bluuebunny/crossref_metadata_2025 huggingface dataset:
Contact finite element stress analysis of the hip joint
Authors: Rapperport D. J. , Carter D. R. , Schurman D. J.
Published: February 2005

Two‐dimensional finite element analyses were conducted of the normal hip using contact elements at the joint surface. The models studied were constructed for a slice through the pubis, acetabulum, and ilium. In the analyses the proximal femur was pressed into the acetabulum and intraarticular pressures and principal stresses in the joint region were determined for different load magnitudes and directions and various boundary conditions. Three sets of boundary conditions were examined: (a) deformable pubic symphysis, (b) rigid pubic symphysis, and (c) simulations of experimental studies. In the deformable model the pubic symphysis was free to displace in the sagittal plane and rotate. In the rigid model the pubic symphysis was rigidly fixed. Superoposterior loading resulted in high‐contact pressures at the acetabular dome for all sets of boundary conditions. For the deformable model subject to a more medially directed load the acetabulum closed in such a manner as to squeeze the head of the femur creating high‐contact pressures superiorly and inferiorly. This resulted in significant compressive stresses in the superior dome cancellous bone and inferior cancellous bone. The cumulative effect of this squeezing action with normal biological remodeling may cause elongation of the femoral head resulting in asphericity and incongruity of the unloaded hip joint articular surfaces. Rigidly fixing the pubic symphysis stiffened the model and resulted in principal stress patterns that did not reflect trabecular density or orientations as well as those of the deformable pubic symphysis model. Finite element simulations of previous experimental studies modeled the close proximity of the fixation to the fixation to the excised acetablulum. These boundary conditions prevented the squeezing caused by pelvis deformations. The resulting contact areas, pressure distributions, and bone stresses were very different from those of more anatomic, deformable pubic symphysis model. These findings demonstrate the sensitivity of hip contact pressures and stresses to imposed boundary conditions and indicate that care should be taken to simulate anatomic conditions in experimental and theoretical studies.
Trabecular bone strength patterns at the proximal tibial epiphysis
Authors: Hvid Ivan , Hansen Stig Lau
Published: February 2005

The longitudinal compressive strength of trabecular bone from the human proximal tibial epiphysis was investigated in 12 autopsy specimens using multiple penetration tests with a small diameter indentor. Strength profiles were visualized by three‐dimensional computerized reconstruction as a function of location on the resection surfaces. There were large variations of the maximal values between individuals, but the patterns obtained were remarkably uniform. The medial condyle showed the highest peak value in all but one knee with a mean medial‐to‐lateral peak value‐ratio of 1.7. At the medial condyle the high strength area was relatively large with peak values being obtained centrally and anteriorly; the lateral condyle showed a more restricted, posteriorly localized area a high strength. Beneath the menisci, bone strength gradually decreased toward the margins of the condyles; likewise, bone strength decreased to reach very low values at the intercondylar region. There was a significant reduction of bone strength with the distance from the subchondral resection surface. This reduction was most pronounced at the high strength areas.
Geometric, elastic, and structural properties of maturing rat femora
Authors: Keller T. S. , Spengler D. M. , Carter D. R.
Published: February 2005

Geometric, elastic, and structural properties of growing rat femora were determined from bending and torsion tests followed by bone sectioning and measurement of areal properties. Rosette strain gages bonded to the bone surface measured the strain during testing. A computer generated elliptical cross‐sectional representation of the cross section geometry was used for calculation of material and structural properties. All structural and material properties increased with increasing age, exhibiting age‐related changes that were best represented by an allometric or “heterauxic” growth pattern (y = axb) up to maturity. The femoral axial, flexural, and torsional rigidity increased 5.7, 10.1, and 14.8 fold, respectively, during maturation from 21 to 119 days of age. The increase in whole bone rigidity during maturation was caused primarily by changes in geometry. The bone tissue tensile longitudinal elastic modulus and shear modulus approximately doubled, and the shear strength increased approximately fourfold over this same period. Following maturity, a much slower increase in bending and torsional properties was noted. The results suggest that bone structural properties are regulated by changes in both geometric and material properties.
Synovial fluid nutrient delivery in the diathrial joint: An analysis of rabbit knee ligaments
Authors: Amiel David , Abel Mark F. , Kleiner Jeffrey B. , Lieber Richard L. , Akeson Wayne H.
Published: February 2005

The role of synovial fluid in providing nutrition to rabbit knee ligaments and menisci was evaluated by intraarticular injection of a labeled collagen precursor, tritiated proline. Incorporation of this substrate as tritiated hydroxyproline was measured in collateral and cruciate ligaments and menisci. The injectate volume (0.35 ml) did not appreciably change the overall joint pressure as measured by a wick catheter; therefore, no alteration of synovial membrane diffusion characteristics resulted. The concentration of the injected proline (0.52 mg%) was well below that normally present in serum (2.65 mg%). Therefore, incorporation of this substrate was not driven by a concentration gradient and represented normal uptake of synovial fluid and physiological incorporation of label as measured by the presence of tritiated hydroxyproline. Autoradiography was performed on all ligaments and menisci, and demonstrated concentration of the isotope and its metabolite (tritiated proline and tritiated hydroxyproline, respectively) in and around fibroblasts. This study indicates that rabbit knee ligaments and menisci can derive nutrition from a synovial fluid source.
The in vivo kinematics of the rheumatoid wrist
Authors: Evans James S. , Blair William F. , Andrews James G. , Crowninshield Roy D.
Published: February 2005

