Fat quantification in dual-layer detector spectral CT: How to handle iron overload, varying tube voltage and radiation dose Indices.

OBJECTIVES: Opposed to other spectral CT techniques, fat quantification in dual-layer detector CT (dlCT) has only recently been developed. The impact of concomitant iron overload and dlCT-specific protocol settings such as the dose right index (DRI), a measure of image noise and tube current, on dlCT fat quantification was unclear. Further, spectral information became newly available <120 kV. Therefore, this study's objective was to evaluate the impact of iron, changing tube voltage, and DRI on dlCT fat quantification. MATERIAL AND METHODS: Phantoms with 0 and 8mg/cm3 iron; 0 and 5mg/cm3 iodine; 0, 10, 20, 35, 50, and 100% fat and liver equivalent, respectively, were scanned with a dlCT (CT7500, Philips, the Netherlands) at 100kV/20DRI, 120kV/20DRI, 140kV/20DRI, and at 120kV/16DRI, 120kV/24DRI. Material decomposition was done for fat, liver, and iodine (A1); for fat, liver, and iron (A2); and for fat, liver, and combined reference values of iodine and iron (A3). All scans were analyzed with reference values from 120kV/20DRI. For statistics, the intraclass correlation coefficient (ICC) and Bland-Altman analyses were used. RESULTS: In phantoms with iron and iodine, results were best for A3 with a mean deviation to phantom fat of 1.3±2.6% (ICC 0.999 [95%-confidence interval 0.996-1]). The standard approach A1 yielded a deviation of -2.5±3.0% (0.998[0.994-0.999]), A2 of 6.1±4.8% (0.991[0.974-0.997]). With A3 and changing tube voltage, the maximal difference between quantified fat and the phantom ground truth occurred at 100kV with 4.6±2.1%. Differences between scans were largest between 100kV and 140kV (2.0%[-7.1-11.2]). The maximal difference of changing DRI occurred between 16 and 24 DRI with 0.4%[-2.2-3.0]. CONCLUSION: For dlCT fat quantification in the presence of iron, material decomposition with combined reference values for iodine and iron delivers the most accurate results. Tube voltage-specific calibration of reference values is advisable while the impact of the DRI on dlCT fat quantification is neglectable.

Assignment of the biological value of solid breast masses based on quantitative evaluations of spectral CT examinations using electron density mapping, Zeffective mapping and iodine mapping.

OBJECTIVE: We aimed to asses, in a clinical setting, whether the newly available quantitative evaluation of electron density (ED) in spectral CT examinations of the breast provide information on the biological identity of solid breast masses and whether ED maps yield added value to the diagnostic information of iodine maps and Zeff maps calculated from the same CT image datasets. METHODS: All patients at the University Breast Cancer Center who underwent a clinically indicated Dual Layer Computed Tomography (DLCT) examination for staging of invasive breast cancer from 2018 to 2020 were prospectively included. Iodine concentration maps, Zeff maps and ED maps were automatically reconstructed from the DLCT datasets. Region of interest (ROI) based evaluations in the breast target lesions and in the aorta were performed semi-automatically in identical anatomical positions using dedicated evaluation software. Case-by-case evaluations were carried independently by 2 of 4 radiologists for each examination, respectively. Statistical analysis derived from the ROIs was done by calculating ROC/AUC curves and Youden indices. RESULTS: The evaluations comprised 166 DLCT examinations. In the ED maps the measurements in the breast target lesions yielded Youden cutpoints of 104.0% (reader 1) and 103.8% (reader 2) resulting in AUCs of 0.63 and 0.67 at the empirical cutpoints. The variables "Zeff" and "iodine content" derived from the target lesions showed superior diagnostical results, with a Youden cutpoint of 8.0 mg/ml in the iodine maps and cutpoints of 1.1/1.2 in the Zeff maps the AUCs ranging from 0.84 to 0.85 (p = 0.023 to <0.000). The computational combination of Zeff and ED measurements in the target lesions yielded a slight AUC increase (readers 1: 0.85-0.87; readers 2: 0.84-0.94). The ratios of the measured values in the target lesions normalized to the values measured in the aorta showed comparable results. The AUCs of ED derived from the cutpoints showed inferior results to those derived from the Zeff maps and iodine maps (ED: 0.64 and 0.66 for reader 1 and 2; Zeff: 0.86 for both readers; iodine content: 0.89 and 0.86 for reader 1 and 2, respectively). The computational combination of the ED results and the Zeff measurements did not lead to a clinically relevant diagnostic gain with AUCs ranging from 0.86 to 0.88. CONCLUSIONS: Quantitative assessments of Zeff, iodine content and ED all targeting the physical and chemical aspects of iodine uptake in solid breast masses confirmed diagnostically robust cutpoints for the differentiation of benign and malignant findings (Zeff < 7.7, iodine content of <0.8 mg/ml). The evaluations of the ED did not indicate any added diagnostic value beyond the quantitative assessments of Zeff and iodine content. Further research is warranted to develop suitable clinical indications for the use of ED maps.

