Abstract. Objectives. Principal Component Analysis (PCA) is a useful method for analysing human motion data. The objective of this study was to use PCA to quantify the biggest variance in knee kinematics waveforms between a Non-Pathological (NP) group and individuals awaiting High Tibial Osteotomy (HTO) surgery. Methods. Thirty knees (29 participants) who were scheduled for HTO surgery were included in this study. Twenty-eight NP volunteers were recruited into the study. Human motion analysis was performed during level gait using a modified Cleveland marker set. Subjects walked at their self-selected speed for a minimum of 6 successful trials. Knee kinematics were calculated within Visual3D (C-Motion). The first three Principal Components (PCs) of each input variable were selected. Single-component reconstruction was performed alongside representative extremes of each PC to aid interpretation of the biomechanical feature reconstructed by each component. Results. Pre-operatively patient demographics included (age: 50.70 (8.71) years; height: 1.75 (.11) m; body mass: 90.57 (20.17) kg; mTFA: 7.75 (3.72) degrees varus; gait speed: 1.06 (0.23) m/s). The HTO cohort was significantly older and had a higher mass than the NP control participants. For knee kinematics the first three PCs explained 88%, 95% and 89% of the sagittal, frontal, and transverse planes, respectively. The main variances can be explained by sagittal plane magnitude differences, peak swing is associated with toe-off, a reduced knee flexion angle is associated with a longer time spent in stance, pre-HTO remain adducted during stance and pre-HTO patients remain more externally rotated during stance and latter part of swing. Conclusions. This study has introduced PCA in trying to better understand the biomechanical differences between a control group and a cohort with medial knee osteoarthritis varus deformity awaiting HTO. Further analysis will be undertaken using PCA comparing pre- and post-surgery which will be of importance in clinical decision making

The Ionising Radiation (Medical Exposure) Regulations 2000 is concerned with: “the making of safety measures in regard to radioactive substances and the emission of ionising radiation”. Responsibility is placed upon the Practitioner, Operator, Referrer and employer. A clinical evaluation of the outcome of each medical exposure must be recorded.” In Ayr Hospital Radiologist report A&E radiographs but not those in fracture clinic unless a specific request was made. Therefore the Surgeon/Trainee must record their interpretation. An audit was completed to review the rate of documentation of the interpretation of radiographs in the clinical records of consecutive patients attending fracture clinics Notes and radiographs were reviewed from 6 separate fracture clinics. 106 patients attended during the time period and were seen by 9 different surgeons; 5 consultants and 4 training grade surgeons. 46 out of 106 patients were x-rayed and interpretation recorded in 38 cases. No interpretation was found in 8 cases, giving an overall compliance of 82.6% with no difference between different grades of surgeon: Consultants 79.2% (19/24); Trainees 86.4% (19/22). These finding were presented at a departmental audit meeting and the audit loop was then closed by a second period of audit with an improvement in the consultants compliance to 100% (22/22) p=0.05 and no significant change in the trainees performance 75% (18/24)

