Anterior approach total hip arthroplasty (AA-THA) has a steep learning curve, with higher complication rates in initial cases. Proper surgical case selection during the learning curve can reduce early risk. This study aims to identify patient and radiographic factors associated with AA-THA difficulty using Machine Learning (ML).

Consecutive primary AA-THA patients from two centres, operated by two expert surgeons, were enrolled (excluding patients with prior hip surgery and first 100 cases per surgeon). K- means prototype clustering – an unsupervised ML algorithm – was used with two variables - operative duration and surgical complications within 6 weeks - to cluster operations into difficult or standard groups.

Radiographic measurements (neck shaft angle, offset, LCEA, inter-teardrop distance, Tonnis grade) were measured by two independent observers. These factors, alongside patient factors (BMI, age, sex, laterality) were employed in a multivariate logistic regression analysis and used for k-means clustering. Significant continuous variables were investigated for predictive accuracy using Receiver Operator Characteristics (ROC).

Out of 328 THAs analyzed, 130 (40%) were classified as difficult and 198 (60%) as standard. Difficult group had a mean operative time of 106mins (range 99–116) with 2 complications, while standard group had a mean operative time of 77mins (range 69–86) with 0 complications. Decreasing inter-teardrop distance (odds ratio [OR] 0.97, 95% confidence interval [CI] 0.95–0.99, p = 0.03) and right-sided operations (OR 1.73, 95% CI 1.10–2.72, p = 0.02) were associated with operative difficulty. However, ROC analysis showed poor predictive accuracy for these factors alone, with area under the curve of 0.56. Inter-observer reliability was reported as excellent (ICC >0.7).

Right-sided hips (for right-hand dominant surgeons) and decreasing inter-teardrop distance were associated with case difficulty in AA-THA. These data could guide case selection during the learning phase. A larger dataset with more complications may reveal further factors.

The Posterior and Lateral approaches are most commonly used for Total Hip Arthroplasty (THA) in the United Kingdom (UK). Fewer than 5% of UK surgeons routinely use the Direct Anterior Approach (DAA). DAA THA is increasing, particularly among surgeons who have learned the technique during overseas fellowships. Whether DAA offers long-term clinical benefit is unclear.

We undertook a retrospective analysis of prospectively collected 10-year, multi-surgeon, multi-centre implant surveillance study data for matched cohorts of patients whose operations were undertaken by either the DAA or posterior approach. All operations were undertaken using uncemented femoral and acetabular components. The implants were different for the two surgical approaches. We report the pre-operative, and post operative six-month, two-year, five-year and 10-year Oxford Hip Score (OHS) and 10-year revision rates.

125 patients underwent DAA THA; these patients were matched against those undergoing the posterior approach through propensity score matching for age, gender and body mass index. The 10-year revision rate for DAA THA was 3.2% (4/125) and 2.4% (3/125) for posterior THA. The difference in revision rate was not statistically significant. Both DAA and Posterior THA pre-operative OHS were comparable at 19.85 and 19.12 respectively. At the six-month time point, there was an OHS improvement of 20.89 points for DAA and 18.82 points for Posterior THA and this was statistically significant (P-Value <0.001). At the two, five and 10-year time-points the OHS and OHS improvement from the pre-operative review were comparable. At the 10-year time point post-op the OHS for DAA THA was 42.63, 42.10 for posterior THA and the mean improvement from pre-op to 10-years post op was 22.78 and 22.98 respectively. There was no statistical difference when comparing the OHS or the OHS mean improvements at the two, five and 10-year point.

Whilst there was greater improvement and statistical significance during the initial six month time period, as time went on there was no statistically significant difference between the outcome measures or revision rates for the two approaches.

Over 8000 total hip arthroplasties (THA) in the UK were revised in 2019, half for aseptic loosening. It is believed that Artificial Intelligence (AI) could identify or predict failing THA and result in early recognition of poorly performing implants and reduce patient suffering.

The aim of this study is to investigate whether Artificial Intelligence based machine learning (ML) / Deep Learning (DL) techniques can train an algorithm to identify and/or predict failing uncemented THA.

Consent was sought from patients followed up in a single design, uncemented THA implant surveillance study (2010–2021). Oxford hip scores and radiographs were collected at yearly intervals. Radiographs were analysed by 3 observers for presence of markers of implant loosening/failure: periprosthetic lucency, cortical hypertrophy, and pedestal formation.

DL using the RGB ResNet 18 model, with images entered chronologically, was trained according to revision status and radiographic features. Data augmentation and cross validation were used to increase the available training data, reduce bias, and improve verification of results.

184 patients consented to inclusion. 6 (3.2%) patients were revised for aseptic loosening. 2097 radiographs were analysed: 21 (11.4%) patients had three radiographic features of failure.

166 patients were used for ML algorithm testing of 3 scenarios to detect those who were revised. 1) The use of revision as an end point was associated with increased variability in accuracy. The area under the curve (AUC) was 23–97%. 2) Using 2/3 radiographic features associated with failure was associated with improved results, AUC: 75–100%. 3) Using 3/3 radiographic features, had less variability, reduced AUC of 73%, but 5/6 patients who had been revised were identified (total 66 identified).

The best algorithm identified the greatest number of revised hips (5/6), predicting failure 2–8 years before revision, before all radiographic features were visible and before a significant fall in the Oxford Hip score. True-Positive: 0.77, False Positive: 0.29.

ML algorithms can identify failing THA before visible features on radiographs or before PROM scores deteriorate. This is an important finding that could identify failing THA early.

Abstract

Abstract

Patient Reported Outcome Measures (PROMs) can be completed using paper and postal services (pPROMS) or via computer, tablet or smartphone (ePROMs). We have investigated whether there are differences in scores depending on the method of PROMs acquisition for the Oxford Knee (OKS) and the EQ-5D scores, at one and two years post operatively.

Patient demographics, mode of preferred data collection and pre-and post-operative PROMs for Total Knee Replacements (TKRs) performed between 1st January 2018 and 31st December 2018 were collected.

During the study period, 1573 patients underwent TKRs. The average OHS and EQ-5D pre-operatively scores was 19.47 and 0.40 respectively. 71.46% opted to undertake post-operative questionnaires using ePROMs. The remaining 28.54% opted for pPROMS. The one and two-year OHS for ePROMS patients increased to 37.64 and 39.76 while the OHS scores for pPROMS patients were 35.71 and 36.83. At the one and two-year post-operative time intervals, a Mann-Whitney test showed statistical significance between the modes of administration for OHS (P-Value = 0.044 and 0.01 respectively). The one and two-year EQ-5D for ePROMS patients increased to 0.76 and 0.78 while the EQ-5D scores for pPROMS patients were 0.73 and 0.76. The P-Value for Mann-Whitney tests comparing the modes of administration for EQ-5D were 0.04 and 0.07 respectively.

There is no agreed mode of PROMs data acquisition for the OKS and EQ-5D Scores. While we have demonstrated an apparent difference in scores depending on the mode of administration, further work is required to establish the influence of potentially confounding factors.

Disease specific or generic Patient Reported Outcome Measures (PROMs) can be completed by patients using paper and postal services (pPROMS) or via computer, tablet or smartphone (ePROMs) or by hybrid data collection, which uses both paper and electronic questionnaires. We have investigated whether there are differences in scores depending on the method of PROMs acquisition for the Oxford Hip Score (OHS) and the EQ-5D scores, at one and two years post operatively.

Patients for this study were identified retrospectively from a prospectively compiled arthroplasty database held at the study centre. Patient demographics, mode of preferred data collection and pre- and post-operative PROMs for Total Hip Replacements (THRs) performed at this centre between 1^st January 2018 and 31^st December 2018 were collected.

