Introduction: Although the primary aim of Total Knee Replacement (TKR) is to relieve chronic joint pain, 10–20% of patients experience unexplained chronic pain after surgery. One possible cause of this pain is central sensitisation. Prolonged exposure to a noxious input can lead the central nervous system to become sensitised to pain (central sensitisation), which can become self-sustaining and persist after the removal of the noxious stimuli i.e after TKR. The aim of this study was to determine if knee osteoarthritis (OA) patients awaiting TKR have evidence of sensory perception abnormalities, by comparing detection and pain thresholds from OA patients to those of age- and gender-matched healthy participants.

Patients and Methods: Quantitative Sensory Testing (QST) was performed on 107 knee OA patients on the waiting list for primary TKR and 50 age- and gender-matched healthy participants without knee pain or TKR. QST assesses somatosensory function through measuring participant responses to external stimuli of controlled intensity. QST was performed on both knees and the pain-free forearm of all participants. Von Frey filaments were used to measure touch detection thresholds, a digital Algometer to measure pressure pain thresholds, and the MSA Thermotest to measure detection and pain thresholds to hot and cold. Significant differences in the median threshold values between knee OA patients and healthy participants were tested for using Mann-Whitney U tests.

Results: Detection thresholds: OA patients had significantly higher detection thresholds for hot and cold (both p< 0.05) in the index knee (but not at other sites) compared to healthy participants. Touch detection thresholds were significantly higher at all body sites in OA patients compared to healthy participants (all p< 0.001).

Pain thresholds: Pressure pain thresholds were significantly lower in OA patients at all body sites (all p< 0.001) but there were no significant differences in hot or cold pain thresholds between OA patients and healthy participants at any body site (all p> 0.05).

Discussion: This study showed that knee OA patients have modality-specific sensory and pain perception abnormalities. These included thermal hypoesthesia (reduced sensitivity) in the index knee and tactile hypoesthesia at all body sites tested, alongside hyperalgesia (increased pain sensitivity) to pressure pain at all body sites. Future research aims to determine if these sensory perception abnormalities are predictive of chronic pain after TKR.

Introduction: Patient satisfaction with the outcome of elective surgery is increasingly used as a measure of the patient’s perception of the success of an operation. Satisfaction is an individualistic complex of factors and measuring satisfaction can add another valuable dimension to outcomes assessment after arthroplasty. The aim of this study was to explore patient satisfaction after lower limb arthroplasty.

Patients and Methods: All patients who had a primary joint replacement at the Avon Orthopaedic Centre over a 3-year period were invited to participate in the study. Participants completed a questionnaire which consisted of the WOMAC, the Joint-Related Quality of Life Scale from the KOOS/HOOS, SF-12 and a validated satisfaction scale. The satisfaction questionnaire measures patient satisfaction with four domains of outcome: overall outcome, pain relief, ability to perform ADLs and ability to participate in leisure activites. Responses are on a 4-point Likert scale which ranges from very satisfied to very dissatisfied. A global satisfaction score was calculated from these responses and then transformed onto a 0–100 scale (100 being best).

Results: Completed questionnaires were received from 2085/3125 patients (67% response rate). 911 respondents had a THR, 866 had a TKR, 157 had a hip resurfacing, 100 had a UKR and 51 had a patellar resurfacing. The mean age of respondents was 70 years and 58% were female. The mean length of follow-up was 28 months.

The median satisfaction score was 100 (interquartile range 75–100). However, within the individual outcome domains dissatisfaction rates were: 9% for pain; 12% for overall outcome; 14% for ADLs; and 17% for leisure activities. To explore differences in satisfaction with age, patients were divided into 3 age groups: < 60 years, 60–80 years and > 80 years. The respective rates of dissatisfaction among the age groups were 13%, 11% and 14%, which were not significantly different (p=0.33). In an analysis of gender and satisfaction, significantly more females were dissatisfied than men (14% vs 10%, p=0.01). When pain, function, quality of life, mental health and physical health were compared between patients who were satisfied (n=1834) and dissatisfied (n=251) with their overall outcome, all outcomes were significantly worse in the dis-satisfied patient group (p< 0.001 for all outcomes).

