bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental method for the measurement of the elastic modulus of trabecular bone tissue
Authors: Mente P. L. , Lewis J. L.
Published: February 2005

A procedure has been developed to measure the elastic modulus of small, irregularly shaped specimens without significantly disturbing the specimen's internal or surface structure. This procedure was developed to measure the average elastic modulus of isolated trabeculae from human cancellous bone tissue. The procedure combines direct testing of a cantilever beam‐type specimen, along with finite element modeling of the specimen and the testing conditions. Initial estimates for the bone tissue material properties are input into the finite element model; differences between the calculated finite element displacement and the experimentally observed displacement allows the actual material modulus to be determined. Machined aluminum and cortical bone specimens were used to test the accuracy and repeatability of the procedure. Manipulations of the finite element models were performed to examine the effect that mesh construction errors might have on the accuracy of the results. None of the parameters examined resulted in changes in the measured finite element displacements of greater than 8%. In tests on six trabecular bone speciments, an average elastic modulus of 7.8 GPa was calculated. Even taking into account the possible sources of error, this value remains significantly less than the accepted value for cortical bone.
“Benign” metastasizing giant cell tumor: Evaluation of nuclear DNA patterns by flow cytometry
Authors: Scott Steven M. , Pritchard Douglas J. , Unni K. Krishnan , Rainwater Leslie M. , Lieber Michael M.
Published: February 2005

Nuclear deoxyribonucleic acid (DNA) ploidy was determined by flow cytometry for nine histologically benign giant cell tumors that developed systemic metastases and for eight tumors that did not metatasize. Specimens from the primary tumor, local recurrences, and pulmonary metastases were evaluated. No feature of the DNA ploidy pattern was identified to distinguish giant cell tumors that metastasized from those did not. The mean percentage of diploid (G0/G1 peak, 2C) cells was 81% in the metastasizing group and 80% in the nonmetastasizing group. The DNA ploidy pattern of the primary tumors was not different from that of their metastases. No DNA aneuploid patterns were observed among the benign tumors.
Intraarticular pressure during continuous passive motion of the human knee
Authors: Pedowitz R. A. , Gershuni D. H. , Crenshaw A. G. , Petras S. L. , Danzig L. A. , Hargens A. R.
Published: February 2005

Intraarticular pressure (IAP) was continuously monitored during continuous passive motion (CPM) of five normal and 11 abnormal human knees using a new fiberoptic, transducer‐tipped Camino catheter. IAP varied in a consistent hysteresis pattern in the normal knees, with subatmospheric pressures recorded at intermediate angles of joint flexion. A similar pattern was recorded in the abnormal knees without cruciate ligament pathology, whereas considerable variability was noted in the knees with cruciate ligament abnormality. IAP was lower in the extension to flexion than in the flexion to extension portion of the CPM cycle, providing evidence of intraarticular fluid flow during portions of the CPM cycle. IAP changes were consistent with “physiologic compartmentation” within the knee at extremes of joint position. Capsular viscoelastic changes and/or synovial fluid volume changes were observed during CPM. The therapeutic mechanism of continuous passive motion may be related to cyclic variation of the intraarticular pressure.
Three‐phase [99mTc]diphosphonate scintimetry in septic and nonseptic arthritis of the immature knee: An experimental investigation in dogs
Authors: Hansen Ebbe Stender , Hjortdal Vibeke Elisabeth , Noer Ivan , Holm Ida Elisabeth , Ewald Henrik , Bünger Cody
Published: February 2005

We compared the informative value of dynamic and static [99mTc]diphosphonate ([99mTc]DPD) scintimetry in early septic arthritis (SA) and chronic nonseptic arthritis (NSA) of the knee in puppies. SA (n = 10), induced by injection of Staphylococcus aureus into one knee, was examined after 48 h. NSA (n = 6) was induced by weekly intraarticular instillation of 1% carragheenan and examined at 2 and 12 weeks. Epiphyseal and metaphyseal count ratios (CRs) between experimental and control joint were calculated in an angiographic phase (0–20 s), a “blood pool” phase (20–256 s), and a bone uptake phase (2 hs). Control dogs (n = 4) had a CR of 1.0 in all regions and phases, the coefficients of variation being 0.06 and 0.03 in dynamic and static phases, respectively. In NSA, all scintimetric phases showed decreased meytaphyseal uptake and largely unchanged epiphyseal uptake. Generally, SA exhibited vastly increased angiographic uptake in all regions and increased epiphyseal blood pool uptake, whereas delayed epiphyseal uptake varied and delayed metaphyseal uptake tended to decrease. Two septic joints had generalized reduction in dynamic uptake probably owing to increased intraarticular pressure; in one of these, dynamic uptake in the distal femoral epiphysis (FE) was totally absent, suggesting temporary circulatory arrest during the dynamic scanning procedure. The use of regional dynamic and static [99mTc]DPD scintimetry increased the pathophysiologic and diagnostic value of joint scintigraphy, especially with respect to the early detection of SA and its avascular complications.
Anterior cruciate ligament: Its normal response and replacement
Authors: Butler David L.
Published: February 2005

