Significant Differences In Stiffness Research Articles

THU0083 Abnormal volumetric density and microarchitecture at the radius in chinese female patients with rheumatoid arthritis: A case-control study

BackgroundGeneralized bone loss at axial and peripheral bone is a common feature of rheumatoid arthritis (RA) and is one of the determinants of the fracture risk. The relationship between decreased...

Shear Force at Failure and Stiffness of All-Inside Meniscal Repair Devices

The purpose of this study was to determine the failure load and stiffness of various meniscal repair devices. A total of 61 fresh-frozen porcine menisci (medial and lateral) were used for the study. A 30-mm vertical, full-thickness tear was created and repaired using one of three all-inside fixation devices and one inside-out repair in the vertical mattress pattern. We used the MaxBraid (Biomet, Warsaw, IN) inside-out suture as a control. The other devices tested were the Meniscal Cinch (Arthrex, Naples, FL), Ultra FasT-Fix (Smith & Nephew, Andover, MA), and the MaxFire MarXmen (Biomet, Warsaw, IN). In addition, two devices, MaxFire MarXmen and Ultra FasT-Fix, were tested using a horizontal mattress configuration. Using the vertical mattress pattern, the Meniscal Cinch had the highest average load to failure. The Meniscal Cinch was significantly less stiff than the other three devices (p < 0.04). For the MarXmen and Ultra FasT-Fix, no differences were noted for load to failure between horizontal and vertical mattress patterns. The mode of failure was significantly different when comparing the two different surgical techniques for the MaxFire MarXmen (p = 0.005). The MaxFire MarXmen device produced a significantly stiffer (p < 0.001) construct when following the manufacturer's instructions (5.8 N/mm) than with the technique used for the other all-inside devices (2.5 N/mm) The Meniscal Cinch had the highest load-to-failure value but the lowest stiffness of the group in the vertical mattress configuration. There was little difference in biomechanical properties between vertical and horizontal repair. Importantly, there was a significant difference in stiffness and failure mode for the MaxFire MarXmen when the manufacturer guidelines were not specifically followed.

Dynamic Biomechanical Examination of the Lumbar Spine with Implanted Total Spinal Segment Replacement (TSSR) Utilizing a Pendulum Testing System

BackgroundBiomechanical investigations of spinal motion preserving implants help in the understanding of their in vivo behavior. In this study, we hypothesized that the lumbar spine with implanted total spinal segment replacement (TSSR) would exhibit decreased dynamic stiffness and more rapid energy absorption compared to native functional spinal units under simulated physiologic motion when tested with the pendulum system.MethodsFive unembalmed, frozen human lumbar functional spinal units were tested on the pendulum system with axial compressive loads of 181 N, 282 N, 385 N, and 488 N before and after Flexuspine total spinal segment replacement implantation. Testing in flexion, extension, and lateral bending began by rotating the pendulum to 5°; resulting in unconstrained oscillatory motion. The number of rotations to equilibrium was recorded and bending stiffness (N-m/°) was calculated and compared for each testing mode.ResultsThe total spinal segment replacement reached equilibrium with significantly fewer cycles to equilibrium compared to the intact functional spinal unit at all loads in flexion (p<0.011), and at loads of 385 N and 488 N in lateral bending (p<0.020). Mean bending stiffness in flexion, extension, and lateral bending increased with increasing load for both the intact functional spinal unit and total spinal segment replacement constructs (p<0.001), with no significant differences in stiffness between the intact functional spinal unit and total spinal segment replacement in any of the test modes (p>0.18).ConclusionsLumbar functional spinal units with implanted total spinal segment replacement were found to have similar dynamic bending stiffness, but absorbed energy at a more rapid rate than intact functional spinal units during cyclic loading with an unconstrained pendulum system. Although the effects on clinical performance of motion preserving devices is not fully known, these results provide further insight into the biomechanical behavior of this device under approximated physiologic loading conditions.

