bluuebunny/crossref_metadata_2025 huggingface dataset:
Maintenance of set force in anterior cruciate ligament grafts
Authors: Stewart Nathaniel J. , Engebretsen Lars , Lewis Jack L. , Lindquist Conrad , Lew William D.
Published: February 2005

This study was undertaken to determine how accurately total graft force and load‐sharing between graft segments could be set and maintained during augmented anterior cruciate ligament (ACL) reconstruction in the goat knee. Special procedures were developed to reduce the effect of tissue creep and to overcome difficulties in the setting of graft force. Five knees from goat cadavers were reconstructed using a bone‐tendon‐bone graft (PT) and a synthetic augmentation device (LAD). Prescribed levels of total graft force and load‐sharing between the autograft and LAD were set under a standardized external joint load. Immediately after fixation, the set force declined an average of 9 and 3% in the LAD and PT, respectively. After three subsequent exercise sequences, the set forces fell from their initial level by an average of 25% for the LAD and 28% for the PT. An analysis of variance did not show the loss of force with exercise to be statistically significant. We conclude from this in vitro study that our method can be used to set forces in an ACL reconstruction with reasonable maintenance of load‐sharing but that losses of approximately 30% of total graft force after exercise of the reconstructed joint are to be expected.
Load transfer with the austin moore cementless hip prosthesis
Authors: Keaveny Tony M. , Bartel Donald L.
Published: February 2005

More than 1,300 Austin Moore hemiarthroplasties have been reviewed in the literature, with no reports of fracture of the stem. Many patients with these hip implants had good function. The lack of stem fractures in patients with good function has not been explained and contrasts with stem fractures that have occurred in patients with cemented prostheses of other designs during the same time. We used three‐dimensional finite‐element analysis and free‐body diagrams to explain the lack of fractures for this device by a description of the probable load‐transfer mechanisms between the prosthesis and the bone. Results from our finite‐element analysis indicate that, with good calcar‐collar support, the stresses in the stem are small because the stem portion of the prosthesis and the bone are uncoupled and, consequently, do not share the resultant bending moment of the head and abductor forces. If the stem is coupled to the bone so that the resultant bending moment is shared, high stresses in the stem are predicted; such stresses are inconsistent with the complete absence of fractures of these prostheses. The results of the finite‐element analysis further showed that loss of calcar‐collar support with proximal fixation through the fenestrations resulted in high stresses in the stem and stress shielding of the proximal medial cortex. The uncoupled prosthesis also may be modeled with a free‐body diagram as a three‐force member loaded at the head, stem tip, and in the proximal region. With this model, it can be shown that the reaction force of the stem tip, and thus the peak bending stress in the stem, increases as calcar‐collar support is decreased. If there is no calcar‐collar support, proximal support must be provided by some combination of integration of bone in the fenestrations and wedging due to the lateral‐medial taper of the device. Stresses in the stem are largest when there is no wedging, but high stresses develop in the cancellous bone in the fenestrations. When there is wedging, stresses in the stem can be low, but stresses in the supporting cancellous bone can be high; additional proximal support through the fenestrations substantially reduces these bone stresses. If reduced stresses in the cancellous bone are indicative of a stable device, these mechanisms indicate that fractures of the Austin Moore prosthesis have not occurred in normally loaded hips because load was transferred primarily either through the collar or by wedging, with additional support at the fenestrations.
Healing of cancellous bone osteotomy in rabbits—Part I: Regulation of bone volume and the regional acceleratory phenomenon in normal bone
Authors: Bogoch E. , Gschwend N. , Rahn B. , Moran E. , Perren S.
Published: February 2005

We performed a simple, undisplaced, incomplete osteotomy of the distal medial condyle of mature New Zealand White rabbits and permitted healing without fixation for 4 weeks. During the recovery period, the rabbits received the bone label calcein in their drinking water. From ground stained and unstained sections, we determined histomorphometric parameters in five zones: osteotomy gap, juxtaosteotomy, lateral condyle, metaphysis, and diaphysis. At 4 weeks, newly formed cancellous bone had obliterated the osteotomy gap. Osteotomy also stimulated new bone formation in cancellous bone of the medial condyle around the osteotomy. At that site, we found a fivefold increase in new bone without a change in bone volume (BV). Stimulation of bone formation was not observed in cancellous bone of the lateral concyle that had not been operated on or in cortical bone of the metaphysis or diaphysis. The maintenance of BV, despite increased new bone formation in the osteotomized medial femoral condyle, was probably due to a local acceleration of bone remodeling.
Muscle contraction increases the structural capacity of the lower leg: An in vivo study in the rat
Authors: Nordsletten Lars , Ekeland Arne
Published: February 2005

A model to study the contribution of muscle contraction to the structural capacity of the rat tibia was developed. The right lower leg was tested to failure in three‐point ventral bending during electrically stimulated muscle contraction. The left lower leg was tested without stimulation, as a control. The mean ultimate bending moment for the stimulated legs was 0.603 Nm, compared with 0.492 Nm for the unstimulated legs (p ≤ 0.001). The ultimate energy absorption was 0.313 and 0.188 J in the stimulated and unstimulated legs, respectively (p ≤ 0.01). Fracture strength has been studied nearly exclusively in dissected bone stripped of all soft tissues. The present investigation suggests that studies of dissected bone are incomplete compared with the in vivo situation, as contraction of the muscles substantially increased the fracture strength of the lower leg in rats.
An experimental canine model of osteonecrosis: Characterization of the repair process
Authors: Malizos Konstantinos N. , Quarles L. Darryl , Seaber Anthony V. , Rizk Wagdy S. , Urbaniak James R.
Published: February 2005

