Background-oriented schlieren sensitivity in terms of geometrical parameters of measurement setup.

Background-oriented schlieren imaging is a recently proposed noninvasive optical method for imaging of full ultrasound fields. In this work, the impact of uncertainty in geometrical parameters of a background-oriented schlieren measurement setup for imaging of full ultrasound fields is studied using numerical simulations. The studied parameters are focal length of the camera and positions and orientations of the camera, water tank, and ultrasound field. The results demonstrate that the most sensitive parameters affecting the accuracy of the reconstructed ultrasound fields are the orientations of the camera that change the direction of an effective optical axis. Other sensitive parameters are the focal length of the camera and the position of the ultrasound field in perpendicular directions of an optical axis. This synthetic study demonstrates the accuracy requirements for calibrating the geometrical parameters of a measurement setup that would be required to achieve accuracy comparable to that of hydrophone measurements using the background-oriented schlieren imaging. Explicitly, limits of the variation ranges of the geometrical parameters resulting in relative error ranges of 5% and 10% are given. The results of this study may contribute to help design future background-oriented schlieren measurement setups intended for measurement of full ultrasound fields.

Assembly of fluorophore J-aggregates with nanospacer onto mesoporous nanoparticles for enhanced photoacoustic imaging.

Many fluorophores, such as indocyanine green (ICG), have poor photostability and low photothermal efficiency hindering their wide application in photoacoustic (PA) tomography. In the present study, a supramolecular assembly approach was used to develop the hybrid nanoparticles (Hy NPs) of ICG and porous silicon (PSi) as a novel contrast agent for PA tomography. ICG was assembled on the PSi NPs to form J-aggregates within 30 min. The Hy NPs presented a red-shifted absorption, improved photothermal stability, and enhanced PA performance. Furthermore, 1-dodecene (DOC) was assembled into the NPs as a 'nanospacer', which enhanced non-radiative decay for increased thermal release. Compared to the Hy NPs, adding DOC into the Hy NPs (DOC-Hy) increased the PA signal by 83%. Finally, the DOC-Hy was detectable in PA tomography at 1.5 cm depth in tissue phantom even though its concentration was as low as 6.25 µg/mL, indicating the potential for deep tissue PA imaging.

Nonlinear estimation of pressure projection of ultrasound fields in background-oriented schlieren imaging.

Background-oriented schlieren imaging is a recently proposed method for measuring projections of ultrasound fields. The method is based on observing deflection of light in a heterogeneous refractive index field that is induced by ultrasound via an acousto-optic effect. The deflection of light manifests as apparent perturbations in an imaged target, forming a potential flow estimation problem. In this work, the potential flow approach is formulated as a nonlinear regularized least-squares approach to alleviate limitations of approaches that linearize the problem. The nonlinear approach is shown to outperform the linear one when estimating projections of medically relevant ultrasound fields.

Computationally Efficient Forward Operator for Photoacoustic Tomography Based on Coordinate Transformations.

Photoacoustic tomography (PAT) is an imaging modality that utilizes the photoacoustic effect. In PAT, a photoacoustic image is computed from measured data by modeling ultrasound propagation in the imaged domain and solving an inverse problem utilizing a discrete forward operator. However, in realistic measurement geometries with several ultrasound transducers and relatively large imaging volume, an explicit formation and use of the forward operator can be computationally prohibitively expensive. In this work, we propose a transformation-based approach for efficient modeling of photoacoustic signals and reconstruction of photoacoustic images. In the approach, the forward operator is constructed for a reference ultrasound transducer and expanded into a general measurement geometry using transformations that map the formulated forward operator in local coordinates to the global coordinates of the measurement geometry. The inverse problem is solved using a Bayesian framework. The approach is evaluated with numerical simulations and experimental data. The results show that the proposed approach produces accurate 3-D photoacoustic images with a significantly reduced computational cost both in memory requirements and time. In the studied cases, depending on the computational factors, such as discretization, over the 30-fold reduction in memory consumption was achieved without a reduction in image quality compared to a conventional approach.

Black Mesoporous Silicon as a Contrast Agent for LED-Based 3D Photoacoustic Tomography.

