Accuracy of pressure and flow capacities of four arthroscopic fluid management systems.

PURPOSE: The present study was conducted to evaluate 4 different fluid delivery systems: Arthrex AR-6450, Stryker 1.5L High Flow Pump, Arthro FMS 4, and Acufex InteliJet. Their flow and pressure capacity, as specified by the manufacturer, and their accuracy, as measured in a standardized fashion, were compared with directly measured pressure values. TYPE OF STUDY: Experimental study. METHODS: Two experiments were performed: (1) the achieved pressure was measured with the pressure sensor within a ball and compared with the preset pressure values. The pressure was increased constantly while the flow was kept constant. (2) maximum flow per minute was tested using a beaker and a stopwatch. RESULTS: The highest measured pressures for the Arthrex and the Stryker pumps were 115 mm Hg (46% of published maximum pressure) and 113 mm Hg (57% of published maximum pressure), respectively. The highest measured pressures for the Arthro FMS 4 and the InteliJet pumps were 251 mm Hg (101% of published pressure) and 132 mm Hg (88% of published maximum pressure), respectively. The maximal flow values for the Arthrex and Stryker pumps were 900 mL/min (56.3%) and 675 mL/min (48%), respectively. The Arthro FMS 4 and InteliJet pumps reached a maximal flow of 450 mL/min (56%) and 1,250 mL/min (62.5%). CONCLUSIONS: In the simpler pumps (Arthrex AR-6450 and Stryker 1.5L High Flow Pump), the pressure on the display must be set to higher values compared with the outflow-controlling pumps (Arthro FMS 4 and InteliJet) to achieve the same intra-articular pressure. All pumps were able to maintain a pressure of 60 mm Hg very accurately. Therefore, a surgeon can trust all of the pumps when the pressure is set below 60 mm Hg.

Alterations of biochemical and two-dimensional biomechanical properties of human skin in diabetes mellitus as compared to effects of in vitro non-enzymatic glycation.

OBJECTIVE: The aim of this study was to evaluate whether multiaxial analysis of diabetes-specific biomechanical changes generated in vitro by non-enzymatic glycation of human skin samples from healthy subjects reflect the changes seen in skin from subjects with diabetes mellitus. DESIGN: Descriptive study. BACKGROUND: Non-enzymatic glycation of skin in vitro causes an increased stiffness comparable to in vivo changes seen in diabetic patients. These changes are probably due to increased cross-linking of collagen molecules. METHODS: Skin specimens from 7 subjects with diabetes mellitus and 7 controls (age range: 74-90) were analyzed for biomechanical changes using a multiaxial tensile testing device. Control skins from healthy individuals in the age range of 50-65 yr were artificially glycated. One part of these samples was coincubated with the glycation inhibitor aminoguanidine. Glycation of tissues was determined by measuring fluorescence of solubilized samples. Multiaxial biomechanical analysis allows the determination of maximum (a(I)) and minimum elastic modulus (a(II)). These parameters describe the amplitude of the elastic stress response, which is exponentially related to strain. RESULTS: Principal stresses, both maximum and minimum, were increased in skins from diabetic subjects as compared to controls. The increases of the principal stresses were comparable to those obtained by in vitro glycation of normal skins. CONCLUSION: These results, which can be detected unequivocally with the multiaxial test mode, show that our in vitro model closely reflects changes in skin samples from individuals with diabetes mellitus. Aminoguanidine partially inhibited these as well as biochemical changes. RELEVANCE: Multiaxial testing of in vitro glycated skin samples can be used as a model for in vivo changes caused by diabetes mellitus. In addition, therapeutical effects of aminoguanidine, an inhibitor of non-enzymatic glycation, can be monitored in this model.

Mechanical properties of a rat patellar tendon stress-shielded in situ.

