bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of molecular weight, calcium stearate, and sterilization methods on the wear of ultra high molecular weight polyethylene acetabular cups in a hip joint simulator
Authors: McKellop Harry A. , Shen Fu‐Wen , Campbell Patricia , Ota Troy
Published: February 2005

Orthopaedic surgeons must currently choose from several types of ultra high molecular weight polyethylene acetabular cups that differ in their material properties and in the methods used for their sterilization. Information on the wear resistance of these different cups may help in the selection process. This study included two separate tests for wear run on a hip simulator to investigate the effect of molecular weight, calcium stearate, and sterilization methods on the wear resistance of ultra high molecular weight polyethylene acetabular cups. Test 1 revealed nearly identical wear rates for acetabular cups with molecular weights in two distinct ranges, as well as for cups with molecular weights in the same range but with or without calcium stearate added. In Test 2, cups that were sterilized in air with gamma irradiation exhibited lower rates of wear than those sterilized with ethylene oxide, presumably due to the crosslinking induced by the irradiation. In addition, cups that were irradiated while packed in a partial vacuum to minimize oxygen absorbed in the surface layer initially showed lower rates of wear than those irradiated in air, with the wear rates becoming similar as wear penetrated the more oxidized surface layer and the more crosslinked subsurface region. Because these tests were run a few months after the irradiation, the potential effects of long‐term oxidation of any residual free radicals in the irradiated materials could not be taken into account. After artificial aging to accelerate oxidative degradation of the materials, the wear rates could be markedly different. Analyses performed after wear indicated that the irradiated (i.e., crosslinked) cups exhibited a smaller proportion of, as well as shorter, fibrils in the wear debris and an increased crystallinity and melting temperature and that gamma irradiation in the low‐oxygen environment reduced the level of oxidation and increased the level of crosslinking in the surface region of the cups.
Increased expression of matrix metalloproteinase‐1 in osteocytes precedes bone resorption as stimulated by disuse: Evidence for autoregulation of the cell's mechanical environment?
Authors: Rubin Clinton , Sun Yan‐Qun , Hadjiargyrou Michael , McLeod Kenneth
Published: February 2005

An in vivo animal model of bone adaptation was used to examine a possible role for matrix metalloproteinase‐1 in the local mediation of bone remodeling: to corrode the coupling of osteocytes to the matrix in an attempt to autoregulate the cell's perception of its mechanical environment. Twelve young (12–16 months old) skeletally mature turkeys were separated into groups to be studied for stimulus periods of either 3 or 30 days. In each animal, the left ulna was functionally isolated and subjected to either disuse or 3,000 microstrain at 1 Hz for 10 minutes per day. The right ulna remained intact and served as an intra‐animal control. No significant differences in bone area were detected at 3 days; however, ulnae subjected to disuse lost 8 ± 4% (±SD) of bone area by 30 days. Over the same period, ulnae subjected to the mechanical stimulus gained 21 ± 9% of bone area. With use of in situ reverse transcription‐polymerase chain reaction, less than 2% of the osteocytes examined from the intact control ulnae stained positively for matrix metalloproteinase‐1 mRNA. An antibody raised against matrix metalloproteinase‐1 revealed no positively labeled osteocytes in the intact ulnae. This low percentage of osteocytes expressing matrix metalloproteinase‐1 mRNA was similar to that seen in ulnae subjected to the osteogenic mechanical stimuli. In contrast, ulnae subjected to either 3 or 30 days of disuse showed evidence of matrix metalloproteinase‐1 mRNA activity in a high percentage of osteocytes (89 ± 5 and 66 ± 8%, respectively; each time point significantly different from intact ulnae, as well as from each other, p < 0.05). The percentage of osteocytes labeled with the anti‐matrix metalloproteinase‐1 antibody was also highly elevated following 3 days of disuse (74 ± 17%). These data demonstrate that an early response of bone to disuse is the upregulation of matrix metalloproteinase‐1 activity in osteocytes. It is proposed that this upregulation of collagenase activity is indicative of the cell's degradation of coupling to the matrix, and it thus reflects the osteocyte's regulation of its own mechanical environment. We believe that such autoregulation of the osteocyte's physical environment will accommodate subtle changes in the bone's functional environment without the need to add or resorb bone tissue.
Effect of lengthening rate on angiogenesis during distraction osteogenesis
Authors: Li G. , Simpson A. H. R. W. , Kenwright J. , Triffitt J. T.
Published: February 2005

This study investigated the angiogenic response to four varying rates (0.3, 0.7, 1.3, and 2.7 mm/day) of distraction in a rabbit model of leg‐lengthening. Immunostaining was performed with use of specific antibodies to type‐IV collagen and endothelial cell antigen to examine semiquantitatively the presence of blood vessels in the developing tissues. With use of the Chalkley counting method, the greatest number of positive staining blood vessel cells was found in the central fibrous zone of the groups that underwent lengthening at 0.7 and 1.3 mm/day compared with any other zone in any group (p < 0.05, t test). There were no statistical differences in the positive labeling indices in the mineralization front and the new bone zone adjacent to the mineralization front in any of the groups. However, the decrease in the number of positive‐staining blood vessel cells in the new bone zone distant to the mineralization front compared with any other zone in any group was statistically significant. The results suggest that during distraction osteogenesis, the precursor cells of new capillaries were present in abundance within the fibrous interzone. These cells connected into the capillary network at the junction of the mineralization front and the fibrous zone. The angiogenic response was weaker in the more mature regions within the new bone zones. A slow rate of distraction (0.3 mm/day) did not maximally stimulate angiogenesis in the central fibrous zone, whereas high rates (2.7 mm/day) appeared to impair this response. In this model of distraction osteogenesis, the vascularization process in the central fibrous zone was maximally stimulated at distraction rates of 0.7 and 1.3 mm/day.
Experimental acute hematogenous osteomyelitis in mice. I. Histopathological and immunological findings
Authors: Chadha Harbinder S. , Fitzgerald Robert H. , Wiater Patrick , Sud Suda , Nasser Sam , Wooley Paul H.
Published: February 2005