Mesoporous silicon (PSi) nanoparticles have been widely studied in different biomedical imaging modalities due to their several beneficial material properties. However, they have not been found to be suitable for photoacoustic imaging due to their poor photothermal conversion performance. In the present study, biodegradable black mesoporous silicon (BPSi) nanoparticles with strong light absorbance were developed as superior image contrast agents for photoacoustic tomography (PAT), which was realized with a light-emitting diode (LED) instead of the commonly used laser. LED-based PAT offers the advantages of low cost, compactness, good mobility, and easy operation as compared to the traditional laser-based PAT modality. Nevertheless, the poor imaging sensitivity of the LED-PAT systems has been the main barrier to prevent their wide biomedical application because the LED light has low optical energy. The present study demonstrated that the imaging sensitivity of the LED-PAT system was significantly enhanced with the PEGylated BPSi (PEG-BPSi) nanoparticles. The PEG-BPSi nanoparticles were clearly detectable with a low concentration of 0.05 mg/mL in vitro and with an LED radiation energy of 5.2 µJ. The required concentration of the PEG-BPSi nanoparticles was 10 times lesser than that of the reference gold nanoparticles to reach the corresponding level of the imaging contrast. The ex vivo studies demonstrated that the submillimeter BPSi nanoparticle-based absorbers were distinguishable in chicken breast tissues. The strong contrast provided by the BPSi particles indicated that these particles can be utilized as novel contrast agents in PAT, especially in LED-based systems with low light intensity.

Modeling of Errors Due to Uncertainties in Ultrasound Sensor Locations in Photoacoustic Tomography.

Photoacoustic tomography is an imaging modality based on the photoacoustic effect caused by the absorption of an externally introduced light pulse. In the inverse problem of photoacoustic tomography, the initial pressure generated through the photoacoustic effect is estimated from a measured photoacoustic time-series utilizing a forward model for ultrasound propagation. Due to the ill-posedness of the inverse problem, errors in the forward model or measurements can result in significant errors in the solution of the inverse problem. In this work, we study modeling of errors caused by uncertainties in ultrasound sensor locations in photoacoustic tomography using a Bayesian framework. The approach is evaluated with simulated and experimental data. The results indicate that the inverse problem of photoacoustic tomography is sensitive even to small uncertainties in sensor locations. Furthermore, these uncertainties can lead to significant errors in the estimates and reduction of the quality of the photoacoustic images. In this work, we show that the errors due to uncertainties in ultrasound sensor locations can be modeled and compensated using Bayesian approximation error modeling.

Acoustic pressure field estimation methods for synthetic schlieren tomography.

Synthetic schlieren tomography is a recently proposed three-dimensional (3D) optical imaging technique for studying ultrasound fields. The imaging setup is composed of an imaged target, a water tank, a camera, and a pulsed light source, which is stroboscopically synchronized with an ultrasound transducer to achieve tomographically stationary imaging of an ultrasound field. In this technique, ultrasound waves change the propagation of light rays by inducing a change in refractive index via the acousto-optic effect. The change manifests as optical flow in the imaged target. By performing the imaging in a tomographic fashion, the two-dimensional tomographic dataset of the optical flow can be transformed into a 3D ultrasound field. In this work, two approaches for acoustic pressure field estimation are introduced. The approaches are based on optical and potential flow regularized least square optimizations where regularization based on the Helmholtz equation is introduced. The methods are validated via simulations in a telecentric setup and are compared quantitatively and qualitatively to a previously introduced method. Cases of a focused, an obliquely propagating, and a standing wave ultrasound field are considered. The simulations demonstrate the efficiency of the introduced methods also in situations in which the previously applied method has weaknesses.

Short-term survival of cementless Oxford unicondylar knee arthroplasty based on the Finnish Arthroplasty Register.