Osteonecrosis of the femoral head was induced in dogs by a process of deep freezing, accompanied by stripping of the soft‐tissue attachments from the femoral neck and intertrochanteric area, in an effort to develop an experimental model to study treatment modalities for avascular necrosis of the hip. Immediate uniform necrosis was created in a defined area. Thereafter, spontaneous healing originated mainly from the adjacent viable bone by migration of undifferentiated mesenchymal tissue into the necrotic bone, genesis of fibrosis, and, finally, formation of new bone. Osteogenesis occurred primarily through intramembranous ossification without a preexisting template. Quantitative measurements showed a difference in the rates of ingrowth and revascularization of the necrotic area during the fibrotic and osteogenic phases of the healing. The de novo osteogenesis was slower than the migration of fibrosis. These findings indicate that, without osteotomy, we can reproducibly create necrosis of bone in a defined area of the proximal femur and induce a reparative process that incompletely heals the defect. Although it does not fully simulate the human disorder of osteonecrosis, our experimental surgical model provides a basis for further laboratory investigation into the management of avascular necrosis of the femoral head.
Sequential appearance of macromolecules in bone induction in the rat
Authors: Hulth Anders , Johnell Olov , Lindberg Lisbeth , Heinegård Dick
Published: February 2005

The appearance of noncollagenous proteins and proteoglycans during induction of cartilage and bone by implanted demineralized bone powder was studied by immunohistochemistry with polyclonal antibodies. Three bone proteins (osteopontin, sialoprotein, and a 62 kDa protein) were present in the bone powder grains before implantation. They appeared to be lost slowly from the granulation tissue but reappeared when bone formation started. The raw powder also contained a cartilage protein, biglycan (S1), chondrocalcin, cartilage oligomeric matrix protein, and the large proteoglycan aggrecan. The amounts of these molecules, however, increased significantly both within and outside the grains on cartilage formation. Cartilage matrix protein (148 kDa protein) appeared sparsely. The 58 kDa protein and fibromodulin (59 kDa protein), particularly the latter, were prevalent in fibrillar bundles. Antibodies against the laminin‐staining vessel basement membranes showed an abundant occurrence of capillaries within the matrix grains in the granulation tissue and in the precartilaginous tissue. Bone powder made noninductive by 4 M guanidine HCl did not induce cartilage and did not stain for antibodies against bone proteins or for molecules restricted to cartilage.
Evaluation of biodegradable cefazolin sodium microspheres for the prevention of infection in rabbits with experimental open tibial fractures stabilized with internal fixation
Authors: Jacob Elliot , Cierny George , Fallon Michael T. , McNeill James F. , Siderys George S.
Published: February 2005

Immediate internal fixation of severe open tibial fractures usually is contraindicated due to the high risk of infection. The objective of this study was to evaluate the efficacy of local antibiotic therapy with biodegradable poly‐(DL‐lactide‐co‐glycolide) cefazolin‐loaded microspheres for the prevention of infection in experimental open fractures stabilized with internal fixation. Rabbits with experimental tibial fractures that were contaminated with Staphylococcus aureus were treated with local application of cefazolin microspheres, an equivalent local dose of free Ancef powder, or systemic Ancef therapy. The bones then were fixed with a four‐hole plate, and the animals were observed for 8 weeks. Clinically, deep infection was present in 86% of control animals that received no antibiotics and in 60% of animals that received a 7 day course of systemic Ancef therapy. In contrast, no infections were noted among any of the surviving rabbits that received local therapy with either cefazolin microspheres or free Ancef powder. Significantly higher levels of serum cefazolin were measured at 1 h for animals treated with free Ancef powder (18.7 ± 6.1 μg/ml) than for those treated with cefazolin microspheres (0.57 ± 0.27 μg/ml). Follow‐up studies are in progress to evaluate further the potential clinical benefits of local antibiotic therapy for the management of contaminated open fractures in humans.
Dual energy x‐ray absorptiometry of implanted femora after cemented and press‐fit total hip arthroplasty in a canine model
Authors: Markel Mark D. , Gottsauner‐Wolf F. , Bogdanske John J. , Wahner Heinz W. , Chao Edmund Y. S.
Published: February 2005

The effect of a press‐fit and cemented titanium alloy endoprosthesis on the measurement of bone mineral density (BMD) of the proximal femur in a canine model with dual energy x‐ray absorptiometry (DXA) was determined. Seven regions of interest, corresponding to zones 1–7 according to Gruen et al., were measured. Eight unpaired femora were scanned with DXA before implantation (five separate scans per femur), after press‐fitting with a titanium alloy femoral component (five separate scans per femur); and after cementing with the same component (five separate scans per femur). When the titanium alloy endoprosthesis was press‐fit, the BMD of five of seven regions of the proximal femur increased significantly (range, 2.7–23.1%; mean, 11.2%), although the mean precision error of this measurement was not altered (before implantation, 1.1%; after press‐fit 1.8%). Cementing of the implant caused a variable effect on BMD, resulting in a decrease in distal regions where cortical bone was relatively thin compared with the cement mantle (regions 3, 4, and 5) and in an increase in the other regions. Cementing of the implant significantly increased the mean precision error of measurement to 7.2% (range, 1.1–12.6%).
Rib cage deformities in scoliosis: Spine morphology, rib cage stiffness, and tomography imaging
Authors: Closkey Robert F. , Schultz Albert B.
Published: February 2005

