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PubMed1996

The lateral synovial recess of the knee: anatomy and role in chronic Iliotibial band friction syndrome.

The tissue deep to the iliotibial band (ITB) and its relationship to the lateral knee joint capsule was studied anatomically and the histopathology of this tissue in chronic iliotibial band friction syndrome (ITBFS) was examined. Findings show that the tissue under the ITB consists of a synovium that is a lateral extension and invagination of the actual knee joint capsule and is not a separate bursa as described in the literature. Additionally, in cases of chronic ITBFS seen in young elite athletes, synovial tissue taken from this lateral synovial recess reveals histological evidence of inflammation and hyperplasia that suggests its involvement in the pathological process.

Adolescent↗
PubMed2000

Low-friction arthroplasty with Boneloc bone-cement: outcome at 2 to 4 years.

We report the clinical and radiologic outcome of 109 Chamley low-friction arthroplasties implanted with Boneloc bone-cement (Biomet, Bridgend, South Wales, UK) into 104 patients. The mean follow-up was 30 months (range, 2-48 months). There were 72 women (mean age, 71 years) and 32 men (mean age, 72). Cartridge-packed cement was used in 37 cases and vacuum-packed cement in 72 cases. Survivorship analysis based on revision for aseptic loosening showed 79% survival at 4 years. Seventeen (15.5%) hips have been revised for aseptic loosening to date, in which all stems and 4 cups were loose. Extensive femoral osteolysis was always present and resulted in 4 cases of femoral cortical perforation at revision. Survivorship analysis based on revision and radiologic failure showed only 55% survival over the same period. When radiologic loosenings were included as failures, the vacuum-packed cement performed significantly worse than the cartridge-packed cement it replaced. These poor results were consistent with the withdrawal of Boneloc from clinical use in 1995, and we recommend indefinite follow-up for surviving prostheses.

Aged↗
PubMed2000

Charnley low-friction arthroplasty for Paget's disease of the hip.

This study investigated the perceived risks and complications associated with total hip arthroplasty for Paget's disease. A total of 98 Charnley low-friction arthroplasties were performed on 76 patients, 27 men (37 hips) and 49 women (61 hips), whose average age was 67.4 years (range, 51-79 years). Intraoperative blood loss averaged 388 mL (range, 110-1,730 mL), and minor heterotopic ossification occurred in 24 hips (25%), with significant changes in 4 hips (4%). After average follow-up of 10.4 years (range, 5.5-20 years), 10 acetabular (10%) and 8 femoral (8%) implants had loosened aseptically, but there was no evidence of progressive protrusio acetabuli or femoral deformity after operation. Survivorship to revision was 98% at 10 years (95% confidence interval [CI], 95%-100%) and 91% at 15 years (95% CI, 80%-100%) for the acetabular component and 93% (95% CI, 87%-99%) and 89% (95% CI, 80%-99%) for the femur. The only increased risk identified was nonunion of the trochanteric osteotomy (13%).

Aged↗
PubMed2003

Influence of demographic and technical variables on the incidence of osteolysis in Charnley primary low-friction hip arthroplasty.

The influence of demographic and technical variables on the incidence of osteolysis in Charnley primary low-friction arthroplasty was investigated. Demographic variables included age, gender, diagnosis, and Charnley joint class. Technical variables included the design of acetabular and femoral components, subchondral plate retention versus removal, and cementing techniques. We analyzed 633 hips (in 494 patients) implanted by a single surgeon between 1970 and 1984 using Kaplan-Meier survival graphs. Radiographically determined osteolysis was defined as the end point. The incidence of osteolysis at 5 years was 2% (confidence interval [CI] +/- 0.5%); at 10 years, 8% (CI +/- 1.6%); at 15 years, 15% (CI +/- 2.2%); and at 20 years, 17% (CI +/- 3.5%). Younger patients (age < 65 years) and men were both found to have a significantly increased incidence of osteolysis (P<.05). No significant association with osteolysis was found for the other demographic and technical variables investigated. Osteolysis predates loosening and failure of hip arthroplasty. Regular assessment with the goal of earlier identification, especially in higher risk younger and male patients, is important to avoid excessive bone loss and technical difficulties in revision surgery.

Adolescent↗
PubMed1992

Factors influencing survivorship of the femoral component after primary low-friction hip arthroplasty.

