[Clinical profile of the new antiarrhythmic drug dronedarone]

The new antiarrhythmic drug dronedarone (SR 33 589) is a benzofuran derivative structurally similar to amiodarone, however is noniodinated. The additional methansulfonylgroup renders it less lipophilic, with a substantially shorter half-life, compared to the parent compound. The electrophysiological properties of both agents are similar with inhibition of Na+, K+, and Ca++ currents (all Vaughan-Williams classes). The agent has been evaluated in a large clinical study program. The daily dose of dronedarone 800 mg has been shown (DAFNE) to be effective and well tolerated. In two design-identical randomised clinical trials (EURIDIS and ADONIS trial) the efficacy of dronedarone to maintain sinus rhythm in patients with chronic atrial fibrillation/flutter was shown to be clearly superior to placebo. The ERATO study showed the rate control properties of dronedarone. In the ATHENA morbidity/mortality study, the combined endpoint death or hospitalisation due to cardiovascular events occurred significantly less often in the dronedarone group compared to the placebo group. Particularly due to its beneficial effects on clinical outcomes such as cardiovascular hospitalizations and death in the context of high tolerability dronedarone appears to be a promising new antiarrhythmic compound.

Modeling posture-dependent leg actuation in sagittal plane locomotion

The spring loaded inverted pendulum template has been shown to accurately model the steady locomotion dynamics of a variety of running animals, and has served as the inspiration for an entire class of dynamic running robots. While the template models the leg dynamics by an energy-conserving spring, insects and animals have structures that dissipate, store and produce energy during a stance phase. Recent investigations into the spring-like properties of limbs, as well as animal response to drop-step perturbations, suggest that animals use their legs to manage energy storage and dissipation, and that this management is important for gait stability. In this paper, we extend our previous analysis of control of the spring loaded inverted pendulum template via changes in the leg touch-down angle to include energy variations during the stance phase. Energy variations are incorporated through leg actuation that varies the force-free leg length during the stance phase, yet maintains qualitatively correct force and velocity profiles. In contrast to the partially asymptotically stable gaits identified in previous analyses, incorporating energy and leg angle variations in this manner produces complete asymptotic stability. Drop-step perturbation simulations reveal that the control strategy is rather robust, with gaits recovering from drops of up to 30% of the nominal hip height.

Leg recirculation in horizontal plane locomotion

A protocol prescribing leg motion during the swing phase is developed for the planar lateral leg spring model of locomotion. Inspired by experimental observations regarding insect leg function when running over rough terrain, the protocol prescribes the angular velocity of the swing-leg relative to the body in a feedforward manner, yielding natural variations in the leg touch-down angle in response to perturbations away from a periodic orbit. Analysis of the reduced order model reveals that periodic gait stability and robustness to external perturbations depends strongly upon the angular velocity of the leg at touch-down. While the leg angular velocity at touch-down provides control over gait stability and can be chosen to stabilize unstable gaits, the resulting basin of stability is much smaller than that observed for the original lateral leg spring model with a fixed leg touch-down angle. Comparisons to experimental leg angular velocity data for running cockroaches reveal that while the proposed protocol is qualitatively correct, smaller leg angular accelerations occur during the second half of the swing phase. Modifications made to the recirculation protocol to better match experimental observations yield large improvements in the basin of stability.

[Modular noncemented femoral stem system in revision total hip arthroplasty]

BACKGROUND

In most cases, loosening of a prosthesis stem is accompanied by periprosthetic osteolysis. This article presents the short-term clinical and radiological results after revision of total hip arthroplasty (THA) with bone substance deficiencies using a modular noncemented femoral stem system (LINK MP).

PATIENTS AND METHODS

Between March 2003 and November 2005, 91 LINK MP modular revision stems were implanted in 90 patients. Eighty-one patients (51 stem revisions, 24 revisions of stem and shell, and six reimplantations after a Girdlestone situation) were available for prospective clinical and radiological evaluation at an average follow-up time of 16.7+/-6.5 (6-36) months. The average patient age at revision was 67.2+/-10.5 (31-87) years.

RESULTS

Bone defects in the proximal femur were evaluated according to the Paprosky classification and showed type 2 in five cases, type 3A in 73 cases, and type 3B in three cases. The Merle d'Aubigné score increased significantly from 10.4+/-2.3 (4-15) preoperatively to 14.7+/-2.2 (9-18) at the latest follow-up (p<0.001). Migration analysis in conventional radiographs revealed an average stem subsidence of 3.4 mm. Thirty-one intraoperative and postoperative complications were noted in 28 (34.5%) patients.

