Clinical, functional and radiographic long-term follow-up (7-12 years) of Birmingham Hip Resurfacing, including metal ions evaluation: a single surgeon series.

Hip resurfacing arthroplasty (HRA) has been advocated as an attractive therapy for a younger, more demanding patient population with debilitating hip osteoarthritis. Controversies surrounding metal-on-metal (MoM) hip resurfacing have, however, led to a significant decline in the popularity of the HRA. Despite this, substantial evidence supports the use of specific implants in a selected group of patients. This is a continued retrospective analysis of a single surgeon series of the Birmingham Hip Resurfacing (BHR). Initial medium-term analysis was done in 2011 and published by Van der Bracht et al.13. This analysis includes a long-term follow-up of 7 to 12 years, including functional scoring (HHS, HOOS and UCLA activity score), metal ion evaluation and survival analysis. Failure was defined as revision for any cause. A total of 267 resurfacing procedures with the BHR were included in 247 patients. We had a mean follow-up of 8.3 years. Overall survival at ten years was 94.8%(97.2% for males and 90.1% for females). There was a statistically significant increase in mean HHS score at follow-up (56.03 - IQR 47-65 to 96.07 - IQR 96-100). Elevated metal ions were correlated with a statistically significant increase in the probability of complications. This cohort study further proved that hip resurfacing arthroplasty with the Birmingham Hip Resurfacing implant provides a good alternative to conventional total hip arthroplasty in young patients. There was a significant increase in functional scores at follow-up. There is further evidence of less favorable outcomes in female patients.

Prevalence and risk factors of scapular stress fracture after reverse shoulder arthroplasty: a multicentric retrospective study.

PURPOSE: Scapular stress fracture (sSF) is a difficult complication to treat after reverse total shoulder arthroplasty (RSA). The aim of this study was to identify the prevalence and possible risk factors in a large population. METHODS: A total of 2165 RSAs that were implanted between January 2006 and October 2017 in five hospitals were evaluated. Within this cohort, sSF was radiologically confirmed. Age, gender, surgical indication and hospital of treatment were determined for the entire cohort. A matched 3:1 case-control study was then performed to investigate several clinical and surgical variables. RESULTS: sSF occurred in 3.1% (63 patients), with a median time interval of five months post-operative [IQR = 9, range: (1-79)]. Within the entire cohort, females (OR = 2.99) and rotator cuff arthropathy (RCA) (OR = 2.79) were more prone to this complication. Age had little influence (OR = 1.03). After exclusion, fifty-five eligible cases were matched to 165 controls based on hospital, gender, age and surgical indication. After univariable analysis, significance was obtained for osteopenia (P = 0.037), osteoporosis (P = 0.032), surgical approach (P = 0.002) and peri-operative acromioclavicular (AC) joint surgery (P = 0.035). Multivariate analysis demonstrated that osteopenia (OR = 3.94), osteoporosis (OR = 2.85) and a deltopectoral approach (OR = 3.70) were independent risk factors. CONCLUSION: According to our findings, older women with poor bone quality and a history of RCA suffered more frequently from sSF. Anterolateral approach during surgery was a surgical protective factor, possibly due to the mobilization of the acromioclavicular joint. Although this study indicates who is at risk for sSF, further investigation for prevention of sSF in these patients is necessary.

Analysis of medium-range order based on simulated segmented ring detector STEM-images: amorphous Si.

Properties of amorphous materials are connected to the local structure at the nanoscale, which is typically described in terms of short- and medium-range order (SRO, MRO). Variable resolution fluctuation electron microscopy (VR-FEM) is a sensitive method to characterize the underlying characteristic length scale of MRO of amorphous samples (Voyles, Gibson and Treacy, J. Electron Microsc. 49 (2000) 259). VR-FEM data was acquired using scanning transmission electron microscopy (STEM), collecting a large number of nano-beam diffraction patterns (NBDPs) with various probe sizes. Here we present an advanced method to accelerate the calculation of simulated FEM normalized variance profiles using a newly developed simulation and analysis approach with segmented ring detectors using the program STEMcl (Radek et al., Ultramicroscopy 188 (2018) 24). VR-FEM simulations are based on structures obtained from molecular dynamics (MD) simulations. A comparison between simulated and experimental VR-FEM profiles with respect to peak position, ratio and shape (and intensity) show good agreement. Moreover, a crystalline cluster of 1 nm in size was embedded into the MD box to test the validity of the paracrystalline approximation with the pair-persistence analysis suggested by Gibson et al. (Gibson, Treacy and Voyles, Ultramicroscopy 83 (2000) 169). The corresponding VR-FEM simulation and calculation of MROs yield close results to the size of the initially embedded crystalline cluster, which supports both the paracrystalline approach and the validity of the segmented detector simulation. Additionally, we conclude that continuous random network (CRN) amorphous silicon models contain a higher degree of MRO than experimentally expected.

