bluuebunny/crossref_metadata_2025 huggingface dataset:
Polyethylene wear vector in vivo: A three‐dimensional analysis using retrieved acetabular components and radiographs
Authors: Yamaguchi Motoi , Hashimoto Yasushi , Akisue Toshihiro , Bauer Thomas W.
Published: February 2005

Polyethylene wear of the acetabular component can be described as one or more vectors. To help clarify the mechanisms of wear advancement in vivo, we used a combination of retrieved implants and radiographs to describe the three‐dimensional wear vectors in total hip arthroplasty. The wear vectors in 41 retrieved implants from a single manufacturer were measured with use of the shadowgraph technique, and the spatial orientation of each implant was calculated from serial anteroposterior pelvic radiographs. On the basis of the combination of the wear vector in the implant and implant orientation in the pelvis, the wear vectors in vivo were determined. The mean wear vector was directed 8.1° lateral in the coronal plane and 4.1° posterior in the sagittal plane. The wear vector in vivo showed a relatively wide range of directions, not necessarily coinciding with the commonly presumed resultant force in the hip. The wear vectors were not associated with the spatial orientation of the acetabular components, but cups with impingement demonstrated more anterior wear than did those without impingement. Our results suggest that the process of polyethylene wear is not as simple as previously described and that several factors influence advancement of wear in vivo.
Differential expression of integrin subunits in canine knee ligament fibroblasts
Authors: Bhargava Madhu M. , Beavis Andrew J. , Edberg Jeffery C. , Warren Russell F. , Attia Erik T. , Hannafin Jo A.
Published: February 2005

A method for measuring the expression of integrin subunits on the cell surface of knee ligament fibroblasts was developed with use of flow cytometry and immunofluorescence. The ligament cells exhibited uniform size and density, as shown by forward and side‐scatter properties, and showed minimal nonspecific binding of isotype control antibodies compared with unstained cells. All cells expressed the α5 integrin subunit; lateral collateral ligament cells stained with antibody to α5 showed a mean fluorescence intensity 2‐fold higher than that of medial collateral ligament cells, 1.5‐fold higher than that of posterior cruciate ligament cells, and 3‐fold higher than that of anterior cruciate ligament cells, indicating a greater expression of the α5 subunit by lateral collateral ligament cells than by medial collateral, posterior cruciate, and anterior cruciate ligament cells. All cells expressed the β1 integrin subunit; the expression by posterior cruciate ligament cells was 3‐fold higher than that by medial collateral ligament or lateral collateral ligament cells and 5‐fold higher than that by anterior cruciate ligament cells. All cells expressed the β3 integrin subunit; the expression by posterior cruciate ligament cells was 1.5, 3, and 4.5‐fold greater than that by lateral collateral, anterior cruciate, and medial collateral ligament cells, respectively. Our data suggest there is a differential expression of integrin subunits in knee ligament fibroblasts, and this in part may explain differences in their attachment and adherence to extracellular matrix molecules.
Adhesion strength differential of human ligament fibroblasts to collagen types I and III
Authors: Yang Li , Tsai Cliff M‐H. , Hsieh Adam H. , Lin Victor S. , Akeson Wayne H. , Paul Sung K‐L.
Published: February 2005

Fibroblasts embedded in the amorphous healing tissue matrix of ligaments migrate into damaged sites during the inflammatory process that precedes the formation of new connective tissue after ligament injury. Cell motility involved in this migration is strongly influenced by cellular adhesion to proteins of the extracellular matrix. The adhesion mechanism of interest in this study is the attachment of fibroblasts from the anterior cruciate and medial collateral ligaments to types I and III collagen, two fibrillar collagens secreted by fibroblasts during tissue repair. Types I and III collagen constitute a major portion of these ligaments and are assembled by fibroblasts into long cable‐like fibrils in the extracellular space. In this study, a micropipette aspiration technique was used to measure the force required to separate fibroblasts of the anterior cruciate and medial collateral ligaments from substrates composed of type I or III collagen, each at a concentration of 2 or 5 μg/ml. Approximately 1,200 fibroblasts from the anterior cruciate ligament and 1,600 from the medial collateral ligament were used, and the adhesion force and area of these cells were determined. Fibroblasts from the anterior cruciate ligament exhibited greater adhesion force than did those from the medial collateral ligament for all concentrations of types I and III collagen. In addition, the adhesiveness of fibroblasts from both ligaments was dependent on seeding time for all experimental conditions. To determine the adhesiveness per unit area, defined here as the adhesion strength, the adhesion force was normalized by the adhesion area. At early seeding times (15‐45 minutes), fibroblasts from the anterior cruciate ligament exhibited greater adhesion strength on surfaces coated with type‐I collagen than did those from the medial collateral ligament. However, for both collagen substrates, adhesion strength for fibroblasts from the anterior cruciate ligament decreased with seeding time whereas that for fibroblasts from the medial collateral ligament remained relatively constant for all seeding periods (15‐75 minutes).
Stiffness, viscosity, and upper‐limb inertia about the glenohumeral abduction axis
Authors: Zhang Li‐Qun , Portland Gregory H. , Wang Guangzhi , Diraimondo Carl A. , Nuber Gordon W. , Bowen Mark K. , Hendrix Ronald W.
Published: February 2005