A computer‐implemented biomechanical model of a thoracolumbar spine and deformable rib cage was used to investigate the influence of spine morphology and rib cage stiffness properties on the rib cage deformities that arise from scoliosis and to study the relationship of actual rib distortions with those seen on computed tomography (CT) scans. For the purposes of this study, it was assumed that rib cage deformities result from forces imposed on the ribs by the deforming spine. When a structurally normal rib cage was allowed to follow freely the imposition of scoliotic curves on the spine, different configurations of scoliosis led to substantial differences in the resulting rib cage deformities. Rib cage lateral offset correlated well with the Cobb angle of the scoliosis but not with the apical vertebral axial rotation, whereas rib cage axial rotation correlated well with apical vertebral axial rotation but not with the Cobb angle. These model‐obtained findings mirror clinical findings that correction of the Cobb angle leads to correction of the lateral offset of the rib cage but does not correlate well with correction of the rib cage axial rotation. The stiffnesses of the ligamentous tissue connecting the sternum to the pelvis, of the costovertebral joints, and of the ribs themselves also influenced the rib deformities substantially. The influence of the sternopelvic ligamentous ties has not been recognized previously. The total rib cage volume remained essentially constant regardless of the severity of the resulting deformity, but the distribution of this volume between convex and concave sides varied somewhat. Simulated CT scans of model rib cages suggested that distortions of individual ribs are substantially exaggerated in such images.
Viscoelastic shear properties of articular cartilage and the effects of glycosidase treatments
Authors: Zhu Wenbo , Mow Van C. , Koob Thomas J. , Eyre David R.
Published: February 2005

The objectives of this study were to determine the viscoelastic shear properties of articular cartilage and to investigate the effects of the alteration of proteoglycan structure on these shear properties. Glycosidase treatments (chondroitinase ABC and Streptomyces hyaluronidase) were used to alter the proteoglycan structure and content of the tissue. The dynamic viscoelastic shear properties of control and treated tissues were measured and statistically compared. Specifically, cylindrical bovine cartilage specimens were subjected to oscillatory shear deformation of small amplitude (γo = 0.001 radian) over a physiological range of frequencies (0.01–20 Hz) and at various compressive strains (5, 9, 12, and 16%). The dynamic complex shear modulus was calculated from the measurements. The experimental results show that the solid matrix of normal articular cartilage exhibits intrinsic viscoelastic properties in shear over the range of frequencies tested. These viscoelastic shear properties were found to be dependent on compressive strains. Our data also provide significant insights into the structure‐function relationships for articular cartilage. Significant correlations were found between the material properties (the magnitude of dynamic shear modulus, the phase shift angle, and the equilibrium compressive modulus), and the biochemical compositions of the cartilage (collagen, proteoglycan, and water contents). The shear modulus was greatly reduced when the proteoglycans were degraded by either chondroitinase ABC or Streptomyces hyaluronidase. The results suggest that the ability of collagen to resist tension elastically provides the stiffness of the cartilage matrix in shear and its elastic energy storage capability. Proteoglycans enmeshed in the collagen matrix inflate the collagen network and induce a tensile prestress in the collagen fibrils. This interaction of the collagen and proteoglycan within the cartilage matrix provides the complex mechanism that allows the tissue to resist shear deformation.
Response of peripheral nerve to cyclic compression in a laboratory rat model
Authors: Szabo R. M. , Sharkey N. A.
Published: February 2005

Repetitive cyclic loading of a nerve has been proposed as a pathogenic factor in the development of occupational compression neuropathies. Little is known about the basic response of peripheral nerve to cyclic compression. We investigated the hypothesis that cyclic compression is more detrimental to nerve function than constant compression. We measured the amplitudes and velocities of distally evoked action potentials in the presence of constant or cyclic compression of the tibial nerve in rats. Seven groups were subjected to constant or cyclic compression for 6 h by a computer controlled, hydraulically activated compression chamber. Nerves were compressed with 0 (control group), 30, 60, or 90 mm Hg of constant pressure or 0–30, 20–50, or 30–60 mm Hg of cyclic compression for ∼20,000 compression cycles. Action potentials were recorded every 15 min. The effects of cyclic compression on nerve conduction were equivalent to the effects of constant compression at the average applied pressure. Cyclic loading itself does not appear to be an important pathogenic factor in the development of nerve conduction block.
Reduction of fretting corrosion of Ti‐6Al‐4V by various surface treatments
Authors: Maurer Anne M. , Brown Stanley A. , Payer Joe H. , Merritt Katharine , Kawalec Jill S.
Published: February 2005

