Viscoelasticity of articular cartilage: Analysing the effect of induced stress and the restraint of bone in a dynamic environment.

The aim of this study was to determine the effect of the induced stress and restraint provided by the underlying bone on the frequency-dependent storage and loss stiffness (for bone restraint) or modulus (for induced stress) of articular cartilage, which characterise its viscoelasticity. Dynamic mechanical analysis has been used to determine the frequency-dependent viscoelastic properties of bovine femoral and humeral head articular cartilage. A sinusoidal load was applied to the specimens and out-of-phase displacement response was measured to determine the phase angle, the storage and loss stiffness or modulus.

Biotransformation of Silver Released from Nanoparticle Coated Titanium Implants Revealed in Regenerating Bone.

Antimicrobial silver nanoparticle coatings have attracted interest for reducing prosthetic joint infection. However, few studies report in vivo investigations of the biotransformation of silver nanoparticles within the regenerating tissue and its impact on bone formation. We present a longitudinal investigation of the osseointegration of silver nanoparticle-coated additive manufactured titanium implants in rat tibial defects.

Ergonomic T-Handle for Minimally Invasive Surgical Instruments.

A T-handle has been designed to be used for minimally invasive implantation of a dynamic hip screw to repair fractures of the proximal femur. It is capable of being used in two actions: (i) push and hold (while using an angle guide) and (ii) application of torque when using the insertion wrench and lag screw tap. The T-handle can be held in a power or precision grip.

Effect of accelerated aging on the viscoelastic properties of a medical grade silicone.

The viscoelastic properties of cylinders (diameter 5 mm, height 2.2 ± 0.2 mm) of Nagor silicone elastomer of medium hardness, were investigated before and after the specimens had undergone accelerated aging in saline solution at 70°C for 38, 76 and 114 days (to simulate aging at 37°C, for 1, 2 and 3 years, respectively).

Wear of the Charité® lumbar intervertebral disc replacement investigated using an electro-mechanical spine simulator.

The Charité(®) lumbar intervertebral disc replacement was subjected to wear testing in an electro-mechanical spine simulator. Sinusoidally varying compression (0.6-2 kN, frequency 2 Hz), rotation (±2°, frequency 1 Hz), flexion-extension (6° to -3°, frequency 1 Hz) and lateral bending (±2°, frequency 1 Hz) were applied out of phase to specimens immersed in diluted calf serum at 37 °C.

Assessment of non-contacting optical methods to measure wear and surface roughness in ceramic total disc replacements.

This study presents a method for measuring the low volumetric wear expected in ceramic total disc replacements, which can be used to replace intervertebral discs in the spine, using non-contacting optical methods. Alumina-on-alumina ball-on-disc tests were conducted with test conditions approximating those of cervical (neck region of the spine) total disc replacement wear tests. The samples were then scanned using a three-dimensional non-contacting optical profilometer and the data used to measure surface roughness and develop a method for measuring the wear volume.

Feasibility of using mixtures of silicone elastomers and silicone oils to model the mechanical behaviour of biological tissues.

Mixtures of silicone elastomer and silicone oil were prepared and the values of their Young's moduli, E, determined in compression. The mixtures had volume fractions, [Formula: see text], of silicone oil in the range of 0-0.73.

Viscoelastic properties of bovine knee joint articular cartilage: dependency on thickness and loading frequency.

Background: The knee is an incongruent joint predisposed to developing osteoarthritis, with certain regions being more at risk of cartilage degeneration even in non-osteoarthrosed joints.At present it is unknown if knee regions prone to cartilage degeneration have similar storage and/or loss stiffness, and frequency-dependent trends, to other knee joint cartilage. The aim of this study was to determine the range of frequency-dependent, viscoelastic stiffness of articular cartilage across the bovine knee joint.

Effect of lubricants on friction in laboratory tests of a total disc replacement device.

Some designs of total disc replacement devices have articulating bearing surfaces, and these devices are tested in vitro with a lubricant of diluted calf serum. It is believed that the lubricant found in total disc replacement devices in vivo is interstitial fluid that may have properties between that in Ringer's solution and diluted calf serum. To investigate the effect of lubricants, a set of friction tests were performed on a generic model of a metal against metal ball-and-socket total disc replacement device.

In vitro investigation of friction at the interface between bone and a surgical instrument.

This study investigated the friction between surgical instruments and bone to aid improvements to instrument design. The bases of orthopaedic surgical instruments are usually made of metal, especially stainless steel. Silicone elastomer was chosen as an alternate biocompatible material, which would be compliant on the bone surface when used as the base of an instrument.

The pathogenesis of degeneration of the intervertebral disc and emerging therapies in the management of back pain.

This article reviews the current knowledge of the intervertebral disc (IVD) and its association with low back pain (LBP). The normal IVD is a largely avascular and aneural structure with a high water content, its nutrients mainly diffusing through the end plates. IVD degeneration occurs when its cells die or become dysfunctional, notably in an acidic environment.

