In conventional DXA (Dual-energy X-ray Absorptiometry) analysis, pixel bone mineral density (BMD) is often averaged at the femoral neck. Neck BMD constitutes the basis for osteoporosis diagnosis and fracture risk assessment. This data averaging, however, limits our understanding of localised spatial BMD patterns that could potentially enhance fracture prediction. DXA region free analysis (RFA) is a validated toolkit for pixel-level BMD analysis. We have previously deployed this toolkit to develop a spatio-temporal atlas of BMD ageing in the femur. This study aims first to introduce bone age to reflect the overall bone structural evolution with ageing, and second to quantify fracture-specific patterns in the femur.

The study dataset comprised 4933 femoral DXA scans from White British women aged 75 years or older. The total number of fractures was 684, of which 178 were reported at the hip within a follow-up period of five years. BMD maps were computed using the RFA toolkit. For each BMD map, bone age was defined as the age for which the L2-norm between the map and the median atlas at that age is minimised. Next, bone maps were normalised for the estimated bone age. A t-test followed by false discovery rate (FDR) analysis was applied to compare between fracture and non-fracture groups.

Excluding the ageing effect revealed subtle localised patterns of loss in BMD oriented in the same direction as principal tensile curves. A new score called f-score was defined by averaging the normalised pixel BMD values over the region with FDR q-value less than 1e–6. The area under the curve (AUC) was 0.731 (95% confidence interval (CI)=0.689–0.761) and 0.736 (95% CI=0.694–0.769) for neck BMD and f-score. Combining bone age and f-score improved the AUC significantly by 3% (AUC=0.761, 95% CI=0.756–0.768) over the neck BMD alone (AUC=0.731, 95% CI=0.726–0.737).

This technique shows promise in characterizing spatially-complex BMD changes, for which the conventional region-based technique is insensitive. DXA RFA shows promise to further improve fracture prediction using spatial BMD distribution.

Ageing is associated with a gradual and progressive bone loss, which predisposes to osteoporosis. Given the close relationship between the involutional bone loss and the underlying mechanism of osteoporosis, improving the understanding of the bone ageing process can lead to enhanced preventive and therapeutic strategies for osteoporosis. To facilitate this understanding, we develop a spatio-temporal atlas of ageing bone in the femur.

We applied our method to a cohort of 11,576 Caucasian women (20–97 years). We amalgamated data from three different studies: 5095 women from the UK Biobank study, 1609 women from the OPUS study, and 5112 women from the MRC-Hip study. The scans are collected using either a Hologic QDR 4500A (Waltham, MA), a Lunar GE iDXA (Madison, WI), or a Lunar GE Prodigy (Madison, WI). Pixel BMD maps were exported using APEX v3.2 and Encore v16 for scans collected on Hologic Inc. and Lunar Corp., respectively. The method utilises a thin plate spline (TPS) registration to warp each scan to a reference mean shape. This image warping, termed Region Free Analysis (RFA), aims to eliminate morphological variation and establish a correspondence between pixel coordinates. At each pixel coordinate, the BMD evolution with ageing was modelled using smooth quantile curves. We deployed the R-package ‘VGAM’ to fit the smooth quantile curves.

Cortical thinning was observed consistently with ageing around the shaft from the 60th onwards. A widespread bone loss was also observed in the trochanteric area. Quantile regression curves demonstrated different rates of bone loss at different anatomic locations. For example, bone loss was observed consistently in the mid-femoral neck, while bone mass was preserved the most in the inferior cortex. The developed atlas provides new insights into the spatial bone loss patterns, for which the conventional DXA analysis is insensitive.

Summary

A retrospective study on 98 patients shows that FE-based bone strength from CT data (using validated FE models) is a suitable candidate to discriminate fractured versus controls within a clinical cohort.

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.

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.

