Aims

The duration of systemic antibiotic treatment following first-stage revision surgery for periprosthetic joint infection (PJI) after total hip arthroplasty (THA) is contentious. Our philosophy is to perform an aggressive debridement, and to use a high local concentration of targeted antibiotics in cement beads and systemic prophylactic antibiotics alone. The aim of this study was to assess the success of this philosophy in the management of PJI of the hip using our two-stage protocol.

Aim

The duration of systemic antibiotic therapy following first-stage surgery is contentious. Our Institution's philosophy is to perform an aggressive debridement, use high concentration targeted antibiotics through cement beads and systemic prophylactic antibiotics alone. In the presence of significant soft tissue infection or microbiological diagnostic uncertainty; systemic antibiotics may be prescribed for 5 days whilst awaiting tissue culture results. The aim of this study was to assess the success of our philosophy in the management of PJI of the hip using our two-stage protocol.

The duration of systemic antibiotics following first-stage surgery is contentious. Our Institution's philosophy is to perform an aggressive debridement, high concentration of targeted antibiotics through cement beads and systemic prophylactic antibiotics alone. In the presence of significant soft tissue infection or microbiological diagnostic uncertainty; systemic antibiotics may be prescribed for 5 days whilst awaiting tissue culture results. The aim of this study was to assess the success of our philosophy for two-stage hip revision.

A retrospective review of our Institution's prospective database was performed to identify all intended two-stage hip revision procedures for PJI. All patients had a confirmed PJI as per MSIS 2013 criteria, minimum 5-years follow up and outcomes according to the MSIS working group outcome-reporting tool; then grouped into “successful” or “unsuccessful” (suppressive antibiotics, further revision for infection, death within 1 year).

383 intended two-stage hip revisions were identified; of which 299 met our inclusion criteria, in 289 patients (6 repeat ipsilateral two-stage, 4 bilateral two-stage). Median follow up was 10.7 years (IQR 6.3 – 15.0). 258 (86%) patients proceeded to 2^nd stage surgery. 91% success rate was observed for those patients who underwent reimplantation, although dropping to 86% when including the patients who did not proceed to second stage. The median duration of post-operative systemic antibiotics was 5 days (IQR 5–9). No significant difference was observed in patients who received either; < / = 48 hours (86%; n=70) compared to > 48 hours antibiotics (86%; n=229; p=0.96) or </= 5 days of antibiotics (88%; n=202) compared to > 5 days antibiotics (82%; p=0.38). A significant majority had gram-positive (88%) infection with 30% being polymicrobial. Greater success rates were observed with two-stage exchange or gram-positive PJI (86%); than for gram-negative PJI (81%) and polymicrobial infection (74%) (p=0.36). Fungal PJI was observed to have a significantly reduced rate of success (n=3; 33%; p=0.03).

Aggressive surgical debridement with high concentration, targeted local antibiotic delivery at time of first stage to manage PJI of the hip provides a high rate of success, responsible antibiotic stewardship and reduced hospital costs.

Aims

The aim of this study was to develop a single-layer hybrid organic-inorganic sol-gel coating that is capable of a controlled antibiotic release for cementless hydroxyapatite (HA)-coated titanium orthopaedic prostheses.

No single test is 100% sensitive and specific for the diagnosis of prosthetic joint infection. Joint aspiration is currently the only preoperative investigation that can establish the identity of the infecting organism and its antibiotic susceptibilities. Frequently when attempting to aspirate a joint a ‘dry tap occurs as fluid cannot be aspirated. In this situation, normal saline may be injected into the joint and then reaspirated to provide fluid for culture.

The aim of this study was to ascertain the diagnostic accuracy of culture of joint aspiratie with or without saline reaspiration in the event of a dry tap.

A retrospective analysis of 580 hip and knee aspirations in patients deemed to have moderate-high risk of infection and ultimately proceeded to revision arthroplasty over 12 years at a large quaternary referral centre where pre operative aspiration is routine.

Fluid was aspirated in 313 (54%) cases and dry taps in which saline injection reaspiration was performed occurred in 267 (46%) cases. Overall sensitivity and specificity of diagnostic aspiration were 84% (78–89%) and 85% (81–88%) respectively. Sensitivity and specificity of saline injection-reaspiration after dry tap were 87% (79–82%) and 79% (72–84%) compared to 81% (71–88%) and 90% (85–93%) for direct aspiration.

Pre operative joint aspiration and culture is a sensitive and specific test for the confirmation of diagnosis in patients at a moderate to high risk of prosthetic joint infection. Culture of saline injection-reaspiration also provides accurate diagnostic information in the event of a dry tap. Both methods allow susceptibility testing of relevant organisms and are therefore able to guide peri-operative and cement instilled antibiotic therapy.

Culture of pre operative joint aspirates provides sensitive and specific diagnostic information including antimicrobial susceptibility results.

Saline injection-reaspiration is a useful additional technique in those patients in whom fluid cannot be aspirated.

Aims

The aim of this study was to establish the diagnostic accuracy of culture of joint aspirate with and without saline injection-reaspiration.

The management of periprosthetic joint infection is challenging and the duration of systemic antibiotic therapy whether it be during the interval phase or after reimplantation of a new prosthesis is controversial. We report our experience of managing chronic periprosthetic infection of the hip by the two stage exchange procedure.

Patients who were scheduled to undergo a two stage revision for chronic periprosthetic infection of the hip were identified from our prospective database.

Of 425 patients with microbiologically proven periprosthetic infection, 369 (87%) underwent a two stage procedure, leaving 56 patients who did not proceed to reimplantation. 41 of these were clinically infection free but for personal or medical reasons did not proceed. The remaining 15 had persistent infection. The mean age at the time of the first stage was 68 years (26 – 92 yrs). 256 (61%) patients were alive for review. The mean time between stages was 6.3 months with a mean follow up after the second stage was 65 months (range 5 to 276 months).

The success rate of a single 1^st stage debridement, confirmed by negative cultures at the time of second stage reimplantation was 94%. 19 patients underwent a repeat 1^st stage debridement and were classed as failures of the 1^st stage. At the time of final review, 340 (92%) patients were deemed infection free out of those who had completed a 2 stage exchange.

The duration of systemic antibiotic treatment after both the 1^st and 2^nd stages was divided into <48 hrs and >48 hours. There was no significant difference in the success of the 1^st stage procedure in patients who received < 48 hours (48% of the patients) as opposed to > 48 hours (p = 0.98, Chi Squared Test, Relative Risk 1.009). Similarly there was no difference in the overall success of the two stage procedure irrespective of the duration of antibiotic therapy with 76% of patients receiving <48hrs of antibiotics after the second stage.

Aggressive surgical debridement together with targeted local and short term systemic antibiotic therapy should be the mainstay of treatment in two stage revision surgery.

Aims

Tantalum (Ta) trabecular metal components are increasingly used to reconstruct major bone defects in revision arthroplasty surgery. It is known that some metals such as silver have antibacterial properties. Recent reports have raised the question regarding whether Ta components are protective against infection in revision surgery. This laboratory study aimed to establish whether Ta has intrinsic antibacterial properties against planktonic bacteria, or the ability to inhibit biofilm formation.