This study investigated immunological responses to Staphylococcus aureus bone infection. Because considerable immunological information is available on the mouse, a murine model of acute hematogenous osteomyelitis was established. Osteomyelitis was created in the proximal tibia of C3H/HeJ mice by a tibial epiphyseal fracture followed by intravenous bacterial inoculation with Staphylococcus aureus (strain LS‐1). Swelling and warmth of the limb was found, and following limb exposure, abscess formation was evident in the proximal tibia. Histological examination revealed distortion primarily at the hypertrophic zone of the physis and polymorphonuclear leukocyte infiltration throughout the damaged area of the proximal tibia. Local infection was demonstrated at the fracture site, evidenced by the recovery of Staphylococcus aureus following microbiological analysis of tissue specimens. Polymerase chain reaction was utilized to detect 16S ribosomal prokaryotic nucleic acid to demonstrate that the diagnosis of osteomyelitis could be established in the absence of conventional microbiological techniques. The infected mice had an increase of circulating large leukocytes (granulocytes) and an elevation of total serum immunoglobulin. Flow cytometry revealed significant increases in splenic B lymphocytes and in lymph‐node CD4+ T lymphocytes. These results indicate that an experimental model of acute hematogenous osteomyelitis that closely resembles the pathology of the disease in humans may be consistently induced in mice. Furthermore, marked immunological changes may be observed in response to the Staphylococcus aureus bone infection.
Increased interleukin‐1β production in the synovium of glenohumeral joints with anterior instability
Authors: Gotoh Masafumi , Hamada Kazutoshi , Yamakawa Hideyuki , Nakamura Masato , Yamazaki Hitoshi , Inoue Akio , Fukuda Hiroaki
Published: February 2005

Macroscopic synovitis of the glenohumeral joint is frequently seen during arthroscopy in patients with anterior instability. Interleukin‐1β is known to be expressed in inflamed tissue, to correlated with the magnitude of inflammation, and to affect articular cartilage in the joint. We hypothesized that chronic synovitis may occur in the glenohumeral joint in patients with anterior instability. The purpose of this study was to examine the expression of interleukin‐1β in the synovium of the glenohumeral joint with anterior instability and to discuss its clinicopathologic significance. Specimens of synovial tissue around the greater tuberosity in the subacromial synovium (as controls) and around the rotator interval in the glenohumeral synovium were obtained from 10 patients who had anterior instability without signs of subacromial impingement. Semiquantitative reverse transcriptase‐polymerase chain reaction was used to compare the levels of interleukin‐1β mRNA expression in the glenohumeral joint with those in the subacromial bursa. We also employed immunohistochemistry and in situ reverse transcriptase‐polymerase chain reaction to detect the cells producing interleukin‐1β protein and mRNA. The levels of interleukin‐1β mRNA expression were significantly higher in the glenohumeral joint than in the subacromial bursa (p < 0.01). Histology showed nonspecific inflammation in all 10 samples of glenohumeral synovium, whereas no inflammation was seen in seven of 10 samples of subacromial synovium. Immunohistochemistry identified interleukin‐1β protein in the vessels and inflammatory and synovial cells (from lining to sublining layers) in synovium of the glenohumeral joint, whereas immunoreactivity was negative in seven subacromial bursa. The remaining three synovial specimens of subacromial bursa, however, showed positive immunoreactivity that was unremarkable and confined around the vessels. In situ reverse transcriptase‐polymerase chain reaction was exclusively performed in the synovial specimens of the glenohumeral joint, which exhibited a positive reaction (in the same kinds of cells as seen with immunohistochemistry) in the lining and sublining layers and to a lesser extent in the stroma. Thus, our data confirmed the increased production of interleukin‐1β in the synovium of the glenohumeral joint in patients with anterior instability, suggesting the presence of chronic inflammation at the site. We conclude that this chronic synovitis may be partly associated with the development of dislocation arthropathy in the long term.
Characterization of chemotactic migration and growth kinetics of canine knee ligament fibroblasts
Authors: Hannafin Jo A. , Attia Erik T. , Warren Russell F. , Bhargava Madhu M.
Published: February 2005