Discussion: Although the median satisfaction score in this study was 100, there was a group of patients who were not satisfied with their outcome. As well as having worse joint pain and function, dissatisfied patients also have significantly worse quality of life, physical health and mental health compared to satisfied patients. In conclusion, patient satisfaction is one of the key outcomes that should be strived for after an elective intervention, and these results indicate that joint replacement is failing to fully satisfy a proportion of patients.

Introduction: Joint replacement has a low mortality rate, few adverse occurrences, excellent survivorship and is considered a cost-effective intervention to reduce disability in the community. However, the assessment of complications and survivorship fail to measure the success of joint replacement in achieving pain relief and restoration of functional ability. The aim of this large cross-sectional postal survey was to provide information on the prevalence of pain, disability, poor quality of life and patient dissatisfaction at 1–3 years after a range of lower limb orthopaedic surgeries in the UK.

Patient and Methods: A questionnaire was posted to all 3,125 consecutive alive patients who underwent a primary THR, hip resurfacing, TKR, UKR or patellar resurfacing at the Avon Orthopaedic Centre between January 2004 – April 2006. The questionnaire included the WOMAC, HOOS/KOOS quality of life scale and a validated satisfaction scale. All questionnaires are scored on a 0–100 scale (worst-best) and a poor outcome was defined as a score of ≤ 50 on the outcome measure.

Results: Completed questionnaires were received from 2,085 patients (response rate of 67%). Patients had a mean age of 67 years and 42% were male. The mean length of follow-up was 28 months (range 14–44 months). 911 patients had a THR, 157 patients had a hip resurfacing, 866 patients had a TKR, 100 patients had a UKR and 51 patients had a patellar resurfacing.

Pain: the prevalence of poor outcomes were 6% of patients with a THR, 4% with a hip resurfacing, 12% with a TKR, 9% with a UKR and 31% with a patellar resurfacing.

Conclusion: This survey has provided descriptive data on the prevalence of patient-reported levels of pain, disability, poor joint-related quality of life and dissatisfaction after lower limb arthroplasty. It is important that patient-reported outcomes after joint replacement are rigorously assessed in order to provide information on which patients do poorly after surgery, with the aim of targeting these patients with an intervention to improve their outcome.

North Bristol Trust Small Grants Scheme provided funding for the consumables for this study.

Background: Because of the changing demographics of the population and improvements in prosthesis design and surgical technique, ever-increasing numbers of younger patients are undergoing joint replacement. Younger patients often receive hip resurfacing rather than conventional THR because of the preservation of bone stock and the lower risk of dislocation. However, pain relief and restoration of function for younger patients is particularly important to continue with a normal, active life. Yet there is little existing research to establish if hip resurfacing results in better patient-reported outcomes than conventional total hip replacement (THR). Therefore, the aim of this study was to compare patient-reported outcomes after hip resurfacing and THR, after controlling for age, gender, general health and length of follow-up.

Methods: A postal survey was sent to all patients who had a hip resurfacing or primary THR between April 2004 - April 2006 at the Avon Orthopaedic Centre. To assess hip pain and function, quality of life, general health and satisfaction with the outcome of surgery, the questionnaire included the WOMAC, HOOS Quality of Life Scale, SF-12 and a validated satisfaction scale. The continuous outcome scores were compared for those who had a THR and those who had hip resurfacing, after adjusting for age, sex, general health and length of follow-up, using Analysis of Variance.

Results: Completed questionnaires were received from 911 THR patients and 157 hip resurfacing patients (response rate of 68% and 71%). Hip resurfacing patients had a mean age of 52 years and 71% were male. THR patients had a mean age of 68 years and 37% were male. After controlling for the effects of age, gender, general health and follow-up length, there was no significant difference in pain (p=0.70), function (0.85), hip-related quality of life (p=0.66) or satisfaction (0.09) between hip resurfacing patients and THR patients at 1–3 years post-operative.

Conclusions: The findings from this study suggest that hip resurfacing has no short-term clinical advantage over conventional THR. A prospective randomised controlled trial is necessary to further compare patient outcomes after hip resurfacing and THR.

Introduction: The long-term results of 70 Harris-Galante I uncemented acetabular components implanted in 53 patients who were under 50 years of age at the time of their hip arthroplasty are presented.

