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. A series of models of a 36mm BIOLOX® Delta THR bearing (DePuy Synthes, Leeds, UK) were generated to match an experimental simulator study which included a mediolateral spring to cause lateral head separation due to a simulated mediolateral component misalignment of 4mm. A static, rigid, frictionless model was implemented in Python (PyEL, runtime: ∼1m), and results were compared against 1) a critically damped dynamic, rigid, FE model (runtime: ∼10h), 2) a critically damped dynamic, rigid, FE model with friction (µ = 0.05) (runtime: ∼10h), and 3) kinematic experimental test data from a hip simulator (ProSim EM13) under matching settings (runtime: ∼6h). Outputs recorded were the variation of mediolateral separation and force with time.INTRODUCTION
METHODS
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. Gait data was acquired from five male and five female unilateral THR patients using a ten camera Vicon system (Oxford Metrics, UK) interfaced with twin force plates (AMTI) and using a CAST marker set. All patients had good surgical outcomes, confirmed by patient-reported outcomes and were considered well-functioning, based on elective walking speed. Joint contact forces and pelvic motions were obtained from the AnyBody modelling system (AnyBody Technologies, DK). Only gait cycle regions with available force plate data were considered. A finite element model of a 32mm head on a featureless hemispherical polyethylene cup, 0.5mm radial clearance, was used to obtain the contact area from the contact force. A bespoke computational tool was used to analyse patients' gait profiles with and without pelvic motions. The risk of edge contact was measured as a “centre proximity angle” between the cup pole and centre of the contact area, and “edge proximity angle” between the cup pole and the furthest contact area point away from the pole. Pelvic tilt, drop and internal-external rotation were considered one at a time and in combinations.Introduction
Methods
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 Six femoral heads from six subjects were tested, a subset (n=3) included a hole drilled into the subchondral area of the femoral head via the femoral neck (University of Leeds, ethical approval MEEC13-002). The simulated lesions provided a method to validate the fracture prediction model with respect of AVN. The femoral heads were then modelled by a beam loaded with a single joint contact load. Material properties were assigned to the beam model from QCT-scans by using a density-modulus relationship. The maximum joint loading at which each bone cross-section was likely to fracture was calculated using a strain based failure criterion. Based on the predicted fracture loads, all six femoral heads (validation set) were classified into two groups, high fracture risk and low fracture risk (Figure 1). Beam theory did not allow for an accurate fracture load to be found because of the geometry of the femoral head. Therefore the predicted fracture loads of each of the six femoral heads was compared to the mean fracture load from twelve previously analysed human femoral heads (reference set) without lesions. The six cemented femurs were compression tested until failure. The subjects with a higher fracture risk were identified using both the experimental and beam tool outputs.Introduction
Methods
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 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. Custom made MATLAB (MathWorks) and Python codes[1] were used to generate bone surfaces, which were developed into finite element models in Abaqus (SIMULIA). Parametric femoral surfaces were defined by a spherical proximal head and ellipse sections through the neck/cam region. This method produced surfaces that were well fitted to bone geometry segmented from CT scans of cam patients and capable of producing trends in results similar to those found using segmented models. A simplified spherical geometry, including the labrum and acetabular cartilage, represented the acetabulum. Femoral parameters were adjusted to define relevant variations in cam size and position. Two radii (small and large cams) and two positions (anterior and superior cams) were defined resulting in four models. Alpha angles of these parametric femurs were measured in an anterior-posterior view and a cross-table lateral view using ImageJ (NIH). A further model was developed using a femur with a medium cam size and position, and the level of acetabular coverage and labrum length were varied. Bones were modelled as rigid bodies and soft tissues were modelled as transversely isotropic linearly elastic materials. With the acetabulum fully constrained in all cases, the femurs were constrained in translation and rotated to simulate flexion followed by internal rotation to cause impingement against the labrum.Introduction
