The effect of structural changes on the low strain rate behaviour of the intervertebral disc.

The annuus fibrosus (AF) and nucleus pulposus (NP) of the intervertebral disc (IVD) work in conjunction to dissipate spinal loads. In this study we have isolated the contribution of the NP to the overall response of the disc and investigated the effect of extreme structural changes to the disc on the mechanical behaviour. Linear stiffness, overall load range, hysteresis area and total energy were used to evaluate the impact of these changes on the spine and surrounding structures.

Properties of PMMA end cap holders affect FE stiffness predictions of vertebral specimens.

Bone cement is often used, in experimental biomechanics, as a potting agent for vertebral bodies (VB). As a consequence, it is usually included in finite element (FE) models to improve accuracy in boundary condition settings. However, bone cement material properties are typically assigned to these models based on literature data obtained from specimens created under conditions which often differ from those employed for cement end caps.

A Novel Modelling Methodology Which Predicts the Structural Behaviour of Vertebral Bodies under Axial Impact Loading: A Finite Element and DIC Study.

Cervical spine injuries (CSIs) arising from collisions are uncommon in contact sports, such as rugby union, but their consequences can be devastating. Several FE modelling approaches are available in the literature, but a fully calibrated and validated FE modelling framework for cervical spines under compressive dynamic-impact loading is still lacking and material properties are not adequately calibrated for such events. This study aimed to develop and validate a methodology for specimen-specific FE modelling of vertebral bodies under impact loading.

Material property calibration is more important than element size and number of different materials on the finite element modelling of vertebral bodies: A Taguchi study.

Finite element (FE) modelling of a vertebral body (VB) is considered challenging due to the many parameters involved such as element size and type, and material properties. Previous studies have reported how these parameters affect the mechanical behaviour of a VB model; however, most studies just compared results without any specific statistical tool to quantify their influence. The Taguchi Method (TM) has been successfully used in manufacturing and biomechanics to evaluate process parameters and to determine optimum set-up conditions.

Musculoskeletal modelling of the human cervical spine for the investigation of injury mechanisms during axial impacts.

Head collisions in sport can result in catastrophic injuries to the cervical spine. Musculoskeletal modelling can help analyse the relationship between motion, external forces and internal loads that lead to injury. However, impact specific musculoskeletal models are lacking as current viscoelastic values used to describe cervical spine joint dynamics have been obtained from unrepresentative quasi-static or static experiments.

The equivalence of multi-axis spine systems: Recommended stiffness limits using a standardized testing protocol.

The complexity of multi-axis spine testing often makes it challenging to compare results from different studies. The aim of this work was to develop and implement a standardized testing protocol across three six-axis spine systems, compare them, and provide stiffness and phase angle limits against which other test systems can be compared. Standardized synthetic lumbar specimens (n=5), comprising three springs embedded in polymer at each end, were tested on each system using pure moments in flexion-extension, lateral bending, and axial rotation.

The application of physiological loading using a dynamic, multi-axis spine simulator.

In-vitro testing protocols used for spine studies should replicate the in-vivo load environment as closely as possible. Unconstrained moments are regularly employed to test spinal specimens in-vitro, but applying such loads dynamically using an active six-axis testing system remains a challenge. The aim of this study was to assess the capability of a custom-developed spine simulator to apply dynamic unconstrained moments with an axial preload.

The influence of tibial component malalignment on bone strain in revision total knee replacement.

Revision total knee replacement is a challenging surgical procedure typically associated with significant loss of bone stock in the proximal tibia. To increase the fixation stability, extended stems are frequently used for the tibial component in revision surgery. The design of the tibial stem influences the load transfer from tibial component to the surrounding bone and is cited as a possible cause for the clinically reported pain in the location of the stem-end.

Dynamic, six-axis stiffness matrix characteristics of the intact intervertebral disc and a disc replacement.

Thorough pre-testing is critical in assessing the likely in vivo performance of spinal devices prior to clinical use. However, there is a lack of data available concerning the dynamic testing of lumbar (porcine model) total disc replacements in all six axes under preload conditions. The aim of this study was to provide new data comparing porcine lumbar spinal specimen stiffness between the intact state and after the implantation of an unconstrained total disc replacement, in 6 degrees of freedom.

An investigation into axial impacts of the cervical spine using digital image correlation.

Background Context: High-energy impacts are commonly encountered during sports such as rugby union. Although catastrophic injuries resulting from such impacts are rare, the consequences can be devastating for all those involved. A greater level of understanding of cervical spine injury mechanisms is required, with the ultimate aim of minimizing such injuries.

The dynamic, six-axis stiffness matrix testing of porcine spinal specimens.

Background Context: Complex testing protocols are required to fully understand the biomechanics of the spine. There remains limited data concerning the mechanical properties of spinal specimens under dynamic loading conditions in six axes.

