Long-term follow-up of total hip arthroplasty using polyethylene-ceramic composite (sandwich) liner.

INTRODUCTION: Ceramic-on-ceramic bearings have been widely used since their introduction in the 1970s. First-generation ceramics have very high fracture (breakage) rates. To overcome this, in the 1990s, modular cotyloid insert designs were developed, consisting of a ceramic and polyethylene composite (sandwich-type) liner; however, high implant fracture rates were observed in the medium term. We aimed to estimate the cumulative incidences of revision surgery (implant failure) and implant failure due to fractures, survival rates (time-to-revision surgery and time-to-fracture), and the long-term clinical and radiological outcomes in our series. METHODS: This was an observational, longitudinal, ambispective, single-centre study based on patients who underwent primary total hip arthroplasty (THA) using a sandwich-type liner (Cerasul), only available in our tertiary hospital between January 1999 and December 2002. Cumulative incidences were estimated and the 95% confidence interval (95% CI) was calculated. The Kaplan-Meier method was used to assess the time-to-revision surgery and time-to-fracture. RESULTS: 54 patients (49 men) were included, accounting for 59 sandwich-type linear implants. The mean (range) age was 47.4 (22-57) years. The primary THA indications were osteoarthritis (28 patients), osteonecrosis (14), childhood pathology sequelae (11), and inflammatory arthritis (6). The cumulative incidence of revision surgery by implants was 8.5% (5/59, 95% CI, 3.5-19.2%), 9.3% by patients (5/54, 95% CI, 4.0-19.9%), and 5.1% by implant fractures (3/59, 95%CI, 1.7-13.9%). The median (Interquartile Range, IQR) time-to-revision surgery was 158 (72.5-161) months, and the time to fracture was 182 (138-215) months. All primary THAs had good clinical and long-term survival outcomes. All implants had signs of solid fixation. CONCLUSIONS: After a 20-year follow-up period, the polyethylene-ceramic sandwich-type liner showed a long survival rate and low cumulative incidence of implant fracture; however, implant fractures remain the main complication. Orthopaedic surgeons should be aware that some patients still have this type of prosthesis and must be capable of responding quickly if a fracture occurs.

Late Breakage of a Dual-Mobility Polyethylene Insert in a Revision Total Hip Arthroplasty: An Unusual Failure Mode.

The use of dual-mobility cups has gained popularity in recent years. Thus, surgeons can expect an increase in known and new causes of failure. We report a previously undescribed form of a late intraprosthetic dislocation consisting of a complete breakage of a polyethylene mobile bearing that suffered a dislocation 3 months after its implantation. Two years later, he began feeling anterior groin pain and suffered gait changes. Computed tomography scan revealed an eccentric alignment of the mobile polyethylene bearing suggestive of poly wear. During the revision surgery, the polyethylene was found to be split in 2. Possible causes of this complication are proposed. Our case shows a previously unreported implant-specific complication, so surgeons can identify it.

Blood Stasis Imaging Predicts Cerebral Microembolism during Acute Myocardial Infarction.

BACKGROUND: Cardioembolic stroke is a major source of mortality and disability worldwide. The authors hypothesized that quantitative characterization of intracardiac blood stasis may be useful to determine cardioembolic risk in order to personalize anticoagulation therapy. The aim of this study was to assess the relationship between image-based metrics of blood stasis in the left ventricle and brain microembolism, a surrogate marker of cardiac embolism, in a controlled animal experimental model of acute myocardial infarction (AMI). METHODS: Intraventricular blood stasis maps were derived from conventional color Doppler echocardiography in 10 pigs during anterior AMI induced by sequential ligation of the mid and proximal left anterior descending coronary artery (AMI-1 and AMI-2 phases). From these maps, indices of global and local blood stasis were calculated, such as the average residence time and the size and ratio of contact with the endocardium of blood regions with long residence times. The incidence of brain microemboli (high-intensity transient signals [HITS]) was monitored using carotid Doppler ultrasound. RESULTS: HITS were detected in 0%, 50%, and 90% of the animals at baseline and during AMI-1 and AMI-2 phases, respectively. The average residence time of blood in the left ventricle increased in parallel. The residence time performed well to predict microemboli (C-index = 0.89, 95% CI, 0.75-1.00) and closely correlated with the number of HITS (R = 0.87, P < .001). Multivariate and mediation analyses demonstrated that the number of HITS during AMI phases was best explained by stasis. Among conventional echocardiographic variables, only apical wall motion score weakly correlated with the number of HITS (R = 0.3, P = .04). Mural thrombosis in the left ventricle was ruled out in all animals. CONCLUSIONS: The degree of stasis of blood in the left ventricle caused by AMI is closely related to the incidence of brain microembolism. Therefore, stasis imaging is a promising tool for a patient-specific assessment of cardioembolic risk.