BACKGROUND: Cementless unicondylar knee arthroplasty (UKA) was introduced to secure long-term fixation and reduce the risk of revision. Experience with cementless UKA fixation is limited. METHODS: The short-term survival (up to five years) of cementless Oxford UKA was assessed using data from the Finish Arthroplasty Register and was compared with that of cemented Oxford 3 UKA and total knee arthroplasty (TKA). Datawere obtained, from the Finnish Arthroplasty Register, on 1076 cementless Oxford UKAs and 2279 cemented Oxford 3 UKAs performed for primary osteoarthritis in 2005-2015. The Kaplan-Meier method, with revision for any reason as the endpoint, was used to assess the survival of these two UKA groups, and the results were compared with that of 65,563 cemented TKAs treated for primary osteoarthritis over the same period. The risk of revision of both Oxford prostheses was compared using Cox regression model, with adjustment for age and sex, with the cemented TKA group as reference. RESULTS: The three-year survival was 93.7% for the cementless Oxford, 92.2% for the cemented Oxford 3, and 97.3% for the cemented TKA. The corresponding figures at five years were 92.3%, 88.9%, and 96.6%, respectively. The revision rate for both the cementless Oxford and the cemented Oxford 3 was significantly increased when compared with the cemented TKA (P < 0.001). CONCLUSIONS: The survival of the cementless Oxford method was higher than that of the cemented Oxford 3 in the short term. The overall survival of Oxford UKA was poor in comparison with contemporary TKAs.

Mechanosensitive meningeal nociception via Piezo channels: Implications for pulsatile pain in migraine?

BACKGROUND: Recent discovery of mechanosensitive Piezo receptors in trigeminal ganglia suggested the novel molecular candidate for generation of migraine pain. However, the contribution of Piezo channels in migraine pathology was not tested yet. Therefore, in this study, we explored a potential involvement of Piezo channels in peripheral trigeminal nociception implicated in generation of migraine pain. METHODS: We used immunohistochemistry, calcium imaging, calcitonin gene related peptide (CGRP) release assay and electrophysiology in mouse and rat isolated trigeminal neurons and rat hemiskulls to study action of various stimulants of Piezo receptors on migraine-related peripheral nociception. RESULTS: We found that essential (35%) fraction of isolated rat trigeminal neurons responded to chemical Piezo1 agonist Yoda1 and about a half of Yoda1 positive neurons responded to hypo-osmotic solution (HOS) and a quarter to mechanical stimulation by focused ultrasound (US). In ex vivo hemiskull preparation, Yoda1 and HOS largely activated persistent nociceptive firing in meningeal branches of trigeminal nerve. By using our novel cluster analysis of pain spikes, we demonstrated that 42% of fibers responded to Piezo1 agonist and 20% of trigeminal fibers were activated by Yoda1 and by capsaicin, suggesting expression of Piezo receptors in TRPV1 positive peptidergic nociceptive nerve fibers. Consistent with this, Yoda1 promoted the release of the key migraine mediator CGRP from hemiskull preparation. CONCLUSION: Taken together, our data suggest the involvement of mechanosensitive Piezo receptors, in particular, Piezo1 subtype in peripheral trigeminal nociception, which provides a new view on mechanotransduction in migraine pathology and suggests novel molecular targets for anti-migraine medicine.

Infection safety of dexamethasone in total hip and total knee arthroplasty: a study of eighteen thousand, eight hundred and seventy two operations.

PURPOSE: Dexamethasone has been shown to prevent post-operative nausea and vomiting (PONV) and seems to reduce post-operative pain. Both factors, which can extend the hospital stay, delay rehabilitation, and impact patient satisfaction. Because of the immunosuppressive and glucose-rising effects of dexamethasone, there has been concern of its safety in arthroplasty surgery. The purpose of our study was to examine infection safety of dexamethasone in arthroplasty surgery with enough large study material to reliably detect a possible, even small, difference in infection incidence. METHODS: A total of 18,872 consecutive primary and revision hip and knee arthroplasties were analyzed with data gathered from clinical information databases and a surgical site infection surveillance database with prospective data collection. Also, emergency operations due to fractures were included except for hip hemiarthroplasties. RESULTS: During the follow-up, 189 (1.0%) prosthetic joint infections (PJIs) occurred: 0.8% after primary arthroplasty and 1.9% after revision arthroplasty. Dexamethasone was used in 2922 (15.5%) operations. The PJI rate in the dexamethasone group was 1.1% (31/2922) and in the non-dexamethasone group 1.0% (161/15950), with no significant difference in the risk of PJI between the two groups (OR 1.052, 95% CI 0.715-1.548, P = 0.773). CONCLUSIONS: In our study material, the use of a single 5-10 mg dose of dexamethasone did not increase the incidence of post-operative PJI. A low dose of dexamethasone may be safely used to prevent PONV and as part of multimodal analgesia on patients undergoing arthroplasty operation.