Titanium and titanium‐6% aluminum‐4% vanadium (Ti‐6Al‐4V) are known to be biocompatible and corrosion resistant. However, there have been numerous reports of elevated tissue levels of titanium due to passive dissolution, wear, or fretting corrosion of implants. Studies were undertaken to determine whether the fretting corrosion of Ti‐6Al‐4V could be reduced by surface treatment of one or both surfaces in a fretting situation. Three different surface treatments were studied: ion implantation, physical vapor deposition nitriding, and plasma ion nitriding. The specimens used were screws fretting against the countersinks of a two‐hole plate. Fretting corrosion was assessed by weight loss, by chemical analysis of test solutions, and by scanning electron microscopy. Surface treatment of one component, the screws, resulted in reduction in the release of titanium to only 18–32% of that seen with the untreated controls. Weight loss of the untreated plates fretted against physical vapor deposition nitrided screws and plasma ion nitrided screws was reduced to 31 and 38% of the control, respectively. The weight loss of plasma nitrided screws was only 30% that of the control. Nitriding of both plates and screws resulted in a further decrease in plate weight loss and metal release. Plasma ion nitriding of both components had the most significant effect, with the weight loss and titanium release being only 11 and 2% of the control values, respectively.
Achilles tendon healing: A correlation between functional and mechanical performance in the rat
Authors: Best Thomas M. , Collins Alison , Lilly Edward G. , Seaber Anthony V. , Goldner Richard , Murrell George A. C.
Published: February 2005

The pathogenesis and treatment of rupture of the Achilles tendon remain a source of controversy. This study presents the results of a biomechanical, functional, and morphological evaluation of a group of rats that had division and repair of the Achilles tendon. A total of 46 rats were used: 18 for biomechanical testing, 18 for functional evaluation, and 10 for histology. Morphological examination revealed an early inflammatory response with loose connective tissue formation that was replaced gradually by fibroblasts and a collagenous matrix. The functional evaluation (Achilles functional index [AFI]) was made from measurements of the hind pawprints of walking rats. Division and repair of the Achilles tendon produced a significant functional impairment (mean [±SEM] AFI = −87 ± 8; p < 0.001), which gradually improved with healing time. The load to failure for the repaired tendons consistently improved with healing time, in a manner similar to the functional recovery. The average deformation (repair/control) varied considerably and was not related to healing time. The stiffness of the repaired tendons increased with healing time and was 60% of the corresponding control side by day 15. The major finding of this study was a strong correlation between the AFI and the failure load of the healing tendon‐bone constructs (250–300 g group, r = 0.97, p < 0.001; 325–375 g group, r = 0.96, p < 0.001).
Cyclic stretching of human osteoblasts affects proliferation and metabolism: A new experimental method and its application
Authors: Neidlinger‐Wilke Cornelia , Wilke Hans‐Joachim , Claes Lutz
Published: February 2005

We developed an experimental system to stimulate cell cultures by uniform and cyclic biaxial strain of the cell culture surface. The studies reported here were designed to determine the uniformity of the strain distribution, the suitability of the surface for the growth of human osteoblasts, and the effects of strain magnitude on cell proliferation and alkaline phosphatase (AP) activity. Subconfluent cell cultures were grown in rectangular silicone dishes that were stretched cyclically (1 Hz) in the long axis by an electromechanical apparatus that controlled peak stretch and cycle frequency. We applied cyclic strains (1.0, 2.4, 5.3, and 8.8% surface strains) for 15 minutes per day on 3 consecutive days. Phase contrast microscopy confirmed the transfer of dish surface strain to the cells. Stretching of the dish resulted in a homogeneous strain distribution that deviated approximately 0.05% from the applied strain. In comparison with plastic dishes, there was a 20% reduction of cell proliferation on the silicone substrate whereas morphology, AP activity, and total protein content of the cells were similar. The proliferation of human osteoblasts was increased significantly (16.4–100%) by 1% strains, although higher strain magnitudes had lesser (nonsignificant) effects or decreased the mitotic activity of the cells. AP and lactate dehydrogenase activities were not influenced significantly by cyclic strains. This study demonstrates that the cell stretching system is suitable for the investigation of the effects of well defined cyclic strains.
Aging, vertebral density, and disc degeneration alter the tensile stress‐strain characteristics of the human anterior longitudinal ligament
Authors: Neumann P. , Ekström L. A. , Keller T. S. , Perry L. , Hansson T. H.
Published: February 2005

The mechanical properties of the human lumbar anterior longitudinal ligament were investigated, and the influence of aging, disc degeneration, and vertebral bone density on these properties was determined. Tensile mechanical properties of the vertebra‐anterior longitudinal ligament‐vertebra complex were determined for 16 segments from cadavera of individuals who had been 21–79 years old (mean, 52.1 years) at the time of death. Regional strain patterns associated with three sites across the width and three sites along the length of the anterior longitudinal ligament were measured with use of a video‐based motion analysis system. In the young, normal anterior longitudinal ligament, the elastic moduli of the insertion and substance regions of the ligament were similar (approximately 500 MPa). During aging (21–79 years), the elastic modulus of the substance region increased 2‐fold, whereas the elastic modulus of the insertion decreased 3‐fold; this resulted in an approximately 5‐fold difference in elastic modulus between these regions in the older spine. The strength of the bone‐ligament complex decreased approximately 2‐fold (from 29 to 13 MPa) over this same age range. The outer portion of the anterior longitudinal ligament consistently had the highest peak tensile strains (11.8 ± 2.7%) in all of the specimens examined. Preparations with nondegenerated discs and high bone density were significantly stronger (66%) and failed in the ligament substance; in contrast, segments from older individuals with degenerated discs and lower bone density failed in the ligament insertion regions.
Electric field stimulation can increase protein synthesis in articular cartilage explants
Authors: Macginitie L. A. , Gluzband Y. A. , Grodzinsky A. J.
Published: February 2005