This article reviews our research studies on the anterior cruciate ligament (ACL). The human ACL was found to be a primary restraint to anterior tibial displacement at both 90° and 30° of flexion. Geometric measurements of the ligament showed it to have a complex macrostructure, consisting of bundles of different lengths, curvatures, and orientations. Similar material properties were measured for subunits from the human anterior and posterior cruciate and lateral collateral ligaments. However, the linear modulus, maximum stress, and strain energy density to maximum stress of the ACL were significantly less than similar properties for patellar tendons. These tissue subunits exhibited nonuniform axial strain during tensile loading, which was partially attributed to differences in bundle crimp period and crimp angle. The structural mechanical properties (stiffness, strength, and energies and elongations to maximum force and failure) of nine commonly used human ACL substitutes were also compared. Only the bone‐patellar tendon‐bone unit had maximum force and stiffness greater than that of the ACL. The patellar tendon, when used as an ACL replacement in the dog and primate, exhibited significant loss in structural mechanical and material properties early after implantation. These properties showed only a gradual improvement up to 1 year after surgery. Maintaining a vascular supply to these grafts or using intermittent passive motion immediately after surgery produced no significant improvement in graft properties in the primate model.
Collagen synthesis during primate flexor tendon repair in vitro
Authors: Russell Jean E. , Manske Paul R.
Published: February 2005

The concept that flexor tendons have the intrinsic capacity to participate actively in the repair process following laceration has been developed in recent years as the result of experimental studies from numerous laboratories. However, the role of the outer/epitenon and inner/endotenon cell populations with regard to protein synthesis is still controversial. The purpose of this study was to investigate the respective participation of these tendon fibroblast populations in the synthesis of the collagen matrix during in vitro repair of the flexor tendon from nonhuman primates, utilizing immunohistochemical techniques and a Type I procollagen antibody. Zone II profundus flexor tendon segments were obtained from young adult Macaca nemestrina monkeys. One centimeter segments were cultured either with or without a transverse laceration across 90% of the midsection of the tendon segment. Frozen sections of the cultured tendon segments were reacted with the (mouse monoclonal) Type I procollagen antisera. At all times of culture of the nonlacerated tendon segment, only a few of the epitenon cells along the surface of the tendon and distant from the cut end stained positively for active collagen synthesis. In the lacerated segments, and as early as 9 days of culture and repair, the procollagen reaction product was starting to appear in those cells of the outer epitenon cell layer. These studies support the concept that the inner fibroblasts do actively participate in collagen production. However, it now also appears that a significant degree of collagen synthesis during tendon repair resides in the outer/epitenon layer of cells enveloping the tendon segment, and that the repair response of the flexor tendon in vitro is proportional to the degree of injury.
Participation of human superficialis flexor tendon segments in repair in vitro
Authors: Mass Daniel P. , Tuel Robert J.
Published: February 2005

We analyzed the healing capability of the human superficialis (sublimus) flexor tendon in response to injury in vitro by performing a morphologic study of tendon repair. Tendon segments were cultured in cell‐free medium for 2, 4, or 8 weeks, and the cut‐end repair sites were compared with those in fresh control segments on light and electron microscopy. Tendon encapsulation had occurred at 2 weeks, by the proliferation and migration of elongated fibroblasts from the epitenon and from collagen bundles of the endotenon to cover the surface of the cut tendon ends. As migrating epitenon cells approached the cut margin, they consistently shifted from a parallel to a circumferential orientation with respect to the tendon axis. By 4 weeks, the encapsulating surface cells had lost their membranous ruffles and had become flattened. Within the capsule, phagocytic cells engulfed collagen debris, and fibroblasts containing extensive rough endoplasmic reticulum profiles and secretory vesicles participated in protein synthesis. The surface of the capsule was smooth and, at 8 weeks, was almost indistinguishable from the epitenon surface of uncultured controls. The capsule now had a collagen‐synthesizing layer of fibroblasts superimposed on layers of maturing collagen bundles that separated restingphase fibroblasts. These findings demonstrate that segments of human superficialis flexor tendons participate in an intrinsic repair response without contributions from extrinsic cells.
The effect of shear fatigue on bovine articular cartilage
Authors: Simon William H. , Mak Arthur , Spirt Adrienne
Published: February 2005

The objective of this study was to investigate the effects of mechanical fatigue in the form of cyclic shear strain on articular cartilage. Three millimeter diameter full‐thickness plugs were cored from the lateral aspect of bovine tibial plateaus. Sinusoidal shear strains of ±5, ±10, and ±15% were applied to the specimens at 100 Hz for 3 h (a total of 108 ±X 104 cycles). The mechanical shear properties of the tissue (loss and storage moduli) were determined as a function of the number of applied strain cycles. A rapid, irreversible decrease of approximately 35% of initial modulus was found to occur in both loss and storage modulus during application of the first 90,000 cycles. Further decay in the moduli was found to occur from 90 ±X 103 to 108 ±X 104 cycles, but was of considerably smaller magnitude than the initial decrease. The moduli remained relatively constant beyond application of 108 ±X 104 cycles. No consistent change in proteoglycan content was found to be associated with the fatigue process when comparing tested specimens with fresh untested tissue, and with experimental controls. In addition, no structural defects in the mechanically altered tissue were revealed by scanning electron microscopy.
Effect of doxorubicin on local recurrence following marginal resection in the MGH‐OGS murine model
Authors: Bell R. S. , O'Connor G. , Bell D. F. , Jacob J.
Published: February 2005