Detecting Bone Marrow Edema of the Extremities on Spectral Computed Tomography Using a Three-Material Decomposition.

BACKGROUND: Detecting bone marrow edema (BME) as a sign of acute fractures is challenging on conventional computed tomography (CT). This study evaluated the diagnostic performance of a three-material decomposition (TMD) approach for detecting traumatic BME of the extremities on spectral computed tomography (SCT). METHODS: This retrospective diagnostic study included 81 bone compartments with and 80 without BME. A TMD application to visualize BME was developed in collaboration with Philips Healthcare. The following bone compartments were included: distal radius, proximal femur, proximal tibia, distal tibia and fibula, and long bone diaphysis. Two blinded radiologists reviewed each case independently in random order for the presence or absence of BME. RESULTS: The interrater reliability was 0.84 (p < 0.001). The different bone compartments showed sensitivities of 86.7% to 93.8%, specificities of 84.2% to 94.1%, positive predictive values of 82.4% to 94.7%, negative predictive values of 87.5% to 93.3%, and area under the curve (AUC) values of 85.7% to 93.1%. The distal radius showed the highest sensitivity and the proximal femur showed the lowest sensitivity, while the proximal femur presented the highest specificity and the distal tibia presented the lowest specificity. CONCLUSIONS: Our TMD approach provides high diagnostic performance for detecting BME of the extremities. Therefore, this approach could be used routinely in the emergency setting.

Comparison of volumetric and areal bone mineral density in CT and scout scans using spectral detector technology.

BACKGROUND: To determine whether denoised areal bone mineral density (BMD) measurements from scout scans in spectral detector computed tomography (CT) correlate with volumetric trabecular BMD for opportunistic osteoporosis screening. METHODS: A 64-slice single-source dual-layer spectral CT scanner was used to acquire scout scan data of 228 lumbar vertebral bodies within 57 patients. Scout scans in anterior-posterior (AP) view were performed with a dose of < 0.06 mSv and spectrally decomposed into areal BMD (aBMD) values. A spectral dictionary denoising algorithm was applied to increase the signal-to-noise ratio (SNR). Volumetric trabecular bone mineral density (vBMD) was determined via material decomposition. A 3D convolutional network for image segmentation and labeling was applied for automated vBMD quantification. Projected maps were used to compare the classification accuracy of AP and lateral scout scans. RESULTS: The denoising algorithm led to the minimization of anticorrelated noise in spectral maps and an SNR increase from 5.23 to 13.4 (p < 0.002). Correlation analysis between vBMD and measured AP aBMD, projected AP, and lateral aBMD showed a Pearson correlation coefficient of 0.68, 0.81, and 0.90, respectively. The sensitivity and specificity for the osteoporosis classification task were higher in lateral projection images than in AP crystallizing in an increased area under the curve value of 0.99 versus 0.90. CONCLUSION: Denoised material-specific aBMD maps show a positive correlation to vBMD, enabling spectral scout scans as an opportunistic predictor for osteoporotic patients. This could be applied routinely as a screening tool in patients undergoing a CT examination. RELEVANCE STATEMENT: Scout-based DEXA could be applied routinely as a screening tool in patients undergoing a CT examination. KEY POINTS: • Spectral scout scans can be used as a dual-energy x-ray absorptiometry-like screening tool. • Spectral dictionary denoising on projection images increases the signal-to-noise ratio. • Positive correlation between volumetric and areal bone mineral density is observed. • Lateral projections increase osteoporosis classification accuracy compared to anterior-posterior projections.

Intermodal correlation of quantitative CT-data and MRI-biomarkers derived from synchronous spectral CT-maps and breast MRI-examinations with molecular biomarkers in invasive ductal breast carcinomas.