Aims

Vancomycin is commonly added to acrylic bone cement during revision arthroplasty surgery. Proprietary cement preparations containing vancomycin are available, but are significantly more expensive. We investigated whether the elution of antibiotic from ‘home-made’ cement containing vancomycin was comparable with more expensive commercially available vancomycin impregnated cement.

Introduction

Data on the outcome of THA in patients under the age of 30 years is sparse. There is a perceived reluctance to offer surgery to young patients on the basis of potential early failure of the implant. We aim to review our experience with THA in this group of patients to establish outcomes in a high volume specialist arthroplasty unit.

Introduction

Tantalum trabecular metal components are increasingly used to reconstruct major bone defects in revision arthroplasty surgery. It is known that some metals such as silver have antibacterial properties. Recent reports have raised the question as to whether Tantalum components are protective against infection in revision surgery. This is based on a retrospective, single institution review, of revision cases comparing tantalum with titanium acetabular implants, which reported a lower incidence of subsequent infection in the tantalum group.

This laboratory study aimed to establish if tantalum had any intrinsic antibacterial properties against planktonic bacteria or ability to inhibit biofilm formation.

Background

An extended trochanteric osteotomy (ETO) is a widely used approach for revision hip arthroplasty. Following an ETO it is common practice to use a long stemmed femoral prosthesis at the second stage to bypass the osteotomy. We propose that at the second stage, if the osteotomy has united, it is appropriate to use a standard length prosthesis, which preserves bone stock for any future revisions.

Introduction

Vancomycin is commonly added to acrylic bone cement during revision arthroplasty surgery. Proprietary cement preparations containing vancomycin are available but significantly more expensive. We investigated whether the antibiotic elution and mechanical strength of ‘home-made’ vancomycin containing bone cement was comparable to commercial vancomycin-impregnated cement.

Peri-prosthetic infection remains a leading cause of revision surgery. Recent publications from the American Musculoskeletal Infection Society have sought to establish a definition of peri-prosthetic infection based on clinical findings and laboratory investigations. The limitations of their approach are discussed and an alternative definition is proposed, which it is felt may better reflect the uncertainties encountered in clinical practice.

Background and objectives

Local bone-related adverse events occur more frequently following metal-on metal hip resurfacing (MOMHR) versus convention total hip arthroplasty (THA). High local tissue levels of cobalt and chromium may contribute to impaired bone health, however the systemic effects on bone of exposure to elevated metal levels after MOMHR are unknown.

Measurements of biochemical markers of bone turnover have been explored as a diagnostic tool for the detection of osteolysis after THA, but their predictive value in individual subjects has been poor. One explanation for this low diagnostic utility is that the mechanism of bone resorption in osteolysis may be different to that occurring in other high bone turnover states, such as osteoporosis, where these markers were principally developed. The aim of this study was to examine the role of the biomarkers urinary ααCTX-I and serum CTX-MMP, that are released in pathological rather than physiological bone turnover states, for detecting periprosthetic osteolysis in a case control study of 23 subjects with osteolysis and 26 controls. All samples were collected between the hours of 0800 and 1000 following an overnight fast, and were assayed using standard techniques. The demographic characteristics of the subjects in both groups were similar. Serum CTX-MMP was greater in the osteolysis versus the control group (P=0.001). Urinary ααCTX-I was similar between osteolysis and control groups (P> 0.05). A cut-off value of 5.50ng/mL CTX-MMP had a sensitivity of 91% (95% CI: 72 to 99) and specificity of 69% (48 to 96) detecting osteolysis (P=0.001). The same cut-off had a sensitivity of 100% (100 to 100) and specificity of 63% (44 to 79) for detecting femoral osteolysis (P=0.0004), and a sensitivity of 89% (65 to 98) and specificity of 58% (39 to 75) for identifying pelvic osteolysis (P=0.014). Serum CTX-MMP shows promise for further investigation as a sensitive bio-marker for detecting periprosthetic osteolysis.

In this 2-year randomised clinical trial we examined whether cemented femoral prosthesis geometry affects the pattern of strain-adaptive bone remodelling in the proximal femur after THA. 128 patients undergoing primary THA were randomised to receive a Charnley (shape-closed, no taper), Exeter (force-closed, double-tapered) or C-stem (forced-closed, triple-tapered) prosthesis. All received a cemented Charnley cup. Proximal femoral BMD change over 2 years was measured by DXA. Urine and serum samples were collected at pre-operative baseline and over 1 year post-operatively. N-telopeptides of type-I-collagen (NTX) was measured in urine as a marker of osteoclast activity and Osteocalcin (OC) in serum as a maker of osteoblast activity. Clinical outcome using the Harris and Oxford hip scores, and prosthesis migration measured using digitised radiographs (EBRA-Digital) were measured over 2 years. The baseline characteristics of the subjects in each group were similar (P> 0.05). Decreases in femoral BMD were observed over the first year for all prosthesis designs. Bone loss was greatest (14%) in the proximal medial femur (region 7). The pattern and amount of bone loss observed was similar between all prosthesis designs (P> 0.05). Transient rises in both osteoclast (NTX) and osteoblast (OC) activity also occurred over year 1, and were similar in pattern in the 3 prosthesis groups (p> 0.05). All prostheses showed migration patterns that were true to their design type and similar improvements in clinical hip scores were observed over the 2 year study. Differences in the proposed mechanism of load transfer between prosthesis and host bone in force-closed versus shape-closed femoral prosthesis designs in THA are not major determinants of prosthesis-related remodelling.

Intrapelvic migration of the acetabular component of a total hip replacement, with severe acetabular destruction making reconstruction impossible, is very rare. We present a patient in whom the component was removed using a laparotomy and a transperitoneal approach with subsequent salvage using a saddle prosthesis and a total femoral replacement.

Introduction: Polymorphisms within genes encoding bone regulatory cytokines influence individuals’ susceptibility to osteolysis after THA. We aimed to determine whether single nucleotide polymorphisms (SNPs) within these genes influence the severity of these osteolytic lesions in 272 patients with established aseptic loosening.

Methods: Assessment of osteolytic lesions was made from pre-revision radiographs in conjunction with direct visualisation in those subjects undergoing surgery. Osteolytic lesions were defined as linear (AAOS pelvic and femoral osteolysis classification grade 0) or expansile, in the presence of segmental or cavitary defects (AAOS grade 1 or greater). We analysed 11 SNPs in the pro-inflammatory cytokines IL-1A, IL-1B, IL-1RA, IL-6 and TNF; 2 SNPs within the FRZB gene, which modulates osteoblast function; and 6 SNPS in the RANK/RANKL/OPG pathway, that modulates osteoclast function.

