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.

Influence of pilot hole diameter in cancellous screw fixation in a reduced density animal bone model.

Background: Screw fixation in osteoporotic bone is clinically challenging. Screw failure rates are growing due to an increasing prevalence of osteoporosis. To address this, biomechanical models are needed to recreate the bone clinically encountered alongside the development of new operative techniques.

Biomechanical testing of fixed and adjustable femoral cortical suspension devices for ACL reconstruction under high loads and extended cyclic loading.

Purpose: To compare loop elongation after 5000 cycles, loop-elongation at failure, and load at failure of the fixed-loop G-Lok device and three adjustable-loop devices (UltraButton, RigidLoop Adjustable and ProCinch RT), during testing over extended cycles under high loading.

Methods: Five devices of each type were tested on a custom-built rig fixed to an Instron machine. The testing protocol had four stages: preloading, cyclic preconditioning, incremental cyclic loading and pull-to-failure.

Novel techniques demonstrate superior fixation of simple transverse patella fractures - A biomechanical study.

Introduction: Traditional tension band wiring (TBW) remains the gold standard treatment for simple transverse patella fractures. Challenges include appropriately siting and bending Kirschner wires without damaging surrounding soft tissues. Damage to soft tissues and malposition of metalwork can lead to complications.

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.

Non-invasive vibrometry-based diagnostic detection of acetabular cup loosening in total hip replacement (THR).

Total hip replacement is aimed at relieving pain and restoring function. Currently, imaging techniques are primarily used as a clinical diagnosis and follow-up method. However, these are unreliable for detecting early loosening, and this has led to the proposal of novel techniques such as vibrometry.

Assessment of Head Displacement and Disassembly Force With Increasing Assembly Load at the Head/Trunnion Junction of a Total Hip Arthroplasty Prosthesis.

Background: Most femoral components used now for total hip arthroplasty are modular, requiring a strong connection at assembly. The aim of this study was to assess the effect of assembly force on the strength of head-trunnion interface and to measure the initial displacement of the head on the trunnion with different assembly forces.

Methods: Three assembly load levels were assessed (A: 2 kN, B: 4 kN, C: 6 kN) with 4 implants in each group.

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 effect of dynamic hip motion on the micromotion of press-fit acetabular cups in six degrees of freedom.

The hip joint is subjected to cyclic loading and motion during activities of daily living and this can induce micromotions at the bone-implant interface of cementless total hip replacements. Initial stability has been identified as a crucial factor to achieve osseointegration and long-term survival. Whilst fixation of femoral stems achieves good clinical results, the fixation of acetabular components remains a challenge.

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.

Development of a non-invasive diagnostic technique for acetabular component loosening in total hip replacements.

Current techniques for diagnosing early loosening of a total hip replacement (THR) are ineffective, especially for the acetabular component. Accordingly, new, accurate, and quantifiable methods are required. The aim of this study was to investigate the viability of vibrational analysis for accurately detecting acetabular component loosening.

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.

A novel method to assess primary stability of press-fit acetabular cups.

Initial stability is an essential prerequisite to achieve osseointegration of press-fit acetabular cups in total hip replacements. Most in vitro methods that assess cup stability do not reproduce physiological loading conditions and use simplified acetabular models with a spherical cavity. The aim of this study was to investigate the effect of bone density and acetabular geometry on cup stability using a novel method for measuring acetabular cup micromotion.

Strong correlation between the morphology of the proximal femur and the geometry of the distal femoral trochlea.

Purpose: Previous investigations suggested that the geometry of the proximal femur may be related to osteoarthritis of the tibiofemoral joint and various patellofemoral joint conditions. This study aims to investigate the correlation between proximal and distal femoral geometry. Such a correlation could aid our understanding of patient complications after total knee arthroplasty (TKA) and be of benefit for further development of kinematic approaches in TKA.

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.

Cement brand and preparation effects cement-in-cement mantle shear strength.

Creating bi-laminar cement mantles as part of revision hip arthroplasty is well-documented but there is a lack of data concerning the effect of cement brand on the procedure. The aim of this study was to compare the shear strength of bi-laminar cement mantles using various combinations of two leading bone cement brands.Bi-laminar cement mantles were created using Simplex P with Tobramycin, and Palacos R+G: Simplex-Simplex (SS); Simplex-Palacos (SP); Palacos-Simplex (PS); and Palacos-Palacos (PP).

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.

Distal stem features improve the torsional resistance of long-stem cemented revision hip stems: an in vitro biomechanical study.

When proximal bone stock is compromised at revision hip arthroplasty, distal fixation is often relied upon for stability of the femoral component. In such circumstances, torsional forces can result in debonding and loosening. This study compared the torsional behaviour of a cemented, polished and featureless (plain) stem with cemented, polished stems featuring fins or flutes.

Stabilization of the syndesmosis in the Maisonneuve fracture--a biomechanical study comparing 2-hole locking plate and quadricortical screw fixation.

Objective: The aim of this study is to determine whether a 2-hole locking plate has biomechanical advantages over conventional screw stabilization of the syndesmosis in this injury pattern.

Methods: Six pairs of fresh-frozen human cadaver lower legs were prepared to simulate an unstable Maisonneuve fracture. Each limb was compared with its pair; the syndesmosis in one being stabilized with two 4.

The effect of 4 mm bicortical drill hole defect on bone strength in a pig femur model.

Introduction: In orthopaedic surgery, small bicortical circular bone defects are often produced as a result of internal fixation of fractures. The aim of this study was to determine the amount of torsional strength reduction in animal bone with a bicortical bone defect and how much residual strength remains if the bicortical bone defect was occluded.

Method: Forty pig femurs were divided into four groups.

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 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.