bluuebunny/crossref_metadata_2025 huggingface dataset:
Recombinant human bone morphogenetic protein‐2 maintains the articular chondrocyte phenotype in long‐term culture
Authors: Sailor Laura Zenzius , Hewick Rodney M. , Morris Elisabeth A.
Published: February 2005

Bone morphogenetic proteins have been shown to increase matrix synthesis by articular chondrocytes in short‐term cultures. Members of this family of proteins have also been shown to induce endochondral ossification in vivo. The present study was performed to determine if the addition of human recombinant bone morphogenetic protein‐2 to a long‐term monolayer articular chondrocyte cell culture system affected the ability of the chondrocytes to divide in vitro, whether the cytokine altered expression of the articular chondrocyte phenotype and synthesis of matrix proteoglycans, and whether the cytokine was capable of inducing differentiation to a hypertrophic chondrocyte. Human recombinant bone morphogenetic protein‐2 did not alter cell proliferation. It caused 3.5–6.2 times more proteoglycan synthesis by articular chondrocytes during each of the time points tested after 4 days in culture. Total proteoglycan accumulation in the extracellular matrix after 28 days in culture was 6.7 times as great in the treated cultures as in the control. Treatment with human recombinant bone morphogenetic protein‐2 maintained the articular chondrocyte phenotype of cells in culture as demonstrated by Northern blot analysis: the expression of type‐I collagen genes was increased and that of type‐II collagen and aggrecan mRNA was lost in untreated chondrocyte cultures after 14–21 days in culture. In contrast, exposure to 100 ng/ml human recombinant bone morphogenetic protein‐2 maintained expression of type‐II collagen and increased expression of aggrecan compared with controls during the 28‐day culture period. Northern blot analysis of the expression of type‐X collagen and osteocalcin by chondrocytes treated with human recombinant bone morphogenetic protein‐2 showed a lack of expression of these genes, indicating no alteration in phenotype. These experiments demonstrated the ability of human recombinant bone morphogenetic protein‐2 to promote the articular chondrocyte phenotype and matrix synthesis in long‐term culture. Characteristics of cell growth were not affected, and the cytokine did not induce differentiation to a hypertrophic chondrocyte.
Significance of granulation tissue in torn supraspinatus insertions: An immunohistochemical study with antibodies against interleukin‐1β, cathepsin D, and matrix metalloprotease‐1
Authors: Gotoh Masafumi , Hamada Kazutoshi , Yamakawa Hideyuki , Tomonaga Akihito , Inoue Akio , Fukuda Hiroaki
Published: February 2005

The pathophysiology of rotator cuff tears can be elucidated by examining the tendinous insertion of the supraspinatus musele. As seen by light microscopy, the granulation tissue around the insertion of a torn supraspinatus tendon appears to induce osteochondral destruction by means of multinucleated giant cells and chemical mediators. The purpose of this study was to examine the contribution of certain chemical mediators to osteochondral destruction using immunohistochemical analysis of interleukin‐β, cathepsin D, and matrix metalloprotease‐1. Sixteen supraspinatus insertions with portions of the greater tuberosity, including eight complete‐thickness tears and eight incomplete‐thickness tears, were obtained during surgery. Six fresh cadaveric supraspinatus tendons without grossly evident tears served as normal controls. Strong immunoreactivity was found in all 16 torn supraspinatus insertions but not in the six insertions of apparently intact tendons. Macrophages and multinucleated giant cells, which showed immunoreactivity for all three chemical mediators, were often found at the interface between the osteochondral margin of the enthesis and the granulation tissue, suggesting that they may be involved in osteochondral destruction. We therefore concluded that, in addition to repetitive subacromial impingement, this granulation tissue may contribute to the development of rotator cuff tears by weakening the insertion.
Biomechanical changes of the wrist flexor and extensor tendons following loss of scaphoid integrity
Authors: Tang Jin Bo , Ryu Jaiyoung , Han JungSoo , Omokawa Shohei , Kish Vincent , Wearden Stanley
Published: February 2005

Loss of integrity of the scaphoid may change the motion center of the entire carpus, and deformities from scaphoid fractures may alter the location of motor tendons of the wrist, thus altering their biomechanics. The goal of this study was to clarify biomechanical changes in these tendons following loss of scaphoid integrity. Excursions and moment arms of the principal flexor and extensor tendons of the wrist were investigated in seven cadaveric upper extremities in intact wrists after simulation of scaphoid waist fracture and after removal of the proximal scaphoid. Excursions of the flexor carpi radialis and ulnaris extensor carpi radialis longus and brevis, and extensor carpi ulnaris tendons were measured with rotary potentiometers during wrist flexion‐extension and radioulnar deviation. Simultaneously, wrist joint angulation was recorded. Moment arms of the tendons were derived from tendon excursions and joint motion. After scaphoid fracture, the moment arms of the flexor carpi radialis and extensor carpi ulnaris tendons increased significantly during wrist flexion‐extension, whereas the moment arms of the extensor carpi radialis longus and brevis tendons decreased significantly. After proximal scaphoid excision, the moment arms of the extensor carpi radialis longus and brevis tendons again decreased significantly during wrist flexion‐extension. The moment arms of the flexor carpi radialis and extensor carpi radialis brevis tendons increased significantly during radioulnar deviation, whereas those of the wrist motors on the ulnar side decreased. These findings indicate the importance of the integrity of the scaphoid in maintaining normal biomechanics of motor tendons of the wrist. An increase in the moment arm of the radial wrist flexor along with a decrease in moment arms of the radial extensors constitutes an etiology for persistent angulation of the scaphoid and the hump‐back deformity. In addition, disturbing the biomechanics of the wrist motor tendons predisposes the carpal joints to abnormal loading, potentially contributing to the development of carpal joint degeneration.
Deformation of loaded articular cartilage prepared for scanning electron microscopy with rapid freezing and freeze‐substitution fixation
Authors: Nötzli Hubert , Clark John
Published: February 2005