Results: Femoral Osteolysis: Carriage of the IL-6 −174C allele was 60% in the expansile osteolysis group versus 80% in the linear osteolysis group (χ2 test p=0.007). Carriage of the OPG −163G allele was 34% in the expansile osteolysis group versus 18% in the linear group (χ2 test p=0.03). The odds ratios for expansile osteolysis associated with carriage of IL-6-174G and OPG −163G were 2.7 (1.3 to 5.7, p=0.008) and 2.3 (1.1 to 5.0, p=0.03) respectively.

Acetabular Osteolysis: No differences in SNP genotype were found between osteolysis groups.

Discussion: The IL-6-174G allele and the OPG-163G allele are over-represented in subjects with expansile femoral versus linear osteolysis, but do not relate to severity of pelvic osteolysis. These differences in association may reflect differences in the mechanism of osteolysis between the bone sites, however, replication of the results are required to confirm this differential association.

Introduction: Between 1990 and 2000 we reconstructed 123 hips in 110 patients using impaction bone grafting with frozen, morsellised irradiated femoral heads and cemented sockets. This review presents the medium to long term survivorship of irradiated allograft in acetabular reconstruction in our cohort of patients.

Patients and Methods: Patients were reviewed in out-patients. Radiographs were examined for union, lucency and component migration.

The mean age at revision with allograft was 64.3 years (26 to 97). 86 hips (70%) in 74 patients were reviewed both clinically and radiologically.

At the time of review 28 patients (29 hips) had died and 5 patients (5 hips) were lost to follow up. Of those patients who had died 18 hips had been followed up to a mean of 66 months (12–145). A further 3 hips were unable to attend for clinical review but had accurate implant-allograft survivorship data.

Their data were included in survivorship analysis to the time of last clinical review.

Results: There have been 19 revisions; 9 for infection, 7 for aseptic loosening and 3 for dislocation. In surviving acetabular reconstructions, union of the graft had occurred in 64 out of 67 hips (95.5%). Radiolucent lines at the bone cement interface were seen in 12 hips (17.9%; 9 in a single DeLee zone and 3 in multiple zones) but none were considered loose. Migration of the acetabular component greater than 5mm was seen in 3 hips (4.5%). Survivorship analysis using revision as an end point for all indications at 10 years was 83.3% (95% C.I. 68 to 89%) and 71.3% (95% C.I. 58 to 84%) at 15 years

Conclusion: Acetabular reconstruction using irradiated allograft and a cemented cup is an effective reliable technique with good results in the medium to long term comparable to series using non irradiated freshly frozen bone.

Between 1988 and 1998 we implanted 318 total hip replacements (THRs) in 287 patients using the Plasmacup (B. Braun Ltd, Sheffield, United Kingdom) and a conventional metal-on-polyethylene articulation. The main indications for THR were primary or secondary osteoarthritis.

At follow-up after a mean 11.6 years (7.6 to 18.4) 17 patients had died and 20 could not be traced leaving a final series of 280 THRs in 250 patients. There were 62 revisions (22.1%) in 59 patients. A total of 43 acetabular shells (15.4%) had been revised and 13 (4.6%) had undergone exchange of the liner. The most frequent indications for revision were osteolysis and aseptic loosening, followed by polyethylene wear. The mean Kaplan-Meier survival of the Plasmacup was 91% at ten years and 58% at 14 years. Osteolysis was found around 36 (17.1%) of the 211 surviving shells. The median annual rate of linear wear in the surviving shells was 0.12 mm/year and 0.25 mm/year in those which had been revised (p < 0.001). Polyethylene wear was a strong independent risk factor for osteolysis and aseptic loosening. The percentage of patients with osteolysis increased proportionately with each quintile of wear-rate.

There is a high late rate of failure of the Plasmacup. Patients with the combination of this prosthesis and bearing should be closely monitored after ten years.

Between 1990 and 2000, 123 hips in 110 patients were reconstructed for aseptic loosening using impaction bone grafting with frozen, irradiated, morsellised femoral heads and cemented acetabular components. This series was reported previously at a mean follow-up of five years. We have extended this follow-up and now describe the outcome of 86 hips in 74 patients at a mean of ten years. There have been 19 revisions, comprising nine for infection, seven for aseptic loosening and three for dislocation. In surviving acetabular reconstructions, union of the graft had occurred in 64 of 67 hips (95.5%).

Survival analysis for all indications at ten years was 83.3% (95% confidence interval (CI) 68 to 89) and 71.3% (95% CI 58 to 84) at 15 years.

Acetabular reconstruction using irradiated allograft and a cemented acetabular component is an effective method of reconstruction, providing results in the medium- to long-term comparable with those of reported series where non-irradiated freshly-frozen bone was used.

Introduction: Between 1987 and 1997 we implanted 319 primary hybrid total hip arthroplasties in 289 patients using the ‘Plasmacup’ (B. Braun Ltd, Sheffield) with a conventional metal on polyethylene articulation. We have observed a high revision rate with this implant recently and therefore undertook a clinical review of this cohort.

Patients and Methods: The indications for surgery were osteoarthritis (223), secondary arthritis (83), inflammatory arthritis (10), and others (3). 17 patients have died and 20 have been lost to follow up. Survival analysis was calculated using implant failure defined as revision (including liner exchange), and includes the censored patients outlined above. Assessment of complications in surviving implants was made using AP radiographs of the hip.

Results: The cup survival rate (Kaplan-Meier method) was 91% at 10 years (95%CI ± 4%) and 67% at 13 years (95%CI +/−9%). The stem survival rate was 96% at 10 years (95%CI +/−3%) and 87% at 13 years (95%CI +/−7%). The median wear in cup revisions for osteolysis was 2.4mm (IQR 1.0–3.2mm), and the median wear in surviving cups was 1.3 mm (IQR 0.8 1.9mm), and was an independent predictor of failure (Cox: p=0.001). There have been 57 revisions (35 cup only, 18 cup and stem, 4 stem only). Indications for revision were osteolysis or loosening (34), wear (18), and infection (5). In surviving cups (214), 29 have expansile acetabular osteolysis and 8 have linear osteolysis. In surviving stems (244), 14 have expansile osteolysis and 23 have linear osteolysis.

Conclusions: There is a high late failure rate of the plasma cup using a conventional metal on polyethylene articulation. Patients with this implant/bearing combination should be closely monitored, particularly after 10 years.

Introduction: The use of prolonged courses of parenteral or oral antibiotic therapy in combination with a two-stage exchange procedure in the management of the infected total hip arthroplasty is reported by many major series.

Methods: We present a series of 114 patients, all with microbiologically proven chronic deep infection, treated with a two-stage exchange with antibiotic loaded cement and where a prolonged course of antibiotic therapy has not been used. The mean follow-up for all patients is 74months (range 2–175months) with all surviving patients having a minimum 2 year follow-up.

Results: Infection was successfully eradicated in 100 patients (88%). The infection cure rate in our series is similar to that reported elsewhere where prolonged adjuvant antibiotic therapy was used.

Discussion: Using the technique described a prolonged course of systemic antibiotics does not appear to be necessary; the high costs of antibiotic administration, both to the patient and care facility are not incurred.