The natural matching of harmonic responses in the pulmonary circulation.

KEY POINTS: The right ventricle of the mammal heart is highly sensitive to the afterload imposed by a combination of the pulmonary circulation and the retrograde contribution of the left heart. Right ventricular afterload can be analysed in terms of pulmonary artery input impedance, which we were able to decompose as the result of the harmonic frequency responses of the pulmonary vessels and the left heart attached in series. Using spectral methods, we found a natural matching between the pulmonary vasculature and the left chambers of the heart. This coupling implies that the upstream transmission of the left heart frequency-response has favourable effects on the pulmonary tree. This physiological mechanism protects the right ventricle against acute changes in preload, and its impairment may be a relevant contribution to right ventricle dysfunction in pulmonary hypertension. ABSTRACT: The right ventricle (RV) of the mammal heart is highly sensitive to the afterload imposed by the pulmonary circulation, and the left heart (LH) retrogradely contributes significantly to this vascular load. Transmission-line theory anticipates that the degree of matching between the frequency responses of the pulmonary vasculature and the LH should modulate the global right haemodynamic burden. We measured simultaneous high-fidelity flow (pulmonary artery) and pressure (pulmonary artery and left atrium) in 18 healthy minipigs under acute haemodynamic interventions. From these data, we decomposed the impedance spectra of the total right-circulation system into the impedance of the pulmonary vessels and the harmonic response of the LH. For frequencies above the first harmonic, total impedance was below the pulmonary impedance during all phases (P < 0.001; pooled phases), demonstrating a favourable effect of the LH harmonic response on RV pulsatile load: the LH harmonic response was responsible for a 20% reduction of pulse pulmonary artery pressure (P < 0.001 vs. a theoretical purely-resistive response) and a 15% increase of pulmonary compliance (P = 0.009). This effect on compliance was highest during acute volume overload. In the normal right circulation, the longitudinal impedance of the pulmonary vasculature is matched to the harmonic response of the LH in a way that efficiently reduces the pulmonary pulsatile vascular load. This source of interaction between the right and left circulations of mammals protects the RV against excessive afterload during acute volume transients and its disruption may be an important contributor to pulmonary hypertension.

Age-Dependence of Flow Homeostasis in the Left Ventricle.

Background: Intracardiac flow homeostasis requires avoiding blood stasis and platelet activation during its transit through the cardiac chambers. However, the foundations of intraventricular blood washout and its exposure to shear stresses have been poorly addressed. We aimed to characterize and quantify these features in a wide population of healthy subjects and assess the relationships of these indices with age. Methods: We used color-Doppler echocardiography and custom post-processing methods to study 149 healthy volunteers from 26 days to 80 years old. From the intraventricular flow-velocity fields we obtained personalized maps of (1) the residence time of blood in the LV, and (2) the shear index, a metric accounting for the strongest occurrence of shear stresses inside the chamber. From these maps we derived quantitative indices of the overall intraventricular blood washout and shear exposure. We addressed the age-dependence of these indices and analyzed their relationship with age-related changes in filling-flow. Results: The entire intraventricular blood pool was replaced before 8 cycles. Average residence time of blood inside the LV was <3 cycles in all subjects and followed an inverse U-shape relationship with age, increasing from median (IQR) of 1.0 (0.7 to 1.2) cycles in the 1st year of life to 1.8 (1.4-2.2) cycles in young adults (17-30 years old), becoming shorter again thereafter. Shear index showed no relation with age and was bounded around 20 dyn·s/cm2. Regions with the longest residence time and highest shear index were identified near the apex. Differences in the degree of apical penetration of the filling waves and the duration of the late-filling phase explained the age-dependence of residence time ( R adj 2 = 0.48, p < 0.001). Conclusions: In average, blood spends 1 to 3 beats inside the LV with very low shear stress rates. The apical region is the most prone to blood stasis, particularly in mid-aged adults. The washout of blood in the normal LV is age-dependent due to physiological changes in the degree of apical penetration of the filling waves.

Systemic vascular load in calcific degenerative aortic valve stenosis: insight from percutaneous valve replacement.

