Our study shows that a tendon rupture can be successfully augmented with Demineralised Cortical Bone (DCB) giving initial appropriate mechanical strength suitable for in vivo use providing the biological reactions to the graft are favourable. Treatment of tendon and ligament injuries remains challenging; the aim is to find a biocompatible substance with mechanical and structural properties that replicate those of normal tendon and ligament. Because of its structural and mechanical properties, we proposed that DCB can be used in repair of tendon and ligament as well as regeneration of the enthesis. DCB is porous, biocompatible and has the potential to be remodelled by the host tissues. 2 studies were designed; in the first we examined the mechanical properties of DCB after gamma irradiation (GI) and freeze drying (FD). In the second we used different techniques for repairing bone-tendon-bone with DCB in order to measure the mechanical performance of the construct.Summary
Introduction
Osseointegrated Amputation Prostheses can be functionalised by both biological augmentation and structural augmentation. These augmentation techniques may aid the formation of a stable skin-implant interface. Current clinical options are limited in restoring function to amputees, and are associated with contact dermatitis and infection at the stump-socket interface. Osseointegrated Amputation Prosthesis attempts to solve issues at the stump-socket interface by directly transferring axial load to the prosthesis, via a skin-penetrating abutment. However, development is needed to achieve a seal at the skin-implant interface to limit infection. Fibronectin, an Extracellular Matrix protein, binds to integrins during wound healing, with the RGD tripeptide being part of the recognition sequence for its integrin binding domain. Summary
Introduction
The aim of this study was test the amount of corrosion occurring at the (Ti) /cobalt chrome (CoCr) interface comparing this with Ti and Ti interfaces. This was compared with retrieved metal work visualised under a scanning electron microscope (SEM). The interface of interest is the interface between rod and the screw. We investigated corrosion seen at that interface with a CoCr rod coupled to a Ti screw versus a Ti rod coupled to a Ti screw (6 screws were used) Implants were loaded according to the ASTM F2193 – 02 Standard Specifications and Test Methods for Components Used in the Surgical Fixation of the Spinal Skeletal System. Pitting potentials were monitored using cyclic potentiodynamic polarization tests (ASTM F2129 – 08 Standard Test Method for Conducting Cyclic Potentiodynamic Polarisation Measurements) to determine corrosion susceptibility. Retrieved implants were visualised under (SEM) to confirm corrosion.Aim:
Methods:
Due to absence of fusion in guided-growth devices for EOS (growing rods, Shilla, LSZ) movement of the rods against their attachment is possible resulting in wear debris formation. It is important to understand the wear resistance of materials used in these devices under appropriate conditions. The aim of our work was to investigate wear resistance of titanium alloy Ti-6Al-4V and superelastic Nitinol. Nitinol has been used recently for correcting scoliosis and may provide a better and more gradual correction than other materials.Introduction:
Aim:
Revision hip arthroplasty is a technically challenging operation as proximal bony deficits preclude the use of standard implants. Longer distally fixing stems are therefore required to achieve primary stability. This work aims to compare the primary stability and biomechanical properties of a new design of tapered fluted modular femoral stem (Redapt®, Smith & Nephew) to that of a conical fluted stem (Restoration®, Stryker). It is hypothesized that the taper will provide improved rotational stability under cyclical loading.Introduction
Aims
There has been widespread concern regarding the adverse tissue reactions after metal-on-metal (MoM) total hip replacements (THR). Concerns have also been expressed with mechanical wear from micromotion and fretting corrosion at the head/stem taper junction in total hip replacements. In order to understand the interface mechanism a study was undertaken in order to investigate the effect of surface finish and contact area associated with modular tapers in total hip replacements with a single combination of materials of modular tapers. An inverted hip replacement setup was used (ASTM F1875-98). 28 mm Cobalt Chrome (CoCr) femoral heads were coupled with either full length (standard) or reduced length (mini) 12/14 Titanium (Ti) stem tapers. These Ti stem tapers had either a rough or smooth surface finish whilst all the head tapers had a smooth surface finish. Wear and corrosion of taper surfaces were compared after samples were sinusoidally loaded between 0.1 kN and 3.1 kN for 10 million cycles at 4 Hz. In test 1 rough mini stem tapers were compared with rough standard stem tapers whilst in test 2 rough mini stem tapers were compared with smooth mini stem tapers. Surface parameters and profiles were measured before and after testing. Electrochemical static and dynamic corrosion tests were performed between rough mini stem tapers and smooth mini stem tapers under loaded and non-loaded conditions.Introduction:
Methods:
High failure rates with large diameter, metal on metal hip replacements have highlighted a potential issue with the head/stem taper junction as one of the significant sources of metal ion release. Postulated reasons as to why this may be such a problem with large head metal on metal hip replacements is due to the increased torque achieved by the larger head size. This may be responsible for applying greater micromotion between the head and stem taper and consequently greater amounts of fretting corrosion. The aim of this study was to perform short term in vitro electrochemical tests to assess the effect of increasing head diameter and torque on the fretting corrosion susceptibility of the head/stem taper interface and to investigate its effect on different material combinations. 36 mm Cobalt Chrome (CoCr) femoral heads were coupled with either a CoCr or Titanium (Ti) stem with 12/14 tapers, all with a smooth surface finish. Increasing perpendicular horizontal offsets in the sagittal plane created incremental increases in torque. Offset increments of 0 mm, 5.4 mm and 7.5 mm were selected (Figure 1) to simulate the torque force equivalent to 9 Nm, 12 Nm and 17 Nm. An inverted hip replacement setup was used (ASTM F1875-98) (Figure 2). Components were statically loaded at 0 kN and 2.3 kN prior to sinusoidal cyclic loading and electrochemical testing. Mean & fretting currents were calculated every 50 cycles up to a maximum of 1000 cycles of sinusoidal cyclic loading at 3 Hz along with the Overall Mean Current (OMC), Overall Mean Fretting Current (OMFC) and Overall Current change (OCC).Introduction:
Methods:
It has been suggested that corrosion and fretting at the taper junctions of stemmed metal-on-metal hip replacements may contribute to their high failure rates. A peer-reviewed semi-quantitative scoring system [Goldberg et al., 2002] has been used to visually assess the severity of corrosion and fretting of the taper junction but has not been validated using multiple examiners. The aim of this study was to assess the inter-observer variability of this method. Macroscopic and stereomicroscopic examinations of the femoral head and stem tapers of 100 retrieved large diameter metal on metal (MOM) hip components were performed by two independent observers using the methods defined by Goldberg et al. [2002] to quantify corrosion and fretting. Scores ranging from 1 (none) to 4 (severe) were assigned to the medial, lateral, posterior and anterior quadrants of the neck taper and the distal and proximal regions of the head taper. An overall score was then assigned to each surface as a whole. Cohen's weighted Kappa statistic (κ) was used to measure the inter-observer agreement. A quadratic weighting scheme, that allocated weights to the importance of disagreements that are proportional to the square of the number of categories apart, was used to take account of scaled disagreement. Kappa values were assessed using previously established criteria where κ ≤ 0 = poor, 0.01 to 0.20 = slight, 0.21 to 0.40 = fair, 0.41 to 0.60 = moderate, 0.61 to 0.80 = substantial, 0.81 to 1 = almost perfect. A sample size of 100 was used in order to detect a coefficient of 0.60 to within 0.25 with 95% confidence with two experienced observers. Statistical analysis was performed using Stata/IC version 12.1 (StataCorp, College Station, TC, USA) and a p value < 0.05 was considered statistically significant.Introduction
Method
Bone-anchored devices have been used as skin-crossing conduits to record neuromuscular signals in sedated animals. Long-term recordings from cognisant subjects must be assessed. Hypothesis A bone-anchored device is suitable as a conduit for epimysial EMG (Electromyogram) recordings and is reliable in the long-term. The bone-anchored device was implanted into the medial aspect of an ovine tibia (n=1), and the epimysial electrode was sutured onto the peroneus tertius muscle. Epimysial and Surface EMG signals were recorded for 12 weeks.Introduction
Methods
Material loss at the head-stem taper junction may contribute to the high early failure rates of stemmed large head metal-on-metal (LH-MOM) hip replacements. We sought to quantify both wear and corrosion and by doing so determine the main mechanism of material loss at the taper. This was a retrospective study of 78 patients having undergone revision of a LH-MOM hip replacement. All relevant clinical data was recorded. Corrosion was assessed using light microscopy and scanning electron microscopy, and graded according to a well-published classification system. We then measured the volumetric wear of the bearing and taper surfaces. Evidence of at least mild taper corrosion was seen in 90% cases, with 46% severely corroded. SEM confirmed the presence of corrosion debris, pits and fretting damage. However, volumetric wear of the taper surfaces was significantly lower than that of the bearing surfaces (p = 0.015). Our study supports corrosion as the predominant mechanism of material loss at the taper junction of LH-MOM hip replacements. Although the volume of material loss is low, the ionic products may be more biologically active compared to the particulate debris arising from the bearing surfaces.