Methods
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. All patients with an acute achilles tendon rupture were treated with the same non-operative LAMP functional rehabilitation regime in a VACOped boot for 8 weeks. 12 months post rupture ATRS scores and objective measures of calf muscle girth and heel raise height were obtained and analysed. Venous thromboembolic rates and rates of re-rupture were recorded.Background
Methods
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. Three-dimensional (3D) computed tomographic (CT) images of 56 subjects (28 males and 28 females) lying supine were obtained from a public image archive (Cancer Image Archive, website: INTRODUCTION
METHODS
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. The components of the THR were aligned and constrained as illustrated in Figure 1. CAD models of commercially available implant geometries were used (DePuy Synthes, Leeds, UK) modified for model simplicity by removing anti-rotation features. The polyethylene cup liner was given elastic-plastic behaviour. An axial load following the Paul cycle pattern (5 repetitive cycles) with maximum of 3KN and swing phase load of 0.3KN, was applied through the cup holder. The effect of translational mismatch was implemented by using a spring element connected to the cup unit on the lateral side. The spring was compressed by a fixed amount to replicate a degree of medial-lateral mismatch of the components. The instantaneous resultant force vector dictated the dynamic sliding behaviour of the cup against the head. In this study, translational medial-lateral mismatch values of 1, 2, 3 and 4mm were used and the medial-lateral dynamic separation, contact pressure maps and plastic strain were recorded.Introduction
Methodology
Acute Achilles tendon (AT) rupture management remains debatable but non-operative functional regimes are beginning to dominate current treatment algorithms. The aim of this study was to identify predictors of functional outcome in patients with AT ruptures treated non-operatively with an immediate weight bearing functional regime in an orthosis. Analysis of prospectively gathered data from a local database of all patients treated non-operativelyat our institution with anAT rupture was performed. Inclusion criteria required a completed Achilles Tendon Rupture Score (ATRS) at a minimum of 8 months post rupture. The ATRS score was correlated against age, gender, time following rupture, duration of treatment in a functional orthoses (8- and 11-week regimes) and complications. 236 patients of average age 49.5 years were included. The mean ATRS on completion of rehabilitation was 74 points. The mean ATRS was significantly lower in the 37 females as compared to the 199 males, 65.8 vs 75.6 (p = 0.013). Age inversely affected ATRS with a Pearsons correlation of −0.2. There was no significant difference in the ATRS score when comparing the two different treatment regime durations. There were 12 episodes of VTE and 4 episodes of re-rupture. The ATRS does not change significantly after 8 months of rupture. Patients with AT ruptures treated non-operatively with a functional rehabilitation regime demonstrate good function with low re-rupture rates. Increasing age and female gender demonstrate inferior functional outcomes.
Low back pain is a common complaint, affecting up to one third of the adult population costing over £1 billion to the NHS each year and £3.5 billion to the UK economy in lost production. The demand for spinal injections is increasing allowing for advanced spinal physiotherapists to perform the procedure. The objective of this study was to investigate outcome following spinal injections performed by consultant spinal surgeon (n=40) and advanced spinal physiotherapists (ASP) (n=40) at our centre. Data on 80 patients who had received caudal epidural (n=36), nerve root block (n=28) and facet joint injections (n=16) form August 2010 to October 2011 consented to be in the study. 40 patients in each group completed Oswestry Disability Index (ODI), Visual Analogue Scores (VAS) before and 6 weeks after the procedure and patient satisfaction questionnaire investigating their experience and any complications related to the spinal injection retrospectively. The study included 32 males and 48 females. Mean age 57 years, range 21–88. [Consultant group M:17, F:23 mean age: 55, range 21–81. ASP group M:15, F:25 mean age 59, range 22–88]. Measures of patient satisfaction and outcome were obtained; using 2 tailed independent samples Introduction and aims
