Temporal lobe sparing radiotherapy with photons or protons for cognitive function preservation in paediatric craniopharyngioma.

BACKGROUND AND PURPOSE: Reducing radiation exposure to the temporal lobes could be beneficial to preserve cognitive function in paediatric brain tumour patients. The distribution of doses to brain substructures associated with cognition (BSCs) both within and outside of the temporal lobe have not been reported. The aim of this study was therefore to investigate temporal lobe sparing photon vs. proton therapy for paediatric suprasellar tumours. MATERIAL AND METHODS: Data from ten anonymized craniopharyngioma patients were used in this study. Temporal lobe sparing volumetric modulated arc therapy (VMAT) and pencil beam scanning (PBS) proton therapy plans were optimized to maintain consistent target metrics as in the delivered double scattering proton therapy (DSPT) plans. Thirty BSCs were delineated, including temporal lobe substructures (i.e. amygdala, hippocampus, entorhinal cortex). The dose/volume fractions to each BSC were analysed, and intelligence quotient (IQ) as well as memory scores were estimated to compare the different modalities. RESULTS: The exposed volumes of the temporal lobes and their substructures were consistently reduced with PBS compared to DSPT and VMAT, e.g. the left hippocampus V10Gy from 100% (VMAT) or 41% (DSPT) to 5% with PBS (p = 0.002). Some of the ventricular substructures were better spared with VMAT compared to both proton modalities. The reduced doses to the temporal lobes achieved with PBS translated into improved predicted memory outcomes, but not for the estimated IQ. CONCLUSION: The irradiated volumes of temporal lobe BSCs were consistently the lowest with PBS, whereas the model-based estimates of cognitive outcomes were less consistent.

In-shoe pressure measurement and foot orthosis research: a giant leap forward or a step too far?

Foot orthoses are believed to exert their therapeutic effect on the human locomotor apparatus by altering the location, magnitude, and temporal patterns of ground reaction forces acting on the plantar foot during weightbearing activities. In-shoe pressure-measurement systems are increasingly being used by clinicians and researchers to assess kinetic changes at the foot-orthosis interface to better understand the function of foot orthoses and to derive more efficacious treatments for many painful foot and lower-extremity abnormalities. This article explores how the inherent three-dimensional surface topography and load-deformation characteristics of foot orthoses may challenge the validity, reliability, and clinical usefulness of the data obtained from in-shoe pressure-measurement systems in the context of foot orthotic therapy and research. The inability of in-shoe pressure-measurement systems to measure shearing forces beneath the foot, the required bending of the flat two-dimensional sensor insole to fit the pressure insole to the three-dimensional curves of the orthosis, the subsequent unbending of the sensor insole to display it on a computer monitor, and variations in the load-deformation characteristics of orthoses are all sources of potential error in examination of the kinetic effects of foot orthoses. Consequently, caution is required when interpreting the results of orthotic research that has used in-shoe pressure insole technology. The limitations of the technology should also be given due respect when in-shoe pressure measurement is used to make clinical decisions and prescribe custom foot orthoses for patients.

Effect of 7-degree rearfoot varus and valgus wedging on rearfoot kinematics and kinetics during the stance phase of walking.

BACKGROUND: The scientific evidence behind the mechanical function of foot orthoses is still controversial. Research studies that have investigated the kinematic effect of foot orthoses on the lower extremity have shown variable results, with orthoses causing either no significant change or a small significant change in foot kinematics. METHODS: The right limbs of 12 healthy asymptomatic individuals were studied in three walking conditions: barefoot, with a 7 degrees rearfoot varus wedge, and with a 7 degrees rearfoot valgus wedge. Kinematic and kinetic variables measured were the foot progression angle, the peak internal tibial rotation angle, and net ankle inversion moments during the stance phase in the three conditions. RESULTS: There were statistically significant differences in the foot progression angle between the barefoot and varus wedge conditions and between the varus and valgus wedge conditions. There were no significant changes in peak internal tibial rotation among the three conditions tested. However, rearfoot varus wedges significantly reduced net ankle inversion moments compared with barefoot and rearfoot valgus wedges. CONCLUSIONS: These results support the idea that foot orthoses work by methods other than by changing kinematic parameters. The present study supports the concept that foot orthoses work primarily by altering kinetics, with their effects on kinematics being secondary.

Static response of maximally pronated and nonmaximally pronated feet to frontal plane wedging of foot orthoses.

BACKGROUND: Research on foot orthoses has shown that their effect on the kinematics of the rearfoot is variable, with no consistent patterns of changes being demonstrated. It has also been hypothesized that the mechanical effect of foot orthoses could be subject specific. The purpose of our study was to determine if maximally pronated feet have a different response to frontal plane wedging of foot orthoses than do nonmaximally pronated feet during static stance. METHODS: One hundred six feet of 53 healthy asymptomatic subjects were divided into two groups (maximally pronated and nonmaximally pronated) on the basis of their subtalar joint rotational position during relaxed bipedal stance. Functional foot orthoses were constructed for each subject and the relaxed calcaneal stance position was measured while standing on five separate frontal plane orthosis wedging conditions, 10 degrees valgus, 5 degrees valgus, no wedging, 5 degrees varus, and 10 degrees varus, to assess changes in calcaneal position. RESULTS: Relative to the no-wedging condition, there were statistically significant differences (P < .05) in calcaneal position between the maximally pronated and the nonmaximally pronated feet with the 10 degrees valgus and the 10 degrees varus wedging conditions. No significant differences in calcaneal position were found with the 5 degrees varus and the 5 degrees valgus wedging conditions. CONCLUSIONS: Our study shows that the response to foot orthoses is variable between individuals. Maximally pronated subjects do not exhibit the same response to frontal plane wedging of foot orthoses as do nonmaximally pronated with 10 degrees wedging. Intrinsic biomechanical factors such as subtalar joint position may influence the response to foot orthoses.