Self-Diffusion in Amorphous Silicon by Local Bond Rearrangements.

Experiments on self-diffusion in amorphous silicon (Si) were performed at temperatures between 460 to 600° C. The amorphous structure was prepared by Si ion implantation of single crystalline Si isotope multilayers epitaxially grown on a silicon-on-insulator wafer. The Si isotope profiles before and after annealing were determined by means of secondary ion mass spectrometry. Isothermal diffusion experiments reveal that structural relaxation does not cause any significant intermixing of the isotope interfaces whereas self-diffusion is significant before the structure recrystallizes. The temperature dependence of self-diffusion is described by an Arrhenius law with an activation enthalpy Q=(2.70±0.11) eV and preexponential factor D_{0}=(5.5_{-3.7}^{+11.1})×10^{-2} cm^{2} s^{-1}. Remarkably, Q equals the activation enthalpy of hydrogen diffusion in amorphous Si, the migration of bond defects determining boron diffusion, and the activation enthalpy of solid phase epitaxial recrystallization reported in the literature. This close agreement provides strong evidence that self-diffusion is mediated by local bond rearrangements rather than by the migration of extended defects as suggested by Strauß et al. (Phys. Rev. Lett. 116, 025901 (2016)PRLTAO0031-900710.1103/PhysRevLett.116.025901).

[Antibiotic stewardship : Measures for optimizing prescription of anti-infective agents]. / "Antibiotic Stewardship" : Maßnahmen zur Optimierung der Verordnung von Antiinfektiva.

Antibiotic stewardship (ABS) comprises a bundle of different interventions to improve anti-infective treatment in a hospital setting. An important component of ABS interventions is the interdisciplinary approach to infection management. Besides improving infrastructural aspects on a hospital level, including surveillance of the use of anti-infective agents and nosocomial infections, collation and interpretation of statistics on resistance and formulation of local treatment guidelines, ABS teams go to the wards and advise treating physicians on antibiotic therapy. Frequent approaches for optimization are selection of substances, administration route, dosing of medication and duration of treatment. An important overall objective of ABS is the reduction of resistance induction in order to preserve the therapeutic efficiency of antibiotics. A number of studies have shown that this goal can be achieved in different clinical settings without negatively affecting patient outcome. The strategies of ABS can also be applied with no problems to critically ill patients on the intensive care unit.

Vacancy-donor complexes in highly n-type Ge doped with As, P and Sb.

Positron annihilation spectroscopy was performed to study defects in Ge doped with As, P and Sb. In each case, the samples had approximately the same dopant concentration ∼10(19) cm(-3). Results from the Doppler broadening and positron lifetime spectroscopies were compared to electronic structure calculations. The positron lifetime results show that the open volume related to the defect centers is not larger than a monovacancy. The results suggest that in the As doped sample the dominant trap at room temperature is a complex consisting of a vacancy and at least three dopant atoms. In the case of P doped Ge the results indicate that two defect complexes compete in positron trapping. Complexes with a higher number of P atoms around the vacancy seem to dominate at room temperature whereas at low temperature positron trapping at centers with fewer P atoms around the vacancy becomes more significant. The complexes with fewer P atoms are more negatively charged. In Sb doped Ge the results suggest that several types of traps are simultaneously competing in positron trapping at all measurement temperatures.

Missed diagnosis of false aneurysm of the superficial femoral artery after closed complex fracture of the distal femur.

This case report presents a 38-year-old male patient who developed a false aneurysm of the superficial femoral artery after minimally invasive plate internal fixation of a comminuted articular distal femoral fracture sustained in a motor vehicle accident. Two days after surgery, the patient developed pain, non-pulsatile swelling on the medial side of the knee and anemia. After about six weeks, diagnosis of false aneurysm of the superficial femoral artery was confirmed by duplex ultrasound and computed tomographic angiography. A percutaneous endovascular procedure was performed to treat the false aneurysm without evacuating the blood collection.