OBJECTIVE: To asses the correlation of data derived from dual-layer (DL)-CT material-maps and breast MRI data with molecular biomarkers in invasive breast carcinomas. METHODS: All patients at the University Breast Cancer Center who underwent a clinically indicated DLCT-scan and a breast MRI for staging of invasive ductal breast cancer from 2016 to 2020 were prospectively included. Iodine concentration-maps, and Zeffective-maps were reconstructed from the CT-datasets. T1w- and T2w-signal intensities, ADC and the clustered shapes of the dynamic-curves (washout, plateau, persistent) were derived from the MRI-datasets. ROI-based evaluations of the cancers and the reference "musculature" were performed semi-automatically in identical anatomical positions using dedicated evaluation software. Statistical analysis was essentially descriptive using Spearmans rank correlation and (multivariable) partial correlation. RESULTS: The signal intensities measured in the 3rd phase of the contrast dynamics correlated at an intermediate level of significance with the iodine content and the Zeffective-values derived from the breast target lesions (Spearmans rank correlation-coefficient r = 0.237/0.236, p = 0.002/0.003). The bivariate and the multivariate analyses displayed correlations of an intermediate significance level of the iodine content and the Zeff-values measured in the breast target lesions with immunhistochemical subtyping (r = 0.211-0.243, p = 0.002-0.009, respectively). The Zeff-values showed the strongest correlations when normalized to the values measured in the musculature and in the aorta (r = -0.237 to -0.305, r=<0.001-0.003). The MRI-assessments showed correlations of intermediate to high significance and low to intermediate significance between the ratios of the T2w-signal intensities and the trends of the dynamic curves measured in the breast target lesions and in musculature and immunohistochemical cancer subtyping, respectively (T2w: r = 0.232-0.249, p = 0.003/0.002; dynamics: r = -0.322/-0.245, p=<0.001/0.002). The ratios of the clustered trends of the dynamic curves measured in the breast target lesions and in musculature correlated with tumor grading on intermediate significance level (r = -0.213 and -0.194, p = 0.007/0.016) and with Ki-67 on a low significance level (bivariate analysis: r = -0.160, p = 0.040). There was only a weak correlation between the ADC-values measured in the breast target lesions and HER2-expression (bivariate ansalysis: r = 0.191, p = 0.030). CONCLUSIONS: Our preliminary results indicate that evaluation of perfusion based DLCT-data and MRI-biomarkers show correlations with the immunhistochemical subtyping of invasive ductal breast carcinomas. Further clinical research is warranted in order to validate the value of the results and define clinical situations in which the use of the described DLCT-biomaker and MRI biomarkers may be helpful in clinical patient care.

Spectral cardiac CT in acute stroke patients.

Cardiac CT obtained in acute ischemic stroke patients can facilitate timely detection of cardiac sources of embolism and guide secondary prevention strategies. Spectral CT exploiting the simultaneous acquisition of separate higher-energy and lower-energy photon spectrum datasets has the potential to improve contrast between thrombi and cardiac structures. This study aimed to investigate the diagnostic value of spectral cardiac CT compared to conventional CT for the detection of cardiac thrombi in acute stroke patients. Patients with acute ischemic stroke undergoing spectral cardiac CT were retrospectively included. Conventional CT images, virtual 55 keV monoenergetic (monoE55), z-effective (zeff), and iodine density images were evaluated for the presence of thrombi. Diagnostic certainty was rated on a 5-point Likert scale. Contrast ratios were calculated for all reconstructions. 63 patients with 20 thrombi were included. Four thrombi were missed on conventional images but detected on spectral reconstructions. MonoE55 achieved the highest scores for diagnostic certainty. Contrast ratios were highest on iodine density images, followed by monoE55, conventional and zeff (p < 0.005). Spectral cardiac CT adds diagnostic benefit for the detection of intra-cardiac thrombi in acute ischemic stroke patients compared to conventional CT.

Correlation of CT-data derived from multiparametric dual-layer CT-maps with immunohistochemical biomarkers in invasive breast carcinomas.