To evaluate the dynamic properties of the shoulder and understand how they are controlled by the central nervous system, glenohumeral‐joint stiffness and viscosity and upper‐limb inertia were quantified under various levels of muscle contraction in seven healthy human subjects. Through a cast attachment, the upper limb was perturbed in a precise pattern by a computer‐controlled servomotor to manifest the dynamic properties of the joint. The recorded joint position and torque were used to estimate joint stiffness and viscosity and upper‐limb inertia. With moderate muscle contraction, the stiffness and viscosity increased several fold. A stiffer shoulder joint associated with stronger muscle contraction made the shoulder more stable and protected it from potential injuries during strenuous tasks. Joint viscosity, especially the stronger viscous damping associated with more strenuous contraction, smoothed shoulder movement and stabilized the joint. From the control viewpoint, the glenohumeral joint responded to the central nervous system more quickly with increasing muscle contraction, which was useful during strenuous tasks. On the other hand, the central nervous system controlled stiffness and viscosity synchronously so that it dealt with only a nearly constant damping ratio of the joint over various levels of contraction, which simplified its task substantially. This approach quantified the dynamic and static properties of the shoulder under various levels of contraction more accurately and completely than a manual test, and it can potentially be used to evaluate changes in these properties caused by musculoskeletal injuries and their surgical treatments.
An in vivo model for load‐modulated remodeling in the rabbit flexor tendon
Authors: Malaviya P. , Bultler D. L. , Boivin G. P. , Smith F. N. L. , Barry F. P. , Murphy J. M. , Vogel K. G.
Published: February 2005

This study tested the hypothesis that eliminating in vivo compression to the wrap‐around, fibrocartilage‐rich zone of the flexor digitorum profundus tendon results in rapid depletion of fibrocartilage and changes in its mechanical properties, microstructure, extracellular matrix composition, and cellularity. The right flexor digitorum profundus tendons of 2.5‐3‐year‐old rabbits were translocated anteriorly to eliminate in vivo compression and shear to the fibrocartilage zone and, at 4 weeks after surgery, were compared with tendons that had sham surgery and with untreated tendons. The translocated tissue showed a significant increase in equilibrium strain under a compressive creep load (p < 0.05). The thickness and area of the fibrocartilage zone also decreased significantly (p < 0.05). The nuclear density decreased by 40% in the fibrocartilage zone (p < 0.005); however, nuclear shape and orientation were not significantly altered. Glycosaminoglycan content in the fibrocartilage zone was also depleted by 40% (p < 0.02). The tightly woven basket weave‐like mesh of collagen fibers in the zone appeared more loosely organized, suggesting matrix reorganization due to translocation. Moreover, immunoreactive type‐II collagen and link protein in the fibrocartilage zone also decreased. With use of this unique in vivo model, this research clearly elucidates how changing tissue function (by removing compressive forces) rapidly alters tissue form.
Biomechanical evaluation of early fracture healing in normal and diabetic rats
Authors: Funk James R. , Hale Joseph E. , Carmines David , Gooch H. Lee , Hurwitz Shepard R.
Published: February 2005

Diabetes mellitus has been shown to alter the properties of bone and impair fracture healing in both humans and animals. The objective of this study was to document changes in the structural and material properties of intact bone and bone with healed fractures in diabetic rats compared with nondiabetic controls after 3 and 4 weeks of healing. Rods were inserted in the right femurs of control rats and rats with streptozotocin‐induced diabetes, and the femurs were fractured in a standardized procedure and then allowed to heal for 3 and 4 weeks. After death, all femurs were mechanically tested to failure in torsion. The degree of healing was quantified for each animal by normalizing mechanical parameters for the femur with a healed fracture with those for the intact contralateral femur. At both time points of healing, diabetic rats exhibited inferior healing compared with that of control animals in terms of failure torque, failure stress, structural stiffness, and material stiffness of the femur with the healed fracture relative to the intact contralateral femur (p < 0.05). Our results demonstrate that the recovery of structural and material strength in femurs with healed fractures in diabetic rats is delayed by at least 1 week compared with that in controls.
Role of alpha‐1 adrenoceptor subtypes mediating constriction of the rabbit ear thermoregulatory microvasculature
Authors: Li Zhongyu , Silver William P. , Koman L. Andrew , Strandhoy Jack W. , Rosencrance Eileen , Gordon Stan , Smith Thomas L.
Published: February 2005