The effects of stress deprivation on the mechanical properties of the patellar tendon (PT) were studied using 14 albino rats. The PT was stress-shielded with cerclages on one side, while the contralateral patellar tendon served as a sham-operated control. After 10 weeks, paired load-strain as well as load-relaxation experiments were performed (11 and 3 specimen pairs, respectively). Mechanical tests showed, irrespective of the cerclage material used, that strain was increased significantly after stress-shielding (P < 0.02). The time constant significantly decreased in the stress-shielded specimens under 5 N loads, which may be considered 'physiological'. Tissue remodeling might explain the observed changes in the viscoelastic behaviour of the stress-shielded tendons. Loading, even in the physiological range of normal daily activity, may lead to an elongation of previously stress-shielded tendons or ligaments and consequently alter the behaviour of a joint.

Comparison of palmar aponeuroses from individuals with diabetes mellitus and Dupuytren's contracture.

It is well known that Dupuytren's contracture is often associated with diabetes mellitus. Palmar fascia from individuals with diabetes mellitus and/or Dupuytren's contracture as well as controls were subjected to differential scanning calorimetry, biomechanical and biochemical analysis. The collagen denaturation temperature of the palmar aponeurosis from individuals with diabetes mellitus in the presence (71.0 degrees C) or absence of Dupuytren's contracture (70. 6 degrees C) was increased as compared with controls (68.5 degrees C), while this parameter was significantly reduced (about 3.5 degrees C) in contracture bands of Dupuytren's contracture. Stress relaxation experiments revealed that the viscous fraction was slightly reduced in diabetes mellitus (6.5%) vs. controls (8.3%), whereas in Dupuytren's contracture, irrespective of additional diabetes mellitus, a pronounced increase of this parameter was seen (36.5% vs. 24.5%) in the presence of diabetes mellitus. The time constants were significantly elevated by both disorders, this increase being more pronounced in Dupuytren's contracture. Taken together, these changes can be explained by increased cross-linking in diabetes mellitus, while in Dupuytren's contracture other structural changes, such as increased collagen type III content and loss of fascicular organization, play an additional role besides the finding of reduced cross linking.

Twisting of patellar tendon grafts does not reduce their mechanical properties.

The purpose of this study was to investigate whether the twisting of a patellar tendon (PT) graft improves or reduces its mechanical properties. Twenty-seven pairs of 10 mm cadaveric PT grafts were tested at a strain rate of 10% min(-1). For each pair, the left specimen served as an unmanipulated control while the right specimen was either left untwisted, twisted + 90 degrees, or twisted - 90 degrees. All avulsion failures were excluded from the data analysis, focusing only on pure in-substance tendon ruptures. Higher ultimate load values than previously reported were obtained for both the twisted and untwisted specimens, without a statistical significant difference between the two. The values obtained for the left and right specimens from Group A were 4014+/-319 and 3973+/-245 N, from Group B 3613+/-207 and 3891+/-14 N, and from Group C 3997+/-278 and 4415+/-507 N, respectively. Stiffness and failure strain were not influenced by the twisting. Neither the presence of a twist, nor the direction of the twist were found to increase the ultimate load of the 10 mm cadaveric patellar tendon graft. Therefore, recommendation for twisting cannot be assessed to its mechanical properties.

Biomechanical stability of abductor pollicis longus muscles with variable numbers of tendinous insertions.

BACKGROUND: In the course of a study of different variants of the tendon of the abductor pollicis longus (APL) muscle, the unusual finding of a tendon with six subdivisions was observed in the first compartment. Using this preparation and others with various numbers of tendons (2, 3, 4, and 6), we intended to establish whether the multitendoned muscles increased the strength of the thumb. METHODS: Fifty-two upper extremities were examined with attention to the tendons of the APL muscle. The strain on each tendon was biomechanically determined using a microcomputer and potentiometer. The stress was measured continuously and plotted against strain. RESULTS: Following treatment with elastase, it is seen that the significance of changes in stability and Young's modulus is inversely proportional to the number of tendons arising from the APL. CONCLUSIONS: Division of the tendon into several parts leads to better mechanical distribution of stress and extension on thumb abduction. In addition, palmar-flexion in the wrist may be supported.