The objectives of this study were (a) to describe the three‐dimensional in vivo kinematic behavior of wrists affected by rheumatoid arthritis, (b) to correlate kinematic parameters and two radiographic indices of carpal disease, and (c) to describe the in vivo kinematic behavior of the Swanson Silastic wrist implant. Fifteen normal wrists, 17 rheumatoid wrists, and 7 wrists with Silastic wrist implants were tested using a three‐dimensional sonic digitizing system. The motion of the hand segment relative to the forearm segment, corresponding to the positions exhibited during flexion‐extension motion (FEM) and radial‐ulnar deviation (RUD), was described using the equivalent screw displacement (ESD) concept. The mean magnitudes of ESD rotation for both FEM and RUD were statistically different (p < 0.05) among the normal, rheumatoid, and implant groups. The remaining ESD parameters (i.e., mean values for the translation, the direction angles of the ESD axis, and the intercepts of this axis with the planes of motion), the minimum separation between the FEM and RUD axes, and the coordinates of the midpoint of this separation were not statistically different (p > 0.05) among the normal, rheumatoid, and implant groups. The two radiographic indices (carpal collapse and carpal translation) did not correlate with the magnitude of rotation or with any other ESD parameter.
Vascular reorganization and return of rigidity in fracture healing
Authors: Chidgey L. , Chakkalakal D. , Blotcky A. , Connolly J. F.
Published: February 2005

The present study addresses the relationship between vascular reorganization and the biomechanical changes occurring during canine long bone fracture healing. A middiaphyseal osteotomy of the radius was performed, and angiographic studies were carried out using India ink injections from 2 to 12 weeks postosteotomy. The radii were harvested, subjected to nondestructive four‐point bend testing on an Instron, and then sectioned and cleared according to the Spaltholtz technique. The observed microangiographic patterns were correlated with the calculated rigidity values. Quantitative bone blood flow measurements around the osteotomy were performed on a different group of animals, using the radiotracer microsphere technique, at 3, 6, and 9 weeks postosteotomy to correlate with our qualitative microangiographic results. We demonstrated a direct and predictable relationship between the phase of vascular reorganization and the rigidity. This correlation was present even in our delayed union specimens.
The in vitro effect of gold complexes on bone resorption
Authors: Katz J. M. , Gray D. H.
Published: February 2005

Mouse calvaria were maintained in organ culture without serum additives. The effects of three gold complexes—aurothioglucose, aurothiomalate, and auranofin—on active bone resorption (45Ca release) and hydroxyproline synthesis were determined. The influence of these compounds on DNA and protein synthesis and lysosomal enzyme release from calvaria was also assessed. All gold complexes reduced bone resorption to some extent, with auranofin being the most potent within a narrow concentration range (10−6 M). This concentration of auranofin also significantly inhibited collagen synthesis, although DNA and protein synthesis were unaffected. None of the compounds tested appeared to mediate their action via significant inhibition of lysosmal enzyme release.
The bone growth chamber for quantification of electrically induces osteogenesis
Authors: Buch F. , Albrektsson T. , Herbst E.
Published: February 2005

A dividable titanium implant was inserted in the tibial metaphysis of rabbits, which permitted a numerical evaluation of ingrowing bone. The implant on the test side was used as cathode and was connected to a subcutaneously located stimulator delivering constant current of either 5 μA, 20 μA, or 50 μA. A corresponding control implant was inserted in the other tibia of the same animal and treated likewise, but was not connected to the stimulator. Distally to each implant, a platinum‐iridium screw was inserted into the cortex and connected on the test side to the stimulator to serve as the anode. The results showed a 2.4‐fold increase in bone formation with 5 μA. In the 20‐μA group, there was 2.6‐fold more bone in the test chambers. Direct current (DC) stimulation with 50 μA caused a clear decrease of bone volume, with an average of 48% less bone in the test implants. The results indicate that 5 and 20 μA direct current enhance bone ingrowth into a titanium implant that is used as a cathode. The osteogenesis seemed to be more pronounced in the case where the chamber was used as a cathode compared to earlier experiments in which the cathode was placed at a distance of 5 mm from the implant.
Cervical spine biomechanics: A review of the literature
Authors: Huelke Donald F. , Nusholtz Guy S.
Published: February 2005

This article reviews the many clinical and laboratory investigative research reports on the frequency, causes, and biomechanics of human cervical spine impact injuries and tolerances. Neck injury mechanisms have been hypothesized from clinically observed cervical spine injuries without laboratory verification. However, many of the laboratory experiments used static loading techniques of cervical spine segments. Only recently have dynamic impact studies been conducted. Results indicate that crown‐of‐head impacts can routinely produce compression of the neck with extension or flexion motion. However, the two‐dimensional (midsagittal) movement of the head bowing into the chest does not routinely produce flexion/compression type damage to the cervical spine. Flexion/compression damage to the cervical spine can be produced by prepositioning the subject so that upon impact, a three‐dimensional motion of the head and neck occurs. Future laboratory research is needed to determine the forces and impact directions required to produce the various known fracture types and dislocations for a clear, accurate description of the cervical spine impact dynamics.
Bone ingrowth into weight‐bearing porous fiber titanium implants. Mechanical and biochemical correlations
Authors: Barth Elin , Ronningen Helge , Solheim Ludvig Fjeld , Saethren Birgitte
Published: February 2005