Calcium Triglyceride Versus Polymethylmethacrylate Augmentation: A Biomechanical Analysis of Pullout Strength

Study DesignBiomechanical pullout study using calcium triglyceride (CTG) and polymethylmethacrylate (PMMA) for screw augmentation. ObjectiveCompare the biomechanical performance of CTG augmentation versus the gold standard, PMMA, in primary and revision models, using a pedicle screw pullout model. Background SummaryCTG is a novel form of bone augmentation with several reported biocompatible properties compared with PMMA. PMMA is the standard of care for pedicle screw augmentation in osteoporotic spine. MethodsBlocks of closed-cell rigid polyurethane foam of uniform density, representing subcortical layer in osteoporotic pedicle, were prepared according to ASTM standards. After the components of PMMA (n = 11) and CTG (n = 11) were individually mixed in a standardized fashion, 0.2 ml was injected from deep to superficial along a predrilled pilot hole followed by immediate insertion of the pedicle screw. An unaugmented group (n = 10) was also prepared. Blocks cured for 24 hrs, and screws were pulled out at a rate of 5 mm/min on materials testing equipment. For the revision model, the unaugmented group, after screw pullout, was augmented with 0.8 ml of PMMA (n = 5) or CTG (n = 5) as detailed above and screw pullout performed similarly. ResultsThe mean pullout strengths (SD) for the intact models were as follows: unaugmented, 976.6 N (94.2 N); PMMA, 1,218.1 N (66.8 N); and CTG, 1,841.6 N (57.4 N). A one-way analysis of variance indicated a significant difference among the primary models (p < .0001). For the revision models, the pullout strength for PMMA was 1,939.2 N (108.9 N) and for CTG, 2,513.0 N (149.1 N), which were statistically different from each other (p < .0003). Stiffness of the constructs was increased with both PMMA and CTG augmentation over no augmentation (p < .0001) although no significant difference in stiffness was detected between the 2 forms of augmentation. ConclusionWe conclude that CTG augmentation of pedicle screws resulted in significantly higher axial pullout strength in primary (p < .0001) and revision (p < .0003) models compared with PMMA.

Investigation on asphalt binder strength at low temperatures

A new strength test method for asphalt binders at low temperatures is investigated in this paper. A modified Bending Beam Rheometer (BBR), capable of applying loads at different rates, is used to obtain asphalt binder flexural strength. Strength values obtained from the BBR test are compared with strength values obtained from the Direct Tension Tester (DTT) test and significant differences are found between the two tests. Additional BBR strength tests are run on asphalt binder beams after replacing the ethanol used in the cooling bath with potassium acetate, similar to DTT testing conditions, and flexural strengths significantly larger than those obtained with ethanol are obtained. Weakest link theory is used to convert three-point bending strength to direct tension strength and to perform volume correction of DTT values. Based on the corrected values, the BBR and DTT strength measurements are similar, when the same cooling medium is used. The effect of the cooling medium on BBR creep stiffness is also evaluated. From the limited experimental tests, it appears that there are no significant differences in stiffness and m-value after 1 h of isothermal storage.

Evaluation of shearwave elastography for the characterisation of focal liver lesions on ultrasound

To determine the elasticity characteristics of focal liver lesions (FLLs) by shearwave elastography (SWE). We used SWE in 108 patients with 161 FLLs and in the adjacent liver for quantitative and qualitative FLLs stiffness assessment. The Mann-Whitney test was used to assess the difference between the groups of lesions where a P value less than 0.05 was considered significant. SWE acquisitions failed in 22 nodules (14 %) in 13 patients. For the 139 lesions successfully evaluated, SWE values were (in kPa), for the 3 focal fatty sparings (FFS) 6.6 ± 0.3, for the 10 adenomas 9.4 ± 4.3, for the 22 haemangiomas 13.8 ± -5.5, for the 16 focal nodular hyperplasias (FNHs) 33 ± -14.7, for the 2 scars 53.7 ± 4.7, for the 26 HCCs 14.86 ± 10, for the 53 metastasis 28.8 ± 16, and for the 7 cholangiocarcinomas 56.9 ± 25.6. FNHs had significant differences in stiffness compared with adenomas (P = 0.0002). Fifty percent of the FNHs had a radial pattern of elevated elasticity. A significant difference was also found between HCCs and cholangiocarcinomas elasticity (P = 0.0004). SWE could be useful in differentiating FNHs and adenomas, or HCCs and cholangiocarcinomas by ultrasound.