High Revision Rate for Large-head Metal-on-metal THA at a Mean of 7.1 Years: A Registry Study.

BACKGROUND: Large-diameter head metal-on-metal (MoM) THA has largely been abandoned as a result of higher than anticipated revision rates. However, the majority of these implants are still in situ. Although earlier reports from the Finnish Arthroplasty Register noted similar short-term survivorship between large-diameter head MoM THA and conventional cemented THA, longer term survivorship of this population is unclear. Although reported revision rates for this implant group have been high, the majority of these implants have not been revised and followup is important to improve long-term management. QUESTIONS/PURPOSES: The purposes of this study were (1) to compare the 10-year competing risk survivorship of large-diameter head MoM THA with the survivorship of conventional THA in the Finnish Arthroplasty Register; (2) to report the large-diameter head MoM THA survival at the manufacturer/brand level; and (3) to identify the most common reasons for revision of large-diameter head MoM THA in the Finnish Arthroplasty Register. METHODS: The six most commonly used large-diameter head (≥ 38 mm) MoM THA devices in Finland between years 2004 and 2013 were selected (n = 10,959 implants). The completeness of the Finnish Registry is > 95% in primary THA and patients are censored from the date of death or at the point of emigration; followup continued until the end of 2015. The conventional THA control group consisted of the two most frequently used devices (Vision/Bimetric and ABG II/ABG II) with metal-on-polyethylene or ceramic-on-ceramic bearing surfaces implanted between 2002 and 2013 (n = 5177). The study group was formed by selecting all pairs of large-diameter head MoM and reference THA protheses within the same age group ( < 49, 50-54, 55-59, 60-64, 65-69, 70-74, and 75+ years), sex, diagnosis (osteoarthritis, other), and hospital yearly operation count (< 100 operations yearly, ≥ 100 operations yearly); 5166 matched pairs were identified. Revision for any reason was considered as the failure endpoint of followup. Implant survival (the proportion not revised) was calculated from corresponding cumulative incidence function adjusted for patient death as a competing event for revision. Large-diameter head MoM implant group revision hazard ratios with 95% confidence intervals were estimated with age group, sex, diagnosis, and hospital yearly operation count as confounding factors in a Cox regression model. RESULTS: Ten-year survivorship free from all-cause revision was lower for THAs that used a large-diameter femoral head than it was for the control group of conventional THA (83% [95% confidence interval {CI}, 82%-84%] versus 92% [95% CI, 91%-93%]). At the implant level, every large-diameter head MoM THA had a higher risk for revision compared with the conventional THA control group from the fourth postoperative year onward. The highest survival of MoM THA was 88% (95% CI, 86%-90%) for the ReCap/Bimetric and the lowest survival was 46% (95% CI, 41%-51%) for the recalled ASR with either the Summit® or Corail® stem. The most common revision reason in the MoM THA group was adverse reaction to metal debris, whereas dislocation was predominant in the conventional THA control group. CONCLUSIONS: The revision rate for all large-diameter head MoM THAs in this timeframe in the Finnish Arthroplasty Register is unacceptably high and in our view supports the decision to abandon their use. In agreement with the directives of other national organizations, we recommend regular followup of all patients with large-diameter head MoM THA. Based on our results, strict guidelines for followup should be maintained over the lifetime of the implant to assess patient symptoms and recommend revision when indicated. LEVEL OF EVIDENCE: Level III, therapeutic study.

What Is the Long-term Survivorship of Cruciate-retaining TKA in the Finnish Registry?