Two hundred sixty-seven consecutive primary low-friction arthroplasties, followed for 5-18 years after surgery, were studied to assess the factors influencing survivorship of the femoral component, using the Kaplan-Meier method. The end point of survivorship was defined radiographically in two ways: incipient failure (subsidence of the femoral component of > or = 2 mm) and definite failure (progressive change of position). Twenty-two femoral components developed incipient failure, and twelve of these advanced to definite failure. A canal filling ratio of the stem of > or = 75%, cement extent distal to the stem tip of > or = 1 cm, use of an intramedullary bone plug, and an exaggerated valgus alignment of the stem correlated positively with survivorship of the femoral component. Calcar resorption and atrophy of the femoral cortex after surgery were associated with aseptic loosening of the femoral component.

Adult↗
PubMed1997

Femoral osteolysis after low-friction arthroplasty. A planimetric study and volumetric estimate.

Sixty-three cases of femoral osteolytic cavities were analyzed in a consecutive series of 680 low-friction arthroplasties of the hip performed in 598 patients between 1971 and 1979. Follow-up evaluation averaged 15 years 9 months (range, 2-22 years). The total cumulative probability of osteolysis developing after 20 years was 11% according to survivorship analysis. The mean time of appearance of the osteolytic lesion was 9 years 3 months after operation. Most of the cavities were seen in Gruen zones 3, 5, and 7 in decreasing order. Osteolytic cavities were classified as follows: group 1, cavities in cases with radiographic definite stem loosening (20 cases); group 2, cavities in cases with an acetabular wear equal to or greater than 2 mm (22 cases); and group 3, cavities in cases combining both of the above-mentioned findings (21 cases). Cementing defects such as voids and thin mantles were less frequent in group 2 than in groups 1 and 3 (P < .005). Poor clinical results were more frequent in groups 1 and 3 (P < .05), in all instances). Focal cavities were more frequent in group 2, and multifocal and diffuse cavities were more frequent in groups 1 and 3 (P < .05). The average planimetric area on radiographic diagnosis was 0.81 cm2, and the average approximate volume was 1.86 cm3, with significant differences among the three groups of cavities. Progression of the cavity area and volume was linear over time (P < .001) and more aggressive in groups 1 and 3 than in group 2 (P < .05). Thus, loosening of the stem was a more deciding factor than acetabular wear in the progression of cavities.

Adult↗
PubMed1998

Long-term results of cemented Charnley low-friction arthroplasty in patients aged less than 30 years.

The results of cemented Charnley low-friction arthroplasty in patients aged less than 30 years are presented. Eighty-three arthroplasties were performed on 55 patients with an average age of 24.9 years (range, 17-29 years) and an average follow-up period of 240 months (20 years; range, 62-360 months). There were 2 nonfatal pulmonary emboli, 2 cases of deep sepsis, and 3 fractured femoral implants. Twenty-eight acetabular components migrated (34%), 25 have been revised (30%), and the average annual acetabular wear rate was 0.12 mm. Sixteen femoral implants subsided (19%), and fracture of the tip of the cement mantle occurred in 8 hips (10%). Nineteen femoral components (23%) were revised; femoral osteolysis was seen in 15 hips (18%) and changes in the calcar in 33 (38%). Acetabular component survivorship was 92% (95% confidence interval, 85-98%) at 10 years, 70% (60-81%) at 20 years, and 68% (57-79%) at 25 years, with the figures for the femoral implant being 93% (87-98%), 76% (66-86%), and 73% (62-85%), respectively.

Adolescent↗
PubMed1998

Wear and fracture of the acetabular cup in Charnley low-friction arthroplasty.

Seven cases of progressive wear-out and fracture of the cemented high-density polyethylene cup in Charnley low-friction arthroplasty were identified in a group of 1,815 revisions of failed total hip arthroplasties. Normal function, rapid wear in the superolateral direction, and localized superolateral loss of bone-cement interface support with perfect medial cup fixation but, above all, asymptomatic nature of the problem until the moment of sudden failure were the characteristic features. The time to failure ranged from 11 to 20 years. Stem fixation remained unaffected. The findings suggest that the problem was wear-out without any changes that could have been attributed to the volume of high-density wear particles shed into the tissues.

Adult↗
PubMed1999

Charnley low-friction arthroplasty in rheumatoid patients: a survival study up to 20 years.

The survivorship of 1,553 consecutive Charnley low-friction arthroplasties (LFA) in 1,086 patients with rheumatoid arthritis (RA) were analyzed. There were 846 women (1,236 hips) and 240 men (317 hips), with a mean age of 53.1 years (range, 24-77 years; standard deviation, 10.7). A uniform postoperative regimen with protected weight bearing for 2 months (6 months in patients with bone grafting on the acetabular side) was used throughout the whole study. The overall survival with revision as the endpoint was 90.5% (95% confidence interval [CI], 88.7-92.2) at 10 years and 83% (95% CI, 80.3-85.7) at 15 years. The survival of the femoral component was 93.2% (95% CI, 91.8-96.7) and 89.9% (95% CI, 88.0-93.0) at 10 and 15 years, and survival of the acetabulum was 93.6% (95% CI, 92.1-95.1) and 87.1% (95% CI, 84.6-89.5) at 10 and 15 years. The indication for revision was late deep infection in 19 patients (1.2%) and in others aseptic loosening of prosthetic components. Young age, male sex, and secondary reactive amyloidosis impaired significantly the survival of LFA in the RA patients. In all, cemented LFA provided good results, and it can be justified for the treatment of hip destruction in RA.