During the study period, 1494 patients underwent THRs and had complete one and two-year PROMs data available for analysis. All pre-operative scores were obtained by pPROMS. The average OHS and EQ-5D pre-operatively scores were 19.51 and 0.36 respectively. 72.02% of the patients consented to undertake post-operative questionnaires using ePROMs. The remaining 27.98% opted for pPROMS. The one and two-year OHS for ePROMS patients increased to 41.31 and 42.14 while the OHS scores for pPROMS patients were 39.80 and 39.83. At the one and two-year post-operative time intervals, a Mann-Whitney test showed statistical significance between the modes of administration for OHS (P-Value =0.044 and 0.01 respectively). The one and two-year EQ-5D for ePROMS patients increased to 0.83 and 0.84 while the EQ-5D scores for pPROMS patients were 0.79 and 0.81. The P-Value for Mann-Whitney tests comparing the modes of administration for EQ-5D were 0.13 and 0.07 respectively.

Within Orthopaedics, PROMs have become the most widely used instrument to assess patients’ subjective outcomes. However, there is no agreed mode of PROMs data acquisition. While we have demonstrated an apparent difference in scores depending on the mode of administration, further work is required to establish the influence of potentially confounding factors such as patient age, gender and familiarity with computer technology.

Clinical decision-making is often based on evidence of outcome after a specific treatment. Surgeons and patients may, have different perceptions and expectations of what to achieve following a Total Hip Replacement (THR). Several studies have shown that unfulfilled expectations are a principal source of patient dissatisfaction and patients are typically overly optimistic with regards to expected outcomes following surgery. Published data on clinical and functional outcomes show that persistence of symptoms, such as pain, and failure to return to preoperative levels of function are normal. To measure patient's expectations we undertook prospective study reviewing patients' expectations in 1800 THRs over a 21-year period (1997–2018).

Of the whole cohort, 48.98% patients reported they wanted a THR to overcome unbearable pain. 11.75 % wanted a THR to be able to walk without a limp. 9.69% wanted to a THR to increase walk endurance. 61.97% reported it was extremely important to decrease pain following a THR. In 2001, the most important reason for a THR reported by patients was to relieve unbearable pain and this remained the same most important reason in 2018. This result was also statistically significant with a p-value of 0.001. 80.36% reported they anticipated ‘no pain’ after recovery from a THR, 16.75% reported they anticipated ‘some pain’ and 2.89% reported they anticipated ‘extreme pain’ following a THR. 74.71% reported it was extremely important to increase their ability to undertake normal activities. 22.06% reported it was very important, 2.40% reported it was moderately important, 0.55% slightly important and 0.28% reported it was not all to important to increase their ability to undertake normal activity.

In conclusion patients' want to reduce their pain, walk normally and increase their level activities. Differences in expectation fulfilment may be due to unrealistic expectations. To achieve optimal outcome managing patient expectations is vital.

Background

For total hip arthroplasty (THA), cognitive training prior to performing real surgery may be an effective adjunct alongside simulation to shorten the learning curve. This study sought to create a cognitive training tool to perform direct anterior approach THA, validated by expert surgeons; and test its use as a training tool compared to conventional material.

Patients need to know the benefits, risks and alternatives to any proposed treatment. Surgeons discussing the risk of a revision procedure becoming necessary, after a hip replacement can draw upon the orthopaedic literature and arthroplasty registries for long-term implant survival. However, early revision is required in a minority of cases. We have investigated the probability for revision hip replacement patients in terms of time-point and indication for revision.

Of the 9,411 Primary Total Hip Replacements (THR), undertaken by 22 surgeons, over an eleven-year period, between January 2004 and March 2015, 1.70% (160) were subsequently reported to the National Joint Registry (NJR) as revised. Each revision case was reviewed under the supervision of senior hip specialist consultants. The modes of failure of were identified through clinical, laboratory and imaging (x-rays, CT, MRI and Isotope scans) studies.

The revision rate for THRs was 0.58% in the first year. This was statistically higher than all subsequent years, P-Value <0.001. There was no statistical difference between any pair of subsequent years. Thereafter, the average revision rate was 0.30% per annum. The odds ratio for revision during the first post–operative year against the subsequent year average was 1.67.

The indications for the early hip revisions in the first three years were infection, dislocation and peri-prosthetic fracture. The data from this study can help better inform patients of the revision rates after a primary THR and allow surgeons to develop implant surveillance strategies among high-risk patients.

INTRODUCTION

Historically, the clinical performance of novel implants was usually reported by designer surgeons who were the first to acquire clinical data. Regional and national registries now provide rapid access to survival data on new implants and drive ODEP ratings. To assess implant performance, clinical and radiological data is required in addition to implant survival. Prospective, multi-surgeon, multi-centre assessments have been advocated as the most meaningful. We report the preliminary results of such a study for the MiniHip™femoral component and Trinity™ acetabular component (Corin Ltd, UK).

We have investigated whether the pattern of subchondral acetabular cyst formation reflects hip pathology and may provide a prognostic indicator for treatment.

A single surgeon series of sequential hip arthroscopies was reviewed to identify the most recent 200 cases undertaken on a previously un-operated joint with pre-operative plain radiographs and computed tomography or magnetic resonance scan available for review. Also, serial “non-arthritic hip scores” (NAHS) recorded pre-operatively, at 6 weeks and 3 months post-surgery. The acetabular Lateral Centre Edge Angle, the Acetabular Index, the FEAR index and the Kallgren and Lawrence grade were determined. All images were reviewed by two independent assessors and divided into four groups according to acetabular subchondral cyst distribution. NC - No cysts - 74 cases (mean: 40.1 years), SPC - a Single Peripheral Cyst – 58 cases (mean: 43.1 years), SDC - a Solitary Dome Cyst – 32 cases (mean: 33 years) and MC - Multiple Cysts – 36 cases (mean: 42.7 years).

No association was identified between gender and patient reported outcomes.

SDC patients were significantly younger than the other three groups (p <0.001). At three months after surgery, the average increase of the NAHS in the four groups was 25.3, 23.5, 4.2 and 4.9 respectively. Acetabular dysplasia was identified in 72% of the SDC group compared to 18%, 16% and 33% in NC, SPC and MC groups. Degenerative change was identified in 86% of the MC group compared to 18%, 40% and 41% of the NC, SPC and SDC groups.

The early patient reported outcome following hip arthroscopy was significantly affected by the location and number of acetabular subchondral cysts. A Solitary Dome Cyst is indicative of underling hip dysplasia. Multiple Cysts are indicative of degenerative disease. The majority of patients in these groups have poor three-month outcomes after hip arthroscopy.

Total Hip Replacement (THR) is widely assumed to resolve sleep disturbance commonly experienced by individuals with hip osteoarthritis (OA). We report a study of 329 THRs with mean age of 71.9 years comparing pre-operative and one and two year post-operative patient reported outcomes for sleep disturbance to determine the veracity of this expectation. Data was collected from the validated Oxford Hip Patient Reported Questionnaire. Specifically, Question 12: “During the past four weeks, have you been troubled by pain from your hip in bed at night?” Answers to the question were multiple choice: No nights (4 points), Only 1 or 2 nights (3 points), Some nights (2 points), Most nights (1 point) and Every Night (0 points)

Pre-operatively, the mean score for patients with hip OA was 1.2/4. This increased to 3.5 at one year and was also maintained at two years. The pre- to post-operative improvement was significant at both one and two years for THR with p <0.00001. Pre-operatively, only 6% of patients with arthritic hips reported that they were never woken from sleep because of their painful hip. One year after THR 72% always enjoyed pain free sleeping and at two years this had risen to 75%. When patients who only experienced disturbance one or two nights per month were included, the three figures increased from 13% to 83% and 83% respectively.

The study confirms that sleep disturbance affects over 90% of patients with arthritic hip joints. Over 80% of THR patients will enjoy sleep that is seldom or never disturbed by their artificial hip. The improvement achieved by THR occurs within a year of surgery and is preserved at two years. In this regard, hip replacement is a highly effective intervention.

