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.

Introduction The CPS-Plus stem (Endoplus UK) is a polished double-taper with rectangular cross section maintained throughout for rotational stability. There are 5 stem sizes with proportionate offset, and 5 neck length options. A unique proximal stem centraliser has been shown to increase proximal cement pressurisation during insertion in-vitro, also assists with alignment of the stem and helps create an even cement mantle. RSA analysis has demonstrated linear subsidence in a vertical plane, without posterior head migration and valgus tilt.

We report a multi-centre prospective clinical trial. 231 hips in 223 patients have been entered into the study. 151 of these have reached 3 years follow-up.

Method Patients were recruited by surgeons working at three centres in the UK, and two in Norway. Merle d Aubigne and Postel, Harris, and Oxford hip scores were recorded pre-operatively and at follow-up (3, 6, 12, 24, 36, 60 months). Radiographic assessment included evaluation of subsidence and the presence of any radiolucencies.

Results Hip scores have been very satisfactory. Radiological subsidence is less than 1.5mm in over 95% of cases and only one stem has subsided more than 3mm. There has been one revision for deep sepsis, 7 dislocations and one femoral fracture, but none of these complications were related to the choice of femoral component. There have been no revisions for aseptic loosening. Kaplan Meier survivorship analysis at 36 months for aseptic stem loosening is 0.997 (95% CI 0.977 – 1) and for all-cause revision is 0.981 (95% CI 0.958 – 1). 53 hips had reached 5-year follow-up at 30/9/04.

Discussion The tradition of polished tapered stems arose from serendipity and most results have been excellent. The CPS-Plus stem represents an attempt to re-examine the issues relating to rotational stability, subsidence, cement pressurisation and offset. Earlier laboratory studies have now been supplemented by this clinical evaluation, performed in a number of different centres by several surgeons, and the evidence is encouraging.

In particular, the RSA subsidence characteristics, cement pressurisation and rotational stability already associated with this implant in-vitro have been supported by excellent survivorship analysis, and the authors believe that increasing familiarity with the concepts raised by this implant will result in clinical benefits in relation to polished taper cemented stem longevity.

Polyethylene liners of modular acetabular components wear and sometimes need to be replaced, despite the metal shell being well fixed. Replacing the liner is a relatively simple procedure, but very little is known of the outcome of liner revision. We prospectively followed up 1126 Harris-Gallante 1 metal backed, uncemented cups for between 9 and 19 years. 38 (3.4%) liners out of 1126 acetabular components wore and required revision. These revisions were then followed up for a mean of 4.8 years. The rate of dislocation was 28.9%. Nine of the dislocations were single dislocations and 2 were recurrent.

The overall re-revision rate was 3 out of 38 total hip replacements (7.9%) at a mean follow up of 4.8 years. This gives a 92.1% survivorship at just under 5 years. In isolated liner revision we had a complication rate of 23%. In liner revision combined with stem revision we had a complication rate of 48%. Possible reasons for high dislocation rates are discussed.

Leaving the well fixed acetabular shell in-situ leads to an increased risk of instability. However, this needs to be balanced against the otherwise low complication rate for liner revision. Patients should be consented accordingly

Introduction: The CPS-Plus stem (Endoplus UK) is a polished double-taper with a rectangular cross section maintained throughout for rotational stability. There are 5 stem sizes with proportionate offset, together with 5 neck length options, and a unique proximal stem centraliser which has been shown to increase proximal cement pressurisation during insertion in-vitro, assists with alignment of the stem and helps create an even cement mantle. RSA analysis has demonstrated linear subsidence in a vertical plane, without the posterior head migration and valgus tilt associated with other designs.

Data on the CPS-Plus stem has been obtained from a multi-centre prospective clinical trial. 231 hips in 223 patients have been entered into the study. 151 of these have reached 3 years follow-up.

Method: Patients were recruited by surgeons working at three centres in the UK and two in Norway. Merle d Aubigne and Postel, Harris, and Oxford hip scores were recorded pre-operatively and at follow-up (3, 6, 12, 24, 36, 60 months). Radiographic assessment included evaluation of subsidence and the presence of any radiolucencies.

Results: Objective and subjective scoring have indicated very satisfactory results. Radiological subsidence is less than 1.5mm in over 95% of cases and only one stem has subsided more than 3mm. There has been one revision for deep sepsis, 7 dislocations and one femoral fracture, but none of these complications were related to the choice of femoral component. There have been no revisions for aseptic loosening. Kaplan Meier survivorship analysis at 36 months for aseptic stem loosening is 0.997 (95% CI 0.977 – 1) and for all-cause revision is 0.981 (95% CI 0.958 – 1).

Discussion: The tradition of polished tapered stems arose from serendipity and most results have been excellent. The CPS-Plus stem represents an attempt to re-examine the issues relating to rotational stability, subsidence, cement pressurisation and offset. Earlier laboratory studies have now been supplemented by this clinical evaluation, performed in a number of different centres by several surgeons, and the evidence is encouraging.

In particular, the RSA subsidence characteristics, cement pressurisation and rotational stability already associated with this implant in-vitro have been supported by excellent survivorship analysis, and the authors believe that increasing familiarity with the concepts raised by this implant will result in clinical benefits in relation to polished taper cemented stem longevity.

Introduction The importance of soft tissue and bone preservation at total hip replacement is well recognised. This paper reviews the results of a stem designed not to contact the femoral cortex, thus ensuring exclusive metaphyseal loading.