Methods: Follow up was both clinical, using Oxford and Harris Hip scores, and radiological. Kaplan-Meier survivorship analysis was performed to calculate the survivorship of the acetabular components. Failure was defined as either liner exchange or acetabular component revision due to aseptic loosening, osteolysis, infection or dislocation.

Results: The mean age of the patients at the time of surgery was 40 years (range 19–49 years), with follow up of between 12 and 16 (mean 13.6) years. All patients’ acetabular components were implanted primarily with cemented femoral components. The mean Oxford Hip Score at the end of the follow-up period was 20 out of 60 (range 12–46) and Harris Hip Score 81 (range 37–100).

At the end of the follow up period, 11 of the 70 acetabular components (polyethylene liner or the acetabular shell) had been revised. The cumulative survival was 94.0% (95% confidence interval 88.4–99.7) with revision of the metal shell as the end point, and 84.0% (95% confidence interval 74.5–93.5) with revision surgery of the acetabular shell or liner due to any reason as an end point. Radiologically, 4 patients require acetabular revision and 22 patients had femoral osteolysis in gruen zone 7, indicative of polyethylene failure. This gave a combined revision, impending revision and zone 7 osteolysis cumulative survival of 55.3% (95% confidence interval 40.6–70.0).

Discussion: In contrast to cemented acetabular components which undergo aseptic loosening and give groin pain, high density polyethylene lined metal shells do not give groin pain but cause silent acetabular and femoral osteolysis. The danger time for osteolysis is between 10–20 years, therefore follow up at that time is essential.

Introduction: Chronic joint pain is the primary reason for individuals electing to undergo TKR and therefore pain relief is an extremely important outcome after surgery. Although the literature suggests that TKR produces excellent pain relief, the prevalence of chronic pain after TKR is often masked in the reporting of mean pain scores. The aim of this study was to explore the prevalence, impact and onset of pain at 1-year after TKR.

Methods: 243 patients (251 knees) were recruited into a multi-centre randomised controlled trial comparing the outcomes of the Kinemax Plus fixed-bearing and mobile-bearing implant. Patients were assessed pre-operatively and then 3 months, 1-year and 2-years post-operatively. At each assessment time patients completed the WOMAC, KOOS quality of life scale, SF-12, American Knee Society Score, Satisfaction Scale for Joint Replacement Arthroplasty and a clinical examination. As part of the clinical assessment patients were asked to rate the pain in their knee as none, mild, occasionally moderate, continually moderate or severe.

Results: To date, 240 knees have reached their 1-year follow-up. Complete data regarding pain ratings was available for 198 patients. The mean age of patients was 68 years (range 40–81) and 52% were male. At 1-year after TKR, 13% of patients had occasionally moderate pain, 6% had continually moderate pain and 6% of patients had severe pain. In total, 25% patients reported moderate-severe pain at 1-year after TKR. 60% patients with pain at 1-year post-operative also experienced moderate-severe pain at 3 months post-operative. Using a Mann-Whitney U test, patients with moderate-severe pain at 1-year after TKR had significantly worse physical function (p< 0.001), knee-related quality of life (p< 0.001) and mental health scores (p< 0.05) than those patients with no-mild pain.

Conclusion: This study suggests the prevalence of pain after TKR is high, with 25% of patients reporting moderate-severe pain at 1-year after TKR. Pain experienced at 1-year post-operative was most frequently preceded by pain at 3-months post-operative, suggesting that for many patients a pain-free period after surgery is not experienced. The pain present at 1-year after TKR affected several domains of life, including functional ability, quality of life and mental health. Future research will focus on developing a pre-operative screening protocol to identify patients at risk of chronic pain after TKR.

This research was supported by funding from Stryker UK.

Background : A composite femoral stem was introduced with a structural stiffness similar to that of the native femur to promote proximal load transfer. This consisted of a cobalt-chromium alloy core surrounded by an injection-moulded layer of polyaryletherketone covered with a porous titanium mesh.