Introduction

Instability accounts for one third of revision total hip arthroplasty(rTHA) performed in the United Kingdom. Removal of well-fixed femoral stems in rTHA is challenging with a risk of blood loss and iatrogenic damage to the femur. The Bioball Universal Adaptor (BUA) (Merete, Germany), a modular head neck extension adaptor, provides a mechanism for optimisation of femoral offset, leg length and femoral anteversion. This can avoid the need for femoral stem revision in selected cases. There is a relative paucity of clinical data available with the use of this device.

Introduction

The Metasul articulation was introduced in the early 1990's. It comprises a 28mm forged, cobalt-chrome head and a forged metal inlay, set into the polyethylene element of the acetabular component. During the 1990's and early 2000's anatomic sized MoM articulations were re-introduced for hip resurfacing and stemmed implant designs. Adverse tissue reactions to metal debris and corrosion products subsequently led to a decline in MoM usage.

Objectives

This study examines variations in knee arthroplasty patient reported outcome measures according to patient age.

Using general practitioner records, hospital medical notes and through direct telephone conversation with patients, we investigated the accuracy of nine patient-reported complications after elective joint replacement surgery of the hip and knee. A total of 402 post-discharge complications were reported after 8546 elective operations that were undertaken within a three-year period. These were reported by 136 men and 240 women with an overall mean age of 71.8 years (34.3–93.2). A total of 319 (79.4%; 95% confidence interval, 75.4%–83.3%) reported complications were confirmed to be correct. Very high rates of correct reporting were demonstrated for infection (94.5%) and further surgery (100%), whereas the rates of reporting deep venous thrombosis (DVT), pulmonary embolism, myocardial infarct and stroke were lower (75%–84.2%). Dislocation, periprosthetic fractures and nerve palsy were associated with modest rates of correct reporting (36%–57.1%). More patients who had had knee surgery delivered incorrect reports of dislocation (p = 0.001) and DVT (p = 0.013). Despite these variations in accuracy, it appears that post-operative complications may form part of a larger patient-reported outcome programme for monitoring outcome after elective joint replacement surgery.

Introduction

Total hip arthroplasty (THA) is undertaken to relieve pain and to restore mobility. The orthopaedic community remains divided on the influence of surgical approach in achieving functional recovery most quickly and effectively. We report a study comparing THA performed through a posterior (Posterior) against anterior approach (Heuter).

Introduction

The outcomes programme of our institution has been developed from a system first used at Epsom and St Helier NHS Trust 15 years ago. The system was implemented at our institution when it opened in 2004, and has been used to collect data on over 17,000 joint replacement operations so far. A bespoke database is used to collect, analyse and report outcome data.

Introduction

The MITCH PCR is an anatomic, flexible, horse-shoe shaped acetabular component, with 2 polar fins. The rationale of the PCR cup design is to reproduce a near-physiological stress distribution in the bone adjacent to the prosthesis. The thin composite cup is designed to fuse and flex in harmony with the surrounding bony structure. Only the pathological acetabular cartilage and underlying subchondral bone of the horseshoe-shaped, load-bearing portion of the acetabular socket is replaced, thus preserving viable bone stock. The PCR is manufactured from injection moulded carbon fibre reinforced polyetheretherketone (PEEK), with a two layer outer surface comprising hydroxyapatite and plasma sprayed commercially pure titanium. It is implanted in conjunction with a large diameter low wear femoral head, producing a bearing that will generate minimal wear debris with relatively inert particles.

Pre-clinical mechanical testing, finite element analysis and biocompatibility studies have been undertaken. FEA evaluation predicts preservation of host bone density in the load bearing segments. A pilot clinical study was completed on a proto-type version of the PCR cup (the “Cambridge” cup), achieving excellent 5 and 10 year results.

Introduction

The need for the stringent surveillance of new devices was recognised by the NICE review of hip replacement surgery in 2000 and led to the Orthopaedic Data Evaluation Panel (ODEP) developing criteria for post-marketing surveillance (PMS) studies. This requirement has been reinforced by the recent recall of ASR devices.

Introduction

Femorotibial malalignment exceeding ±3° is a recognised contributor of early mechanical failure after total knee replacement (TKR). The angle between the mechanical and anatomical axes of the femur remains the best guide to restore alignment. We investigated where the femoral head lies relative to the pelvis and how its position varies with respect to recognised demographic and anatomic parameters. We have tested the hypothesis of the senior author that the position of the centre of the femoral head varies very little, and if its location can be identified, it could serve to outline the mechanical axis of the femur without the need for sophisticated imaging.

Purpose

To examine the clinical characteristics of patients undergoing knee arthroplasty with a pre-operative Oxford Knee Score >34 (‘good’/‘excellent’), and assess the appropriateness of surgical intervention for this group.

Purpose

The Oxford Knee Score (OKS) is a validated and widely used PROM that has been successfully used in assessing the outcome of knee arthroplasty (KA). It has been adopted as the nationally agreed outcome measure for this procedure and is now routinely collected. Increasingly, it is being used on an individual patient basis as a pre-operative measure of osteoarthritis and the need for joint replacement, despite not being validated for this use. The aim of this paper is to present evidence that challenges this new role for the OKS.

The Oxford Knee Score (OKS) is a valid and reliable self-administered patient questionnaire that enables assessment of the outcome following total knee replacement (TKR). There is as yet no literature on the behavioral trends of the OKS over time. Our aim is to present a retrospective audit of the OKS for patients who have undergone TKR during the past ten years.

We retrospectively analysed 3276 OKS of patients who had a primary TKR and had been registered as part of a multi-surgeon, outcome-monitoring program at St. Helier hospital. The OKS was gathered pre-operatively and post-operatively by means of postal questionnaires at annual intervals. Patients were grouped as per their age at operation into four groups: 60, 61-70, 71- 80 and >80. A cross-sectional analysis of OKS at different time points was performed.

The numbers of OKS available for analysis were 504 pre-operatively, 589 at one-year, 512 at two-year and gradually decreasing numbers with 87 knees ten-year post-operatively. There was as expected a significant decrease (improvement) of the OKS between pre-operative and one-year post-operative period and then reached a plateau. Beyond eight years, there is a gradual rise in the score (deterioration). The younger patients (60) showed a significant increase in their average OKS between one and five-years post-operatively. However beyond five years, they followed the trend of their older counterparts. When the twelve questions in the OKS were analysed, certain components revealed greater improvement (e.g. description of knee pain and limping) than others (e.g. night pain).

The OKS is seen to plateau a year after TKR. According to the OKS the outcome of the TKR is not as good in the younger age group as compared to the older age group. Further investigation is required to ascertain the cause of this observed difference.

The performance of total knee arthroplasty in deeply flexed postures is of increasing concern as the procedure is performed on younger, more physically active and more culturally diverse populations. Several implant design factors, including tibiofemoral conformity, tibial slope and posterior condylar geometry have been shown directly to affect deep flexion performance.

The goal of this study was to evaluate the performance of a fixed-bearing, asymmetric, medial rotation arthroplasty design during kneeling activities.

Thirteen study participants (15 knees) with primary total knee arthroplasty (Medial Rotation Knee, Finsbury, Surrey, UK) were observed while doing a step activity and kneeling on a padded bench from 90° to maximum comfortable flexion using lateral fluoroscopy. Subjects averaged 74 years of age and nine were female. Subjects were an average of 17 months post-operative, and scored 94 points on the International Knee Score and 99 on the Functional Score. Digitised fluoroscopic images were corrected for geometric distortion and 3D models of the implant components were registered to determine the 3D position and orientation of the implants in each image.

During the step activity, the medial and the lateral femoral contact point stayed fairly constant with no axial rotation from 0 to 100° of flexion. At maximum kneeling flexion, the knees exhibited 119° of implant flexion (101°-139°), 7° (-7° to 17°) tibial internal rotation, and the lateral condyle translated backwards by 11 mm.

Patients with medial rotation knee arthroplasty exhibited medial pivot action with no paradoxical translation. The knees exhibited excellent kneeling flexion and posterior translation of the femur with respect to the tibia. The axial rotation in MRK was within the range of normal knee kinematics from -10 to 120 (perhaps 140).