An acute in vivo preparation of the microvasculature of the rabbit ear was used to evaluate the functional role of alpha1 (α1)‐adrenoceptor subtypes in thermoregulatory microcirculation. The effect of α1‐adrenoceptor subtype blockade on phenylephrine‐induced vasoconstriction was assessed with the α1A, α1B, and α1D‐adrenoceptor‐selective antagonists 5‐methyl‐urapidil (10−8 M), chloroethylclonidine (10−5 M), and 8‐[2‐[4(2‐methoxyphenyl)‐1‐piperazinyl]ethyl]‐8‐azaspirol[4.5]decane‐7,9‐dionedihydrochloride (BMY7378) (10−6 M), respectively. The results demonstrated that pretreatment of the ear microvasculature with 5‐methylurapidil or BMY7378 shifted the phenylephrine concentration‐response curve rightward and significantly changed the log of the phenylephrine concentration, causing half‐maximum stimulation (EC50) in arterioles (p < 0.05). BMY7378 shifted the phenylephrine concentration‐response curve of the arteriovenous anastomoses about 100‐fold rightward (p < 0.05). All three α1‐adrenoceptor antagonists eliminated the vasoconstrictive effects of phenylephrine on venules. The results indicate that the ear microvasculature has a heterogenous distribution of α1‐adrenoceptor subtypes. The α1A and α1D‐adrenoceptor subtypes appear to have a greater influence on constrictive function in arterioles, whereas the α1D‐adrenoceptor is the dominant constrictor of arteriovenous anastomoses. In general, the α1‐adrenoceptor does not play a major vasoconstrictor role in venules. Chloroethylclonidine, an irreversible α1B‐adrenoceptor antagonist, induced contractile responses in the ear microvasculature, probably due to its α2‐adrenoceptor agonist effects. This study extended our understanding of the adrenergic receptor control mechanisms of a cutaneous thermoregulatory end organ characterized by two parallel perfusion circuits providing nutritional and thrmoregulatory functions.
In vivo technique to quantify the internal‐external rotation kinematics of the human glenohumeral joint
Authors: Novotny John E. , Woolley C. Todd , Nichols Claude E. , Beynnon Bruce D.
Published: February 2005

Internal and external rotation of the humerus are often related to instability, injury mechanisms, and surgical and rehabilitation outcomes at the glenohumeral joint. The goal of this study was to develop a technique to quantify the internal‐external rotation kinematics of the glenohumeral joint in human subjects, including the rotational range of motion, neutral‐zone laxity, and flexibility. For both arms of 10 normal subjects, the rotational range of motion of the humerus was assessed at 45° of abduction with 4 Nm of appplied moment to produce internal and external rotations about the long axis. The neutral zone was defined as the portion of the rotational range of motion that occurred between +1 and −1 Nm of applied internal‐external rotation torque. The flexibility was determined from the slope of the moment‐rotation curve from 1 to 4 Nm of applied moment. The repeatability of the device during two trials on the same day and two trials 1 week apart was determined. There were no significant differences between the two same‐day and two across‐day trials for each outcome measure. The internal‐external rotational range of motion was 139.4° (SD 40.5°). The neutral‐zone laxity was 77.8° (SD 46.0°). With a linear approximation, the external rotation flexibility (20.1° Nm [SD 13.7°/Nm]) was four times greater than the internal rotation flexibility (5.8°/Nm [SD 5.1°/Nm]). The changes in the magnitude of the laxity, the ratio between the laxity and the range of motion, or the values for flexibility determined with this technique could be used to describe joint laxity, surgical outcome, and rehabilitation progress.
Adhesion formation can be reduced by the suppression of transforming growth factor‐β1 activity
Authors: Fukui Naoshi , Tashiro Toshiyuki , Hiraoka Hisatada , Oda Hiromi , Nakamura Kozo
Published: February 2005

Surgery or trauma often results in restrictive adhesions around joints or tendons that cause severe functional impairment. The formation of adhesion is essentially a fibrogenetic process; therefore, peptide growth factors, such as transforming growth factor‐β, are assumed to play central roles in its development. The purpose of this study was to test the hypothesis that suppression of transforming growth factor‐β1 activity reduces adhesion formation. Sixty rabbits were prepared and randomly divided into six groups of 10. Intraarticular adhesions were created in the right knee joints by cortical bone shaving and subsequent cast immobilization for 4 weeks. In animals in three of the six groups, transforming growth factor‐β1 activity was suppressed by continuous administration of the neutralizing antibody in three graded doses; animals in the other three groups were used as controls. Four weeks after the surgery, the casts were removed and the adhesions were assessed macroscopically, histologically, biomechanically, and biochemically. Gross observation showed that the neutralizing antibody had suppressed adhesion formation in a dose‐dependent manner. This is consistent with biomechanical measurement results demonstrating that the antibody reduced the flexion contractures. Histologically, the adhesion in our model was fibrous tissue and the adhesions in the animals in the antibody groups were thin and loose in comparison with the controls. Biochemical analyses further supported these results, demonstrating that administration of the antibody reduced collagen content in the adhesions with a predominance of type‐I collagen. Thus, this study showed that suppression of the actions of transforming growth factor‐β1 reduced adhesion formation. Considering the various possible measures to control the activity of the growth factor, suppression of transforming growth factor‐β may be a novel, potent approach to preventing adhesions.
Increased concentrations of nitrate and nitrite in the cyst fluid suggesting increased nitric oxide synthesis in solitary bone cysts
Authors: Komiya Setsuro , Kawabata Rikimaru , Zenmyo Michihisa , Hashimoto Sanshiro , Inoue Akio
Published: February 2005