In vivo tests of an improved method for functional location of the subtalar joint axis.

The subtalar joint is important in frontal plane movement and posture of the hindfoot. Abnormal subtalar joint moments caused by muscle forces and the ground reaction force acting on the foot are thought to play a role in various foot deformities. Calculating joint moments typically requires knowledge of the location of the joint axis; however, location of the subtalar axis from measured movement is difficult because the talus cannot be tracked using skin-mounted markers. The accuracy of a novel technique for locating the subtalar axis was assessed in vivo using magnetic resonance imaging. The method was also tested with skin-mounted markers and video motion analysis. The technique involves applying forces to the foot that cause pure subtalar joint motion (with negligible talocrural joint motion), and then using helical axis decomposition of the resulting tibiocalcaneal motion. The resulting subtalar axis estimates differed by 6 degrees on average from the true best-fit subtalar axes in the MRI tests. Motion was found to have been applied primarily about the subtalar joint with an average of only 3 degrees of talocrural joint motion. The proposed method provides a potential means for obtaining subject-specific subtalar axis estimates which can then be used in inverse dynamic analyses and subject-specific musculoskeletal models.

Determination of subtalar joint axis location by restriction of talocrural joint motion.

The location of the subtalar joint axis is an important determinant of the mechanical function of the foot. The moments of muscle forces and of the ground reaction force about the subtalar joint are dependent upon the location of this joint axis. There is substantial variation in subtalar axis location across subjects, but current methods for determining its location are often invasive or involve expensive imaging protocols. A novel technique for location of the subtalar axis is presented in which the talocrural joint is passively immobilized so that motion of the tibia relative to the calcaneus can be used to estimate the subtalar axis. This paper presents results of cadaver testing in which accuracy of the technique was assessed by comparing helical axes computed from calcaneus-tibia bone motions to axes computed from calcaneus-talus bone motions. Only small motions at the talocrural joint were observed, and good estimates of the subtalar axis (errors less than 15 degrees and 2mm) were achieved in four of six specimens.

The subtalar joint axis locator: a preliminary report.

A new clinical device, the subtalar joint axis locator, was created to track the three-dimensional location of the subtalar joint axis during weightbearing movements of the foot. The assumption was that if the anterior exit point of the subtalar joint axis is stationary relative to the dorsal aspect of the talar neck, then, by performing radiographs of the feet with the subtalar joint axis locator in place on the foot, the ability of the locator to track rotations and translations of the talar neck and thus the subtalar joint axis in space could be approximated. In this preliminary study of two adults, the subtalar joint axis locator accurately tracked the talar neck position during weightbearing rotational motions of the subtalar joint. The device was also used in a series of subjects to determine its dynamic capabilities. It is possible, then, that the subtalar joint axis locator can reliably track the spatial location of the subtalar joint axis during weightbearing movements of the foot.

Effects of simulated genu valgum and genu varum on ground reaction forces and subtalar joint function during gait.

The mechanical effects of genu valgum and varum deformities on the subtalar joint were investigated. First, a theoretical model of the forces within the foot and lower extremity during relaxed bipedal stance was developed predicting the rotational effect on the subtalar joint due to genu valgum and varum deformities. Second, a kinetic gait study was performed involving 15 subjects who walked with simulated genu valgum and genu varum over a force plate and a plantar pressure mat to determine the changes in the ground reaction force vector within the frontal plane and the changes in the center-of-pressure location on the plantar foot. These results predicted that a genu varum deformity would tend to cause a subtalar pronation moment to increase or a supination moment to decrease during the contact and propulsion phases of walking. With genu valgum, it was determined that during the contact phase a subtalar pronation moment would increase, whereas in the early propulsive phase, a subtalar supination moment would increase or a pronation moment would decrease. However, the current inability to track the spatial position of the subtalar joint axis makes it difficult to determine the absolute direction and magnitudes of the subtalar joint moments.

Reliability and accuracy of biomechanical measurements of the lower extremities.

The reliability of biomechanical measurements of the lower extremities, as they are commonly used in podiatric practice, was quantified by means of intraclass correlation coefficients (ICCs). This was done not only to evaluate interrater and intrarater reliability but also to provide an estimate for the accuracy of the measurements. The measurement protocol involved 30 asymptomatic subjects and five raters of varying experience. Each subject was measured twice by the same rater, with the retest immediately following the test. The study demonstrated that the interrater ICCs were quite low (< or =0.51), except for the measurements of relaxed calcaneal stance position and forefoot varus (both 0.61 and 0.62 for left and right, respectively). However, the intrarater ICCs were relatively high (>0.8) for most raters and measurement variables. Measurement accuracy was moderate between raters.

Biological adaptabilities and quantum entropies.

The entropy-based theory of adaptability set forth by Michael Conrad in the early 1970s continued to appear in his work for over two decades, and was the subject of the only book he published in his lifetime. He applied this theory to a host of subjects ranging from enzyme dynamics to sociology. This paper reviews the formalism of adaptability theory, clarifying some of its mathematical and interpretive difficulties. The theory frames the computational tradeoff principle, a thesis that was the most frequently recurring claim in his work. The formulation of adaptability theory presented here allows the introduction of quantum entropy functions into the theory, revealing an interesting relationship between adaptability and another one of Conrad's deep preoccupations, the role of quantum processes in life.