Aims

To establish the cost of primary hip (THR) and knee (TKR) arthroplasty in an elective orthopaedic centre in the UK and to compare it with current government reimbursement to NHS hospitals and the costs in North America.

Introduction: Increased cell senescence has been reported in the human intervertebral disc (IVD) and was associated with degenerative pathology, particularly herniation. Increased IVD innervation and blood vessel ingrowth is associated with disc degeneration and the development of back pain. This preliminary study examines whether there is a relationship between the prevalence of senescent IVD cells and the extent to which the tissue is innervated and/or vascularised.

Methods: Specimens of herniated IVD (n=16 patients: aged 36–71) were stained for senescence associated β-galactosidase activity (SA β-gal), then snap frozen and cryosectioned prior to immunolocalisation procedures to detect nerves (NF200) or blood vessels (CD34). Stained sections were counterstained with DAPI to reveal cell nuclei. The proportion of SA β-gal +ve cells was scored and the extent of neural and blood vessel ingrowth semi-quantitated.

Results: The proportion of SA β gal +ve IVD cells ranged from 6% – 91% (median=16%) and was significantly correlated with age. The degree of neural or blood vessel ingrowth ranged from tissue which contained numerous (i.e. ≥10) positive cells/cell processes to tissue which was completely aneural or avascular. However, there was no clear relationship between the presence of SA β-gal +ve IVD cells and IVD innervation or vascularisation.

Conclusions: Cell senescence has been associated with up-regulated expression of catabolic enzymes, e.g. MMPs and increased synthesis of trophic cytokines, e.g. VEGF. Such cellular activity might by thought to contribute to the pathological ingrowth of nerves or blood vessels into the IVD. The data presented here, however, does not support such a hypothesis.

Conflicts of Interest: None

Source of Funding: Institute of Orthopaedics, RJAH Orthopaedic Hospital

Introduction: Intervertebral disc (IVD) cell transplantation is used to treat back pain. However, IVD cell activity may also contribute to pathology, e.g. IVD cells can undergo senescence or promote nerve growth, which in the IVD is associated with discogenic back pain. Serum deprivation of bovine IVD cells results in cell senescence. We have examined the influence of oxygen supply combined with serum deprivation on human IVD cells.

Methods: Cells from herniated IVD (n=3 patients) were subjected to serum deprivation and then cultured under hypoxic (1%) or atmospheric (21%) conditions for 10 days. IVD cell growth, viability and cell senescence (via Senescence Associated β-galactosidase activity; SA β-gal) were examined. The growth and migration of HMEC-1 (endothelial) and SH-SY5Y (neuronal) cells treated with conditioned medium from the IVD cell cultures (1% versus 21% oxygen) were subsequently monitored.

Results: Hypoxia significantly decreased IVD cell proliferation, but was also found to reduce cell senescence. Hence, the proportions of SA β-gal positive IVD cells in 1% and 21% oxygen at day 10 were 18±6% and 56±10%, respectively. There was no marked difference in cell viability (> 95%). Conditioned medium from IVD cells cultured under hypoxia stimulated endothelial and neural cell growth (determined via the MTS assay) and endothelial cell migration and neurite outgrowth to an extent that was significantly greater than conditioned medium from IVD cells cultured at 21% oxygen.

Conclusions: The trophic activity of human IVD cells is responsive to oxygen supply. However, hypoxia may influence the capacity of IVD cells to reduce back pain for better or worse.

Conflicts of Interest: None

Source of Funding: Institute of Orthopaedics, RJAH Orthopaedic Hospital.

Background: Tranexamic acid has been shown to be effective in reducing blood loss and transfusion requirement in cardiac surgery and total knee replacement surgery. The most effective dose of tranexamic acid in hip arthroplasty surgery is not yet known. We investigated the effect of a pre-operative bolus 1g intravenous tranexamic acid on intra- and post-operative blood loss, transfusion requirement, and risk of venous thromboembolism following total hip arthroplasty.

Results: We report a cohort comparison study of 73 patients who underwent primary hip arthroplasty. Thirty-six patients received tranexamic acid (TA group), and thirty-seven received no tranexamic acid (control group). Blood loss was measured directly intra-operatively, and indirectly post-operatively by haemoglobin and haematocrit measurement. Deep vein thrombosis (DVT) was investigated by venography.

Patient demographics were similar between both groups. There was no significant difference in intra-operative blood loss between both groups. The early post-operative blood loss and total blood loss were significantly less in the tranexamic acid group. This effect of tranexamic acid was more significant in females who showed a dose-related relationship between tranexamic acid dose and blood loss. Fewer patients in the tranexamic acid group required blood transfusion. There was no increased incidence of DVT in the tranexamic acid group.

The use of a single pre-operative 1g bolus of tranexamic acid administered before surgery is a safe, cost-effective method of reducing post-operative blood loss following total hip arthroplasty. The effect is more significant in females at this dose.

Aim: To assess the functional outcome and longevity of patients who are mentally competent when they sustain an intra-capsular fracture of the femoral neck.

Methods: Prospective cohort study of fifty female patients over the age of seventy years of age with a displaced intra-capsular fracture of the femoral neck. Patients with known, cognitive impairment terminal illness or active infection were excluded from the study. Patients were treated with a large head total hip replacement. Functional outcome was assessed using the the Barthel index score and the Charnley-modified Merle d’Aubigne score yearly for five years. The Oxford hip score was also recorded annually from three to ten years post op. The date and cause of death were recorded from hospital notes and death certificates.

Results: The mean age at time of femoral neck fracture was 81 years. Three patients died before discharge from hospital. The mortality rates were 18% at twelve months, 28% at two years, 44% at five years and 92% at ten years. Those patients surviving had mean Oxford scores of 24 at 3 years, 26 at 5 years, 23 at 7 years and 25 at ten years. The cause of death was ischaemic heart disease in 22%, cancer in 10%, bronchopneumonia in 12% and simply ‘old age’ in 14%.

Conclusion: Elderly female patients who are not cognitively impaired at the time of displaced intra-capsular fracture of the femoral neck have a 56% chance of living five years. Function scores in the survivors are maintained, and are better than would be expected if the patients had undergone hip hemiarthroplasty. Total hip replacement in this population may be justified.

Aims: Minimum ten year clinical, radiological and postmortem results of the flexible Cambridge Cup. This acetabular prosthesis was designed to replace the horseshoe shaped articular cartilage and provide physiological loading with minimal resection of healthy bone.

Method: Fifty female patients aged over 70 years with a displaced intra-capsular fracture of the femoral neck were recruited to the ethically-approved prospective study. They underwent implantation of the Cambridge Cup, which has an outer polybutyleneterephthalate shell and an inner UHMWPE bearing, with a Thompson-type hemiarthroplasty. The cups were manufactured with a 60μm plasma-sprayed coating of hydroxyapatite. This was removed from half the cups to simulate the effects of long-term HA resorption. Implants were sterilised by gamma irradiation in air. Independent clinical and radiological assessments were undertaken before discharge, at 6 weeks, one year, 18 months, two -, five-, seven- and ten years. Patients were scored using the Barthel Index, the Charnley-modified Merle d’Aubigne scores and latterly the Oxford hip score. The date and cause of death were obtained from hospital records and death certificates. Fifteen Cambridge Cups were retrieved post-mortem for histological and wear analysis

Results: The mean functional scores recovered to levels before fracture. These scores decreased with advancing age at five years. The mortality rates were 16%, 28%, 46% and 92% at 1, 2, 5 and 10 years. The Oxford hip scores in patients surviving between five and ten years were maintained.

The HA coated implants remained asymptomatic. Three uncoated components required revision for migration. No evidence of accelerated UHMWPE wear was seen on retrievals or radiographs. Histological analysis of the retrieved HA coated specimens showed excellent bony fixation, uncoated cups showed predominantly fibrous tissue.

Conclusion: The uncemented Cambridge Cup was implanted in a challenging environment of osteoporotic bone. Clinical, radiographic and post-mortem results up to ten years are excellent.