Migration and proliferation of ligament fibroblasts are essential for the healing of ligament injuries. This study was designed to evaluate the migration of intraarticular (anterior and posterior cruciate) and extraarticular (medial and lateral collateral) ligament fibroblasts in response to cytokines and to determine the effect of cell passage on cell proliferation. Recombinant human platelet‐derived growth factor, hepatocyte growth factor/scatter factor, and bone morphogenic protein‐2 stimulated the migration of all ligament cells in a dose‐dependent manner, with optimal migration at 10 ng/ml. Recombinant human epithelial growth factor preferentially stimulated the migration of intraarticular ligament fibroblasts, whereas recombinant human interleukin‐1 was more effective with extraarticular ligament fibroblasts. Recombinant human insulin‐like growth factor‐1, insulin‐like growth factor‐2, transforming growth factor‐beta, and fibroblast growth factor had no significant effect on the migration of ligament‐derived fibroblasts. These data suggest that specific cytokines stimulate the migration of knee ligament fibroblasts and provide a rationale for possible therapeutic approacnes to optimize ligament healing. Fibroblasts derived from the anterior cruciate ligament have been shown to proliferate at a slower rate than those derived from the medial collateral ligament. We have extended these observations and have demonstrated that fibroblasts from both the posterior and anterior cruciate ligaments proliferate at a slower rate than lateral and medial collateral ligament‐derived fibroblasts. The differences between the growth rates of intraarticular and extraarticular fibroblasts become insignificant with serial passaging of the cells.
Estrogen level alters the failure load of the rabbit anterior cruciate ligament
Authors: Slauterbeck James , Clevenger Chris , Lundberg William , Burchfield Daniel M.
Published: February 2005

We hypothesized that increasing the level of circulating serum estrogen would decrease the load at failure for the rabbit anterior cruciate ligament. We developed an animal model in which hormonal manipulations could be correlated with load at failure for the anterior cruciate ligament. Sixteen New Zealand White ovariectomized rabbits were matched and divided into two groups. The eight rabbits that were not treated with the estrogen supplement (Group O) and the eight that were treated with the supplement (Group E) were housed for 30 days. Serum estrogen levels were measured. The knees were stripped of all soft tissue, and the load at failure for the anterior cruciate ligament was measured in a materials testing machine with a displacement rate of 0.5 mm/sec. The load at failure for all 16 specimens in Group E (446 ± 54 N) (mean ± SD) was significantly reduced (p = 0.02) compared with that for the nine specimens in Group O (503 ± 48 N). It is recognized that an increased number of anterior cruciate ligament injuries occurs in female athletes. Although the mechanism responsible for failure of the anterior cruciate ligament in women is yet to be defined, this experiment suggests that estrogen may alter ligament strength.
Influences of inflation rate and duration on vasodilatory effect by intermittent pneumatic compression in distant skeletal muscle
Authors: Liu Kang , Chen Long‐En , Seaber Anthony V. , Urbaniak James R.
Published: February 2005

Previous study has demonstrated that application of intermittent pneumatic compression on legs can cause vasodilation in distant skeletal muscle at the microcirculation level. This study evaluated the influence of inflation rate and peak‐pressure duration on the vasodilatory effects of intermittent pneumatic compression. The cremaster muscles of 50 male rats were exposed and divided into five groups of 10 each. A specially designed intermittent pneumatic‐compression device was applied in a medial‐lateral fashion to both legs of all rats for 60 minutes, with an inflation rate and peak‐pressure duration of 0.5 and 5 seconds, respectively, in group A, 5 and 0 seconds in group B, 5 and 5 seconds in group C, 10 and 0 seconds in group D, and 10 and 5 seconds in group E. Diameters of arterial segments were measured in vessels of three size categories (10–20, 21–40, and 41–70 μm) for 120 minutes. The results showed that the greatest increase in diameter was produced by intermittent pneumatic compression with the shortest inflation rate (0.5 seconds). A moderate increase resulted from compression with an inflation rate of 5 seconds, and no effective vasodilation occurred during compression with the longest inflation rate (10 seconds). When the groups with different inflation rates but the same peak‐pressure duration were compared, there was a significant difference between any two groups among groups A, C, and E and between groups B and D. When the groups with different peak‐pressure durations but the same inflation rate were compared, compression with a peak‐pressure duration of 5 seconds caused a generally similar degree of diameter change as did compression without inflation at peak pressure. The findings suggest that inflation rate plays an important role in the modulation of distant microcirculation induced by intermittent pneumatic compression whereas peak‐pressure duration does not significantly influence the vasodilatory effects of the compression. This may be due to the fact that rapid inflation produces a significant increase in shear stress on the vascular wall, which stimulates vascular endothelium to release nitric oxide, causing systemic vasodilation.
Tensile properties of articular cartilage are altered by meniscectomy in a canine model of osteoarthritis
Authors: Elliott Dawn M. , Guilak Farshid , Parker Vail T. , Wang Jean Y. , Setton Lori A.
Published: February 2005