OBJECTIVE: To examine the correlation of quantitative measurements from material decomposition maps calculated from dual-layer CT (DLCT)-image datasets with immunohistochemical biomarkers of invasive breast carcinomas. MATERIAL AND METHODS: All patients at the University Breast Cancer Center who underwent a clinically indicated dual-layer CT-scan for staging of invasive ductal breast carcinoma from 01/2016 to 07/2020 were prospectively included. Iodine concentration maps and maps of the effective atomic numbers (Zeffective) were reconstructed from the image datasets. ROI-based evaluations of the index tumors and predefined references tissues for normalization were performed semi-automatically in identical anatomical positions using dedicated evaluation software. Statistical analysis was essentially descriptive using Spearmans rank correlation and (multivariable) partial correlation. RESULTS: Bivariate showed statistically significant correlations of iodine contents (r = -0.154/-0.202/0.180, p = 0.039/0.006/0.015), and Zeffective-values (r = -0.158/-0.199/0.179, p = 0.034/0.007/0.016) for all 184 carcinomas and the subgroup of 168 invasive ductal carcinomas. The results were confirmed by multivariate analyses with "age", "diameter" and "ACR-grade" as possible confounders. Normalization of the measured target values with those in the aorta confirmed significant correlations of iodine content and Zeffective compared to Estrogen (r = 0.174, p = 0.019), Progesteron (r = 0.168/0.177, p = 0.024/0.017), and HER2 receptor expression (r = -0.222/-0.184, p = 0.003/0.013). All CT-parameters showed significant correlations with immunohistochemical subtyping (r = 0.191/0.192, p = 0.010). CONCLUSIONS: Our preliminary results indicate that iodine content and Zeffective-values derived from DLCT-examinations correlate with hormone receptor expression in invasive breast carcinomas. Assignments to benign entities already seam feasible in clinical routine CT-diagnostics. After further investigations iodine content and Zeffective may be translated as diagnostical and prognostical biomarkers into clinical routine in the long term.

Dual-Layer Spectral-Computed Tomography Enhances the Separability of Calcium-Based Implant Material from Bone: An Ex Vivo Quantitative Imaging Study.

Local treatment of bone loss with an injection of a resorbable, calcium-based implant material to replace bone has a long history of clinical use. The in vivo discrimination of changes in bone versus implant is challenging with standard computed tomography (CT). However, spectral-CT techniques enable the separation between tissues of similar densities but different chemical compositions. Dual-layer spectral-CT imaging and postprocessing analysis methods were applied to investigate the separability of AGN1 (a triphasic calcium-based implant) and bone after AGN1 injection in n = 10 male cadaveric femurs ex vivo. Using the area under the curve (AUC) from receiver-operating characteristic (ROC) analyses, the separability of AGN1 from bone was assessed for AGN1 (postoperatively) versus compact and versus femoral neck cancellous bone (both preoperatively). CT techniques included conventional Hounsfield (HU) and density-equivalent units (BMD, mg hydroxyapatite [HA]/cm3 ) and spectral-CT measures of effective atomic number (Zeff) and electron density (ED). The samples had a wide range of femoral neck BMD (55.66 to 241.71 mg HA/cm3 ). At the injection site average BMD, HU, Zeff, and ED increased from 69.5 mg HA/cm3 , 109 HU, 104.38 EDW, and 8.30 Zeff in the preoperative to 1233 mg HA/cm3 , 1741 HU, 181.27 EDW, and 13.55 Zeff in the postoperative CT scan, respectively. For compact bone at the femoral shaft the preoperative values were 1124.15 mg HA/cm3 , 1648 HU, 177 EDW, and 13.06 Zeff and were maintained postoperatively. Zeff showed substantially sharper distributions and significantly greater separability compared to ED, BMD, and HU (all p < 0.002, for both regions) with average AUCs for BMD, HU, ED, and Zeff of 0.670, 0.640, 0.645, and 0.753 for AGN1 versus compact and 0.996, 0.995, 0.994, and 0.998 for AGN1 versus femoral neck cancellous sites, respectively. Spectral-CT permits better discrimination of calcium-based implants like AGN1 from bone ex vivo. Our results warrant application of spectral-CT in patients undergoing procedures with similar implants. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Fat Quantification in Dual-Layer Detector Spectral Computed Tomography: Experimental Development and First In-Patient Validation.