BACKGROUND: Survival of cruciate-retaining (CR) TKA is generally good, but there may be important differences in survivorship among devices, and different designs may not all be equally patellar-friendly. Large registry databases are needed to identify small but important differences between devices. QUESTIONS/PURPOSES: The purposes of this study were (1) to assess the long-term survivorship of the most common CR TKA devices with revision for any reason as the endpoint and compare the revision risk of these devices after controlling for the potentially confounding variables of age, sex, hospital volume, and primary diagnosis; and (2) to analyze these same devices with revision for secondary resurfacing of the patella as a separate endpoint. METHODS: Data were collected from the Finnish Arthroplasty Register. Over 95% of all primary TKAs are captured in the Finnish Register. We assessed Kaplan-Meier (KM) survivorship for each of the four most frequently used CR TKA designs used between years 2005 and 2015: Triathlon CR (n = 34,337), Nexgen CR Flex (n = 15,723), PFC Sigma CR (n = 15,541), and Vanguard CR (n = 9461), with revision for any reason as the endpoint. Revision was defined as a reoperation in which at least one of the components was exchanged (including insert exchange). Revisions in which the patella was not resurfaced at the primary operation and was resurfaced in the revision were studied as a separate endpoint. The mean followup times were 4.0 (range, 0-11.0) years for Triathlon CR, 3.8 (range, 0-11.0) years for Nexgen CR Flex, 5.1 (range, 0-11.0 ) years for PFC Sigma CR, and 4.9 (range, 0-10.9) years for Vanguard CR (p < 0.001). The group demographics were clinically comparable. We compared the risk of revision of these devices in the Cox multiple regression model with adjustment for hospital volume, age, sex, and primary diagnosis. There were some differences in the incidence of patellar resurfacing at the time of index arthroplasty (Nexgen CR flex 18.7%, PFC Sigma CR 18.4%, Triathlon CR 11.3%, Vanguard CR 14.4%), which was controlled by the Cox model. Implant survival analyses for Triathlon CR, Nexgen CR Flex, and PFC Sigma CR were also performed at the hospital level for the 25 largest TKA providers in Finland. RESULTS: The overall 10-year KM survivorships were 96% (95% confidence interval [CI], 95-96) for Nexgen CR Flex, 96% (95% CI, 96-97) for PFC Sigma CR, 94% (95% CI, 93-95) for Triathlon CR, and 94% (95% CI, 93-95) for Vanguard CR. After controlling for potential confounding variables like age, sex, hospital volume, and primary diagnosis, both Triathlon CR (hazard ratio [HR], 1.4; 95% CI, 1.2-1.6; p < 0.01) and Vanguard CR (HR, 1.4; 95% CI, 1.2-1.6; p < 0.01) had an increased risk for revision compared with the Nexgen CR Flex (the reference device). When revision with patellar resurfacing served as the endpoint, after controlling for those same confounding variables, Triathlon CR had a higher risk for revision than Nexgen CR Flex (HR, 1.8; 95% CI, 1.4-2.2; p < 0.01). CONCLUSIONS: Despite slight differences among the studied devices, the overall 10-year survivorship of the current devices studied was good. However, there were differences in implant survival between the study devices, especially when revision for late patellar resurfacing was analyzed. Further studies adjusted for additional hospital and surgeon variables will be needed to examine and confirm our results. LEVEL OF EVIDENCE: Level III, therapeutic study.

Ultrasound field characterization using synthetic schlieren tomography.

Synthetic schlieren imaging, also known as background oriented schlieren imaging, is used to determine the acoustical field of a focused ultrasound transducer operating at 1.01 MHz frequency with peak pressure amplitude of 0.97 MPa. The measurement setup is composed of a commercial off-the-shelf digital single-lens reflex (DSLR) camera with an ordinary objective, a high power light-emitting diode driven in pulsating mode, water tank, ultrasound transducer, rotation stage, and driving electronics. Measurements are performed in tomographic fashion by rotating the ultrasound transducer within the water tank and photographing an imaged target behind the ultrasound field. The photographs are processed with a Horn-Schunck-type algorithm, commonly used in optical flow analysis, in order to determine the deflection of light rays as caused by ultrasound field induced acousto-optic effect. Inverse Radon transform is then used, with the deflection data, to obtain three-dimensional spatial distribution of the pressure field gradient, from which an approximation of the ultrasonic pressure field is computed. The pressure field obtained with synthetic schlieren tomography is then compared to hydrophone measurements mainly qualitatively.

Effects of thromboprophylactic doses of apixaban and rivaroxaban on coagulation and thrombin generation in association with total hip replacement.