Loss of or damage to the meniscus alters the pattern of loading in the knee joint and frequently leads to cartilage degeneration and osteoarthritis. The mechanical properties of articular cartilage have been shown to reflect the extent of cartilage degeneration in human osteoarthritis and in experimental models of joint disease, but there is little experimental data documenting changes in cartilage mechanics following meniscectomy. We hypothesized that the tensile properties of the surface zone of articular cartilage are altered following total medial meniscectomy. Twelve mongrel dogs underwent complete resection of the medial meniscus in the right knee, and the femoral cartilage was studied 12 weeks after the operation. We performed uniaxial, tensile stress‐relaxation tests to determine the equilibrium tensile modulus of surface‐zone cartilage. Water and glycosaminoglycan content were also measured at site‐matched locations. The tensile moduli of the cartilage decreased significantly following meniscectomy. The linear region modulus decreased by 40%, from 25.5 ± 7.7 to 15.3 ± 7.2 MPa. There was a weak (r = −0.45), but significant, correlation between the linear region modulus and the gross morphological grade for cartilage damage. Water and glycosaminoglycan content did not change following meniscectomy. Composition was not correlated with mechanical properties or morphological grade, suggesting that cartilage structure may play a more important role than composition in determining the mechanical properties. The observed decrease in cartilage material properties provides a quantitative measure of the loss of cartilage function following meniscectomy and reflects a pattern of change that is consistent with damage to the collagen‐proteoglycan solid network.
Dynamic measurement of bone blood perfusion with modified laser doppler imaging
Authors: Chan Roxane C. , Forrester Kevin , McDougall Jason J. , Bray Robert C. , Zernicke Ronald F.
Published: February 2005

Although the mechanisms are not clearly defined, blood flow may play an important role in moderating skeletal adaptation. Most techniques currently available to measure blood flow in bone are time‐consuming and require destruction of the tissue, but laser Doppler technology offers a less invasive method. The present study assessed whether laser Doppler perfusion imaging could detect changes in perfusion in cortical bone. By use of modified laser Doppler perfusion imaging with an adjustable, incorporated, near infrared‐laser gain photodetection system, perfusion of blood in the mid‐diaphyseal tibial cortex of New Zealand White rabbits (n = 5) was measured before, during, and after occlusion of the femoral artery. During occlusion, perfusion decreased 69% compared with control levels; removal of the arterial clip caused flux values to return to near normal. Laser Doppler perfusion imaging provides a two‐dimensional image related to blood flow, and the results of this pilot study suggest that it may be an effective technique for imaging in vivo dynamic changes in perfusion in cortical bone.
Pertussis toxin‐sensitive G proteins as mediators of stretch‐induced decrease in nitric‐oxide release of osteoblast‐like cells
Authors: Hara Fumihiko , Fukuda Kanji , Ueno Mitsuo , Hamanishi Chiaki , Tanaka Seisuke
Published: February 2005

Mechanical loading plays an important role in regulating bone remodeling, and nitric oxide may be one regulator of this process. To determine how mechanical stress modulates osteoblast function, we loaded cyclic tensile stretch on osteoblast‐like cells and measured levels of nitric oxide in the medium. High frequency of stretch at any magnitude inhibited release of nitric oxide; however, low frequency of stretch enhanced its release from the static control. To examine the involvement of G protein (guanine nucleotidebinding regulatory protein) in stress‐inhibited release of nitric oxide, we added pertussis toxin, a specific inhibitor of the Gi class, and found that it completely reversed the stress‐inhibited release. These data support the idea that pertussis toxin‐sensitive G protein is activated in the presence of cyclic tensile stretch.
Novel formulation of fibroblast growth factor‐2 in a hyaluronan gel accelerates fracture healing in nonhuman primates
Authors: Radomsky Michael L. , Aufdemorte Thomas B. , Swain Larry D. , Casey Fox W. , Spiro Robert C. , Poser James W.
Published: February 2005

Recent advances in understanding the biology of fracture healing and the availability of specific macromolecules has resulted in the development of novel treatments for injuries to bone. Fibroblast growth factor‐2 or basic fibroblast growth factor (4 mg/ml), a potent mitogen, and hyaluronan (20 mg/ml), an extra‐cellular matrix component, were combined into a viscous gel formulation intended for direct, percutaneous injection into fresh fractures. In an experimental primate fracture model, a bilateral 1‐mm‐gap osteotomy was surgically created in the fibulae of baboons. A single direct administration of this hyaluronan/fibroblast growth factor‐2 formulation to the defect site significantly promoted local fracture healing as evidenced by increased callus formation and mechanical strength. Radiographic analysis showed that the callus area was statistically significantly larger at the treated sites than at the untreated sites. Specimens treated with 0.1, 0.25, and 0.75 ml hyaluronan/fibroblast growth factor‐2 demonstrated a 48, 50, and 34% greater average load at failure and an 82, 104, and 66% greater energy to failure than the untreated controls, respectively. By histologic analysis, the callus size, periosteal reaction, vascularity, and cellularity were consistently more pronounced in the treated osteotomies than in the untreated controls. These results suggest that hyaluronan/fibroblast growth factor‐2 may provide a significant advance in the treatment of fractures.
Osteoclastogenesis is repressed by mechanical strain in an in vitro model
Authors: Rubin J. , Fan X. , Biskobing D. M. , Taylor W. R. , Rubin C. T.
Published: February 2005