Introduction: There are few published reports outlining the outcome of those patients who have undergone revision hip arthroplasty surgery for recurrent infection.

From a consecutive series of 114 patients who had undergone a two-stage exchange without prolonged antibiotic therapy we report the outcome of those patients who continued to have persistent infection.

Methods: Fourteen patients were identified, all with microbiologically proven recurrent deep infection. Seven patients have undertaken further attempts at cure by a two-stage exchange and where again a prolonged course of antibiotic therapy was not routinely used. Infection was eradicated in six out of the seven patients (84%). The mean follow-up of this group is 90 months (range 25–150 months).

Results: From the initial series an overall cure rate of 93% was seen. The other patient has a pseudarthrosis.

Seven patients elected not to undergo a further two-stage revision. Five patients have retained their arthroplasty with lifelong suppressive antibiotic therapy. One has a pseudarthrosis and one disarticulation has taken place for inadequate tissue cover.

Discussion: This series would suggest that in patients willing to undertake further surgery in an attempt to eradicate infection they stand a good chance of a successful outcome.

Introduction: The concept that aseptic loosening is a function of polyethylene wear has led to the introduction of cross-linked polyethylene in THA. We studied the relationship between polyethylene wear rate and aseptic loosening to model the potential effects of wear-reducing strategies on the failure rate for each prosthetic component.

Methods: 350 subjects who had previously undergone Charnley THA were divided into 3 groups: Controls (n=273); isolated femoral stem looseners (n=43); and isolated cup looseners (n=34). Polyethylene wear was measured using a validated method (EBRA). The relationship between wear rate and loosening was examined using logistic regression analysis, and estimates of the effect of wear rate modulation made using odds-ratios (OR ).

Results: The median annual wear rate in the controls (0.07mm) was lower than both stem looseners (0.09mm, p=0.002) and cup looseners (0.18mm, p< 0.001). The OR of cup loosening increased 4.7 times per standard deviation (SD) increase in wear rate above the reference (control) population (p< 0.001). The OR of stem loosening increased 1.7 times per SD, but was not independent of other risk factors (p> 0.05). The potential reduction in risk of loosening was calculated using the following formula: (OR ^SD2)/(OR ^SD1), where 1 and 2 are the predicted mean z-score wear rates of modified versus conventional polyethylene. Thus, for a 25% or 50% reduction in wear rate, the incidence of cup loosening may reduce by 71% and 293%, respectively. The rate of stem loosening may reduce by 7% and 17%, respectively.

Discussion: The use of cross-linked-polyethylene has the potential for a major impact on the incidence of cemented cup loosening. However their effect on femoral stem loosening may be limited.

Introduction: Bone phenotype, such as osteoarthritis (OA) pattern and development of osteolysis or heterotopic ossification (HO) after THA, may be governed by genetic and environmental factors. We investigated whether single nucleotide polymorphisms within the gene encoding secreted-Frizzled Related Protein-3, FRZB Arg200Trp and FRZB Arg324Gly influence bone phenotype.

Methods: Genomic DNA was extracted from 609 subjects at a mean of 11 years following cemented THA for idiopathic osteoarthritis. Pre-operative OA was defined using The American College of Rheumatology criteria and post operative HO after primary THA was assessed using Brooker’s classification

Results: For FRZB Arg200Trp, minor allele carriage (MAC) was greater in subjects with pre-operative pelvic osteophytes (n=267) versus those without osteophytes (n=34) (MAC 27.9% versus 6.3%, Fisher’s exact test p=0.037). There were no associations with other radiographic criteria of OA. MAC was also higher in HO+ve subjects (n=291) versus HO-ve subjects (n=341), (MAC 21.7% versus 12.0%, χ² test p=0.063). Finally MAC was 14.2% in osteolysis +ve subjects (n=268) and 21.7% in osteolysis –ve subjects (n=341) (χ² test p=0.041).

The adjusted odds ratios for pelvic osteophytes and HO with carriage of the rare FRZB 200 variant were 4.34 (1.01–18.7 p=0.048) and 1.64 (1.05 to 2.54, p=0.028) respectively. The adjusted odds ratio for osteolysis was 0.62 (0.38 to 0.99 p=0.049).

There were no bone phenotype associations with the FRZB Arg324Gly variants.

Discussion: Carriage of the FRZB 200Trp allele is positively associated with osteophyte and HO formation and negatively associated with osteolysis, suggesting this locus may be a marker for pro-osteoblastic activity.

Introduction: Bone cements produced by different manufacturers vary in their mechanical properties and antibiotic elution characteristics. Small changes in the formulation of a bone cement, which may not be apparent to surgeons, may also affect these properties. The manufacturing method of Palacos bone cement with added gentamicin has recently changed. We have carried out a study to examine the mechanical characteristics and antibiotic elution of Schering-Plough Palacos (‘old’ version), Heraeus Palacos (‘new’ version) and Depuy CMW Smartset bone cements.

Methods: Schering-Plough Palacos R40G (contains 0.5g gentamicin per 40g mix), Heraeus Palacos R+G (contains 0.5g gentamicin per 40g mix) and Depuy-CMW Smartset GHV (contains 1g gentamicin per 40g mix) were used. 40g samples of the three cements with no additional vancomycin, 1g and 2g vancomycin were prepared by a standard method using vacuum mixing in a syringe. Antibiotic elution over a five week period was measured using an immunoassay method. Standard mechanical testing was carried out according to methods defined in ISO 5833.

Results: Both Heraeus Palacos and Smartset bone cements performed significantly better than Schering-Plough Palacos in terms of mechanical characteristics both with and without additional antibiotics. All cements show a deterioration in flexural strength with increasing addition of vancomycin although staying above ISO minimum levels. Both Heraeus Palacos and Smartset elute significantly more gentamicin cumulatively than Schering-Plough Palacos. Smartset elutes significantly more vancomycin cumulatively compared with Heraeus Palacos.

Discussion: Both Heraeus Palacos and Smartset Bone cements elute significantly more gentamicin than Schering-Plough Palacos with no deterioration in mechanical characteristics. Smartset also elutes significantly more vancomycin than Heraeus Palacos without adverse affect on mechanical characteristics. Although marketed as the ‘original’ Palacos, Heraeus Palacos has significantly altered mechanical and antibiotic elution characteristics compared with previous versions.

Aims: Dislocation is one of the commonest complications following total hip arthroplasty. A significant proportion of these patients go on to have recurrent dislocations. Many factors have been identified as contributing to the risk of dislocation but treatment of recurrent dislocation is challenging. The use of semicaptive acetabular components is a potential solution to the problem of recurrent dislocation but there are few studies into the efficacy of these implants.

Methods: Patients who underwent revision of their total hip arthroplasty to a semi-captive socket at the Lower Limb Arthroplasty Unit, Northern General Hospital, Sheffield between 2001 and March 2006 were studied. A proforma was designed and data was obtained from patients’ medical records. The number of dislocations both prior to revision to a semi-captive component and the following revision to a semi-captive acetabular component were recorded including the method of reduction Reasons for revision and the number and reasons for previous revisions were noted.