Methodology Eighty-one consecutive metaphyseal bearing cementless stems were followed up for 2 – 6 years (mean 3 years 9 months).

There were 27 male and 46 female patients (8 bilateral). The mean age was 42 (range 18 to 57). Secondary osteoarthritis was the most common presenting pathology. There were no exclusion criteria beyond those applicable to any replacement arthroplasty.

Results One hip was revised for deep infection. Five hips required cerclage wiring of an intra-operative calcar fracture and there was one post-operative dislocation. One patient, who was being treated for an acute psychotic condition, complained of severe pain. Three patients complained of mild to moderate discomfort in the region of the greater trochanter. The remaining patients were asymptomatic and there was no thigh pain.

There was no evidence of stem subsidence. A sclerotic line was frequently observed around the non-coated distal stem. Buttressing of the coated area was almost universally seen in the metaphyseal region. There were no radiolucent lines in any of the zones around the textured area in the metaphyseal region.

Conclusion These findings persuaded the authors that the stem of the femoral component was superfluous. This paper includes a preliminary report of the initial experience with a conservative, bone and soft tissue sparing metaphyseal femoral implant. Early results are encouraging.

The static properties of bone cements have been widely reported in the literature (Lewis, 1997, Khun, 2000, Armstrong 2002). Commercial bone cements are expected to perform above the minimum values in static tests specified by ISO 5833: 2002. It has been suggested that the viscoelastic properties of bone cement, such as creep and stress relaxation, might bear more relevance to the in-vivo behaviour of the cement-implant construct (Lee 2002). This study aimed to compare numerous properties of Simplex P, Simplex Antibiotic and Simplex Tobramycin and identify those properties most sensitive to subtle changes in cement composition. The three cements were chosen on the basis that they are characterised by the same liquid and powder compositions, the only difference being represented by the type and amount of added antibiotics. In Simplex Antibiotic the additives are 0.5g Erythromycin and 3 million I.U. Colistin, while in Antibiotic Simplex with Tobramycin the only additive is 0.5g of Tobramycin. 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 and stress relaxation tests were performed in four point bending configuration. Porosity was measured on the mid cross section of the creep samples using a digital image technique. All cements exhibited properties compatible with the ISO standard, but in plain Simplex the ISO minimum for bending and compressive strength was within the variation of the batches tested. Bending strength measurements were the least sensitive to differences in the cements. Plain Simplex displayed lower bending and compressive strength but higher bending modulus than the antibiotic laden options. The bending modulus could only discriminate between Simplex P and Simplex Antibiotic (p=0.02). Differences in the compressive strength of the three cements were significant, with the plain option being the weakest. Stress relaxation only discriminated between plain and Tobramycin loaded cement (p=0.028), while creep was more sensitive to differences and allowed distinction between plain and antibiotic loaded bone cements. The creep behaviour correlated with the cross sectional porosity measurements. This study demonstrated that the static tests specified by the current international standard are not as sensitive to subtle changes in the composition of the material as the time temperature dependent parameters characteristic of creep and stress relaxation. The authors advocate the evaluation of time and temperature dependent characteristics as a complement to the current standard.

Aim: The Low Contact Stress (LCS) Total Knee Replacements (TKR) is a well-established mobile bearing prosthesis with more than 25 year experience, while the Kinemax Plus is a well established fixed bearing prosthesis. We examined whether reproducing the joint line height to within 5 mm of the pre-operative joint line height had any impact on the clinical outcome in the two different types of Total Knee Replacements.

Method: 48 consecutive LCS knee replacements with a minimum of 2 years follow up had their pre and postoperative joint line (using Figgie’s method) and range of movement (ROM) measured. We used the Oxford Knee Score as a clinical outcome measurement tool.

A cohort group of 53 CR Kinemax plus TKR from the Bristol Knee group was matched for age and sex. They had the same parameters measured.

Results: Accurate joint line restoration was achieved significantly more frequently (P< 0.05) in the Kinemax group. Better post-operative ROM also occurred in the Kinemax group than the LCS, p = 0.03 and the former produced a bigger gain in ROM p < 0.01. However, no difference in the Oxford Knee Score existed between the two prostheses, p = 0.28.

Joint line: elevation K+ LCS

0–2 mm (16/48) = 33% (26/53) = 49% 2–5 mm (14/48) = 29% (14/53) = 26%> 5 mm (18/48) = 38% (12/53) = 25%

There was no significant difference in the ROM or Oxford Knee Score when the joint line was not elevated versus elevated for each prosthesis. However, there was suggestion that the ROM in LCS might be more sensitive to joint line changes, although this was not significant.

ROM

K+ LCS

Normal joint line 116° 105°

Elevated joint line 108° 101°

Conclusion: Accurate joint line restoration could not be shown to correlate with either improved ROM or Oxford knee score; probably because of the small mount of elevation encountered and the small study size. There was a significantly greater post-operative increase in ROM with the Kinemax Plus relative to the LCS, and a significantly closer restoration of the joint line with the Kinemax Plus, both with respect to the actual measurement and with respect to the proportion of cases in which the joint line was accurately reproduced. This is surprising since in most K+ cases additional distal femur had been resected to avoid a tight knee. While in the LCS group special efforts had been made to achieve accurate restoration of the joint level.

