right differences in the fatigue or monotonic properties, and the presence of a gauge had no effect on modulus measured by a linear variable differential transducer. However, gauge‐measured moduli were about 1 GPa less than transducer‐measured values. Fatigue life was independent of which side of the beam was in tension, and there were significant variations in mechanical properties around the cortex. The lateral region was stiffer than the dorsal region but the latter had a longer fatigue life. The fixed cylindrical supports used in this experimental eventually produced slight wear grooves, causing artifactual stiffening at the end of the load cycle in some specimens. A second experiment using roller supports confirmed the reason for this stiffening. It also showed that fatigue life was shorter when roller supports were used but regional differences were similar.
Atrophic nonunion can be predicted with dual energy x‐ray absorptiometry in a canine ostectomy model
Authors: Markel Mark D. , Bogdanske John J. , Xiang Zhuzai , Klohnen Andreas
Published: February 2005

This study demonstrated that dual energy x‐ray absorptiometry can be used to distinguish between normal union and atrophic nonunion, with high sensitivity and high negative predictive value, by 8 weeks after surgery in a canine model. Eighteen adult mixed‐breed dogs were divided into two equal groups: normal union and atrophic nonunion. In the normal union group, a 5 mm mid‐diaphyseal transverse ostectomy was performed in the right tibia, and the bone was stabilized with a unilateral external fixator. In the atrophic nonunion group, a 5 mm mid‐diaphyseal ostectomy was performed; the distal 1.5 cm of the bone ends, including the periosteum, were frozen twice to −20°C using liquid nitrogen and thawed slowly twice; and the bone was stabilized with a unilateral external fixator. The members of the research team were blinded to the group assignments until after all dogs were killed and all data were acquired. Radiography and dual energy x‐ray absorptiometry of both tibiae were performed at week 1, 2, 3, 4, 6, 8, 10, 12, 14, and 16 after surgery. All dogs were killed at 16 weeks, and the torsional stiffness and maximum torque of both tibiae of five dogs in each group were determined. Mechanically, the tibiae in the normal union group had significantly higher maximum torque (43‐fold higher) and torsional stiffness (86‐fold higher) than the tibiae in the atrophic nonunion group. The sensitivity and negative predictive value of dual energy x‐ray absorptiometry for predicting nonunion were 100% by 8 weeks after surgery. The specificity and positive predictive value reached 78 and 82%, respectively, by 16 weeks. Radiographic scores were significantly higher for the union group than for the nonunion group beginning at 2 weeks after surgery. The earliest time after surgery that radiography classified an ostectomy as a nonunion was significantly later (4.6 ± 1.2 weeks) than for dual energy x‐ray absorptiometry (2.6 ± 1.4 weeks). Before these results can be extrapolated to human applications, further animal studies must be performed to evaluate clinically or experimentally induced fractures, or both, rather than the well defined ostectomies that were performed in this study.
Effect of stress deprivation and cyclic tensile loading on the material and morphologic properties of canine flexor digitorum profundus tendon: An in vitro study
Authors: Hannafin Jo A. , Arnoczky Steven P. , Hoonjan Amardeep , Torzilli Peter A.
Published: February 2005

The effect of stress deprivation and cyclic tensile loading on the mechanical and histologic properties of the canine flexor digitorum profundus tendon was examined using an in vitro system. Stress deprivation resulted in a progressive and statistically significant decrease in the tensile modulus over an 8‐week period. Histologically, stress‐deprived tendons demonstrated quantitative changes in the morphology and number of cells and in the alignment of collagen. The change in tensile properties was not associated with an alteration in the water content of the tissue, but the change appeared to be dependent on the presence of a viable cell population. Dead (acellular) tendons did not undergo any alteration in tensile modulus in this in vitro system. In vitro cyclic tensile loading of tendons over a 4‐week time period resulted in a significant increase in the tensile modulus (93% of the control) compared with that of the stress‐deprived tendons (68% of the control). This loading regimen also maintained the normal histologic pattern of the tendons. The results of this study are similar to those previously reported for in vivo studies and suggest that this in vitro model may represent a valid system with which to test the effects of various stress conditions on the tensile properties of tissues.
Combined knee loading states that generate high anterior cruciate ligament forces
Authors: Markolf Keith L. , Burchfield Daniel M. , Shapiro Matthew M. , Shepard Michael F. , Finerman Gerald A. M. , Slauterbeck James L.
Published: February 2005