To investigate the effect of joint loading on collagen fibers in articular cartilage, 45 knees of adult rabbits were examined by scaning electron microscopy. The knees were loaded at the patella with a simulated “quadriceps force” of 0.5‐4 times body weight for 0.5 or 25 minutes, plunge‐frozen, and fixed by freezesubstitution with aldehydes. Six knees were loaded for 3 hours and then fixed conventionally. Fixed tibial plateaus were examined and then freeze‐fractured through the area of tibiofemoral contact, dried, coated, and examined by scanning electron microscopy to assess the overall deformation of the tibial articular surface and matrix collagen fibers. With tissue prepared by conventional fixation used as a standard, the quality of fixation was graded by light and transmission electron microscopy of patellar cartilage taken from half of the freeze‐fixed knees. In loaded specimens, an indentation was present where the femur contacted the tibial plateau. The diameter and apparent depth of the dent were proportional to the magnitude and duration of the load; no dent was seen in the controls. The thickness of the cartilage at the center of the indentation was reduced 15‐80%. Meniscectomy always produced larger deformations in otherwise equivalent conditions. Icecrystal damage to cells was evident by transmission electron microscopy and scanning electron microscopy, but at magnifications as high as ×30,000 the collagen fibrils prepared by freeze‐substitution and conventional aqueous methods were identical. In loaded regions, the collagen matrix of the tibial cartilage was deformed in two ways: (a) radial collagen fibers exhibited a periodic crimp, and (b) in regions where an indentation was created by the femoral condyle, the radial fibers were bent, in effect creating tangential zone where none had existed before. The radial fibers apparently are loaded axially and buckle under normal loads.
Expression of MAGE genes in osteosarcoma
Authors: Sudo Takao , Kuramoto Terukazu , Komiya Setsuro , Inoue Akio , Itoh Kyogo
Published: February 2005

Expression of MAGE genes that encode tumor‐rejection antigens recognized by cytotoxic T lymphocytes with major histocompatibility complex class‐I antigens was investigated in human osteosarcomas (20 cell lines and eight fresh tumor tissues). MAGE‐1,2,3,4, and 6 genes were expressed at the mRNA level in 11(52.4%), 10(47.6%), 10(47.6%), one (4.8%) and 10 (47.6%) of 21 tumor cell lines, respectively, and in five (62.5%), six (75%), five (62.5%), one (12.5%) and five (62.5%) of eight fresh tumor tissues as determined by the reverse transcription‐polymerase chain reaction method. MAGE‐1 or 4 protein was detected by immunoblot analysis in eight of 11 or one of one tumor cell lines, respectively where it was expressed at the mRNA level. Major histocompatibility complex class‐I antigens were expressed 19 of 21 tumor cell lines. These results suggest that MAGE tumor‐rejection antigens are expressed in substantial numbers of osteosarcomas in a major histocompatibility class‐I‐restricted manner.
Chondrocyte biosynthesis correlates with local tissue strain in statically compressed adult articular cartilage
Authors: Wong M. , Wuethrich P. , Buschmann M. D. , Eggli P. , Hunziker E.
Published: February 2005

In this study, we investigated the depth‐dependent metabolic and structural responses of adult articular cartilage to large‐strain, static, unconfined compression. Changes in cell biosynthetic activity and several morphometry‐based structural parameters (cell density, cell volume fraction, cell surface‐area density, mean cell surface area, and mean cell volume) were measured at eight sites representing different depth‐zones between the articular surface and the cartilage/bone border. In addition, local axial strain in the superficial, transitional, upper radial, and lower radial zones was estimated on the basis of the change in cell density values. Static compression of articular cartilage revealed a highly heterogeneous deformation profile through the depth of the sample as well as zone‐specific changes in biosynthetic activity, as reflected by incorporation of [3H]proline. The axial strains in the top layers were greater than the applied surface‐to‐surface strain, whereas axial strains adjacent to the cartilage/bone border were significantly less than the applied strain. Zonal changes in cell density and axial strain that occurred during static compression correlated well with alterations in metabolic activity. These coordinated changes between cell biosynthesis and cartilage structure suggest that zone‐specific variations in mechanical stimuli could be responsible for spatially varied patterns of cartilage metabolic activity under load.
Contact pressure and tension in anterior cruciate ligament grafts subjected to roof impingement during passive extension
Authors: Goss Ben C. , Hull M. L. , Howell Stephen M.
Published: February 2005