Biomechanical interpretations of bone adaptation in biological reconstructions following bone tumors would be crucial for orthopedic oncologists, particularly if based on quantitative observations. This would help to plan for surgical treatments, rehabilitative programs and communication with the patients. In particular, outcomes of the Capanna technique, which combines bone allograft and vascularized fibula autograft, lead to stable and durable reconstructions [1, 2], and different remodeling patterns have been described [3] as a response to mechanical loading. However, there are several events that are not understood and require a biomechanical interpretation, as the evolution patterns can evolve towards conditions that threaten the strength of the reconstruction. We aimed to (i) analyze the biomechanical adaptation of a femoral reconstruction after Ewing sarcoma, in terms of morphological and densitometric evolution of bone from CT data, internal loads acting on the bone during movement, mechanical competence of the reconstruction, and (ii) relate in-progress bone resorption to the mechanical stimulus induced by different motor activities. Eight CT datasets of a patient (8 yrs at surgery using the Capanna technique) during 76-month follow-up were available. The evolution of bone morphology, density and moments of inertia was quantified. At the last control, the patient underwent gait analysis (walking, chair rise/sit, stair ascent/descent, squat). We created a multiscale musculoskeletal and finite element model from CT scans and motion analysis data at the end of follow-up, using state-of-the-art modeling workflows [4, 5], to analyze muscle and joint loads, and to compare the mechanical competence of the reconstructed bone with the contralateral limb, in the current real condition and in a possible revision surgery that removed proximal screws. Although there were no reconstruction complications and osteo-fusion with intense remodeling between allograft and autograft was shown, there was a progressive decrease in allograft cortical thickness and density. There were strategies of muscle coordination that led to differences in joint loads between limbs more marked in more demanding motor activities, and generally larger in the contralateral limb. The operated femur presented a markedly low ratio of physiological strain due to load-sharing with the metal implant, particularly in the lateral aspect. A possible revision surgery removing the three most proximal screws would help restore a physiological strain configuration, while the safety of the reconstruction would not be threatened. We suggest that bone resorption is related to load-sharing and to the internal forces exerted during movement, and the mechanical stimulus should be improved by adopting modifications in the surgical treatment and by promoting physical therapy aimed at specific muscle strengthening

Patient-reported outcomes (PROs) are widely used in the orthopaedic field to assess the impact of conservative and surgical interventions from a patient's perspective. Available instruments cover a range of outcome parameters, such as pain, function, stiffness, quality of life or joint awareness. Choice of instrument for a specific study for clinical practice should include the appraisal of the psychometric characteristics of the measure. The presentation will focus on the assessment of the psychometric characteristics of PRO instruments and provide criteria for evaluating those. The concepts of objectivity, reliability and validity will be explained in the context of PRO instrument and the interpretation of score points derived from PRO instruments will be discussed detailing concepts such as minimal important change/difference, norm data, and thresholds based on external criteria. Finally, international guidelines that define standards for the various procedures on development, validation and translation of PRO instruments will be summarised

The treatment of extremity ballistic injury is challenging in that the zone of injury can be extensive and determining the surgical exposure can be difficult. We describe a method of pre-operative evaluation of the zone of injury in conjunction with the regional anesthesiologist utilizing ultrasound to determine the presence of nerve disruption. This non-invasive method of examination may elucidate whether significant nerve exists and may also serve to pinpoint the location of injury. Such information allows the surgeon to more effectively and efficiently surgically expose the zone of injury and understand the boundaries of the nerve outside the zone of injury. Moreover, such preoperative evaluation may at times obviate the need for exploratory surgery at all. It is important for the anesthesiologist and surgeon to work together with respect to the ability to both interpret the ultrasound images and to clinically correlate the findings. The zone of tissue disruption in ballistic injuries is extremely variable. It is beneficial to both the surgeon and patient to engage in a collaborative effort with an experienced regional anesthesiologist who is well-versed in interpretation of ultrasound images and tissue plane disruption in an effort to minimize surgical time and the potential unintended consequences of unnecessary exploration. We present a series of cases representing instances wherein the zone of injury was small, extensive, and a unique situation in which there was in fact no injury present despite clinical symptoms and MRI consistent with radial nerve disruption

This edition of Cochrane Corner looks at some of the work published by the Cochrane Collaboration, covering pharmacological interventions for the prevention of bleeding in people undergoing definitive fixation or joint replacement for hip, pelvic, and long bone fractures; interventions for reducing red blood cell transfusion in adults undergoing hip fracture surgery: an overview of systematic reviews; and pharmacological treatments for low back pain in adults: an overview of Cochrane Reviews