It has been hypothesized that the electric fields associated with the dynamic loading of cartilage may affect its growth, remodeling, and biosynthesis. While the application of exogenous fields has been shown to modulate cartilage biosynthesis, it is not known what range of field magnitudes and frequencies can alter biosynthesis and how they relate to the magnitudes and frequencies of endogenous fields. Such information is necessary to understand and identify mechanisms by which fields may act on cartilage metabolism. In this study, incorporation of 35S‐methionine was used as a marker for electric field‐induced changes in chondrocyte protein synthesis in disks of cartilage from the femoropatellar groove of 1 to 2‐week‐old calves. The cartilage was stimulated sinusoidally at 1, 10, 100, 103 Hz with current densities of 10–30 mA/cm2. Incorporation was assessed in control disks maintained in the absence of applied current at 37, 41, and 43°C. The possibility that applied currents would induce synthesis of the same stress proteins that are caused by heating or other mechanisms was assessed by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis and examination of gel fluorographs. Total radiolabel incorporation in cartilage that had been stimulated relative to incorporation in the controls increased with current density magnitudes greater than 10 mA/cm2. The increase was greatest at 100 Hz and 1 kHz, and it depended on the position on the joint surface from which the cartilage samples were taken. Together, these results suggest that endogenous electric fields could affect cartilage biosynthesis. Stress proteins were not induced at any current density when the electrodes were electrically connected but chemically isolated from the media by agarose bridges. Stress proteins were observed for disks incubated at temperatures greater than 39°C (no field) and when the stimulating platinum electrodes were in direct contact with the media bathing the cartilage disks. Therefore, the increase in incorporation of 35S‐methionine due to applied fields with the use of chemically isolated electrodes did not appear to be associated with stress response.
Kinematics of the trapeziometacarpal joint after sectioning of ligaments
Authors: Imaeda Toshihiko , Niebur Glen , An Kai‐Nan , Cooney William P.
Published: February 2005

This study was designed to examine the roles of ligaments in the maintenance of the articular kinematics of the trapeziometacarpal joint. Circumduction of the trapeziometacarpal joint was studied in 12 hands from fresh human cadavera. With use of a magnetic tracking system, changes in the motion of the base of the first metacarpal after ligament sectioning were analyzed and compared with those of the normal joint. Two sets of ligaments were sectioned: (a) the anterior oblique and ulnar collateral ligaments and (b) the first intermetacarpal ligament and the ulnar joint capsule. Sectioning of the anterior oblique and ulnar collateral ligaments resulted in a significant dorsal‐ulnar shift in the path of the base of the first metacarpal. However, sectioning of the first intermetacarpal ligament did not affect the movement pattern of the center of the base. The anterior oblique and ulnar collateral ligaments provided constraint of the trapeziometacarpal joint during circumduction of the thumb.
Cortical and trabecular bone contribute strength to the osteopenic distal radius
Authors: Spadaro J. A. , Werner F. W. , Brenner R. A. , Fortino M. D. , Fay L. A. , Edwards W. T.
Published: February 2005

Fractures of the distal radius are common, especially in postmenopausal women, and their prevalence increases with age. Knowledge of the factors that increase the risk of fracture in this metaphyseal region would have predictive and therapeutic implications. Of particular interest in this study were (a) the relative contributions of cortical and trabecular bone to the strength of the distal radius and (b) the best radiographic features to use as strength indicators. In 21 forearms from fresh cadavera (median age at the time of death, 75 years), single photon absorptiometry and quantitative computed tomography were used to determine bone mineral content (BMC), density (BMC/W), and cross‐sectional properties of the radius at distal and midshaft sites. Mechanical testing of the forearms then was used to determine the ultimate force and energy to cause the type of fracture that might be caused by a fall on the outstretched hand. Twelve of the 17 tested specimens sustained a fracture of the distal radius, and five sustained a fracture of the scaphoid. In the group of fractures of the distal radius, we found the cross‐sectional area and moment of inertia of the cortical shell at the metaphyseal site to be better correlates of strength than the trabecular area and trabecular moment. In contrast, strength correlated much better with trabecular density than with cortical density. Overall, the best correlates of strength were the BMC and BMC/W at either the distal or proximal site. On balance, these results suggest that the thin cortical shell contributes substantially more to the mechanical strength of the distal radius than has been commonly appreciated.
Nonuniform distribution of collagen density in human knee ligaments
Authors: Mommersteeg T. J. A. , Blankevoort L. , Kooloos R. J. G. M. , Hendriks J. C. M. , Kauer J. M. G. , Huiskes R.
Published: February 2005