Introduction: Impaction bone grafting is a very useful technique in the armament of a revision hip surgeon. Traditionally fresh frozen allograft has been used for this technique. However there are concerns about the transmission of viral proteins and prions through this form of allograft.As a result irradiated bone graft has been favoured in some centres. There is no long term series describing the results of impaction bone grafting using irradiated bone

Method: We describe a series of 58 cases of acetabular revision surgery done at the Avon Orthopaedic Centre between 1995 and 2001 and followed up over a period of 48–90 months. The preoperative bone defect was graded by the Paprosky classification. There were 10cases of type 1,15 type 2a, 5 type 2b, 7 type 2c, 14 type 3a and 7 type 3c.50 cases were operated by the two senior surgeons and 8 were senior trainees.All uncontained defects were first contained by using a mesh or cages. The bone graft used was freeze-dried femoral head allograft, which was milled and used without defatting. The cases were followed up clinically and radiologically.Case notes were reviewed to gain information about the primary prosthesis, and operative details as well as the cause of the revision. All the cases were the first revisions.

The radiological picture was evaluated for signs of incorporation, remodelling, loosening and migration of the cemented acetabular component. Clinical evaluation was from the last clinic visit and included the presence of pain, mobility status, range of movement and patient satisfaction. Revision was the end point of the study

Results: There were no cases which underwent loosening and all the cups were stable.1 case had recurrent dislocation and was revised.26 (44.8%) cases showed changes of incorporation, and 4 cases (6%)showed changes of remodelling.23 cases (39.6%) underwent femoral impaction grafting as well. Clinically the results were satisfactory with absence of pain in 38 cases (65%). Trochanteric pain was present in 3 cases.

Conclusion: The results suggested that the results of impaction bone grafting on the acetabular side using irradiated bone graft are comparable to those with fresh frozen allograft and significantly better than those on the femoral side. This could be attributed to the compressive forces acting across the acetabular side as against the predominantly shear forces acting on the femur. The low percentage of remodelling remains a concern and warrants further studies.

Introduction Significant cortical bone mass has been demonstrated at the proximo-lateral flare of the femur (Fetto et al). Experiments have shown that if a femoral stem has a medial and lateral flare proximally, the loads are transferred to the proximal femur and stress protection in this area is avoided. Furthermore, the results suggested that a stem below the lesser trochanter was unnecessary (Walker et al).

Methodology This paper reports on two cohorts of ten patients that had either a short stemmed fully coated implant (Group I) or an unstemmed metaphyseal implant on which all but the polished tip was coated (Group II). All implants were customised based on pre-operative CT data. All hips had serial post-operative AP and lateral radiographs and bone densitometry was assessed with DEXA scanning.

Results The most recent post-operative radiographs of all patients in Group I revealed buttressing in zone IV with trabeculae streaming from the cortices onto the tip of the stem. Qualitatively there appeared to be osteope-nia in Gruen zones I and VII. The x-rays of the Group II patients revealed good condensation of bone along the textured surface in zone I and VII with preservation of bone density in these regions. These findings were confirmed by the DEXA results which showed a reduction of the BMD in zones I and VII in Group I, while Group II revealed preservation of the BMD in these zones.

Conclusion A conservative prosthesis without a stem which effectively loads both medial and lateral proximal femoral flares not only removes less bone at the index operation but preserves proximal bone stock in the longer term.

The National Institute for Clinical Excellence (NICE) was set up in the UK ‘to provide patients, health professionals and the public with authoritative, robust and reliable guidance on current best practice. In March 2000, NICE provided national guidelines for the selection of prostheses for total hip replacement.

Aim: To determine how useful the 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.

Method: We surveyed 100 patients, 50 Orthopaedic Surgeons, 40 Orthopaedic nurses and posted a questionnaire to GPs, to which 79 replied (56% response rate).

Results: 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 practise. 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 8% found them useful.

Conclusion: NICE has failed to communicate its guidelines to both patients and the public. Few of the health-care professionals found the guidelines of use in their day to day practice. In this instance, NICE has failed to fulfil its mission statement of providing patients and healthcare professionals with reliable guidance on hip replacement prostheses.

Aseptic loosening remains a long-term problem in total hip replacement. This phenomenon is prevalent even if modern cementing techniques seem to have reduced its incidence. Osteolysis has been deemed as a disease of access to fixation interfaces (1), either the stem- or bone-cement interface in hip replacement. This can be attributed in part to the quality of the cement in the proximity of the stem. It has been noted that due to thermal effects, polymerisation of bone cement starts at the bone-cement interface and gradually moves inwards towards the stem.

Femoral component heating was first proposed as a method to reduce the curing time of bone cement (2). This practice was later found to reduce the porosity at the stem-cement interface (3) and also to improve the interface shear strength (4). This study aimed to investigate the effect of femoral stem heating on two bone cements (Simplex P (Stryker) and Palacos R (Biomet Merck)) over a range of mantle thicknessess.

The model femora used for this study were maintained at a constant temperature of 37C while the stem temperature varied between 21, 37 and 44C. The femoral moulds were formed from dental plaster with a similar thermal conductivity to bone. Mould sizes were created to generate cement mantles of 2, 5 and 7.5mm thickness.

In the 2mm Simplex P cement mantles there was very little porosity evident. It was concentrated in the proximity of the stem when the component was kept at 21C and disappeared as the stem was heated to higher temperatures. Minimal porosity could be identified in the thicker mantles with no apparent differences between temperatures. There were no temperature trends evident from within this cement group. Palacos R cement has been reported to have a higher porosity than Simplex in a number of studies (5, 6). With the 2mm Pala-cos mantles, the increased stem temperatures reduced the porosity at the stem-cement interface. There was however no obvious difference between the 37 and 44C temperatures, where porosity seemed to be evident in the midsection of the mantle. This trend was also identified in the thicker cement mantles. The porosity did not extend out to the cement-bone interface under any conditions.