The medical model of history, examination and investigation forms the bedrock of diagnosis and management of all patients. The essence is the recognition of patterns of symptoms and signs. In the modern era there are an increasing number of non-medical resources ranging from web-based information, computer diagnostic aids and non-specialist healthcare professionals to provide a diagnosis and commence management of a wide range of conditions, including knee problems. We analysed the quality and patterns of clinical presentation in order to answer the question how closely clinical symptoms and examination findings correlate to diagnosis based on MRI scan and/or arthroscopic findings. The analysis was a dataset of a consecutive series of patients, aged 18 to 45, with no past history of knee problems or end stage arthritis, presenting to a single specialist triage physiotherapist, working within an integrated knee service, who fully completed a standardised knee assessment proforma of presenting symptoms and signs at a large district general hospital. The study comprises 86 patients and 98 knees. We analysed this data based on diagnostic findings of MRI scan or arthroscopy to provide definitive intra-articular diagnosis. Based on standard textbook descriptions of common presentations, we went on to define the patients' presentation history and examination as typical or atypical, with typical meaning the symptoms and signs correlated with the diagnosis. The null hypothesis is that patients have a high chance of typical presentations for common knee conditions. In the 75% of patients with a significant intra-articular pathology we found the majority had chondral rather than meniscal tears 1.7 to 1. Forty four percent of patients had atypical symptoms and 71% had atypical clinical signs, 30% and only 26% of the cohort had both typical symptoms and signs together, reflecting a surprisingly low positive predictive probability of symptoms and signs in this group of patients, particularly those with chondral lesions which was 44%. In this cohort, 57% of the cohort has 3 or more multiple diagnoses. In the diagnostically normal group, 43% had symptoms and signs typical for a meniscal tear. We conclude that clinical symptoms and signs surprisingly inaccurate in guiding intra-articular pathology within the knee, even in a sub-set considered the easy and accurate to assess. The number of multiple diagnoses and the incidence of false positive results also means that simplistic interpretations of non-definitive diagnoses and linear causation of pain pathways should be treated cautiously

We undertook a retrospective audit to assess quality of service provided by Nurse-Led Review Clinic at Glasgow Royal Infirmary for patients sustaining ankle fracture requiring surgical stabilisation. Nursing staff had received training from the senior author regarding clinical examination and radiograph interpretation. We retrospectively reviewed the clinical documentation and radiographs of 104 patients who attended from January 2009 to December 2009. Any clinical issues were identified and radiographs were scrutinised by two of the authors to assess accuracy of interpretation. Nurse-led management was then assessed as to its appropriateness. Finally two retrospective questionnaires were used to assess both the nurses and patients satisfaction with the clinic. Nurse-led clinic protocol: First appointment 10 days: Wound review, application of lightweight plaster. Second appointment 6 weeks: Removal of plaster, check radiographs. Final appointment 12 weeks: Clinical assessment, radiographs, discharge. Clinical assessment: ensure wound satisfactory, range of movement and weight-bearing are improving. Radiographic criteria: 6 weeks: Assess for talar shift, lucency or metal-work concerns. 12 weeks: Assess evidence of fracture union, infection, loosening or backing out. If any concerns with the patients' progress nursing staff would discuss with the consultant. First appointment: 7 wound problems. 5 managed by nurses and resolved. 2 discussed with surgeon, 1 settled, 1 required oral antibiotics. 3 radiographs discussed with surgeon. 2 conservative management. 1 re-operation. Second appointment: 7 wounds managed by nurses. 1 failure of fixation, discussed for re-operation. 2 concerns regarding metal in joint – treated conservatively. Final appointment: 7 referred to physiotherapy as slow to fully weight-bear. 5 discussed for removal of syndesmosis screw. 1 screw in joint, admitted for re-operation. Clinical care provided at Nurse-Led clinic is appropriate and effective. Both nursing staff and patients were satisfied with the care provided. Nurse-led clinic reduces demands on fracture clinic appointments and is a safe, cost effective initiative