Anatomic single-bundle ACL surgery: consequences of tibial tunnel diameter and drill-guide angle on tibial footprint coverage.

PURPOSE: To investigate the consequences of differences in drill-guide angle and tibial tunnel diameter on the amount of tibial anatomical anterior cruciate ligament (ACL) footprint coverage and the risk of overhang of the tibial tunnel aperture over the edges of the native tibial ACL footprint. METHODS: Twenty fresh-frozen adult human knee specimens with a median age of 46 years were used for this study. Digital templates mimicking the ellipsoid aperture of tibial tunnels with a different drill-guide angle and a different diameter were designed. The centres of these templates were positioned over the geometric centre of the tibial ACL footprint. The amount of tibial ACL footprint coverage and overhang was calculated. Risk factors for overhang were determined. Footprint coverage and the risk of overhang were also compared between a lateral tibial tunnel and a classic antero-medial tibial tunnel. RESULTS: A larger tibial tunnel diameter and a smaller drill-guide angle both will create significant more footprint coverage and overhang. In 45% of the knees, an overhang was created with a 10-mm diameter tibial tunnel with drill-guide angle 45°. Furthermore, a lateral tibial tunnel was found not to be at increased risk of overhang. CONCLUSION: A larger tibial tunnel diameter and a smaller drill-guide angle both will increase the amount of footprint coverage. Inversely, larger tibial tunnel diameters and smaller drill-guide angles will increase the risk of overhang of the tibial tunnel aperture over the edges of the native tibial ACL footprint. A lateral tibial tunnel does not increase the risk of overhang.

Can a tibial tunnel in ACL surgery be placed anatomically without impinging on the femoral notch? A risk factor analysis.

PURPOSE: To analyze anatomical risk factors and surgical technique dependent variables, which determine the risk for femoral notch impingement in anatomically correct placed tibial tunnels for anterior cruciate ligament (ACL) surgery. METHODS: Twenty fresh frozen adult human knee specimens under the age of 65 years were used. Digital templates mimicking a tibial tunnel aperture at the tibia plateau were designed for different tibial tunnel diameters and different drill-guide angles. The centres of these templates were placed over the geometric centre of the native tibial ACL footprint. The distances between the anterior borders of the templates and the anterior borders of the footprints (graft free zone) were measured and compared. Furthermore, anatomic risk factors for femoral notch impingement were determined. RESULTS: The graft free zone was statistically significantly longer for larger drill-guide angles compared to smaller drill-guide angles (p < 0.00001). Furthermore, 8 mm diameter tibial tunnels had a statistically significant larger graft free zone compared to 10-mm-diameter tibial tunnels (p < 0.00001). For the 10 mm diameter tibial tunnels with drill-guide angle of 45°, 9 out of 20 knees (45 %) were "at risk" for notching and 4 out of 20 knees (20 %) had "definite" notching. For 10-mm tunnels with drill-guide angle of 45°, a risk for notching was associated with smaller tibial ACL footprint (p < 0.05). CONCLUSION: If a perfect centrally positioned tibial tunnel is drilled, a real risk for femoral notch impingement exists depending on the size of the tibial ACL footprint and surgery-related factors. Therefore, in anatomical tibial tunnel placement in single bundle ACL reconstruction surgery, particular attention should be paid to size of the tunnel and drill-guide angle to minimize the risk of femoral notch impingement.

Indications and limits of meniscal allografts.

Meniscal allograft transplantation has emerged as a useful treatment for carefully selected patients. The aim of this review of meniscal allograft transplantation is to put this procedure into a clinical perspective. Since there still is a lack of consensus on how the success of meniscal transplantation should be evaluated it is difficult to compare study outcomes. Nevertheless, almost all studies report an increase in patient satisfaction and improvement in pain and function. Clinical and functional outcome is improved in the majority of patients. Progression of cartilage degeneration according to MRI and radiological criteria was halted in a number of patients, indicating a chondroprotective effect. Joint space narrowing is only significantly progressive at long-term follow-up. On magnetic resonance imaging, shrinkage is seen after some years, but more in lyophilized allografts. Second-look arthroscopy usually shows good healing to the capsule. Overall, the clinical results of this type of surgery are encouraging and long-lasting in a well selected patient population who suffered a total meniscectomy. Meniscal allografting appears to becoming the golden standard therapy for these type of patients.