Total hip arthroplasty (THA) wear debris induced macrophage expression of pro-inflammatory cytokines has been associated with osteolysis both in vitro and in animal and human subjects. Interleukin-1 receptor antagonist (IL-1RA) is an anti-inflammatory cytokine which may limit bone destruction. Polymorphisms (SNPs) within the IL-1RN gene are associated with differences in susceptibility to infectious and inflammatory conditions and disorders of bone remodelling. This study investigated the association between the IL-1RA+2018T/C SNP (rs419598) and osteolysis after THA, and with mRNA and protein expression in an in-vitro wear debris-macrophage stimulation assay.

611 North European Caucasians who had received a cemented THA for primary osteoarthritis were genotyped for the IL-1RN+2018 SNP using Taqman methods. 62 subjects with a Charnley THA were selected from the genotyping population. Control subjects had no radiographic osteolysis and the osteolysis group had previously undergone revision surgery for aseptic loosening. Peripheral blood mononuclear cells were extracted and stimulated with endotoxin-stripped titanium particles (TiCL, endotoxin level 0 Eu/ml) and endotoxin-stripped particles with adherent LPS added back (TiAB, endotoxin level 140 Eu/ml); non-stimulated and LPS-stimulated cells were used as negative and positive controls. Cell lysate IL-1RA mRNA levels were assessed by rqRT-PCT following a 3-hour stimulation. Cell supernatant IL-1RA protein levels were assayed after 24 hours stimulation using a multiplex method.

The IL-1RN+2018C allele was underrepresented in patients with osteolysis after THA versus control THA subjects (chi-squared test 5.96, P=0.015). After correction for other risk factors for osteolysis, the adjusted odds ratio for osteolysis associated with carriage of the IL-1RN+2018C SNP was 0.69 (0.48 to 0.99, p=0.048). IL-1RA mRNA expression increased linearly with IL-1RN+2018C allele copy number in gene-dose dependent manner (ANOVA p=0.013). The IL-1RA+2018C allele did not significantly affect IL-1RA protein expression (ANOVA p> 0.05), however a similar trend towards increased levels with increased C allele copy number was observed.

Carriage of the IL-1RA+2018C allele is associated with both a decreased risk of osteolysis after THA and increased IL-1RA mRNA expression in-vitro. The mechanism for this functional effect remains unclear, however these findings support the importance of the IL-1RA in osteolysis and aseptic loosening.

Background: Balloon kyphoplasty is a minimally invasive treatment for acute vertebral fractures that aims to reduce and correct vertebral deformity by inserting expandable balloon tamps and then stabilize the body by filling it with bone cement. The effect of balloon kyphoplasty on quality of life has not been tested in a randomized trial.

Methods: Patients with up to 3 non-traumatic acute vertebral compression fractures were enrolled within 3 months of diagnosis and randomly assigned to receive either balloon kyphoplasty (N=149) or usual nonsurgical care (N=151). Measurements of quality of life, back pain and function, and days of disability and bed rest and spine radiographs were assessed through 12 months of follow-up.

Results: Compared with those assigned to nonsurgical care, participants assigned to balloon kyphoplasty had 5.2 points (95% CI, 2.9 to 7.4; p< 0.0001) greater improvement in the physical component of the SF-36 quality of life questionnaire at one month and 1.5 points (95% CI, − 0.8 to 3.8; p=0.2) at twelve months. Those in the balloon kyphoplasty group also had greater improvement in quality of life by the EuroQol questionnaire at one (0.18 points; 95% CI, 0.08 to 0.28; p=0.0003) and twelve months (0.12 points; 95% CI, 0.01 to 0.22; p=0.025) and improved disability by the Roland-Morris scale at one month (4.0 points; 95% CI, 2.6 to 5.5; p< 0.0001) and twelve months (2.6 points; 95% CI, 1.0 to 4.1; p=0.0012). Balloon kyphoplasty patients had less back pain on a 0 to 10-point numeric rating scale at seven days (2.2 points; 95% CI, 1.6 to 2.8; p< 0.0001) and twelve months (0.9 points; 95% CI, 0.3 to 1.5; p=0.0034) and reported fewer days of limited activity at one month (2.9 days per 2 weeks; 95% CI, 1.3 to 4.6; p=0.0004) and twelve months (1.6; 95% CI, − 0.1 to 3.3; p=0.068). Fewer patients assigned to balloon kyphoplasty took pain medications or used walking aids during follow-up. There was no significant difference in the number of patients with adverse events or serious adverse events in the kyphoplasty and nonsurgical groups. New radiographically detected vertebral fractures occurred in 41.8% of subjects in the balloon kyphoplasty and 37.8% in the nonsurgical group (4% difference; 95% CI − 7.5 to 15.6; p=0.5) and were not statistically different.

