Autologous osteochondral grafting has demonstrated positive outcomes for treating articular cartilage defects by replacing the damaged region with a cylindrical graft consisting of bone with a layer of cartilage, taken from a non-loadbearing region of the knee. Despite positive clinical use, factors that cause graft subsidence or poor integration are relatively unknown. The aim of this study was to develop finite element (FE) models of osteochondral grafts within a tibiofemoral joint and to investigate parameters affecting osteochondral graft stability.

Initial experimental tests on cadaveric femurs were performed to calibrate the bone properties and graft-bone frictional forces for use in corresponding FE models, generated from µCT scan data. The effects of cartilage defects and osteochondral graft repair were measured by examining contact pressure changes using in vitro tests on a single cadaveric human tibiofemoral joint. Six defects were created in the femoral condyles which were subsequently treated with osteochondral autografts or metal pins. Matching µCT scan-based FE models were created, and the contact patches were compared. Sensitivity to graft bone properties was investigated.

The bone material properties and graft-bone frictional forces were successfully calibrated from the initial tests with good resulting levels of agreement (CCC=0.87). The tibiofemoral joint experiment provided a range of cases to model. These cases were well captured experimentally and represented accurately in the FE models. Graft properties relative to host bone had large effects on immediate graft stability despite limited changes to resultant cartilage contact pressure.

Model confidence was built through extensive validation and sensitivity testing, and demonstrated that specimen-specific properties were required to accurately represent graft behaviour. The results indicate that graft bone properties affect the immediate stability, which is important for the selection of allografts and design of future synthetic grafts.

The aim of this work was to develop a novel, accessible and low-cost method, which is sufficient to measure changes in meniscal position in a whole-knee joint model performing dynamic motion in a knee simulator.

An optical tracking method using motion markers, MATLAB (MATLAB, The MathWorks Inc.) and a miniature camera system (Raspberry Pi, UK) was developed. Method feasibility was assessed on porcine whole joint knee samples (n = 4) dissected and cemented to be used in the simulator (1). Markers were placed on three regions (medial, posterior, anterior) of the medial meniscus with corresponding reference markers on the tibial plateau, so the relative meniscal position could be calculated. The Leeds high kinematics gait profile scaled to the parameters of a pig (1, 2) was driven in displacement control at 0.5 Hz. Videos were recorded at cycle-3 and cycle-50. Conditions tested were the capsule retained (intact), capsule removed and a medial posterior root tear. Mean relative displacement values were taken at time-points relating to the peaks of the axial force and flexion-extension gait inputs, as well as the range between the maximum and minimum values. A one-way ANOVA followed by Tukey post hoc analysis were used to assess differences (p = 0.05).

The method was able to measure relative meniscal displacement for all three meniscal regions. The medial region showed the greatest difference between the conditions. A significant increase (p < 0.05) for the root tear condition was found at 0.28s and 0.90s (axial load peaks) during cycle-3. Mean relative displacement for the root tear condition decreased by 0.29 mm between cycle-3 and cycle-50 at the 0.28s time-point. No statistically significant differences were found when ranges were compared at cycle-3 and cycle-50.

The method was sensitive to measure a substantial difference in medial-lateral relative displacement between an intact and a torn state. Meniscus extrusion was detected for the root tear condition throughout test duration. Further work will progress onto human specimens and apply an intervention condition.

Cam-type femoroacetabular impingement is caused by bone excess on the femoral neck abutting the acetabular rim. This can cause cartilage and labral damage due to increased contact pressure as the cam moves into the acetabulum. However, the damage mechanism and the influence of individual mechanical factors (such as sliding distance) are poorly understood. The aim of this study was to identify the cam sliding distance during impingement for different activities in the hip joint.

Motion data for 12 different motion activities from 18 subjects, were applied to a hip shape model (selected as most likely to cause damage, anteriorly positioned with a maximum alpha angle of 80°). The model comprised of a pointwise representation of the acetabular rim and points on the femoral head and neck where the shape deviated from a sphere (software:Matlab).