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. Methods. Patients over the age of 16 years undergoing an elbow CT scan within one week of a documented elbow dislocation between 1st June 2010 and 1st June 2014 were included in the study. Three orthopaedic registrars independently reviewed both the initial dislocation and immediate post reduction plain radiographs to identify any associated bony injuries. This radiograph review was repeated by each registrar after two weeks. The incidence of associated injuries as well as the inter- and intra-observer variability was calculated. Results. 28 patients were included in the study. 54% of the patients were female and the mean age was 45 years (range 16 to 90 years). The incidence of a radial head fracture was 54%, coronoid fracture 43% and epicondyle avulsion 18% on CT. The inter-observer reliability was only shown to be fair amongst registrars and the intra-observer variability moderate. Conclusions. Computerised tomography is a useful adjunct in the assessment of associated osseous injuries following an elbow dislocation due to the presence of a high number of injuries. Plain radiographs alone have been shown to have only a fair and moderate inter and intra-observer variability respectively, therefore a low threshold to obtain further 3D imaging should be practised. Level of Evidence. IV

Joint arthroplasty is a common surgical procedure, with over 185,000 primary hip and knee arthroplasties performed in England, Wales and Northern Ireland in 2014. After total hip or knee arthroplasty, about 1% of patients develop deep prosthetic joint infection (PJI), which usually requires further major operations to clear the infection. Although PJI affects only a small percentage of patients it is one of the most devastating complications associated with this procedure. Research evidence has focussed on clinical effectiveness of revision surgery while there has been less focus on the impact on patients and support needs. Using a systematic review approach, the aim of this study was to assess support needs and evaluate what interventions are routinely offered to support patients undergoing treatment for PJI following hip or knee arthroplasty. We systematically searched MEDLINE, Embase, Web of Science, PsycINFO, Cinahl, Social Science Citation Index, and The Cochrane Library from 1980 to February 15, 2015 for observational (prospective cohort, nested case-control, case-control, and retrospective cohort) studies, qualitative studies, and clinical trials that report on the support needs and interventions for patients being treated for PJI or other major adverse occurrences following joint arthroplasty. Data were extracted by two independent investigators and consensus reached with involvement of a third. Of 4,161 potentially relevant citations, we identified one case-control, one prospective cohort and two qualitative studies for inclusion in the synthesis. Patients report that PJI and treatment had a profoundly negative impact affecting physical, emotional, social and economic aspects of their lives. No study evaluated support interventions for PJI or other major adverse occurrences following hip and knee arthroplasty. The interpretation of study results is limited by variation in study design, outcome measures and the small number of relevant eligible studies. Findings show that patients undergoing treatment for PJI have extensive physical, psychological, social and economic support needs. Our review highlights a lack of evidence about support strategies for patients undergoing treatment for PJI and other adverse occurrences. There is a need to design, implement and evaluate interventions to support these patients

Background. Visual representation help make the ever-increasing data more attractive, thought provoking and informative. In the field of surgical training, Procedure Based Assessment is a structured method of assessing surgical performance and skills of trainees in the UK and is a valuable tool for trainers in the Annual Review of Competence Progression. Trainers can view PBA's on the online-based Intercollegiate Surgical Curriculum Programme individually in a long-form format with no visual representation. Aim. To assess the effect of an originally devised EVR tool of PBA's in the context of ARCP on 10 aspects including speed of assessment, assimilation of data, ease of interpretation and identification of trainees’ weaknesses and strengths. Methodology. 1) ISCP PBA data collected for three volunteered specialty trainees (ST4, ST5 & ST6) enrolled in Warwick Trauma and Orthopaedic training programme, for a six-month period from 1st July 2013 till 31st December 2013. 2) An EVR was generated using Tableau Desktop software, and two other EVR's originally devised to visually represent the trainees’ PBA's and integrated into three interactive PDF files. 3) Twelve trainer consultants participated in a mock ARCP and rated their experience in assessing the trainee's using the new EVR method compared to the ISCP website on three surveys. 4) A mock ARCP was set up for 12 consultants. To minimise bias, six assessors were randomised into two equal groups. Groups A were asked to use the ISCP website to formulate an ARCP decision and then use the EVR interactive tool. Group B used the EVR tool followed by browsing the ISCP website. 5) Assessors rated their experience after using each method and also at the end of the mock ARCP on three surveys. Responses recorded on a Visual Analogue Scale and statistically analysed using non-parametric a two-tailed Mann Whitney U test. Results. Comparing responses to the EVR and ISCP surveys shows that users thought that using the EVR tool is more useful, accessible, easy to learn and use, time efficient and appealing. It also allowed them to better identify trainees’ areas of strengths and weaknesses and formulate a final ARCP outcome decision in relation to PBA's (p < 0.001). Strong agreement to develop the EVR tool and have incorporated into the current ISCP website have been demonstrated (p < 0.001). Comparison of total responses to the EVR and ISCP surveys between group A and group B showed no significant statistical difference. Conclusion. The project shows that Enhanced Visual Representation tool has the potential to be a positive addition to the ISCP website to improve the process of surgical training and feedback