Material and Methods: 31 consecutive primary total hip replacement stems were implanted in 26 patients with an average age of 37 years (range 17–57) using the Epoch stem (Zimmer, Warsaw, IN) as part of a prospective multi-centre trial. A cementless Harris-Galante I acetabular component with a 28mm polyethylene insert (Zimmer) was used in 29 cases, a Plasmacup with 28mm polyethylene insert (Aesculap, Tuttlingen, Germany) in 1 case and a bipolar head in 1 case. Annual follow-up with Harris Hip Scores and radiographic evaluation was performed for a mean of 10.1 years.

Results : Harris Hip Scores improved from a mean of 52 points preoperatively to 90 at the time of last follow-up. Radiographs showed no stem migration or loosening. 4 cases with polyethylene wear showed trochanteric osteolysis. Specific radiographic features noted were a sclerotic halo in Gruen zones 1 in 8 cases, calcar rounding in 10 cases and improvement in calcar appearance with squaring of the calcar in 4 cases. Calcar resorption was seen in 1 case associated with polyethylene wear. There have been 8 instances of revision of the head or acetabular component- 3 liner exchanges for polyethylene wear, 3 acetabular component revisions for liner dissociation with associated cup damage, 1 acetabular component revision for infection and 1 bipolar head revised to unipolar head with cementless acetabular component for pain. No stem has required or requires revision.

Conclusion : The Epoch stem resulted in an excellent clinical outcome with evidence of radiographic stability and proximal bone preservation, and no cases of stem revision in a cohort of young patients with long-term follow-up.

Bone stock loss is a major challenge to the revision hip surgeon. Impaction grafting is frequently the preferred option for the surgeon when faced with bone stock deficiency. This retrospective study assesses a consecutive series of patients who underwent revision hip replacement with femoral impaction grafting during the period 1994–2001. Radiographic measurement for stem subsidence was carried out by 2 independent observers on pre-operative and post-operative radiographs at 6 months, 1 year, 18 months and 2 years following surgery. Graft incorporation and trabecular remodelling were also subjectively assessed. Irradiated bone allograft was used in all cases.

Sixty-nine hips were reviewed. Radiographic analysis revealed graft incorporation in 38% of cases. However, there was no evidence of trabecular remodelling. Moderate subsidence (5–10 mm) occurred in 10 cases (14.5%), and massive subsidence (> 10 mm) occurred in 5 cases (7.2%). The survivorship with re-revision or need for further surgery as the end point was 92.8% at an average of 28 months.

The results obtained in this study are less favourable than other reported studies of revision of the femoral stem using impaction bone grafting. The absence of the characteristic changes of graft remodelling reported in other series raises concerns that irradiated bone graft may be a significant factor in the post-operative progress.

We compared patient-reported outcomes of the Kinemax fixed- and mobile-bearing total knee replacement in a multi-centre randomised controlled trial. Patients were randomised to the fixed- or the mobile-bearing prosthesis via a sealed envelope method after the bone cuts had been made in the operating theatre. Randomisation was stratified by centre and diagnosis. Patients were assessed pre-operatively and at eight to 12 weeks, one year and two years post-operatively. Validated questionnaires were used which included the Western Ontario MacMasters University, Short-Form 12, Mental Health Index-5, Knee Injury and Osteoarthritis Outcome Score for Knee-Related Quality of Life and Function in Sport and Recreation scales and a validated scale of satisfaction post-operatively. In total, 242 patients (250 knees) with a mean age of 68 years (40 to 80) were recruited from four NHS orthopaedic centres. Of these, 132 patients (54.5%) were women.

No statistically significant differences could be identified in any of the patient-reported outcome scores between patients who received the fixed-bearing or the mobile-bearing knee up to two-years post-operatively.

Cemented, polished, tapered stems have produced excellent results, but some early failures occur in younger patients. The CPS-Plus stem (Plus Orthopedics AG, Switzerland) is a polished double taper with rectangular cross section for improved rotational stability. A unique proximal stem centraliser increases cement pressurisation, assists alignment and creates an even cement mantle.

Radiostereometric analysis has demonstrated linear subsidence in a vertical plane, without any rotation or tilt. These features should improve implant durability. Midterm (5 years) results of a prospective international multicentre study are presented.

Materials and Methods: 222 patients (230 hips) were recruited to this IRB-approved study at three centres in the UK and two in Norway. Clinical and radiographic outcomes were assessed at regular intervals.