Publication of normal and expected outcome scores is necessary to provide a benchmark for auditing purposes following arthroplasty surgery. We have used the Oxford knee score to monitor the progress of knee replacements undertaken since 1995, the start of our review programme. 4847 Oxford assessments were analysed over an 8 year follow-up period.

The mean pre-operative Oxford knee score was 39.2, all post-operative reviews showed a significant improvement. Patients with a BMI > 40, and the under 50 age group showed early deterioration in outcome scores, returning to pre-operative levels by 5 and 7 years respectively. There was no significant difference in outcome between surgeons performing < 20 knee replacements a year and those performing > 100 / year.

The age of the patient at the time of surgery and the pre-operative body habitus have been identified as factors affecting long term outcome of total knee replacement surgery. Awareness of these factors may assist surgeons in advising patients of their expected outcomes following surgery.

Sectioned femoral components retrieved from failed hip resurfacing arthroplasties show resorption of proximal femoral bone or formation of a fibrous membrane at the bone cement interface. Our study uses Finite Element Analysis (FEA) to examine the effects of the implant orientation on bone remodelling following hip resurfacing arthroplasty. A radiographic analysis of the proximal femur following hip resurfacing was conducted in order to draw a comparison to the FEA findings.

A 3D FEA model of the Birmingham Hip Resurfacing (BHR) was created based on the geometry and material properties of a 45 year-old female donor hip. Hip joint and muscle loads were applied. Bone remodelling stimuli was determined using changes in strain energy. A range of implant orientations were compared to study the affect on bone remodelling. A retrospective radiological analysis was undertaken on 100 hips with a minimum of 5 years follow up. Femoral neck diameter was measured at post-op, 2 and 5 years, as well as neck and stem shaft angles.

FEA showed that valgus orientation was associated with increased resorption underneath the shell. Varus orientation showed increased bone formation at the stem tip. The radiological analysis identified 2 distinct patterns of neck thinning. Slow thinners (76%) had < 5% reduction in neck diameter at 2 years and < 10% at 5 years. Rapid thinner (24%) had > 5% thinning at 2 years and > 10% at 5 years. The mean percentage reduction in neck diameter was significantly different between the two groups at the two time points (p< 0.01). The rapid group had a higher proportion of valgus aligned implants (88%) and a significant decrease in reconstructed offset (p=0.0023).

The FEA results have shown that stem alignment can affect bone resorption resurfacing. FEA results were consistent with the radiological findings. Additional retrieval studies are necessary to help understand aetiology of implant failures.

Adverse bone remodeling in the proximal femur may be detrimental to the long term survival of resurfacing prosthesis. Bone resorption beneath the femoral shell and thinning of the femoral neck have been observed. We present a radiological analysis of the incidence, rate, site of neck thinning and changes observed within the femoral neck, in 100 cases, with a minimum of five years follow-up.

Femoral neck diameter was measured at zero, two and five years post-operatively, at the head neck junction and five mm distally. Pre and post-operative head to neck ratios, natural and reconstructed offset, femoral neck-shaft and stem-shaft angles and cup inclination angle were measured.

Two distinct patterns of neck thinning were observed. In 76 cases (slow thinning group), we observed a reduction of < 5% of original neck diameter at two years and < 10 % at five years (mean 1.5%, sd+/− 1.5). In 24 cases (rapid thinning group), a reduction of > 5% of original neck diameter at two years and > 10% at five years (mean 10.4%, sd+/− 4.8) was observed. The difference in the percentage reduction in neck diameter was significantly different between the two groups at both time points (p< 0.01). Larger head-neck ratios were observed in the rapid thinning group, both pre and post operatively (p< 0.01).

The viability of bone underneath the femoral head may be compromised as a consequence of a non-physiological bone loading mechanism. FEA has predicted stress shielding underneath the femoral head and loading of the mini stem. Compromised blood supply of the retained epiphyseal remnant may play a part in femoral head resorption.

Femoral neck thinning is a phenomenon of unproven aetiology which affects almost 25% of our resurfacing cases.

Introduction: Sectioned femoral components retrieved from failed hip resurfacing arthroplasties show resorption of proximal femoral bone or formation of a fibrous membrane at the bone cement interface, in a proportion of cases. We hypothesize that both scenarios create a functional discontinuity zone (FDZ), which exacerbates offloading the proximal bone and promoting resorption. Our study uses finite element modeling to examine the effects of the presence of an FDZ on bone remodeling following hip resurfacing arthroplasty. A radiographic analysis of the proximal femur following hip resurfacing was also conducted in order to draw a comparison to clinical findings.

Methods: The hip resurfacing FE models were oriented in 3 distinct stem-shaft angles: 136 ‘neutral’, 120 ‘varus’ and 150 ‘valgus’. A low-modulus (2 MPa) FDZ (approx. 2 mm thick) was simulated beneath the implant head. Femoral joint and muscle loads were applied to simulate peak joint loading during gait. Interface stress was compared for the normal and simulated FDZ resurfaced femurs. Bone remodeling stimuli was determined using changes in strain energy. A retrospective radiological analysis was undertaken on 98 hips (74 males and 24 females) with a minimum of 5 years follow up. Measurements of the prosthesis-shaft angle, pre–and post-operative femoral head offset and femoral neck diameter at 2 and 5 years were undertaken.

Results: The presence of the simulated FDZ in the FE analysis resulted in increased proximal-medial bone resorption and slightly greater bone formation surrounding the stem. Correspondingly, device-bone interface stresses were found to decrease proximally under the loading platform and increase at the stem, particularly adjacent to the stem-head junction. The valgus BHR femur led to increased resorption, especially around the periphery of the neck and on the medial side. The radiological analysis identified 2 groups; 22 hips (Group 1) had a mean 5.61mm (sd 2.07) reduction in neck diameter over 5 years and 76 hips (Group 2) demonstrated slow reduction in neck diameter, mean 1.13mm (sd 0.97). Neck thinning at 2 and 5 years was significantly greater for Group 1 (p< 0.0001). Group 1 hips had significantly greater reduction in femoral offset (p=0.041), with greater valgus angle oriented components (p=0.09). Reduction in femoral offset was significantly associated with greater valgus orientations (p< 0.0001). The Group 1 revision rate was 36.4% compared to 2.6% in Group 2 (p< 0.0001).

Discussion: The FE results support the hypothesis that the presence of a FDZ decreases load transfer to the proximal bone, resulting in increased medial stress shielding and resorption. These results are consistent with the Group 1 clinical findings. In order to better understand the cause of implant failures in hip resurfacing arthroplasty, additional retrieval studies are necessary.

Aim: The aim of this study was to determine whether increasing obesity has an influence on the age at which joint replacements are undertaken at our centre.

Materials and Methods: The database was analyzed for age, oxford score and body mass index (BMI) at the time of surgery.

The patients were divided into 5 groups based on their BMI, BMI< 25(normal), 25–29.9(overweight), 30–34.9(obese), 35–39.9(moderately obese), 40 or more(morbidly obese).

BMI < 25 was treated as a control group for comparison.

Statistical analysis was done using t test.

Results: In total, 1369 patients were analyzed, 1025 with hip replacement and 344 with knee replacement The difference in mean oxford score at surgery was not statistically significant between the groups (p> .05). For those undergoing hip replacement, the mean age of morbidly obese was 10 years less as compared to those with BMI < 25. For those with knee replacement, the same difference was 13 years. The age at surgery fell as the BMI > 35 for both hip and knee replacement (p< . 05). This association was found to be stronger for patients with knee replacement than with hip replacement.

Conclusion: This study shows that there is a positive association between obesity and the age at which hip and replacements are required. Obese people with BMI > 35 are likely to require joint replacement at an earlier age as compared to people with BMI < 25. The age at which joint replacement in required falls as the BMI increases over 35. This association is strong for patients requiring total knee replacement, and moderate for patients with hip replacement.