CONCLUSION

After a short-term follow-up, the modular noncemented femoral stem system LINK MP was shown to be a reliable tool for revision of THA with bony defects of the proximal femur. Our results are comparable to those for other modular noncemented revision stems. As expected, complication rates were higher than with primary THA.

Dynamics and stability of lateral plane locomotion on inclines

An actuated, lateral leg spring model is developed to investigate lateral plane locomotion dynamics and stability on inclines. A single actuation input, the force-free leg length, is varied in a feedforward fashion to explicitly and implicitly match prescribed lateral and fore-aft force profiles, respectively. Forward dynamic simulations incorporating the prescribed leg actuation are employed to identify periodic orbits for gaits in which the leg acts to either push the body away from or pull the body towards the foot placement point. Gait stability and robustness to external perturbation are found to vary significantly as a function of slope and velocity for each type of leg function. Results of these analyses suggest that the switch in leg function from pushing to pulling is governed by gait robustness, and occurs at increasing inclines for increasing velocities.

Large-scale production of Ba(2+)-alginate-coated islets of Langerhans for immunoisolation

Islet xenografts immunisolated in alginate capsules have been proposed by many groups for clinical islet transplantation. However, diffusion limitations and the total volume of microcapsules required for transplantation are, among other things, factors which have so far prevented successful clinical application. In this study, these problems have been overcome by immobilisation of rat and porcine islets in a Ba(2+)-cross-linked alignate matrix using an air jet droplet generator technique in combination with subsequent density-gradient purification. This procedure leads to high yields of islets coated with a tailored, thin layer of cross-linked alginate which protects the islets against cytotoxic compounds present in human plasma. The recovery of encapsulated rat and porcine islets was about 70%. Empty capsules were nearly completely removed. Using this technique, the total volume of the resulting microcapsules increased only by a factor of about 1.5 compared to the volume of free islets. The technique can be used for large-scale production of coated islets.

[Matched pair analysis: Innex FIXUC vs. NexGen LPS]

AIM

The aim of the present retrospective matched pair study was to compare the clinical results of patients undergoing total knee arthroplasty (TKA) with 2 different operation strategies: tibia first vs. femur first for ligament balancing and rotational alignment of the femoral component.

METHODS

In this study 30 patients underwent TKA with the fixed bearing prosthesis Innex FIXUC between 2003 and 2005. In the same period of time the posterior stabilised prosthesis NexGen LPS was implanted in 123 patients. Out of these, 30 patients were matched to the 30 patients of the Innex group based on the parameters age, gender, height, weight and BMI. All implants were cemented. Clinical examination was rated using UCLA score, Knee Society score, Lequesne score for knees, a visual analogue scale (VAS) for pain and the Feller patellar score. Three patients in the Innex group were lost to follow-up, and 27 matched pairs could finally be analysed.

RESULTS

At a mean follow-up of 25 months (Innex) and 3 years (NexGen) statistically significant differences (p < 0.05) with advantages for the NexGen were found in the UCLA activity score (4.9 vs. 5.9, p = 0.013), in part A (knee score) of the Knee Society score (78.9 vs. 91.0, p = 0.002) as well as the total score (153.9 vs. 173.2, p = 0.012), VAS (2.1 vs. 0.6, p = 0.003) and in the Lequesne knee score (5.7 vs. 3.6, p = 0.024). No statistically significant differences (p < 0.05) were found in the function score of the Knee Society score and the patellar score (Feller).

CONCLUSION

In the described setting there were functional advantages for the NexGen prosthesis (femur first) at a comparable revision rate. However, satisfactory results with the Innex FIXUC are possible, too.

Improving horizontal plane locomotion via leg angle control

The lateral leg spring model has been shown to accurately represent horizontal plane locomotion characteristics of sprawled posture insects such as the cockroach Blaberus discoidalis. While passively stable periodic gaits result from employing a constant leg touch-down angle for this model, utilizing a similar protocol for a point mass model of locomotion in three dimensions produces only unstable periodic gaits. In this work, we return to the horizontal plane model and develop a simple control law that prescribes variations in the leg touch-down angle in response to external perturbations. The resulting control law applies control once per stance phase, at the instant of leg touch-down, and depends upon previous leg angles defined in the body reference frame. As a result, our control action is consistent with the neural activity evidenced by B. discoidalis during locomotion over flat and rough terrain, and utilizes variables easily sensed by insect mechanoreceptors. Application of control in the lateral leg spring model is shown to improve stability of periodic gaits, enable stabilization of previously unstable periodic gaits, and maintain or improve the basin of stability of periodic gaits. The magnitude of leg touch-down angle variations utilized during stabilization appear consistent with the natural variations evidenced by single legs during locomotion over flat terrain.