This study analyses the changes in porosity across the mantle of the cement as the temperature of the stem component is increased. The initial results confirm that the porosity at the stem cement mantle is decreased but indicate that the porosity within the body of the cement is increased as the temperature of the stem is increased.

Metal-on-metal joint replacements have been reintroduced despite some concerns regarding the 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 orthopaedic joint replacement prostheses at the time of revision arthroplasty.

Methods: 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 and no implant in situ. 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. Metal levels were measured in the synovial fluid samples using atomic absorption spectroscopy.

Results: 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 substantially more cobalt and chromium than the fluids retrieved from cobalt chrome-on-polyethylene joints. Stainless steel-on-polyethylene synovial fluids contained the least metal.

Conclusions: 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. Further research is needed in this field.

Introduction and Aims: Eight thousand Duraloc 300 cups were implanted worldwide in 2002. To our knowledge, no 10-year results have been published to date. We undertook this study to ascertain whether this optimism was justified.

Method: One hundred consecutive total hip replacements using a Duraloc 300 cup were reviewed at a minimum of 10 years. Post-operative x-rays were analysed for cup placement and interface gaps. Follow-up films were analysed for lucent lines, osteolysis, wear and migration.

Kaplan-Meier survivorship analysis was performed.

Results: All components were found to be stable with no evidence of loosening or migration. The mean rate of wear was 0.12mm per year. Three hips developed pelvic osteolysis in zone 2 at the level of the apex hole, of which two have successfully undergone a bone grafting procedure and one patient is awaiting surgery.

Conclusion: The Duraloc 300 cup has excellent 10-year results with no cases of loosening. There was a low incidence of pelvic osteolysis. Cementless fixation provides dynamic biological fixation, which is continuously renewed with the passage of time. There is no reason to believe that the durability of fixation will not extend well beyond 10 years.

Introduction: In-vivo elution studies on Antibiotic-loaded Bone Cement (ABC) have concentrated on the short to medium term. This unit has previously described gentamicin release from cement during revision surgery and its presence in the joint aspirates of THAs at up to 12 years. We elected to study the late elutional behaviour of gentamicin-loaded cement in THA.

Methods: 51 patients undergoing revision THA surgery, for aseptic failure, at our centre were studied. Details of the original operation and the subsequent clinical and radiographic course were noted. Pre-operative urine samples and intra-operative joint fluid aspirates (prior to cement disruption) were assayed for their gentamicin concentrations using a fluorescence polarisation immunoassay (Abbott TDX). Cement samples underwent a Bacillus subtilis agar plate inhibition bioassay to assess for antimicrobial activity.

Results: Urine samples were obtained in 43 (84%) of the cases. All were negative for gentamicin (sensitivity level of 0.06 mg/L). Cement samples were retrieved in 36 cases (71%) and all of these (100%) demonstrated significant antimicrobial activity when compared to a standard 10 mg gentamicin disc. In 25 cases (49%) the joints were aspirated and 8 (32%) of these had a gentamicin concentration > 0.1 mg/L. The concentrations however were all below the Minimum Inhibitory Concentration (MIC) for intermediate sensitivity organisms. The longest interval between the primary and revision operations, in these positive cases was 25 years!

Conclusions: This study uniquely demonstrates sequestration of gentamicin within cement for up to 27 years. In addition, one third of joint aspirates had detectable though subtherapeutic gentamicin concentrations at up to 25 years. There was no evidence of late systemic release. These low concentrations of antibiotics, released after many years, are probably a potent stimulus to the emergence of resistant organisms. The use of antibiotic-loaded bone cement in primary THA remains controversial and requires further scrutiny.

Introduction Presently, many instruments exist for assessing both patient and surgeon-based satisfaction after joint replacement, including both generic and disease specific measures. Our aim was to derive and assess the validity of a reduced function scale of the WOMAC for patients with osteoarthritis of the hip and knee.

Methods All unilateral data from 12 centres world-wide (UK, US, Canada and Australia) involved in an international, multi-centre outcome study for patients undergoing TKR were included for analysis. The reduced scale was derived from pre-operative and three month postoperative data using a combination of data-driven analysis and purely clinical methods. The reduced WOMAC was then extensively validated in three key areas; validity, reliability and responsiveness using 12 month post-operative data from the study and data from the Medicare Hip Replacement Study. Data from 898 patients pre-operatively and 806 patients at three months was used for the data driven section of analysis. For the clinical section, 30 members of the orthopaedic community were surveyed as to their opinions of which items should be retained in the reduced version of the scale. These results were then combined to produce a reduced function scale of seven items to be used in conjunction with the five item pain scale. This reduced scale was then scrutinised to ensure it’s validity (both construct and content), reliability (both internal consistency and reproducibility) and responsiveness (using Standardised Response Means).

Results The items retained were: ascending stairs, rising from sitting, getting in/out of car, going shopping, rising from bed, taking off socks and sitting. The scales’s construct validity was confirmed by significant positive correlation with the SF-36 physical component score, the knee society function score, the Oxford knee score, and for the hip data, the Harris Hip Score and SF-12 physical component score. Cronbach’s alpha was consistently high (a> 0.85) with the reduced scale, showing it to be reliable.