Falls and fall-related injuries can have devastating health consequences and form a growing economic burden for the healthcare system. To identify individuals at risk for preventive measures and therapies, fall risk assessment scores have been developed. However, they are costly in terms of time and effort and rely on the subjective interpretation of a skilled professional making them less suitable for frequent assessment or in a screening situation. Small wearable sensors as activity monitor can objectively provide movement information during daily-life tasks. It is the aim of this study is to evaluate whether the activity parameters from wearable monitors correlate with fall risk scores and may predict conventional assessment scores. Physical activity data were collected from nineteen home-dwelling frail elderly (n=19, female=10; age=81±5.6 years, GFI=5.4±1.9, MMSE=27.4±1.5) during waking hours of 4 consecutive days, wearing a wearable 9-axis activity monitor (56×40×15mm, 25g) on the lateral side of the right thigh. The signal was analysed using self-developed, previously validated algorithms (Matlab) producing the following parameters: time spent walking, step count, sit-stand-transfer counts, mean cadence (steps/min), count of stair uses and intensity counts >1.5G. Conventional fall risk assessment was performed using the Tinetti sore (range: 0–28=best), a widely used tool directly determining the likelihood of falls and the Short Physical Performance Battery (SPPB, range: 0–12=best) which measures lower extremity performance as a validated proxy of fall risk. The anxiety to fall during activities of daily living was assessed using the self-reported Short Falls Efficacy Scale-International (FES-I, range: 7–28=worst). Correlations between activity parameters and conventional scores were tested using Pearson's r. The activity parameters (daily means) for the 19 participants were 70.8min (SD=28.7; min-max= 22.8–126.6) of walking, 4427 steps (SD=2344; min-max= 1391–8269) with a cadence 79.3 steps per minute (SD=17.1; min-max=52.8–103.9) and 33.3 sit-stand transfers (SD=9.7; min-max=8.8–48.0). The average Tinetti score was 21.2 (SD=5.1; min-max=10.0–27.0), with SPPB scoring 7.8 (SD=2.4; min-max=3.0–12.0), and FES-I 4.6 (SD=5.1; min-max=7.0–23.0). Strong (r≥0.6) and significant correlations existed between the walking cadence and the Tinetti (r=.60, p=<.01) and SPPB (r=.71, p=<.01) scores. No other correlations were found between the activity parameters and the Tinetti, SPPB and none with the psychological FES-I questionnaire. Conventional fall risk scores and activity data are comparable to literature values and thus representative of home-dwelling frail elderly including a wide range covered for both dimensions. No quantitative activity measure had a predictive value for fall risk assessment. Strongly correlated with Tinetti and SPPB, objectively measured cadence as a qualitative parameter seems a useful parameter for remotely identifying fall risk in frail elderly. The perceived anxiety to falls was not correlated to quantitative and qualitative activity parameters suggesting that this psychological aspect hardly affects activity. Wearable activity monitors seem a valid tool to assess fall risk remotely and thus allow low cost, frequent and large group screening of frail elderly towards a health economically viable tool for a growing societal need. The predictive quality of activity monitored data may be increased by deriving additional qualitative measures from the activity data