Bone ingrowth into weight‐bearing porous fiber Ti‐6AI‐4V implants in rat tibias was assessed for the amount, composition, and mineralization rate 3, 12, and 26 weeks after implantation. The data were compared with the ipsiand contralateral metaphyseal controls and related to the ultimate bending stresses of the distal bone/implant interfaces. From the 3rd to the 12th week there was rapid bone ingrowth and also marked decline in mineralization rate of the ingrowing bone. After 12 weeks the implants were macroscopically pervaded by bone. The ultimate bending stresses increased from the 3rd to the 12th week and reached 45% of that of controls after 26 weeks. There was a linear proportionality between the amount of bone ingrowth and interfacial strength but a curvilinear relationship between bone maturity in terms of calcium/hydroxyproline and calcium/phosphorous ratios and interfacial strength. Stepwise multiple regression analysis showed that the interfacial strength depends on the amount and the maturity of the ingrown bone. Compared with the calcium/hydroxyproline ratio, the calcium/phosphorous ratio was an unreliable predictor of interfacial strength.
Incorporation of purified plasma fibronectin into explants of articular cartilage from disease‐free and osteoarthritic canine joints
Authors: Burton‐Wurster Nancy , Lust George
Published: February 2005

The purpose of this study was to determine if articular cartilage was able to accumulate fibronectin, a large molecule of 440,000 daltons, from the external medium, and if so, to compare the extent of accumulation by normal and osteoarthritic cartilage and to localize the sites of fibronectin accumulation within the articular cartilage. The uptake of canine serum albumin, another protein present in plasma and synovial fluid with a lower molecular weight (67,000 daltons) and a lower pI, was compared. Purified plasma fibronectin and canine albumin were labelled with 125I or N‐hydroxysuccinimidobiotin by standard procedures and incubated with articular cartilage explants. The 125I‐fibronectin that had bound to cartilage components was extracted with 4 M urea, and both extract and cartilage residues were counted. Cartilage accumulated fibronectin to a greater extent than albumin. For normal cartilage, a level of saturation appeared to be reached at an external concentration for fibronectin of about 150 μg/ml. Degenerated cartilage accumulated about 10‐fold more fibronectin than normal cartilage. Biotinylated fibronectin was localized within frozen sections of articular cartilage by probing with peroxidase‐linked avidin. Fibronectin accumulation in normal cartilage was restricted to the articular surface and the cut edge. In degenerated cartilage, penetration of fibronectin was more extensive but proceeded only from the articular surface. Staining of adjacent sections with peroxidase‐linked antifibronectin antibody confirmed previous observations that endogenous fibronectin is present throughout the cartilage matrix. The possibility that synovial fluid fibronectin could be a source of cartilage fibronectin, especially in degenerated cartilage, was discussed.
Effect of flexor sheath integrity on tendon gliding: A biomechanical and histologic study
Authors: Peterson William W. , Manske Paul R. , Kain Christopher C. , Lesker Peggy A.
Published: February 2005

The effect on tendon gliding of flexor sheath excision versus incision/closure following primary flexor tendon repair was examined biomechanically and histologically in forty‐one chickens. There was no significant difference in either the tendon excursion required to fully flex the digit or in the work of flexion (the integration of the forces that resist tendon gliding during excursion) between the sheath excised and sheath closed groups. The results were unaffected by postoperative immobilization or intermittent passive motion. Histologically, it was noted that at 3 weeks the healing tendon was surrounded by a layer of granulation tissue that was nearly indentical in both the sheath excised and the sheath closed digits. Of note was the finding that a synovial lining could not be identified in those digits that had previously undergone sheath closure. However, at 6 weeks postoperatively, a new gliding surface could be identified surrounding the tendon in both the sheath excised and the sheath closed digits. This study indicates that closure of the flexor sheath after primary tendon repair does not improve tendon gliding as measured biomechanically. Despite its repair, the flexor sheath does not maintain its synovial characteristics as demonstrated histologically, and a new sheath must subsequently be formed.
Origin of replacement cells for the anterior cruciate ligament autograft
Authors: Kleiner Jeffrey B. , Amiel David , Roux Richard D. , Akeson Wayne H.
Published: February 2005