Despite the fact that preoperative chemotherapy causes substantial necrosis in the primary osteosarcoma tumor, most authorities recommend resecting these lesions with a wide margin of normal tissue to avoid local recurrence. This study evaluated the effect of systemic chemotherapy (doxorubicin) on tumor growth and histology in the MGH‐OGS transplantable murine model and examined whether this drug prevents local recurrence after resection of the tumor with positive microscopic margins. The results indicate that doxorubicin caused prolonged cessation of tumor growth, produced substantial necrosis within the lesion, and decreased the risk of local relapse following marginal surgery. The drug effect was dose‐dependent and drug efficacy in preventing local relapse was maximal with administration prior to or at the time of surgery.
Transcortical streaming potentials are generated by circulatory pressure gradients in living canine tibia
Authors: Otter M. W. , Palmieri V. R. , Cochran G. V. B.
Published: February 2005

Electrical potentials associated with the pulse pressure have been observed in a canine tibia model in vivo. As the medullary pressure rises during pulsing, the periosteal bone surface becomes positive with respect to the endosteal surface. This pattern is consistent with streaming potentials generated by outward flow of fluid through bone with a negatively charged matrix (negative zeta potential). Both the medullary pressure and electric potential oscillations are halted by occlusion of the femoral artery. Furthermore, systemic administration of epinephrine decreases the amplitude of the medullary pressure and the electric potential by the same fraction. Streaming potentials generated by blood flow are distinct from those generated by mechanical deformation and may have additional significance in relation to fracture healing and/or etiology of osteoporosis.
Repair of cartilaginous fractures during chick limb development
Authors: McCullagh J. J. , Gill P. , Wilson D. J.
Published: February 2005

The embryonic chick wing has been used extensively in experimental analyses of the mechanisms involved in limb development. This study employs the embryonic wing in an examination of the possible origin of congential pseudoarthrosis, a poorly understood limb disorder. To this end, chick radii were fractured in the middiaphysis prior to the onset of osteogenesis (6.5–7 days of incubation). The subsequent development of the fractured elements was examined using both whole mount preparations and histology. Callus cartilage did not form around any of the fractures. Nonetheless, the majority (29 of 33 specimens) of fractures united during primary osteogenesis (within 24–36 h of the operation), with bone formation occurring both across the fracture site and also over the cut ends of the cartilage. In addition, bones that exhibited a configuration, similar to that described as giving rise to a type II congenital pseudoarthrotic condition were obtained. Typically, these bones showed an “hourglass” constriction midshaft and anterior bowing. These results suggest that the embryonic chick limb may serve as a useful experimental model system for the investigation of this congenital limb disorder.
Resistance of a defect of the supraspinatus tendon to intraarticular hydrodynamic pressure: An experimental study on rabbits
Authors: Björkenheim Jan‐Magnus , Paavolainen Pekka , Ahovuo Juhani , Slätis Pär
Published: February 2005

The healing of a standardized defect of the supraspinatus tendon in a time‐related series on rabbits was monitored with arthrography and simultaneous determination of the intra‐articular hydrodynamic pressure of the glenohumeral joint. All normal glenohumeral joints produced a biphasic pressure versus volume curve. Rupture of a normal glenohumeral joint occurred at a pressure level of 140–170 mm Hg and was located in the area around the biceps tendon sheath. In joints with a defect of the supraspinatus tendon, leakage of the contrast medium was evident up to the sixth week, at an intra‐articular pressure varying from 40 to 100 mm Hg. After week 6, no leakage of the cuff was seen during the determination of the intraarticular pressure. This was in accordance with the histological findings: the defect was covered with solid scar tissue from the ninth week onward. Resistance to hydrodynamic intra‐articular pressure proved a reliable method of determining the strength of the healing of the supraspinal defects.
Comparison of the effects of adriamycin and methotrexate on orthotopic and induced heterotopic bone in rats
Authors: Nilsson Olle S. , Bauer Henrik C. F. , Brostrōm Lars‐Åke
Published: February 2005

The effect of the two antineoplastic drugs, Adriamycin and methotrexate, on orthotopic bone, and on the induction of experimental heterotopic bone in rats was analyzed. The drugs were administered as single injections: Adriamycin in s.c. doses of 0.5 and 2 mg/kg body weight and methotrexate i.v. 100 and 250 mg/kg body weight followed by leucovorin rescue after 2 h. A passing, but significant, decrease in body weights occurred in the methotrexate‐treated animals, but not in those given Adriamycin. Analysis of the amount of heterotopic bone formed 4 weeks after induction by demineralized bone matrix revealed a 30–40% decrease in the groups treated with either of the antineoplastic agents, whereas orthotopic bone was unaffected. Six weeks after the treatment the net effect on the induced bone had decreased. The present study shows that the two antineoplastic drugs Adriamycin and methotrexate inhibit heterotopic new bone formation induced by demineralized bone matrix in rats to an equal extent, although their mode of action on the cellular level is entirely different, and that the inhibitory effect of a single treatment diminishes in the presence of a continuous inductive process.
Effects of exercise on blood flow to canine articular tissues
Authors: Simkin Peter A. , Huang Alice , Benedict Richard S.
Published: February 2005