Contact between an anterior cruciate ligament graft and the intercondylar roof has been termed roof impingement. Grafts with impingement sustain permanent damage, and if the injury is extensive enough, then the graft may fail, causing recurrent instability. This study evaluated two mechanical factors that could be responsible for the graft injury associated with roof impingement: an increase in graft tension or elevated pressures between the graft and the roof, or both. An anterior cruciate ligament reconstruction was performed using an Achilles tendon graft in five fresh‐frozen cadaveric knees. Using a six‐degree‐of‐freedom load application system, the anterior displacement of the knee with the native anterior cruciate ligament was restored in the reconstructed knee at a flexion angle of 30° and with an anterior force of 200 N applied. Pressure between the graft and intercondylar roof, graft tension, and flexion angle were measured during passive knee extension for three tibial tunnel placements (anterior, center, and posterior). Intercondylar roof impingement increased the contact pressure between the graft and the roof but had no significant effect on graft tension. Therefore, during passive knee extension, the contact pressure between the anterior cruciate ligament graft and the intercondylar roof is a more likely cause of graft damage than increased graft tension.
Osteoclast formation during tumor osteolysis does not require proliferating osteoclast precursor cells
Authors: Clohisy Denis R. , Ramnaraine Margaret L. R.
Published: February 2005

The cellular mechanism or mechanisms through which tumors induce osteoclast formation at sites of tumor osteolysis is unknown. To test the hypothesis that osteoclast formation at sites of tumor osteolysis reflects influences that tumors have on proliferating osteoclast precursor cells, a novel in vivo experimental model was developed that produced mice that were deficient in osteoclasts (op/op) and were depleted (by way of total body irradiation) of proliferating osteoclast precursor cells. The femora of irradiated op/op mice were injected with tumor cells (2472 clone) that had been previously shown to form osteolytic tumors and to induce focal osteoclastogenesis, and the influence of these tumor cells on osteoclast formation was determined in op/op mice that were depleted of proliferating osteoelast precursor cells. The results indicated that 2472 tumor cells induced osteoclast formation in op/op mice despite the absence of proliferating osteoclast precursor cells. This finding disproved the hypothesis under investigation and suggests that osteoclast formation at sites of tumor osteolysis reflects influences of tumors on postmitotic, not proliferating, osteoclast precursor cells.
Effect of radial shortening on muscle length and moment arms of the wrist flexors and extensors
Authors: Tang Jin Bo , Ryu Jaiyoung , Kish Vincent , Wearden Stanley
Published: February 2005

The purpose of this study was to determine the effect of distal radial shortening on muscle length and moment arm of the wrist flexors and extensors. In eight cadaveric upper extremities, distal radius fractures were simulated by an ostectomy. The distal radius was progressively shortened by 2.5, 5.0, 7.5, and 10 mm. Changes in the resting length of the flexor carpi radialis and ulnaris, extensor carpi radialis longus and brevis, and extensor carpi ulnaris muscles were measured with rotary potentiometers at neutral position, flexion, extension, and radial and ulnar deviation of the wrists. The wrists were passively moved through flexion‐extension and radioulnar deviation, and tendon excursions and wrist joint angulation were recorded simultaneously. Tendon moment arms were derived from tendon excursions and joint motion. The results showed that either muscle, length or moment arm of the principal wrist flexors and extensors was significantly affected by the radial shortening. Muscle length decreased significantly after radial shortening in all the wrist flexors and extensors except for the extensor carpi ulnaris. The moment arm of the extensor carpi ulnaris tendon decreased significantly during either wrist flexion‐extension or radioulnar deviation. The extensor carpi radialis brevis and flexor carpi ulnaris tendons also showed a significant decrease in their moment arms during radioulnar deviation of the wrist. Radial shortening of only 2.5 mm caused statistically significant changes in muscle length and moment arm of the wrist flexors and extensors. Increasing the extent of radial shortening exaggerated the biomechanical changes in the wrist motors. These results validate the importance of normal radial length for wrist kinetics and, from a biomechanical perspective, support complete correction of radial shortening after distal radius fractures.
Effects of static fingertip loading on carpal tunnel pressure
Authors: Rempel David , Keir Peter J. , Smutz W. Paul , Hargens Alan
Published: February 2005

The purpose of this study was to explore the relationship between carpal tunnel pressure and fingertip force during a simple pressing task. Carpal tunnel pressure was measured in 15 healthy volunteers by means of a saline‐filled catheter inserted percutaneously into the carpal tunnel of the nondominant hand. The subjects pressed on a load cell with the tip of the index finger and with 0, 6, 9, and 12 N of force. The task was repeated in 10 wrist postures: neutral; 10 and 20° of ulnar deviation; 10° of radial deviation; and 15, 30, and 45° of both flexion and extension. Fingertip loading significantly increased carpal tunnel pressure for all wrist angles (p = 0.0001). Post hoc analyses identified significant increases (p <0.05) in carpal tunnel pressure between unloaded (0 N) and all loaded conditions, as well as between the 6 and 12 N load conditions. This study demonstrates that the process whereby fingertip loading elevates carpal tunnel pressure is independent of wrist posture and that relatively small fingertip loads have a large effect on carpal tunnel pressure. It also reveals the response characteristics of carpal tunnel pressure to fingertip loading, which is one step in understanding the relationship between sustained grip and pinch activities and the aggravation or development of median neuropathy at the wrist.
Anatomy of the human patellofemoral joint articular cartilage: Surface curvature analysis
Authors: Kwak S. Daniel , Colman William W. , Ateshian Gerard A. , Grelsamer Ronald P. , Henry Jack H. , Mow Van C.
Published: February 2005