Adult↗
PubMed2005

Significance of frictional heating for effects of high pressure homogenisation on milk.

High pressure homogenisation (HPH) is a novel dairy processing tool, which has many effects on enzymes, microbes, fat globules and proteins in milk. The effects of HPH on milk are due to a combination of shear forces and frictional heating of the milk during processing; the relative importance of these different factors is unclear, and was the focus of this study. The effect of milk inlet temperature (in the range 10-50 degrees C) on residual plasmin, alkaline phosphatase, lactoperoxidase and lipase activities in raw whole bovine milk homogenised at 200 MPa was investigated. HPH caused significant heating of the milk; outlet temperature increased in a linear fashion (0.5887 degrees C/ degrees C, R2=0.9994) with increasing inlet temperature. As milk was held for 20 s at the final temperature before cooling, samples of the same milk were heated isothermally in glass capillary tubes for the same time/temperature combinations. Inactivation profiles of alkaline phosphatase in milk were similar for isothermal heating or HPH, indicating that loss of enzyme activity was due to heating alone. Loss of plasmin and lactoperoxidase activity in HPH milk, however, was greater than that in heated milk. Large differences in residual lipase activities in milks subjected to heating or HPH were observed due to the significant increase in lipase activity in homogenised milk. Denaturation of beta-lactoglobulin was more extensive following HPH than the equivalent heat treatment. Inactivation of plasmin was correlated with increasing fat/serum interfacial area but was not correlated with denaturation of beta-lactoglobulin. Thus, while some effects of HPH on milk are due to thermal effects alone, many are induced by the combination of forces and heating to which the milk is exposed during HPH.

Alkaline Phosphatase↗
PubMed2001

Dielectric friction in capillary electrophoresis: mobility of organic anions in mixed methanol-water media.

The mobilities of a series of organic carboxylates and sulfonates, ranging in charge from -1 to -4, were investigated by capillary electrophoresis using buffers containing 0 to 75% (v/v) methanol. Effective mobilities were measured at a series of ionic strengths, and were extrapolated to zero ionic strength using Pitts' equation to yield absolute mobilities. Generally, higher-charged ions were more strongly influenced by ionic strength, as predicted by the Pitts' equation. Some differences in the ionic strength effects for anions of like charge were observed and were consistent with the relaxation effect. The absolute mobilities of anions were altered by the addition of methanol to the buffer. Analytes with higher charge-to-size ratios were slowed to a greater extent than were ions with lower charge-to-size. As a result, dramatic changes in relative mobility were observed, such as a reversal in migration order between anions of -1 and -4 charge at 75% methanol and 20 mM ionic strength. The mobility changes caused by the addition of methanol are attributed to dielectric friction. Mobilities in the methanol-water solutions were found to depend on analyte charge-to-size and solvent dielectric relaxation time (tau) and were inversely dependent upon solvent dielectric constant (epsilon), as predicted by the Hubbard-Onsager mobility model.

Journal Article↗
PubMed2003

Viscosity as an experimental tool in studying the mechanism of stereoselective and product-selective chemical transformations through frictional impositions.

In the present Account, we examine the viscosity dependence as a function of temperature, pressure, and solvent polarity for the double inversion in the photolytic azoalkane denitrogenation, the thermal isomerization of housanes, and stereochemical memory versus Curtin-Hammett behavior in radical-cation rearrangements. The analysis of these stereoselective and product-selective viscosity studies in terms of the simple free-volume model demonstrates the utility of frictional effects for the elucidation of complex reaction mechanisms in molecular transformations.

Journal Article↗
PubMed2003

Charge-transfer mechanism for cytochrome c adsorbed on nanometer thick films. Distinguishing frictional control from conformational gating.