A rabbit model for anterior cruciate ligament (ACL) reconstruction using autogenous avascular patellar tendon (PT) was utilized to study the early events of graft incorporation. Histological observations demonstrated that autografts were centrally acellular with a peripheral rim of cells at 2 weeks, a central focal proliferation of cells at 3 weeks, and a cellular homogeneous distribution by 4‐weeks postoperation. Graft necrosis followed by cellular proliferation suggested that a different population of cells other than the native PT fibroblasts may be inhabiting the graft. The extrinsic contribution of cells was studied by selective destruction of native PT cells with liquid nitrogen immersion prior to reconstruction of the ACL. The intrinsic contribution of cells was evaluated by sequestration of the PT graft in a semipermeable membrane before it was used to reconstruct the ACL. Histological analysis of tissue that was liquid N2 treated, used as an autograft, and then harvested 3‐weeks post‐operation revealed fibroblastic incorporation of the graft. In contrast, no cells were observed in semipermeable membrane sequestered autografts. These data suggest that autogenous ACL autografts of PT origin are repopulated by cells of external origin. In vitro control studies that were carried out in parallel demonstrated that PT fibroblasts could survive in tissue culture, but not in the synovial environment of the ACL. This suggests that fibroblasts from different sources have different, tissue‐specific nutritional requirements.
Biochemical, histological, and biomechanical analyses of canine tendon
Authors: Okuda Y. , Gorski J. P. , An K.‐N. , Amadio P. C.
Published: February 2005

To define the matrix composition and architecture of canine flexor tendon, and to correlate tissue structure with applied mechanical loading, five anatomical regions of flexor tendon were studied. Histologically, two prominent fibrocartilaginous areas were observed on concave aspects of the tendon. The location of the major fibrocartilaginous area at the metacarpophalangeal joint correlated well with the region predicted by biomechanical modeling to be under greatest compressive loads during standing and claw movement. Comparative biochemical analysis showed an elevated water content, a fivefold higher hexuronic acid content, and a larger hydroxylysine/hydroxyproline ratio in this region relative to that for more tendinous areas. The major glycosaminoglycan component of fibrocartilaginous areas was chondroitin sulfate, whereas in other areas dermatan sulfate and hyaluronic acid dominated. Cell density and DNA analyses indicated a slightly higher cellularity for fibrocartilaginous areas and the region of vinculum insertion. These data document the existence of discrete areas of specialization within the flexor tendon that appear to be an adaptation to nutritional and mechanical factors.
Fracture failure mechanisms in patients with osteogenesis imperfecta
Authors: Alman Benjamin , Frasca Peter
Published: February 2005

This investigation examines the failure mechanism of bone from patients with osteogenesis imperfecta (OI). Mechanical testing and ultrastructural analysis of surgically obtained bone specimens, from patients with OI and from approximately age matched normal controls, were performed. Small rectangular bone samples (1.0 mm × 1.2 mm × 15mm) with a prismatic cross section were put under three‐point bending to determine the work to fracture. Furthermore, the fracture surface was observed with scanning electron microscopy (SEM). The SEM observation of partially dissected lamellae was also performed to determine the collagen organization of the bone. The OI bone has a consistently lower work to fracture and reduced collagen organization than the normal controls. The fracture surface of the OI bone is rough and exhibits a “pull‐out” type of morpholgy, as opposed to the smoother fracture surface of the controls. This study shows that a relatively simple mechanical test utilizing a small amount of bone can differentiate between a diseased state (OI) and a normal state of bone.
Evaluation of double‐exposure holographic interferometry for biomechanical measurements in vitro
Authors: Manley M. T. , Ovryn B. , Stern L. S.
Published: February 2005

Double‐exposure holographic interferometry is a nondestructive testing technique for measuring displacement and strain in a test object. A standard hologram contains three‐dimensional information about an object. However, the holographic interferogram has additional information, as a series of interferece bands overlaid on the three‐dimensional image of the object contains information about object deformation. Interferograms were produced for intact cadaveric femora and cadaveric femora with implanted titanium alloy and cobalt‐chromium alloy femoral components. A force was applied to the femoral head to simulate single leg stance, and changes in specimen deformation were observed as additional incremental loads were applied. We have observed that the femur behaves as a bending beam and that the holographic technique allows the position of maximal deflection to be identified and the magnitude of femoral displacement from the load axis to be determined at any point within the field of view. The effects of the modulus of the implanted stem on the bending characteristics of the composite structure were clearly seen in the interferograms. This communication presents a photographic analysis of the double exposure interferograms recorded, as well as a critique of the technique for biomechanical measurements in vitro.
Differences in matrix vesicle concentration among growth plate zones
Authors: Buckwalter Joseph A. , Mower Donald , Schaeffer Janice
Published: February 2005

We studied the proximal tibial growth plates of 15‐day‐old mice to determine if matrix vesicle concentration varies among growth plate zones or between the pericellular and territorial matrix compartment and the interterritorial matrix compartment. Growth plates were examined by electron microscopy and divided into five zones: reserve zone (RZ), upper proliferative zone (UPZ), lower proliferative zone (LPZ), upper hypertrophic zone (UHZ), and lower hypertrophic zone (LHZ) which included the calcifying zone. We measured the diameter and volume fraction of matrix vesicles and calculated their numerical density and volume per cell and number per cell in the pericellular and territorial matrix and in the interterritorial matrix of each zone. In the pericellular and territorial matrix compartment, the matrix vesicle concentration progressively decreased from the RZ to the LHZ. Changes in matrix vesicle concentration in the interterritorial matrix followed a different pattern. Between the RZ and the UPZ, matrix vesicle numerical density declined slightly and then increased to peak values in the LPZ and UHZ, followed by a decline between the UHZ and the LHZ. These changes in matrix vesicle concentration paralleled previously reported changes in intramitochondrial calcium content (8), suggesting that matrix vesicle production in growth plate may be related to intracellular calcium concentration. The existence of the maximum concentration of matrix vesicles in the LPZ and UHZ longitudinal septa which do not mineralize followed by a decline in matrix vesicle concentration in the LHZ longitudinal septa which mineralize suggests that a high concentration of matrix vesicles may be needed to prepare the matrix for mineralization or to initiate mineralization and that matrix vesicles are depleted during mineralization.
In‐vitro ligament tension pattern in the flexed knee in passive loading
Authors: Ahmed A. M. , Hyder A. , Burke D. L. , Chan K. H.
Published: February 2005