Articular cartilage surfaces of 49 human patellae and 24 distal femora were characterized by identifying distinctive features with surface curvature analysis. Paired specimens from the same donor generally exhibited natural symmetry, so only results from nonpaired specimens were considered (39 patellae and 19 femora). In 23 of 39 patellae, proximal median and lateral transverse ridges extended to form an oblique ridge resembling a skewed lambda (λ). Most of the unpaired patellae (37 of 39) exhibited only a single lateral transverse ridge, and most (32 of 39) had an odd facet. All but one patella exhibited a concave depression in the lateral and medial facets and a sellar area in the proximal region. All distal femoral surfaces exhibited a sellar trochlea. The concavity of the trochlea was greatest in the posterioraspect, near the intercondylar notch.
Growth hormone secretagogue increases muscle strength during remobilization after canine hindlimb immobilization
Authors: Lieber Richard L. , Jacks Thomas M. , Mohler Randall L. , Schleim Klaus , Haven Michelle , Cuizon Denise , Gershuni David H. , Lopez Michael A. , Hora Donald , Nargund Ravi , Feeney William , Hickey Gerard J.
Published: February 2005

Twenty‐two beagles were divided into two equal groups, and the right hindlimb of each animal was immobilized at 105° of knee flexion by external fixation. After 10 weeks of fixation, the device was removed, allowing free mobility for the following 5 weeks. Each day throughout the 15 weeks, one group received a growth hormone secretagogue (treatment) at a dose of 5 mg/kg, and the other received a lactose placebo (control). At weeks 0, 10, and 15, strength as indicated by maximum isometric extension torque was measuredin the right hindlimb, biopsies of the vastus lateralis muscle were taken, and the dogs were weighed. Weekly blood samples were analyzed for insulin‐like growth factor‐I, blood urea nitrogen, and creatine phosphokaase. Between weeks 0 and 10, tetanic torque declined by about 60% (p < 0.001) in both groups, with no significant difference between the groups (p > 0.7). Between weeks 10 and 15, tetanic torque in the treated group increased by 0.81 Nm; this was significantly greater than the increase of 0.25 Nm in the placebo group (p < 0.05). The diameters of slow (type‐1) and fast (type‐2) fibers measured from the vastus lateralis muscle followed the same trend. At all time points, fiber diameter correlated strongly with torque; this argues against nonmuscular causes such as nerve injury for strength loss. The mean levels of insulin‐like growth factor‐1 increased 100% by week 4 in the treated group and remained elevated by about 60% throughout the experiment. Levels of insulin‐like growth factor‐1 in the placebo group decreased 30% within week 1 and remained depressed throughout the experiment. Our interpretation of these data suggests that the growth hormone secretagogue elevated levels of serum insulin‐like growth factor‐1, which in turn increased the size and strength of the quadriceos muscle during remobilization. These data may ultimately have therapeutic application to humans during rehabilitation after prolonged inactivity.
Prosthetic metals impair murine immune response and cytokine release in vivo and in vitro
Authors: Wang James Y. , Wicklund Barb H. , Gustilo Ramon B. , Tsukayama Dean T.
Published: February 2005

This study was designed to investigate whether prosthetic metals adversely affect immune responses and the release of immunoregulatory cytokines in vivo and in vitro. Titanium and cobalt‐chromium alloy were injected into the peritoneal cavity of female mice. At 5, 8, and 12 weeks after the injection, the levels of cobalt and chromium in the blood were significantly increased compared with the levels in control mice; the level of titanium was not significantly changed until 12 weeks. The release of interleukin‐2 was significantly inhibited by cobalt‐chromium particles after 3 weeks; titanium particles did not have the same effect until 8 and 12 weeks. The release of interleukin‐γ was significantly inhibited by cobalt‐chromium particles after 3 weeks but was not significantly inhibited by titanium particles until 12 weeks. The release of interferon‐y was significantly inhibited by cobalt‐chromium particles only at 12 weeks and was not inhibited by titanium particles. The proliferation of T cells was significantly inhibited by cobalt‐chromium particles at 3 weeks and by titanium particles at 8 and 12 weeks, and the proliferation of B cells was significantly inhibited by cobalt‐chromium particles after 3 weeks but was not inhibited by titanium particles. The production of immunoglobulin by lipopolysaccharide‐stimulated B cells was also significantly reduced by cobalt‐chromium particles after 3 weeks and by titanium particles at 8 and 12 weeks. The cytokine release by lymphocytes, proliferation of T and B cells, and immunoglobulin production by B cells were also significantly inhibited by titanium and cobalt‐chromium particles, as well as by titanium, cobalt, and chromium ions in vitro, whereas these metals are not cytotoxic to murine lymphocytes in vitro. The data indicate that the metal‐induced immunosuppression may be another important factor in the development of implant‐associated infection in patients with a prosthesis.
Biochemical and molecular homogeneity in the patellar tendon of the immature pig
Authors: Yin C. , Wayne J. S. , Jiranek W. A. , Zuelzer W. A.
Published: February 2005