We measured articular blood flow by standard microsphere techniques in normal adult dogs at rest and during treadmill exercise. All animals but one underwent β‐adrenergic blockade as part of another experimental protocol. Expressed in μl/min/g ± SEM, baseline flow values to articular tissues were: knee synovium 26 ± 4, femoral condyle 130 ± 21, tibial plateau 182 ± 29, articular fat pad 9 ± 2, knee ligaments 17 ± 3, menisci 34 ± 6, wirst synovium 19 ± 4, distal radius 65 ± 13, and lunate bone 59 ± 13. Blood flow increased with exercise in all soft tissue of both the knee (stifle joint) and the wrist (radiocarpal joint). Geometric mean exercise/rest flow ratios ranged from a low of 1.44 (p < 0.05) in the menisci of the knee to a high of 7.25 (p < 0.001) in the synovium of the wirst. In contrast, blood flow did not rise in juxtaarticular bones and fell significantly in femoral condyles (mean flow ratio 0.71, p < 0.005). These findings indicate that articular soft tissues derive increased perfusion from the redistribution of blood flow that accompanies short‐term exercise. In contrast, flow to juxtaarticular bone does not increase under these conditions.
Statistical significance and statistical power in hypothesis testing
Authors: Lieber Richard L.
Published: February 2005

Experimental design requires estimation of the sample size required to produce a meaningful conclusion. Often, experimental results are performed with sample sizes which are inappropriate to adequately support the conclusions made. In this paper, two factors which are involved in sample size estimation are detailed—namely type I (α) and type II (β) error. Type I error can be considered a “false positive” result while type II error can be considered a “false negative” result. Obviously, both types of error should be avoided. The choice of values for α and β is based on an investigator's understanding of the experimental system, not on arbitrary statistical rules. Examples relating to the choice of α and β are presented, along with a series of suggestions for use in experimental design.
Quantitation and relative distribution of extracellular matrix in Staphylococcus epidermidis biofilm
Authors: Van Pett K. , Schurman D. J. , Smith R. Lane
Published: February 2005

The relationship between adherence of bacteria to foreign boides and their deposition of extracellular matrix was examined on glass and suture material. To quantitate bacterial adherence, uptake of [3H] thymidine into bacterial DNA was analyzed. Corresponding amounts of extracellular matrix were measured by a new technique using [14C]glucose incorporation. This study shows that [14C]glucose preferentially labeled bacterial strains in proportion to biofilm production. The ratio of 3H14C in high biofilm producers was 0.9 and in low producers it was 3.7. Radioactive identification of organisms as high and low producers was confirmed byelectron microscopy. The results presented here show that production and accumulation of biofilm over time is a stable characteristic in different strains of S. epidermidis. The use of ratios reflecting radiolobeling of bacteria and biofilm by [3H]thymidine and [14C]glucose, respectively, is a quantitative yet simple technique to assess extracellular matrix of different strains of S. epidermidis.
Effects of isolated rheumatoid synovial cells on cartilage degradation in vitro
Authors: Keller Kenneth , Shortkroff Sonya , Sledge Clement B. , Thornhill Thomas S.
Published: February 2005

Rheumatoid synovium in coculture with cartilage has been shown to release a factor(s) that stimulates the depletion of glycosaminoglycans (GAG) from cartilage matrix. Human rheumatoid synovium was enzymatically disaggregated and the isolated cells were subjected to a variety of mechanical and immunological treatments. Synovial cell conditioned media (SCCM) were prepared and analyzed for their ability to stimulate GAG depletion. SCCM prepared from increasing concentrations of isolated synovial cells demonstrated cartilage degradative activity in a dose‐dependent manner. This activity was characterized as interleukin‐l like and was found mostly within the adherent cell population where the synovial macrophages retained significant degradative ability. T cells alone were found to have no direct degradative effect on cartilage, but their presence appeared to augment the response of the adherent cells. The techiques described here provide a quantitative model for examining the degradative factors from synovium as well as the cellular interactions that promote their release.
An investigation of a compliant interface for press‐fit joint replacement
Authors: Walker P. S. , Rodger R. F. , Miegel R. E. , Schiller A. L. , Deland J. T. , Robertson D. D.
Published: February 2005

Earlier in vitro studies showed that a compliant layer between a metal surface and trabecular bone improved the load distribution. In this study, the behavior of a compliant layer of Dacron velour was investigated in vivo using a patella resurfacing in a sheep as a model. Bilateral cases were used to compare the velour interface with a direct metal‐to‐bone interface. For the metal patellas, a fibrous layer developed adjacent to the metal while the underlying bone formed a new subchondral‐like layer. With the velour interface, fibrous tissue invaded the velour, followed later by bone, which sometimes reached the metal surface. For follow‐ups of 8 months or more, the load across the interface was transferred over localised patches, for both the press‐fit and velour interfaces. There was no significant difference in the areas of contact. There was evidence that this was due to the irregularity of the bony surface beneath the fibrous layer, or to bone nodules actually growing up to the metal. It was concluded that in this in vivo model, the velour layer did not retain a more uniform load distribution compared with the press‐fit joint, due to the nature of the bone and fibrous tissue that formed at the interfaces.
Factors affecting graft force in surgical reconstruction of the anterior cruciate ligament
Authors: Lewis Jack L. , Lew William D. , Engebretsen Lars , Hunter Robert E. , Kowalczyk Curtis
Published: February 2005