Comparison of normal and in vitro aging by non-enzymatic glycation as verified by differential scanning calorimetry.

The biomechanical parameters of rat tail tendons (RTTs) from 35-, 64-, 180- and 900-day-old animals, corresponding to the early maturation phase, the mature and the senescent state were determined. The increase of maximum stiffness, ultimate stress and the elastic fraction of stress was most pronounced in the maturation phase. Differential scanning calorimetry (DSC) experiments were performed showing an almost linear increase of the collagen denaturation temperature in the age range 35-139 days. After 14 days incubation in glucose, we observed a marked increase of the biomechanical parameters in the young, an increase of maximum stiffness in mature, and only slight alterations of the biomechanical behavior in senescent RTTs. Both glucose incorporation and formation of advanced glycation end products were most prominent in 35-day-old RTTs. These biochemical findings were in excellent agreement with the enhancement of the collagen denaturation temperature after the incubation phase. Results suggest that the validity of the term 'accelerated aging' depends on the experimental approach, i.e. biomechanical tests, thermal isometric contraction or DSC.

Two-dimensional stress-relaxation behavior of human skin as influenced by non-enzymatic glycation and the inhibitory agent aminoguanidine.

In order to simulate the in vivo stress alterations of diabetic skin in an in vitro model, we examined the viscoelastic properties of long-term glycated human skin samples. Since skin is subjected to biaxial tension, we used two-dimensional multiaxial testing which better reflects the in vivo situation than the uniaxial testing mode. For native skin samples from the abdominal region we found a direction-dependent elastic stress strain behavior. The viscous stress component was separated from the elastic stress component by relaxation tests at consecutive incremental steps of radial strains. We hypothesize that glycation-induced changes in the tissue stiffness are generated in a direction-dependent mode. A marked increase of the direction-dependent stiffness was found upon long-term incubation with glucose-6-phosphate. This increase was statistically significant for the maximum principal elastic stress component which was highly correlated with the degree of non-enzymatic collagen modification. The viscous fractions obtained from two-dimensional relaxation tests at consecutive radial strains were inversely correlated with non-enzymatic modification. Only at 30% radial strain a significant decrease of the viscous fraction engendered by glucose-6-phosphate was observed together with a direction-dependent significant increase of the expectation value of the time constant. The biomechanical and biochemical effects of long-term glycation could be partially reversed by aminoguanidine, a potential therapeutic agent for patients with diabetes mellitus. Our findings suggest that additional cross-links generated by long-term glycation cause two-dimensional biomechanical alterations in human skin, which can be unequivocally detected by multiaxial testing.

Effects of aminoguanidine on adhesion molecule expression of human endothelial cells.

The effect of aminoguanidine (AG) on the expression of adhesion molecules on nonactivated human umbilical vein endothelial cells (HUVEC) was investigated in vitro. Nonactivated HUVEC cultivated on long-term glycated fibronectin (FN) as compared to native FN showed a significant upregulation of intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1) and CD31 which could be further promoted by long-term glycated bovine serum albumin. AG, at a concentration of 0.01 mol/l, caused an upregulation of ICAM-1 of 48 +/- 17.4% in HUVEC cultivated on gelatin. In contrast, VCAM-1 and E-selectin remained unaffected. At this concentration, formation of advanced glycation end products (AGE) was inhibited by 57%, as determined immunologically, and by 50%, as verified by AGE-specific fluorescence. A hypothesis concerning the upregulation of ICAM-1 by AG as compared to VCAM-1 is proposed relating to its relative redox insensitivity. Our results demonstrate that the beneficial effect of AG in reducing the risk of accelerated development of atherosclerosis in diabetic patients by inhibiting formation of AGE on matrix proteins such as FN might be hampered by its tendency to upregulate ICAM-1 on endothelial cells.

Comparison of the effect of different inhibitors of the non-enzymatic glycation of rat tail tendons and bovine serum albumin.