Patellar tendon is widely used for reconstruction of the anterior cruciate ligament. However, few studies have investigated the tendon's homogeneity, a characteristic often assumed of it in experiments. In this study, the assumption that the patellar tendon is homogeneous was tested by dividing the central half of the tendon into six sections along its length and width and comparing commonly measured biochemical parameters and patterns of gene expression among these sections. No significant differences were found between the sections for any of the studied parameters: water content (p > 0.5). DNA content (p > 0.9), total collagen content (p > 0.8), amount of type‐I collagen (p > 0.7) or type‐III collagen (p > 0.7), or expression of mRNA (p > 0.9). For all parameters, the minimum power value for statistical analyses was greater than 0.80. It was concluded that the central half of the tendon is homogeneous in terms of all of the measured parameters. The results provide important information for the many experiments that sample part of the patellar tendon to infer the characteristics of the whole tendon, e.g., biopsy studies.
Chondrocyte transplantation to articular cartilage explants in vitro
Authors: Chen Albert C. , Nagrampa Jennifer P. , Schinagl Robert M. , Lottman Lisa M. , Sah Robert L.
Published: February 2005

The transplantation of chondrocytes has shown promise for augmenting the repair of defects in articular cartilage. This in vitro study examined the efficiency of the transplantation of bovine chondrocytes onto articular cartilage disks and the ability of the transplanted chondrocytes to subsequently synthesize and deposit proteoglycan. The radiolabeling of chondrocyte cultures with [3H]thymidine, followed by 4 days of chase incubation, resulted in the incorporation of 98% of the radiolabel into DNA (as assessed by susceptibility to DNase). At the end of the culture period, the [3H]DNA was stable, with a half‐life of radioactivity loss into the medium of 73 days. With use of radiolabeled chondrocytes for quantitation, the efficiency of transplantation onto a cartilage substrate was 93 ± 4% for seeding densities of as much as 650,000 cells per cm2 and a seeding duration of 1 hour. These findings were confirmed both by tracking cells stained with 5‐chlormethylfluorescein diacetate and by quantitating DNA. During the 16 hours after seeding onto a cartilage substrate (in which the endogenous cells had been lysed by lyophilization), the transplanted cells synthesized sulfated proteoglycan in direct proportion to the number of cells seeded. Most (83%) of the newly synthesized proteoglycan was released into the medium rather than retained within the layer of transplanted cells and the recipient cartilage substrate. Comparative studies with lyophilized‐rehydrated or live cartilage as the recipient substrate indicated a similar efficiency of chondrocyte seeding and proteoglycan synthesis by the seeded chondrocytes. The transplanted cells retained the chondrocyte phenotype, as judged by a high proportion of the [35S]macromolecules being in the form of aggrecan that was capable of aggregating with hyaluronan and link protein, as well as by immunostaining within and around the transplanted cells for type‐II, but not type‐1, collagen. These results indicate that the number of chondrocytes transplanted onto a cut cartilage surface greatly affects the level of matrix synthesis; this in turn may affect repair.
Chondrogenic phenotype of perichondrium‐derived chondroprogenitor cells is influenced by transforming growth factor‐beta 1
Authors: Dounchis J. S. , Goomer R. S. , Harwood F. L. , Khatod M. , Coutts R. D. , Amiel D.
Published: February 2005

Our laboratory has developed a method for the repair of osteochondral defects by implanting cultured perichondrial cells attached to a biodegradable polylactic acid scaffold. The success of this approach depends in part on the proliferative characteristics and the phenotype of the implanted cells. Transforming growth factor‐beta 1 has been reported to influence these parameters in several mesenchymal‐derived tissues in vitro and in vivo. The chondrocytic phenotype is marked by an enhanced expression of the collagen type‐II gene. In this study, cultures grown from explants of rabbit rib perichondrium were exposed to exogenously added transforming growth factor‐beta 1 at concentrations of 0.1–10 ng/ml of media. Cell proliferation and collagen gene expression were measured. The expression of types I and II collagen genes was analyzed by Northern blot and reverse transcriptase‐polymerase chain reaction. The exogenous addition of transforming growth factor‐beta 1 at a concentration of 0.1–10 ng/ml resulted in tritiated thymidine uptake by perichondrial cells, with optimum proliferative effects at 0.1 ng/ml. Transforming growth factor‐beta 1 added at concentrations of 0.1 and 0.5 ng/ml significantly upregulated the expression of type‐II collagen mRNAs. The results suggest that, when the chondrocytic phenotype is defined by markedly enhanced type‐II collagen gene expression, the chondrocytic phenotype of explant cultures of perichondrium‐derived cells is enhanced by the Kogenous; addition of transforming growth factor‐beta 1.
Repeatability of patellar cartilage thickness patterns in the living, using a fat‐suppressed magnetic resonance imaging sequence with short acquisition time and three‐dimensinal data processing
Authors: Tieschky Marcus , Faber Sonja , Haubner Michael , Kolem Heiner , Schulte Erik , Englmeier Karl‐Hans , Reiser Maximilian , Eckstein Felix
Published: February 2005