BACKGROUND: Systemic arterial load impacts the symptomatic status and outcome of patients with calcific degenerative aortic stenosis (AS). However, assessing vascular properties is challenging because the arterial tree's behavior could be influenced by the valvular obstruction. OBJECTIVES: This study sought to characterize the interaction between valvular and vascular functions in patients with AS by using transcatheter aortic valve replacement (TAVR) as a clinical model of isolated intervention. METHODS: Aortic pressure and flow were measured simultaneously using high-fidelity sensors in 23 patients (mean 79 ± 7 years of age) before and after TAVR. Blood pressure and clinical response were registered at 6-month follow-up. RESULTS: Systolic and pulse arterial pressures, as well as indices of vascular function (vascular resistance, aortic input impedance, compliance, and arterial elastance), were significantly modified by TAVR, exhibiting stiffer vascular behavior post-intervention (all, p < 0.05). Peak left ventricular pressure decreased after TAVR (186 ± 36 mm Hg vs. 162 ± 23 mm Hg, respectively; p = 0.003) but remained at >140 mm Hg in 70% of patients. Wave intensity analysis showed abnormally low forward and backward compression waves at baseline, increasing significantly after TAVR. Stroke volume decreased (-21 ± 19%; p < 0.001) and correlated with continuous and pulsatile indices of arterial load. In the 48 h following TAVR, a hypertensive response was observed in 12 patients (52%), and after 6-month follow-up, 5 patients required further intensification of discharge antihypertensive therapy. CONCLUSIONS: Vascular function in calcific degenerative AS is conditioned by the upstream valvular obstruction that dampens forward and backward compression waves in the arterial tree. An increase in vascular load after TAVR limits the procedure's acute afterload relief.

The role of elastic restoring forces in right-ventricular filling.

AIMS: The physiological determinants of RV diastolic function remain poorly understood. We aimed to quantify the contribution of elastic recoil to RV filling and determine its sensitivity to interventricular interaction. METHODS AND RESULTS: High-fidelity pressure-volume loops and simultaneous 3-dimensional ultrasound sequences were obtained in 13 pigs undergoing inotropic modulation, volume overload, and acute pressure overload induced by endotoxin infusion. Using a validated method, we isolated elastic restoring forces from ongoing relaxation using conventional pressure-volume data. The RV contracted below the equilibrium volume in >75% of the data sets. Consequently, elastic recoil generated strong sub-atmospheric passive pressure at the onset of diastole [-3 (-4 to -2) mmHg at baseline]. Stronger restoring suction pressure was related to a shorter isovolumic relaxation period, a higher rapid filling fraction, and lower atrial pressures (all P < 0.05). Restoring forces were mostly determined by the position of operating volumes around the equilibrium volume. By this mechanism, the negative inotropic effect of beta-blockade reduced and sometimes abolished restoring forces. During acute pressure overload, restoring forces initially decreased, but recovered at advanced stages. This biphasic response was related to alterations of septal curvature induced by changes in the diastolic LV-RV pressure balance. The constant of elastic recoil was closely related to the constant of passive stiffness (R = 0.69). CONCLUSION: The RV works as a suction pump, exploiting contraction energy to facilitate filling by means of strong elastic recoil. Restoring forces are influenced by the inotropic state and RV conformational changes mediated by direct ventricular interdependence.

Diastolic chamber properties of the left ventricle assessed by global fitting of pressure-volume data: improving the gold standard of diastolic function.

In cardiovascular research, relaxation and stiffness are calculated from pressure-volume (PV) curves by separately fitting the data during the isovolumic and end-diastolic phases (end-diastolic PV relationship), respectively. This method is limited because it assumes uncoupled active and passive properties during these phases, it penalizes statistical power, and it cannot account for elastic restoring forces. We aimed to improve this analysis by implementing a method based on global optimization of all PV diastolic data. In 1,000 Monte Carlo experiments, the optimization algorithm recovered entered parameters of diastolic properties below and above the equilibrium volume (intraclass correlation coefficients = 0.99). Inotropic modulation experiments in 26 pigs modified passive pressure generated by restoring forces due to changes in the operative and/or equilibrium volumes. Volume overload and coronary microembolization caused incomplete relaxation at end diastole (active pressure > 0.5 mmHg), rendering the end-diastolic PV relationship method ill-posed. In 28 patients undergoing PV cardiac catheterization, the new algorithm reduced the confidence intervals of stiffness parameters by one-fifth. The Jacobian matrix allowed visualizing the contribution of each property to instantaneous diastolic pressure on a per-patient basis. The algorithm allowed estimating stiffness from single-beat PV data (derivative of left ventricular pressure with respect to volume at end-diastolic volume intraclass correlation coefficient = 0.65, error = 0.07 ± 0.24 mmHg/ml). Thus, in clinical and preclinical research, global optimization algorithms provide the most complete, accurate, and reproducible assessment of global left ventricular diastolic chamber properties from PV data. Using global optimization, we were able to fully uncouple relaxation and passive PV curves for the first time in the intact heart.

Noninvasive estimation of the rate of relaxation by the analysis of intraventricular pressure gradients.