Applicability of sheep and pig models for cancellous bone in human vertebral bodies.

The mineral content of cancellous bone from sheep and pig vertebral bodies was determined by ashing at 800 degrees C. The results were compared with published results for human vertebral cancellous bone. The results for sheep (0.

Design of a surgical instrument for removing bone to provide screw access to a spinal fusion cage.

A surgical instrument to aid implantation of a range of lumbar spinal fusion cages has been developed. Once the cage is in position, the entrance to screw holes is partially blocked by the edge of the vertebral body. In order to insert fixation screws to secure the cage between the vertebrae, some part of the blocking edge has to be removed.

Evaluation of a transient, simultaneous, arbitrary Lagrange-Euler based multi-physics method for simulating the mitral heart valve.

A transient multi-physics model of the mitral heart valve has been developed, which allows simultaneous calculation of fluid flow and structural deformation. A recently developed contact method has been applied to enable simulation of systole (the stage when blood pressure is elevated within the heart to pump blood to the body). The geometry was simplified to represent the mitral valve within the heart walls in two dimensions.

Biomechanical assessment of surgical repair of the mitral valve.

Repair of the mitral valve is defined (loosely) as a procedure that alters the valve structure, without replacement, enabling the natural valve itself to continue to perform under the physical conditions to which it is exposed. As the mitral valve is driven by flow and pressure, it should be feasible to analyse and assess its function, failure and repair as a mechanical system. This article reviews the current state of mechanical evaluation of surgical repairs of the failed mitral valve of the heart.

Polymer-on-metal or metal-on-polymer total disc arthroplasty: does it make a difference?

Study Design: Mechanical testing of total disc arthroplasty (TDA).

Objective: To compare the friction between a polymer socket-on-metal ball and metal socket-on-polymer ball TDA.

Summary Of Background Data: A degenerate intervertebral disc can be replaced by TDA.

Effect of axial load on the flexural properties of an elastomeric total disc replacement.

Study Design: Twelve Cadisc-L devices were subjected to flexion (0°-6°) and extension (0° to -3°) motions at compressive loads between 500 N and 2000 N at a flexural rate between 0.25°/s and 3.0°/s.

Range of motion of the metacarpophalangeal joint in rheumatoid patients, with and without a flexible joint replacement prosthesis, compared with normal subjects.

Background: The metacarpophalangeal is commonly affected by rheumatoid arthritis. This may lead to joint replacement with a flexible prosthesis. The aims of this study were to determine the effects of rheumatoid arthritis on joint motion and to determine whether joint replacement needs to restore the full range of motion.

Effect of side holes in cervical fusion cages: a finite element analysis study.

The objective of this study was to investigate the effect of side holes on the predicted von Mises stress levels in cervical spinal fusion cages subjected to compressive loading. Models with between zero and ten side holes were developed. Finite element analysis (FEA) was used to simulate compression of the cage, made from the polymer PEEK (polyetheretherketone), between two adjacent vertebrae.

Friction in metal-on-metal total disc arthroplasty: effect of ball radius.

Total disc arthroplasty (TDA) can be used to replace a degenerated intervertebral disc in the spine. There are different designs of prosthetic discs, but one of the most common is a ball-and-socket combination. Contact between the bearing surfaces can result in high frictional torque, which can then result in wear and implant loosening.

Effect of calcium alginate concentration on viability and proliferation of encapsulated fibroblasts.

Alginate hydrogels have been used widely in tissue engineering for cell encapsulation for several reasons: low toxicity, the ability to gel under gentle condition and compatibility with cells. In this study, we determined the effect of different concentrations of alginate on encapsulation of 3T3 fibroblast cells at two different cell seeding densities. Live/dead staining and MTT assay were performed at regular intervals up to 4 weeks.

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 effect of screw insertion angle and thread type on the pullout strength of bone screws in normal and osteoporotic cancellous bone models.

Screw fixation can be extremely difficult to achieve in osteoporotic (OP) bone because of its low strength. This study determined how pullout strength is affected by placing different bone screws at varying angles in normal and OP bone models. Pullout tests of screws placed axially, and at angles to the pullout axis (ranging from 10° to 40°), were performed in 0.

Swelling of medical grade silicones in liquids and calculation of their cross-link densities.

Four medical grade silicones were swollen, until they reached equilibrium (i.e. constant mass) in eight liquids at 25 degrees C.

Lower limb involvement in spinal function and low back pain.

Aim: To evaluate evidence for involvement of the lower limb in spinal function and low back pain (LBP).

Design: A hypothesis based on a critical review of the relevant biomechanical and clinical literature.

Results: The spine resembles an inverted pendulum that supports the weight of the upper body; its stability requires a moving base that is provided by the joints of the lower limb, especially the hip.