Results: 160 hips in 153 patients were available for full clinical and radiographic evaluation. 27 patients have died, 30 patients were unable to attend (outcome known) and 12 patients have not reached 5 years follow-up.

The mean Harris hip score improved from 42 preoperatively to 91. There have been no revisions for aseptic loosening and none of the stems have radiographic evidence of loosening. There has been one revision for deep sepsis. With revision for aseptic loosening as an endpoint, stem survivorship is 100%.

Conclusion: The design of the CPS-Plus stem attempts to address the issues of cement pressurization, rotational stability, and subsidence. Earlier laboratory studies have now been supplemented by this clinical evaluation, performed in a number of different centres by several surgeons, and the midterm results are very encouraging.

Our aim was to determine the pre-operative sporting profiles of patients undergoing primary joint replacement and to establish if they were able to return to sport after surgery. A postal survey was completed by 2085 patients between one and three years after operation. They had undergone one of five operations, namely total hip replacement, hip resurfacing, total knee replacement, unicompartmental knee replacement or patellar resurfacing. In the three years before operation 726 (34.8%) patients were participating in sport, the most common being swimming, walking and golf. A total of 446 (61.4%) had returned to their sporting activities by one to three years after operation and 192 (26.4%) were unable to do so because of their joint replacement, with the most common reason being pain. The largest decline was in high-impact sports including badminton, tennis and dancing. After controlling for the influence of age and gender, there was no significant difference in the rate of return to sport according to the type of operation.

The visco-elastic behaviour of acrylic bone cement is a key feature of cement-implant performance. The ability of the cement to creep in conjunction with a force-closed design of stem (collarless polished taper) affords protection of the vital bone-cement interface. Most surgeons in the UK use antibiotic-laden PMMA in primary total joint arthroplasty. In revision surgery the use of bespoke antibiotic-cement combinations is common.

The aim of this study was to elicit the effect of antibiotics upon the physical properties of bone cement.

Methods: The static properties of the cements were assessed following protocols described in ISO 5833: 2002, while the viscoelastic properties of the cement were measured with in-house developed apparatus in quasi-static conditions. Creep tests were performed in four point bending configuration over a 72 hour period in physiological conditions. Porosity was measured on the mid cross section of the creep samples using a digital image technique.

The cements used were Palacos R40 and Palacos R with gentamicin. The antibiotics added included fucidin, erythromycin, teicoplanin and vancomycin in 500mg powder aliquots up to a maximum of 1g per 40 g mix.

All data were analysed using ANOVA with Bonfer-roni post-hoc test. Pearson’s correlation coefficient was used to investigate the association between physical factors (SPSS).

Results: The static and working properties did not vary significantly with antibiotic additions. The mean creep of the cement increased in line with the amount of antibiotic added. The specific antibiotic was not relevant. The differences were statistically significant. Mean porosity also increased with antibiotic mass. There was a linear relationship between cement porosity and creep!

Conclusions: Despite modern mixing techniques the porosity of bone cement increases with antibiotic additions. This increased porosity is related to the greater creep seen in the cement. Surgeons should apply these findings when planning revision hip surgery.

The visco-elastic behaviour of cement, is a key feature of cement-implant performance in total hip arthroplasty.

The aim of this study was to describe the creep behaviour of the leading plain bone cements under standardised physiological in-vitro conditions.

Methods: Cements were mixed under vacuum conditions as per manufacturers instructions. Moulds were used to to produce beams of standard dimensions. These were stored in saline at 37oC for 21 days to ensure thorough polymerisation. Under the same conditions, the beams were tested for 72 hours in a 12-station quasi-static creep rig, using a four-point bending configuration. The rig applied a constant stress of 8MPa to each beam and the deflection was recorded at 8-minute intervals by a data-logging device. The porosity was measured in the mid-cross section of each beam sample using a digital image technique.

The cements tested were Palacos R, CMW1 and Smartset GHV and Surgical Simplex P.

All data were analysed using ANOVA with Bonfer-roni post-hoc test (SPSS).

