The term heterotopic ossification (HO) describes lamellar bone formation within soft tissues following injury. A genome-wide scan of patients after hip arthroplasty has identified that variation within the lncRNA CASC20 is associated with HO susceptibility. Previous findings in our lab have demonstrated upregulation of CASC20 during BMP2-induced osteodifferentiation of adipose-derived stem cells (hMAD) alongside osteodifferentiation markers, RUNX2 and OSX. We hypothesize that CASC20 is a novel regulator of bone formation and aim to investigate CASC20 function in bone formation. 1) We used miRanda prediction algorithm and the ENCORI database to respectively predict which miRNAs CASC20 interacts with and to select for experimentally validated miRNAs. 2) We characterized the expression and functional role of CASC20-interacting miRNAs by respectively analyzing publicly available datasets (GSE107279 and pubmed.ncbi.nlm.nih.gov/26175215/) and by using Gene Ontology (GO) analysis. 3) We overexpressed CASC20 in hMAD using a lentiviral system and tested the effect of CASC20 overexpression in osteodifferentiation and expression of putative CASC20-interacting miRNAs.Abstract
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Conventional approaches (including Tobit) do not accurately account for ceiling effects in PROMs nor give uncertainty estimates. Here, a classifier neural network was used to estimate postoperative PROMs prior to surgery and compared with conventional methods. The Oxford Knee Score (OKS) and the Oxford Hip Score (OHS) were estimated with separate models. English NJR data from 2009 to 2018 was used, with 278.655 knee and 249.634 hip replacements. For both OKS and OHS estimations, the input variables included age, BMI, surgery date, sex, ASA, thromboprophylaxis, anaesthetic and preoperative PROMs responses. Bearing, fixation, head size and approach were also included for OHS and knee type for OKS estimation. A classifier neural network (NN) was compared with linear or Tobit regression, XGB and regression NN. The performance metrics were the root mean square error (RMSE), maximum absolute error (MAE) and area under curve (AUC). 95% confidence intervals were computed using 5-fold cross-validation.Abstract
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In this phase 2 clinical trial (EudraCT 2011-000541-20) we examined the effect of denosumab versus placebo on osteolytic lesion activity in patients undergoing revision surgery after THA. Men and women ≥ 30 years old scheduled for revision surgery for symptomatic, radiologically-confirmed osteolysis were randomised (1:1) to receive either denosumab 60mg or placebo subcutaneously eight weeks prior to operation. At surgery, biopsies from the osteolytic membrane-bone interface were taken for histomorphometric analysis of osteoclast number, the primary outcome measure. Secondary outcome measures included other static histomorphometric indices and systemic bone turnover markers. Adverse events and patient-reported clinical outcome scores were recorded as safety endpoints.Abstract
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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.
The development of an algorithm that provides accurate individualised estimates of revision risk could help patients make informed surgical treatment choices. This requires building a survival model based on fixed and modifiable risk factors that predict outcome at the individual level. Here we compare different survival models for predicting prosthesis survivorship after hip replacement for osteoarthritis using data from the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man. In this comparative study we implemented parametric and flexible parametric (FP) methods and random survival forests (RSF). The overall performance of the parametric models was compared using Akaike information criterion (AIC). The preferred parametric model and the RSF algorithm were further compared in terms of the Brier score, concordance index (C index) and calibration. The dataset contains 327 238 hip replacements for osteoarthritis carried out in England and Wales between 2003 and 2015. The AIC value for the FP model was the lowest. The averages of survival probability estimates were in good agreement with the observed values for the FP model and the RSF algorithm. The integrated Brier score of the FP model and the RSF approach over 10 years were similar: 0.011 (95% confidence interval: 0.011–0.011). The C index of the FP model at 10 years was 59.4% (95% confidence interval: 59.4%–59.4%). This was 56.2% (56.1%–56.3%) for the RSF method. The FP model outperformed other commonly used survival models across chosen validation criteria. However, it does not provide high discriminatory power at the individual level. Models with more comprehensive risk adjustment may provide additional insights for individual risk.