The movement of each femoral point was tracked in 3D while an activity motion was applied, and impingement recorded when overlap between a cam point and the acetabular rim occurred. Sliding distance was recorded during impingement for each relevant femoral point.

Angular sliding distances varied for different activities. The highest mean (±SD) sliding distance was for leg-crossing (42.62±17.96mm) and lowest the trailing hip in golf swing (2.17±1.11mm). The high standard deviation in the leg crossing sliding distances, indicates subjects may perform this activity in a different manner.

This study quantified sliding distance during cam impingement for different activities. This is an important parameter for determining how much the hip moves during activities that may cause damage and will provide information for future experimental studies.

Variations in component positioning of total hip replacements can lead to edge loading of the liner, and potentially affect device longevity. These effects are evaluated using ISO 14242:4 edge loading test results in a dynamic system. Mediolateral translation of one of the components during testing is caused by a compressed spring, and therefore the kinematics will depend on the spring stiffness and damping coefficient, and the mass of the translating component and fixture. This study aims to describe the sensitivity of the liner plastic strain to these variables, to better understand how tests using different simulator designs might produce different amounts of liner rim deformation.

A dynamic explicit deformable finite element model with 36mm Pinnacle metal-on-polyethylene bearing geometry (DePuy Synthes, Leeds, UK) was used with material properties for conventional UHMWPE. Setup was 65° clinical inclination, 4mm mismatch, 70N swing phase load, and 100N/mm spring. Fixture mass was varied from 0.5-5kg, spring damping coefficient was varied from 0-2Ns/mm. They were changed independently, and in combination.

Maximum separation values were relatively insensitive to changes in the mass, damping coefficient, or both. The sensitivity of peak plastic strain, to this range of inputs, was similar to changing the swing phase load from 70N to approximately 150N – 200N. Increasing the fixture mass and/or damping coefficient increased the peak plastic strain, with values from 0.15-0.19.

Liner plastic deformation was sensitive to the spring damping and fixture mass, which may explain some of the differences in fatigue and deformation results in UHMWPE liners tested on different machines or with modified fixtures. These values should be described when reporting the results of ISO14242:4 testing.

Acknowledgements

Funded by EPSRC grant EP/N02480X/1; CAD supplied by DePuy Synthes.

The Exeter^™ V40 cemented polished tapered stem system has demonstrated excellent long-term outcomes. This paper presents a systematic review of the existing literature and reports on a large case series comparing implant fractures between the Exeter V40 series; 125 mm and conventional length stem systems.

A systematic literature search was performed adhering to PRISMA criteria. In parallel we performed a retrospective single centre study of Exeter^™ V40 femoral stem prosthetic fractures between April 2003– June 2020.

There are 25 reported cases of such prosthetic fractures confined to small case series and case reports within the literature. We report an additional 19 cases to the literature (mean age 66.3 ± 11.7 years; 12 female [63%]; body mass index 32.9 ± 5.9 kg/m²). The mean time from index procedure to fracture was 7.8 years (2.5–16.3, ±3.6). Exeter V40 stem fracture incidence was 0.27%. Incidence was significantly higher in 125 mm length stems compared to ≥150 mm length stems (1.26% vs 0.13%, respectively, p <0.001) and revision arthroplasty (1.209% vs 0.149%, p <0.001). When comparing different stem length cohorts, 125-mm short-stem were associated with stem body fractures (92% vs 29%, p = 0.0095), earlier time to fracture (6.2 vs 11.0 years, p = 0.0018), younger patient age at time of fracture (62.7 vs 72.6 years old, p = 0.037) and female sex (75% vs 43%, p = 0.33).

This case series in conjunction with the systematic review provides evidence stem morphology plays a role in femoral implant fracture. This complication remains rare, although we report a significantly higher incidence at up to 17 years follow-up than in the literature. As femoral geometries remain the same, increasing BMIs in THR patients should raise concern. Short 125 mm length Exeter V40 stems undoubtedly have a role in restoring anatomy and biomechanics in smaller femoral geometries, although the surgeon has to appreciate the higher risk of stem fracture and the associated predisposing factors which may necessitate meticulous surgical technique and planning.