It is generally recognized that the mechanical properties of soft connective tissues are affected by their structural components. We documented collagen density distributions in human knee ligaments to quantify differences in density within and between these ligaments. In order to explain the variations in mechanical properties within and between different knee ligaments as described in the literature, the distributions of collagen density were correlated with these biomechanical findings. Human knee ligaments were shown to be nonhomogeneous structures with regard to collagen density. The anterior bundles of all ligaments contained significantly more collagen mass per unit of volume than the posterior bundles did. The percentage differences between the anterior and posterior bundles, in relation to the posterior bundles, were about 25% for the anterior cruciate ligament (ACL) and the collateral ligaments and about 10% for the posterior cruciate ligament (PCL). Along the cruciate ligaments, the central segments had higher collagen densities than did segments adjacent to the ligament insertions (ACL 9%, PCL 24%). The collagen density in the ACL was significantly lower than that in the other ligaments. These variations within and between the ligaments correlate well with the variations in mechanical properties described in the literature; however, other structural differences have to be taken into account to fully explain the variations in mechanical properties from the structural components.
Blood flow in the human achilles tendon assessed by laser doppler flowmetry
Authors: Åstroöm Mats , Westlin Nils
Published: February 2005

This study evaluated microvascular perfusion in the human Achilles tendon by laser Doppler flowmetry (LDF) at rest, during vascular occlusion, and during passive stretch and isometric contraction of the triceps surae. In 40 healthy volunteers, an intratendinous needle probe was introduced 5 mm above the distal insertion, at the midportion, and at the musculotendinous junction of both legs. Values were obtained at rest and during temporary vascular occlusion. Twenty‐eight of the subjects also were assessed during physical provocation by passive stretch and isometric contraction of the triceps surae. Blood flow was significantly lower near the calcaneal insertion but otherwise was distributed evenly in the tendon. The output signal showed a pulsatile variation synchronous with heart activity, and temporary vascular occlusion always caused a pronounced reduction in LDF values. Passive stretch and isometric contraction induced a progressive decline in LDF values as tension increased. Hyperemia often appeared after contraction. Tendon blood flow was higher in women and decreased with increasing age.
Chondrocyte cells respond mechanically to compressive loads
Authors: Freeman P. M. , Natarajan R. N. , Kimura J. H. , Andriacchi T. P.
Published: February 2005

Many studies have illustrated the effect of mechanical loading on articular cartilage and the corresponding changes in chondrocyte metabolism, yet the mechanism through which the cells respond to loading still is unclear. The purpose of this study was to evaluate the change in shape of chondrocytes under a statically applied uniaxial compressive load. Isolated chondrocytes from rat chondrosarcoma were embedded in 2% agarose gel. Strains of 5, 10, and 15% were applied, and images of the cell were recorded from initial loading to equilibrium (15 minutes). A finite‐element model was used to model the experimental setup and to estimate the mechanical properties of the chondrocyte at equilibrium. The transient behavior of the composite in the experiment was analyzed with use of a standard linear viscoelastic model. We found that all cells decreased in cross‐sectional area under each of the applied compressive strains. In the finite‐element model, the elasticity of the chondrocyte was similar to that of the surrounding agarose gel (4.0 kPa) and had a Poisson's ratio of 0.4. Viscoelastic analysis showed that the chondrocytes contributed a significant viscoelastic component to the behavior of the composite in comparison with the agarose gel alone. If a decrease in cell volume proportional to the decrease in cross‐sectional area is assumed, the decrease observed was greater than would be predicted by a passive cellular response due to an equivalent osmotic pressure. This indicates that the chondrocyte may be altering its intracellular composition by cellular processes in response to mechanical loading.
Effects of lathyritic drugs and lathyritic demineralized bone matrix on induced and sustained osteogenesis
Authors: Di Cesare Paul E. , Nimni Marcel E. , Yazdi Mohamadreza , Cheung David T.
Published: February 2005

Demineralized bone matrix was implanted in normal and lathyritic rats. At 2 weeks, the bone that formed in the lathyritic animals had an elevated alkaline phosphatase activity and a reduced calcium content compared with the controls. Four weeks after implantation, these biochemical parameters were reversed, with a decrease in alkaline phosphatase activity and an increase in calcium content to control levels. the histology of the recovered implants revealed new bone formation. Lathyritic demineralized bone matrix was prepared from bones of rats fed β‐aminopropionitrile for 2 weeks (2‐week BAPN‐DBM) or 4 weeks (4‐week BAPN‐DBN), and was implanted in normal rats. Two weeks after implantation, both preparations of lathyritic demineralized bone matrix demonstrated early bone formation, although alkaline phosphatase activity and calcium content were reduced. By 4 weeks after implantation, no biochemical or histological evidence of bone formation remained at the site of the 4‐week BAPN‐DBM implants; continued but reduced bone formation was observed at the site of the 2‐week BAPN‐DBM implants. Reconstitution of inactivated normal demineralized bone matrix with the guanidine‐soluble extracts restored the osteoinductive capacity. However, reconsistution of inactivated lathyritic demineralized bone matrix (4‐week BAPN‐DBM) failed to restore the osteoinductive capacity. These results indicate that the degree of crosslinking of the collagen matrix that acts as a carrier for osteoinductive proteins plays a key role in inducing and sustaining osteogenesis.
Mechanical and biochemical changes in the superficial zone of articular cartilage in canine experimental osteoarthritis
Authors: Guilak Farshid , Ratcliffe Anthony , Lane Nancy , Rosenwasser Melvin P. , Mow Van C.
Published: February 2005