OBJECTIVES: Fat quantification by dual-energy computed tomography (DECT) provides contrast-independent objective results, for example, on hepatic steatosis or muscle quality as parameters of prognostic relevance. To date, fat quantification has only been developed and used for source-based DECT techniques as fast kVp-switching CT or dual-source CT, which require a prospective selection of the dual-energy imaging mode.It was the purpose of this study to develop a material decomposition algorithm for fat quantification in phantoms and validate it in vivo for patient liver and skeletal muscle using a dual-layer detector-based spectral CT (dlsCT), which automatically generates spectral information with every scan. MATERIALS AND METHODS: For this feasibility study, phantoms were created with 0%, 5%, 10%, 25%, and 40% fat and 0, 4.9, and 7.0 mg/mL iodine, respectively. Phantom scans were performed with the IQon spectral CT (Philips, the Netherlands) at 120 kV and 140 kV and 3 T magnetic resonance (MR) (Philips, the Netherlands) chemical-shift relaxometry (MRR) and MR spectroscopy (MRS). Based on maps of the photoelectric effect and Compton scattering, 3-material decomposition was done for fat, iodine, and phantom material in the image space.After written consent, 10 patients (mean age, 55 ± 18 years; 6 men) in need of a CT staging were prospectively included. All patients received contrast-enhanced abdominal dlsCT scans at 120 kV and MR imaging scans for MRR. As reference tissue for the liver and the skeletal muscle, retrospectively available non-contrast-enhanced spectral CT data sets were used. Agreement between dlsCT and MR was evaluated for the phantoms, 3 hepatic and 2 muscular regions of interest per patient by intraclass correlation coefficients (ICCs) and Bland-Altman analyses. RESULTS: The ICC was excellent in the phantoms for both 120 kV and 140 kV (dlsCT vs MRR 0.98 [95% confidence interval (CI), 0.94-0.99]; dlsCT vs MRS 0.96 [95% CI, 0.87-0.99]) and in the skeletal muscle (0.96 [95% CI, 0.89-0.98]). For log-transformed liver fat values, the ICC was moderate (0.75 [95% CI, 0.48-0.88]). Bland-Altman analysis yielded a mean difference of -0.7% (95% CI, -4.5 to 3.1) for the liver and of 0.5% (95% CI, -4.3 to 5.3) for the skeletal muscle. Interobserver and intraobserver agreement were excellent (>0.9). CONCLUSIONS: Fat quantification was developed for dlsCT and agreement with MR techniques demonstrated for patient liver and muscle. Hepatic steatosis and myosteatosis can be detected in dlsCT scans from clinical routine, which retrospectively provide spectral information independent of the imaging mode.

Clearing the air on surgical plume.

BACKGROUND: Surgical smoke or plume is produced by a variety of surgical coagulators and dissectors. A number of jurisdictions have recently introduced policies to reduce the associated occupational health risks including WorkSafe Victoria and New South Wales Health. METHOD: This paper is a narrative review of potential risks, including any associated with COVID-19, and options for mitigation. RESULTS: Surgical smoke or plume contains potentially toxic chemicals, some of which are carcinogens. Plume may also contain live virus, notably Human Papilloma and Hepatitis B, though any possible viral transmission is limited to a few case reports. Despite identifying COVID-19 ribonucleic acid fragments in various body tissues and fluids there are no current reports of COVID-19 transmission. Although plume is rapidly removed from the atmosphere in modern operating rooms, it is still inhaled by the operative team. Mitigation should include ensuring diathermy devices have evacuators while plume extraction should be standard for laparoscopic procedures. Consideration needs to be given to the potential to compromise the operating field of view, or the noise of the extractor impairing communication. There is an increasing range of suitable products on the market. The future includes pendant systems built into the operating room. CONCLUSION: The potential risks associated with surgical plume cannot be ignored. Health services should invest in plume extraction devices with a view to protecting their staff. The conduct of the operation should not be compromised by the devices chosen. Future operating theatres need to be designed to minimize exposure to plume.

Diagnostic Accuracy of Dual-Layer Spectral CT Using Electron Density Images to Detect Post-Traumatic Prevertebral Hematoma of the Cervical Spine.

PURPOSE: To investigate the diagnostic value of dual-layer spectral detector computed tomography (SDCT) in detecting posttraumatic prevertebral hematoma of the cervical spine by including electron density images. METHODS: 38 patients with post-traumatic imaging of the cervical spine were included in this study and received both SDCT and MRI examinations. MRI was set as the reference and combined conventional/electron density (C + ED) images were compared to conventional CT (CCT) images alone. RESULTS: A total of 18 prevertebral hematomas were identified. Reader 1 identified 14 of 18 and reader 2 15 of 18 prevertebral hematomas by using C + ED reconstructions. Readers 1 and 2 detected 6 and 9 of 18 hematomas on CCT, respectively. CCT showed a sensitivity of 33-50 % and a specificity of 75-80 %, while for C + ED reconstructed images the sensitivity was 77-83 % and the specificity was 85-90 %. Accuracy increased from 55-66 % to 84 % by using C + ED images. The minimum thickness for detecting hematoma on C + ED images was 3 mm. The sizes of prevertebral hematoma on CCT/C + ED were not significantly under- or overestimated compared to the MRI reference. There was a significant difference between the two readers for measuring hematoma sizes on CCT (p = 0.04). Readers showed an excellent inter-rater reliability (kappa = 0.82) for C + ED images and a moderative inter-rater reliability (kappa = 0.44) for CCT. CONCLUSION: With SDCT, the diagnostic accuracy for detecting post-traumatic prevertebral hematoma is improved by using combined conventional and electron density reconstructions compared to conventional images alone. KEY POINTS: · SDCT has a high potential for detecting post-traumatic prevertebral hematomas of the cervical spine by using combined conventional and electron density images.. · Prevertebral hematomas with a thickness of less than 3 mm cannot be reliably identified by SDCT.. · There is no discernible value of conventional SDCT images for diagnosing prevertebral hematoma.. CITATION FORMAT: · Sedaghat S, Langguth P, Larsen N et al. Diagnostic Accuracy of Dual-Layer Spectral CT Using Electron Density Images to Detect Post-Traumatic Prevertebral Hematoma of the Cervical Spine. Fortschr Röntgenstr 2021; 193: 1445 - 1450.

