Pedicle Screw Surgery in the UK and Ireland: A Questionnaire Study

Pedicle screw (PS) malpositioning rates are high in spine surgery. This has resulted in the use of computed navigational aids to reduce the rate of malposition; but these are often expensive and limited in availability. A simple mechanical device to aid PS insertion might overcome some of these disadvantages. The purpose of this study was to determine the demand and design criteria for a simple device to aid PS placement, as well as to collect opinions and experiences on PS surgery in the UK and Ireland. A postal questionnaire was sent to 422 spinal surgeons in the UK and Ireland. 101 questionnaires were received; 67 of these (16% of total sent) contained useful information. 78% of surgeons experienced problems with PS placement. The need for a simple mechanical device to aid PS placement was expressed by 59% of respondent surgeons. The proportion of respondents that inserted PSs in the cervical spine was 14%; PSs are mainly inserted in the thoracic, lumbar and sacral spine, but potential exists for a PS placement aid for the cervical and thoracic spine. From the experiences of these 67 surgeons, there is evidence to suggest that surgeons would prefer a pedicle aid that is multiple use, one-piece, hand-held, radiolucent, unilateral and uses the line of sight principle in traditional open surgery. Based on the experiences of 67 surgeons, there is evidence to suggest that computed navigational aids are not readily used in PS surgery and that a simple mechanical device could be a better option. This paper provides useful data for improving the outcomes of spinal surgery

A Review of the Design Process for Implantable Orthopedic Medical Devices

The design process for medical devices is highly regulated to ensure the safety of patients. This paper will present a review of the design process for implantable orthopedic medical devices. It will cover the main stages of feasibility, design reviews, design, design verification, manufacture, design validation, design transfer and design changes

MULTIPLE SCATTERING IN THE EXAFS OF CALCIUM PHOSPHATES

Pour analyser les spectres EXAFS de l'hydroxyapatite, du brushite et du monetite qui one été enregistrés au dessus de la limite d'absorption K de calcium, il faut utiliser la diffusion multiple par les atomes de phosphore à une distance de 0,37 nm du calcium. Si on n'utilise pas la diffusion multiple, quelques-uns des paramètres variables prennent des valeurs qui ne sont pas physiquement raisonnable. Nous n'avons jamais été obligés de varier les valeurs des rayons des atomes par plus de 0,01 nm de leur valeur dans les structures reconnues des cristaux.Analysis of the EXAFS spectra of hydroxyapatite, brushite and monetite, recorded above the calcium K edge, requires the inclusion of multiple scattering by phosphorus atoms at 0.37 nm, from calcium. If multiple scattering is not included, some variable parameters acquire physically unreasonable values. Atomic radii never had to be varied by more than 0.01 nm from their values in the accepted crystal structures

EXAFS CHARACTERISATION OF POORLY CRYSTALLINE DEPOSITS FROM BIOLOGICAL SYSTEMS IN THE PRESENCE OF HIGHLY CRYSTALLINE MINERAL

EXAFS peut être utiliser pour établir l'identité de la phase d'un dépôt amorphe calcifié melangé avec une phase crystalline que ne contient pas de calcium. Dans un tel mélange, il n'est peut être pas possible de distinguer la phase amorphe par le diffraction des rayons X. Cette application d'EXAFS est illustrée par l'identification du phosphate de calcium qui est déposé, en association avec le struvite, dans les cathéters urinaires incrustés.EXAFS can be used to characterise the phase of an amorphous calcified deposit mixed with a crystalline phase which does not contain calcium. In such a mixture, the amorphous phase may not be detectable by X-ray diffraction. This application of EXAFS is illustrated by the characterisation of the calcium phosphate deposited in association with struvite in encrusted urinary catheters

Computer and experimental modelling of blood flow through the mitral valve of the heart

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Influence of fibril taper on the function of collagen to reinforce extracellular matrix

Collagen fibrils provide tensile reinforcement for extracellular matrix. In at least some tissues, the fibrils have a paraboloidal taper at their ends. The purpose of this paper is to determine the implications of this taper for the function of collagen fibrils. When a tissue is subjected to low mechanical forces, stress will be transferred to the fibrils elastically. This process was modelled using finite element analysis because there is no analytical theory for elastic stress transfer to a non-cylindrical fibril. When the tissue is subjected to higher mechanical forces, stress will be transferred plastically. This process was modelled analytically. For both elastic and plastic stress transfer, a paraboloidal taper leads to a more uniform distribution of axial tensile stress along the fibril than would be generated if it were cylindrical. The tapered fibril requires half the volume of collagen than a cylindrical fibril of the same length and the stress is shared more evenly along its length. It is also less likely to fracture than a cylindrical fibril of the same length in a tissue subjected to the same mechanical force