The changes in the tensile mechanical properties and biochemical composition of the superficial zone of articular cartilage were examined in a canine model of early osteoarthritis generated by transection of the anterior cruciate ligament. Sixteen weeks following ligament transection, the tensile stiffness of the articular cartilage was decreased by 44% and the ion‐induced stress relaxation of the tissue was increased by 57% compared with the contralateral control. Biochemical analyses indicated that the water content of the experimental tissue was increased by 13%, which was reflected as an apparent 37% decrease in the proteoglycan content and a 36% decrease in the collagen content (expressed per wet weight). The hydroxypyridinium crosslink density was decreased in the experimental tissue by 11%. A significant negative correlation was found between the ion‐induced stress relaxation and the hydroxypyridinium crosslink density in both control tissue (R = −0.56) and experimental tissue (R = −0.70). No correlation was noted between the tensile stiffness and the biochemical composition of the tissue. These results suggest that, in the superficial zone of articular cartilage, the structure of the tissue may play a more important role than the composition in the determination of its mechanical properties. A major event observed in the model of early osteoarthritis appears to be the disruption and remodeling of the collagen network in the superficial zone of the articular cartilage.
Chondrocyte‐fibrin matrix transplants for resurfacing extensive articular cartilage defects
Authors: Hendrickson Dean A. , Nixon Alan J. , Grande Daniel A. , Todhunter Rory J. , Minor Ronald M. , Erb Hollis , Lust George
Published: February 2005

Cartilage resurfacing by chondrocyte implantation, with fibrin used as a vehicle, was examined in large (12 mm) full‐thickness articular cartilage defects in horses. Articular chondrocytes, isolated from a 9‐day‐old foal, were mixed with fibrinogen and injected with thrombin, in a 1:1 mixture, into 12 mm circular defects on the lateral trochlea of the distal femur of eight normal horses. The contralateral femoropatellar (knee) joint served as a control in which the defect was left empty. Synovial fluid from the femoropatellar joints was sampled on days 0, 4, 7, 30, 120, and 240 postoperatively. Groups of four horses were killed at 4 or 8 months postoperatively, and the repair tissue was evaluated by gross and histologic examination with use of hematoxylin and eosin and safranin O staining and by autoradiography. Biochemical analyses included quantitation of proteoglycan, total collagen, and type‐II collagen in the repair tissue. Grossly, grafted defects had improved filling of the cartilage lesions: histologically, these areas consisted of differentiated chondrocytes in the deep and middle zones. The cellular arrangement in these zones resembled that of hyaline cartilage. The control defects contained poorly attached fibrous tissue throughout. Grafted tissue at 8 months had increased proteoglycan synthesis evident by both safranin O staining and autoradiography. Glycosaminoglycan quantitation by dye‐binding assay confirmed a significantly elevated glycosaminoglycan content in grafted defects (58.8 μg/mg of dry weight) compared with control defects (27.4 μg/mg; p < 0.05). Similarly, the levels of chondroitin sulfate/dermatan sulfate was significantly elevated in the grafted defects, and this was the predominant glycosaminoglycan epitope present. There was a statistically significant (p < 0.05) increase in type‐II collagen in the grafted tissue at 8 months (61.2% grafted; 25.1% control). This resurfacing attempt with use of allograft chondrocytes, secured in large full‐thickness articular defects with polymerized fibrin, resulted in an improved cartilage surface in comparison with the control defects, a significantly greater aggrecan level, and a significantly higher proportion of type‐II collagen.
Infection at the site of implanted materials with and without preadhered bacteria
Authors: Chang C. C. , Merritt K.
Published: February 2005

A study was undertaken to examine the role of bacterial adherence in the development of infection at the site of an implant. The amount of in vitro adherence of Staphylococcus epidermidis was greatest for stainless steel, followed by polymethylmethacrylate and commercially pure titanium, and was least for polymethylmethacrylate with gentamicin. These materials then were preincubated with S. epidermidis and implanted. The number of organisms that were isolated and the rate of infection followed the same pattern as that in the in vitro studies. Materials that were not preincubated with bacteria also were implanted and bacteria were injected into the site. The number of organisms isolated from the site and the rate of infection were lower than those for the preincubated materials, but the trend was the same as in both the in vitro and the in vivo studies. The rates of infection and colonization correlated with the propensity for the organisms to adhere to a given material. Materials colonized with S. epidermidis at the time of implantation caused a high rate of infection. The ability of organisms to adhere to a material in vitro is correlated with their propensity to cause biomaterial‐based infection.
Comparison of the inflammatory response to particulate polymethylmethacrylate debris with and without barium sulfate
Authors: Lazarus M. D. , Cuckler J. M. , Schumacher H. R. , Ducheyne P. , Baker D. G.
Published: February 2005