The effect of the maximum unloaded graft length (Lo) and femoral fixation hole location on graft force with the knee under anteriorly directed tibial loads was measured in five fresh cadaver knees with a reconstruction of the anterior cruciate ligament (ACL). The reconstruction was performed using a composite graft consisting of the semitendinosus and gracilis tendons augmented with the Kennedy ligament augmentation device (LAD). Buckle transducers were used to measure ligament and graft forces. The total graft force was adjusted to match the intact ACL at 30° flexion using a force‐setting method so that a standardized reference configuration could be repeatedly obtained. The graft force was highly sensitive to L0, typically changing by 50% with a change in L0 of 3 mm. Variation in femoral hole location of 5 mm anterior, posterior, proximal, and distal to the anatomic position produced changes in graft force, particularly at 60° and 90° flexion; however, these changes were not statistically significant. The effect of femoral hole location varied considerably between knees. This variability makes predicting proper hole placement difficult, and suggests the need to adjust each knee at surgery to account for this variable femoral hole position sensitivity.
The effect of a brain lesion on bone healing
Authors: Spencer R. F. , Bullock R. , Cooper K. , Norman R. J. , Becker P. J.
Published: February 2005

Using a feline model, the effects of stereotaxic brain lesions producing unilateral spasticity on bilateral fibular osteotomies were observed. Healing in spastic limbs occurred with more new bone formation than on the contralateral (control) side. Union appeared to be slightly faster in spastic limbs. Histomorphometric analysis of resected fibular specimens following union revealed little difference between spastic and non‐spastic limbs. When these brain‐lesioned animals were compared with a group with identical osteotomies but no brain lesions in respect of various systemic biochemical and endocrine parameters, no differences were found.
Morphometric and anisotropic symmetries of the canine distal femur
Authors: Kuhn J. L. , Goulet R. W. , Pappas M. , Goldstein S. A.
Published: February 2005

The purpose of this study was to investigate the homotypical variation in morphologic and anisotropic properties of trabecular bone from paired canine distal femurs. A microcomputed tomography system was used to produce three‐dimensional digital reconstructions of the trabecular bone structures. The results showed that the mean bilateral differences in all bone morphology variables were < 5%. Differences in measures of degree of anisotropy were also < 5% between matched sites from left and right sides. In general, the bilateral difference in angle of orientation was < 15%. These data are valuable for calculating the appropriate sample size to use in experiments using the contralateral canine femur as a control. The results and general approach of the study may have significance for the future use of other contralateral trabecular bone sites as controls.
Muscle activities during asymmetric trunk angular accelerations
Authors: Marras W. S. , Mirka G. A.
Published: February 2005

The objective of this study was to characterize trunk muscle and intra‐abdominal pressure behavior during extensions of the trunk when angular trunk acceleration levels and trunk twist were varied during lifting exertions. Since force is related to acceleration, it was believed that changes in trunk acceleration would cause activity changes in the muscles and abdominal cavity pressurization mechanics that load the spine during manual materials handling tasks. The electromyographic activity of 10 trunk muscles and intra‐abdominal pressure were studied in 39 subjects as they moved their trunks under high, medium, and low constant angular acceleration conditions. The results indicated that almost all the muscles were affected by acceleration and asymmetry. Muscle activities of up to 50% of maximum were observed even though a minimal amount of torque was being produced by the back. Coactivation of muscles was also apparent. Muscles located at the greatest distances from the spine such as the latissimus dorsi and oblique groups, increased their activities the most as trunk acceleration increased. Muscles located farthest from the spine also played an important role as the trunk became more asymmetric. Intra‐abdominal pressure changed minimally over the test conditions. The nature of these responses and their impact on spine loading are discussed.
A quantitative assessment of cross‐sectional cortical bone remodeling in the femoral diaphysis following hip arthroplasty in elderly females
Authors: Torchia Michael E. , Ruff Christopher B.
Published: February 2005