Functional loading provides a site‐specific signal for the regulation of bone mass and morphology. To determine if strain can inhibit the resorptive component of bone remodeling, osteoclast formation was assessed in marrow cultures plated on flexible membranes subjected to 5% strain for 10 cycles/minute, 24 hours per day. Cultures strained during days 2 through 7 inhibited osteoclast formation to 61 ± 7% of control cultures (P < 0.05), a degree of inhibition similar to that observed when the cultures were subjected to strains during only days 2 through 4 but also evaluated on day 7 (67 ± 4% of control; p < 0.05). In contrast, straining of cultures during days 5 through 7 had little influence on inhibiting the formation of osteoclasts (94 ± 5% of control; no significant difference). The nonuniformly strained substrate was subdivided into three concentric rings, and cultures were used to examine the site‐specificity of the inhibition caused by strain. Osteoclast formation in the outermost boundary, Which was distended from 3.6 to 5%, was 41 ± 7% of that observed in outer regions of control wells. The inhibitory potential of mechanical strain was reduced within the middle ring (73 ± 6% of control osteoclasts: p < 0.01). where the strain ranged from 0.2 to 3.6%. The central region, which experienced strains equivalent to those in the middle ring (0.2 to ‐4% strain), showed inhibition of osteoclast formation to a similar degree (75 ± 6% of control). Media harvested from strained cultures failed to inhibit osteoclast formation in unstrained cultures; this implies that the inhibitory effect of strain depended on the direct interaction of the cell with the substrate rather than by a humoral factor. A second device, where a uniform strain was delivered at 1.8% throughout the entire plate, inhibited osteoclast recruitment to 48 ± 3.6%, emphasizing that uniform strain in the absence of shear stress constrains osteoclast recruitment. These in vitro experiments can but model the complex environment generated by in vivo mechanical strains; however, they provide the first direct evidence that strain must be considered as inhibitory to osteoclast recruitment.
Step activity monitor: Increased accuracy in quantifying ambulatory activity
Authors: Shepherd Eric F. , Toloza Eileen , McClung Christian D. , Schmalzried Thomas P.
Published: February 2005

This study compares the accuracy of a two‐dimensional accelerometer worn on the ankle (a step activity monitor) with that of an electronic, digital pedometer worn on the belt line. Twenty‐nine human subjects were evaluated while they briskly walked 400 M, slowly walked 10 M, and ascended and descended a flight of stairs. The step activity monitor had less error in all activities; its mean absolute error was 0.54%, whereas that of the pedometer was 2.82%. The difference was more pronounced in obese subjects (body mass index greater than 30), with an overall mean absolute error of 0.48% for the step activity monitor and 6.12% for the pedometer (nearly 13 times that of the step activity monitor). For subjects with a body mass index less than 30, the step activity monitor had an overall error of 0.56% and the pedometer had an overall error of 1.56% (less than 3 times that of the step activity monitor). The absolute error of the pedometer was positively correlated with body mass index (r = 0.792, p < 0.0001) and weight (r = 0.753, p < 0.0001), whereas the error of the step activity monitor was not significantly correlated with either. Neither device was significantly biased by age, gender, or the presence of a lower‐extremity joint prosthesis. The accuracy and additional capabilities, including a real‐time memory record of activity, of the step activity monitor make it well suited for objectively quantifying ambulatory activity, especially for obese subjects.
Ultrasonographic measurement of the mechanical properties of the sole under the metatarsal heads
Authors: Wang Chung‐Li , Hsu Tsz‐Ching , Shau Yio‐Wha , Shieh Jeng‐Yi , Hsu Kuang‐Hung
Published: February 2005

The sole under the metatarsal heads functions as a shock absorber during walking and running. The mechanical properties of the sole provide the primary defense against the development of metatarsalgia and foot ulceration. However, limited information about these properties has been documented. In this study, we used ultrasonography to evaluate the mechanical properties, including unloaded thickness, compressibility index, elastic modulus, and energy dissipation ratio, of the sole in 20 healthy subjects. The unloaded thickness decreased progressively from the first to the fifth metatarsal heads, with values of 1.50, 1.36, 1.25, 1.14, and 1.04 cm. The sole under the first metatarsal head had the greatest values for the compressibility index and elastic modulus (55.9% and 1.39 kg/cm2), and the sole under the third metatarsal head had the smallest values (50.8% and 1.23 kg/cm2). The sole under the fifth metatarsal head had the greatest energy dissipation ratio (33.7%), followed by that under the third, second, first, and fourth metatarsal heads. Multivariate adjusted linear regression showed that the unloaded thickness, compressibility index, and elastic modulus values increased significantly with age and body weight (p < 0.05) and that the energy dissipation ratio increased significantly with body weight (p < 0.05).
Shear mechanical properties of human lumbar annulus fibrosus
Authors: Iatridis James C. , Kumar Sanjay , Foster Robert J. , Weidenbaum Mark , Mow Van C.
Published: February 2005

Function, failure, and remodeling of the intervertebral disc are all related to the stress and strain fields in the tissue and may be calculatd by finite element models with accurate material properties, realistic geometry, and appropriate boundary conditions. There is no comprehensive study in the literature investigating the shear material properties of the annulus fibrosus. This study obtained shear material properties of the annulus fibrosus and tested the hypothesis that these properties are affected by the amplitude and frequency of shearing, applied compressive stress, and degenerative state of the tissue. Cylindrical specimens with an axial orientation from seven nondegenerated and six degenerated discs were tested in torsional shear under dynamic and static conditions. Frequency sweep experiments over a physiological range of frequencies (0.1‐100 rad/sec) at a shear strain amplitude of 0.05 rad were performed under three different axial compressive stresses (17.5, 25, and 35 kPa). At the largest compressive stress, shear strain sweep experiments (strain amplitude range: 0.005‐0.15 rad at a frequency of 5 rad/sec) and transient stress‐relaxation tests (shear strain range: 0.02‐0.15 rad) were performed. The annulus fibrosus material was less stiff and more dissipative at larger shear strain amplitudes, stiffer at higher frequencies of oscillation, and stiffer and less dissipative at larger axial compressive stresses. The dynamic shear modulus, |G*|, had values ranging from 100 to 400 kPa, depending on the experimental condition and degenerative level. The shear behavior was also predominantly elastic, with values for the tangent of the phase angle (tanδ) ranging from 0.1 to 0.7. The annulus material also became stiffer and more dissipative with degenerative grade; however, this was not statistically significant. The results indicated that nonlinearities, compression/shear coupling, intrinsic viscoelasticity, and, to a lesser degree, degeneration all affect the shear material behavior of the annulus fibrosus, with important implications for load‐carriage mechanisms in the intervertebral disc. These material complexities should be considered when choosing material constants for finite element models.
Gene expression in menisci from the knees of skeletally immature and mature female rabbits
Authors: Le Graverand Marie‐Pierre Hellio , Reno Carol , Hart David A.
Published: February 2005