The etiology and treatment of a solitary bone cyst have remained undefined. Surgical treatments have not been encouraging, because a less invasive corticosteroid‐injection treatment has afforded good results. However, there has been little scientific rationale supporting corticosteroid treatment. In recent reports, bone‐resorbing factors, including matrix metalloproteinases, prostaglandins, interleukin‐1, and oxygen free radicals, have been demonstrated in the cyst fluid. To better elucidate the pathophysiology of the solitary bone cyst, we examined the activities of nitric oxide and cytokines in the cyst fluid as well as in the cyst membrane. The levels of nitrate and nitrite were significantly higher in the cyst fluid than in serum. Immunostaining of cells in the stroma and lining cells of the cyst wall was strongly positive for inducible nitric synthase. The levels of interleukin‐6 and interleukin‐1β in the cyst fluid were elevated, and cells in the cyst membrane were positive for tumor necrosis factor‐α, interleukin‐6, and interleukin‐1β. Cultured cells from the cyst membrane were induced in the production of nitrate and nitrite in response to cytokine treatment. These findings suggest that the solitary bone cyst was in a state favorable for the production of nitric oxide.
Mechanical performance of standard and cannulated 4.0‐mm cancellous bone screws
Authors: Brown Greg A. , McCarthy Tracey , Bourgeault Craig A. , Callahan Dennis J.
Published: February 2005

The mechanical performance of bone screws is determined by their pull‐out strength (holding power), compressive force, stripping torque, yield bending moment, ultimate bending moment, and fatigue strength. These parameters are related to the parameters of the screw design, including major thread diameter, minor thread diameter, thread length, pitch, shaft diameter, cannulation diameter, and material properties. The goal of the study was to theoretically predict the static performance of five 4.0‐mm, 45–46‐mm‐long, cancellous, partially threaded standard and cannulated bone screws and compare the predictions with experimental measurements. A secondary goal was to determine if cannulation of the bone screw diminished its mechanical performance. The predicted values for pull‐out force, compressive force, and stripping torque were determined by the thread length, major thread diameter, and thread shape factor. The screws with the largest major thread diameter and longest thread length had the greatest pull‐out force, compressive strength, and stripping torque. However, when correcting for the thread length, a higher thread shape factor compensated for a smaller major diameter. The coefficient of determination (r2) for the correlation between the predicted and measured pull‐out force improved from 0.75 to 0.90 when the theoretical model included the thread shape factor. The yield and ultimate bending moments are a function of the section modulus and material properties of the screw. The Ace solid screw had the greatest section modulus and yield and ultimate bending moments. The experimental data support the theoretical models for predicting the mechanical performance of bone screws. The disign of the bone screws can be optimized on the basis of theoretical modeling. The strong correlation between the predicted and measured parameters allows comparison between bone screws without repeated experimental tests. Theoretical and experimental results show that cannulation of the bone screw did not inherently diminish its mechanical performance.
Regulation by IGF‐I and TGF‐β1 of swarm‐rat chondrosarcoma chondrocytes
Authors: Matsumura Takashi , Whelan Mary C. , Li Xiao Q. , Trippel Stephen B.
Published: February 2005

The growth factors transforming growth factor‐beta 1 and insulin‐like growth factor‐I influence a wide range of cellular actions, including the growth of several neoplastic cell types. Their role in the regulation of neoplastic chondrocytes remains unclear. We tested the hypotheses that transforming growth factor‐beta 1 and insulin‐like growth factor‐I differentially regulate neoplastic chondrocytes and interact to modulate the mitotic and matrix synthetic activities of neoplastic chondrocytes. We used Swarm‐rat chondrosarcoma chondrocytes to investigate the effect of each factor individually and of both factors in combination on [3H]thymidine incorporation into DNA and on [35S]sulfate incorporation into glycosaminoglycans. Each factor increased [3H]thymidine incorporation 2.7‐fold; transforming growth factor‐beta 1 achieved this effect at a 20‐fold lower concentration than insulin‐like growth factor‐I. In contrast, insulin‐like growth factor‐I stimulated [35S]sulfate incorporation 3.5‐fold; this was twice the maximal effect of transforming growth factor‐beta 1. Transforming growth factor‐beta 1 and insulin‐like growth factor‐I each decreased the proportion of newly synthesized glycosaminoglycans that were retained in the cells and pericellular matrix, indicating that the anabolic effect of these factors is only partly directed toward cell‐associated matrix production. The mitogenic and matrix synthetic actions of insulin‐like growth factor‐I and transforming growth factor‐beta 1 were synergistic. In concert, they increased [3H]thymidine incorporation approximately 12‐fold, an effect three times greater than the sum of the maximal stimulation achieved by each factor individually. Similarly, transforming growth factor‐beta 1 and insulin‐like growth factor‐I together increased glycosaminoglycan synthesis approximately two times more than the sum of their maximal individual effects. Taken together, these data indicate that these chondrosarcoma chondrocytes are positively regulated by insulin‐like growth factor‐I and transforming growth factor‐beta 1 and that these growth factors interact to augment the mitotic and matrix synthetic actions of the chondrocytes. If supported in human models, the sensitivity to growth factors of these cells suggests that interventions directed toward growth factor inhibition may be of therapeutic value.
Simultaneous changes in the mechanical properties, quantitative collagen organization, and proteoglycan concentration of articular cartilage following canine meniscectomy
Authors: LeRoux Michelle A. , Arokoski Jari , Vail T. Parker , Guilak Farshid , Hyttinen Mika M. , Kiviranta Ilkka , Setton Lori A.
Published: February 2005