A quantitative assessment of cross‐sectional cortical bone remodeling in the femoral diaphysis following hip arthroplasty was made by direct in vitro measurements of cross‐sectional geometric properties. We obtained eight femora from four female cadavers ranging in age from 77 to 96 years. In three cases unilateral uncemented Austin Moore implants were used, and in one case a unilateral cemented Thompson prosthesis had been implanted. The time of implantation in the two specimens where this information could be obtained was greater than 40 months. Sections were made at 12 diaphyseal locations from the superior aspect of the lesser trochanter through the distal diaphysis. Section properties (areas and second moments of area, or area moments of inertia) were determined by tracing photographs of the cross‐sections with a digitizer. In this sample of prosthetic femora, we found reductions in both total subperiosteal area (TA) and endosteal area (ENDA) relative to the contralateral unoperated side in most sections distal to the lesser trochanter. The average pairwise reduction in ENDA for this region was 21.1 mm2, reaching statistical significance in one distal diaphyseal section. The average decline in TA in this region was 10.2 mm2. Because the reduction in endosteal dimensions was generally greater than the reduction in subperiosteal dimensions, cortical area (CA) was maintained or increased throughout the distal 80% of this region in prosthetic femora with an average increase in CA of 9.3 mm2, reaching statistical significance in one mid‐diaphyseal section. A completely different pattern of remodeling occurred in the two most proximal sections through the lesser trochanter and base of the femoral neck. Here, both endosteal and subperiosteal dimensions increased in the prosthetic femora, but ENDA increased more than TA, resulting in cortical thinning. The average pairwise increase in ENDA and TA, and loss in CA for these two sections was 59.8 mm2, 15.7 mm2, and 44.1 mm2, respectively, with a near‐significant increase in ENDA in one section and a significant loss of CA in the other. In comparisons between the methods of fixation, the three uncemented specimens demonstrated an increase in mediolateral bending rigidity (relative to the contralateral unoperated side) in the sections surrounding the stem tip, wherease the cemented specimen lost mediolateral bending rigidity in this region. Changes in cross‐sectional cortical bone geometry following prosthetic implantation throughout the entire femoral diaphysis, even well below the stem tip, have not been reported previously in the literature.
The influence of fixation peg design on the shear stability of prosthetic implants
Authors: Giori N. J. , Beaupré G. S. , Carter D. R.
Published: February 2005

The variety of fixation peg designs existing on prosthetic implants indicates uncertainty regarding the optimum design of fixation pegs for the reduction of stress and relative motion at the bone‐implant interface. Fixation pegs have a number of important functions on a prosthesis, one of which is to reduce shear stress and shear displacement at the bone‐implant interface. This is a parametric study intended to identify trends in the shear stability of prostheses incorporating a range of fixation peg designs. The parameters varied included the number of fixation pegs on a surface, the size of the pegs, and the aspect ratio (length/diameter) of the pegs. Mechanical tests were performed on urethane foam blocks with mechanical properties comparable to trabecular bone. The results indicated the following: (a) Fixation pegs act independently in resisting shearing force if they are spaced sufficiently far apart. (b) For any given shear displacement, smaller pegs generate a greater resistive shear force per unit of peg projected area in the direction of the applied load than larger pegs having the same aspect ratio. (c) Smaller diameter pegs cause the supporting material to yield at lower displacements. (d) Pegs with a high aspect ratio provide high shear stability with a minimum amount of bone removed, but may bend if the aspect ratio becomes excessive. (e) Smaller, slender pegs generate a greater resistive shear force at a given displacement per unit of peg volume than larger, lower aspect ratio pegs. The results of this study suggest that it may be possible to design prostheses with multiple smaller fixation pegs that conserve bone stock, distribute stress more uniformly to the supporting bone, and have stronger and stiffer shear fixation than prostheses with fewer larger pegs.
The effects of initial end contact on medial collateral ligament healing: A morphological and biomechanical study in a rabbit model
Authors: Chimich D. , Frank C. , Shrive N. , Dougall H. , Bray R.
Published: February 2005

In this investigation, the effect of initial end contact on medial collateral ligament (MCL) healing was studied in the rabbit model. Sixty‐eight 1‐year‐old New Zealand white rabbits were separated into two groups. In one group, a 4 mm saggital Z‐plasty was performed in the right MCL midsubstance (contact group), and in the other group, an analogous 4 mm midsubstance segment was removed (gap group). Left knees were unoperated to serve as internal contralateral MCL controls. Animals had unrestricted cage activity until sacrifice in groups of eight at 3, 6, 14, and 40 weeks postoperatively. Early results demonstrated that contact and gap injuries healed with what appeared to be scar tissue both morphologically and biomechanically. In both groups, laxities recovered to their contralateral values within 6 weeks and biomechanical viscoelastic behaviors recovered to 68–92% of contralaterals by 14–40 weeks. Despite these similarities, contacts showed morphological and biomechanical evidence of improved healing over gaps. Contact scars remodeled more quickly, recovered laxity more quickly, and were generally colser to contralaterals than gaps in terms of their structural strength, stiffness, and material behaviors, after 40 weeks of healing. With the exception of appearances and failure stress, all measured properties of contact healing MCLs were statistically indistinguishable from contralateral MCLs at 40 weeks of healing. These advantages of contact healing in this model support speculations that there are differences in the early rate and possibly in the later quality of ligament healing when cut rabbit MCL ends are in proximity. Longer‐term studies to define end points and mechanisms of healing are required.
Electromyographic activity of the abdominal and low back musculature during the generation of isometric and dynamic axial trunk torque: Implications for lumbar mechanics
Authors: McGill Stuart M.
Published: February 2005