Particulate polymethylmethacrylate debris has been implicated in the inflammatory response observed surrounding loosened cemented implants. The rat subcutaneous pouch model and the Howie implant model (used to study bone resorption) were used to quantify the response to mechanically produced endotoxin‐free polymethylmethacrylate debris with and without 10% (wt/vol) BaSO4. In the rat subcutaneous pouch model, the inflammatory response to polymethylmethacrylate particles containing BaSO4 was greater than the response to plain polymethylmethacrylate particles of similar size. Increased inflammation was measured by leukocyte counts and levels of prostaglandin E2, tumor necrosis factor, and neutral metalloprotease. In addition, particulate polymethylmethacrylate with BaSO4 caused significantly greater bone resorption in the Howie model than did particulate plain polymethylmethacrylate. In in vitro studies, particulate polymethylmethacrylate with BaSO4 stimulated more prostaglandin E2, neutral metalloprotease, and tumor necrosis factor from human monocytes in culture and stimulated greater proliferation of synovial cells than did particulate plain polymethylmethacrylate. The presence of BaSO4 appears to significantly intensify the inflammatory response to polymethylmethacrylate debris.
Effects of thapsigargin, an intracellular calcium‐mobilizing agent, on synthesis and secretion of cartilage collagen and proteoglycan
Authors: Clark Charles C. , Iannotti Joseph P. , Misra Sanjay , Richards Charlotte F.
Published: February 2005

The calcium‐mobilizing agents thapsigargin and 2.5‐di‐(tert‐butyl)‐1,4‐benzo‐hydroquinone were shown to markedly elevate the intracellular calcium concentration of chick embryo chondrocytes in a dose‐dependent manner. Under these conditions, the metabolism of macromolecules was variably affected. The synthesis and secretion of protein in general, and of collagen in particular, were significantly inhibited; in contrast, proteoglycan synthesis (but not glycosaminoglycan synthesis) was inhibited, whereas secretion was unaffected. Flunarizine, which prevented the thapsigargin‐induced intracellular calcium elevation, and EGTA, which caused only a transient thapsigargin‐induced intracellulr calcium elevation, did not reverse these alterations. It was concluded, therefore, that the observed effects of thapsigargin and 2,5‐di‐(tert‐butyl)‐1,4‐benzohydroquinone on chondrocyte macromolecule metabolism were not related to the ability of these drugs to increase the cytosolic free calcium concentration but may have been due to the specific depletion of the calcium sequestered in the endoplasmic reticulum. The differential effect of these drugs on protein and proteoglycan secretion suggests that the intracellular trafficking of these two classes of macromolecules may be controlled independently.
Response of three murine macrophage populations to particulate debris: Bone resorption in organ cultures
Authors: Glant Tibor T. , Jacobs Joshua J.
Published: February 2005

Particulate wear debris from bone cement or prosthetic components can stimulate macrophages to cause bone resorption. We compared the effect of particle composition (titanium and polymethylmethacrylate as inherent components of prosthetic materials or bone cement and polystyrene as a reference material) on the secretion of interleukin‐1 and prostaglandin E2 by periotoneal macrophages and monocyte/macrophage cell lines (P388D1 and IC‐21) and on the bone‐resorbing activity of conditioned medium harvested from these particle‐challenged macrophages. Titanium particles (1–3 μm) in peritoneal macrophage cultures exhibited significantly enhanced bone‐resorbing activity measured as 45Ca release, whereas polymethylmethacrylate and polystyrene exhibited this effect to a greater extent in the P388D1 and IC‐21 monocyte/macrophage cultures. Although exogenous prostaglandin E2 and recombinant human interleukin‐1 could significantly increase the 45Ca release and indomethacin significantly reduced both the spontaneous calcium efflux and active 45Ca release from calvarial bones labeled in vivo, the levels of interleukin‐1 and prostaglandin E2, alone or together, did not always correlate with the bone‐resorbing activity of conditioned media. Thus, the actual levels of potent bone‐resorbing agents (prostaglandin E2 and interleukin‐1) measured in conditioned tissue culture media did not necessarily reflect the bone‐resorbing capability. An important result of this study is that different macrophage populations may respond differently to the same microenvironmental signal, which in our investigation was particulate wear debris of differing composition and size.
Hisotological and radiographic determination of the age of physeal closure of the distal femur, proximal tibia, and proximal fibula of the New Zealand white rabbit
Authors: Kaweblum Moises , Aguilar Maria Del Carmen , Blancas Eduardo , Kaweblum Jaime , Lehman Wallace B. , Grant Alfred D. , Strongwater Allan M.
Published: February 2005

A longitudinal study was performed in a series of 124 New Zealand White rabbits to determine the radiographic versus the histologic age of closure of the growth plates of the distal femur, proximal tibia, and proximal fibula. Periodic assessment was made by standard radiographs and histological studies. Histologically, growth plates in the distal femur closed at 19–24 weeks; growth plates in the proximal tibia, at 25–32 weeks; and growth plates in the proximal fibula, at 26–32 weeks. Radiographically, evidence of closure of growth plates in the distal femur occurred at 20–23 weeks; in the proximal tibia, at 22–27 weeks; and in the proximal fibula, at 23–31 weeks. A discrepancy in age between radiographic and histologic closure of the growth plate occurred in 3.6% of the femora, 10.9% of the tibias, and 16% of the fibulas.