It has been speculated that high wear at the head-stem taper may contribute to the high failure rates reported for stemmed large head metal-on-metal (LH-MOM) hips. In this study of 53 retrieved LH-MOM hip replacements, we sought to determine the relative contributions of the bearing and taper surfaces to the total wear volume. Prior to revision, we recorded the relevant clinical variables, including whole blood cobalt and chromium levels. Volumetric wear of the bearing surfaces was measured using a coordinate measuring machine and of the taper surfaces using a roundness measuring machine. The mean taper wear volume was lower than the combined bearing surface wear volume (p = 0.015). On average the taper contributed 32.9% of the total wear volume, and in only 28% cases was the taper wear volume greater than the bearing surface wear volume. Despite contributing less to the total material loss than the bearing surfaces, the head-stem taper junction remains an important source of implant-derived wear debris. Furthermore, material loss at the taper is likely to involve corrosion and it is possible that the material released may be more biologically active than that from the bearing surface.
Repair of tendon injuries aims to restore length, mechanical strength and function. We hypothesise that Demineralised Cortical Bone (DCB) present in biological tendon environment will result in remodelling of the DCB into ligament tissue. A cadaveric study was carried out to optimize the technique. The distal 1cm of the patellar tendon was excised and DCB was used to bridge the defect. 4 models were examined, Model-1: one anchor, Model-2: 2 anchors, Model-3: 2 anchors with double looped off-loading thread, Model-4: 2 anchors with 3 threads off-loading loop. 6 mature sheep undergone surgical resection of the distal 1cm of the right patellar tendon. Repair was done using DCB with 2 anchors. Immediate mobilisation was allowed, animals were sacrificed at 12 weeks. Force plate assessments were done at weeks 3, 6, 9 and 12. Radiographs were taken and pQCT scan was done prior to histological analysis. In the cadaveric study, the median failure force for the 4 models; 250N, 290N, 767N and 934N respectively. In the animal study, none of the specimens showed evidence of ossification of the DCB. One animal failed to show satisfactory progress, X-rays showed patella alta, on specimen retrieval there was no damage to the DCB and sutures and no evidence of anchor pullout. Functional weight bearing was 79% at week12. Histological analysis proved remodelling of the collagen leading to ligamentisation of the DCB. Results prove that DCB can be used as biological tendon substitute, combined with the use of suture bone anchor early mobilisation can be achieved.
Treatment of tendon and ligament injuries remains challenging; the aim is to find a biocompatible substance with mechanical and structural properties that replicate those of normal tendon and ligament. We examined the mechanical properties of Demineralised Cortical Bone (DCB) after gamma irradiation (GI) and freeze drying (FD). We also used different techniques for repairing bone-tendon-bone with DCB in order to measure the mechanical performance of the construct. DCB specimens were allocated into 4 groups; FD, GI, combination of both or none. The maximum tensile forces and stresses were measured. 4 cadaveric models of repair of 1cm patellar tendon defect using DCB were designed; model-1 using one bone anchor, Model-2 using 2 bone anchors, Model-3 off-loading by continuous thread looped twice through bony tunnels, Model-4 off-loading with 3 hand braided threads. Force to failure and mode were recorded for each sample. FD groups results were statistically higher (p=<0.05) compared to non-FD groups, while there was no statistical difference between GI and non-GI groups. The median failure force for model-1: 250N, model-2: 290N, model-3: 767N and model-4: 934N. There was no statistical significance between model-1 and model-2 (p=0.249), however statistical significance was found between other models (p=<0.006). GI has no significant effect on mechanical strength of the CDB while FD may have positive effect on its mechanical strength. Our study shows that a tendon rupture can be successfully augmented with CDB giving initial appropriate mechanical strength suitable for in vivo use providing the biological reactions to the graft are favourable.