Point defect engineering strategies to retard phosphorous diffusion in germanium.

The diffusion of phosphorous in germanium is very fast, requiring point defect engineering strategies to retard it in support of technological application. Density functional theory corroborated with hybrid density functional calculations are used to investigate the influence of the isovalent codopants tin and hafnium in the migration of phosphorous via the vacancy-mediated diffusion process. The migration energy barriers for phosphorous are increased significantly in the presence of oversized isovalent codopants. Therefore, it is proposed that tin and in particular hafnium codoping are efficient point defect engineering strategies to retard phosphorous migration.

Oxygen transport and mitochondrial function in porcine septic shock, cardiogenic shock, and hypoxaemia.

INTRODUCTION: The relevance of tissue oxygenation in the pathogenesis of organ dysfunction during sepsis is controversial. We compared oxygen transport, lactate metabolism, and mitochondrial function in pigs with septic shock, cardiogenic shock, or hypoxic hypoxia. METHODS: Thirty-two anaesthetized, ventilated pigs were randomized to faecal peritonitis (P), cardiac tamponade (CT), hypoxic hypoxia (HH) or controls. Systemic and regional blood flows, lactate, mitochondrial respiration, and tissue hypoxia-inducible factor 1 alpha (HIF-1α) were measured for 24 h. RESULTS: Mortality was 50% in each intervention group. While systemic oxygen consumption (VO(2) ) was maintained in all groups, hepatic VO(2) tended to decrease in CT [0.84 (0.5-1.3) vs. 0.42 (0.06-0.8)/ml/min/kg; P = 0.06]. In P, fractional hepatic, celiac trunk, and portal vein blood flows, and especially renal blood flow [by 46 (14-91)%; P = 0.001] decreased. In CT, renal blood flow [by 50.4 (23-81)%; P = 0.004] and in HH, superior mesenteric blood flow decreased [by 38.9 (16-100)%, P = 0.009]. Hepatic lactate influx increased > 100% in P and HH, and > 200% in CT (all P < 0.02). Hepatic lactate uptake remained unchanged in P and HH and converted to release in CT. Mitochondrial respiration remained normal. Muscle adenosine triphosphate (ATP) concentrations decreased in P (5.9 ± 1.4 µmol/g wt vs. 2.8 ± 2.7 µmol/g wt, P = 0.04). HIF-1α expression was not detectable in any group. CONCLUSION: We conclude that despite shock and renal hypoperfusion, tissue hypoxia is not a major pathophysiological issue in early and established faecal peritonitis. The reasons for reduced skeletal muscle tissue ATP levels in the presence of well-preserved in-vitro muscle mitochondrial respiration should be further investigated.

The effect of propofol and desflurane anaesthesia on human hepatic blood flow: a pilot study.

This study tested the hypothesis that propofol is associated with a higher hepatic blood flow in humans compared with desflurane. Using a cross over study design, 10 patients received first propofol and then desflurane, and a further 10 patients received desflurane and then propofol. Blood flow index in the right and middle hepatic veins, stroke volume index and cardiac index were assessed by transoesophageal echocardiography. Mean arterial blood pressure, stroke volume index and cardiac index were the same in both groups. Propofol was associated with significantly greater blood flow index in the right hepatic vein (median (IQR [range]) 199 (146-237 [66-388]) vs. 149 (112-189 [42-309]) ml.min(-1).m(-2); p = 0.005) and middle hepatic vein (150 (122-191 [57-341]) vs. 125 (92-149 [47-362]) ml.min(-1).m(-2); p < 0.001) compared with desflurane. In routine clinical conditions, propofol anaesthesia was associated with significantly greater hepatic blood flow than desflurane anaesthesia.

Is there any superiority in the clinical outcome of mobile-bearing knee prosthesis designs compared to fixed-bearing total knee prosthesis designs in the treatment of osteoarthritis of the knee joint? A review of the literature.