Does the dynamic sling effect of the Latarjet procedure improve shoulder stability? A biomechanical evaluation

Glenohumeral instability with glenoid bone loss is commonly treated with the Latarjet procedure. The procedure involves transfer of the coracoid and conjoint tendon, which is thought to provide a stabilizing sling effect; however, its significance is unknown. This study evaluated the effects of the Latarjet procedure, with and without conjoint tendon loading, on shoulder stability and range of motion (ROM). A custom simulator was used to evaluate anterior shoulder stability and ROM in 8 cadaveric shoulders. Testing conditions included intact, 30% glenoid defect, and Latarjet with and without conjoint loading. Unloaded and 10-N loaded states were tested in adduction and 90° abduction. Outcome variables included dislocation, stiffness (neutral and 60° external rotation), and internal-external rotational ROM. All 30% defects dislocated in abduction external rotation. The loaded Latarjet prevented dislocation in all specimens, whereas the unloaded Latarjet stabilized 6 of 8 specimens. In abduction external rotation, there were no significant differences in stiffness between loaded and unloaded transfers (P = .176). In adduction, there were no significant differences between the intact and the loaded Latarjet (P ≥ .228); however, in neutral rotation, the unloaded Latarjet (P = .015) and the 30% defects (P = .011) were significantly less stiff. Rotational ROM in abduction was significantly reduced with the loaded Latarjet (P = .014) compared with unloaded Latarjet, and no differences were found in adduction. These findings indicate that glenohumeral stability is improved, but not fully restored to intact, with conjoint tendon loading. The results support the existence of the sling effect and its importance in augmenting stability provided by the transferred coracoid.

Effect of muscle preserved on tendon graft on intra-articular healing in anterior cruciate ligament reconstruction

The aim of this study was to determine the impact on intra-articular healing of muscle tissue retained on tendon grafts used for anterior cruciate ligament (ACL) reconstruction. In an animal study on 40 New Zealand rabbits, a semi-tendon/semi-muscle graft (SSG) and a total tendon graft (TTG) were individually harvested from the Achilles tendons in each animal. After transecting the ACLs in both knees of each rabbit, SSG and TTG were randomly used on bilateral sides of the knee for ACL reconstruction. After 2, 4, and 8weeks, functional scoring, gross observations, and histological evaluations of the repaired knees were performed (each time point; n=10). Biomechanical testing was conducted on remaining animals at 8weeks (n=10). At 2, 4, and 8weeks after surgery, there were no statistically significant differences in functional scores between the SSG group and TTG group (n.s.). As healing progressed, skeletal muscle on the SSG was gradually absorbed with a corresponding decrease in graft diameter, compared to TTG, at each time point (P<0.001). However, healing and incorporation of the intra-articular graft in the SSG were more apparent than those in the TTG, based on histology. The vascularity and cellularity in the center of the sample were significantly greater in the SSG group than the TTG group at all the time points (P<0.01). At 8weeks, the SSG group's ultimate failure load, yield load, and elongation at failure were significantly less than for the TTG group (P<0.01). There were no significant differences in stiffness between the two groups with biomechanical testing (n.s.). Results of this study indicate that muscle left on tendon grafts promotes intra-articular healing and remodeling of the graft in a rabbit model. However, excessive amounts of retained skeletal muscle weaken tendon graft's strength for ACL reconstruction. Preserving small amounts of muscle on tendon grafts is feasible for improving the biological success of ACL reconstruction in humans.