Injuries to the anterior cruciate ligament frequently occur under combined mechanisms of loading. This in vitro study was designed to measure levels of ligament force under dual combinations of individual loading states and to determine which combinations generated high force. Resultant force was recorded as the knee was extended passively from 90° of flexion to 5° of hyperextension under constant tibial loadings. The individual loading states were 100 N of anterior tibial force, 10 Nm of varus and valgus moment, and 10 Nm of internal and external tibial torque. Straight anterior tibial force was the most direct loading, mechanism; the mean ligament force was approximately equal to applied anterior tibial force near 30° of flexion and to 150% of applied tibial force at full extension. The addition of internal tibial torque to a knee loaded by anterior tibial force produced dramatic increases of force at full extension and hyperextension. This loading combination produced the highest ligament forces recorded in the study and is the most dangerous in terms of potential injury to the ligament. In direct contrast, the addition of external tibial torque to a knee loaded by anterior tibial force decreased the force dramatically for flexed positions of the knee; at close to 90° of flexion, the anterior cruciate ligament became completely unloaded. The addition of varus moment to a knee loaded by anterior tibial force increased the force in extension and hyperextension, whereas the addition of valgus moment increased the force at flexed positions. These states of combined loading also could present an increased risk for injury. Internal tibial torque is an important loading mechanism of the anterior cruciate ligament for an extended knee. The overall risk of injury to the ligament from varus or valgus moment applied in combination with internal tibial torque is similar to the risk from internal tibial torque alone. External tibial torque was a relatively unimportant mechanism for generating anterior cruciate ligament force.
Formation of osteoclast‐like cells is suppressed by low frequency, low intensity electric fields
Authors: Rubin Janet , McLeod Kenneth J. , Titus Louisa , Nanes Mark S. , Catherwood Bayard D. , Rubin Clinton T.
Published: February 2005

With use of a solenoid to generate uniform time‐varying electric fields, the effect of extremely low frequency electric fields on osteoclast‐like cell formation stimulated by 1,25(OH)2D3 was studied in primary murine marrow culture. Recruitment of osteoclast‐like cells was assessed by counting multinuclear, tartrateresistant acid phosphatase positive cells on day 8 of culture. A solenoid was used to impose uniform time‐varying electric fields on cells: sham exposures were performed with an identical solenoid with a null net electric field. During the experiments, both solenoids heated interiorly to approximately 1.5°C above ambient incubator temperature. As a result of the heating, cultures in the sham solenoid formed more osteoclast‐like cells than those on the incubator shelf (132 ± 12%). For this reason, cells exposed to the sham solenoid were used for comparison with cultures exposed to the active coil. Marrow cells were plated at 1.4 × 106/cm2 in square chamber dishes and exposed to 60 Hz electric fields at 9.6 μV/cm from days 1 to 8. Field exposure inhibited osteoclast‐like cell recruitment by 17 ± 3% as compared with sham exposure (p < 0.0001). Several variables, including initial cell plating density, addition of prostaglandin E2 to enhance osteoclast‐like cell recruitment, and field parameters, were also assessed. In this secondary series, extremely low frequency fields inhibited osteoclast‐like cell formation by 24 ± 4% (p < 0.0001), with their inhibitory effect consistent throughout all variations in protocol. These experiments demonstrate that extremely low intensity, low frequency sinusoidal electric fields suppress the formation of osteoclast‐like cells in marrow culture. The in vitro results support in vivo findings that demonstrate that electric fields inhibit the onset of osteopenia and the progression of osteonecrosis: this suggests that extremely low frequency fields may inhibit osteoclast recruitment in vivo.
Determinants of femoral geometry and structure during adolescent growth
Authors: van der Meulen Marjolein C. H. , Ashford Marvin W. , Kiratli B. Jenny , Bachrach Laura K. , Carter Dennis R.
Published: February 2005

