Epidemiology of meniscus position: associations with knee symptoms and osteoarthritis

Meniscal extrusion (ME) in the knee joint is defined as when the peripheral border of the meniscus is substantially located outside the joint margin. Prior studies have reported that ME is associated with meniscal tears, meniscal degeneration, and the presence of knee osteoarthritis (OA). Medial ME of the body of 3 mm or more, as seen on knee Magnetic Resonance Imaging (MRI) has a wide acceptance to be regarded as “pathologic”. However, it is still unclear if ME is associated with knee pain. My aims with this thesis were to: i) study the normal ME with its change over time and its relationship with meniscus tear/damage in knees without OA; ii) to scrutinize the widely accepted 3 mm cut-off for “pathological” medial ME; iii) determine an optimal cut-off for ME associated with radiographic knee OA, bone marrow lesions (BMLs) and cartilage damage; and iv) investigate the association between medial ME and pain in knees without radiographic OA.In paper I we used 118 subjects from the Osteoarthritis Initiative (OAI) “non-exposed” reference cohort (aged 45-79 years, free of knee pain, radiographic knee OA and risk factors for knee OA) and in papers 2-4 1004 subjects from the community based Framingham Osteoarthritis Study (aged 50–90 years, selection not made on the basis of knee problems). MRI´s were read for ME, cartilage coverage, BMLs and cartilage damage. Knee x-rays were read according to the Kellgren and Lawrence scale. I estimated changes in ME over 4 years using repeat knee MRI. I evaluated the 3 mm cut-off and estimated a new cut-off for “pathologic” extrusion. The odds ratio (OR) for pain as outcome, with ME as exposure was estimated and adjusted for age, sex, body mass index, meniscal tear, BMLs, cartilage damage and previous knee injury as confounders.In the OAI-cohort we found only minor increase in medial ME over 4 years. In the Framingham cohort ME was on average 2.7 mm medially and 1.8 mm laterally. Cartilage coverage was about 30% of ipsilateral cartilage surface. Meniscal damage was associated with more ME medially. A new estimated 4 mm cut-off maximizes the sum of sensitivity and specificity for the OA features radiographic OA, BML and cartilage damage. The OR for knee pain was 1.15 (95% confidence interval 0.97, 1.37) per 1 mm more ME, indicating only a weak association with pain.In conclusion my thesis delivers an array of novel normative data for meniscus body position on MRI, as well as its associations with meniscal damage and knee OA. Medial ME is strongly associated with knee OA. The cut-off value 4 mm may be a more optimal cut-off to use than 3 mm to be considered ”pathologic”. Further, medial ME per se seems to have a weak association with pain in knees free of radiographic OA.

The Internet and Trade

This paper aims to assess the effects of internet usage on bilateral trade volumes. Increasingly companies are conducting business online. If the effect of an increased internet usage on trade is positive then it would be yet another reason for policy makers to invest in the development and expansion of IT infrastructure. Three main models are specified using the fixed effects estimator, including the least squares estimator and a Poisson maximum likelihood estimator. This paper uses an extensive panel data set of 180 countries and the most recent internet usage data available (2000-2014) to examine the effects of internet usage on bilateral trade. By using a gravity model specification the results are indicating a significant positive relationship between internet usage and bilateral trade performance. The effect is larger when more weight is given to countries with smaller internet usage rates. The spatial relationship of this effect is also examined via a Hausman-Taylor estimation and a random effects model. The results from these models indicates that there is a proximity effect, the larger the distance between trading countries, the smaller the effect of internet usage on trade

Moment Estimation Using a Marginalized Transform

We present a method for estimating mean and covariance of a transformed Gaussian random variable. The method is based on evaluations of the transforming function and resembles the unscented transform and Gauss-Hermite integration in that respect. The information provided by the evaluations is used in a Bayesian framework to form a posterior description of the parameters in a model of the transforming function. Estimates are then derived by marginalizing these parameters from the analytical expression of the mean and covariance. An estimation algorithm, based on the assumption that the transforming function can be described using Hermite polynomials, is presented and applied to the non-linear filtering problem. The resulting marginalized transform (MT) estimator is compared to the cubature rule, the unscented transform and the divided difference estimator. The evaluations show that the presented method performs better than these methods, more specifically in estimating the covariance matrix. Contrary to the unscented transform, the resulting approximation of the covariance matrix is guaranteed to be positive-semidefinite

Resource Management and Prioritization in an Embedded Linux System

This master thesis tackles the problem of limited computing resources on a camera that is executing computing applications together with image acquisition and streaming. The thesis was carried out at Axis Communications in cooperation with the Department of Automatic Control at Lund University. The problem of limited resources on an Axis camera is handled by a two part solution where a resource manager (RM) distributes the available resources and services can adapt their service level (SL) in order to finish their jobs on time. The solution is based on game theory, where services are players, varying their service levels in order to get a good match between given resources and their computing requirements. This service level adaptation scheme is implemented for the streaming service on the camera and for some test services, performing mathematical operations. The resource manager is incorporated into systemd, and uses cgroups [16] to distribute the computing capacity. The experimental results show that the resource manager is fully operational and capable of managing and prioritizing resources as intended on the embedded system

Resolving issues of scaling for gramian-based input–output pairing methods

A key problem in process control is to decide which inputs should control which outputs. There are multiple ways to solve this problem, among them using gramian-based measures, which include the Hankel interaction index array, the participation matrix and the (Formula presented.) method. The gramian-based measures, however, have issues with input and output scaling. Generally, this is resolved by scaling all inputs and outputs to have equal range. However, we demonstrate how this can result in an incorrect pairing and examine alternative methods of scaling the gramian-based measures, using either row or column sums or by utilising the Sinkhorn-Knopp algorithm. To systematically analyse the benefits of the scaling schemes, a multiple-input multiple-output model generator is used to test the different schemes on a large number of systems. This assessment shows considerable benefits to be gained from the alternative scaling of the gramian-based measures, especially when using the Sinkhorn-Knopp algorithm