A mechanistic model for permeability evolution in fractured sorbing media

A mechanistic model is presented to represent the evolution of permeability in fractured sorbing media such as coal beds and organic‐rich shales. This model accommodates key competing processes of poromechanical dilation and sorption‐induced swelling. We show that the significant difference in stiffness between fracture and matrix transforms the composite system from globally unconstrained to locally constrained by the development of a virtual “stiff shell” that envelops the perimeter of a representative elementary volume containing a fracture. It is this transformation that results in swelling‐induced permeability reduction at low (sorbing) gas pressures and self consistently allows competitive dilation of the fracture as gas pressures are increased. Importantly, net dilation is shown to require a mismatch in the Biot coefficients of fracture and matrix with the coefficient for the fracture exceeding that for the matrix—a condition that is logically met. Permeability evolution is cast in terms of series and parallel models with the series model better replicating observational data. The model may be cast in terms of nondimensional parameters representing sorptive and poromechanical effects and modulated by the sensitivity of the fracture network to dilation or compaction of the individual fractures. This latter parameter encapsulates the effects of fracture spacing and initial permeability and scale changes in permeability driven by either sorption or poromechanical effects. This model is applied to well‐controlled observational data for different ranks of coals and different gases (He, CO2) and satisfactory agreement is obtained.

Fracture fixation with two locking screws versus three non-locking screws

ObjectivesWe aimed to further evaluate the biomechanical characteristics of two locking screws versus three standard bicortical screws in synthetic models of normal and osteoporotic bone.MethodsSynthetic tubular bone models representing normal bone density and osteoporotic bone density were used. Artificial fracture gaps of 1 cm were created in each specimen before fixation with one of two constructs: 1) two locking screws using a five-hole locking compression plate (LCP) plate; or 2) three non-locking screws with a seven-hole LCP plate across each side of the fracture gap. The stiffness, maximum displacement, mode of failure and number of cycles to failure were recorded under progressive cyclic torsional and eccentric axial loading.ResultsLocking plates in normal bone survived 10% fewer cycles to failure during cyclic axial loading, but there was no significant difference in maximum displacement or failure load. Locking plates in osteoporotic bone showed less displacement (p = 0.02), but no significant difference in number of cycles to failure or failure load during cyclic axial loading (p = 0.46 and p = 0.25, respectively). Locking plates in normal bone had lower stiffness and torque during torsion testing (both p = 0.03), but there was no significant difference in rotation (angular displacement) (p = 0.84). Locking plates in osteoporotic bone showed lower torque and rotation (p = 0.008), but there was no significant difference in stiffness during torsion testing (p = 0.69).ConclusionsThe mechanical performance of locking plate constructs, using only two screws, is comparable to three non-locking screw constructs in osteoporotic bone. Normal bone loaded with either an axial or torsional moment showed slightly better performance with the non-locking construct.

Repair of pars interarticularis defect utilizing a pedicle and laminar screw construct: a new technique based on anatomical and biomechanical analysis

The theoretical advantage of pars interarticularis repair over spinal fusion to correct pars defects is that the treatment is a direct osteosynthesis that preserves motion at the involved functional spinal unit. Several techniques and constructs have been used to achieve greater rigidity, but these techniques may risk entry into the spinal canal, and adverse events are common. A pedicle and laminar screw construct placed entirely outside the spinal canal may offer greater stiffness and achieve higher pars defect healing rates. The purpose of this study was to biomechanically assess an intralaminar screw construct in cadaveric lumbar spines in comparison with other types of constructs typically used in pars repair and to quantify the sizes of screws that can be placed safely in both normal and spondylolytic vertebrae. The L-4 and L-5 laminae in patients with spondylolysis and in controls who underwent CT (n = 41, each group) were measured by analysis of conventional axial CT images and multiplanar reformations constructed on a Vitrea workstation to determine the feasibility of translaminar fixation with a 4.5-mm-diameter screw. Biomechanical tests for torsion and flexion-extension were performed on 8 fresh human cadaveric lumbar spines before and after modeling for bilateral spondylolytic defects. Three pars repair techniques were tested at each level and in the following sequence: pedicle screw-cable, pedicle screw-rod-hook, and pedicle screw-intralaminar screw. The majority of laminae can accept 4.5 × 25-mm screws. The cable construct allowed the greatest motion and least stability across the defect in all biomechanical tests. The hook and laminar screw constructs performed similarly in all tests and exhibited no significant difference in stiffness. A surgically placed intralaminar screw construct may be a safe and effective alternative to current pars repair methods.