There are many methods for analysing wear volume in failed polyethylene acetabular components. We compared a radiological technique with three recognised ex vivo methods of measurement. We tested 18 ultra-high-molecular-weight polyethylene acetabular components revised for wear and aseptic loosening, of which 13 had pre-revision radiographs, from which the wear volume was calculated based upon the linear wear. We used a shadowgraph technique on silicone casts of all of the retrievals and a coordinate measuring method on the components directly. For these techniques, the wear vector was calculated for each component and the wear volume extrapolated using mathematical equations. The volumetric wear was also measured directly using a fluid-displacement method. The results of each technique were compared. The series had high wear volumes (mean 1385 mm. 3. ; 730 to 1850) and high wear rates (mean 205 mm. 3. /year; 92 to 363). There were wide variations in the measurements of wear volume between the radiological and the other techniques. Radiograph-derived wear volume correlated poorly with that of the fluid-displacement method, co-ordinate measuring method and shadowgraph methods, becoming less accurate as the wear increased. The mean overestimation in radiological wear volume was 47.7% of the fluid-displacement method wear volume. Fluid-displacement method, coordinate measuring method and shadowgraph determinations of wear volume were all better than that of the radiograph-derived linear measurements since they took into account the direction of wear. However, only radiological techniques can be used in vivo and remain useful for monitoring linear wear in the clinical setting. Interpretation of radiological measurements of acetabular wear must be done judiciously in the clinical setting. In vitro laboratory techniques, in particular the fluid-displacement method, remain the most accurate and reliable methods of assessing the wear of acetabular polyethylene

Introduction. Risk factors for disc degeneration depend on how the condition is defined, i.e. on the specific disc degeneration “phenotype”. We present evidence that there are two major and largely-distinct types of disc degeneration. Methods. The relevant research literature was reviewed and re-interpreted. Evidence. In the . upper. lumbar and thoracic spine, disc degeneration is closely associated with endplate defects and with inflammatory changes in the vertebral bodies. It has a relatively high heritability (i.e. a strong genetic influence), and its incidence does not increase markedly with age. In the . lower. lumbar spine, disc degeneration is closely associated with radial fissures and nucleus herniation. Here it has a relatively low heritability, and a correspondingly stronger association with mechanical loading, and its incidence increases steadily throughout life. Mechanical experiments on cadaveric spines show that endplate fracture and nucleus herniation can be caused by compressive loading, and by bending combined with compression, respectively. Both lesions cause an immediate decompression of the nucleus, so that it becomes difficult to create subsequently the other lesion in the same disc. This suggests distinct phenotypes. Interpretation. The two types of disc degeneration are not entirely distinct, because disc herniation sometimes occurs at upper lumbar levels. Nevertheless, it may be useful to recognise two phenotypes when it comes to explaining and treating discogenic pain. Some other common disc changes (such as water loss and bulging) are attributable to ageing rather than degeneration, whereas disc narrowing probably represents a final common pathway for both types of disc degeneration. Conflicts of Interest. None. Source of Funding. None. This abstract has not been previously published in whole or in part; nor has it been presented previously at a national meeting

Introduction. Discogenic pain is associated with ingrowth of blood vessels and nerves, but uncertainty over the extent of ingrowth is hindering development of appropriate treatments. We hypothesise that adult human annulus fibrosus is such a dense crosslinked tissue that ingrowth via the annulus is confined to a) peripheral regions, and b) fissures extending into the annulus. Methods. Disc tissue was examined from 61 patients (aged 37–75 yrs) undergoing surgery for disc herniation, degeneration or scoliosis. 5 µm sections were stained with H&E to identify structures and tissue types. 30 µm frozen sections were examined using confocal microscopy, following immunostaining for CD31 (an endothelial cell marker), PGP 9.5 and Substance P (general and nociceptive nerve markers, respectively). Fluorescent tags were attached to the antibodies. ‘Volocity’ software was used to calculate numbers and total cross-sectional area of labelled structures, and to measure their distance from the nearest free surface (disc periphery, or annulus fissure). Results. Maximum penetration of blood vessels and nerves from the peripheral annulus was 4,800 µm and 2,200 µm respectively. Maximum distance of nerves and vessels from the nearest free surface was 236 µm and 888 µm. Substance P (but not PGP 9.5) was co-localised with blood vessels, and both number and area of Substance P-stained structures were inversely correlated with grade of disc degeneration. Interpretation. Thick sections and fluorescent markers can show reliably where labelled structures are not present. Results therefore support our hypothesis: deep penetration of nerves into the human annulus occurs only if fissures are present. No conflicts of interest. No funding obtained. This abstract has not been previously published in whole or in part; nor has it been presented previously at a national meeting

