The correlation of urethral resistance pressure with maximum urethral closure pressure and stress incontinence

OBJECTIVE: Aim of the study was to correlate urethral retro resistance pressure with the maximum urethral closure pressure (MUCP) and functional urethral length (FUL) in patients with urinary incontinence and healthy individuals. STUDY DESIGN: Two hundred and twenty patients with the complaint of urinary incontinence had a urodynamic examination including urethral pressure profiles and URP. Additionally, 15 healthy individuals without the complaint of any incontinence had their URP and urethral pressure profiles measured. The correlation of MUCP, FUL and URP were calculated using Graph Pad Instat 4.0 for windows. RESULTS: URP correlates well with the diagnosis of urodynamic stress incontinence. Correlation coefficient between URP and MUCP is 0.9262. Healthy individuals have significantly higher values for URP and MUCP. CONCLUSION: URP is a valuable less invasive test than conventional urethral function tests for the diagnosis of urodynamic incontinence with an excellent correlation of MUCP and URP.

The Young's modulus of fetal preterm and term amniotic membranes

OBJECTIVE: To examine the Young's modulus of the human amniotic membranes, as well as its relationship to gestational age. To determine whether cellular and material-related parameters affect this modulus. STUDY DESIGN: In a prospective study at the Obstetric outpatient clinic of the University Hospital Zurich Young's modulus, thickness and mesenchymal:epithelial cell ratio of amniotic membranes of preterm (N=23) and term (N=40) placentae were examined. Significance (P<0.05) was calculated with the Mann-Whitney two-sample rank sum test and Wilcoxon signed rank test, while correlations were made using the Spearman's correlation. RESULTS: The Young's modulus of preterm amniotic membranes was significantly higher than that of term membranes. It varied within the same amniotic membrane. The thickness of the amnion in both preterm and term membranes did not differ significantly. The thinner the preterm and term amniotic membranes, the higher the Young's modulus was. There was no relation to the mesenchymal:epithelial cell ratio in the amnion. CONCLUSIONS: Preterm amniotic membranes are stiffer than term amniotic membranes. Tentatively, we hypothesise that there may be a correlation between the extracellular matrix components and the elastic properties of the membrane.

Adjacent vertebral failure after vertebroplasty: a biomechanical study of low-modulus PMMA cement

PMMA is the most common bone substitute used for vertebroplasty. An increased fracture rate of the adjacent vertebrae has been observed after vertebroplasty. Decreased failure strength has been noted in a laboratory study of augmented functional spine units (FSUs), where the adjacent, non-augmented vertebral body always failed. This may provide evidence that rigid cement augmentation may facilitate the subsequent collapse of the adjacent vertebrae. The purpose of this study was to evaluate whether the decrease in failure strength of augmented FSUs can be avoided using low-modulus PMMA bone cement. In cadaveric FSUs, overall stiffness, failure strength and stiffness of the two vertebral bodies were determined under compression for both the treated and untreated specimens. Augmentation was performed on the caudal vertebrae with either regular or low-modulus PMMA. Endplate and wedge-shaped fractures occurred in the cranial and caudal vertebrae in the ratios endplate:wedge (cranial:caudal): 3:8 (5:6), 4:7 (7:4) and 10:1 (10:1) for control, low-modulus and regular cement group, respectively. The mean failure strength was 3.3 +/- 1 MPa with low-modulus cement, 2.9 +/- 1.2 MPa with regular cement and 3.6 +/- 1.3 MPa for the control group. Differences between the groups were not significant (p = 0.754 and p = 0.375, respectively, for low-modulus cement vs. control and regular cement vs. control). Overall FSU stiffness was not significantly affected by augmentation. Significant differences were observed for the stiffness differences of the cranial to the caudal vertebral body for the regular PMMA group to the other groups (p < 0.003). The individual vertebral stiffness values clearly showed the stiffening effect of the regular cement and the lesser alteration of the stiffness of the augmented vertebrae using the low-modulus PMMA compared to the control group (p = 0.999). In vitro biomechanical study and biomechanical evaluation of the hypothesis state that the failure strength of augmented functional spine units could be better preserved using low-modulus PMMA in comparison to regular PMMA cement.

Properties of an injectable low modulus PMMA bone cement for osteoporotic bone

The use of polymethylmethacrylate (PMMA) cement to reinforce fragile or broken vertebral bodies (vertebroplasty) leads to extensive bone stiffening. Fractures in the adjacent vertebrae may be the consequence of this procedure. PMMA with a reduced Young's modulus may be more suitable. The goal of this study was to produce and characterize stiffness adapted PMMA bone cements. Porous PMMA bone cements were produced by combining PMMA with various volume fractions of an aqueous sodium hyaluronate solution. Porosity, Young's modulus, yield strength, polymerization temperature, setting time, viscosity, injectability, and monomer release of those porous cements were investigated. Samples presented pores with diameters in the range of 25-260 microm and porosity up to 56%. Young's modulus and yield strength decreased from 930 to 50 MPa and from 39 to 1.3 MPa between 0 and 56% porosity, respectively. The polymerization temperature decreased from 68 degrees C (0%, regular cement) to 41 degrees C for cement having 30% aqueous fraction. Setting time decreased from 1020 s (0%, regular cement) to 720 s for the 30% composition. Viscosity of the 30% composition (145 Pa s) was higher than the ones received from regular cement and the 45% composition (100-125 Pa s). The monomer release was in the range of 4-10 mg/mL for all porosities; showing no higher release for the porous materials. The generation of pores using an aqueous gel seems to be a promising method to make the PMMA cement more compliant and lower its mechanical properties to values close to those of cancellous bone.

Isometric rate of force development, maximum voluntary contraction, and balance in women with and without joint hypermobility

OBJECTIVE: To determine differences between hypermobile subjects and controls in terms of maximum strength, rate of force development, and balance. METHODS: We recruited 13 subjects with hypermobility and 18 controls. Rate of force development and maximal voluntary contraction (MVC) during single leg knee extension of the right knee were measured isometrically for each subject. Balance was tested twice on a force plate with 15-second single-leg stands on the right leg. Rate of force development (N/second) and MVC (N) were extracted from the force-time curve as maximal rate of force development (= limit Deltaforce/Deltatime) and the absolute maximal value, respectively. RESULTS: The hypermobile subjects showed a significantly higher value for rate of force development (15.2% higher; P = 0.038, P = 0.453, epsilon = 0.693) and rate of force development related to body weight (16.4% higher; P = 0.018, P = 0.601, epsilon = 0.834) than the controls. The groups did not differ significantly in MVC (P = 0.767, P = 0.136, epsilon = 0.065), and MVC related to body weight varied randomly between the groups (P = 0.921, P = 0.050, epsilon = 0.000). In balance testing, the mediolateral sway of the hypermobile subjects showed significantly higher values (11.6% higher; P = 0.034, P = 0.050, epsilon = 0.000) than that of controls, but there was no significant difference (4.9% difference; P = 0.953, P = 0.050, epsilon = 0.000) in anteroposterior sway between the 2 groups. CONCLUSION: Hypermobile women without acute symptoms or limitations in activities of daily life have a higher rate of force development in the knee extensors and a higher mediolateral sway than controls with normal joint mobility.