To substantiate the validity and relevance of the mobile-bearing knee prosthesis design compared to the fixed-bearing design, concerning the clinical outcome, this review was conducted. Articles published in 6 major orthopaedic journals were screened. Only randomized controlled trials, which investigate the clinical outcome, were included. The clinical outcome parameters of each study were analysed. Despite the numerous quantities of publications in orthopaedic literature, we could conclude, that only a few of them are randomized controlled trials. Although better kinematics of mobile-bearing knee prosthesis designs compared to fixed-bearing knee prosthesis designs are reported, no superiority of one of the bearing designs concerning clinical outcome could be revealed. Because no superiority of one of the designs concerning revision rate, survival and outcome can be found, the cheaper one should be the one to be recommended. For this reason, we advise that further research, comparing the costs and cost-benefit of mobile-bearing compared to fixed-bearing knee prosthesis designs, should be performed.

Efficacy of an extracorporeal endotoxin adsorber system during hyperdynamic porcine endotoxemia.

BACKGROUND: Endotoxemia is a crucial factor in the pathogenesis of sepsis. Elimination of endotoxin is aimed at the reduction of sepsis-related morbidity and lethality. The objective of this study was to examine the impact of an endotoxin adsorber on hemodynamics, O(2) exchange and metabolism during resuscitated porcine endotoxemia. METHODS: Twenty pigs were randomized into 2 intervention groups (n = 7 each) and 1 control group (n = 6). Endotoxemia was induced by continuous intravenous application of lipopolysaccharide for 8 h. Adsorber therapy was started at the same time as the induction of endotoxemia or 2 h later. An extracorporeal hemoperfusion device using immobilized human serum albumin for endotoxin adsorption was used. RESULTS: Hemodynamic, metabolic and acid-base parameters, as well as the kinetics of interleukin (IL)-6, IL-8, IL-10 and tumor necrosis factor-alpha, were characteristic for endotoxic shock. Endotoxin plasma levels were low (arterial, hepatic and portal vein). None of the parameters were significantly influenced by the adsorber system. CONCLUSION: Despite typical clinical signs of endotoxemia, the adsorber system had no significant effect on hemodynamic, metabolic and acid-base parameters during endotoxic shock. The reasons for the absence of an effect are elusive; however, failure of the method per se or exceeded capacity of the adsorber cannot be excluded.

Interstitial-mediated diffusion in germanium under proton irradiation.

We report experiments on the impact of 2.5 MeV proton irradiation on self-diffusion and dopant diffusion in germanium (Ge). Self-diffusion under irradiation reveals an unusual depth independent broadening of the Ge isotope multilayer structure. This behavior and the observed enhanced diffusion of B and retarded diffusion of P demonstrates that an interstitial-mediated diffusion process dominates in Ge under irradiation. This fundamental finding opens up unique ways to suppress vacancy-mediated diffusion in Ge and to solve the donor deactivation problem that hinders the fabrication of Ge-based nanoelectronic devices.

Time- and dose-related regional fluxes of tissue-type plasminogen activator in anesthetized endotoxemic pigs.

BACKGROUND: Acute endotoxinemia elicits an early fibrinolytic response. This study analyzes the effects of the dose and duration of endotoxin infusion on arterial levels of tissue-type plasminogen activator (tPA) and pulmonary, mesenteric and hepatic plasma tPA fluxes. METHODS: Pigs were randomized to receive an acute, high-dose (for 6 h, n=13, high ETX) or a prolonged, low-dose (for 18 h, n=18, low ETX) infusion of endotoxin or saline vehicle alone (for 18 h, n=14, control). All animals were fluid resuscitated to maintain a normodynamic circulation. Systemic and regional blood flows were measured and arterial, pulmonary arterial, portal and hepatic venous blood samples were analyzed to calculate regional net fluxes of tPA. Plasma tumor necrosis factor (TNF-alpha) levels were analyzed. RESULTS: Mesenteric tPA release and hepatic uptake increased maximally at 1.5 h in ETX groups related to dose. Maximal mesenteric tPA release [high ETX 612 (138-1185) microg/min/kg, low ETX 72 (32-94) microg/min/kg, median+/-interquartile range] and hepatic tPA uptake [high ETX -1549 (-1134 to -2194) microg/min/kg, low ETX -153 (-105 to -307) microg/min/kg] correlated to TNF-alpha levels. Regional tPA fluxes returned to baseline levels at 6 h in both ETX groups and also remained low during sustained low ETX. No changes were observed in control animals. CONCLUSIONS: Endotoxemia induces an early increase in mesenteric tPA release and hepatic tPA uptake related to the severity of endotoxemia. The time patterns of changes in mesenteric and hepatic tPA fluxes are similar in acute high-dose endotoxemia and sustained low-dose endotoxemia.