The biomechanical and biochemical properties of collagen are changed by non-enzymatic glycation culminating in increased cross-linking. We have previously shown that dibasic amino acids such as L-arginine inhibit in vitro the non-enzymatic glycation of soluble proteins and insoluble connective tissue macromolecules. In the present in vitro study we obtained evidence that the nucleophilic hydrazine derivative aminoguanidine and the non-steroidal anti-rheumatic drug ibuprofen inhibit the formation of fluorescent advanced glycation end products (AGEs) to a comparable extent, while arginine is ineffective as a consequence of its tendency to form AGEs itself. Periodic replacement of glycated arginine in the rat tail tendon system, however, engendered an inhibition of fluorescence similar to that obtained by the other inhibitors. Long-term glycation of rat tail tendons caused a significant increase in Young's modulus, which could also be inhibited by periodically renewed arginine. In contrast to ibuprofen, aminoguanidine and arginine-lysine inhibited the marked increase in maximum contraction force of long-term glycated rat tail tendons. As opposed to other inhibitors, aminoguanidine also reduced the thermal contraction force of native tendons, shifted the maximum contraction temperature to markedly lower values and solubilized a significant part of the rat tail tendon collagen. These findings indicate that the in vitro alterations of rat tail tendon collagen induced by non-enzymatic glycation can be prevented by arginine, arginine-lysine and aminoguanidine. However, collagen structure is seriously affected by aminoguanidine.

On the orthogonal anisotropy of human skin as a function of anatomical region.

Skin samples were obtained from 8 anatomical sites of 6 human deceased at ages ranging from 30 to 80 years 24 hours post mortem. As shown by biochemical analysis the collagen content varied between 71% and 78% depending on the anatomical location of the skin samples. The content of collagen type III was in the range of 19.2% to 22.2% of the total collagen concentration. As to the biomechanical analysis the axes of minimum and maximum shrinkage after excision were determined and correlated with Langer cleavage line drawn on the specimen with a marker after incision. Two-dimensional biomechanical tests were conducted with a multiaxial tensile testing device consisting of 12 loading axes. The in vivo configuration was a circle with 30 mm diameter. The in vivo stresses were determined by restoring the original shape of the specimen. According to the nonlinear stress-strain relationship incremental strains were applied to the sample with the in vivo configuration and states of uniform extension as reference. The corresponding stresses were recorded after stress relaxation was completed and the equilibrium stresses were regarded as the elastic contribution to the viscoelastic biomechanical behavior. The elastic parameters as a function of the initial strain level were calculated using a set of different incremental strains and stresses. The highest in vivo stresses were found in patella, and upper and lower back. The maximum deviation of the direction of maximum in vivo stress from the Langer cleavage line was found in upper back, the volar part of thigh, and sternum. In vivo orthogonal anisotropy was most pronounced in patella and hollow of the knee.

Two-dimensional elastic properties of human skin in terms of an incremental model at the in vivo configuration.

The two-dimensional biomechanical behaviour and the collagen content of human skin samples from different anatomical sites was examined. The axes of minimum and maximum shrinkage after excision were determined and correlated with the 'Langer' cleavage lines. Test equipment was developed to restore the original geometry and to measure the loads acting perpendicular to the circumference of the skin specimens. These loads were normalized with respect to the thickness and collagen content and considered as the in vivo tension generated by the surrounding skin area. Using the in vivo geometry of the specimen as reference a set of incremental strains was applied. After stress relaxation was completed the final values of stresses were recorded and related to the incremental strains. The two-dimensional stress-strain relationship was the basis for the evaluation of the incremental elastic moduli. Orthotropic mechanical behaviour was found mainly in regions of reduced in vivo tension. The relationship between the degree of anisotropy at the in vivo configuration and the morphological structure is discussed.

Mechanical properties of peripheral nerves.