Implementing a standardized and symptom-oriented flowchart "Kielsflow" for advanced cardiac imaging in a 24/7 interdisciplinary emergency department using spectral CT.

This work focuses on implementing a standardized and symptom-oriented flowchart for advanced cardiac imaging in a 24/7 emergency setting using a dual-layer spectral detector CT system. This flowchart was designed to optimize patient management and standardize imaging workflow. It includes acquisition parameters and contrast agent protocols for the most relevant clinical questions regarding cardiac CT imaging in the interdisciplinary emergency department. The automated reconstruction of symptom-oriented spectral images represents an additional strength here. This implementation is designed to be time-efficient and user-friendly and improves diagnostic quality, independent of the qualification level of clinical and technical personnel.

Individuals with type 2 diabetes mellitus show dimorphic and heterogeneous patterns of loss in femoral bone quality.

Type 2 diabetes mellitus (T2DM), a metabolic disease on the rise, is associated with substantial increase in bone fracture risk. Because individuals with T2DM have normal or high bone mineral density (BMD), osteodensitometric measurements of BMD do not predict fracture risk with T2DM. Here, we aim to identify the underlying mechanism of the diabetes-induced fracture risk using a high-resolution multi-scale analysis of human cortical bone with special emphasis on osseous cellular activity. Specifically, we show increased cortical porosity in a subgroup of T2DM individuals accompanied by changed mineralization patterns and glycoxidative damage to bone protein, caused by non-enzymatic glycation of bone by reducing sugar. Furthermore, the high porosity T2DM subgroup presents with higher regional mineralization heterogeneity and lower mineral maturity, whereas in the T2DM subgroup regional higher mineral-to-matrix ratio was observed. Both T2DM groups show significantly higher carboxymethyl-lysine accumulation. Our results show a dimorphic pattern of cortical bone reorganization in individuals afflicted with T2DM and hence provide new insight into the diabetic bone disease leading to increased fracture risk.

Time-dependent Viscoelastic Response of Acetabular Bone and Implant Seating during Dynamic Implantation of Press-fit Cups.

Deformation of an acetabular cup implant during cementless implantation is indicative of the radial compressive forces, and such of the initial implant fixation strength. Stress relaxation in the surrounding bone tissue following implantation could reduce the deformation of the cup and thus primary implant fixation. The aim of this study was therefore to determine the early shape change of the implanted cup immediately after implantation with different press-fit levels and whether recording the force during cup impaction can be used to estimate initial cup fixation. Cup implantations into porcine acetabulae (n=10) were performed using a drop tower. The force induced by the drop weight and cup seating after each impact was recorded. Deformation of the implanted cup was determined with strain gauges over a period of 10min. Lever-out torques were measured to assess the initial fixation strength. Stress relaxation in the bone caused a reduction in cup deformation of 13.52±4.06% after 1min and 29.34±5.11% after 10min. The fixation strength increased with a higher force magnitude during impaction (Rs2=0.810, p=0.037). Reduction of the radial compressive forces due to stress relaxation of the surrounding bone should be considered during press-fit cup implantation in order to compensate for the reduced fixation strength over time. In addition, recording the implantation force could help to estimate initial fixation strength.

The influence of broach design on bone friction and osseodensification in total hip arthroplasty.