Results: Average time of follow up was 22 months (range 2 months – 5 years 1 month). Following revision of total hip arthroplasty to a semi-captive component, 78% suffered no further dislocations. Of those patients who went on to redislocate, three went on to have recurrent dislocations and all were reduced by closed reduction. One patient redislocated and underwent a second revision to a semi-captive acetabular component, which was successful and underwent no further dislocations.

Discussion. The results of this study show the use of semicaptive acetabular components in revision surgery for dislocation following total hip arthroplasty to be a highly effective solution to the problem of recurrent dislocation.

Introduction: Aseptic loosening due to periprosthetic osteolysis is the main cause of implant failure after total hip arthroplasty (THA). Some previous studies have suggested a link between pattern of pre-operative osteoarthritis (OA) and subsequent aseptic loosening. Specifically, atrophic OA may predict implant loosening^1,2 however this remains controversial.³

Methods: We retrospectively assessed the survival of 301 cemented THAs inserted for idiopathic osteoarthritis to determine whether pre-operative patterns of osteoarthritis predict subsequent risk of osteolysis. There were 204 control subjects and 97 subjects with osteolysis. The mean age of patients at insertion of primary implant was 63.4 years and lysis free survival or follow up was 10.6 years. The osteoblastic response in OA was assessed using Bombelli’s classification. The American College of Rheumatology criteria for radiographic evidence of OA was used to assess the pattern of OA prior to primary THA

Results: Atrophic OA was not a risk factor for osteolysis. Atrophic OA in osteolysis group was 16% versus 14% in the control group (χ² test p> 0.05). There was no association between osteolysis and joint space narrowing, femoral or pelvic osteophytes, femoral or pelvic sclerosis, femoral or pelvic cysts and femoral head collapse (χ² test p> 0.05 all comparisons).

Conclusion: The morphological pattern of OA does not predict osteolysis after THA

Introduction: The concept that aseptic loosening is a function of polyethylene wear has led to the use of cross-linked polyethylene in total hip arthroplasty (THA). We studied the relationship between polyethylene wear rate and aseptic loosening in order to model the potential effects of wear-reducing strategies on the failure rate for each prosthetic component.

Methods: 350 subjects who had previously undergone Charnley THA were divided into 3 groups: Controls (n=273); those with loosening of only the femoral stem (n=43); and those with only cup loosening (n=34). Poly-ethylene wear was measured using a validated method (EBRA). The relationship between wear rate and loosening was examined using logistic regression analysis, and estimates of the effect of wear rate modulation made using odds-ratios.

Results: The median annual wear rate in the controls (0.07mm) was lower than both stem looseners (0.09mm, p=0.002) and cup looseners (0.18mm, p< 0.001). The odds of cup loosening increased 4.7 times per standard deviation (SD) increase in wear rate above the reference (control) population (p< 0.001). The odds of stem loosening increased 1.7 times per SD, but was not independent of other risk factors (p> 0.05). The potential reduction in risk of loosening was calculated using the following formula: (OR^SD2)/(OR^SD1), where 1 and 2 are the new and old mean z-score wear rates. Thus, for a 25% or 50% reduction in wear rate, the incidence of cup loosening may reduce by 71% and 293%, respectively. The rate of stem loosening may, at best, reduce by 7% and 17%, respectively.

Discussion: Wear reduction strategies, such as cross-linked polyethylene, have the potential for a major impact on the incidence of cemented cup, but not stem, loosening.

Introduction: It is common practice to use additional antibiotics in bone cement for revision hip surgery. Ideally antibiotic elution would initially be rapid and then reduce to zero in order to reduce the risk of antibiotic resistance developing. There is evidence that the addition of antibiotics to bone cement leads to deterioration in mechanical properties. We have carried out a study to see if the addition of vancomycin to Palacos R40G and Smartset GHV affects their in-vitro antibiotic elution and mechanical properties.

Methods: Palacos R40G (contains 0.5g gentamycin per 40g mix) and Smartset GHV (contains 1g gentamycin per 40g mix) were used. 40g samples of the two cements with no additional vancomycin, 1g and 2g vancomycin were prepared by a standard method using vacuum mixing in a syringe. Antibiotic elution over a five week period was measured using an immunoassay method. Standard mechanical testing was carried out according to methods defined in ISO 5833.

Results: Smartset GHV eluted double the quantity of gentamycin as Palacos R40G, as would be expected. Both cements eluted more gentamycin when vancomycin was added. Smartset appears to elute more vancomycin than Palacos initially and then shows a more rapid tailing off. The mechanical properties of the two cements were the same with no statistical differences found between them. Both showed deterioration in flexural strength with addition of increasing vancomycin.

Discussion: Smartset may have improved qualities of antibiotic elution as compared with Palacos with similar mechanical properties. The presence of higher initial quantities of gentamycin does not lead to reduced mechanical properties.

Introduction: The correct identification of the infecting micro-organism in prosthetic joint infections is difficult and there is no single method that is wholly reliable. We report a novel method intended to improve accuracy by disrupting the biofilm surrounding the prosthesis and transferring samples rapidly to culture medium.

Method: Explanted prostheses from 20 revision operations were sampled by pressing a microbiology swab or by passing a No.10 surgical blade along it. The sample so obtained was plated immediately in the operating theatre onto horse-agar petri dishes. These were incubated in aerobic conditions in the laboratory. Culture results were compared with those obtained from our standard detection method using multiple tissue samples with are plated or grown in prolonged aerobic and anaerobic culture broth.

Results: The method proved practical to perform in practice. When compared with multiple tissue samples as the standard, the Positive Predictive Value was 90%, Negative Predictive Value 80%, sensitivity 82%, specificity 89%. In 4 of the 10 true positive samples, the theatre-inoculated samples yielded early results within 3 days, while conventional method yielded positives only later on prolonged culture.

Discussion: The above pilot is to continue and has started to alter our practice in sample taking. Blade-scrape does appear to penetrate the biofilm successfully. Growing confidence in interpretation and ease in reading the plates mean that in certain cases, we consider the results to be more reliable than traditional tissue culture. Direct plating also reduces the chance of bacterial overgrowth in broth inhibiting colonies of secondary infective organisms. Further refinement is needed, particularly with regard to anaerobic bacteria. Inaccuracies have resulted when agar plates are allowed to go out of date.

Introduction: Activated peri-prosthetic macrophages release pro-inflammatory cytokines, including interleukin-6 (IL-6), that stimulate osteoclast activation and aseptic loosening. Natural sequence variations (polymorphisms) within the IL-6 gene promoter region are associated with diseases characterised by increased osteoclast activity, including osteoporosis, and affect IL-6 production in-vitro. We tested whether polymorphisms in the IL-6 gene promoter influence the risk of aseptic loosening after total hip arthroplasty (THA).