Conclusion: Compared to nonsurgical treatment, balloon kyphoplasty safely improved quality of life and reduced back pain, disability and the use of pain medications and walking aids. Significant improvements in multiple measurements of quality of life, pain and disability continue for at least 1 year. Balloon kyphoplasty did not increase adverse events including the risk of vertebral fractures (Clinicaltrials.gov number, NCT00211211).

Introduction: Immune responses in patients susceptible to aseptic loosening may differ to those without this susceptibility. We compared stimulated cytokine mRNA and protein expression in peripheral blood mononuclear cells (PBMC) in 34 subjects (M:F 16:18; mean age 75 years) with previous revision surgery for aseptic loosening versus 28 subjects (14:14; 75 years) with well-fixed implants after Charnley THA for osteoarthritis.

Methods: Extracted PBMCs were stimulated with endotoxin (LPS 200ng/mL), endotoxin-free titanium particles (Ti, endotoxin level =0 Eu/mL), or particles with adherent LPS (TiLPS, 140 Eu/mL). Cell lysate IL-1α, IL-1β, IL-1RA, IL-6, IL-10, IL-18, and TNF mRNA were assayed after 3 hours stimulation using standard rqRT-PCR techniques. Cell supernatant IL-1β, IL-1RA, IL-6 and TNF protein were assayed after 24 hours stimulation using a multiplex method.

Results: mRNA and protein levels in non-stimulated cells were lower in revision versus control subjects for all cytokines (p< 0.05 all analyses). mRNA expression relative to baseline was greater in revision subjects versus controls for all cytokines and all modes of stimulation (LPS, Ti, and TiLPS, p< 0.05 all analyses). LPS induced the greatest inflammatory cytokine response at both the mRNA and protein level in both groups, TiLPS particles induced a more attenuated response, and responses to Ti particles were weakest. In the control group endotoxin free particles showed a negative cytokine mRNA response for IL-1α, IL-1β, and IL-6 (p< 0.05), and reduced protein levels for IL-1β, IL-1RA, IL-6, and TNF versus non-stimulated cells (p< 0.05).

Discussion: Patients with a susceptibility to aseptic loosening have lower baseline but greater stimulated immune responses versus patients without loosening that may contribute to the pathogenesis of aseptic loosening.

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: 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: 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.

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.

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.

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.

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.

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.

Background: The stability of fracture fixation is influenced by the type of fixation, densitometric and geometric structure of the bone. DXA measures the integral mass of trabecular and cortical bone mineral but cannot discriminate between the structurally and mechanically separate constitutes. Distribution and organisation of bone mass (the geometric structure) has the final determination of the mechanical properties of bone. Pq CT scan is able to measure densitometric and geometric parameters of bone structure. However, there are no reports in the literature on the relationship between these measurements and the strength of fracture fixation. Our aim is to study the correlation between geometric and densitometric measurements of Pq CT scan, with the strength of fixation of bicondylar tibial plateau fractures and to assess the role of both trabecular and cancellous bone in that strength.