Tendon injuries remain challenging, secondary healing and prolonged immobilisation result in suboptimal outcome. Previous study by our group showed that demineralised bone matrix (DBM) can result in faster healing of a tendon enthesis. The aim of this study is to test different ways augmenting tendon with DBM to enhance tendon repair and regeneration. DBM strips were prepared from tibias of mature ewes. Patella, patellar tendon and tibias were dissected and the distal 1 cm of the patellar tendon was excised. 4 models were designed; Model-1, DBM strip was used to bridge the gap between the tendon and the tibial tuberosity. The DBM strip was stitched to the tendon using one bone anchor. Model-2, similar to model 1 with the use of 2 anchors. Model-3, similar to model 2, construct was off loaded by continuous thread looped twice through bony tunnels sited in the patella and in the tibial tuberosity. Model-4, similar to model 3 with 3 threads as off loading loop. All models were tested for pullout force and mode of failure.Introduction
Methods
Demineralised Bone Matrix (DBM) is widely used in Orthopaedics and dentistry as a bone graft substitute and may be used to augment bone formation in load bearing applications. In this study we examine the effect of gamma irradiation and freeze drying on the tensile strength of Demineralised Cortical Bone (DCB). Tibias were harvested from mature ewes and cut into bony strips. Demineralisation was done using 0.6M HCL and confirmed by X-ray. Specimens were washed until a pH of 7.0 +/_ 0.2 was achieved in the washing solutions. Specimens were allocated into 4 groups; group (A) non freeze dried non gamma irradiated, group (B) freeze dried non gamma irradiated, group (C) non freeze dried gamma irradiated mention the level of gamma irradiation and group (D) freeze dried and gamma irradiated. The maximum tensile force and stress were measured. Statistical analysis using the Mann-Whitney U test was carried out.Introduction
Methods
Following amputation, residual stumps used to attach the external prostheses can be associated with sores, infection and skin necrosis. These problems could be overcome by off loading the soft tissues. Intraosseous transcutaneous amputation prostheses (ITAP) attach external implants directly to residual bone reducing these complications. However, a tight seal at the skin implant interface is crucial in preventing epithelial down-growth and infection. Fibronectin (Fn) and laminin 332 (Ln), enhance early cell growth and adhesion of keratinocytes. Silanization to titanium alloy (Ti) allows these proteins to bond to the metal directly. We hypothesize that silanized dual coatings of fibronectin and laminin (SiFnLn) will be more durable than absorbed proteins and that keratinocyte adhesion will be increased compared with Ti controls and single silanized proteins. 10 mm diameter Ti alloy discs were polished, sterilized and silanized. The kinetics of silanized single and dual protein coating attachment onto titanium alloy was quantified using radio-labelled Fn(125I-Fn) and Ln(125I-Ln). Coating durability was assessed when soaked in fetal calf serum (FCS) for 0, 1, 24, 48, 72hrs. Data was compared to un-silanized Ti discs with the same amount of adsorbed proteins. In order to study cell attachment 20 × 103 keratinocytes were seeded on the discs (n = 6): silanized (Si), silanized fibronectin (SiFn), silanized laminin (SiLn), silanized dual coating (SiFnLn) for 1, 4 and 24hrs. Adhesion of cells was assessed using mouse vinculin antibody for 2hrs and alexafluor for 1hr which stains focal adhesions responsible for attaching cells to surfaces. Axiovision Image Analysis software was used to measure cell area, vinculin markers per cell unit and per unit cell area on 15 cells per disc. Data was analysed in SPSS and significance was assumed at the 0.05 level.Introduction
Methods