Heterotopic ossification (HO) is lamellar bone formation that occurs within tissues that do not normally have properties of ossification. The pathoaetiology of HO is poorly understood. We conducted a genome wide association study to better understand the genetic architecture of HO. 891 patients of European descent (410 HO cases) following THA for primary osteoarthritis were recruited from the UK. HO was assessed from plain AP radiographs of the pelvis. Genomic DNA was extracted, genotyped using the Illumina 610 beadchip and referenced using the 1000 Genome Project panel. HO susceptibility case-control analysis and an evaluation of disease severity in those with HO was undertaken using SNPTESTv2.3.0 on>10 million variants. We tested variants most strongly associated with HO in an independent UK THA replication cohort comprising 209 cases and 211 controls. The datasets were meta-analysed using PLINK. In the discovery cohort 70 signals with an index variant at p<9×10–5 were suggestively associated with HO susceptibility. The strongest signal lay just downstream of the gene ARHGAP18 (rs59084763, effect allele frequency (EAF) 0.19, OR1.87 [1.48–2.38], p=2.48×10–8), the second strongest signal lay within the long non-coding (LNC) RNA gene CASC20 (rs11699612, EAF 0.25, OR1.73 [1.1.40–2.16, p=9.3×10–8). In the discovery cohort 73 signals with an index variant at p<9×10–5 were associated with HO severity. At replication, 12 of the leading 14 susceptibility signals showed a concordant direction of allelic effect and 5 replicated at nominal significance. Following meta-analysis, the lead replicating susceptibility signal was the CASC20 variant rs11699612 (p=2.71×10–11). We identify consistent replicating association of variation within the LNC RNA CASC20 with HO susceptibility after THA. Although the function of CASC20 is currently unknown, possible mechanisms include transcriptional, post-transcriptional and epigenetic regulation of downstream target genes. The work presented here provides new avenues for the development of novel predictive and therapeutic approaches towards HO.
Commonly used alterations of prosthetic surfaces include grit-blasting (GB), plasma-sprayed titanium (Ti) or hydroxyapatite (HA) coating. Systemic concentrations of cobalt (Co) and chromium (Cr) are elevated in patients with metal-on-metal hip replacement, but can occur for all modular hip replacements. Here, we use whole genome microarrays to assess differential gene expression in primary human osteoblasts grown in vitro and on these prosthesis surfaces following exposure to clinically relevant concentrations of Co and Cr. Mesenchymal cells obtained from bone-fragments of 3 patients undergoing joint replacement surgery were differentiated into osteoblasts. Subsequently, cells were cultured in vitro on tissue-culture plates (TCP), or on GB, Ti and HA surfaces (JRI Orthopaedics Ltd, Sheffield, UK). Following 24hr exposure to a combination of clinically equivalent concentrations of Co2+:Cr3+, RNA was extracted and hybridized to SurePrint-G3 Gene Expression Microarray. Probe signals were normalised using ‘Limma’ package on R-Bioconductor and differential gene expression assessed with empirical Bayes approach (Log2FC>1.00, P<0.001 for differentially expressed genes). For cells grown on TCP, 11 genes were upregulated with 500μg/L Co2+:Cr3+. Of these, 4 were associated to HIF-1 signalling based on KEGG pathway analysis (P=5.4e-5). Exposure to 1000μg/L Co2+:Cr3+ altered expression at 164 loci for HA surfaces, and a separate 50 loci for Ti surfaces compared to GB surfaces. Genes for osteoblast differentiation (BMP2 and RGS2) were downregulated on HA surfaces compared to GB, whilst genes for cell-adhesion (ESAM), vesicular trafficking (RAB37) and protection against oxidative damage (NRF2) were upregulated. Ti surfaces caused an upregulation in ERBB3 and CNTF, which are associated with inhibition of osteoblast differentiation and mineralisation, when compared to GB surfaces. This study confirms the role of HIF-1 signalling in response to prosthesis generated metal ions, and is the first to provide a comprehensive genome-wide insight into transcriptional response of osteoblasts at prosthesis surface to clinically equivalent metal exposure.
We aimed to evaluate the precision and longitudinal sensitivity of measurement of bone mineral density (BMD) in the pelvis and to determine the effect of bone cement on the measurement of BMD in femoral regions of interest (ROI) after total hip arthroplasty (THA). A series of 29 patients had duplicate dual-energy x-ray absorptiometry (DXA) scans of the hip within 13 months of THA. Pelvic analyses using 3- and 4-ROI models gave a coefficient of variation (CV) of 2.5% to 3.6% and of 2.5% to 4.8%, respectively. Repeat scans in 17 subjects one year later showed a significant change in BMD in three regions using the 4-ROI model, compared with change in only one region with the 3-ROI model (p <
0.05). Manual exclusion of cement from femoral ROIs increased the net CV from 1.6% to 3.6% (p = 0.001), and decreased the measured BMD by 20% (t = 12.1, p <
0.001). Studies of two cement phantoms in vitro showed a small downward drift in bone cement BMD giving a measurement error of less than 0.03 g/cm2/year associated with inclusion of cement in femoral ROIs. Changes in pelvic periprosthetic BMD are best detected using a 4-ROI model. Analysis of femoral ROI is more precise without exclusion of cement although an awareness of its effect on the measurement of the BMD is needed.