The mechanical properties and microstructure of articular cartilage from the canine tibial plateau were studied 12 weeks after total medial meniscectomy. The organization of the birefringent collagen network was measured with quantitative polarized light microscopy to determine the thickness and the degree of organization of the superficial and deep zones. The zonal concentration of sulfated glycosaminoglycan was quantified with digital densitometry of safranin‐O staining. Equilibrium compressive and shear properties, as well as dynamic shear properties, were measured at sites adjacent to those of microstructural analysis. The results evinced significant loss of cartilage function following meniscectomy, with decreases of 20–50% in the compressive and shear moduli. There was no evidence of alterations in the degree of collagen fibrillar organization, although a complete loss of the surface zone was seen in 60% of the samples that underwent meniscectomy. Meniscectomy resulted in a decreased concentration of sulfated glycosaminoglycan, and significant positive correlations were found between the equilibrium compressive modulus and the glycosaminoglycan content. Furthermore, the shear properties of cartilage correlated directly with collagen fibrillar organization measured at the superficial zone of corresponding sites. These findings demonstrate that meniscectomy leads to impaired mechanical function of articular cartilage, with significant evidence of quantitative correlations between cartilage microstructure and mechanics.
Pressure‐induced periprosthetic osteolysis: A rat model
Authors: Skripitz Ralf , Aspenberg Per
Published: February 2005

Recent animal experiments have indicated that oscillating fluid pressure at the interface of bone and implant can lead to osteolysis. However, external nonphysiologic saline solutions were used to generate the pressure in these studies. In the present study on 15 Sprague‐Dawley rats, hydrostatic pressure fluctuations were applied to bone through body fluids, by compressing a soft‐tissue membrane adjacent to the proximal tibia. A titanium plate was fixed to the bone surface. After 28 days of osseointegration of the plate, a 1‐mm‐wide gap was created between it and the cortical bone and 5 days were given for fibrous tissue to form. Load was transmitted to this soft tissue by applying force on a piston mounted in the plate. In six rats, a cyclic pressure of 0.6 MPa was then applied to this tissue by 20 cycles twice a day with a frequency of 0.17 Hz for 5 days. The remaining rats served as controls, with the piston left untouched in its upper position. All of the rats were killed 10 days after creation of the gap. Histological sections were produced at a right angle to the loaded surface, In the pressurized specimens, osteoclastic bone resorption was dramatic. In all specimens, the original cortex was almost entirely resorbed but new woven bone had formed deeper in the marrow and walled off a cystic lesion. When necrotic remnants of the cortex were still in place, new woven bone was seen on the side away from the piston. This “lee effect” may indicate that bone formation was inhibited by fluid flow away from the pressurized tissue. The specimens with a nonloaded piston showed no signs of resorption. This new experimental model shows again that a moderate rise of hydrostatic pressure at the interface of bone and implant leads to considerable bone resorption. This could be a mechanism of prosthetic loosening.
Effects of hydroxyapatite coating on Ti‐6 Al‐4V implant‐site infection in a rabbit tibial model
Authors: Vogely H. Ch. , Oosterbos C. J. M. , Puts E. W. A. , Nijhof M. W. , Nikkels P. G. J. , Fleer A. , Tonino A. J. , Dhert W. J. A. , Verbout A. J.
Published: February 2005

To investigate the effect of implant type after direct contamination, a hydroxyapatite‐coated or noncoated Ti‐6Al‐4V implant was inserted into both tibiae of 32 New Zealand White rabbits. Prior to implantation, the left tibia was contaminated with increasing concentrations of Staphylococcus aureus (102‐105 colony‐forming units), ranging from very low (102) to relatively high (105). Four weeks after implantation, half of the tibial bone adjacent to the implant was harvested for bacteriological examination. Bacterial counts were quantified by plating serial dilutions. For the histological evaluation, sections of the implant with the remaining tibia were examined by semiquantitative scoring of infection parameters. The bacteriological data showed the inoculum dose and implant type to have a significant effect on the culture outcome: more bacteria were retrieved from the hydroxyapatite‐coated implants than from the noncoated titanium implants. Histological evaluation showed an increased score for the infected left tibiae compared with their contralateral control. In addition, with increasing inoculum dosage, the difference between the two types of implant increased. We demonstrated that infections can occur with biocompatible, noncemented implants and that they are related to the dose of the original inoculum. Bacteria were more likely to grow onto or next to the hydroxyapatite implants than on titanium implants and resulted in a more severe histopathological characterization of infection.
Biological and mechanical characteristics of the interface between a new swelling anchor and bone
Authors: Gualtieri Gina M. , Siegler Sorin , Hume Eric L. , Kalidindi Surya R.
Published: February 2005

We recently evaluated the peak pullout loads for anchors made from our new copolymeric swellingtype material compared with anchors made of a nonswelling material. In vitro and in vivo peak pullout loads of these anchors were evaluated after different intervals of implantation in the lateral femoral condyles of New Zealand White rabbits. Scanning electron microscopy and energy dispersive x‐ray analyses were additionally performed on selected retrieved samples after pullout to examine the characteristics of bone attachment to the implant. The mean peak pullout load was greater for the swelling anchors than for the nonswelling anchors after 48 hours in vitro (46.0 ± 15.8 compared with 10.8 ± 9.1 N, p = 0.0541). After 2 weeks in vivo, it was significantly greater for the swelling anchors than for the nonswelling controls (177.7 ± 41.3 compared with 53.7 ± 17.5 N, p = 0.0024). The peak pullout load was also greater for the swelling anchors after 8 weeks in vivo; however, this difference was less pronounced than at 2 weeks (101.8 ± 35.0 compared with 58.9 ± 9.7 N, p = 0.0508). Furthermore, the swelling implants tended to induce bone deposition at the bone‐implant interface. Results from this investigation reveal that the new family of dynamic implants has potential for applications requiring fixation to cancellous or osteoporotic bone.
Anatomical effects of periosteal elevation
Authors: Brownlow H. C. , Reed A. , Joyner C. , Simpson A. H. R. W.
Published: February 2005