Factor Xa inhibitors (FXaI) apixaban and rivaroxaban are used for thromboprophylaxis after major elective orthopaedic surgery. Because few patient sample studies exist, we postoperatively assessed patients undergoing unilateral total hip arthroplasty, including 22 treated with apixaban (2.5 mg BID) and 20 treated with rivaroxaban (10 mg OD). We collected blood samples before and 3 h after drug intake at 4 time points, preoperatively, as well as on day 1, week 1 (day 2-8) and day 28 post-operation. APTT and PT were immediately analysed. Calibrated anti-FXa activity, Russel's Viper Venom Time (RVVT) and thrombin generation (TG; Calibrated Automated Thrombogram®) captured the effects of FXaI on coagulation and TG. APTT and PT remained within the reference interval throughout, and did not correlate with FXaI levels (PT R2 = 0.44, APTT R2 = 0.07). Mean apixaban concentration at the peak varied by eightfold (19-153 ng/mL), but rivaroxaban only by 1.5-fold (111-183 ng/mL). Rivaroxaban, but not apixaban prolonged RVVT at peak levels. Both FXaIs had a prolonged lag time of TG (p < 0.001). Rivaroxaban decreased ETP peak at all time points and reached a minimum at day 28 (540 nM/min at rivaroxaban 184 ng/mL, p < 0.001), while rivaroxaban trough levels were low and ETP values normal. However, with apixaban, after an initial decrease, ETP did not differ between peak and trough levels until decreasing on day 28 at peak (990 nM/min at apixaban 112 ng/mL, p = 0.005). In conclusion, due to different dosing and pharmacology rivaroxaban and apixaban distinctly inhibited TG under postoperative conditions.

[Diagnosis and treatment of prosthetic hip and knee joint infections]. / Lonkan ja polven tekonivelinfektioiden diagnostikka ja hoito.

Successful replacement arthroplasty enhances the patient's functional capacity, alleviates pain and improves the quality of life. Prosthetic joint infection is one of the most dangerous complications following replacement arthroplasty. In cases of suspected prosthetic joint infection it is essential to consult with the prosthetic joint unit and abstain from starting antibiotics before the appropriate microbiological samples. The diagnosis is made on the basis of history, clinical picture, levels of inflammatory markers, synovial fluid cells and microbiological findings. The most common options of surgical treatment are early debridement and replacement of loose parts, and replacement of the prosthesis. Antimicrobial drug therapy will be planned according to the surgical mode of treatment and the causative bacterium.

Nonuniform temperature rise in in vitro osteoblast ultrasound exposures with associated bioeffect.

There is a growing interest to use ultrasound to stimulate cellular material in vitro conditions for the treatment of musculoskeletal disorders. However, the beneficial effect resulting from ultrasound exposure is not accurately specified. Many in vitro ultrasound setups are very vulnerable to temperature elevation due to sound absorption, sound reflections, and inadequate heat transfer. The objective of this study is to show that temperature variations capable of modifying biological results may exist in common in vitro exposure system. Human osteoblastic MG-63 cells plated on a 24-well cell plate were treated with pulsed ultrasound in 37 °C water bath (10 min, frequency = 1.035 MHz, burst length = 200 µs, pulse repetition frequency = 1 kHz, duty cycle = 0.2, temporal-average acoustic power = 2 W, and peak pressure = 670-730 kPa) and the activation of heat-dependent canonical Wnt cell signaling was measured. The ultrasound-induced temperature rise was measured with thermocouples and infrared imaging. Chamber-to-chamber comparison showed substantial temperature variation (41.6 °C versus 49.1 °C) among the different chambers. The chamber walls were the most susceptible to heating. The variations in the chamber temperatures correlated to variations in the cell signaling levels (1.3-fold versus 11.5-fold increase). These observations underline the need for system-specific temperature measurements during in vitro exposures.

Study of factors affecting the magnitude and nature of ultrasound exposure with in vitro set-ups.

