Do non-rearfoot runners experience greater second metatarsal stresses than rearfoot runners?

Stress fracture of the second metatarsal is a common and problematic injury for runners. The choice of foot strike pattern is known to affect external kinetics and kinematics but its effect on internal loading of the metatarsals is not well understood. Models of various complexities can be used to investigate the effects of running characteristics on metatarsal stresses. This study aimed to compare second metatarsal stress between habitual rearfoot and non-rearfoot strikers during barefoot running, using a novel participant-specific finite element model, including accurate metatarsal and soft tissue geometry. Synchronised force and kinematic data were collected during barefoot overground running from 20 participants (12 rearfoot strikers). Stresses were calculated using a previously evaluated and published 3D finite element model. Non-rearfoot strikers demonstrated greater external loading and joint contact forces than rearfoot runners, but there were no differences in stresses between groups. Additionally, the study allowed for a qualitative assessment of bone geometries and stresses. No correlation was found between bone volume and stresses, however, there was found to be a large variation in metatarsal shapes, possibly accounting for the lack of difference in stresses. This emphasises the importance of bone geometry when estimating bone stress and supports the suggestion that external forces should not be assumed to be representative of internal loading.

Three dimensional finite element modelling of metatarsal stresses during running.

Second metatarsal stress fractures are a problematic injury for runners and are formed when the rate of repair of bone is outpaced by the damage accumulated during loading. Measuring the peak stresses on the bone during running gives an indication of damage accumulation but direct measurement is invasive. Finite element modelling is a viable alternative method of accurately estimating bone stresses but tends to be too computationally expensive for use in applied research. This study presents a novel and simple finite element model which can estimate bone stresses on the second metatarsal during the stance phase of walking and running, accounting for joint reaction forces and soft tissue effects. The influence of the forces and kinematic inputs to the model and the presence of the soft tissues was quantified using a sensitivity analysis. The magnitudes of maximum stress from the model are similar to existing finite element models and bone staple strain gauge values collected during walking and running. The model was found to be most sensitive to the pitch angle of the metatarsal and the joint reaction forces and was less sensitive to the ground reaction forces under the metatarsal head, suggesting that direct measurement of external forces should not be assumed to represent internal stresses.

Incorporating subject-specific geometry to compare metatarsal stress during running with different foot strike patterns.

Stress fracture of the second metatarsal is a common and problematic injury for runners. The choice of foot strike pattern is known to affect external kinetics and kinematics but its effect on internal loading of the metatarsals is not well understood. Subject-specific models of the second metatarsal can be used to investigate internal loading in a non-invasive manner. This study aimed to compare second metatarsal stress between habitual rearfoot and non-rearfoot strikers during barefoot running, using a novel subject-specific mathematical model, including accurate metatarsal geometry. Synchronised force and kinematic data were collected during barefoot overground running from 20 participants (12 rearfoot strikers). Stresses were calculated at the plantar and dorsal periphery of the midshaft of the metatarsal using a subject-specific beam theory model. Non-rearfoot strikers demonstrated greater external loading, bending moments and compressive forces than rearfoot strikers, but there were no differences in peak stresses between groups. Statistical parametric analysis revealed that non-rearfoot strikers had greater second metatarsal stresses during early stance but that there was no difference in peak stresses. This emphasises the importance of bone geometry when estimating bone stress and supports the suggestion that external forces should not be assumed to be representative of internal loading.

Ectopic splenic tissue failed to prevent fatal pneumococcal septicaemia after splenectomy for trauma.

Despite heterotopic splenic tissue, fatal fulminating pneumococcal septicaemia occurred in 2 patients who had had splenectomy for trauma. A girl aged 12 who died 8 years after splenectomy had over a hundred nodules, the largest weighing 3 g. A man of 19 who died 9 years after splenectomy had splenic tissue weighing 92 g. The presence of splenic tissue did not itself protect these patients from overwhelming infection and its ectopic situation with the consequent alteration in blood-supply may be of greater importance than the amount of splenic tissue present.

Carboxyhaemoglobin dissociation in the cadaver following attempted resuscitation.

A series of 300 cases of fatal carbon-monoxide poisoning showed wide variations in carboxyhaemoglobin saturation. Levels below 50% in 24 subjects under the age of 70 were probably falsely low following attempted resuscitation on the way to hospital. Artificial respiration, especially with oxygen-rich gas, causes dissociation of carboxyhaemoglobin in the lungs of the cadaver while movement of blood into and out of the lungs, with mixing, lowers the saturation levels in the neighbouring large veins. In four cases subclavian blood showed saturation levels much lower than blood from sites further from the lungs. Blood should be taken from the femoral vein to get true readings.