Peripheral nerve trunks are viscoelastic tissues with unique mechanical characteristics. Tensile strength, which includes elastic limit and mechanical failure, concerns surgeons. This study shows that measurements of the load necessary to achieve certain elongations on specimens outside the body do not correspond with in situ measurements. The necessary load is influenced by the presence or absence of branches and by the amount of fibrosis. Because of transverse contraction, elongation beyond a certain limit substantially decreases intrafascicular volume, leading to increased intrafascicular pressure. Stress relaxation is effective only if the nerve repair site is maintained under constant tension. Its beneficial effect disappears after 10 minutes if the repaired nerve is returned to a relaxed state. Therefore, tension at the repair site should be minimized.

Biomechanical properties of normal tendons, normal palmar aponeuroses and palmar aponeuroses from patients with Dupuytren's disease subjected to elastase and chondroitinase treatment.

Normal tendons, normal palmar aponeuroses and specimens from patients with Dupuytren's disease, namely apparently normal palmar aponeuroses and contracture bands were subjected to elastase and chondroitinase ABC digestion. Maximum Young's modulus, normalized hysteresis loop and residual elongation were determined before and after enzyme treatment. In normal tendons, normal and apparently normal palmar aponeuroses both normalized hysteresis loop and residual elongation increased significantly after elastase treatment, whereas the stiffness decreased. Normalized hysteresis loop and residual elongation display changes corresponding to the amount of digested elastin. The increased viscosity of untreated contracture bands containing less elastin, as compared to normal palmar aponeurosis, was not affected by elastase. Obviously, the elastic fibers in normal shape and distribution are responsible for maintaining an elastic status with a low viscous stress component. With the exception of contracture bands chondroitinase ABC caused a minor increase of residual elongation and as opposed to elastase a decrease of normalized hysteresis loop indicating an increased mobility of the tissue fibers.

Biomechanical properties of normal tendons, normal palmar aponeuroses, and tissues from patients with Dupuytren's disease subjected to elastase and chondroitinase treatment.

Normal tendons, normal palmar aponeuroses and palmar aponeuroses from patients with Dupuytren's disease were subjected to elastase or chondroitinase treatment. Young's modulus was derived from the linear portion of stress-strain graph. It showed the lowest value for the apparently normal palmar aponeuroses and the highest value for tendon samples. Elastase treatment caused an increase of extensibility and a reduction of Young's modulus of normal palmar aponeuroses and tendons, but not of contracture bands. In normal tendons, normal palmar aponeuroses and apparently normal palmar aponeuroses residual strain and hysteresis loop increased significantly as a linear function of the amount of digested elastin. In contrast these biomechanical parameters were not affected significantly in contracture bands. In normal and apparently normal areas incubation with chondroitinase ABC resulted in a significant increase of residual strain and, as opposed to elastase, a decrease of normalized hysteresis loop. In contracture bands, however, these biomechanical parameters remained unchanged. RELEVANCE: The increasing evidence of a correlation between morphological changes of palmar elastin and ground substance with the progress of Dupuytren's disease emphasizes the need to determine the relative importance of these connective tissue components for the pathogenesis of Dupuytren's disease.

Measurement of stress-strain relationship and stress relaxation in various synthetic ligaments.

In an experimental study various synthetic augmentation devices for knee ligament surgery were tested in a servo-mechanical universal tensile testing machine under uniaxial loading. Two tests were done to elucidate the mechanical behaviour: stress relaxation and stress-strain relationship. Regarding the point of failure or rupture, the strongest ligament was the Trevira at 1800 N, followed by the 8-mm-wide Kennedy LAD at 1720 N. At a working load of 500 N the Gore-tex band, the Trevira, and the Kennedy-LAD stretched by between 2% and 3%. For synthetic augmentation in repair of proximally ruptured anterior cruciate ligaments we recommend a synthetic ligament that reaches failure point at a load of more than 1000 N with an alteration in length of less than 5%. Otherwise, stress protection of the biological reconstruction in full extension will be impossible. The requisite criteria were fulfilled by the Trevira, Kennedy-LAD and Gore-tex synthetic ligaments.

Mechanical changes in rat tail tendons induced by dibasic amino acids as a function of age.