Therapeutic ultrasound is a clinically applied method to improve fracture healing and holds great potential as a manipulator of biologic material relevant to tissue engineering approaches. Unfortunately, the cell stimulating property of ultrasound is not known, which inhibits the optimal use of this technique. Additionally, many in vitro studies in this field use ultrasound configurations that are vulnerable to errors during calibration and use. These errors arise from the structural simplicity and incomplete characterization of these configurations. In this study, pulse-echo ultrasound, laser Doppler vibrometry and Schlieren imaging were applied to noninvasively characterize common in vitro experimental configurations. Fine wire thermocouple measurements were conducted to characterize any possible temperature rise during the ultrasound exposures. The results quantified the frequency dependent sound transmission through culture wells and the standing wave effect within the cell volume. These effects can cause uncertainty of up to 700% in the actual ultrasound exposure experienced by the cell. A temperature rise of 2.7°C was measured from an ultrasound configuration commonly used in vitro ultrasound studies. Furthermore, wave mode conversion in culture wells was observed, emphasizing the complexity of these sonications. Similar type Lamb waves have been observed in bone in vivo. Thus, Lamb waves may be a mechanism for stimulating the cells.

The incidence of knee arthroplasty for primary osteoarthritis grows rapidly among baby boomers: a population-based study in Finland.

OBJECTIVE: Total knee arthroplasty (TKA) is a commonly used treatment for severe primary knee osteoarthritis (OA) that is refractory to conservative treatment. Despite the presumed increase in the use of this treatment modality in younger patients, there are few published data concerning this. The aim of our study was to examine the changes in the age- and sex-standardized incidence of TKA and unicondylar knee arthroplasty (UKA) in Finland during 1980-2006 and to identify factors that might affect the incidence during this period. METHODS: We obtained data on UKAs and TKAs from the Finnish Arthroplasty Registry and population data from Statistics Finland to analyze the incidence of UKAs and TKAs in Finland for the period 1980-2006. The effects of sex, age group, and hospital volume on the incidence of these procedures were also evaluated. RESULTS: The annual cumulative incidence of UKAs and TKAs has increased rapidly from 1980 to 2006 among 30-59-year-old inhabitants of Finland. For UKAs, the incidence increased from 0.2 per 100,000 inhabitants to 10 per 100,000, and for TKAs, the incidence increased from 0.5 per 100,000 to 65 per 100,000. The incidence remained higher among women during the entire study period. Most of the increase occurred among patients ages 50-59 years. The incidence grew more rapidly in low-volume and intermediate-volume hospitals. CONCLUSION: We demonstrated a rapid increase in the incidence of arthroplasty among patients with primary knee OA in Finland, especially in those ages 50-59 years. There was no single explanatory factor behind this finding, although some of the growth might be due to the increased incidence noted in low- and intermediate-volume hospitals.

Ultrasound-induced activation of Wnt signaling in human MG-63 osteoblastic cells.

The benefit from an ultrasound (US) exposure for fracture healing has been clearly shown. However, the molecular mechanisms behind this effect are not fully known. Recently, the canonical Wnt signaling pathway has been recognized as one of the essential regulators of osteoblastogenesis and bone mass, and thereby considered crucial for bone health. Mechanical loading and fluid shear stress have been reported to activate the canonical Wnt signaling pathway in bone cells, but previous reports on the effects of therapeutic US on Wnt signaling in general or in bone, in particular, have not been published yet. Therefore, activation of Wnt signaling pathway was assayed in human osteoblastic cells, and indeed, this pathway was found to be activated in MG-63 cells through the phosphoinositol 3-kinase/Akt (PI3K/Akt) and mTOR cascades following a single 10 min US exposure (2 W, 1.035 MHz). In addition to the reporter assay results, the Wnt pathway activation was also observed as nuclear localization of beta-catenin. Wnt activation showed also temperature dependence at elevated temperatures, and the expression of canonical Wnt ligands was induced under the thermal exposures. However, existence of a specific, non-thermal US component was evident as well, perhaps evidence of a potential dual action of therapeutic US on bone. Neither US nor heat exposures affected cell viability in our experiments. In summary, this is the first study to report that Wnt signaling cascade, important for osteoblast function and bone health, is one of the pathways activated by therapeutic US as well as by hyperthermia in human osteoblastic cells. Our results provide evidence for the potential molecular mechanisms behind the beneficial effects of US on fracture healing. Combinations of US, heat, and possible pharmacological treatment could provide useful flexibility for clinical cases in treating various bone disorders.