A fast, reproducible, and noninvasive method is required for quantifying cartilage thickness clinically and for studying the deformation of articular cartilage during and after mechanical loading in vivo. The objective of the current investigation was to test the repeatability of regional distribution patterns of patellar cartilage thickness in the living on the basis of a fat‐suppressed magnetic resonance imaging sequence with a short acquisition time and three‐dimensional digital data processing. The knees of eight healthy volunteers were transversally imaged with a fat‐suppressed FLASH‐3D (fast low angle shot) sequence (acquisition time: 4 minutes and 10 seconds). In each case, the joint was newly positioned before each of the six replicate measurements was taken. The patellar cartilage was reconstructed three‐dimensionally, and the distribution of cartilage thickness was determined with a three‐dimensional minimal‐distance algorithm. Whereas the cartilage volume ranged from 3,198 to 7,149 mm3, the mean coefficient of variation for the 6‐fold volume measurement was 1.35%. On average, 75.1% (±4.1%) of all test pixels could be attributed to the same cartilage thickness interval (0.5 mm) by image analysis; 14.8% (±2.4%) deviated by one interval; 6.6% (±1.5%), by two intervals; and 3.5% (±1.8%), by more than two intervals. We conclude that, on the basis of a magnetic resonance imaging sequence with an acquisition time of less than 5 minutes, the quantitative distribution of cartilage thickness can be determined with high precision in vivo.
Residual stresses in ultra‐high molecular weight polyethylene loaded cyclically by a rigid moving indenter in nonconforming geometries
Authors: Estupiñán Jaime A. , Bartel Donald L. , Wright Timothy M.
Published: February 2005

The characterization of stress and deformation fields that incorporate moving cyclic loads and nonlinear material response in ultra‐high molecular weight polyethylene components for total knee replacements is required to quantify mechanisms of surface damage. A simulation of stresses in polyethylene components for total knee replacement subjected to cyclic moving loads was performed with use of nonlinear finite element analysis. Convergence to a steady‐state cycle of stress and deformation was observed within five cycles of loading. Differential plastic deformation under the surface of the polyethylene led to horizontal residual stresses that were tensile at the surface and compressive in the subsurface. The magnitudes of the residual J stresses indicate their importance in surface failure mechanisms. Horizontal residual tensile stresses at the surface are consistent with the initiation and propagation of surface cracks that could cause pitting in polyethylene. Horizontal residual compressive stresses under the surface could cause such cracks to arrest or turn and thus limit damage to a region just beneath the surface. The results emphasize the importance of incorporating nonlinear effects to simulate long‐term stress fields associated with surface damage in polyethylene.
Kinematics of the glenohumeral joint with bankart lesion and repair
Authors: Novotny John E. , Nichols Claude E. , Beynnon Bruce D.
Published: February 2005

A Bankart repair is performed to reduce abnormal translations of the humeral head on the glenoid due to a Bankart lesion, a separation of the capsulolabral complex from the glenoid rim. However, this is often accompanied by a loss of rotational range of motion that may lead to decreased function and osteoarthritis. This loss of rotation, coupled to the goal of reducing humeral translations, may be a result of the amount of imbrication of the capsule during repair. To determine the effects of capsular imbrication, we investigated how two Bankart repairs (2.5 and 5.0 mm of capsular imbrication) and a Bankart lesion altered the translations and rotations of the human glenohumeral joint in vitro. Coupled moments were applied to the unconstrained humerus in abduction‐adduction, in flexion‐extension, and to simulate the cocked phase of throwing. Motion was measured with an electromagnetic system. There were no differences in the kinematics betweenthe intact specimens and those with a Bankart lesion or between normal specimens and the first (2.5 mm) Bankart repair. The first repair significantly reduced external rotation for the cocked phase of throwing compared with the Bankart lesion: from 46.8 ± 23.6° to 32.4 ± 14.2° (±SD). The second (5.0 mm) Bankart repair produced significantly different posterior translation (‐4.7 ± 3.9 mm) of the humeral head relative to the glenoid compared with normal (5.1 ± 4.7 mm anterior) and the first repair (6.1 ± 8.3 mm anterior), as the humerus moved from full flexion to full extension. Differences were also found for all rotations in the cocked phase of throwing. For the second repair, the humerus extended 24.3° and externally rotated 18.6° less than normal and was abducted 15.4° more. These results indicate that both Bankart repairs do little to affect humeral translations with unconstrained moment loading but that rotations are affected during the cocked phase of throwing, with significant losses of external and extension rotations.
Osteoblast cytoskeletal modulation in response to mechanical strain in vitro
Authors: Meazzini M. C. , Toma C. D. , Schaffef J. L. , Gray M. L. , Gerstenfeld L. C.
Published: February 2005