Research that involves harvesting the periosteum is common. The exact technique of harvesting is rarely described: however, it may be of vital importance because techniques may vary in their ability to raise the osteogenic cambial layer, which is reported to be tightly adherent to the underlying cortex. This study was performed to define how the cambial and fibrous layers of the periosteum are affected by different techniques of stripping. The periosteum was raised from the tibia and the humerus of adult rabbits with four stripping techniques. The stripped bone surface was examined histologically and with a scanning electron microscope to determine whether the fibrous and cambial layers of the periosteum had been removed and whether there had been damage to the underlying cortex. The results from the two anatomical sites were the same. Raising the periosteum with cortical bone chips (shingling) or with a periosteal elevator removed both layers of the periosteum and caused considerable damage to the surface of the cortex. Raising the periosteum with a sharp scalpel or by simply pulling it off removed the fibrous layer but left the osteogenic layer intact adherent to the cortex. We conclude that some techniques of periosteal elevation fail to harvest the osteogenic layer and therefore may lead to unexpected experimental results. We suggest that authors describe the exact technique of periosteal stripping that was employed.
Rapid quantitative bioassay of osteoinduction
Authors: Adkisson Huston Davis , Strauss‐Schoenberger Jena , Gillis Mary , Wilkins Ross , Jackson Marc , Hruska Keith A.
Published: February 2005

We developed a reproducible, relatively rapid bioassay that quantitatively correlates with the osteoinductive capacity of demineralized bone matrix obtained from human long bones. We have found that Saos human osteosarcoma cells proliferate in response to incubation with demineralized bone matrix and that an index of this proliferative activity correlates with demineralized bone matrix‐induced osteogenesisin vivo. The bioassay (Saos cell proliferation) had an interassay coefficient of variation of 23 ± 2% and an intra‐assay cocfficient of 11 ± 1%. Cell proliferation was normalized to a standard sample of demineralized bone matrix with a clinically high osteoinductive capacity, which was assigned a value of one. The Saos cell proliferation for each sample was related to the standard and assigned a value placing it into thc low (0.00‐0.39), intermediate (0.40‐0.69). or high (0.70‐1.49) osteoinductivc index group. Osteoinduction of human demineralized bone matrix was quantitated by expressing new bone formation as a function of the total bone volume (new bone plus the demineralized bone powder). The demineralized bone matrix was placed in pouches formed in the rectus abdominis muscles of athymic rats, and endochondral bone formation was assessed at 35 days following implantation, when marrow spaces in the ossicles were formed by new bone bridging the spaces between demineralized bone matrix particles. The proliferative index correlated with the area of new bone formation in histological sections ol the newly formed ossicles. When the proliferative index (the osteoinductive index) was divided into low, intermediate. and high groups, the correlation between it and new bone formation (osteoinduction) was 0.850 (p < 0.0005) in 25 samples of demineralized bone matrix. There was no overlap in the osteoinduction stimulated between the samples with low and high osteoinductive indices. We conclude that the proliferation assay is useful for the routine screening of bone allograft donors for osteoinductivc potential. Furthermore, the two‐dimensional area of new bone formation. as it relates to total new bone area, is a quantitative measure of osteoinduction.
Decorin antisense gene therapy improves functional healing of early rabbit ligament scar with enhanced collagen fibrillogenesis in vivo
Authors: Nakamura Norimasa , Hart David A. , Boorman Richard S. , Kaneda Yasufumi , Shrive Nigel G. , Marchuk Linda L. , Shino Konsei , Ochi Takahiro , Frank Cyril B.
Published: February 2005

Injured ligaments heal with scar tissue, which has mechanical properties inferior to those of normal ligament, potentially resulting in re‐injury, joint instability, and subsequent degenerative arthritis. In ligament scars, normal large‐diameter collagen fibrils have been shown to be replaced by a homogenous population of small collagen fibrils. Because collagen is a major tensile load‐bearing matrix element and because the proteoglycan decorin is known to inhibit collagen fibrillogenesis, we hypothesized that the restoration of larger collagen fibrils in a rabbit ligament scar, by down‐regulating the proteoglycan decorin, would improve the mechanical properties of scar. In contrast to sense and injection‐treated controls, in vivo treatment of injured ligament by antisense decorin oligodeoxynucleotides led to an increased development of larger collagen fibrils in early scar and a significant improvement in both scar failure strength (83–85% improvement at 6 weeks; p < 0.01) and scar creep elongation (33–48% less irrecoverable creep; p < 0.03) under loading. This is the first report that in vivo manipulation of collagen fibrillogenesis improves tissue function during repair processes with gene therapy. These findings not only suggest the potential use of this type of approach to improve the healing of various soft tissues (skin, ligament, tendon, and so on) but also support the use of such methods to better understand specific structure‐function relationships in scars.
Tenascin‐C in tendon regions subjected to compression
Authors: Mehr D. , Pardubsky P. D. , Martin J. A. , Buckwalter J. A.
Published: February 2005