Results: Palacos R exhibited the highest mean deflection at 72 hours (0.86+/- 0.21mm) followed by Surgical Simplex P (0.85 +/- 0.18mm), CMW1 (0.72 +/- 0.09mm) and Smartset GHV (0.60 +/- 0.16mm). The difference between the two DePuy cements and Palacos R (p=0.03) and Surgical Simplex P (p=0.04) were statistically sig-nificant. None of the beams failed during the test. The creep behaviour correlated with the cross-sectional porosity measurements.

Conclusions: This study has shown that there are sig-nificant differences in the creep bahaviour of the leading medium and high viscosity bone cements. In particular Palacos R and Surgical Simplex P demonstrate ‘High’ creep and the DePuy cements ‘Low’ creep. Creep appears sensitive to subtle changes in the composition of the material. This may be reflected in the clinical behaviour of different bone cements and stresses the importance of the time-dependent properties of PMMA.

Cobalt chrome-on-cobalt chrome bearing surfaces have been re-introduced despite some concerns regarding potential risks posed by soluble metallic by-products. We have investigated whether there are metal-selective differences between the levels of genetic damage caused to a human cell line when cultured with synovial fluids retrieved from various designs of orthopaedic joint replacement prostheses at the time of revision arthroplasty.

Synovial fluids were retrieved from revision hip and knee arthroplasty patients with bearings made from cobalt chrome-on-cobalt chrome, cobalt chrome-on-polyethylene and stainless steel-on-polyethylene. Control synovial fluids were retrieved from primary arthroplasty cases with osteoarthritis. Synovial fluid was cultured with human primary fibroblasts for 48 hours in a cell culture system under standardised conditions. The “Comet” assay was used with an image analysis system to measure levels of DNA damage caused by the various synovial fluid samples.

Synovial fluids from cobalt chrome-on-cobalt chrome and cobalt chrome-on-polyethylene joint replacements both caused substantial levels of genetic damage as detected by the Comet assay. Synovial fluids retrieved from stainless steel-on-polyethylene joints caused low levels of damage. The difference between these groups was highly statistically significant (p< 0.001). Control synovial fluids from osteoarthritic joints caused minimal changes. Atomic absorption spectroscopy demonstrated that the metal-on-metal synovial fluids contained the highest levels of cobalt and chromium. Different alloys used in orthopaedic implants are associated with different levels of DNA damage to cultured human cells in vitro. We are able to demonstrate that this damage is attributable at least in part to the metal content of the synovial fluid samples. We have no evidence for any long-term health risk to patients with such implants.

Restoration of bone stock is the single greatest challenge facing the revision hip surgeon today. This has been dealt with by means of impaction grafting with morsellised allograft from donor femoral heads.

Alternatives to allograft have been sought. This study investigates the use of a porous biphasic ceramic in impaction grafting of the femur.

Impaction grafting of the femur was performed in four groups of sheep. Group one received pure allograft, group two 50% allograft and 50% BoneSave, group three 50% allograft and 50% BoneSave 2 and group four 10% allograft and 90% BoneSave as the graft material.

Function was assessed by measuring peak vertical reaction forces. Changes in bone mineral density were measured by DEXA scanning. Loosening and subsidence were assessed radiographically and by examination of explanted specimens.

All outcome measures showed no statistically significant difference between the four groups after eighteen months of full function.

Conclusion: When used as allograft expanders, Bone-Save and similar porous biphasic ceramics perform as well as pure allograft in impaction grafting of the femur.

The National Institute for Clinical Excellence (NICE) was set up to provide patients, health professionals and the public with authoritative, robust and reliable guidance on current “best practice”.

To determine how useful for NICE guidelines for Selection of Prostheses for Primary Total Hip Replacement were to patients who were undergoing total hip replacement (THR) and the health professionals who were looking after them. We surveyed 100 patients, 50 Orthopaedic Surgeons, 40 Orthopaedic nurses and posted a questionnaire to GPs, to which 79 replied (56% response rate).

19% of patients had heard of NICE but only 2% were aware of the existence of NICE guidelines on THR and 1% found them useful. Almost all orthopaedic surgeons had heard of NICE and their guidelines for THR, with 74% knowing what the guidelines actually stated but only 14% finding them useful. 78% of surgeons believed that their preferred hip replacement conformed to NICE guidelines, 2% knew that they did not conform and 20% did not know. 27% of general practitioners knew of the guidelines, but only 5% knew what they actually stated and 1% found them useful in their practice. Most nursing staff working in orthopaedic areas had heard of NICE (83%). 43% knew of the NICE guidelines but only 13% knew the actual guidelines and % found them useful.