Conclusions The SRM’s indicated that the reduced scale may even be better at detecting change than the full scale.

Introduction The reduced WOMAC function scale has been developed and initial validity performed. However, further validation and recommendations for the treatment of missing values is required. The aim of this study is to further assess the validity of the reduced function scale of the WOMAC and recommend a protocol for the treatment of missing values.

Method Further validation of the reduced scale was performed via a cross-over study of 100 pre-operative total joint replacement patients, each being randomised to receive either the full or reduced scale along with the pain scale, and then the alternate version upon admission. Data utilised in the development of the reduced scale was used to develop a missing value protocol, where the number of valid responses for several protocols was examined, as well as comparison of the means and standard deviations. Of the consenting 100 patients, 66 continued onto admission. The median time between administrations of the questionnaires was 14 days (range zero to 72 days).

Results There was no significant difference between pain scores for each questionnaire using the paired t-test (p=0.56). Similarly, there was no significant difference between the full and reduced function scales (p=0.65). The standard protocol for the full scale is that if there are four or more missing items, the patient’s response is invalid. But when there are one to three items missing, the average value for the sub-scale is substituted in lieu of these missing values. Examining the frequencies of valid responses, means and standard deviations when using different missing value protocols (none missing, zero or one, up to two and up to three missing), indicated that there was no substantial benefit between the ‘up to two’ missing and ‘up to three’ missing response protocols. However, for this small gain, the supposition that the completed items are representative of the missing ones rises from 29% (two of seven items) to 43% (three of seven items) should be considered unacceptable.

Conclusions The reduced WOMAC function scale has been further validated. It is proposed that where three or more responses are missing, the patients response is regarded as invalid. Where there are one or two items missing, the average value for the sub-scale is substituted in lieu of these missing values.

Aims: Periprosthetic osteolysis, generally ascribed to cup polyethylene debris is the most common reason for revision THR. We carried out a radiological – retrieval study in 63 patients undergoing revision THR in order to explore potential correlation between osteolysis and wear in the cup. Material and Methods: 43 intact polyethylene liners were retrieved following revision THR because aseptic loosening. Radiological osteolysis was assessed from the De Lee and Gruen zones. The linear wear depth in the cups was measured using the shadowgraph technique and the volumetric wear was assessed using the Hashimoto formula. Statistical analysis was performed using the SPSS® software package. Results: There was a statistically significant inverse correlation between Volumetric Wear Rate (VWR)-Total Femoral Osteolysis (TFO) (p=0.024), VWR -Total Osteolysis TO (p=0.003), Volumetric Wear (VW) – TFO (p=0.015), and a trend between VW – TO (p=0.087). This shows that increased levels of osteolysis appear to be associated with lower VWR. Conclusions: Overall these results demonstrate an overall inverse relationship between long term wear of the polyethylene and periprosthetic osteolysis in pre-revision patients. Restriction in the mobility-activity could be a reason for that.

Aims: The reliability of accurately determining wear in polyethylene cups using plain x-rays has been questioned by many authors. In order to explore the accuracy of wear assessment radiologically, we carried out a radiological-retrieval study in 63 patients undergoing revision THR.

Methods:We retrieved 45 intact polyethylene liners from patients after revision THR. The Linear Wear Depth (LWD) in the cups was assessed radiologically measuring the femoral head eccentricity on the plain non-weight bearing x-ray films. The LWD was assessed in the laboratory using the shadowgraph technique. Statistical analysis was performed using the SPSS® software package.

Results: Themean radiological eccentricity of the femoral head was 2.09±2.17 mm (ranging from 0 to 9.50) and the mean LWD 3.52±1.85 mm (ranging from 0.50 to 9.29). The results of Wilcoxon sign ranks test indicated that this 1.43mm-difference is statistically significant (p< 0.001). The measured wear on the plain x-rays was 40,6% less than the true linear wear measured on the retrieved cup.

Conclusions: It is obvious that the radiological eccentricity of the femoral head underestimates the Linear Wear Depth (“true wear”) quite substantially. That difference could be less if the x-rays had been taken weight bearing.

Aims: It is well established that implant characteristics influence the Volumetric Wear Rate (VWR) of the polyethylene cup at the Total Hip Replacement (THR). In order to explore these, a retrieval study in 63 patients having revision THR was carried out. Methods: 45 intact THR components were retrieved from patients after revision THR. The polyethylene VWR was assessed in the laboratory using the shadowgraph technique. Implant features such as femoral head size, stem/cup modularity and liner thickness were recorded. Statistical analysis to identify potential correlations with the VWR was performed. Results: 22 mm diameter femoral heads produced significantly lower VWR values than 28 mm (p=0.006) and 32 mm (p< 0.001), however, there was no significant difference between the 28mm and 32mm (p=0.375) heads. There was no statistically significant difference between the mean VWR in the metal-backed and the all-polyethylene cups with the first 25% higher than the second. However, the femoral stems with a modular head generated a VWR about 3.5 times higher than the solid monoblock femoral components (p< 0.001). Polyethylene thickness didn’t influence statistically significantly the VWR (p=0.135). Conclusions: Modular implants with large femoral head size significantly influence the polyethylene wear rate. However, in this study, the liner thickness did not influence the wear rate, although it is recognised that there is probably a critical thickness below which wear is accelerated.