Methods: 614 Caucasians, 292 men and 322 women, mean age 75.8 years who had undergone primary cemented THA for idiopathic osteoarthritis a mean of 13.4 years previously were recruited. Peripheral blood was taken and DNA extracted using standard techniques. Subjects were genotyped for the IL-6 -174, -572, and -597 promoter single nucleotide polymorphisms using the Taqman 5′ nuclease method.

Results: The allele frequencies and carriage rates for both alleles at promoter positions −174, −572, and −597 were similar between controls and aseptic loosening subjects (Table, χ² P> 0.05 all comparisons).

Discussion: Although Il-6 has been implicated in the pathogenesis of aseptic loosening and the −174, −572, and −597 polymorphisms are associated with bone loosing pathologies, they do not appear to play a major role in aseptic loosening after THA.

Bone cements produced by different manufacturers vary in their mechanical properties and antibiotic elution characteristics. Small changes in the formulation of a bone cement, which may not be apparent to surgeons, can also affect these properties. The supplier of Palacos bone cement with added gentamicin changed in 2005. We carried out a study to examine the mechanical characteristics and antibiotic elution of Schering-Plough Palacos, Heraeus Palacos and Depuy CMW Smartset bone cements.

Both Heraeus Palacos and Smartset bone cements performed significantly better than Schering-Plough Palacos in terms of mechanical characteristics, with and without additional vancomycin (p < 0.001). All cements show a deterioration in flexural strength with increasing addition of vancomycin, albeit staying above ISO minimum levels. Both Heraeus Palacos and Smartset elute significantly more gentamicin cumulatively than Schering-Plough Palacos. Smartset elutes significantly more vancomycin cumulatively than Heraeus Palacos.

The improved antibiotic elution characteristics of Smartset and Heraeus Palacos are not associated with a deterioration in mechanical properties. Although marketed as the ‘original’ Palacos, Heraeus Palacos has significantly altered mechanical and antibiotic elution characteristics compared with the most commonly-used previous version.

Between 1980 and 2000, 63 support rings were used in the management of acetabular deficiency in a series of 60 patients, with a mean follow-up of 8.75 years (2 months to 23.8 years). There was a minimum five-year follow-up for successful reconstructions. The indication for revision surgery was aseptic loosening in 30 cases and infection in 33. All cases were Paprosky III defects; IIIA in 33 patients (52.4%) and IIIB in 30 (47.6%), including four with pelvic dissociation. A total of 26 patients (43.3%) have died since surgery, and 34 (56.7%) remain under clinical review. With acetabular revision for infection or aseptic loosening as the definition of failure, we report success in 53 (84%) of the reconstructions. A total of 12 failures (19%) required further surgery, four (6.3%) for aseptic loosening of the acetabular construct, six (9.5%) for recurrent infection and two (3.2%) for recurrent dislocation requiring captive components. Complications, seen in 11 patients (18.3%), included six femoral or sciatic neuropraxias which all resolved, one grade III heterotopic ossification, one on-table acetabular revision for instability, and three early post-operative dislocations managed by manipulation under anaesthesia, with no further instability.

We recommend support rings and morcellised bone graft for significant acetabular bone deficiency that cannot be reconstructed using mesh.

We present a series of 114 patients with microbiologically-proven chronically-infected total hip replacement, treated between 1991 and 2004 by a two-stage exchange procedure with antibiotic-loaded cement, but without the use of a prolonged course of antibiotic therapy. The mean follow-up for all patients was 74 months (2 to 175) with all surviving patients having a minimum follow-up of two years. Infection was successfully eradicated in 100 patients (87.7%), a rate which is similar to that reported by others, but where prolonged adjuvant antibiotic therapy has been used. Using the technique described, a prolonged course of systemic antibiotics does not appear to be essential and the high cost of the administration of antibiotics can be avoided.

We report a case of local compression-induced transient femoral nerve palsy in a 46-year-old man. He had previously undergone surgical release of the soft tissues anterior to both hip joints because of contractures following spinal injury. An MRI scan confirmed a synovial cyst originating from the left hip joint, lying adjacent to the femoral nerve. The cyst expanded on standing, causing a transient femoral nerve palsy. The symptoms resolved after excision of the cyst.

Bleeding is a major complication of revision total hip replacement. We report a case where the inflated balloon of a urinary catheter was used to temporarily control intrapelvic bleeding from the superior gluteal artery, while definitive measures for endovascular embolisation were made.

Dual energy X-ray absorptiometry (DXA) is a precise tool for measuring bone mineral density (BMD) around total joint prostheses. The Hologic ‘metal-removal hip’ analysis package (Hologic Inc, Waltham, Massachusetts) is a DOS-based analysis platform that has been previously validated for measurement of pelvic and proximal BMD after total hip arthroplasty (THA). This software has undergone a change in the operating platform to a Windows-based system that has also incorporated changes to DXA image manipulation on-screen. These changes may affect the magnitude of random error (precision) and systematic error (bias) when compared with measurements made using the previously validated DOS-based system. These factors could influence interpretation of longitudinal studies commenced using the DOS system and later completed using the Windows system. The aims of this study were to compare the precision and bias of pelvic and femoral periprosthetic BMD measurements made using the Windows versus the DOS analysis platform of the Hologic ‘metal-removal hip’ software. A total of 29 subjects (17 men and 12 women) with a mean age of 51years (SD±10), who had undergone hybrid THA using a cemented stem and uncemented cup. Subjects underwent duplicate DXA scans of the hemipelvis and proximal femur taken on the same day after a period for repositioning.. Scans were obtained with the patient lying supine in the scanner with the legs in extension and the foot in a neutral position. Scans were carried out using the same Hologic QDR 4500-A fan-beam densitometer in ‘metal-removal hip’ scanning mode. The DXA scan acquisitions were analysed using both the DOS and the Windows versions of the analysis software. The same observer made all analyses (NRS). Pelvic scans were analysed using a four region of interest model and femoral scans were analysed using a seven region of interest model. Precision was expressed as coefficient of variation (CV%) and compared between methods using the F-test. Systematic bias was examined using the Bland and Altman method and paired t-test. The CV% for the pelvic regions of interest (n=4) varied from 3.92 to 8.54 and from 2.36 to 5.96 for the Windows and DOS systems, respectively. The CV% for the net pelvic region was 3.04 and 2.36 for Windows versus DOS, respectively (F- test, p> 0.05). The CV% for the femoral regions of interest (n=7) varied from 1.58 to 4.14 and from 1.84 to 4.65 for the Windows and DOS systems, respectively. The CV% for the net femoral region was 1.75 and 1.51 for Windows versus DOS, respectively (F- test, p> 0.05). Absolute BMD values for the net pelvic region were similar (Bland-Altman, Windows minus DOS value mean = -1.0%, 95% CI −7.5 to 5.6; t-test p.0.05). Absolute BMD values for the net femoral region were also similar (Bland-Altman, Windows minus DOS value mean = 1.3%, 95% CI −8.3 to 10.8; t-test p.0.05). In summary precision of the measurements using the 2 operating systems was similar and there was no systematic bias between methods. These data suggest that scans analysed using each platform may be used interchangeably within the same study subjects, without the need of a calibration correction.