Method: Eight Fresh frozen human cadaveric tibias were collected from subjects without a medical history of skeletal pathology. The proximal 10% of the tibia was scanned in a peripheral quantitative computer tomography scanner 1mm thick transverse slides, the cancellous and cortical bone mineral density of the proximal tibia were measured. The geometrical parameters: cortical area, trabecular area, bone strength index (BSI) and the Stress strain index (SSI) as non invasive indicators of the mechanical strength of the bone, were also calculated. A bicondylar tibial plateau fracture was simulated, stabilised, and then tested. All tibias were fixed with Dual buttress plating using a standard AO technique. Cyclic axial compression tests were performed. Inter-fragmentary shear displacements were measured using four extensometers. Failure was defined as over 3mm displacement.

Results: Except for the cortical density, there was a strong correlation between failure load and geometric and densitometric parameters. The trabecular density was the best predictor of fixation strength of tibial plateau fracture.

Discussion: Trabecular density is a more reliable parameter to measure than the cortical density. Therefore, the fixation strength of tibial plateau fracture is dominantly influenced by the mechanical properties of cancelous bone. Cortical bone has a secondary role.

These results highlight the importance of fixation techniques that rely on cancellous bone anchoring such as tensioned fine wire fixation in tibial plateau fractures.

Objective: To examine the relationship between three measurements of bone quality and bone strength of the tibial plateau, and the relationships between these measurements. Methods: The bone quality of sixteen cadaveric tibias was assessed for density and architecture using three methods: DXA, pQCT, and spectral analysis of digitised radiographs. These bone quality measurements were correlated with the þxation strength of a bicondylar plateau fracture, obtained by mechanical testing. Results: All three techniques correlate strongly with the mechanical strength of the þxed tibial plateau, with the highest correlation being with DXA (r=0.81, P< 0.001), and pQCT (r=0.79, P< 0.001); followed by spectral analysis (r= 0.5, P,0.01). DXA correlates strongly with pQCT (r=0.95, P< 0.001); Whereas, spectral analysis has a weaker correlation with both DXA (r=0.65, P< 0.01), and pQCT (r=0.69, P< 0.01). Discussion: This is the þrst study of bone quality assessment in the tibial plateau, and as with studies at other sites, DXA showed that BMD has the best correlation with mechanical failure. Both DXA and pQCT are a reßection of density assessment which explains the strong correlation seen. However, the strength of bone is a function of not just quantity and density but also its structure. This was assessed using spectral analysis which involves image processing and pattern recognition algorithm of the trabecular structure. This measures structure only and this may explain the lower correlation with bone strength. Nevertheless we feel that further analysis may demonstrate a speciþc use of this technique to compliment either DXA or PqCT in providing complete assessment of the bone.

Objective: To assess the inßuence of bone density on the þxation strength of bicondylar tibial plateau fractures. Method: Sixteen cadaver tibias were randomised into two groups to receive either dual plating or ring external þxation to stabilise a bicondylar tibial plateau fracture created with a standard method. The randomisation was stratiþed by BMD measured by DXA (above and below the mean). Cyclic axial compression tests were performed with increasing peak loads. Inter-fragmentary shear displacements were measured using four extensometers. Failure was deþned as over 3mm displacement. Results: There was a strong correlation between failure load and BMD [r=0.81, P< 0.001]. The mean failure load of the low BMD group (2701 N) was signiþcantly less than that with the high BMD (4530 N) [t-test=0.003]. The failure loads of the two þxation groups were not signiþcantly different (3520 N for the dual plating and 3710 N for the external þxation) [t-test=0.78]. BMD had a signiþcant effect on the failure load in the dual plating group [t-test=0.03], but not in the external þxation group [t-test=0.1]. Discussion: Failure of þxation has been reported as a common complication of bicondylar tibial plateau fractures with a rate as high as 30%. Osteoporosis and poor bone quality are considered important contributory factors. In our study this inßuence was evident with plating, but not with ring þxation. Ring þxation may be the preferred method of þxation for tibial plateau fractures in the elderly and osteoporotic patients.