Aims: Irradiated allograft bone may help to reduce the risk of transmission of infectious agents from donor to recipient. The purpose of this study was to establish the results of impaction bone grafting of acetabular defects with froze, irradiated allograft bone. Methods: All patients treated by a single surgeon with impaction bone grafting of acetabular defects at revision total hip replacement were reviewed retrospectively. All operations were performed during the period 1994–2000. The mean follow-up was 50 months (range 30–96 months). Case notes and X rays were reviewed and analysed. The Paprosky grade of acetabular defects was determined from the pre-operative X rays and the surgeonñs operation note. Post-operative X rays were reviewed to establish the extent and rate of new bone in-growth. Functional outcomes were determined by way of self-administered questionnaires. Results: Complete records and X rays were obtained for 33 patients who underwent revision hip arthroplasty with impaction bone grafting of the acetabulum using frozen, irradiated allograft bone. There were no complications associated with the bone grafts and no patient required a re-operation. Review of serial X rays conþrmed in-growth of host bone and the functional outcome was satisfactory. Overall 29 patients (88%) declared themselves satis-þed with the outcome of their operation and 32 patients (97%) improved functionally after the operation. Conclusions: These results indicate that satisfactory results can be achieved with impaction bone grafting using frozen, irradiated allograft bone. The use of irradiated bone graft can potentially reduce the risk of disease transmission from donor to recipient without compromising the surgical results.

Aims: Although there have been theoretical expectations of increased polyethylene wear rate with the time a THR is in situ, wear rate is reported to slow down. We performed this study aiming to identify the relationship between wear rate and time of service for the prosthesis. Material and Methods: 45 intact polyethylene liners were retrieved from patients undergoing revision THR. The LWD was measured in the laboratory using the shadowgraph technique. Dividing LWD with time the prosthesis was in place allowed assessment of the Linear Wear Rate (LWR). A correlation between LWR and time of service was explored. Statistical analysis was performed using the SPSS® software package. Results: Linear Wear Rate (LWR) was not stable with time. There was a significant inverse correlation (p< 0.001) between the time that the prosthesis was in place and LWR. This relationship was stronger for the first 6 years of the THR service (p=0.005), while LWR does not change significantly after the 6th year of prosthesis implantation (p=0.060). Conclusions: The LWR is higher in the beginning either as result of the initial higher creep or because of initial lower conformity of the femoral head within the acetabular cup. As conformity increases, the LWR reduces to a more stable value.

Aims: Optimisation of femoral stem load transfer potentially encourages new bone growth. The effect of increasing the taper angle of a highly polished double tapered stem on stability and hoop strain is investigated.

Methods: An in-vitro model femur was instrumented at 3 levels with 10 strain gauges, proximally (channel 1–4), mid taper level (channel 5–8) and distally (channel 9–10). Under controlled conditions surgical Simplex P cement (Stryker Howmedica Osteonics) was prepared and introduced into the canal of the model femur. The Exeter (Stryker Howmedica Osteonics) stem with centraliser was inserted using a standardised technique. The cementation process was repeated 5 times for each stem. The mantle and stem were subjected to cyclic loading at 1 Hz to 0.5kN using an Instron 8511 servohydraulic materials testing machine. The subsidence of the stem and hoop strains generated were recorded. Each experiment was repeated 6 times.

Results: The average subsidence of all the stems was 0.2mm with a standard deviation varying between 0.1 and 0.2. All the stems showed similar patterns of loading, with no significant difference.

Conclusions: The results suggest that within a purely cemented environment the taper angle of the stem used is irrelevant with regard to the hoop strain and the stability of the construct. The authors therefore suggest that size of stem does not matter.

Irradiated allograft bone may help to reduce the risk of transmission of infectious agents from donor to recipient. The purpose of this study was to establish the results of impaction bone grafting of acetabular defects using irradiated allograft bone.

Patients treated with impaction bone grafting of ace-tabular defects between 1994 and 2000 were reviewed retrospectively. The mean follow-up was 50months (range 30–96months). Case notes and Xrays were reviewed and analysed. The Paprosky grade of acetabular defects was determined. Functional outcomes were determined by way of self-administered questionnaires.

Complete records and Xrays were obtained for 33 patients who underwent impaction bone grafting of the acetabulum using freeze-dried, irradiated bone. The Paprosky classifications of the defects were as follows: 3 type 1, 10 type 2A, 4 type 2B, 4 type 2C, 10 type 3A and 2 type 3B.

There were no complications associated with the bone grafts and no patient required reoperation. Review of serial Xrays confirmed ingrowth of host bone. The functional results obtained were as follows: 17 patients (52%) could walk an unlimited distance. 11 patients (33%) required no walking aids whilst a further 17 (52%) required a single cane to mobilise. 21 patients (64%) were able to use public transport after the operation. 20 patients (61%) reported little or no pain. 9 patients (28%) had no limp and 14 patients (42%) had a slight limp. Overall 29 patients (88%) declared themselves to be satisfied with the outcome of their surgery. 32 patients (97%) improved functionally after their operation.

These results indicate that satisfactory results can be achieved with impaction bone grafting using irradiated, frozen allograft bone. The use of irradiated bone graft can potentially reduce the risks of disease transmission from donor to recipient without compromising the surgical results.

We report the results of seventy-six Harris Galante Porous Cups (HGP 1) in sixty-three patients treated by Total Hip Arthroplasty (THA) with a diagnosis of avascular necrosis (AVN) of the femur (grade III and IV). The cups were inserted between 1986 and 1994 and followed prospectively. Seventy hips with a follow up of more than five years (mean 7.6 years) were reviewed.