This study, using the sensitive molecular technique of semiquantitative reverse transcription‐polymerase chain reaction, evaluated mRNA levels for several molecules in medial and lateral menisci from the knees of skeletally mature and immature rabbits. Total RNA was extracted from the medial and lateral menisci of New Zealand White rabbits with the TRIspin method. Total RNA and DNA were similar in the two menisci of both immature and mature rabbits. The total RNA was reverse‐transcribed and analyzed by semiquantitative polymerase chain reaction using rabbit‐specific primer sets; levels of mRNA for a subset of molecules differed between the medial and lateral menisci. These variations in mRNA levels were also influenced by the degree of skeletal maturity of the rabbits. For most of the genes, mRNA levels were generally higher in the medial than in the lateral meniscus. The medial meniscus from immature and mature rabbits had significantly increased levels of mRNA for molecules such as transforming growth factor‐β, cyclooxygenase‐2, and tissue inhibitor of metalloprotease‐1. In contrast, compared with mRNA in the lateral meniscus, that for types II and III collagen, biglycan, insulin‐like growth factor‐2, plasminogen activator inhibitor‐1, and matrix metalloprotease‐1 was significantly increased in the medial meniscus of mature rabbits only and that for versican and type‐I collagen was significantly increased in the medial meniscus of immature rabbits only. Levels of mRNA for inducible nitric oxide synthase and basic fibroblast growth factor were similar in both menisci for both age groups. The present study demonstrates that regulation of mRNA levels in medial and lateral menisci is tissue‐specific and influenced by the skeletal maturity of the animals.
PT‐12, a putative ras‐activated proliferation‐dependent gene, is expressed in patellar tendon and not in anterior cruciate ligament
Authors: Goomer R. S. , Maris T. , Ostrander R. , Amiel D.
Published: February 2005

We describe a gene (PT‐12) that is expressed in the patellar tendon and not in the anterior cruciate ligament. We used a recently developed polymerase chain reaction‐based subtractive cDNA analysis to discover genes that are overexpressed in the patellar tendon but not expressed in the anterior cruciate ligament; the long‐term objective was to find genes that are central to the self‐repair of the patellar tendon, in contrast with the inability of the anterior curciate ligament to launch a repair response following injury. PT‐12 is a homologue of human S2 or mouse LLRep3 ribosomal genes, which are known to be overexpressed in highly proliferating cells. This study opens a new vista to the development of techniques and reagents to study the differences between two periarticular tissues (i.e., the patellar tendon and anterior cruciate ligament) that differ primarily in their ability to self‐repair.
In situ force distribution in the glenohumeral joint capsule during anterior‐posterior loading
Authors: Debski Richard E. , Wong Eric K. , Woo Savio L‐Y. , Sakane Masataka , Fu Freddie H. , Warner Jon J. P.
Published: February 2005

Our objective was to examine the function of the glenohumeral capsule and ligaments during application of an anterior‐posterior load by directly measuring the in situ force distribution in these structures as well as the compliance of the joint. We hypothesized that interaction between different regions of the capsule due to its continuous nature results in a complex force distribution throughout the glenohumeral joint capsule. A robotic/universal force‐moment sensor testing system was utilized to determine the force distribution in the glenohumeral capsule and ligaments of intact shoulder specimens and the joint kinematics resulting from the application of external loads at four abduction angles. Our results suggest that the glenohumeral capsule carries no force when the humeral head is centered in the glenoid with the humerus in anatomic rotation. However, once an anterior‐posterior load is applied to the joint, the glenohumeral ligaments carry force (during anterior loading, the superior glenohumeral‐coracohumeral ligaments carried 26 ± 16 N at 0° and the anterior band of the inferior glenohumeral ligament carried 30 ± 21 N at 90°). Therefore, the patient's ability to use the arm with the humerus in anatomic rotation should not be limited following repair procedures for shoulder instability because the repaired capsuloligamentous structures should not carry force during this motion. Separation of the capsule into its components revealed that forces are being transmitted between each region and that the glenohumeral ligaments do not act as traditional ligaments that carry a pure tensile force along their length. The interrelationship of the glenohumeral ligaments forms the biomechanical basis for the capsular shift procedure. The compliance of the joint under our loading conditions indicates that the passive properties of the capsule provide little resistance to motion of the humerus during 10 mm of anterior or posterior translation with anatomic humeral rotation. Finally, this knowledge also enchances the understanding of arm positioning relative to the portion of the glenohumeral capsule that limits translation during examination under anesthesia.
Contrast‐enhanced magnetic resonance imaging in a nontraumatic rabbit osteonecrosis model
Authors: Sakai Takashi , Sugano Nobuhiko , Tsuji Takashi , Miyazawa Tomoaki , Nakamura Nobuo , Haraguchi Keiji , Ochi Takahiro , Ohzono Kenji
Published: February 2005

