Assessment of coxarthritis risk with dimensionless biomechanical parameters.

PURPOSE: Unfavourable distribution of contact stress over the load bearing area is considered a risk factor for early coxarthritis and it is of interest to outline respective biomechanical parameters for its prediction. The purpose of the work was to develop a transparent mathematical model which can be used to assess contact stress in the hip from imaged structures of pelvis and proximal femora, in large population studies and in clinical practice. METHODS: We upgraded a previously validated three-dimensional mathematical model of the human hip in the one-legged stance HIPSTRESS by introducing parameters independent from the size of the structures in the images. We validated a new parameter - dimensionless peak stress normalized by the body weight and by the radius of the femoral head (pmaxr²/WB) on the population of 172 hips that were in the childhood subjected to the Perthes disease and exhibited increased proportion of dysplastic hips. RESULTS: The dimensionless parameter pmaxr²/WB exhibited smaller number of indecisive cases of hip dysplasia predicted by the model than the previously used parameter pmax/WB (6% vs. 81%, respectively). A threshold for an increased risk of early coxarthritis development by the HIPSTRESS parameter H = pmaxr²/WB was found to be 2. CONCLUSIONS: We proposed a dimensionless peak stress on the load bearing area with the border value of 2 as a decisive parameter over which hips are at risk for early development of degenerative processes and presented a method for determination of biomechanical parameters with the use of nomogram.

Applicability of extracellular vesicles in clinical studies.

BACKGROUND: Extracellular vesicles (EVs) are submicron cellular fragments that mediate intercellular communication. EVs have in the last decade attracted major interest as biomarkers or platforms for biomarkers of health and disease. To better understand the reasons why despite great expectations and considerable effort, EV-based methods have not yet been introduced into clinical practice, we present a systematic analysis of published results of clinical studies. MATERIALS AND METHODS: Clinical studies on populations of body fluid samples, published from 2010 to including 2015, applying centrifugation of fluid human samples with centrifuge accelerations up to about 25 000 g and flow cytometry for detection of EVs were analysed with respect to statistical significance (p), statistical power (P), clinical significance (CS), defined as the difference between the means divided by the sum of standard deviations, and size of the populations (Nmin ), defined as the number of samples in the smaller group. RESULTS: Final analysis included 65 publications with 716 comparisons reporting 308 (43%) statistically significant differences (P < 0·05), 242 (34%) had statistical power P > 0·8 and 88 (12%) had clinical importance CS > 1·96. None of comparison with CS > 1·96 included populations in which the smaller group consisted of 50 or more samples. CONCLUSIONS: To fulfil claimed expectations for EV-based methods as promising diagnostic tools, more evidence on EV-based mechanisms of diseases should be gathered. Also, the methods of EV harvesting and assessment should be improved to yield better repeatability and thus allow clinical studies with larger number of samples.