Our goal was to understand developmental determinants of femoral structure during growth and sexual maturation by relating femoral measurements to gender and developmental factors (age, pubertal stage, height, and body mass). The bone mineral content of the femur was measured by dual energy x‐ray absorptiometry in 101 healthy Caucasian adolescents and young adults, 9–26 years of age. After some simplifying assumptions had been made, cross‐sectional geometric properties of the femoral midshaft were estimated. Two geometry‐based structural indicators, the section modulus and whole bone strength index, were calculated to assess the structural characteristics of the femur. Femoral strength, as described by these structural indicators, increased dramatically from childhood through young adulthood. Regressions were performed between these femoral measurements and the developmental factors. Our data show that of age, pubertal stage, body mass, and height, body mass is the strongest predictor of femoral cross‐sectional properties, and the correlation of body mass with femoral cross‐sectional structure is independent of gender. A model including all four developmental factors and gender did not substantially increase the accuracy of predictions compared with the model with body mass alone. In light of previous research, we hypothesize that body mass is an indicator of in vivo loading and that this in vivo loading influences the cross‐sectional growth of the long bones.
Friction and stem stiffness affect dynamic interface motion in total hip replacement
Authors: Kuiper Jan Herman , Huiskes Rik
Published: February 2005

Large cyclic movements between the femoral stem and bone during the first weeks after total hip arthroplasty may hamper bone ingrowth and adversely affect the eventual success of the arthroplasty. Little is known, however, about the magnitude of the motions and its relationship to design and surgical factors. A two‐dimensional finite element model of a cementless prosthesis inserted into the proximal femur was constructed to study the effects of two mechanical variables—the stiffness of the implant and the coefficient of friction between bone and implant—on the magnitude of the motions. We investigated the influences of these variables on the subsidence of the prosthesis, the magnitudes of the cyclic motions, and the level of the interface stresses. The presence of friction reduced cyclic motions by about 85% compared with a frictionless interface. Once friction was assumed, varying the coefficient of friction had little effect. The effect of friction on the interface stress state and gross subsidence of the prosthesis was not as great as on cyclic motion. Implant stiffness also affected the magnitudes and distributions of the cyclic motions along the interface. A flexible stem generated motions about three to four times larger proximally than those of a stiff stem, which generated larger motions distally. The influence of stem stiffness on interface stresses and prosthetic subsidence was less than on cyclic motion. The location of the peak shear stresses at the interface around a bonded prosthesis corresponded to the location where cyclic interface motion was maximal for an unbonded prosthesis. However, no direct relationship was found between the magnitudes of peak stresses and the amplitudes of cyclic motions.
Differential effects of serum, insulin‐like growth factor‐I, and fibroblast growth factor‐2 on the maintenance of cartilage physical properties during long‐term culture
Authors: Sah Robert L. , Trippel Stephen B. , Grodzinsky Alan J.
Published: February 2005