Rat tail tendons from 54-day-old and 900-day-old animals were incubated with different concentrations of the dibasic amino acids, lysine and arginine. We observed a significant incorporation of these amino acids into the tendons. Uniaxial tension tests and relaxation experiments were performed at strain levels within the linear portion of the stress-strain relationship. The incorporation of the amino acids resulted in a decrease of ultimate stress and maximum Young's modulus and, after separation of the elastic and viscous stress components, in a decrease of the elastic fraction. The incorporation of amino acids and the resulting mechanical alterations were more pronounced in the young animals. The reversibility of the effects induced by the amino acids was tested. After the glycosaminoglycan chains were digested with chondroitinase ABC, we showed that the dibasic amino acids bind predominantly to the proteoglycan matrix. A possible analogy to the effects of amino acid incorporation on biomechanics and swelling with a monovalent cation such as Na+ is discussed.

The influence of L-arginine on biomechanical parameters of native and nonenzymatically glycated rat tail tendons.

Rat tail tendons from animals of an age range from 35 days to 900 days were glycated using different glucose concentrations. After nonenzymatic glycation the biomechanical properties of tendons from young rats approached that of old tendons. In tendons from old animals the glucose incorporation was significantly lower than in young rat tail tendons. Addition of L-arginine to the glucose solution reduced the incorporation of glucose especially in young rats. The concentration of early glycation products and of advanced glycation end products were measured via affinity chromatography on boronic acid agarose and relative fluorescence per collagen content respectively. Both parameters were significantly reduced by an addition of 10 mmol/l arginine. Biomechanical changes due to glycation were partially reversed. Incubation of rat tail tendons in L-arginine in the absence of glucose caused a dose dependent binding of the amino acid mainly to the proteoglycan matrix. High concentrations of L-arginine induced pronounced biomechanical alterations contrary to the action of glucose. The biomechanical effect of L-arginine is compared to the action of Na+ and Ca2+ and discussed on the basis of a structural model of the proteoglycan matrix. Incubation of already glycated rat tail tendons with L-arginine caused a reduction of the elastic stress component This effect was diminished by increasing the preincubation interval with glucose. The equilibrium values of the elastic fraction were achieved after approximately five days incubation with the amino acid.

Microsurgical neurolysis: its anatomical and physiological basis and its classification.

Neurolysis is a procedure which has to be performed if the gliding apparatus of a peripheral nerve does not function, and consequently, adhesions and fibrosis develop. The gliding tissue has to provide the ability for the nerve to adapt to the different position of the extremity by longitudinal passive movement. The paraneurium provides movements between the nerve and the surrounding tissue; the interfascicular epineurium provides the possibility of the movement within the nerve. Internal neurolysis is defined as surgery within the nerve if the epifascicular epineurium is completely transected. A classification of different degrees of fibrosis is given with special reference to the procedure which has to be done in each case. Neurolysis is a step-wise procedure with the aim to decompress the fascicles and which is immediately stopped if this aim is achieved. In very severe cases, if the gliding tissue does not regenerate, a gliding tissue flap to envelope the nerve may solve the problem.

Alterations of biochemical and biomechanical properties of rat tail tendons caused by non-enzymatic glycation and their inhibition by dibasic amino acids arginine and lysine.

The influence of dibasic amino acids arginine and lysine on non-enzymatic glycation of tail tendon fibers from old (900-day-old) and young (61-day-old) rats was investigated in vitro. The biomechanical changes in tendon fibers of young rats after an incubation interval of 7 or 14 days in a glucose solution were abolished by the addition of arginine or lysine (molar ratio amino acid:glucose 1:10). Glucose incorporation into rat tail tendon fibers as well as Amadori product formation was decreased significantly in the presence of the amino acids. The inhibitory effect of arginine was further confirmed by measurement of the amount of ketoamine formed during the glycation reaction using soluble albumin as a protein target. The effective inhibition of non-enzymatic glycation by arginine or lysine suggests their potential use in vivo as a means of controlling protein over-glycation.