This study focused on the electromyographic activity of the trunk musculature, given the well‐documented link between occupational twisting and the increased incidence of low back pain. Ten men and 15 women volunteered for this study, in which several aspects of muscle activity were examined. The first aspect assessed the myoelectric relationships during isometric exertions. There was great variability in this relationship between muscles and between subjects. Further, the myoelectric activity levels (normalized to maximal electrical activity) obtained from nontwist activities were not maximal despite maximal efforts to generate axial torque (e.g., rectus abdominis, maximum voluntary contraction; 22% external oblique, 52%; internal oblique, 55%; latissimus dorsi, 74%; upper erector spinae [T9], 61%; lower erector spinae [L3], 33%). In the second aspect of the study, muscle activity was examined during dynamic axial twist trials conducted at a velocity of 30 and 60°/s. The latissimus dorsi and external oblique appeared to be strongly involved in the generation of axial torque throughout the twist range and activity in the upper erector spinae displayed a strong link with axial torque and direction of twist, even though they have no mechanical potential to contribute axial torque, suggesting a stabilization role. The third aspect of the study was comprised of the formulation of a model consisting of a three‐dimensional pelvis, rib cage, and lumbar vertebrae and driven from kinematic measures of axial twist and muscle electromyograms. The relatively low levels of normalized myoelectric activity during maximal twisting efforts coupled with large levels of agonist–antagonist cocontraction caused the model to severely underpredict measured torques (e.g., 14 Nm predicted for 91 Nm measured). Such dominant coactivity suggests that stabilization of the joints during twisting is far more important to the iumbar spine than production of large levels of axial torque.
Interaction between active and passive knee stabilizers during level walking
Authors: Schipplein O. D. , Andriacchi T. P.
Published: February 2005

The gait of normal subjects and patients with varus deformities at the knee was studied by analyzing the interaction between the dynamic (muscular) and passive (ligamentous) restraints affecting lateral stability of the knee. A statically determinant model predicted that the midstance‐phase adducting moment during normal gait would cause lateral knee joint opening if either antagonistic muscle force and/or pretension in the lateral soft tissues were not present at the knee. The patient group tended to compensate for a high midstance‐phase adducting moment by walking with a style of gait that demanded more muscle force (greater flexion‐extension moments). This walking style reduced the chance of lateral joint opening. It can be speculated that this style of gait would help to maintain equilibrium at the knee. The higher muscle force would aid in resisting the adducting moment, keeping the joint closed laterally and thus increasing the stability of the knee.
The impact response of the seated subject
Authors: Broman Holger , Pope Malcolm H. , Benda Michal , Svensson Magnus , Ottosson Charlotte , Hansson Tommy
Published: February 2005

An impact method for establishing the dynamic response of the seated subject is introduced. The method employs a pendulum to apply the impact to the suspended seat. Pins are placed in the spinous process at L3. Highly reproducible results are obtained. The results were not affected by the amplitude of impact, implying a linear system. A marked peak of transmissibility is found in the 4–5 Hz range and an attenuation peak is found close to 8 Hz. Both muscle contraction and postural changes affect the dynamic response. A relaxed posture shows greater gain and attenuation peaks. A valsalva stiffens the system and reduces the effective damping. The vertical response of the body probably shows in the 5–6 Hz peak, while the rotational response is probably encompassed in the 8 Hz attenuation peak.
Age‐related changes in the human femoral cortex
Authors: Simmons E. D. , Pritzker K. P. H. , Grynpas M. D.
Published: February 2005

Bone undergoes structural changes with aging, but the nature of qualitative changes remains to be established. Blocks of midshaft femur were taken at autopsy from men of four different age groups: 20–25 years, 40–45 years, 60–65 years, and 80–85 years. Each femoral specimen was analyzed by density fractionation, a technique that allows the separation of bone by extent of mineralization and maturity. In the 20–25 group, lower density bone predominates. The 40–45 group is characterized by more highly mineralized bone with an increase in the 2.1–2.2 g/cc fraction. At 60–65 years, an increase in the lower density fraction was found, indicating an increase in new bone formation. At 80–85 years, there is an increase in the highest density bone (2.2–2.3 g/cc), which may represent regions of interstitial bone not properly removed through remodeling processes. Chemical studies did not reveal any change in Ca, P, Ca + PO4, or Ca/P molar ratio with respect to age. X‐ray diffraction studies show no changes in apatite crystal size with respect to age or degree of mineralization. Morphological studies documented increased remodeling activity and endosteal trabecularization in the older age groups, as well as increased intracortical porosity. An increase in the highest density fraction with aging may represent a pool of bone mineral that is less accessible to remodeling, which may be the interstitial bone.
Heterogeneity of blood flow in tibial cortical bone: An experimental investigation using microspheres
Authors: Willans S. M. , McCarthy I. D.
Published: February 2005