Introduction. Herniated disc tissue removed at surgery usually appears degenerated, and MRI often reveals degenerative changes in adjacent discs and vertebrae. This has fostered the belief that a disc must be degenerated before it can herniate, which has medicolegal significance. We hypothesise that degenerative changes in herniated disc tissues differ from those found in tissues that have degenerated in-situ, and are consistent with being consequences rather than causes of herniation. Methods. Surgically-removed discs were examined using histology, immunohistochemistry and confocal microscopy. 21 samples of herniated tissues were compared with age-matched tissues excised from 11 patients whose discs had reached a similar Pfirrman grade of degeneration but without herniating. Degenerative changes were assessed separately in three tissue types (where present): nucleus, inner annulus, and outer annulus. Mann-Whitney U tests were used to compare ‘herniated’ vs ‘in-situ’ tissues. Results. Herniated tissues showed significantly greater cellularity (annulus), greater proteoglycan loss (outer annulus), greater neovascularisation (annulus), greater innervation (annulus) as judged by PGP 9.5 staining, greater expression of matrix-degrading enzymes MMP1 and MMP3 (inner annulus), but less cell clustering (outer annulus). Some similar but non-significant differences were seen in nucleus tissues. Interpretation. Herniated tissues that escape the pressurised confines of the disc are free to swell, lose proteoglycans and come into contact with blood cells. These events could explain most of the differences between herniated tissues and those that degenerated ‘in situ’. Results support our hypothesis, and warn against assuming that degenerative changes always precede (or cause) disc herniation. No conflicts of interest. No funding obtained. This abstract has not been previously published in whole or in part; nor has it been presented previously at a national meeting

The annulus fibrosus (AF) of the intervertebral disc (IVD) has a unique, complex structure. If engineered tissues for the IVD are to be successfully developed, it is essential that the constituent level mechanics of the tissues in their natural form are fully understood (Nerurkar, J. Biomech. 2010). Published finite element (FE) models of the IVD do not represent lamellae behaviour and are validated using bulk mechanics of the intervertebral joint. This study aims to develop models of the IVD that include representation of the lamellae structure of the AF and the behaviour of this tissue within the disc. METHODS. Three FE models of a vertebra-disc-vertebra section were developed considering the following scenarios of the AF:. Homogenous AF. Concentric rings representing AF's lamellae structure with frictionless contact between rings. Concentric rings with ‘interface’ elements representing the interlamellar space; properties were derived through calibration of a separate model of an AF tissue sample with histological studies of the AF (Gregory, J. Biomechs. 2009). Displacements, stiffness and disc bulge were compared with the literature. RESULTS & CONCLUSIONS. The properties derived for the interface elements were stiffer than those for the AF tissue. this is in agreement with in vitro studies that have examined the mechanisms by which the lamellae fail prior to the interlamellar interaction (Veres, Spine, 2010). The macro-scale performance of the disc was sensitive to how the interlamellar interactions were modelled. Disc stiffness reduced by 7.1% between the homogenous and frictionless models. Use of the interface model improved the agreement with the in vitro performance of the disc: 5.8% error was recorded for disc stiffness and 2.1% error for disc bulge. The mechanics of the lamellae within the AF changed significantly between the frictionless and interface models. The relative displacement of adjacent lamellae was reduced by 15% between the frictionless and interface models. This study shows that the representation of the lamina structure of the AF affects the mechanics of the whole disc. Discrepancies in the modelling of interlamellar mechanics could have a significant effect on the interpretation of several important aspects of the biomechanics of the IVD