The effects of fetal bovine serum, insulin‐like growth factor‐I, and fibnoblast growth factor‐2 on the regulation of the functional physical properties of adult bovine cartilage explants during an incubation period of 18–20 days was determined, and the relationship between the measured functional properties of the cartilage and the tissue composition was assessed. Cartilage disks were tested in the uniaxial radially confined configuration by the application of low amplitude oscillatory displacement and measurement of the resultant load and streaming potential. For the control cartilage terminated just after explant, the modulus was 0.39 ± 0.28 MPa, the open circuit hydraulic permeability was 2.0 ± 1.0 × 10−15 m2/(Pa•c), and the electrokinetic (streaming potential) coefficient was −2.3 ± 0.6 mV/MPa. Incubation of cartilage in medium supplemented with serum or insulin‐like growth factor‐I resulted in maintenance of the modulus and electrokinetic coefficient, whereas incubation in basal medium or medium supplemented with fibroblast growth factor‐2 led to a marked decrease from control values in the modulus and the amplitude of the electrokinetic coefficient. All of the culture conditions examined resulted in an increase in permeability that was not statistically significant. The variation in the electromechanical properties of all the cartilage samples tested was related to the density of tissue proteoglycan and collagen (hydroxyproline). The modulus was correlated with both the density of tissue proteoglycan (+0.014 MPa/[mg/ml]) and the density of tissue hydroxyproline (+0.008 MPa/[mg/ml]). The electrokinetic coefficient was also correlated with the density of proteoglycan (−0.080 [mV/MPa]/[mg/ml]) and the density of hydroxyproline (+0.064 [mV/MPa]/[mg/ml]). These data indicate that the regulation of chondrocyte matrix metabolism by growth factors can significantly affect the physical properties and function of cartilage.
Effect of loading and fracture motions on diaphyseal tibial fractures
Authors: Sarmiento Augusto , McKellop Harry A. , Llinas Adolfo , Park Sang‐Hyun , Lu Bin , Stetson William , Rao Raj
Published: February 2005

A computerized motion sensor was used to record the three‐dimensional components of interfragmentary motion during healing in three patients with closed, low‐energy fractures of the tibial diaphysis treated with functional braces. At the first measurement session, 2 weeks after fracture, the patients applied approximately 15 kg to the injured limb. Although this produced 1–4 mm of translation of the fragments, this was recovered when the load was removed. The maximum rotational and angulatory displacements often occurred as the patients rose from the chair with no weight applied to the limb and frequently were reduced as the 15 kg of load was applied. Under load, the maximum axial rotation was 3° and the maximum angular displacement was 1°. As with the translations, the initial rotational and angulatory positions of the fragments were recovered when the load was removed and the patient returned to the seated position. At 8 weeks, the patient applied full body weight, producing a maximum interfragmentary translation of 0.5 mm and maximum axial rotation or angulation of 0.5°. Abundant peripheral callus formed in all three fractures, and they healed by 15 weeks through typical gradual consolidation and mineralization of the callus, accompanied by a corresponding reduction in interfragmentary motions.
Recorticalization after bifocal internal bone transport in the double‐plated sheep femur
Authors: Windhager R. , Großschmidt K. , Tsuboyama T. , Siegl H. , Heinzl H. , Seidl G. , Plenk H.
Published: February 2005

Distraction osteogenesis and bone remodelling after the end of bone transport were investigated in one femur each of six adult male sheep. A newly designed internal distraction device was used. A custommade osteosynthesis plate was fixed on the lateral side of the femur, and two transporting plates driven by a transcutaneously inserted screwdriver moved two bone cylinders simultaneously over a 40 mm defect. An additional plate was applied ventrally to stabilize the device. Bone transport was begun 2 weeks postoperatively at 1 mm/day at each transporting plate until they came into contact. New bone formation within the distraction gaps was evaluated by computed tomography scans and was quantified at 4 and 6 months by dual energy x‐ray absorptiometry as well as histomorphometry on polyfluorochrome‐labelled undecalcified ground sections and microradiographs. At 4 months, all distraction gaps were bridged by abundant newly formed bone trabeculae, which were reduced and condensed to cortex‐like layers of new bone at 6 months. Less new bone was always found under the lateral device than in the unplated medial and dorsal segments, but the amount of new bone under the ventral plate was comparable with that in the unplated regions. The results of this pilot study show that distraction osteogenesis can be achieved with an internal device such as this one and that recorticalization and restoration of a medullary canal occur despite the relatively rigid internal stabilization by the plates.