NICE has failed to communicate its guidelines to both patients and the public. None of the groups found the guidelines useful. NICE has failed to fulfil its mission statement and may instead have other motives, such as empowering centralised regulation of healthcare in the NHS.

Metal-on-metal bearing surfaces have been reintroduced for use in total hip replacement, despite concerns regarding the potential risks posed by metallic by-products. We have compared periprosthetic tissues from metal-on-metal and metal-on-polyethylene hip replacements at revision surgery with control tissues at primary arthroplasty.

Tissues were obtained from 9 control, 25 contemporary metal-on-metal, 9 CoCr-on-polyethylene and 10 titanium-on-polyethylene hip replacement arthroplasties. Each was processed for routine histology with Haematoxylin and Eosin. Quantitative stereological analysis was performed at the light microscopic level.

Metal-on-metal sections showed more surface ulceration and this was correlated with the density of inflammation in the deeper tissues layers. Metal-on-metal tissues displayed a pattern of well-demarcated tissue layers, which were rarely seen in metal-on-polyethylene cases. In metal-on-polyethylene cases, the inflammation was predominantly histiocytic. Metal-on-metal cases by contrast showed a lymphocytic infiltrate with abundant plasma cells. Metal-on-metal tissues showed a striking pattern of peri-vascular inflammation with prominent lymphocytic cuffs especially deep to areas of surface ulceration. Levels of inflammation were higher in cases revised for failure than in those retrieved at autopsy or exploratory surgery. Total replacement and surface replacement designs of metal-on-metal arthroplasty showed similar histological changes. Plasma cells were not seen in any of the metal-on-polyethylene cases. The differences between the patterns of inflammation and cellular infiltration seen in metal-on-metal and metal-on-polyethylene tissues were highly statistically significant.

The pattern and type of inflammation in periprosthetic tissues from metal-on-metal and metal-on-poly-ethylene arthroplasties is very different. Our findings support the conclusion that metal-on-metal articulations are capable of generating a form of immunological response to metallic wear debris that has not been described previously. The incidence and clinical implications of these immunological responses in failed metal-on-metal joints are unknown.

Introduction: Joint replacement surgery is one of the most common operations that take place in United Kingdom. The major problem in total hip arthroplasty is the generation of particulate wear debris and the subsequent biological responses. Wear debris induces osteolysis and a subsequent failure of the implant that lead to the liberation of greater quantities of particulate and soluble debris to bone marrow, blood, lymph nodes, liver and spleen. Recently, it has been suggested that these adverse effects depend not only on the chemical composition but also on the particulate nature of the material (size and shape). Particle size has been shown to influence the inflammatory response of macrophages to wear debris. This study evaluated whether particle size also influences the viability and mutagenic damage.

Methods: Cobalt chrome alloy particles of two sizes (large 2.9±1.1μm, small 0.07±0.04 μm) were generated and characterised by Scanning Electron Microscopy. Different concentrations of particles were added to primary human fibroblasts in tissue culture. The release of cytokines in the medium was assayed by Enzyme-Linked ImunnoSorbent Assay (ELISA). Cell viability was determined by MTT conversion and the degree of DNA damage was quantitatively analysed by the Alkaline Single Cell Gel Electrophoresis (COMET) assay with image analysis.

Results: Small particles initialise DNA damage at much lower volumetric concentrations (0.05 and 0.5 μm³/cell) than larger particles (500 μm³/cell). The difference in the doses was approximately related to the difference in surface area of the particles. DNA damage was related to a delayed decrease in cell viability, which was noted after three days of exposure.

In contrast, the release of the inflammatory cytokine TNF-α and the multifunctional growth factor TGF-β-2 occurred at lower doses (0.0005 to 5 μm³/cell for TNF-α and 0.5 to 50 μm³/cell for TGF-β-2). No release of IL-6 was detected at any dose. Only growth factor FGF-23 was increased in similar pattern to the DNA damage.

Conclusions: This study has demonstrated important differences between the mutagenicity, toxicity and inflammatory potential of small (nanometre sized) and large (micrometer sized) chrome particles.