Barium diffusion in mixed cation glasses.

Diffusion of barium (Ba) in mixed cation glasses of the composition xNa2O x (3 - x)BaO.4SiO2 with x = 0.0, 0.1, 0.3 and 1.0 and 0.4K2O.2.6BaO.4SiO2 was investigated by means of the radiotracer diffusion technique below the respective glass transition temperatures. In accord with our previous results of calcium (Ca) diffusion in soda-lime silicate glasses (F. Natrup et al., Phys. Chem. Chem. Phys., 2005, 7, 2279), the mobility of alkaline-earth ions increases with the alkali content in all analyzed glass systems with no decrease in the diffusion activation enthalpy, but a raise in the pre-exponential factor. A distinct dependency of the activation enthalpy of alkaline-earth ions on the type and content of the alkali ions in the glass is observed. The results provide evidence for elastic and electrostatic contributions to cation diffusion in glasses and support the formation of dissimilar cation pairs, that were derived from nuclear magnetic resonance (NMR) investigations of soda-lime silicate glasses and glasses containing sodium and barium. Finally, a striking correlation between the pre-exponential factor of alkaline-earth ion diffusion in soda-lime and potassium barium glasses is found, the origin of which remains unsolved.

Oxygen extraction in pigs subjected to low-dose infusion of endotoxin after major abdominal surgery.

BACKGROUND: Sepsis may impair O(2) extraction due to blood flow redistribution or decreased utilization of the available oxygen. METHODS: We assessed the effect of endotoxemia on systemic and regional O(2) extraction and lactate handling in pigs, randomized to receive either endotoxin (0.4 microg kg(-1) h(-1); n = 10) or saline infusion (controls; n = 9) for 12 h. RESULTS: High baseline regional and systemic O(2) extraction in the endotoxin group (median 56%, range 45-77%) and in the controls (67%, 49-72%) was maintained until the end of the experiment (endotoxin group: 60%, 50-71%; controls: 60%, 50-74%) despite hypotension and a decrease in stroke volume in endotoxic animals. Hepatic lactate exchange decreased during endotoxemia from 14 micromol kg(-1) min(-1) (range 10-28 micromol kg(-1) min(-1)) to 10 (range 3-15) micromol kg(-1) min(-1); P < 0.01), but remained stable in the controls, with 13 micromol min(-1) (4-18 micromol min(-1)) at baseline and 7 micromol min(-1) (3-17 micromol min(-1)) after 12 h of saline infusion. CONCLUSIONS: The high and sustained oxygen consumption and oxygen extraction in this endotoxemic model speak against any major impairment of hepatosplanchnic or systemic oxygen extraction and oxidative metabolism. The reduced hepatic lactate exchange despite an unchanged hepatic lactate influx suggests altered metabolic activities independent of oxygen consumption.

Cation diffusion and ionic conductivity in soda-lime silicate glasses.

We have studied the mobilities of calcium and sodium ions in silicate glasses of compositions xNa2O (3 - x)CaO x 4SiO2 with x = 0.0, 0.1, 0.3, 1.0 and 3.0 by means of radiotracer diffusion, electrical conductivity measurements, and dynamic mechanical thermal analyses. In glasses containing sodium oxide, the Na+ ions are much more mobile than the Ca2+ ions, and are, therefore, governing the electrical conductivity. In the pure calcium silicate glass, the activation energy of Ca2+ diffusion is higher than the activation energy of the electrical conductivity. This provides strong evidence that the electrical conductivity of this glass is not determined by the migration of Ca2+ ions, but by impurity charge carriers, which are most likely Na+ ions. We sketch the composition-dependent mobilities of Na+ and Ca2+ ions in soda-lime silicate glasses with variable Na2O and CaO content. Our results indicate that the coordination environment of Ca2+ ions remains unchanged when CaO is replaced by Na2O which is consistent with recent results of molecular dynamic simulations. Moreover, our results confirm the formation of dissimilar Na-Ca pairs which lead to a non-random mixing of the cations in the glass. The formation of such pairs was recently deduced from nuclear magnetic resonance spectra of soda-lime silicate glasses.