Bisphosphonates reduce peri-prosthetic bone loss in the short term after total hip replacement but the mid- and longer term effects are not known. The aims of this randomised trial were to examine the effect of a single dose of 90 mg of pamidronate on the clinical and radiological outcome and peri-prosthetic bone mineral density in 50 patients (56 hips) over a five-year period, following total hip replacement.

At five years, 37 patients (42 hips) returned for assessment. The Harris hip scores were similar in the pamidronate and placebo groups throughout the study. Also at five years, four patients, two from each group had osteolytic lesions on plain radiography. These were located around the acetabular component in three patients and in the femoral calcar in one. The femoral and acetabular peri-prosthetic bone mineral density in the pamidronate group and the control group was similar at five years.

Pamidronate given as a single post-operative dose does not appear to influence the clinical outcome or prevent the development of osteolytic lesions at five years after total hip replacement.

Peri-prosthetic bone loss may contribute to aseptic loosening after THA. The aims of this randomised controlled trial extension study were to study the effect of pamidronate therapy on Peri-prosthetic bone mineral density (BMD) and Peri-prosthetic osteolysis over 5 years after primary THA.

50 patients were enrolled in the study in 1998. All received a hybrid THA (Ultima-TPS stem, Plasmacup) for osteoarthritis. Subjects were randomised to receive either 90mg of pamidronate or placebo by intravenous infusion on the 5^th post-operative day. At 5 years 36 patients (41 Hips: placebo n=21, pamidronate n=20) returned for measurement of BMD and clinical and plain radiographic assessment. Five patients had died and nine had withdrawn from the study.

The effect of pamidronate in maintaining femoral bone mass in the region of the calcar previously reported at 2 years was maintained at 5 years (Gruen zone 6 pamidronate versus placebo ANOVA P=0.038; Gruen zone 7 ANOVA P=0.048). No differences in pelvic BMD were found between treatment groups at 5 years. Harris hip scores used to evaluate clinical outcome did not show any significant difference between the 2 groups over the 5-year period. (Mann Whitney p> 0.05). Isolated expansile osteolytic lesions were identified on AP radiographs of the hip at 5 years in 4 patients (2 placebo, 2 pamidronate; P> 0.05). One patient had a 5x9mm lytic lesion in the region of the femoral calcar, and 3 patients had pelvic lytic lesions in the region of the acetabular dome (largest measuring 20x10mm).

Single-dose peri-operative pamidronate therapy preserves femoral calcar bone mass over a 5 year period after THA. However, although the number of subjects with osteolysis is small, we have seen no difference in the rate of osteolytic lesions between treatment groups. Long term study of this patient group is required to examine the rate of aseptic loosening between the treatment groups.

Aims and Objectives Hybrid hip replacement became popular in some centres for younger patients with expected lower rates of acetabular loosening and subsequent revision. We have previously reported our 5 year results and now have further follow-up data on the same cohort of patients.

Materials and Methods 86 uncemented acetabular components of the same design were implanted into 68 patients between 1992 and 1997 who were prospectively followed with respect to clinical outcome, polyethylene wear and intention to revise as a definition of failure.

Results Data is available on 73 acetabular cups with a mean follow-up of 9.5 years. The failure rate is 22%. 9 patients have been revised and 7 further patients await revision for polyethylene wear and osteolysis which in some cases has been very aggressive. Further patients have advanced wear and early lysis which is under close observation.

Conclusion The prosthesis studied has a high failure rate. Patients often report few symptoms until advanced osteolysis has occurred. We recommend that all patients with this type of prosthesis be recalled for frequent radiological review and report on an implant which seems to be failing unacceptably early.

The use of prolonged courses of parenteral or oral antibiotic therapy in the management of two stage revision of infected total knee arthroplasty is reported by all major series.

We present a series of 59 consecutive patients, all with microbiologically proven deep infection managed at our unit where a prolonged course of antibiotic therapy has not been routinely used. The mean follow-up is 56.4 months (range 24–114 months). Of the 38 patients undergoing a staged exchange, infection was successfully eradicated in 34 patients (89%) with recurrent or persistent infection in 4 (11%). The infection cure rate in our series is similar that reported elsewhere.

A prolonged course of antibiotic therapy does not seem to alter the incidence of recurrent or persistent infection. The costs of antibiotic administration are high, both to the patient and care facility. It may be unnecessary.

In-vitro evidence suggests that wear debris can alter osteoblast function resulting in decreased bone matrix production and negative remodelling balance. FRZB encodes for Secreted Frizzled-Related Protein 3 which may play a role in bone formation and osteoarthritis. This study was undertaken to investigate whether the recently described single nucleotide polymorphisms (SNPs) at positions [+6] and [+109] of the FRZB gene are associated with osteolysis after THA.

Genomic DNA was extracted from 481 North European Caucasians at a mean of 12 years following cemented THA for idiopathic osteoarthritis. The control group consisted of 267 subjects and the osteolysis group 214 subjects. The [+6] and [+109] FRZB SNPs were genotyped using standard techniques.

For the FRZB [+6] SNP, the rare T allele was significantly over-represented in control versus the osteolysis group (χ² test for trend, p=0.02,). The odds ratio for osteolysis associated with carriage of the [+6] T-allele versus the [+6] C-allele was 0.58 (95%CI 0.36 to 0.94), p=0.03. The odds ratio for osteolysis associated with carriage of the [+109] G-allele versus the [+109] C-allele was 0.66 (0.38 to 1.12), p=0.15. A number of covariates have previously been described in this cohort and after adjustment for the effects of these covariates, the odds ratio for osteolysis with carriage of the [+6] T-allele was 0.69 (0.42–1.16).

We found that the FRZB [+6] T-allele is less common in subjects with osteolysis after THA versus controls, suggesting that allelic variants of genes associated with bone formation pathways may have a role in modulating the risk of osteolysis. However its loss of significance after correction for other factors suggests an interaction between this allele and other risk factors in osteolysis.

The pattern and magnitude of pelvic periprosthetic bone loss around cementless metal-backed acetabular implants have previously been described. The pattern of periprosthetic BMD change around cemented all-polyethylene acetabular implants is unreported. The aims of this study were to determine the precision of pelvic BMD measurements around the Charnley cup and to examine the longitudinal pattern of BMD change over the first 2 years after surgery.

19 subjects who had previously received a Charnley cup for osteoarthritis underwent duplicate measurements of pelvic BMD after repositioning using an Hologic QDR 4500A densitometer. Scan analysis was carried out using a 4-region of interest model according to a protocol previously described. In-vivo precision was expressed as coefficient of variation (CV%) for each region of interest. The precision of pelvic periprosthetic BMD measurements were 7.7%, 9.8%, 10.8%, and 9.9% for regions 1 to 4, respectively.