BACKGROUND: The process of cavity preparation by broaching has an impact on the primary stability of uncemented hip stems and on the periprosthetic fracture risk. Osseodensifying broaches may increase primary stability, but have the potential to raise cortex strains and facilitate fracture. The aim of this study was to determine the influence of broach design on the forces acting during broaching, on the microstructure of the broached bone bed and the amount and depth of osseodensification. METHODS: Broach models representing compaction, blunt extraction and sharp extraction broaches, were used for quasi-static simulation of femoral cavity preparation on bovine trabecular bone cuboids. Broaching forces were measured and micro-computed tomography scans performed prior and after testing. Friction coefficients during broaching, bone densification parameters and size of the debris particles pushed into the bone were determined. FINDINGS: Friction coefficients during sharp extraction exceeded those during compaction and blunt extraction broaching (by 38% and 37%, P < .001). Total bone densification was enhanced for compaction and blunt extraction compared to sharp extraction broaching (increase of 121% and 117%, P = .005), resulting from higher densification depths for compaction (P = .001) and higher maximum densification for blunt extraction broaching (P = .008), with the latter producing fewer large particles than compaction broaching (P = .005). INTERPRETATION: Higher friction coefficients indicate a decreased periprosthetic fracture risk with sharp extraction broaches for equal implantation forces. The blunt extraction and compaction designs investigated densified the bone to a similar extent. Blunt extraction broaching may support better osseointegration due to smaller bone debris particles.

Responsiveness of a Balance Assessment Using a Mobile Application.

BACKGROUND: Balance assessment is used by clinicians as part of athlete concussion screening. The King-Devick (K-D) Balance app is designed to provide an objective balance assessment value. The purpose of this study was to investigate the responsiveness of a balance assessment using the K-D Balance app. HYPOTHESIS: The K-D Balance app will demonstrate acceptable responsiveness for balance assessment. STUDY DESIGN: Repeated-measures study. LEVEL OF EVIDENCE: Level 5. METHODS: A convenience sample of 25 participants between the ages of 20 and 25 years completed testing procedures. A battery of balance tests using the K-D Balance app on an iPhone were conducted 1 week apart. After a 5-minute warm-up, 3 stances were assessed: double leg, tandem right, and tandem left. The K-D Balance app guided the test positions and test times. A value representing movement was generated by the app algorithm. Analysis included descriptive statistics along with intraclass correlation coefficient and minimal detectable change (MDC). RESULTS: The median score of the K-D test was 0.5 for session 1 and 0.4 for session 2. The ICC was 0.42 (95% CI, 0.04-0.70), and the MDC was 1.58. CONCLUSION: The MDC value of 1.58 represents the threshold of meaningful change in balance, as measured with the K-D Balance app. CLINICAL RELEVANCE: Clinicians can use the results of this study to objectively assess changes in balance over time using the K-D Balance app.

Analysis of the bone ultrastructure around biodegradable Mg-xGd implants using small angle X-ray scattering and X-ray diffraction.

Magnesium alloys are increasingly researched as temporary biodegradable metal implants in bone applications due to their mechanical properties which are more similar to bone than conventional implant metals and the fact that Magnesium occurs naturally within the body. However, the degradation processes in vivo and in particular the interaction of the bone with the degrading material need to be further investigated. In this study we are presenting the first quantitative comparison of the bone ultrastructure formed at the interface of biodegradable Mg-5Gd and Mg-10Gd implants and titanium and PEEK implants after 4, 8 and 12 weeks healing time using two-dimensional small angle X-ray scattering and X-ray diffraction. Differences in mineralization, orientation and thickness of the hydroxyapatite are assessed. We find statistically significant (p < 0.05) differences for the lattice spacing of the (310)-reflex of hydroxyapatite between titanium and Mg-xGd materials, as well as for the (310) crystal size between titanium and Mg-5Gd, indicating a possible deposition of Mg within the bone matrix. The (310) lattice spacing and crystallite size further differ significantly between implant degradation layer and surrounding bone (p < 0.001 for Mg-10Gd), suggesting apatite formation with significant amounts of Gd and Mg within the degradation layer. STATEMENT OF SIGNIFICANCE: Biodegradable Magnesium-based alloys are emerging as a viable alternative for temporary bone implant applications. However, in order to understand if the degradation of the implant material influences the bone ultrastructure, it is necessary to study the bone structure using high-resolution techniques. We have therefore employed 2D small angle X-ray scattering and X-ray diffraction to study the bone ultrastructure surrounding Magnesium-Gadolinium alloys as well as Titanium and PEEK alloys at three different healing times. This is the first time, that the bone ultrastructure around these materials is directly compared and that a statistical evaluation is performed. We found differences indicating a possible deposition of Mg within the bone matrix as well as a local deposition of Mg and/or Gd at the implant site. DATA AVAILABILITY STATEMENT: The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

Deformation of acetabular press-fit cups: Influence of design and surgical factors.