At last review the mean Harris Hip Score was 94 (standard deviation (& dcl001;) .8), preoperatively the mean had been 29 (& dcl001;14.7). Radiographically there was no evidence of acetabular migration. The revision rate of the femoral prosthesis was 8.6%, however only three stems (4.3%) were revised for loosening the rest being revised to allow down sizing of the femoral head. The revision rate for the acetabular prosthesis was 7.1%, (five cups). At the time of revision none of the cups were clinically loose and only required the liner to be changed. The complication rate was low with no deep infections or dislocations and only nine hips, (11.8%) with grade III heterotopic ossification. Survival analysis for both stem and cup at 8 years is 96.3% (confidence interval 91 – 100%), with a worst-case survival of 93.6%, (C.I 87.4 – 99.9%)

Previous studies of patients undergoing cemented THA for the treatment of advanced AVN have reported a high incidence of component loosening. This study shows good medium term results using the Harris Galante Porous cup for acetabular reconstruction with cemented femoral components for the treatment of this difficult problem.

Presently, many instruments exist for assessing both patient - and surgeon-based satisfaction after joint replacement, including both generic (measures of general health status) and disease specific measures. As such, the US PORT study (1995) recommends use of both the WOMAC and SF-36. However, this means that studies need to incorporate at least these two lengthy questionnaires into protocols, which increases the pressure on patients for both time and difficulty, but also introduces some duplication of data.

The SF-36 has been successfully reduced and validated to a 12 item questionnaire (SF-12) which can be used as a summarised generic health score. It would be of great benefit if a reduced version of the WOMAC could be derived to give a similar summarised disease-specific measurement tool.

To derive and assess the validity of a reduced function scale of the WOMAC for patients with osteoarthritis of the hip and knee.

All unilateral data from 12 centres world-wide (UK US Canada and Australia) involved in an international, multi-centre outcome study for patients undergoing TKR were included for analysis. The reduced scale was derived from pre-op and 3 month post op data using a combination of data-driven analysis and purely clinical methods. The reduced WOMAC was then extensively validated in three key areas; validity, reliability and responsiveness using 12 month post-op data from the study and data from the Medicare Hip Replacement Study.

Data from 898 patients pre-operatively and 806 patients at 3-months were used for the data driven section of analysis. For the clinical section, 30 members of the orthopaedic community were surveyed as to their opinions of which items should be retained in the reduced version of the scale. These results were then combined to produce a reduced function scale of 7 items to be used in conjunction with the 5-item pain scale. The questions remaining in the scale (and their original number in the scale) were: 2) ascending stairs, 3) rising from sitting, 6) walking on flat, 7) getting in/out of car, 9) putting on socks/stockings, 10) rising from bed and 14) sitting. This reduced scale was then scrutinised to ensure it’s validity (both construct and content), reliability (both internal consistency and reproducibility) and responsiveness (using Standardised Response Means). When examining 12 month data the reduced scale compared favourably with the full scale both overall, and when sub-divided by age, sex and country. It’s construct validity was confirmed by significant positive correlation with the SF-36 physical component score, the knee society function score, the Oxford knee score, and for the hip data, the Harris hip score and SF-12 physical component score. Cronbach’s alpha was consistently high (α> 0.85) with the reduced scale, showing it to be reliable, and the SRM’s indicated that the reduced scale may even be better at detecting change than the full scale.

This reduced WOMAC has been successfully derived and validated for use as a summarised and more practical version of the full WOMAC scale.

Periprosthetic fractures may occur intraoperatively or postoperatively. The incidence of is approximately 0.6% in primary and 2.4% in revision total hip arthroplasty. Predisposing factors include stress risers, osteolysis, osteopoenia, singly or in combination. Focusing on postoperative fractures, this paper provides a management algorithm.

If the fracture is stable, conservative treatment is appropriate. If the fracture is not stable, one needs to determine whether the prosthesis is loose or not. If the prosthesis is loose, further management will depend on the quality of the bone stock. Good bone stock will allow revision with a long stem or impaction grafting, while poor bone stock will require extensive allografting. Similarly, the adequacy of the bone stock determines the management regime if the pros-thesis is not loose. In the presence of good bone stock, it is usually possible to carry out open reduction and internal fixation. Poor bone stock requires bicortical onlay allografting.

From 1994 to 1998 36 periprosthetic fractures, 14 with stable implants and 22 with unstable, were treated. The stable implants were treated with Dall Miles plates, fixed with cables and crimp-sleeves, bicortical screws distal to the fracture and unicortical screws proximally. The fracture united in 11 hips, two of which subsequently required prosthetic revision for femoral loosening. In one hip the fixation failed with fracture of the cables. Despite other adverse reports, this type of system is recommended for fixation of periprosthetic fractures where the prosthesis is stable.

The 22 periprosthetic fractures with unstable implants were treated using the Bicontact long stem revision implant. Two distal interlocking screws provided early rotational and axial stability, and 14 patients had additional allografting.

Radiological evidence of fracture healing was apparent in all cases. One prosthesis subsided by more than 5 mm with fracture of the interlocking screws. Cementless long stem revision is the treatment of choice for periprosthetic fractures associated with a loose implant.

To ensure successful outcome it is necessary to determine the extent of the fracture, to assess fracture stability and to appreciate the available and appropriate treatment options. It is necessary to ‘be prepared’: these are challenging problems and the final decision often hinges on intraoperative findings.