Using nanometer thick tunneling barriers with specifically attached cytochrome c, the electron-transfer rate constant was studied as a function of the SAM composition (alkane versus terthiophene), the omega-terminating group type (pyridine, imidazole, nitrile), and the solution viscosity. At large electrode-reactant separations, the pyridine terminated alkanethiols exhibit an exponential decline of the rate constant with increasing electron-transfer distance. At short separations, a plateau behavior, analogous to systems involving -COOH terminal groups to which cytochrome c can be attached electrostatically, is observed. The dependence of the rate constant in the plateau region on system properties is investigated. The rate constant is insensitive to the mode of attachment to the surface but displays a significant viscosity dependence, change with spacer composition (alkane versus terthiophene), and nature of the solvent (H(2)O versus D(2)O). Based on these findings and others, the conclusion is drawn that the charge-transfer rate constant at short distance is determined by polarization relaxation processes in the structure, rather than the electron tunneling probability or large-amplitude conformational rearrangement (gating). The transition in reaction mechanism with distance reflects a gradual transition between the tunneling and frictional mechanisms. This conclusion is consistent with data from a number of other sources as well.

Adsorption↗
PubMed2005

Solvent friction effect on intramolecular electron transfer.

U-shaped donor-bridge-acceptor molecules with different electronic couplings have been investigated as a function of temperature in solvents with slow polarization relaxation, in particular, N-methylacetamide (NMA) and N-methylpropionamide (NMP). At high temperature, the electron-transfer rate is well described by a nonadiabatic model; however, the rate at low temperature is controlled by the solvent friction. The change of the electron-transfer mechanism is discussed and compared with theoretical models.

Journal Article↗
PubMed2005

Ultrafast electron dynamics at metal interfaces: intraband relaxation of image state electrons as friction.

Two-photon photoemission of image potential states above monolayers of p-xylene/Ag(111) shows that electrons with different momenta have very different rise and decay rates as a function of parallel momentum. The dynamics are due to energy and momentum loss (intraband relaxation), which we model as a stochastic process isomorphic to the overdamped motion of a harmonic oscillator. The method extracts a friction coefficient from the data which can be explained by electron-electron scattering in a formalism based on the Lindhard dielectric function. One-electron excitations (interband transistions) dominate the dissipation mechanism, with a smaller contribution from collective electronic excitations (plasmons).

Journal Article↗
PubMed2006

Generalization of the friction theory for viscosity modeling.

The friction theory (FT) approach relates the viscosity of a fluid to its equation of state (EoS), and it is known to give good results for a large number of compounds over wide ranges of temperature and pressure. Previous FT versions were restricted to use EoS of the van der Waals type, i.e., EoS explicitly consisting of a repulsive and an attractive term, which limited the number of usable EoS as well as the accuracy of the viscosity predictions. In this work, the restriction is removed by means of a pragmatic generalized definition of repulsive and attractive terms based on the internal pressure concept. As a result, the FT theory can be extended to practically all types of EoS, from theoretical ones (e.g., EoS based on thermostatistical or renormalization theories) to the highly accurate empirical reference EoS. In combination with the later, the FT is shown to represent experimental viscosity data for several fluids, including water, with an accuracy as high as that required for reference models. Additionally, some relevant phenomena, such as the critical anomaly, appear to follow naturally from the physics already built into the EoS.

Journal Article↗
PubMed2005

Packing of simulated friction modifier additives under confinement.

Molecular dynamics simulations have been conducted to obtain detailed information regarding molecular structure and packing of surfactant-like "friction modifier" (FM) chains adsorbed to two confining surfaces under sliding conditions. The simulations are interpreted via the density profile, position-dependent fluctuations in the density profile, and parallel, interlayer position correlation functions. Heterogeneous FM structures were obtained. The adsorbed FM chains were found to form semi-ordered monolayers perpendicular to the atomically well-defined surface, with distinct segment positions in the density profile. More fluid layers with broader density profiles and larger fluctuations were formed by some unoriented FM chains oriented preferentially parallel to the surface, between the opposing monolayers. Segment position correlations parallel to the surface in the adsorbed layers were found at separations up to 30 A. These packings persisted for longer than 4 ns under sliding conditions that ranged from 0 to 7.5 m s(-1) (0 to 0.075 A ps(-1)). Monolayer structures were observed to remain unchanged under a wide range of normal pressures, with the corresponding changes in volume occurring in the gap between monolayers or between a monolayer and trapped fluid.

Journal Article↗
PubMed1998

Friction in hip-joint prostheses and its influence on the fixation of the artificial head.

The head of an implanted hip joint endoprosthesis is exposed to torques, which are transferred during gait due to the friction between the head and the cup prosthesis. In prostheses with ceramic ball heads, which are widely used now, and in which the head is fixed onto the stem by conical clamping, these torques could possibly affect the connection. In this study, torques transferred from the cup to the head are compared to the torques which are required to loosen the head from the metallic spigot. The results show that for the investigated head and taper types and sizes, under normal conditions the connection is safe with respect to undesired rotation. However, it is shown that for polluted sliding surfaces the fixation strength could possibly be exceeded.

Journal Article↗