BACKGROUND: Deformation of acetabular cups when press-fitted into an undersized cavity is inevitable due to the inhomogeneous stiffness of acetabular bone. Thinner cups or screw holes might increase the risk of high cup deformation. The aim of this study was to examine the influence of cup design and liner assembly on the deformation response during cup implantation. METHODS: Acetabular cups with different designs were implanted into polyurethane foam models simulating the anatomical situation with nominal press-fits of 1mm and without nominal press-fits (line-to-line). Deformations were determined using a tactile coordinate measuring machine. A 3D laser scanner was used to determine the contact conditions at the cup-cavity interface. Polyethylene and ceramic liners were assembled to the implanted cups and the influence of the insertion on the deformation response evaluated. Fixation strength of the cups was determined by push-out testing. FINDINGS: Cup deformation increased with smaller wall thickness (P < 0.037) and screw holes (P < 0.001). Insertion of ceramic liners reduced the deformation (P < 0.001), whereas polyethylene liners adapted to the deformation of the implanted cups (P > 0.999). Thin-walled cups exhibited a higher fixation strength for similar implantation forces (P = 0.011). INTERPRETATION: Thin-walled cups achieved higher fixation strengths and might be more bone-preserving. However, in combination with screw holes and high press-fit levels, wall thickness should be considered carefully to avoid excessive cup deformations leading to potential complications during liner assembly. Line-to-line insertion of thin-walled cups should be accompanied with a rough surface coating to minimize the loss of fixation strength due to the low press-fit fixation.

Transferrin receptor 2 controls bone mass and pathological bone formation via BMP and Wnt signaling.

Transferrin receptor 2 (Tfr2) is mainly expressed in the liver and controls iron homeostasis. Here, we identify Tfr2 as a regulator of bone homeostasis that inhibits bone formation. Mice lacking Tfr2 display increased bone mass and mineralization independent of iron homeostasis and hepatic Tfr2. Bone marrow transplantation experiments and studies of cell-specific Tfr2 knockout mice demonstrate that Tfr2 impairs BMP-p38MAPK signaling and decreases expression of the Wnt inhibitor sclerostin specifically in osteoblasts. Reactivation of MAPK or overexpression of sclerostin rescues skeletal abnormalities in Tfr2 knockout mice. We further show that the extracellular domain of Tfr2 binds BMPs and inhibits BMP-2-induced heterotopic ossification by acting as a decoy receptor. These data indicate that Tfr2 limits bone formation by modulating BMP signaling, possibly through direct interaction with BMP either as a receptor or as a co-receptor in a complex with other BMP receptors. Finally, the Tfr2 extracellular domain may be effective in the treatment of conditions associated with pathological bone formation.

The influence of cavity preparation and press-fit cup implantation on restoring the hip rotation center.

BACKGROUND: Reaming of the acetabular cavity and cup implantation directly influence the hip rotation center and contact area between implant and bone. Previous studies have reported on an altered rotation center after total hip arthroplasty, but have not studied the influence of reaming and cup implantation separately. Aim of this study was therefore to analyze the individual influence of acetabular reaming and subsequent cup implantation on the rotation center and how this influences the contact conditions at the bone-implant interface. METHODS: Acetabular press-fit cups were implanted into the left and right hips of three full cadavers (n = 6). CT scans were performed to calculate the change in hip rotation center after reaming and prior to liner insertion. 3D models of the cups were used to determine the polar gap, the contact conditions and the effective press-fit. FINDINGS: Reaming the acetabular cavity shifted the rotation center medially (median 5.8 mm, range 4.8-9.1), superiorly (5.3 mm, 3.0-7.0) and posteriorly (2.9 mm, 1.0-5.3). With cup implantation, the rotation center shifted back towards the native position, but no full restoration was observed. The degree of shift increased with the size of polar gap (rs = 0.829, P = .042), which inversely reduced the contact area (rs = 0.886, P = .019). INTERPRETATION: This study reveals that the dominant factor in hip rotation center restoration is the reaming process, while the cup implantation for a given nominal press-fit has only a small influence. Increasing the press-fit would improve the restoration but bares the danger of insufficient bone coverage and periprosthetic fractures due to the high forces needed.