Tensions generated in selected bands of the four major ligaments of the flexed knee (40–90°) have been measured in vitro when the tibia is subjected to passive anterior translation and axial rotation with and without a compressive preload. The measurements were made in 30 fresh‐frozen specimens using the buckle transducer attached to the anteromedial band of the anterior cruciate ligament [ACL (am)], the posterior fibers of the posterior cruciate ligament [PCL (pf)], the superficia fibres of the medial collateral ligament [MCL (sf)], and in the total lateral collateral ligament (LCL). Particular attention was placed on the evaluation of the performance of the transducer specific to such measurements in order to minimize the errors associated with the use of this transducer. The results indicate that, among the measured ligaments, substantial tension (>20 N) is generated only in the ACL (am) in tibial anterior translation up to 5 mm. The tension pattern generated in response to tibial axial rotation, however, is complex and exhibits considerable variation between specimens. In general, both the MCL (sf) and LCL are tensed at all tested flexion angles, with the tension in external rotation being significantly greater than in internal rotation. At 40° of flexion, the ACL (am) bears tension mainly in internal rotation, while at 90° of flexion the PCL (pf) is tensed in both senses of rotation. The response of the LCL shows marked variation among specimens; very small tension (15 N) is generated in internal rotation in 48% of the specimens, and in either sense of rotation in 20% of the specimens. The tension in the ACL (am) in internal rotation is invariably greater in those specimens in which LCL tension is negligible. This correlation between increased ACL (am) function and inadequate LCL restraint appears significant in terms of ACL injury and repair.
Effect of postnatal age on the ultrastructure of six anatomical areas of canine flexor digitorum profundus tendon
Authors: Okuda Y. , Gorski J. P. , Amadio P. C.
Published: February 2005

We report findings of a transmission electron microscopic study comparing the morphological appearance of cells and extracellular matrix of two fibrocartilaginous regions of canine flexor digitorum profoundus (FDP) tendon with that for typical tendinous regions. In addition, we determined the size distribution of collagen fibrils in six anatomical areas of the tendon from animals of three different ages. Average collagen fibril diameters for each of the six anatomical sites of 11‐week‐old FDP tendon were consistently different from that for older tissue. As growth proceeds, fibrils in tendinous regions almost double in size and take on a broad bimodal distribution. Collagen diameters in fibrocartilaginous areas do not increase, but rather decrease in size with age. Finally, the cells and associated pericellular matrix of fibrocartilaginous areas of adolescent and mature FDP tendon are ultrastructurally distinct from those of typical tendinous regions. On the contrary, the cellular morphology of 11‐week‐old tendon was invariant regardless of the anatomical region examined. In summary, fibrocartilage of canine FDP tendon, although not evident at 11 weeks of age, is well established by 6–12 months after birth and is the result of cellular and extracellular matrix specialization.
Local compression patterns beneath pneumatic tourniquets applied to arms and thighs of human cadavera
Authors: Hargens Alan R. , McClure A. Gavin , Skyhar Michael J. , Lieber Richard L. , Gershuni David H. , Akeson Wayne H.
Published: February 2005

Distributions of tissue fluid pressure were examined beneath a standard pneumatic tourniquet in six upper extremities and six lower extremities of fresh human cadavera, disarticulated at the shoulder and hip, respectively. A standard 8‐cm‐wide tourniquet cuff was applied at mid‐humerus or mid‐femur position. Tissue fluid pressures were measured by 100‐cm‐long slit catheters inserted parallel to the bone at four tissue depths: (a) subcutaneous, (b) subfascial, (c) mid‐muscle, and (d) adjacent to bone. All arms and thighs were studied at the following cuff pressures: 100, 150, 200, 250, 300, 400, and 500 mm Hg. Tissue fluid pressure was always maximal in subcutaneous tissue at mid‐cuff. Transmission of cuff pressures to deeper tissues was significantly less (p < 0.01) in the thighs with a girth of 40–52 cm than in the arms with a girth of 22–23 cm. At the four tissue depths studied, tissue fluid pressures fell steeply in a longitudinal direction near the cuff edge to levels near zero at points 1–2 cm outside each cuff edge. Our results suggest that wider cuffs are required on thighs than on arms to provide a bloodless field during limb surgery and to minimize underlying tissue injury associated with high cuff pressures. Our recommendation for wider tourniquet cuffs than those presently used during orthopaedic surgery is contrary to recent prevailing knowledge.
Natural history of acute septic arthritis in an avian model
Authors: Alderson Mark , Nade Sydney
Published: February 2005