Tendon regions subjected almost exclusively to tension differ from regions subjected to high levels of compression as well as tension. Regions not exposed to compression consist primarily of spindle‐shaped fibroblasts surrounded by densely packed longitudinally oriented collagen fibrils formed principally from type‐I collagen. In contrast, regions subjected to compression have a fibrocartilagenous structure and composition: they consist of spherical cells surrounded by a matrix containing hyaline cartilage proteoglycans (aggrecan) and type‐II collagen as well as type‐I collagen. Reducing their adhesion to the matrix may help cells in the latter regions establish and maintain a spherical shape and minimize their deformation when the tissue is subjected to mechanical stress. We hypothesized that expression of tenascin‐C, an anti‐adhesive protein, is part of the adaptation of tendon cells to compression that helps establish and maintain fibrocartilagenous regions. To test this hypothesis, we compared segments of bovine flexor tendons subjected to repetitive compression (distal) with segments that are not subjected to compression (proximal) to determine whether they differed in tenascin‐C content and expression. RNA and protein analyses showed that tenascin‐C expression was elevated in the distal tendon. Tendon cells from the distal segment expressed more tenascin‐C mRNA than did cells from the proximal segments for as long as 4 days in cell culture, indicating that increased tenascin‐C expression is a relatively stable feature of the distal cells. Moreover, purified tenascin‐C inhibited the attachment of cultured tendon cells to fibronectin. These observations support the hypothesis that tenascin‐C expression is a cellular adaptation to compression that helps establish and maintain fibrocartilagenous regions of tendons by decreasing cell‐matrix adhesion.
Increased matrix synthesis following adenoviral transfer of a transforming growth factor β1 gene into articular chondrocytes
Authors: Shuler Franklin D. , Georgescu Helga I. , Niyibizi Christopher , Studer Rebecca K. , Mi Zhibao , Johnstone Brian , Robbins Paul D. , Evans Christopher H.
Published: February 2005

Monolayer cultures of lapine articular chondrocytes were transduced with first‐generation adenoviral vectors carrying lacZ or transforming growth factor β1 genes under the transcriptional control of the human cytomegalovirus early promoter. High concentrations of transforming growth factor β1 were produced by chondrocytes following transfer of the transforming growth factor β1 gene but not the lacZ gene. Transduced chondrocytes responded to the elevated endogenous production of transforming growth factor β1 by increasing their synthesis of proteoglycan, collagen, and noncollagenous proteins in a dose‐dependent fashion. The increases in collagen synthesis were not accompanied by alterations in the collagen phenotype; type‐II collagen remained the predominant collagen. Transforming growth factor β1 could not, however, rescue the collagen phenotype of cells that had undergone phenotypic modulation as a result of serial passaging. These data demonstrate that chondrocytes can be genetically manipulated to produce and respond to the potentially therapeutic cytokine transforming growth factor β1. This technology has a number of experimental and therapeutic applications, including those related to the study and treatment of arthritis and cartilage repair.
Molecular cloning, sequencing, and tissue and developmental expression of mouse cartilage oligomeric matrix protein (COMP)
Authors: Fang Carrie , Carlson Cathy S. , Leslie Michael P. , Tulli Hermina , Stolerman Elliot , Perris Roberto , Ni Ligong , Di Cesare Paul E.
Published: February 2005

Mouse cartilage oligomeric matrix protein cDNA was cloned and sequenced by a reverse transcription‐polymerase chain reaction. The open reading frame encoded a product of 755 amino acids that shares a high degree of identity to and possesses all the characteristic molecular features of both rat and human cartilage oligomeric matrix protein. This suggests that cartilage oligomeric matrix protein is highly conserved during evolution. The clone was 83, 84, and 95% indentical to human, bovine, and rat cartilage oligomeric matrix protein cDNA, respectively. In tissues from the adult mouse, cartilage oligomeric matrix protein was expressed not only in cartilage and tendon but in trachea, bone, skeletal muscle, eye, heart, and placenta as well, and no expression was found in other tissues. Immunohistology revealed that cartilage oligomeric matrix was deposited as early as 10 days post coitus in predifferentiated mouse embryo mesenchyme. It was detected in all cartilaginous tissues and in the skeletal muscles of the embryo at day 13. As development progressed, accumulation of cartilage oligomeric matrix protein was marked in the growth plate. At 19 days post coitus, it was prominently deposited in the hypertrophic zone of the growth plate, perichondrium, and periosteum and in the superficial layer of the articular cartilage surface but was absent in the more central areas of the epiphyseal cartilage. The restricted tissue distribution and expression of cartilage oligomeric matrix protein in developing as well as adult mouse tissues suggest the regulation of this protein at the transcriptional level. The findings reported herein are the first detailed characterization of the distribution of cartilage oligomeric matrix protein during early skeletal development of the mouse.
Influence of muscular activity on local mineralization patterns in metatarsals of the embryonic mouse
Authors: Tanck E. , Blankevoort L. , Haaijman A. , Burger E. H. , Huiskes R.
Published: February 2005