Purpose: To provide new data on the mechanical properties of functional spinal unit (FSU) and isolated disc (ISD) spinal specimens in 6 df.

Pectoralis major tendon repair: a biomechanical study of suture button versus transosseous suture techniques.

Purpose: Pectoralis major tendon avulsion injury benefits from surgical repair. The technique used and speed of rehabilitation in this demanding population remains subject to debate. We performed a biomechanical study comparing suture button (Pec Button™, Arthrex, Naples, FL) with a transosseous suture technique (FibreWire, Arthrex, Naples, FL).

The development of a dynamic, six-axis spine simulator.

Background Context: Although a great deal of research has been completed to characterize the stiffness of spinal specimens, there remains a limited understanding of the spine in 6 df and there is a lack of data from dynamic testing in six axes.

Purpose: This study details the development and validation of a dynamic six-axis spine simulator.

Study Design: Biomechanical study.

A biomechanical evaluation of hinged total knee replacement prostheses.

The number of total knee replacements being performed worldwide is undergoing an unprecedented increase. Hinged total knee replacements, used in complex salvage and revision procedures, currently account for a small but growing proportion of prostheses implanted. Modern hinged prostheses share the same basic configuration, allowing flexion-extension and tibial rotation.

Intradiscal pressure changes with dynamic pedicle screw systems.

Study Design: In vitro study using porcine spines instrumented with pedicle screw and rod fixation.

Objectives: To determine the intradiscal pressure (IDP) changes with the use of dynamic and rigid pedicle screw systems in simulated spinal fusion.

Summary Of Background Data: The intervertebral discs are prone to injury under conditions of altered IDP.

Ultrasound mimics the effect of mechanical loading on bone formation in vivo on rat ulnae.

While the effect of ultrasound as an extreme example of low-magnitude high-frequency stimulation has been explored in the response of bone to injury, little is known about its effect on normal bone. This experiment was designed to test the hypothesis that ultrasound exerts a similar influence on bone as mechanical stimulation at a physiological level. Three groups of female Wistar rats were anaesthetised (6 per group).

Ultrasound transmission loss across transverse and oblique bone fractures: an in vitro study.

An axial transmission technique has been used to investigate the changes in the first arrival time and signal amplitude of 200 kHz ultrasonic waves travelling across different fracture geometries. Results taken from intact bovine femora were compared with those produced when a transverse and an oblique fracture were simulated. The arrival time and signal amplitude displayed a different variation with receiver position for the two geometries and a given fracture gap width.

Locking plates increase the strength of dynamic hip screws.

Introduction: Failure of a dynamic hip screw (DHS) fixation leads to decreased mobility of the patient and frequently to a decrease in general health. The most common mode of failure of a DHS is cut out of the lag screw from the femoral head. The second most common mode of failure is lift-off of the plate from the femur.

In vitro pressurization of the acetabular cement mantle: the effect of a flange.

A model was developed to assess the effect of an acetabular flange on pressure within different zones of the cement mantle during insertion. Two prosthetic designs were assessed in 3 different sizes. Flanged components produced significantly higher mean pressures than unflanged ones (P < .

Mechanical characterisation of three percutaneous vertebroplasty biomaterials.

Percutanous vertebroplasty (PVP) is gaining popularity for the treatment of vertebral compression fractures. The need of obtaining low viscosity materials for injection through small bore needles and the necessity of visualising the fluid flow during injection have led users to the formulation of a number of ad-hoc recipes aimed at adapting PMMA cements for this use. Industry, on its part, has addressed these requirements by developing specific products for this application.

Factors affecting the mechanical and viscoelastic properties of acrylic bone cement.

The aim of this paper is to report a series of experiments investigating the factors that influence the viscoelastic properties of acrylic bone cement. The effects of the brand of cement, the length of time since mixing, temperature, the hydration of the cement, and the influence of fat and or blood in the environment on the creep and stress relaxation behavior of the cement have been studied in laboratory-prepared specimens in tension, compression and four point bending. Although there are significant differences in the viscoelastic behavior of some of the different brands of polymethylmethacrylate based cements, these differences are small by comparison with the major effects that can be exerted by the length of time since mixing and some environmental factors.

An in-vitro investigation of the CPS-Plus femoral stem: influence of the proximal centraliser on cement pressurisation during stem insertion.

The CPS-Plus stem is designed for use with a proximal and distal stem centraliser. This in-vitro study examined the cement pressurisation achieved during insertion of the CPS-Plus femoral stem into a model femur. Cement pressures were measured at proximal, mid and distal stem levels.

Mechanical characteristics of antibiotic-laden bone cement.

We studied the mechanical characteristics of cement-antibiotic combinations in vitro. Palacos R was tested without antibiotics, with gentamicin alone and with gentamicin plus vancomycin or flucloxacillin. Palacos LV was studied only with gentamicin added.