The structural integrity of microfilaments has been shown to be necessary for the signal transduction of mechanical stimuli within osteoblasts. Qualitative and quantitative changes within the cytoskeleton of osteoblasts may therefore be crucial components of the signal transduction processes of these cells in response to mechanical stimulation. Avian osteoblasts were strained with a device that deforms a flexible, cell‐laden membrane at a defined frequency and intensity in a uniform biaxial manner. We examined the effects of mechanical strain on the accumulation of protein and the expression of the major cytoskeletal elements and specific integrin‐binding (arginine‐glycine‐aspartic acid) proteins of these cells. Mechanical strain increased the level of total extracellular matrix‐accumulated fibronectin by approximately 150% and decreased that of osteopontin by approximately 60% but had no quantifiable effect on the accumulation of β1 integrin subunit or collagen type I. An examination of the major elements of the cytoskeleton demonstrated that neither the level of actin nor that of the intermediate filament protein vimentin changed; however, the amount of tubulin decreased by approximately 75% and the amount of vinculin, a major protein of focal adhesion complexes, increased by approximately 250%. An analysis of protein synthesis by two‐dimensional gel electrophoresis of [35S]methionine‐labeled cytoskeletal proteins demonstrated that the changes in the accumulation of vinculin and tubulin resulted from their altered synthesis. Messenger RNA analysis confirmed that the changes in accumulation and protein synthesis observed for vinculin, fibronectin, and osteopontin were controlled at a pretranslational level. Immunofluorescent microscopy demonstrated that mechanical strain led to increased formation and thickening of actin stress fibers, with a commensurate dissociation in microtubules and a clear increase in levels of vinculin at the peripheral edges of the cells. In conclusion, the elevated rate of synthesis and the increased accumulation of vinculin and fibronectin, as well as the increase in the number and size of stress fibers and focal adhesion complexes, suggest that mechanical strain leads to a coordinated change both in the cytoskeleton and in extracellular matrix proteins that will facilitate tighter adhesion of an osteoblast to its extracellular matrix.
Expression of a stable articular cartilage phenotype without evidence of hypertrophy by adult human articular chondrocytes in vitro
Authors: Binette François , McQuaid David P. , Haudenschild Dominik R. , Yaeger Peter C. , McPherson John M. , Tubo Ross
Published: February 2005

Chondrocytes that were isolated from adult human articular cartilage changed phenotype during monolayer tissue culture, as characterized by a fibroblastic morphology and cellular proliferation. Increased proliferation was accompanied by downregulation of the cartilage‐specific extracellular matrix proteoglycan, aggrecan, by cessation of type‐II collagen expression, and by upregulation of type‐I collagen and versican. This phenomenon observed in monolayer was reversible after the transfer of cells to a suspension culture system. The transfer of chondrocytes to suspension culture in alginate beads resulted in the rapid upregulation of aggrecan and type‐II collagen and the downregulation of expression of versican and type‐I collagen. Type‐X collagen and osteopontin, markers of chondrocyte hypertrophy and commitment to endochondral ossification, were not expressed by adult articular chondrocytes cultured in alginate, even after 5 months. In contrast, type‐X collagen was expressed within 2 weeks in a population of cells derived from a fetal growth plate. The inability of adult articular chondrocytes to express markers of chondrocyte hypertrophy has underscored the fundamental distinction between the differentiation pathways that lead to articular cartilage or to bone. Adult articular chondrocytes expressed only hyaline articular cartilage markers without evidence of hypertrophy.
Exposure of cartilage to a fibronectin fragment amplifies catabolic processes while also enhancing anabolic processes to limit damage
Authors: Homandberg Gene A. , Wen Catherine
Published: February 2005

The addition of fibronectin fragments to cultured cartilage causes an initial suppression of proteoglycan synthesis, induction of matrix metalloproteinases, and resultant decrease in proteoglycan content by about 50% during the first few days in culture. Because the proteoglycan loss appears to be limited, we investigated whether the fibronectin fragments induce anabolic responses that might counter the damage. The effects of various lengths of exposure of cultured cartilage to the fibronectin fragment on proteoglycan content, proteoglycan synthesis rates, stromelysin‐1 release, and tumor necrosis factor‐α, interleukin‐1α, and interleukin‐6 release were investigated. The results showed that about 7 days of exposure of cultured cartilage to the fibronectin fragment was required for maximal cytokine release, proteoglycan depletion, and stromelysin‐1 release. However, nearly maximal suppression of proteoglycan synthesis occurred within 1 day of the addition of the fibronectin fragment and, after its removal, the rates increased to supernormal levels. Decreasing exposure to 3 days caused only a small decrease in cartilage proteoglycan content, although stromelysin‐1 release still occurred. Decreasing exposure to 1 day caused an immediate increase in proteoglycan synthesis and an increase to supernormal proteoglycan contents. The effect of first treating cartilage with the fibronectin fragment for various periods and then allowing a recovery was to make the cartilage more resistant to secondary exposures. This study shows that cartilage damage can be caused by short exposures to the fibronectin fragment and that exposures either optimal or suboptimal for damage additionally amplify anabolic processes to make the cartilage resistant to further damage and, thus, condition it against pending amplification of damage.
Vascular and structural changes in rat femora following nailing and intramedullary occlusion
Authors: Grundnes Oliver , Gjerdet Nils R. , Utvåg Stein Erik , Reikerås Olav
Published: February 2005