Method and Materials
Fractures of the femoral head are a challenging problem. The most often performed head preserving procedure worldwide is closed reduction and insertion of cannulated screws under fluoroscopic control. The use of navigation is still experimental in general trauma since rigid reference markers must be attached to all fragments. The examined system (Surgix®, Tel Aviv, Israel) is a fluoroscopy based image analysing system. It consists of a workstation and X-ray opaque markers in surgical tools. When the tool is visible in a C-arm shot a trajectory is displayed as additional layer in the image to serve as guidance for the surgeon. Forty synthetic femurs (Synbone®, Malans, Switzerland) were used and placed inside foam to simulate the soft tissue of the thigh. The models were equipped with 4.5mm radio-opaque markers at the fovea capitis femoris as target point. The aim was to bring the tip of a K-wire as close as possible to the target point entering the bone at the lateral base of the greater trochanter in a center-center position. Twenty were done under image guidance and 20 were operated the conventional way. Outcome measures included the accuracy (the distance between the tip of the wire and the target in a CT), the number of guide wire insertions, procedure duration, radiation exposure and learning curve. In the image guided group optimal guide wire placement was accomplished on first pass in 65% of the cases as compared to 5% in the conventional group (p = < 0.0001). The average number of trial and error was significantly lower in the guided group (1.7 vs. 5.8, p = < 0.0001). Consequently the average duration of the guided procedure was significantly shorter (p = 0.0008) along with radiation exposure time reduced by over 70% (p = 0.0002). The guidance system hit averaged 5.8 mm off target as compared to 5.3 mm for the freehand method (p = 0.3319). Image based guidance significantly shortened the procedure, reduced the radiation exposure and the number of trials without changing the surgeons workflow and can be used in trauma cases were reference marker based navigation is not applicable.
Computer assisted surgery (CAS) is used in trauma surgery to reduce radiation and improve accuracy but it is time consuming. Some trials for navigation in small bone fractures were made, but they are still experimental. One major problem is the fixation of the dynamic reference base for navigation. We evaluated the benefit of a new image based guidance-system (Surgix®, Tel Aviv, Israel) for fracture treatment in scaphoid bones compared to the conventional method without navigation. The system consists of a workstation and surgical devices with embedded radio opaque markers. These markers as well as the object of interest must be on the same C-arm shot. If a tool is detected in an image by the attached workstation additional information such as trajectories are displayed in the original fluoroscopic image to serve the surgeon as aiming device. The system needs no referencing and no change of the workflow. For this study 20 synthetic hand models (Synbone®, Malans, Switzerland) were randomised in two groups. Aim of this study was a central guide-wire placement in the scaphoid bone, which was blindly measured by using postoperative CT-scans. Significant distinctions related to the duration of surgery, emission of radiation, radiation dose, and trials of guide-wire positioning were observed. By using the system the surgery duration was with 50 % shortened (p = 0.0054) compared to the conventional group. One reason might be the significant reduction of trials to achieve a central guide-wire placement in the bone (p = 0.0032). Consequently the radiation exposure for the surgeon and the patient could be shortened by reduction of radiation emission (p = 0.0014) and radiation dose (p = 0.0019). By using the imaged based guidance system a reduction of surgery duration, radiation exposure for the patient and the surgeon can be achieved. By a reduced number of trials for achieving a central guide-wire position the risk of weakening the bone structure can be minimised as well by using the system. The system seems helpful where navigation is not applicable up to now. The surgical workflow does not have to be chanced.