An experimental model of acute septic arthritis is described, utilizing the injection of S. Aureus into chicken hock joints. The course of the infection was monitored over a 14‐day period by measurement of chicken growth rate, histopathology of the joint, number of bacteria, and number and type of leukocytes in the synovial fluid. Bacterial numbers decreased initially then increased rapidly over the first 24 h. Leukocyte counts rose sharply, starting between 60 and 90 min after injection. Gross destruction of articular cartilage was observed at 4 days, and appeared to be initiated by the adherence of the staphylococci to the cartilage surface followed by their penetration and invasion of vascular tunnels in the epiphyseal cartilage. Extensive (but focal) erosion of the articular surface was evident by 14 days.
Normative childhood EMG gait patterns
Authors: Shiavi Richard G. , Green Neil , McFadyen Brad , Frazer Mardon , Chen Jason
Published: February 2005

The population characteristics of the linear envelopes of the electromyograms measured from seven lower extremity muscles in children were studied during locomotion. The variability and changes in pattern with respect to walking speed and age were investigated using statistical properties and analysis of variance of the envelopes. All muscles studied showed changes in their patterns that were associated with different walking speeds. Some changes concerned the relative intensity of existing phases of activity. The most remarkable trend was that all envelopes tended to have more consistent patterns as speed increased. With regard to age, within the span of 4–11 years, only the two high muscles studied demonstrated appreciable differences.
Warping of cross sections in the torsion of long bones with internal fracture fixation plates
Authors: Beaupré G. S. , Carter D. R.
Published: February 2005

Torsion of noncircular beams results in warping of each cross section. When noncircular cross sections are constrained to remain plane, the resulting shear stress distribution is different from what Saint Venant torsion (with warping) would predict. This has practical implications to the stress analysis of plated long bones subjected to torsional loadings. Analyses in which warping is not allowed predict incorrect stress fields in the plate and bone and overpredict the amount of stress shielding associated with fracture plate fixation.
Surface strain on human intervertebral discs
Authors: Stokes Ian A. F.
Published: February 2005

The biomechanical functions of the internal components of the intervertebral disc are not well understood. The surface deformation of 17 human cadaveric lumbar intervertebral discs was studied by photogrammetry by adhering small optical targets to the disc surface and thereby recording the length, bulge, and vertical height of lines on the disc surface representing annular fibers. Discs were studied in pure compression, flexion and extension, axial rotation, and shear. Two definitions of a fiber were investigated: first with the end‐points of the fiber on the vertebra (“bone‐to‐bone” definition), second, where the end points of the fiber were just before the disc vertebra junction (the “disc‐only” definition). Measurements were compared with a “constant‐volume” physical model and with a mathematical model of the intervertebral disc. Fiber strains were 6% or less under physiological conditions. Comparison of results from the two definitions of fiber length showed greater strains for the disc‐only definition in compressive loading. Fiber strains were less than in the constant‐volume model of comparable dimensions in compressive loading by a factor of about two, thus suggesting fluid loss or end‐plate deformations in the physiologic conditions. The mathematical model indicated that the surface strain for intervertebral discs is very sensitive to the disc‐height: diameter ratio and to fluid loss from the disc but is less sensitive to the helix angle of the fibers.
The evaluation of a biphasic calcium phosphate ceramic for use in grafting long‐bone diaphyseal defects
Authors: Moore D. C. , Chapman M. W. , Manske D.
Published: February 2005

The effectiveness of a sintered hydroxyapatite‐tricalcium phosphate (HA‐TCP) ceramic in bridging large diaphyseal defects in the canine ulna was studied. One‐hundred percent morselized HA‐TCP, a 50:50 mixture of morselized HA‐TCP, and autogenous cancellous bone, and 100% autogenous cancellous bone were used to bridge 2.5‐cm defects in the left ulnae of three groups of six dogs each. At 24 weeks the ulnae were explanted and studied by radiography, microradiography, mechanical testing, and histology. Pure HA/TCP was not osteoinductive, and four of six ulnae in this group progressed to a fibrous nonunion. The HA/TCP‐cancellous bone mixture and pure cancellous bone were approximately equal in effect, leading to good callus formation at 4 weeks and strong bony union by 24 weeks, with no evidence of bioincompatibility. Morselized HA/TCP promises to be useful as a graft extender when mixed with autogenous cancellous bone.
Comparison of the fatigue characteristics of centrifuged and uncentrifuged simplex P bone cement
Authors: Davies Jeff P. , Burke Dennis W. , O'Connor Daniel O. , Harris William H.
Published: February 2005

Fatigue test specimens of Simplex P bone cement (Howmedica Inc., Rutherford, NJ) prepared according to the manufacturer's instructions and specimens of Simplex P prepared by centrifuging the cement immediately after mixing were subjected to fully reversed tension‐compression fatigue tests at initial strain levels ranging from 0.01 to 0.001. S:N curves for both cement preparations were generated and compared on the basis of regression analysis, Weibull analysis, and Student's t tests. Centrifuged Simplex P was able to withstand significantly more fatigue cycles than uncentrifuged Simplex P at all strain levels tested. Importantly, at the more physiologic strain levels of 2,000 and 1,000 microstrain, the centrifuged cement demonstrated superior fatigue life. Specifically, at the 1,000‐microstrain level eight of the 11 uncentrifuged specimens fractured before undergoing 10 million cycles. Of those that failed, the average number of cycles to failure was 1.8 million with a range of 560,000 to 4 million cycles. In contrast, all 11 centrifuged specimens tested at 1,000 microstrain remained intact at 10 million cycles.
Effect of patellar shaving in the rabbit
Authors: Mitchell Nelson , Shepard Nora
Published: February 2005