Because there are a number of complicating factors, total hip arthroplasty (THA) performed following acetabular fractures has a less favourable prognosis than when done for primary degenerative arthritis. Patients who have had ace-tabular fracture and present for consideration of THA need careful clinical and radiological assessment. Investigation should include AP and lateral radiographs, 45° inlet/outlet views, obturator and iliac obliques, Judet views and CT scan, with or without 3D reconstruction. There are various classifications defining whether the bone deficiency is contained or uncontained and the extent of the structural defect. Treatment options include autograft, allograft together with mesh, screws, plates, rings, cages, etc.

It is probably preferable to undertake THA sooner (as soon as there is radiological evidence of incongruent articular surfaces) rather than later, as this reduces the delay between fracture and recovery from THA, and any inadequate reduction can be minimised or corrected. The surgical approach must allow adequate access for the intended reconstruction. Small contained or uncontained defects can be treated with cemented or cementless implants and limited grafting. Large defects require structural reinforcement, bone grafting, a retaining cage and, unless a custom-made implant is used, cemented fixation.

Potential problems at the time of surgery include sciatic nerve injury (beware the ‘double crush syndrome’) obstructive hardware, heterotopic ossification, avascular necrosis of the acetabulum and occult infection. Patients who are elderly or who present with markedly impacted fracture, extensive abrasion or fracture of the femoral head, displaced femoral neck fracture, and extensive acetabular comminution in the presence of osteopoenic bone, may warrant acute management with THA.

Early experience of THA in the treatment of selected acute fractures is encouraging. However, the clinical results of THA after fractures of the acetabulum are often disappointing, and there is no current evidence that open reduction and internal fixation improves the success of the subsequent THA.

THA following acetabular fractures is a challenging procedure with a high complication rate. Appropriate investigation and preoperative planning reduces the risk of complications.

We reviewed the outcome of prosthesis-to-bone fixation of the rough titanium femoral stem of an Ultraloc prosthesis (Zimmer, USA).

Between 1989 and 1991, 41 of 55 patients were traced for long-term review at a mean of 107 months (55 to 139). The primary pathology was avascular necrosis in 18 patients, osteoarthritis in 16, ankylosing spondylitis in two and Perthes’ disease in one, and there were two cases each of trauma and dysplasia. There was an equal number of men and women, whose mean age at operation was 47 years (24 to 66).

Radiological assessment of the stems revealed well-fixed stems in 40 patients (97.6%). In 20 stems small granulomata due to polyethylene wear were found in Gruen zones 1 and 7, and in one stem in zones 1, 6 and 7. Only one stem required revision for loosening (done at 59 months), but cups (48.8%) were loose. Three patients required revision owing to polyethylene wear and one for sepsis. In all four cases, removal of the stem was extremely difficult. The remaining 16 hips await revision.

Although the results obtained using an Ultraloc prosthesis are poor, from the point of view of fixation the stem has functioned successfully. However, the formation of granulomata causes cup loosening.

We evaluate the results of total hip arthroplasty using either a porous-coated or a hydroxyapatite (HA) coated femoral component.

For a prospective trial we selected a cohort of young patients with a mean age of 39 (19 to 56). They were randomly selected to have either a one-third porous-coated or one-third HA-coated uncemented femoral component. One of two experienced hip surgeons performed the operations. Within the constraints of pathology, the approach and surgical technique was the same in all the cases. Patients were followed-up clinically and radiologically for a mean period of 102 months (87 to 113).

To date there have been no revisions. All components have remained well fixed and there is no evidence of progressive subsidence.

We found no significant difference between porous-coated or HA-coated stems.

Reports in the literature of the incidence of dislocation following primary total hip arthroplasty (THA) vary from 0.5% to 5%. Contributing factors include surgical approach, loss of the abductor mechanism, a decreased offset of the hip joint, malorientation of the components, specific design features of the components, soft tissue laxity and lack of patient compliance.

The increased rate of dislocation with a posterior approach has been dramatically reduced with an enhanced posterior soft tissue repair. Component features associated with an increased risk of dislocation include reduced head/neck offset, an asymmetrical cup and possibly the head size.

Component malorientation is probably the most important factor leading to recurrent dislocation. With the patient in a lateral position, there can be unpredictable variation in the position of the pelvis, and intraoperative movements aggravated this. Uncertainty about the position of the pelvis at the time of insertion of the acetabular component may lead to malpositioning.

The surgeon should attempt to ensure adequate repair of the posterior capsule and external rotators. It is important to reproduce the offset, insert the components with the correct orientation, avoid impingement, and ensure patient compliance in the early postoperative period.

Dislocations are considered early if they occur within three months of THA and late after three months, and management varies accordingly.

While every effort should be made to avoid dislocation following THA, there is no learning curve: reviewing a series of 10 400 THA procedures performed at the Mayo Clinic, Woo and Morrey (1982) reported that the dislocation rate remained between 2% and 3%.

We report the results of a 4- to 17-year clinical and radiological follow-up of 264 Charnley first-generation stems in comparison with those of 402 second- and subsequent-generation stems. The incidence of fracture was 4.1% in first-generation stems and 0.5% in second- and subsequent-generation stems. The incidence of stem loosening requiring or likely to require revision was 3.1% in first-generation and 11.4% in second-generation stems. We believe that the increased loosening rate in second- and subsequent-generation stems is due to their larger cross-sectional area, which produces an increase in flexural stiffness.