Intraosseous transcutaneous amputation prostheses (ITAP) provide an alternative means of attaching artificial limbs for amputees. Conventional stump-socket devices are associated with soft tissue complications including; pressure sores and tissue necrosis. ITAP resolves these problems by attaching the exo-prosthesis transcutaneously to the skeleton. The aim of this study is to increase the attachment of dermal fibroblasts to titanium alloy in vitro. Fibronectin (Fn) and laminin 332 (Ln) enhance early cell growth and adhesion. We hypothesize that silanized dual coatings of fibronectin and laminin (SiFnLn) will be more durable when compared with adsorbed dual coating (AdFnLn), and will enhance early fibroblast growth and adhesion compared to single coatings. The kinetics of dual single and dual protein coating attachment onto titanium alloy was quantified on silanized 10mm diameter discs using radiolabelled Fn (125I-Fn) and Ln (125I-Ln). Sixty discs were polished, sterilized and silanized. Coating durability was assessed when soaked in fetal calf serum (FCS) for 0, 1, 24, 48 and 72hrs. Data was compared to un-silanized Ti discs with the same coatings. Five thousand human dermal fibroblasts were seeded on discs (n = 6) of Ti polished alone (Pol), Ti with adsorbed fibronectin (AdFn), Ti with adsorbed laminin (AdLn), Ti adsorbed dual coating (AdFnLn), Ti silanized (Si), Ti silanized with fibronectin (SiFn), Ti silanized with laminin (SiLn), Ti silanized with a dual coating (SiFnLn) for 24hrs. In order to measure cell adhesion fibroblasts were fixed, vinculin stained using mouse vinculin antibody and alexa fluor. Axiovision Image Analysis software was used to measure cell area, vinculin focal adhesion markers per cell and per unit cell area. Data was analysed in SPSS and significance was assumed at the 0.05 level.Introduction
Methods
Autologous bone grafts are considered gold standard in the repair of bone defects. However they are limited in supply and are associated with donor site morbidity. This has led to the development of synthetic bone graft substitute (BGS) materials, many of which have been reported as being osteoinductive. The structure of the BGS is important and bone formation has been observed in scaffolds with a macroporous morphology. Smaller pores termed ‘strut porosity’ may also be important for osteoinduction. The aim of this study was to compare the osteoinductive ability of one silicate-substituted calcium phosphate (SiCaP) with differing strut porosities in an ectopic ovine model. Our hypothesis was that SiCaP with greater strut porosity would be more osteoinductive. The osteoinduction of SiCaP BGS with two different strut porosities (AF and AF++) was investigated. The materials had an identical chemical composition and morphological structure but differing strut porosity (AF=22.5%, AF++=47%). Implants were inserted into the paraspinal muscles in skeletally mature sheep. Procedures were carried out in compliance with UK Home Office regulations. There were 12 implants in each group. Implants remained in vivo for 8 and 12 weeks and on retrieval were prepared for undecalcified histology. Sections were stained and examined using light microscopy. A line intersection method was used to quantify bone, implant and implant surface/bone contact within seven random regions of interest along each implant. A Mann-Whitney U test was used for statistical analysis where p values < 0.05 were considered significant.INTRODUCTION
METHODS
Extendable proximal femoral replacements(PFR) are used in children with bone tumours in proximity to the proximal femoral physis, previously treated by hip disarticulation. Long-axis growth is preserved, allowing limb salvage. Since 1986, survival outcomes after limb salvage and amputation have been known to be equal. Retrospective review of all patients <16years undergoing extendable PFR at Royal National Orthopaedic Hospital (UK) between 04/1996 and 01/2006, recording complications, failures, procedures undertaken and patient outcomes.Background
Method
Extendable partial femoral replacements (EPFR) permit limb salvage in children with bone tumours in proximity to the physis. Older designs were extended through large incisions or minimally invasive surgery. Modern EPFR are lengthened non-invasively. Lengthening improves functional score (Futani, 2006) but has been associated with complications including infection (Jeys, 2005). This study is the first to look specifically at the relationship between EPFR lengthening and complications. Retrospective review of 51 paediatric (<16 years) oncology patients undergoing primary (1 °) EPFR (minimally/noninvasive) between 06/1994 and 01/2006. Exclusions: 1 patient with 5cm extension without medical intervention and 5 patients with incomplete data.Background
Method