This study addressed the theory that local mechanical loading may influence the development of embryonic long bones. Embryonic mouse metatarsal rudiments were cultured as whole organs, and the geometry of the primary ossification center was compared with that of rudiments that had developed in utero. The mineralization front in vivo was found to be nearly straight, whereas in vitro it acquired a more convex shape due to a slower mineralization rate at the periphery of the mineralized cylinder. A poroelastic finite element analysis was performed to calculate the local distributions of distortional strain and fluid pressure at the mineralization front in the metatarsal during loading in vivo as a result of muscle contractions in the embryonic hindlimbs. The distribution of fluid pressure from the finite element analysis could not explain the difference in mineralization shape. The most likely candidate for the difference was the distortional strain, resulting from muscle contraction, which is absent in vitro, because its value at the periphery was significantly higher than in the center of the tissue. Without external loads, the mineralization process may be considered as pre‐programmed, starting at the center of the tissue and resulting in a spherical mineralization front. Strain modulates the rate of the mineralization process in vivo, resulting in the straight mineralization front. These results confirm that disturbances in muscle development are likely to produce disturbed mineralization patterns, resulting in a disordered osteogenic process.
Pulsed electromagnetic field stimulation of MG63 osteoblast‐like cells affects differentiation and local factor production
Authors: Lohmann C. H. , Schwartz Z. , Liu Y. , Guerkov H. , Dean D. D. , Simon B. , Boyan B. D.
Published: February 2005

Pulsed electromagnetic field stimulation has been used to promote the healing of chronic nonunions and fractures with delayed healing, but relatively little is known about its effects on osteogenic cells or the mechanisms involved. The purpose of this study was to examine the response of osteoblast‐like cells to a pulsed electromagnetic field signal used clinically and to determine if the signal modulates the production of autocrine factors associated with differentiation. Confluent cultures of MG63 human osteoblast‐like cells were placed between Helmholtz coils and exposed to a pulsed electromagnetic signal consisting of a burst of 20 pulses repeating at 15 Hz for 8 hours per day for 1, 2, or 4 days. Controls were cultured under identical conditions, but no signal was applied. Treated and control cultures were alternated between two comparable incubators and, therefore, between active coils; measurement of the temperature of the incubators and the culture medium indicated that application of the signal did not generate heat above the level found in the control incubator or culture medium. The pulsed electromagnetic signal caused a reduction in cell proliferation on the basis of cell number and [3H]thymidine incorporation. Cellular alkaline phosphatase‐specific activity increased in the cultures exposed to the signal, with maximum effects at day 1. In contrast, enzyme activity in the cell‐layer lysates, which included alkaline phosphatase‐enriched extracellular matrix vesicles, continued to increase with the time of exposure to the signal. After 1 and 2 days of exposure, collagen synthesis and osteocalcin production were greater than in the control cultures. Prostaglandin E2 in the treated cultures was significantly reduced at 1 and 2 days, whereas transforming growth factor‐β1 was increased; at 4 days of treatment, however, the levels of both local factors were similar to those in the controls. The results indicate enhanced differentiation as the net effect of pulsed electromagnetic fields on osteoblasts, as evidenced by decreased proliferation and increased alkaline phosphatase‐specific activity, osteocalcin synthesis, and collagen production. Pulsed electromagnetic field stimulation appears to promote the production of matrix vesicles on the basis of higher levels of alkaline phosphatase at 4 days in the cell layers than in the isolated cells, commensurate with osteogenic differentiation in response to transforming growth factor‐β1. The results indicate that osteoblasts are sensitive to pulsed electromagnetic field stimulation, which alters cell activity through changes in local factor production.
Biomechanical consequences of an isolated overload on the human vertebral body
Authors: Kopperdahl David L. , Pearlman Jonathan L. , Keaveny Tony M.
Published: February 2005

The biomechanical consequences of an isolated overload to the vertebral body may play a role in the etiology of vertebral fracture. In this context, we quantified residual strains and reductions in stiffness and ultimate load when vertebral bodies were loaded to various levels beyond the elastic regimen and related these properties to the externally applied strain and bone density. Twenty‐three vertebral bodies (T11‐L4, from 23 cadavers aged 20–90 years) were loaded once in compression to a randomized nominal strain level between 0.37 and 4.5%, unloaded, and then reloaded to 10% strain. Residual strains of up to 1.36% developed on unloading and depended on the applied strain (r2 = 0.85) but not on density (p = 0.25). Percentage reductions in stiffness and ultimate load of up to 83.7 and 52.5%, respectively, depended on both applied strain (r2 = 0.90 and r2 = 0.32, respectively) and density (r2 = 0.23 and r2 = 0.22, respectively). Development of residual strains is indicative of permanent deformations, whereas percentage reductions in stiffness are direct measures of effective mechanical damage. These results therefore demonstrate that substantial mechanical damage—which is not visible from radiographs—can develop in the vertebral body after isolated overloads, as well as subtle but significant permanent deformations. This behavior is similar to that observed previously for cylindrical cores of trabecular bone. Taken together, these findings indicate that the damage behavior of the lumbar and lower thoracic vertebral body is dominated by the trabecular bone and may be an important factor in the etiology of vertebral fracture.