We investigated early osteonecrosis using in vivo magnetic resonance imaging in a nontraumatic rabbit model of serum‐sickness osteonecrosis in which osteonecrosis was induced after two intravenous injections of horse serum with a 3‐week interval. One week (group A, 17 rabbits) and 3 weeks (group B, 13 rabbits) after the second serum injection coronal magnetic resonance images of the femur were obtained and it was removed for histological study. Some of the necrotic lesions in the diaphysis were detected on T1‐weighted, T2‐weighted, or fat‐suppression T1‐weighted images (six of 24 necrotic lesions in group A and 16 of 18 in group B), and all of the necrotic lesions in the epiphysis, metaphysis, and diaphysis were detected on T1‐weighted or fat‐suppression T1‐weighted images enhanced with gadolinium‐diethylene triamine penta‐acetic acid. All focal homogeneous enhanced areas on T1‐weighted or fat suppression T1‐weighted images corresponded to necrotic lesions (22 of 24 necrotic lesions in group A and 18 of 18 in group B); the contours of the enhanced areas were displayed more clearly on the fat‐suppression T1‐weighted than on the T1‐weighted images. The fat‐suppression T1‐weighted image enhanced with gadolinium‐diethylene triamine pentaacetic acid was thus the most sensitive and specific of five kinds of magnetic resonance images for the detection of early necrotic lesions. The results suggest that this image may be useful for early diagnosis of clinical osteonecrosis and for obtaining information about the pathomechanism of osteonecrosis.
Measurement and removal of adherent endotoxin from titanium particles and implant surfaces
Authors: Ragab Ashraf A , Van De Motter Renee , Lavish Sandra A. , Goldberg Victor M. , Ninomiya James T. , Carlin Cathleen R. , Greenfield Edward M.
Published: February 2005

Aseptic loosening is thought to be due primarily to osteolysis induced by cytokines and prostaglandins that are produced in response to implant‐derived wear particles. Because endotoxin has many of the same effects as have been reported for wear particles, we hypothesized that adherent endotoxin may be responsible for the biological responses induced by wear particles. We demonstrated the presence of significant levels of adherent endotoxin on commonly used preparations of titanium particles as well as on titanium and titanium‐alloy implant surfaces. In contrast, supernatants obtained by centrifugation of particle suspensions contained approximately 1% as much endotoxin as did the particles. Therefore, it is erroneous to assume that particles do not contain endotoxin on the basis of data that it cannot be detected in their supernatants or filtrates. These results emphasize the importance of considering the potential role of adherent endotoxin when examining the in vitro effects of wear particles and the in vivo performance of orthopaedic implants. We also developed a protocol that removed more than 99.94% of the adherent endotoxin from the titanium particles without detectably affecting their size or shape. The removal of adherent endotoxin will allow comparison of the biological responses induced by particles with or without adherent endotoxin.
Integrative cartilage repair: Inhibition by β‐aminopropionitrile
Authors: Ahsan Tabassum , Lottman Lisa M. , Harwood Fred , Amiel David , Sah Robert L.
Published: February 2005

The effects of β‐aminopropionitrile, a known inhibitor of lysyl oxidase, on the extractability of newly synthesized collagen and integrative cartilage repair were determined in explant cultures of adult bovine articular cartilage. Dose‐escalation studies indicated that treatment of cartilage explants for 6 days with β‐aminopropionitrile caused a dose‐dependent inhibition of proteoglycan synthesis ([35S]sulfate incorporation) with a 50% inhibition at 2.2 mM. However, 0.25 mM β‐aminopropionitrile had no detectable effect on proteoglycan synthesis and was thus used for subsequent experiments. Treatment of cartilage with β‐aminopropionitrile for 14 days increased the extractability of newly synthesized collagen with 4 M guanidine‐HCI while having little effect on proteoglycan synthesis, proteoglycan deposition, or cartilage cellularity (DNA content). In untreated cultures, the percentage of radiolabeled collagen ([3H]hydroxyproline) that was extractable after 1 day of radiolabeling, 6 days of radiolabeling, or 6 days of label and 6 days of chase decreased from 81 to 25 and 9%, respectively. In β‐aminopropionitrile‐treated cultures, the extractability was relatively higher (96, 62, and 47%, respectively). Treatment with β‐aminopropionitrile after radiolabeling with [14C]lysine also significantly inhibited the formation of the reducible crosslink [14C]dihydroxylysinonorleucine without affecting the overall deposition in cartilage of [14C]lysine and [14C]hydroxylysine. In functional repair studies, treatment with β‐aminopropionitrile caused an almost complete inhibition of integration between pairs of cartilage explants maintained in apposition for 2 weeks. These results indicate that β‐aminopropionitrile blocks the formation of collagen crosslinks in cartilage explants and suggest that such crosslinks are critical to integrative cartilage repair.
Hyaluronan suppresses fibronectin fragment‐mediated damage to human cartilage explant cultures by enhancing proteoglycan synthesis
Authors: Kang Yong , Eger Wolfgang , Koepp Holger , Williams James M. , Kuettner Klaus E. , Homandberg Gene A.
Published: February 2005