Aims

The Exeter V40 cemented polished tapered stem system has demonstrated excellent long-term outcomes. This paper presents a systematic review of the existing literature and reports on a large case series comparing implant fractures between the Exeter V40 series; 125 mm and conventional length stem systems.

Abstract

Abstract

INTRODUCTION

There is great potential for the use of computational tools within the design and test cycle for joint replacement devices.

The increasing need for stratified treatments that are more relevant to specific patients, and implant testing under more realistic, less idealised, conditions, will progressively increase the pre-clinical experimental testing work load. If the outcomes of experimental tests can be predicted using low cost computational tools, then these tools can be embedded early in the design cycle, e.g. benchmarking various design concepts, optimising component geometrical features and virtually predicting factors affecting the implant performance. Rapid, predictive tools could also allow population-stratified scenario testing at an early design stage, resulting in devices which are better suited to a patient-specific approach to treatment.

The aim of the current study was to demonstrate the ability of a rapid computational analysis tool to predict the behaviour of a total hip replacement (THR) device, specifically the risk of edge loading due to separation under experimental conditions.

Introduction

One of the known mechanisms which could contribute to the failure of total hip replacements (THR) is edge contact. Failures associated with edge contact include rim damage and lysis due to altered loading and torques. Recent study on four THR patients showed that the inclusion of pelvic motions in a contact model increased the risk of edge contact in some patients. The aim of current study was to determine whether pelvic motions have the same effect on contact location for a larger patient cohort and determine the contribution of each of the pelvic rotations to this effect.

Acetabular tissue damage is implicated in osteoarthritis (OA) and investigation of in situ acetabular soft tissues behaviour will improve understanding of tissue properties and interconnections. The study aim was to visualise acetabular soft tissues under load and to quantify displacements using computed tomography (CT) scans (XtremeCT, Scano Medical).

A CT scan (resolution 82 μm) was performed on the disarticulated, unloaded porcine acetabulum. The femoral head was soaked in Sodium Iodide (NaI) solution and cling film wrapped to prevent transfer to the acetabular side. The joint was realigned, compressed using cable ties and re-scanned. The two images were down-sampled to 0.3 mm. Acetabular bone and soft tissues were segmented. Bony features were used to register the two background images, using Simpleware ScanIP 7.0 (Synopsys), to the same position and orientation (volume difference < 5%). Acetabular soft tissues displacements were measured by tracking the same points at the tissue edges on the two acetabular masks, along with difference in bone position as an additional error assessment.

The use of radiopaque solution provided a clear contrast allowing separation of the femoral and acetabular soft tissues in the loaded image. The image registration process resulted in a difference in bone position in the areas of interest equivalent to image resolution (0.3 mm, a mean of 3 repeats by same user). A labral tip displacement of 1.7 mm and a cartilage thickness change from 1.5 mm unloaded to 0.9 mm loaded, were recorded.

The combination of contrast enhancement, registration and focused local measurement was precise enough to reduce bone alignment error to that of image resolution and reveal local soft tissue displacements. These measurement methods can be used to develop models of soft tissues properties and behaviour, and therapy for hip tissue damage at early stage may be reviewed and optimised.

Introduction

Up to 60% of total hip arthroplasties (THA) in Asian populations arise from avascular necrosis (AVN), a bone disease that can lead to femoral head collapse. Current diagnostic methods to classify AVN have poor reproducibility and are not reliable in assessing the fracture risk. Femoral heads with an immediate fracture risk should be treated with a THA, conservative treatments are only successful in some cases and cause unnecessary patient suffering if used inappropriately. There is potential to improve the assessment of the fracture risk by using a combination of density-calibrated computed tomographic (QCT) imaging and engineering beam theory. The aim of this study was to validate the novel fracture prediction method against in-vitro compression tests on a series of six human femur specimens.