Effective block diagonal preconditioners for Biot's consolidation equations in piled‐raft foundations

SUMMARYThe finite element (FE) simulation of large‐scale soil–structure interaction problems (e.g. piled‐raft, tunnelling, and excavation) typically involves structural and geomaterials with significant differences in stiffness and permeability. The symmetric quasi‐minimal residual solver coupled with recently developed generalized Jacobi, modified symmetric successive over‐relaxation (MSSOR), or standard incomplete LU factorization (ILU) preconditioners can be ineffective for this class of problems. Inexact block diagonal preconditioners that are inexpensive approximations of the theoretical form are systematically evaluated for mitigating the coupled adverse effects because of such heterogeneous material properties (stiffness and permeability) and because of the percentage of the structural component in the system in piled‐raft foundations. Such mitigation led the proposed preconditioners to offer a significant saving in runtime (up to more than 10 times faster) in comparison with generalized Jacobi, modified symmetric successive over‐relaxation, and ILU preconditioners in simulating piled‐raft foundations. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Does the Extent of Prebending Affect the Stability of Femoral Shaft Fractures Stabilized by Titanium Elastic Nails? A Biomechanical Investigation on an Adolescent Femur Model

Elastic stable intramedullary nailing (ESIN) is a common procedure for stabilization of femoral shaft fractures in childhood. Prebending of the nail is generally recommended to achieve optimal nail tension at the fracture site. To our knowledge there are no published data on the effects of prebending on stability. The purpose of this biomechanical study was to compare the effects of different degrees of prebending on the stability of transverse femoral fractures after ESIN using a bone model. Standardized transverse midshaft fractures were created in 20 synthetic, biomechanically validated adolescent bones (4th Generation Composite Femur--Sawbones Europe AB, Sweden) that were stabilized with 2 titanium nails (TEN) each (4 mm diameter, Synthes) and inserted in standardized retrograde technique. The 4 test series addressed nail prebending at 0 degree, 30 degrees, 45 degrees, and 60 degrees. The models were tested biomechanically in 4-point bending in the coronal and sagittal planes, relative stiffness was determined and analyzed statistically. The level of significance was set at P < 0.05. Comparison of the individual groups showed no significant differences in stiffness for different degrees of prebending in the coronal plane. Significantly reduced stiffness was found in the sagittal plane for the group with 60-degree prebending compared with the 0-degree, 30-degree, and 45-degree prebending groups. Intragroup comparison in the coronal and sagittal planes yielded a significantly reduced stiffness in the sagittal plane compared with the coronal plane in the group with 60-degree prebending. The 45-degree prebending group showed a similar tendency and in the 0-degree and 30-degree prebending groups there were no significant differences. On a synthetic bone model, prebending of TEN was found to affect the stability of transverse fractures of the femoral shaft, whereby indiscriminate prebending will reduce stability in the sagittal plane.Despite limited extrapolation of the findings to the in vivo situation, it can be stated that prebending of TEN by 0 to 30 degrees offers the greatest stability in the coronal and sagittal planes for transverse fractures of the femoral shaft.

Evaluation of Risk for Secondary Fracture After Removal of a New Femoral Neck Plate for Intracapsular Hip Fractures