Hyaluronic acid, recently renamed hyaluronan, has been used as a therapeutic intervention in the treatment of osteoarthritis. We have reported that high‐molecular‐weight (800 kDa) hyaluronan is effective in blocking the catabolic action of fibronectin fragments in explant cultures of bovine cartilage and in an experimentalin vivomodel of damage to the rabbit knee joint. The fibronectin fragments induce catabolic cytokines in human cartilage, which, in turn, suppress proteoglycan synthesis and induce matrix metalloproteinases to decrease the proteoglycan content. Since the clinical target of high‐molecular‐weight hyaluronan is human cartilage, which may differ in certain ways from bovine cartilage, we tested the effect on human knee cartilage. We found that 1 mg/ml hyaluronan completely blocked fibronectin fragment‐mediated decreases in proteoglycan content in five of five specimens of cartilage from the human knee. This was associated with binding of exogenous hyaluronan to the superficial surface, suppressed penetration of the fibronectin fragment into the cartilage, decreased expression for the first week in culture of one of the matrix metalloproteinases involved in cartilage degradation, matrix metalloproteinase‐3, and proteoglycan synthesis rates that increased to supernormal levels. However, the appearance of the NITEGE and VDIPEN neoepitopes, indices of cartilage degradation, was not blocked but was delayed by 1 week. The addition of hyaluronan to cartilage previously damaged by the fibronectin fragments or to osteoarthritic cartilage fully restored the proteoglycan content to control levels. We conclude that hyaluronan blocked damage at least partly by blocking penetration of the fibronectin fragments and slowing matrix metalloproteinase expression. However, the major effect on blocking damage and promoting repair may be through enhanced proteoglycan synthesis, a mechanism that requires further study. Nonetheless, these data clearly demonstrate that hyaluronan completely protected human cartilage in explant culture and facilitated a full restoration of proteoglycan in damaged cartilage.
Transplantation of cryopreserved osteochondral dowel allografts for repair of focal articular defects in an ovine model
Authors: Schachar Norman S. , Novak Kelli , Hurtig Mark , Muldrew Ken , McPherson Roger , Wohl Greg , Zernicke Ronald F. , McGann Locksley E.
Published: February 2005

The purpose of this study was to test whether successful cryopreservation of osteochondral tissue is possible and whether, with the appropriate surgical procedure, it can be used for the successful repair of focal articular defects within joints. Fresh (nonfrozen) and snap‐frozen (plunged in liquid nitrogen and thawed in a water bath at 37°C, repeated three times) autografts were used as positive and negative controls, respectively. Snap‐frozen, frozen (fresh tissue placed in a freezer at −80°C), and cryopreserved (immersed in 10% dimethyl sulfoxide for 30 minutes and then frozen at 1°C/min to −80°C) allografts were transplanted into the knees of adult sheep. Outcomes were evaluated 3, 6, and 12 months after transplantation. The morphological, histological, biochemical, and biomechanical behaviors and characteristics of the graft cartilage, the host cartilage adjacent to the grafts, and the opposing tibial cartilage were assessed. Freezing protocols that yielded poor chondrocyte recovery after thawing (frozen and snap‐frozen) resulted in poor overall graft outcome. The cryopreservation protocol, however, resulted in intermediate recovery (50%) of chondrocytes and in intermediate overall graft outcome compared with fresh autografts. The membrane integrity of the allograft chondrocytes immediately following cryopreservation was identified as the most reliable predictor of long‐term outcome of the graft. Further improvements in cryopreservation technique may lead to an effective method of banking osteochondral tissue for successful transplantation for the repair of focal defects and larger joint reconstructions.
Multidrug resistance‐1 and p‐glycoprotein in human chondrosarcoma cell lines: Expression correlates with decreased intracellular doxorubicin and in vitro chemoresistance
Authors: Wyman James J. , Hornstein Abby M. , Meitner Patricia A. , Mak Solida , Verdier Patrick , Block Joel A. , Pan J. , Terek Richard M.
Published: February 2005

We report on two chondrosarcoma cell lines, FS and AQ, that may be used as models of multidrug resistance in chondrosarcoma. Multidrug resistance‐1 expression was assayed with reverse transcription‐polymerase chain reaction. Immunostaining for the multidrug resistance‐1 product, P‐glycoprotein, was performed with the monoclonal antibody C494. Intracellular levels of doxorubicin were measured by fluorescent emission at 590 nm after 1 hour of incubation with the agent and again after 1, 2, and 4‐hour washout periods. Chemosensitivity was assayed by staining micropellet cultures of AQ and FS cells with fluorescein acetate before and after the cells were exposed to varying doses of doxorubicin for 48 hours. Cytotoxicity was assessed by comparison of computer‐processed images before and after treatment. The FS cell line was positive for multidrug resistance‐1 expression, stained heavily for P‐glycoprotein, and had significantly lower intracellular levels of doxorubicin than the AQ cell line, which was negative for multidrug resistance‐1 and P‐glycoprotein. Chemosensitivity testing showed that the FS cell line was significantly more resistant to doxorubicin than was the AQ cell line at all doses tested. Our results show that multidrug resistance‐1 expression in a human chondrosarcoma cell line results in resistance to doxorubicin in vitro.