Shaving of the articular cartilage on the undersurface of the patella was carried out in mature white New Zealand rabbits to determine whether the removed cartilage reformed or the shaving led to later evidence of degenerative arthritis. The animals were followed for as long as 15 months after surgery, at which time patellae were removed and examined by light and electron microscopy. The depth of shaving varied considerably; however, no evidence of repair and no evidence of degenerative arthritis was noted in either the superficial or deeply shaved patellae. It is concluded that such superficial cartilage defects neither repair or produce subsequent degenerative arthritis.
New experimental procedures to evaluate the biomechanical properties of healing canine medial collateral ligaments
Authors: Woo Savio L.‐Y. , Gomez Mark A. , Inoue Masahiro , Akeson Wayne H.
Published: February 2005

Both clinical and animal studies have indicated that early mobilization and exercise may improve the healing of injured medical collateral ligaments (MCLs). To investigate these effects, transected canine MCLs were subjected to three different treatment regimens: (a) no surgical repair with 6 weeks mobilization; (b) surgical repair with 3 weeks immobilization followed by 3 weeks remobilization; and (c) surgical repair with 6 weeks immobilization. After sacrifice, knee laxity was measured in a newly designed varusvalgus (V‐V) laxity device. Each knee was tested subsequently in tension to determine the structual properties of the femur‐MCL‐tibia complex (FMTC) and the mechanical properties of the healing MCL substance. It was found that the V‐V laxity increased for all experimental knees, but that early mobilization enhanced joint stability. The structural properties of the FMTC and the mechanical properties of the MCL substance were also lower than the contralateral controls. Again, the early mobilization groups had better results.
Production of a reproducible spinal burst fracture for use in biomechanical testing
Authors: Cotterill Paul C. , Kostuik J. P. , Wilson J. A. , Fernie G. R. , Maki B. E.
Published: February 2005

We have developed a technique to create a reproducible spinal burst fracture of the 12th vertebral body using 6–8‐week‐old calf spines with ribs, muscles, and vessels resected. We used the entire thoracolumbar segment of 20 calf spines with a standardized 5‐mm‐deep slice placed onto the body of T12 and the T11–12 disc. We then delivered a proximal‐axial impact to the vertically mounted spine, preflexed to 15° of forward flexion, by dropping a 32‐kg weight, guided by a 1.55‐m steel rod (potential energy = 487 J). Motion was limited to anterior flexion only, at the T12–13 disc, by splinting the rest of the spinal segments. Fractures were documented with the use of radiographs and computed tomography (CT) scans. We noted disruption of the vertebral column and end plates, fracture of the posterior body wall, fracture of the pedicles, and retropulsion of bony fragments into the neural canal. With the production of a reproducible spinal burst fracture model, various spinal fixation devices can be applied and tested.
Streaming potentials: A sensitive index of enzymatic degradation in articular cartilage
Authors: Frank Eliot H. , Grodzinsky Alan J. , Koob Thomas J. , Eyre David R.
Published: February 2005

Under physiological conditions, the extracellular matrix of articular cartilage contains a high fixed‐charge density, associated with its ionized proteoglycan (PG) molecules. Compression of the highly charged cartilage matrix within the physologic range leads to the production of electrical streaming potentials. We observed significant changes in the potential response due to chemical modifications of the matrix, such as extraction of PG and glycosaminoglycan (GAG) moieties using chondroitinase‐ABC and trypsin. The streaming potential was a sensitive index of the degradative loss of these matrix constituents and of the kinetics of the enzymatic degradative process.
Interaction between intrinsic knee mechanics and the knee extensor mechanism
Authors: Draganich L. F. , Andriacchi T. P. , Andersson G. B. J.
Published: February 2005

The ability of the quadriceps muscles to extend the knee was studied relative to the intrinsic mechanical features of the knee joint. The quadriceps mechanical efficiency changed by nearly 50% between 0 and 90° of knee flexion. The peak efficiency occurred at ∼20° of knee flexion. The mechanical efficiency of the quadriceps was dependent on the movement of the net anteroposterior (AP) tibiofemoral contact center of pressure, the change in patellar ligament angle, and the change in the quadriceps‐to‐ligament force transfer ratio. The average net AP tibiofemoral contact center of pressure moved posteriorly on the tibial plateau as the knee flexed from 0 to 90°. The excision of both cruciate ligaments reversed the posteriorly directed movement of the net AP tibiofemoral contact center of pressure at flexion angles from 60 to 90°, resulting in a reduction in extension moment.
Limb lengthening by epiphyseal distraction. An experimental study in the caprine femur
Authors: Steen Harald , Fjeld Terje O. , Rönningen Helge , Langeland Norvald , Gjerdet Nils R. , Bjerkreim Ingjald
Published: February 2005