The potential for bone remodeling in the proximal femur may be detrimental to the long term survival of resurfacing prosthesis.

A retrospective analysis of radiological changes in the femoral neck was undertaken for 96 patients (100 hips, 76 males and 24 females), with a minimum of 5 years following hip resurfacing. The mean age at surgery was 53.8 years. Femoral neck diameter was measured post-operatively, at 2 and 5 years. Pre and post-operative head to neck ratios, femoral head-shaft offset, femoral neck and implant stem-shaft angles were also measured.

Two groups of patients were identified with differing rates of reduction in their femoral neck diameter. Over the first 2 years, Group A (24%) mean reduction was 2.02mm/year while Group B (76%) mean reduction was 0.33 mm/year. At 5 years, the Group A mean reduction was 5.64mm (sd±2.03mm) while Group B reduction was 1.16mm, (sd±0.97mm). The difference was significant at both time points (p< 0.01). Larger head-neck ratios were observed in the group A, both pre and post operatively (p< 0.01).

Finite Element Analysis has predicted stress shielding underneath the femoral head and loading of the mini stem. This may explain bone resorption underneath the shell and remodeling around the mini stem. Compromised blood supply of the retained epiphyseal remnant may also play a part in femoral head resorption. Group A with a larger proportion of females and femoral heads will potentially have a larger proportion of epiphyseal remnant retained. A further mechanism that could be influential in the development of neck thinning and bone resorption may be due to fluid pumping mechanism causing osteolytic erosion at the bone cement interface.

In conclusion, femoral neck thinning is a phenomenon of unproven aetiology which is affecting almost 25% of our resurfacing cases. Further investigations are needed to determine its aetiology and remedy.

INTRODUCTION: The American Knee Society score (AKSS) and the Oxford Knee score (OKS) are widely used health outcome measures for total knee replacements. The AKSS is a surgeon-assessed, variable weighted knee score. The OKS is a patient assessed equally weighted score. Our aim was to evaluate whether patient self assessment is a viable alternative to clinical review and whether it can provide enough information to identify which patient would require a clinic visit.

As there had been no previous studies correlating the two scoring systems, we investigated whether a correlation exists between the two scores at 2, 5 and 10 year periods. A correlation would allow us to determine what OKS value would achieve 90% sensitivity in identifying patients requiring clinical review at the above time points. This strategy would reduce the number of clinical visits required and its associated cost.

METHODS: We reviewed the data gathered prospectively from January 2000 to April 2006. All patients were part of an ongoing multi-surgeon single institution Knee Arthroplasty Outcome Programme. Preoperative, 2, 5 and 10 year post-operative OKS and AKSS were gathered from different cohorts. This method of comparison has been validated by previous publications. The scores were then analyzed using the Pearson correlation and linear regression. Different OKS values were analyzed for sensitivity and specificity.

RESULTS: 175 patients completed both the OKS and AKSS questionnaires preoperatively. 312 completed both scores at 2 years; 124 at 5 years and 57 patients at 10 years. The mean OKS, and the two AKSS components, the Knee score and Functional score improved significantly 2 years postoperatively when compared to their preoperative values. The Functional score deteriorated significantly from 5 to 10 years (p< 0.0001). There was good correlation between the OKS and the Knee score and Functional score at 2 years and a moderate correlation at 5 to 10 years. OKS > 24 showed more than 90 % sensitivity in identifying poor Knee scores in the 2, 5 and 10 year periods.

CONCLUSION: In this study, the good correlation of OKS and AKSS at 2-years suggests that postal Oxford questionnaire is sufficient in following up patients in the short term after total knee replacement. However, the moderate correlation at 5 and 10 years suggests that clinical evaluation is necessary.

We recommend that at 2 years, all patients complete an OKS questionnaire and if this is above 24, a clinical evaluation maybe required. Using this OKS value as a screening technique would allow a reduction of up to 50% in clinic visits and outpatient costs at the 2 year follow-up. This reduction is not as great at the 5 and 10 year periods. At these time periods, we recommend a clinical follow-up.

Aim: Our aim was to determine the in-hospital costs of total hip replacement (THR) and total knee replacement (TKR), and compare them to their reimbursement under the national tariff system and to our North American colleagues.

Methods: In 2004 an elective orthopaedic centre was set up in South West London which performs mainly primary lower limb arthroplasty. We used a retrospective analysis of financial statements from September 2004- December 2005 inclusive to establish operative costs (including implant), perioperative costs and post operative costs until discharge.

Results: A consecutive series of 1538 primary TKR patients (mean age = 72.2) and 1118 primary THR patients (mean age = 70.8) was studied from September 2004 to December 2005 accounting for 88% of the workload. Average post operative stay was 6.5 days for TKRs and 5.7 for THRs and 66% of the patients were ASA grade III or over. The cost including implant of a THR was £6054, and for a TKR it was £6499. After adjustment to allow direct comparison to tariff, our THR cost is 2.3% less than and 1.0% more than the 2004/5 and 2005/6 tariffs respectively. Our adjusted TKR cost is 5.0 % and 4.2% less than the 2004/5 and 2005/6 tariffs respectively. Our cemented and uncemented THR costs are 8.0% less than and 6.6% more than their respective tariffs introduced for the first time in 2005/6. Overall there is no large discrepancy between our THR/TKR costs and tariff reimbursements.

Discussion: Although in our unit our costs are similar to the re-imbursements used in the UK, we question the ability of general NHS hospitals in the UK to perform at these levels and prices for three reasons. Firstly, our high volume of joint replacement activity has enabled us to negotiate the most favourable implant prices in the UK. Secondly, length of stay in our unit is approximately 60% of national average. Thirdly, our unit is run without many of the infrastructure costs of a general hospital as well as the cost incurred by training junior staff and research and development. Costs were also found to be favourable compared with our American colleagues and similar to our Canadian colleagues.

Conclusion: Our elective only orthopaedic centre provides a cost effect way of performing primary arthroplasty surgery while maintaining high standards of care and twenty-four hour intensive care cover. We believe this cost effectiveness may be unachievable in general NHS hospitals in the UK.

Computer navigation assistance in total knee arthroplasty (TKA) results in more consistently accurate postoperative alignment of the knee prostheses. However the medium and long term clinical outcomes of computer-navigated TKA are not widely published. Our aim was to compare patient perceived outcomes between computer navigation assisted and conventional TKA using the Oxford knee score (OKS).

We retrospectively collected data on 441 primary TKA carried out by a single surgeon in a dedicated arthroplasty centre over a period of four years. These were divided according to use of computer navigation (group A) or standard instrumentation (group B). There were no statistical differences in baseline Oxford knee score (OKS) and demographic data between the groups. 238 of these had at least a one-year follow-up with 109 in group A and 129 in group B. Two year follow-up data was available for 105 knees with 48 in group A and 57 in group B and a three year follow-up for 45 with 21 and 24 in groups A and B respectively. 12 patients had completed four year follow-up with seven and five knees in groups A and B respectively.

The mean OKS at 1-year follow up was 24.98 (range 12– 54, SD 9.34) for group A and 26.54 (range 12– 51, SD 10.18) for group B (p = 0.25). Similarly at 2-years the mean OKS was 25.40 (range 12– 53, SD 9.51) for group A and 25.56 (range 12– 46, SD 9.67) for group B (p = 0.94). The results were similar for three and four-year follow ups with p values not significant. This study thus revealed that computer assisted TKA does not appear to result in better patient satisfaction when compared to standard instrumentation at midterm follow up.

It is known from long term analysis of conventional TKA that mal-aligned implants have significantly higher failure rates beyond eight to ten years. As use of computer navigation assistance results in a less number of mal-aligned knee prostheses, we believe that these knees will have improved survivorship. The differences in OKS between the two groups should therefore be evident after eight to ten years.

Introduction: Obesity [Body Mass Index (BMI) > 30] is seen in a growing percentage of patients seeking joint replacement surgery. Recent studies have shown no clear influence of obesity on the five-year, clinical outcome of total knee replacement; except for the morbidly obese (BMI > 40). Computer navigation has shown improved consistency of prosthetic component alignment. However, this aid does significantly increase operation time.