Introduction: Immediate postoperative stability of cementless hip stems is one of the key factors for the long-term success of total hip replacement. The ability to discriminate between stable and unstable stems in the laboratory constitutes a desirable tool for the industry, as it would allow the identification of unsuitable stem designs prior to clinical trials. The use of composite femora for stability investigations is wide spread [1,2] even though their use in this application is yet to be validated. This study is aimed at establishing whether Sawbones composite femora are suitable for the assessment of migration and micromotion of a cementless hip stem. The stability of two SL Plus stems (Precision Implants, CH) implanted into Sawbone was compared to that of two SL Plus stems implanted into cadaveric femora. Ethical approval was obtained for the harvest and use of cadaveric material.

Methods: Stability was assessed in terms of micromotion and migration. Micromotion was defined as the recoverable movement of the implant relative to the bone under cyclic loading. Migration was defined as the non-recoverable movement of the implant with respect to the surrounding bone. Movement of the implant with respect to the surrounding bone was monitored at two locations on the lateral side of the stem by means of two custom made transducers based on the concept described by Berzins et al [3]. Each femur was tested in two different sinusoidal loading configurations: single leg stance (SLS-11° of adduction and 7° of flexion) [4] loaded up to 400N and stair climbing (SC-11° of adduction and 32° of flexion) loaded up to 300N. The effect of the abductor muscles was included in the model [5]. Each test consisted of 200 loading cycles applied at 50 Hz. The captured data was post-processed by a MATLAB routine and converted into translations and rotations of the stem with respect to the bone.

Results: The proximal part of the implant was subject to the highest amplitudes of micromotion in both loading configurations independent of the host. During SLS the largest micromotion was measured in the direction of the axis of the femur, this amplitude was in the order of 20 μm for the stems implanted in sawbones and varied between 13 and 39 μm for the stems implanted in cadaveric femora. The migration of the implants was minimal both in SLS and SC for both hosts with values measured in the sawbones model nearly on order of magnitude smaller than the cadaveric. In the case of SLS the prevalent movement consisted of a translation along the axis of the bone, while during SC the rotations became prevalent.

Discussion: This study has demonstrated that Sawbones provide an effective model to establish micromotion with oscillation patterns and orders of magnitiude similar to cadaveric bone. However the migration is much more dependent on the quality of fit and the internal geometry of the femur and therefore more caution should be placed on interpreting migration data from Sawbones models.

Wear debris from worn cobalt chrome joint replacements causes an increase in chromosomal translocations and aneuploidy. In this study the relationship between the amount of DNA damage and the changes in gene expression was investigated in human fibroblasts after exposure to artificial cobalt chrome particles. The comparison was made with different doses of particles, at different time intervals and in fibroblasts of different ages, those that had completed 10 population doublings (10 PD fibroblasts) and those that had completed 35 population doublings (35 PD fibroblasts). The genes (TGF-©¬2, p38 MAPK, Integrin ¥â1, SOD1, Caspase 10, PURA, FRA-1 and VNR) were chosen after a previous screen with cDNA microarrays. The percentage of senescent cells was evaluated using an immunohistochemical assay for ¥â-galactosidase activity. The 35 PD fibroblasts showed significantly more ¥â-galactosidase activity than the 10 PD fibroblasts. The level of DNA damage, as detected with the alkaline comet assay, was greater at higher doses, at longer exposures (up to 24 hours) and in 10 PD fibroblasts. The expression of all the genes listed above was generally lower after exposure to cobalt chrome particles using semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). The reduction in gene expression, like the increase in DNA damage was greater at higher doses and at longer exposure times. After 24hr exposure the reduction in gene expression was greater in 10 PD fibroblasts compared to 35 PD fibroblasts. After 6hr exposure this was only true at higher doses of particles and the opposite was seen after a lower dose of particles. These results show that levels of gene expression of TGF-©¬2, p38 MAPK, Integrin ¥â1, SOD1, Caspase10, PURA, FRA-1 and VNR may be correlated with the level of DNA damage and that this depends on the dose and length of exposure and the age of the cells. This highlights the potential importance of these genes in the mutagenicity of cobalt chrome particles in human fibroblasts.