Influence of muscle forces on femoral strain distribution

Musculoskeletal loading influences the stresses and strains within the human femur and thereby affects the processes of bone modeling and remodeling. It is essential for implant design and simulations of bone modeling processes to identify locally high or low strain values which may lead to bone resorption and thereby affect the clinical outcome. Using a finite element model the stresses and strains of a femur with all thigh muscle and joint contact forces were calculated for four phases of a gait cycle. Reduced load sets with only a few major muscles were analyzed alternatively. In a completely balanced femur with all thigh muscles the stress and strain patterns are characterized by combined bending and torsion throughout the bone. Similar to in vivo recordings, the model with all thigh muscles showed peak surface strains below 2000 mu epsilon (45% gait cycle). Under simplified load regimes surface strains reached values close to 3000 mu epsilon. Within the proximal femur, the simplified load regimes produced differences in strain as high as 26% in comparison to those with all thigh muscles included. This difference is reduced to 5% if the adductors are added to a loading consisting of hip contact, abductors and ilio-tibial band. This study demonstrates the importance of an ensemble of muscle forces to reproduce a physiological strain distribution in the femur. Analytical attempts to simulate bone modeling, remodeling or bone density distributions should therefore rely on fully balanced external load regimes which account for the role of the various soft tissue forces

Distribution and seasonality of microbial indicators and thermophilic campylobacters in two freshwater sites on the River Lune in North West England.

Two freshwater bathing sites, the Crook O'Lune and the University Boathouse, on the River Lune in the north-west of England, were monitored over a 2 year period for the faecal indicators, faecal coliforms and faecal streptococci, the pathogens, Salmonella and Campylobacter, and compliance with the EU Directive on Bathing Water Quality. Faecal indicator numbers showed no seasonal variation, with numbers in the bathing season similar to those in the non-bathing season. They were consistently above the EU Guideline and Imperative standards so that if the EU Bathing Water Quality Directive (76/160/EEC) were applied, neither site would comply. Faecal indicator numbers in the sediments were an order of magnitude higher than in the overlying water. Campylobacter numbers showed seasonal variation in the water with higher counts in winter than in the summer, although numbers were low. Higher numbers were found in the sediments but there was no seasonal variation. Analysis of various inputs showed that indicators and campylobacters came from a mixture of sources, namely a sewage treatment works, agricultural run-off, streams and mallards. Microbial numbers in the water at the Crook O'Lune, which is closer to the sources of pollution, were twice those at the Boathouse. In the sediments they were six to eight times higher. Faecal coliforms were all identified as Escherichia coli of which 80% were a single biotype. Faecal streptococci were all enterococci of which 55% were E. avium, 38%E. faecalis and 7%E. durans. Salmonella was not isolated from either the water column or the sediments. Campylobacters were mainly Camp. jejuni, followed by Camp. coli, UPTC and Camp. lari