Aims:

To compare tourniquet times of standard and computer assisted total knee arthroplasty in patients with BMI more than 30

Methods and Results: A retrospective analysis of 82, obese, total knee replacements performed by a single surgeon, at a dedicated arthroplasty centre, was undertaken. Conventional knee replacement instrumentation (Plus Orthopaedics, UK) was used in 42 cases and computer assisted navigation (Galileo- Plus Orthopaedics) in 39 cases. The patients were divided into three equal sized groups (1, 2 & 3), in chronological order. Each group comprised fourteen knees undertaken using standard surgical technique and thirteen knees using computer assisted navigation.

Group1 had average tourniquet times of 95.69 and 111.67 minutes in the standard and computer assisted groups respectively (p 0.01). Group 2 tourniquet times were 80.75 and 92.33 minutes (p 0.05). Group 3 tourniquet times were 84.5 and 87.5 minutes; these were not significantly different.

Conclusions: As the surgeon acquired experience of computer assisted navigation, his tourniquet times decreased and by the end of our study period, there was no longer any difference between the tourniquet times for conventional and computer assisted knee replacement in this subgroup of obese patients. We hypothesise that in obese patients, computer assisted navigation helps the surgeon to overcome jig alignment uncertainty and thus improves accuracy of component alignment without any significant time penalty.

There has been renewed interest in metal-on-metal bearings as hip resurfacing components for treatment in young, active patients. This study examines the effects of fixation (cemented or uncemented heads) and bone-implant interface conditions (stem-bone and head-bone) on the biomechanics of the Birmingham hip resurfacing (BHR) arthroplasty, using high resolution, 3-d computational models of the bilateral pelvis from a 45-year-old donor. Femoral bone stress and strain in the natural and BHR hips were compared. Bone remodelling stimuli were also determined for the BHR hips using changes in strain energy. Proximal femoral bone stress and strain were non-physiological when the BHR femoral component was fixed to bone. The reduction of strain energy within the femoral head was of sufficient magnitude to invoke early bone resorption. Less reduction of stress was demonstrated when the BHR femoral component was completely debonded from bone. Bone apposition around the distal stem was predicted based on the stress and strain transfer through the stem. Femoral stress or strain patterns were not affected by the type of fixation medium used (cemented vs. Uncemented). Analysis of proximal stress and strain shielding in the BHR arthroplasty provides a plausible mechanism for overall structural weakening due to loss of bony support. It is postulated that the proximal bone resorption and distal bone formation may progress to neck thinning as increasing stress and strain transfer occurs through the stem. This may be further exacerbated by additional proximal bone loss through avascular necrosis. Medium term retrieval specimens have shown bone remodelling that is consistent with our results. It is unclear if the clinical consequences of neck thinning will become more evident in longer-term follow-ups of the BHR.

One potential limitation with uncemented, hemispherical metal-backed acetabular components is stress shielding of bony structures due to the mismatch in elastic modulus between the metal backing and the peri-prosthetic bone. A proposed substitute is a horseshoe-shaped acetabular component, which replicates the bony anatomy. One such device, the Cambridge cup, has shown successful clinical and radiological outcomes at five years follow-up (Brooks 2004, Field 2005). We conducted a study of the Cambridge cup from a biomechanical perspective, using validated, high-resolution computational models of the bilateral hip. Peri-prosthetic stress and strain fields associated with the Cambridge cup were compared to those for the natural hip and a reconstructed hip with a conventional metal-backed hemispherical cup during peak gait loading. We found that the hemispherical cup caused an unphysiologic distribution of bone stresses in the superior roof and unphysiologic strain transfer around the acetabular fossa. These stress distributions are consistent with bone remodelling. In contrast, the peri-acetabular stresses and strains produced by the Cambridge cup differed from the natural hip but were more physiologic than the conventional hemispherical design. With the Cambridge cup, stresses in the superior acetabular roof, directly underneath the central bearing region, were greater than with the conventional design. Despite the thin bearing, the peak liner stresses in the Cambridge cup (max. tensile stress: 1.2 MPa; yield stress: 4.5 MPa) were much lower than the reported material strengths. Fossa loading by the hemispherical cup has been suggested as a possible mechanism for decreased implant stability (Widmer 2002). Conversely, the Cambridge cup produced semi-lunar peri-prosthetic stress fields, consistent with contact regions measured in natural hips (Widmer 2002). These analyses provide a better understanding of the biomechanics of the reconstructed acetabulum and suggest that a change in component geometry may promote long-term fixation in the pelvis.

Introduction: Measurement of outcome after THR is becoming increasingly important. NICE guidelines have been established and ODEP have stipulated target criteria for the successful evaluation of novel implants. To date, a streamlined, efficient Outcome Programme has not been developed which satisfies the required follow-up criteria. A Programme has been developed at our unit and its evolution is reported.

Methods: A database was created with the assistance of a database developer and an “Outcome Co-ordinator” was appointed to operate the database and manage the programme.

Operation data is now entered onto the database by the surgeon or co-ordinator at the time of surgery. Thereafter, the database automatically produces annual Oxford Hip Questionnaires, EQ-5D questionnaires and invite letters to patients for clinical review at stipulated time-points.

Questionnaires are returned by patients and scanned. This data is then electronically imported to the database without transcription error. Patients attend special Outcome clinics, staffed by Research Fellows and SpR’s, who examine the relevant hip and review their radiographs. The findings are recorded and the paper forms scanned and imported into the database. Non-responders are identified from the database and are chased up via telephone by the coordinator.

Data is extracted from the database with queries and presented using database reports.

Results: 2455 THR’s have been recorded on the database (2127 primaries, 328 revisions) 1937 patients continue under active review for THR. The percentage of patients lost to follow-up is only 2%, 10%, 15% at 2, 5 and 10 years respectively.

Discussion: An efficient system has been developed to maximise the follow-up of patients post THR. The burden on outpatient clinics is reduced and meaningful outcome measures are obtained. The programme could easily be extended to other centres throughout the UK and the benchmarks set by ODEP and NICE can also be attained.

Introduction: The Cambridge Acetabular cup is a unique, uncemented prosthesis that has been designed to transmit load to the supporting bone using a flexible material, carbon fibre reinforced polybutyleneterephthalate (CFRPBT). This should significantly reduce bone loss and provide long term stability. The cup consists of a ultra high molecular weight polyethylene liner within a carbon fibre composite backing that was tested with either a plasma sprayed HA coating or with the coating removed. The cup is a horseshoe shaped insert of similar thickness to the cartilage layer and transmits force only to the regions of the acetabulum originally covered with cartilage. The purpose of this study was to evaluate the response of bone and surrounding tissues to the presence of the cup in retrieved human specimens.

Methods: We examined 12 cementless Cambridge acetabular implants that were retrieved at autopsy between 2 and 84 months following surgery. Nine of the implants were coated with HA and three were uncoated. The implant and the surrounding bone were fixed, dehydrated and embedded in polymethylmethacrylate. Sections were cut parallel to the opening of the cup and in two different planes diagonally through the cup. The sections were surface stained with toluidine blue and examined by light microscopy. Image analysis was used to measure the percentage of bone apposition to the implant, the area of bone and fibrous tissue around the implant and the thickness of hydroxyapatite coating.

Results: All 9 HA coated implants showed good bone contact with a mean bone apposition and standard deviation of 50.9% +/− 17.5%. The thickness of the HA coating decreased with time and where this was occurring bone remodelling was seen adjacent to the HA surface. However, even in specimens where the HA coating had been removed completely good bone apposition to the CFRPBT remained. Bone marrow was seen apposed to the implant surface where HA and bone had both been resorbed with little or no fibrous tissue. The uncoated implants showed significantly less bone apposition than the HA coated specimens, mean 11.4% +/− 9.9%(p < 0.01) and significant amounts of fibrous tissue at the interface.