The purpose of this study was to evaluate biomechanical, structural, and blood flow changes of the femoral canal in rats 12 weeks after intramedullary reaming, nailing, or occlusion. In one group, reaming alone was performed. In a second group, reaming was followed by use of a tight‐fit steel nail. In a third group, reaming was followed by use of inert silicone that totally plugged the medullary cavity. A fourth group served as the control. The acute mechanical and vascular effects caused by reaming and nailing were determined in a separate group. Reaming and nail insertion reduced blood flow in femoral bone to about one‐third. Reaming reduced bending moment by approximately 40%, whereas bending rigidity was unchanged. After 12 weeks, the cortical bone blood flow was significantly increased in both the nailed and the silicone‐plugged bones compared with the reamed and control groups. The bending moment and energy absorption in the silicone group were inferior to those of the other groups. There were no differences in either the external or internal diameter or the medullary and net bone areas. In the silicone group, both the number and the area of large pores (larger than 10 μm) significantly increased in comparison with the other groups; hence, bone porosity was increased. This increment was confined to large pores. It is concluded that medullary occlusion contributes to structural and blood flow changes in bone.
Regional gene therapy with a BMP‐2‐producing murine stromal cell line induces heterotopic and orthotopic bone formation in rodents
Authors: Lieberman Jay R. , Le Lu Q. , Wu Lilly , Finerman Gerald A. M. , Berk Arnie , Witte Owen N. , Stevenson Sharon
Published: February 2005

The ability to continuously deliver osteoinductive proteins to a specific anatomic site would facilitate the treatment of fracture nonunions and other clinical problems associated with bone loss. We have developed a murine model of regional gene therapy. A bone‐marrow stromal cell line infected with an adenovirus expressing recombinant bone morphogenetic protein‐2 cDNA secreted biologically active bone morphogenetic protein‐2. These bone morphogenetic protein‐2‐producing cells were able to induce abundant heterotopic bone formation when implanted into the quadriceps muscle of severe combined immune deficient mice and also successfully healed large segmental femoral defects in nude rats. These studies demonstrate that regional gene therapy with continuous delivery of osteoinductive factors to a specific anatomic site can enhance the formation and repair of bone.
Pre‐yield and post‐yield shear behavior of the cement‐bone interface
Authors: Mann Kenneth A. , Allen Matthew J. , Ayers David C.
Published: February 2005

Aseptic loosening of cemented total hip replacements is thought to involve mechanical failure of the cement‐bone interface. However, the mechanical response of the interface, particularly the post‐yield, behavior, is not well understood. The purpose of this study was to determine the constitutive behavior of the cement‐bone interface for loading in shear using a combination of experimental and finite element methods. A total of 55 cement‐bone specimens (5 × 10 × 15‐20 mm) from the proximal femur of human cadavers were loaded to failure under displacement control with use of a custom shear test jig. Finite element models of the test specimens were made and included provision for a two‐parameter nonlinear interface model at the cement‐bone interface. The experimental tests revealed a complicated load versus displacement response with an initial linear region and a reduction in slope until the ultimate strength (2.25 ± 1.49 MPa) was reached, followed by an exponential decrease in load with increasing displacement until the entire interface debonded. Failure most often occurred at the cement‐bone interface, where the cement penetraed into the bone with bone remaining in the cement in 30 specimens and with bone remaining in the cement and cement spicules remaining in the bone in 22 specimens. The adjacent bulk bone and cement did not appear, to permanently deformed. Finite element models of the test specimens revealed that failure initiated at the base of the test specimen before the peak load had been reached. The two interface parameters, interface strength (2.71 ± 1.90 MPa) and interface‐softening exponent (4.96 ± 3.47 1/mm), could be determined directly from the experimental data and provided a good fit with the experimental structural response for a wide range of interface strengths. These results show that the cement‐bone interface does not fail abruptly when the shean strength is reached but absorbs a substantial amount of energy with post‐yield strain‐softening behavior.
Effect of static compression on proteoglycan biosynthesis by chondrocytes transplanted to articular cartilage in vitro
Authors: Chen Albert C. , Sah Robert L.
Published: February 2005

Transplantation of chondrocytes by injection or within carrier matrices has shown promise for augmenting the repair of articular cartilage defects. In vivo, transplanted chondrocytes are exposed to mechanical forces. This in vitro study examined the effect of a step application of compressive load to chondrocytes after the cells had been seeded onto a cartilage surface. Bovine chondrocytes were transplanted onto bovine cartilage disks, allowed to attach for 1 hour or 4 days, and subjected to compression through overlying cartilage disks in a confined compression configuration. Before use, the disks were lyophilized to lyse the endogenous chondrocytes and thereby allow assessment of the metabolic activity of the transplanted cells. During a 16‐hour application of compressive stress of 0‐24‐0.72 MPa, proteoglycan synthesis, assessed as [35S]sulfate incorporation into macromolecules. was inhibited by approximately 68% after the 1‐hour attachment and by approximately 45% after the 4‐day attachment. Cell retention after the application of load was assessed by use of [3H]thymidine‐tagged chondrocytes and quantitation of the displacement of radioactivity. After the 1‐hour seeding period, loading induced a dose‐dependent dislodgment of [3H]radioactivity (as much as 35%) from the tissue bilayer. In contrast, after the 4‐day seeding period, there was no detectable effect of loading on chondrocyte dislodgment with an 8–12% release of radioactivity. The inhibitory effect of a 16‐hour compression of 0.48 MPa applied after the 4‐day seeding period was studied further. This protocol did not appear to have an irreversible effect on chondrocyte metabolism; at 2 days after the release of load, proteoglycan synthesis by the loaded cells was stimulated by 41% compared with transplanted cells that were not subjected to loading. These results suggest that the application of static compressive stress to chondrocytes at a cartilage surface may affect biosynthesis by these cells and thus subsequent integrative cartilage repair. Such an effect may have implications for optimization of the tightness of the press fit of a cell‐laden cartilaginous construct into an articular defect.