Epiphyseal distraction of the left distal femur was accomplished in 10 goats (aged 3–4.5 months). A modified Hoffmann external fixation device was used as a unilateral distraction frame. A distraction rate of 1.5 mm/day was applied for 5.5 weeks. Epiphysiolysis occurred after 3–7 days of distraction. After the lengthening procedure, the growth plate had reduced in height in eight animals on radiographic examination. In two animals the growth plate was fused. Three animals were killed at 4 (Group 1) and 8 (Group 2) weeks and four animals at 16 (Group 3) weeks after the end of the distraction period. The gain in leg length obtained by distraction was reduced owing to growth retardation in the distal femur of the operated limb. The average final lengthening was 24.9, 19.4, and 13.4% in Groups 1,2, and 3, respectively. Femur and tibia from both sides were tested mechanically in torsion. Only one femur fractured in the elongation area. All but one elongated femur fractured in the area of the diaphysis subjected to distractional force. The torsional strength of the elongated femur compared with control was reduced to ∼50% in all groups. The corresponding torsional strength of the tibia on the elongated extremity compared with control was reduced to ∼75% in all groups. The difference in relative strength of femur compared with that of tibia was statistically significant. This finding can be explained by a stress‐protective effect on the femur in the distraction area caused by the external device.
Pin tract infections: A canine model
Authors: Respet Patrick J. , Kleinman Paul G. , Meinhard Bruce P.
Published: February 2005

The purpose of this study was to examine three issues: the relationship between the length of time of skeletal pin insertion and bacterial infection, the connection between skin organisms and the intramedullary infecting agent, and the length of time necessary for the medullary canal to sterilize itself after pin removal. Skeletal pins were inserted in a group of dogs, and a direct correlation was found between the duration of time that the pins remained in the bone and positive intramedullary cultures. The infecting agent in 88% of the medullary cultures was also cultured from the skin. In a second group of dogs, the pins remained in place for 1, 2, 3, or 4 weeks, respectively. The pins were removed, and the pin tracts were permitted to heal for varying periods of time. The medullary canals were then cultured. No medullary canal was infected when the pin tracts were allowed to heal for ≥3 weeks. Therefore, if pin tracts are allowed to heal for at least 3 weeks prior to performance of osteosynthesis, the chances of deep infection are probably lessened.
Stresses in plated long‐bones: The role of screw tightness and interface slipping
Authors: Beaupré Gary S. , Carter Dennis R. , Orr Tracy E. , Csongradi John
Published: February 2005

Using a three‐dimensional finite element model of a plated long bone, we studied the influence of screw tightness, sliding frictional interfaces, and loading magnitude on the stresses within the plated bone. The model incorporated frictional interface elements that allowed stress‐free separation under tensile loading to occur between the plate and bone and between the screw heads and the plate. The applied loading simulated both static preloads created by tightening the screws that secure the plate to the bone and physiologic loads created by activity. Initial screw tightening with plate application created regions of bone hydrostatic compressive stress that may be partly responsible for ischemia under the plate. The inclusion of frictional interfaces resulted in a nonlinear relationship between physiologic load and bone strain that was dependent on screw tightness. This nonlinear response correlated well with the results of previous in vitro studies showing that slippage between the plate and the bone can occur at physiologic load levels. The results showed that the effect of such slippage can be at least as important as plate meterial, rigidity, and placement in determining the degree of stress shielding. The results also indicated that previous plated bone models that assumed tight interfaces may have overestimated the extent of mechanical stress shielding.
Biomplant surfaces: Binding of fibronectin and fibroblast adhesion
Authors: Cannas Mario , Denicolai Fernando , Webb Lawrence X. , Gristina Anthony G.
Published: February 2005

The adhesion of baby hamster kidney 21C/13 fibroblasts to surfaces of passivated titanium, carbon fibers, bioactive glasses B5 and B6, fibronectin‐precoated passivated titanium, and fibronectin‐precoated B6 was quantified. The order of adhesive cell avidity for the uncoated surfaces was passivated titanium (greatest), B6 and carbon fibers (intermediate), and B5 (least). Precoating with fibronectin enhanced the adhesive characteristics of fibroblasts on passivated titanium and B6 by 74% and 118%, respectively.
Mathematical analysis of computed carpal models
Authors: Belsole Robert J. , Hilbelink Don R. , Llewellyn J. Anthony , Stenzler Stephen , Greene Thomas L. , Dale Mark
Published: February 2005

The computed carpal models from digital computed tomography (CT) data obtained in this study compare favorably to natural anatomy. A new application of algebraic analysis of this data provides mathematical markers from which to calculate the position and orientation of each carpal bone. When the origin of the spatial coordinates of a carpal bone is transferred to the centroid of the bone, the data can be treated as three‐dimensional pattern vectors describing its surface. It is then possible to calculate vectors that are the principal axes of the geometry. These axes provided references that were used to calculate position and orientation of the carpal bones in three wrist specimens. Comparisons of volumes, surface areas, and sizes and proportions of five computed images of each carpal bone from two of these wrists demonstrate the reliability of the technique. The analysis of CT scans of ceramics with known boundaries allows an estimation of its accuracy. The technique is well suited to the future study of normal wrist kinematic and pathological conditions.