Longitudinal BMD changes were measured over a 2 year period in 32 patients (mean age 74 years; 22 women) undergoing cemented THA for unilateral osteoarthritis (17 right-sided). Transient decreases in BMD were observed in regions 2 and 3 (behind the dome of the implant) at 3 months (−9.0% and −13.2%, respectively; P< 0.05) and at 1 year (−8.1% and −9.3%; P< 0.05). By 2 years there had been some recovery in bone mass (BMD−6.9% and −2.6% respectively). No significant changes in BMD for regions 1 and 4 (located at the rim of the implant) were found.

The precision of pelvic periprosthetic BMD measurements for the cemented Charnley cup are poorer than those we have previously reported for cementless cups and may be due, in part, to cement artifact. The pattern of BMD change observed for the Charnley implant suggests that load transfer between the implant and the pelvis occurs principally at the implant rim. The magnitude of bone loss is similar to that we have previously reported for cementless metal-backed acetabular implants.

The Exeter (Howmedica Ltd) and Ultima-TPS (Depuy Ltd) implants are both collarless, polished, double-tapered, cemented femoral implants. The Exeter is manufactured in stainless steel and has an excellent long-term survivorship. The Ultima-TPS is manufactured in cobalt-chrome and has been recently introduced. The aim of this study was to compare the early performance of these implants in a 2-year randomised clinical trial.

65 patients with unilateral hip osteoarthritis were randomised to receive either the Exeter or TPS stem. All received a Charnley Cup. Outcome measures included the Oxford Hip Questionnaire, proximal femoral bone mineral density (BMD) measured by dual energy x-ray absorptiometry, and implant subsidence measured using EBRA. At 2 years 43 patients (66%) were reviewed. 22 patients (mean age 70 years, 16 female, BMI 27.9Kg/m²) received the TPS implant, and 21 patients (mean age 70 years, 15 female, BMI 28.9Kg/m²) received the Exeter implant. 19 patients withdrew for reasons unrelated to the study, 2 died, and 1 was withdrawn after deep wound infection.

Complete Oxford hip scores were available pre-operatively and at 2 years in 37 patients (n=20 TPS). Median (IQR) pre-operative hip scores were 51 (43 to 54) and 48 (36 to 53) for the TPS and Exeter implants, respectively. At 2 years the hip scores improved to 24 (18 to 31) and 22 (16 to 31), respectively. There were no differences in scores between groups at each time-point. There were no differences in BMD between groups at pre-operative baseline, 3 months, 1 and 2 years (Gruen zones 1–7, all time-points; n=19 TPS, n=13 Exeter implants: P> 0.05). Maximum bone loss was seen in Gruen zone 7 at 2 years for bone implants (TPS-11%, Exeter -14%, P> 0.05). Measurement of subsidence over 2 years using EBRA was possible in 20 patients (n=7 TPS, n=13 Exeter). Mean subsidence at 2 years was 1.62mm for the TPS implant and 1.60mm for the Exeter implant (P> 0.05). There was no plain radiographic evidence of osteolysis in either group.

These data suggest that the early performance of the two implants studied is similar. However, long-term survivorship data is required to confirm their equivalency.

Phagocytosis of wear particles by perimplant macrophages results in cytokine release and osteoclast activation and osteolysis. Some investigators have proposed that this response may be mediated by adherent endotoxin. The aim of this study was to determine the role of endotoxin in modulating pro-inflammatory cytokine mRNA expression of macrophages when stimulated with titanium particles using relative quantitative real-time polymerase chain reaction (rqRT-PCR)

Human peripheral blood mononuclear cells were isolated from healthy subjects and plated in chamber slides. Three types of titanium particles were prepared; commercially pure titanium particles (cpTi), endotoxin stripped particles and endotoxin stripped particles with endotoxin (LPS) added back. Endotoxin levels of 450, 0 and 140 Eu/ml respectively were confirmed by high sensitivity Limulus Amebocyte Lysate assay. Macrophages were stimulated with particle concentrations of 0, 8.3, 83 and 830 particles per cell at time points 0 and 3 hours. LPS (200ng/ml) was used as a positive control. rqRT-PCR was performed using standard techniques.

Stimulation of human macrophages with cpTi demonstrated a significant dose dependent increase in TNFα, IL-1A, IL-1B and, IL-6. (Kruskal-Wallis p=0.01, p=0.017, p=0.001 and p=0.013 respectively). IL-18 mRNA levels were not increased (P> 0.05). The expression of mRNA following stimulation with the highest dose of titanium particles was similar to that following LPS stimulation. Endotoxin-free cpTi particles did not elicit any increase in mRNA expression above base line levels (P > 0.05, all cytokines). This lack of response was rescued in endotoxin-stripped particles with LPS added back. Particle dose dependent increases in cytokine mRNA levels were observed for TNFα, IL-1A, IL-1B and, IL-6 mRNA but not IL-18 (p=0.01, p=0.01, p=0.01, p=0.05 and p=0.> 0.05 respectively).

Our results show that adherent endotoxin plays a role in modulating particle induced pro-inflammatory cytokine mRNA expression in-vitro. Further study is required in evaluating the role of adherent endotoxin in vivo

Cytokine mediated activation of osteoclasts can lead to peri-implant osteolysis and aseptic loosening. The aim of this study was to determine the IL-1β and TNFα mRNA cytokine expression profile of human macrophages when stimulated with polyethylene particles using relative quantitative real-time polymerase chain reaction (rqRT-PCR).

Human peripheral blood monocytes or human monocytes from the cell line THP-1 were used in this study. rqRT-PCR conditions were optimized by stimulating human macrophages with 200ng/ml lipopolysaccharide (LPS). The median CV% value for duplicate measures was 12.6 (range 4.5–54). Stimulation assays were performed using unfractionated endotoxin-free commercial polyethylene particles (median size 7μm); or fractionated particles (size range 0.1–1.2μm). Human macrophages were stimulated with high dose unfractionated polyethylene particles at 0, 3500 or 10500 mm³/cell or with fractionated polyethylene particles at 0 and 100mm³/cell at time points 0 and 3 hours. Low dose unfractionated polyethylene stimulation was performed on THP-1 cells at 0, 50, 100, 1000 and 10000 mm³/cell. In all experiments LPS stimulation was used as a positive control. RNA was extracted and rqRT-PCR was performed using standard techniques

High dose unfractionated polyethylene stimulation did not result in a significant difference in cytokine mRNA levels between groups. Using fractionated polyethylene, a small increase in IL-1β mRNA was identified (21% versus maximal stimulation using LPS). Low dose unfractionated polyethylene stimulation of THP-1 cells demonstrated dose dependent decreases in TNFα and IL-1β mRNA expression that was not due to inhibition of RNA extraction or a decrease of cell viability.

Endotoxin-free polyethylene particles do not appear to be a major stimulus for IL-1β and TNFα mRNA production as measured by rqRT-PCR. We did observe a small positive effect on IL-1β mRNA expression using a fractionated polyethylene stimulus. However it remains unclear whether this effect is due to fractionation of particles into the submicron range or is due to introduction of endotoxin during the filtration process.