Introduction

Geometric variations of the hip joint can give rise to repeated abnormal contact between the femur and acetabular rim, resulting in cartilage and labrum damage. Population-based geometric parameterisation can facilitate the flexible and automated in silico generation of a range of clinically relevant hip geometries, allowing the position and size of cams to be defined precisely in three dimensions. This is advantageous compared to alpha angles, which are unreliable for stratifying populations by cam type. Alpha angles provide an indication of cam size in a single two-dimensional view, and high alpha angles have been observed in asymptomatic individuals.

Parametric geometries can be developed into finite element models to assess the potential effects of morphological variations in bone on soft tissue strains. The aim of this study was to demonstrate the capabilities of our parameterisation research tool by assessing impingement severity resulting from a range of parametrically varied femoral and acetabular geometries.

Aims

To investigate whether the duration of pain has an influence on the clinical outcomes of patients with low back pain (LBP) managed through the North East of England Regional Back Pain and Radicular Pain Pathway (NERBPP).

Background

Conservative treatment of acute AT ruptures with functional rehabilitation has demonstrated superior results with equal reported re-rupture rates but without the added complications of surgical treatment.

There is no consensus on the duration and method of treatment using functional rehabilitation regimes.

The purpose of this paper is to define our treatment regime, the Leicester Achilles Management Protocol (LAMP), supported with patient reported outcomes and objective measures of assessment.

Introduction

The stability of the elbow joint following an acute elbow dislocation is dependent on associated injuries. The ability to identify these concomitant injuries correctly directs management and improves the chances of a successful outcome. Interpretation of plain radiographs in the presence of either a dislocation or post-reduction films with plaster in-situ is difficult. This study aimed to assess the ability of orthopaedic registrars to accurately identify associated bony injuries on initial plain radiographs using CT as the gold standard for comparison.

INTRODUCTION

Mal-positioning of the acetabular component in total hip replacement (THR) could lead to edge loading, accelerated component wear, impingement and dislocation [1,2]. In order to achieve a successful position for the acetabular component, the assessment of the acetabular orientation with reference to different coordinate systems is important [3]. The aims of the present study were to establish a pelvic coordinate system and a global body coordinate system, and to assess the acetabular orientations of natural hips with reference to the two coordinate systems.

Introduction

The performance of total hip replacement (THR) devices can be affected by the quality of the tissues surrounding the joint or the mismatch of the component centres during hip replacement surgery. Experimental studies have shown that these factors can cause the separation of the two components during walking cycle (dynamic separation) and the contact of the femoral head with the rim of the acetabular liner (edge loading), which can lead to increased wear and shortened implant lifespan¹. There is a need for flexible pre-clinical testing tools which allow THR devices to be assessed under these adverse conditions. In this work, a novel dynamic finite element model was developed that is able to generate dynamic separation as it occurs during the gait cycle. In addition, the ability to interrogate contact mechanics and material strain under separation conditions provides a unique means of assessing the severity of edge loading. This study demonstrates these model capabilities for a range of simulated surgical translational mismatch values, for ceramic-on-polyethylene implants.

Aims

The importance of accurate identification and reporting of surgical site infection (SSI) is well recognised but poorly defined. Public Health England (PHE) mandated collection of orthopaedic SSI data in 2004. Data submission is required in one of four categories (hip prosthesis, knee prosthesis, repair of neck of femur, reduction of long bone fracture) for one quarter per year. Trusts are encouraged to carry out post-discharge surveillance but this is not mandatory. Recent papers in the orthopaedic literature have highlighted the importance of SSI surveillance and the heterogeneity of surveillance methods. However, details of current orthopaedic SSI surveillance practice has not been described or quantified.

Aims

We present a case series of five patients who had revision surgery following magnetic controlled growing rods (MGCR) for early onset scoliosis. Metallosis was found during revision in four out of five patients and we postulated a mechanism for rod failure based on retrieval analysis.