To determine whether a new femoral neck plate has a higher risk for secondary fracture after implant removal than the current standard treatment for intracapsular hip fractures. Six pairs of human cadaver femora (age, 56 ± 5.6 years; range, 48-64 years; two female and four male donors) were instrumented with the femoral neck plate (FNP) or the compression hip screw combined with an antirotation screw (CHS) in a paired study design. After removal of the implants, axial compression tests to failure of the bones were conducted. Maximum force to failure of the bones after implant removal was determined. Axial stiffness of the bones before surgery and after implant removal was determined. The FNP resulted in a mean failure load of 4687 ± 1743 N (mean ± standard deviation) and the CHS resulted in a mean failure load of 4892 ± 1608 N with no significant difference between the two implant groups (P = 0.405). There was no significant difference in stiffness (P = 0.214) between the FNP (1240 ± 362 N/mm) and the CHS (1293 ± 304 N/mm). The cavities left by the surgery had no effect on the bone stiffness (P > 0.05). The mean failure load of all specimens correlated with the bone mineral density in the proximal part of the femurs by R² = 0.715 (P = 0.001). The FNP demonstrated a similar failure load after implant removal compared with the CHS, although the FNP left a 39% larger cavity in the bone.

Biomechanical Testing of a Novel Suture Pattern for Repair of Equine Tendon Lacerations

To compare in vitro biomechanical properties of a novel suture pattern to a current standard for primary repair of equine superficial digital flexor tendon (SDFT) laceration. In vitro randomized, paired design. Cadaveric equine forelimb SDFT (n = 24). The 3-loop pulley (3LP) and 6-strand Savage (SSS) suture patterns were applied to transected equine SDFT. Ultimate failure load, stiffness, mode of failure, and load required to form a 3-mm gap were obtained using a materials testing system and synchronized high-speed video analysis. Statistical comparisons were made using Student's t-test, with significance set at P < .05. The SSS repair failed at a higher ultimate load (421.1 N ± 47.6) than the 3LP repair (193.7 N ± 43.0; P < .001). There was no significant difference in stiffness (P = .99). Failure mode was suture breakage for all SSS repair and suture pull through for all 3LP repair. The maximum load to create a 3-mm gap in the SSS repair (102.0 N ± 22.4) was not significantly different from the 3LP repair (109.9 N ± 16.0; P = .27). SSS tenorrhaphy has improved strength and resistance to pull through compared with 3LP for equine SDFT in a single load-to-failure test. Load required to form a 3-mm gap was not significantly different between SSS and 3LP.

Comparative Analysis of the Structural Properties of the Collateral Ligaments of the Human Knee

Controlled laboratory study. Varus knee instability arising from lateral collateral ligament (LCL) injury increases stress on cruciate ligament grafts, potentially leading to failure of reconstructed ligaments. In contrast to the medial collateral ligament (MCL), little is known about the structural properties of the LCL. To compare the tensile properties of the LCL and MCL complex of the human knee joint. Ten fresh-frozen cadaveric knees (mean ± SD age, 81 ± 11 years), free of gross musculoskeletal pathology, were obtained. Following dissection, the length, width, and thickness of the ligaments were measured using calipers, and bone-ligament-bone preparations were mounted in a uniaxial load frame. After preconditioning, specimens were extended to failure at a rate of 500 mm/min (approximately 20%/s). Force and crosshead displacement were used to calculate structural properties, including stiffness, yield strength, ultimate tensile strength, and failure energy. The fan-shaped MCL was significantly longer (60%; P<.001), wider (680%; P<.001), and thinner (19%; P = .009) than the cord-like LCL. The LCL failed at either the fibular attachment (n = 6) or midsubstance (n = 4), while failure of the MCL primarily occurred at the femoral attachment (n = 7). Although the ultimate tensile strength of the MCL (mean ± SD, 799 ± 209 N) was twice that of the LCL (392 ± 104 N; P<.001), there was no significant difference in stiffness of the ligaments (MCL, 63 ± 14 N/mm; LCL, 59 ± 12 N/mm). Despite differences in geometry and strength, there was no significant difference in stiffness of the MCL and LCL when tested in vitro.