The distribution of tibial blood flow was measured by injecting approximately (600–1000) X 103 15 μ microspheres, labelled with either tin‐113 (113Sn) or cobalt‐57 (57Co) into femoral arteries of five mature greyhounds. The diaphyseal cortex, stripped of periosteum and devoid of marrow, was sawn into 40 pieces (10 transverse sections X 4 anatomical quarters/section). Relative deposition densities of the 113Sn microspheres in 40 pieces of cortex were found. These values, together with their associated masses, proved, from a statistical point of view, that flow rate heterogeneity was substantial in the diaphysis. In particular, for the diaphyseal cortex, distribution of relative deposition densities (flow rates) in six bones was found to be positively‐skewed with a relative dispersion ((SD/mean) x 100) of ∼40%.
Effects of gamma irradiation on the initial mechanical and material properties of goat bone‐patellar tendon‐bone allografts
Authors: Gibbons M. J. , Butler D. L. , Grood E. S. , Bylski‐Austrow D. I. , Levy M. S. , Noyes F. R.
Published: February 2005

The effects of 60Co gamma irradiation on the initial mechanical properties of the composite bone‐patellar tendon‐bone unit (CU) and the tendon midsubstance (TM) were studied. Frozen specimens were exposed to either 2 or 3 Mrad of gamma irradiation. Paired frozen specimens served as intraanimal controls. Treatment effects on the CU were assessed using four mechanical parameters. Effects on the TM were assessed using four material parameters measured using an optical surface‐strain analysis system. The maximum force and strain energy to maximum force of the composite unit were significantly reduced 27% and 40%, respectively, after 3 Mrad of irradiation (p < .05). Mechanical properties of the CU were not significantly altered, however, following 2 Mrad of irradiation. Based on individual paired contrasts between treatment and control, significant differences were also found in the material properties of the tendon midsubstance. The maximum stress, maximum strain, and strain energy density to maximum stress were significantly reduced following 3 Mrad, but not 2 Mrad, of irradiation. The results provide important “time zero” material property data, which will be useful for later anterior cruciate ligament reconstruction studies using irradiated allograft patellar tendons in the goat model and other animal models as well.
Cell patterns in the surface of rabbit articular cartilage revealed by the backscatter mode of scanning electron microscopy
Authors: Clark John M. , Rudd Eric
Published: February 2005

To study the distribution of cells in the surface layer of articular cartilage, rabbit hip and knee specimens were stained with silver and studied by scanning electron microscopy (SEM). The cartilage was treated en bloc using the Gomori methenamine silver technique, which stains the nuclei of exposed cells with reduced silver. The intact surface was then studied with a binocular microscope and SEM in the backscatter mode Only those cells within 30 μm of the surface stained, permitting that population to be imaged selectively. Depressions in the surface were related to groups of cells in clusters or rows bounded by collagen fibers. This study demonstrates the effectiveness of backscatter imaging in the study of chondrocytes. The relationship between surface contours and underlying cells is more complex than previously described.
Cartilage synthesizes the serine protease inhibitor PAI‐1: Support for the involvement of serine proteases in cartilage remodeling
Authors: Treadwell Benjamin V. , Pavia Michele , Towle Christine A. , Cooley Vernon J. , Mankin Henry J.
Published: February 2005

The work described here demonstrates the synthesis by human articular cartilage of plasminogen activator inhibitor‐1 (PAI‐1), a potent inhibitor of the serine protease tissue plasminogen activator (tPA). We also present data demonstrating an increase in PAI‐1 messenger ribonucleic acid (mRNA) in chondrocytes exposed to the cytokine interleukin‐1 (IL‐1). Interestingly, this elevation of steady‐state mRNA levels does not appear to result in an increase in synthesis of PAI‐1 protein. Northern blot analysis reveals that of the two mRNA species (3.4 kb, 2.4 kb) previously reported for PAI‐1, only the larger species (3.4 kb) appears to be synthesized by chrondrocytes. Our data demonstrate the IL‐1‐stimulated production by cartilage of tissue plasminogen activator. We also show evidence for the presence of plasminogen in cartilage. A scheme is presented indicating the probable importance of the serine proteases (tPA and plasminogen) and PAI‐1 in cartilage degradation.
Intramuscular pressure and electromyography in four shoulder muscles
Authors: Järvholm Ulf , Palmerud Gunnar , Karlsson Dan , Herberts Peter , Kadefors Roland
Published: February 2005

Estimations of shoulder muscle load are important in biomechanic and ergonomic research. We have studied shoulder muscle load in the trapezius (six subjects), deltoid (six subjects), infraspinatus (eight subjects), and supraspinatus (seven subjects) muscles with simultaneous intramuscular pressure (IMP) and intramuscular bipolar electromyography (EMG) recordings. For imposition of shoulder muscle load, the arm was positioned in abduction or flexion with different hand loads (0, 1, or 2 kg), or isometric force registrations were performed. The microcapillary infusion technique was used for IMP recordings. The IMP in the supra‐ and infraspinatus muscles were high compared with the trapezius and deltoid muscles in abducted arm positions. In all test situations, IMP and EMG gave a similar description of local muscle load. IMP at maximal voluntary contraction was highest in the supraspinatus and infraspinatus muscles. Both IMP and EMG in all four muscles showed an almost linear correlation to recorded isometric external force. The difference in IMP between shoulder muscles in the same arm position may be due to muscle anatomy, muscle function, and compliance of surrounding tissues. Because a high IMP may impede muscle blood flow, our findings may possibly explain the physiological stress on the rotator cuff muscles as compared with the deltoid and trapezius muscles in work with elevated arms.