BACKGROUND: During late ejection, myocardial relaxation causes systolic flow to decelerate and stop, and this phenomenon is coupled with the generation of a pressure gradient inside the left ventricle (LV). We hypothesized that the peak reverse ejection intraventricular pressure difference (REIVPD) between the LV apex and the outflow tract could be a useful method to improve the assessment of LV relaxation using Doppler echocardiography. METHODS AND RESULTS: Three sets of animal experiments and 1 clinical study were designed. In 6 pigs, a close relationship between REIVPD and the intensity of the relaxation wave (R(rm)=0.89) was demonstrated using wave intensity analysis of high-fidelity pressure-volume-velocity data. In 19 animals, REIVPD sensitively detected modifications of the lusotropic state and closely correlated with the time constant of LV relaxation (τ) within animals (R(rm)=-0.93). Load-dependence analysis in 5 pigs showed that REIVPD remained stable up to values of 35% to 40% acute preload reduction. Clinical validation was tested in 50 patients (23 with normal systolic function) undergoing simultaneous Doppler echocardiography and high-fidelity LV pressure measurements on the same beat. REIVPD and tissue Doppler mitral annulus velocity (e') were independently related to τ, but the REIVPD · e' product correlated better with τ than either variable separately (bootstrap-corrected correlation coefficients: R=-0.84 versus -0.71, and -0.70, respectively, P<0.05). Area under the receiver operating characteristic curve to predict impaired relaxation (τ>50 ms) for e' · REIVPD was 0.96 (95% confidence interval, 0.85 to 0.99). CONCLUSIONS: The Doppler-derived REIVPD provides a sensitive, reliable, reproducible, and relatively load-independent index of the rate of LV relaxation. Combined with tissue Doppler measurements of longitudinal function, this method improves noninvasive assessment of LV relaxation in the clinical setting.

Density scaling laws for the structure of granular deposits.

The structure of granular deposits growing by arriving particles is analyzed using three-dimensional on-lattice Monte Carlo modeling of convective-diffusive particle deposition. The deposit density profile rho(h) depends on the particle dynamics and becomes formed by three different regions: a denser near-wall region at the deposit bottom in contact with the original plain surface, a middle uniform region with constant mean density, and an open and lighter active-growth region at the deposit outer surface. Fitting expressions for rho(h) valid in each region are proposed, based on the known features of deposits formed in the two limiting cases: ballistic deposition and diffusion-limited deposition. Also, a composite expression for rho(h) fitting the density profile throughout the deposit is given. All these expressions are written in terms of a length scale l(Pe) dependent on the particle Péclet number, which provides the relative importance of the convective motion to the diffusive transport for the particle.

Noninvasive assessment of the right ventricular filling pressure gradient.

BACKGROUND: The physiological basis of right ventricular (RV) diastolic function remains incompletely studied in humans. The driving force responsible for RV filling, the pressure gradient along the RV inlet from the right atrium to the RV apex, has never been measured in the clinical setting. METHODS AND RESULTS: We validated a method for measuring the RV filling pressure difference (RVFPD) from color Doppler M-mode recordings in 12 pigs undergoing interventions on RV preload, afterload, and lusitropic states (error, -0.1+/-0.4 mm Hg compared with micromanometers; intraclass correlation coefficient, 0.88). Peak early RVFPD correlated directly with mean right atrial pressure and inversely with the time constant of RV relaxation. In 21 patients with dilated cardiomyopathy, the peak RVFPD was 1.0 mm Hg (95% CI, 0.8 to 1.2), significantly lower than in age-matched control subjects (1.4 mm Hg; 95% CI, 1.2 to 1.6). In another population of 19 young healthy volunteers, the peak RVFPD was 2.3 mm Hg (95% CI, 2.0 to 2.6), which was reduced by nitroglycerine and esmolol and was augmented by volume overload and atropine infusions. RVFPD was generated almost exclusively by inertial forces. CONCLUSIONS: For the first time, the RV driving filling force can be accurately measured noninvasively in the clinical setting, and the method is sensitive to detect the effects of preload, chronotropic, and lusitropic states. In patients with dilated cardiomyopathy, the RV filling force is markedly reduced, indicating severely impaired RV relaxation. These findings suggest that this is a useful tool for improving the clinical assessment of RV diastolic function.

Relationship between particle deposit characteristics and the mechanism of particle arrival.

An on-lattice Monte Carlo model is implemented for the simulation of particle deposit growth by advection and diffusion towards a flat surface. The particle deposit structure is characterized by its bulk (density) and interface (mean height and surface width) properties. Numerical correlations, fitted by simple expressions, are reported for these magnitudes, relating them to time (number of deposited particles) and Peclet number. Also a heuristic argument is presented which relates deposit density to local diffusion-limited-aggregation-like processes and interfacial dynamics to the KPZ model.