Discussion: The results of this study indicate that the anatomic design of the Cambridge Cup with a flexible CFRPBT backing and HA coating encourages good bone apposition. In the absence of HA the results are generally poor with less bone apposition and often a fibrous membrane at the implant surface. There was a decrease in HA thickness with time in situ and cell mediated bone remodelling seems to be the most likely explanation of the HA loss. However, good bone apposition was seen to the CFRPBT surface even after complete HA resorption in contrast to the uncoated specimens. Though the mean bone apposition percentage to the HA coated implants declined with time, the bone was replaced by marrow apposed to the implant surface. This is in contrast to the uncoated implants where fibrous tissue becomes apposed to the implant surface. We believe this is due to micro-motion occurring at the bone implant interface. The HA coating appears necessary to provide good initial bone bonding to the implant surface that is maintained even after complete loss of HA.

Aims: To compare the femoral stem position and alignment, using different methods of insertion. The Exeter stem has been compared with a new tri-tapered, polished, cannulated, cemented, femoral component.

Method: We have reviewed 100 post operative AP and 50 lateral radiographs for each group. Analysis determined both stem tip position and stem alignment. The groups of subjects were of comparable age, sex and Body Mass Index.

Results: Values for mean distance from canal centre were calculated, for the Exeter group this was 1.511 ± 1.226 and Tri-Taper group 0.778 ±. 0.748. This was statistically signiþcant (p=0.0059). In our Exeter series of results we have shown that 71% of stem tips had been inserted within 2mm of central, this compares with 94% in the Tri-Taper series. On the lateral radiographs of the Exeter series the mean posterior distance was 2.245 ± 1.316, the mean anterior distance was 1.068 ± 0.528. In the Tri-Taper series the mean posterior distance was 1.123 ± 0.926, the mean anterior distance was 1.057 ± 0.590. The difference between the two groups was not statistically signiþcant (p=0.054). The alignment results show that only 78% of stems are aligned neutrally compared with 91% of tri-taper stems (p= 0.0454).

Conclusion: These results are comparable with previous cannulated and Exeter stem studies. This conþrms that optimal distal stem position and stem alignment can be achieved by using a cannulated stem rather than the application of a distal centralising device.

We report a three year Medical Devices Agency and Local Ethical Committee approved prospective study for a new tri-tapered polished cannulated cemented femoral component. Our stem was implanted in 53 primary total hip replacements. Eleven male patients (11 hips) and 39 female patients (39 hips). The mean age at surgery was 73 (range 65 to 84). The mean weight was 71.76 kg (range 49.3 kg to 94.6 kg) with a mean BMI of 28 (range 20.20 to 40.26). All patients had a pre operative diagnosis of osteoarthritis. All the hips were implanted via the anterolateral approach. Twenty-six (51%) hips were implanted by a single consultant and 24 (49%) were implanted by six different registrars. Pre-operative and sequential post-operative clinical and radiological evaluations were undertaken.

The mean pre-operative Oxford hip score was 47 points.which declined 19 points at three years. Radiological analysis, using the Johnston criteria, did not reveal any untoward features. Prosthetic stem migration was measured using a technique developed in our unit and validated as accurate to 0.61 mm; as previously reported. Stem migration measured averaged 1.38 mm (n=52; sd ±1.38) 6 months post implantation. This progressed to 1.71 mm (n=50; SD=1.18) at one year; 1.61mm (n=48; sd ±1.17) at 2 years. and 1.55 mm (n=28; SD 1.13). At 3 years average stem migration for hips implanted by the registrar group and the consultant group was not sig-nificantly different (p=0.2048) and the migration curve, against time was similar for both groups.

Our study has demonstrated initial component migration, comparable to that of other polished tapered cemented stem designs. The improvement in Oxford hip score parallels other reported series and no adverse radiological signs have been observed. Long-term surveillance of our cohort will provide further data to compare the new design with substantial equivalents. More sophisticated studies, such as RSA analysis would provide further data on early femoral component migration.

Aim: Evaluate a novel horseshoe shaped cup designed by the senior authors to minimise the resection of healthy bone in total hip arthroplasty.

Method: Fifty female patients with a displaced, subcapital, femoral neck fractures were chosen for the study. In half of the group of patients, the composite support shell was coated with HA, with the other half remaining uncoated. Clinical and radiological assessments were undertaken regularly for 5 years.

Results: To date 20 patients have died and 13 have withdrawn from the study due to poor medical health unrelated to the study. Charnley modified Merle d’Aubigne score at 5 years was as good as the preoperative score with 80% of patients having full range of movement, no pain and walking unaided.

Radiographic results showed no evidence of loosening of HA coated cups, in contrast to non HA coated cups which migrated significantly in 80% of cases. Four patients with loose non HA coated cups underwent revision surgery.

Conclusion: It replaces the cartilage and underlying sub-chondral bone of the acetabulum socket with a cup that is designed to flex in harmony with the surrounding bony structure. This trial has demonstrated success at 5 years with the HA coated Cambridge Acetabular Cup. Cups from which HA coating has been removed have migrated significantly in 80% of cases. There is an advantage of the HA fixation which will be taken into account before wider clinical usage is advocated.

Hip resurfacing is widely recognised as a bone conserving procedure with respect to proximal femoral resection. However, it has been argued that this is not the case for the acetabulum due to the thickness of the acetabular component and the large diameter bearing surfaces. We have investigated whether the Birmingham Hip is a bone conserving procedure with respect to the acetabular bone stock.

Data was obtained from 257 consecutive Midland Medical Technology (MMT) surface replacements and 458 primary hybrid total hip replacements implanted under our care. The surface replacement group comprised 185 males (185 hips) and 72 females (72 hips) with a mean age at surgery of 55 years. The hybrid primary total hip replacement group comprised 207 males (207) and 251 females (251 hips). The mean age at surgery was 65 years old. In the surface replacement group the mean uncemented acetabular size implanted was 54.88 mm (females = 51.9 mm; males = 57.8 mm). In the hybrid primary total hip replacement group the mean uncemented acetabular size of 55.04 mm (females =52.9 mm; males = 57.2 mm).

Statistical analysis was undertaken to compare the uncemented acetabular sizes in the surface replacement group with the uncemented acetabular sizes implanted in the primary hybrid total hip replacement group. We report no significant difference in the size of acetabular component used for the two groups (p = 0.4629; 95% C.I. −0.28 to 0.61). The effect of gender was analysed and the mean size of uncemented acetabular component implanted in males for the surface replacement group was not significantly different (p = 0.06) to the hybrid primary total hip replacement group. However the mean size of uncemented acetabular component in females for the surface replacement group was significantly smaller (p = 0.016) compared to the primary total hip replacement group.

We conclude hip resurfacing is not bone sacrificing on the acetabular bone stock and can be bone conserving for females.

The novel horseshoe shaped cup was designed by the senior authors to minimise the resection of healthy bone in total hip arthroplasty. It replaces the cartilage and underlying sub-chondral bone of the acetabulum socket with a cup that is designed to flex in harmony with the surrounding bony structure.

Fifty female patients with a displaced, subcapital, femoral neck fractures were chosen for the study. In half of the group of patients, the composite support shell was coated with HA, with the other half remaining uncoated. Clinical and radiological assessments were undertaken regularly for five years.

To date 20 patients have died and 13 have withdrawn from the study due to poor medical health unrelated to the study. Charnley modified Merle d’Aubigne score at five years was as good as the preoperative score with 80% of patients having full range of movement, no pain and walking unaided.

Radiographic results showed no evidence of loosening of HA coated cups, in contrast to non HA coated cups which migrated significantly in 80% of cases. Four patients with loose non HA coated cups underwent revision surgery.

This trial has demonstrated success at 5 years with the HA coated Cambridge Acetabular Cup. Cups from which HA coating has been removed have migrated significantly in 80% of cases. There is an advantage of the HA fixation which will be taken into account before wider clinical usage is advocated.