Initial stability of two different adhesives compared to suture repair for acute Achilles tendon rupture—A biomechanical evaluation

Treatment of acute subcutaneous Achilles tendon rupture remains challenging. Whereas the results of conservative and operative treatment are inconsistent, early mobilisation treatment seems to be beneficial. Besides suture repair, operative treatment using adhesives reveals promising results. Our hypothesis was that a gluing technique provides initial stability comparable to sutures. In a biomechanical study, 18 fresh frozen sheep Achilles tendons were used to compare the biomechanical properties of suture repair using PDS® II and Bunnell's technique to tendon gluing using BioGlue® and Tissucol®. Load to failure testing was performed. Ultimate failure loads of sutures (146.2 ± 30.8 N) are significantly superior to the techniques using BioGlue® (38.4 ± 18.3 N; p <0.0001) or Tissucol® (4.7 ± 2.5 N; p <0.0001). Interestingly, no significant differences in stiffness were found between the application of BioGlue® and PDS® II. Suture repair provides significantly superior biomechanical properties compared to the use of both tested adhesives BioGlue® and Tissucol®. Based on the presented data we recommend the use of suture material for open Achilles tendon repair.

Device, protocol and measurement of regional spinal stiffness

Spinal stiffness is commonly assessed by manual therapists but the methodology varies widely. The current study presents a novel device – Therapeutic Spinal Mobilizer – to measure spinal stiffness safely and reliably. The methodology developed allows exertion of a force perpendicular to the spinal skin surface over a selected spinous process at a preselected frequency for predetermined duration cyclically in a repeatable manner. The loading rate is governed by the gravity feed. The force applied and displacements produced were used to calculate the spinal stiffness at that level.The results revealed a significant difference in stiffness due to magnitude of load (loading rate) (p<0.01) but no significant difference in stiffness between different cycles of loading with same load. The phase of respiration significantly affected stiffness, with total lung capacity being stiffest and residual functional capacity the least stiff (p<0.05). There was a significant difference in stiffness of the three spinal levels tested (p<0.05).In conclusion, the standardized methodology revealed that spinal stiffness of one region may be very different from another. Different loads yield significantly different stiffness (p<0.01).

Nature of passive musculoarticular stiffness increase of ankle in female subjects with fibromyalgia syndrome

The objective of this study was to assess the passive elastic and viscous stiffness components of ankle in young, middle-aged and old adult female fibromyalgia subjects and compare the results with age-matched healthy control subjects. The passive musculoarticular stiffness of the ankles of 60 fibromyalgia subjects and 52 controls was quantified by measuring the ankle resistance to imposed sinusoidal rotary displacements at nine different oscillation frequencies. For each frequency, the resulting torque response of the ankles was decomposed into elastic and viscous components of the total stiffness. The self-perceived stiffness intensity of the ankles was assessed in fibromyalgia subjects by means of a visual analogue scale. Two-way ANOVA test indicated a significant effect of fibromyalgia (P < 0.001) and age (P < 0.001) on elastic stiffness results and a significant effect of age (P < 0.001) on viscous stiffness results. Post hoc Holm-Sidak test indicated that younger and middle-aged fibromyalgia subjects had a significant elastic stiffness increase of more than two times that of controls (P = 0.038 and P < 0.001, respectively). Middle-aged fibromyalgia subjects had a significant viscous stiffness increase of 1.2 times that of controls (P = 0.038). No significant differences in stiffness were observed between older fibromyalgia subjects and controls. In conclusion, the self-perceived stiffness increase of ankle reported by younger and middle-aged fibromyalgia subjects is due to changes in elastic and/or viscous musculoarticular structures around the ankle. The absence of changes in older fibromyalgia subjects is probably related to the ageing process of controls.

In vitro indentation to determine the mechanical properties of epidermis

The lack of understanding of the mechanical behavior of the human skin layers makes the development of drug delivery using microneedles or microjets a challenging task. In particular, the key mechanical properties of the epidermis composed of stratum corneum and viable epidermis should be better understood.Micro-indentation experiments were applied, using a spherical tip with a large diameter to the sample thickness ratio. The Young's moduli were derived via an analytical and a numerical method. The tests showed that the analytical method was not appropriate to assess the Young's moduli. That is why a numerical model was used to obtain the correct stiffness. When loaded perpendicularly, the stiffness of both the epidermis and stratum corneum vary between 1 and 2MPa. No significant differences in stiffness between the stratum corneum and viable epidermis were observed.