Replacing bone lost as a consequence of trauma or disease is a major challenge in the treatment of musculoskeletal disorders. Tissue engineering strategies seek to harness the potential of stem cells to regenerate lost or damaged tissue. Bone marrow aspirate (BMA) provides a promising autologous source of skeletal stem cells (SSCs) however, previous studies have demonstrated that the concentration of SSCs required for robust tissue regeneration is below levels present in iliac crest BMA, emphasising the need for cell enrichment strategies prior to clinical application. To develop a novel strategy to enrich skeletal stem cells (SSCs) from human BMA, clinically applicable for intra-operative orthopaedic use.Background
Aims
To assess the accuracy of posterior and anterolateral methods of injection into the subacromial space (SAS) of the shoulder. Ethical approval was obtained and 50 patients (23 women and 27 men) with mean age of 64.5 years (42-87 years) and clinical diagnosis of subacromial impingement were recruited. Patients with old or recent shoulder fracture, bleeding disorders, and allergy to iodine were excluded. All injections were given by the consultant or an experienced registrar after obtaining informed consent. Patients were randomised into posterior and anterolateral groups and the method of injection was revealed by opening sealed envelopes just before the injection. A combination of 3mls 0.5% bupivacaine and 2mls of radiographic dye (Niopam) was injected in the subacromial space (SAS) using either anterolateral (n-22) and posterior approaches (28). AP and lateral radiographs of shoulder were taken after injection and were reported by a Consultant Radiologist blinded to the method of injection. Visual analogue scale (VAS) and Constant-Murley shoulder score was used to assess pain and function respectively. Both scores were determined before and 30 minutes after the injection.Aims
Patients and methods
We aimed (1) to determine the factors which influence outcome after surgery for CES and (2) to study CES MRI measurements. 56 patients with evidence of a sphincteric disturbance who underwent urgent surgery (1994-2002) were identified and invited to clinic. 31 MRIs were available for analysis and randomised with 19 MRIs of patients undergoing discectomy for persistent radiculopathy. Observers estimated the percentage of spinal canal compromise and indicated whether they thought the scan findings could produce CES and whether the discs looked degenerate. Measurements were repeated after two weeks. (1) 42 patients attended (mean follow up 60 months; range 25–114). Mean age at onset was 41 years (range 24–67). 26 patients were operated on within 48 hours of onset. Acute onset of sphincteric symptoms and the time to operation did not influence the outcomes. Leg weakness at onset persisted in a significant number at follow-up (p<0.005). Bowel disturbance at presentation was associated with sexual problems (<0.005) at follow-up. Urinary disturbance at presentation did not affect the outcomes. The 13 patients who failed their post-operative trial without catheter had worse outcomes. The SF36 scores at follow-up were reduced compared to age-matched norms in the population. The mean ODI was 29, LBOS 42 and VAS 4.5. (2) No significant correlations were found between MRI canal compromise and clinical outcome. There was moderate to substantial agreement for intra- and inter-observer reproducibility. Due to small numbers we cannot make the conclusion that delay to surgery influences outcome. Based on the SF36, LBOS and ODI scores, patients who have had CES do not return to a normal status. Using MRI alone, the correct identification of CES has sensitivity 68%, specificity 80% positive predictive value 84% and negative predictive value 60%. CES occurs in degenerate discs.Conclusions
In suspected scaphoid fracture the initial scaphoid series plain radiographs are 84-94% sensitive for scaphoid fractures. Patients are immobilised awaiting diagnosis. Unnecessary lengthy immobilisation leads to lost productivity and may leave the wrist stiff. Early accurate diagnosis would improve patient management. Although Magnetic Resonance Imaging (MRI) has come to be regarded as the gold standard in identifying occult scaphoid injury, recent evidence suggests Computer Tomography (CT) to be more accurate in identifying scaphoid cortical fracture. Additionally CT and USS are frequently a more available resource than MRI. We hypothesised that 16 slice CT is superior to high spatial resolution Ultrasonography (USS) in the diagnosis of radiograph negative suspected cortical scaphoid fracture and that a 5 point clinical examination will help to identify patients most likely to have sustained a fracture within this group. 100 patients with two negative scaphoid series and at least two out of five established clinical signs of scaphoid injury (anatomical snuffbox tenderness (AST), scaphoid tubercle tenderness (STT), effusion, pain on circumduction and pain on axial loading) were prospectively investigated with CT and USS. MRI was arranged for patient with persistent symptoms but negative CT/USS.Background
Methods
