Potency and recovery characteristics of rocuronium mixed with sodium bicarbonate.

Sodium bicarbonate may be added to rocuronium to decrease pain on injection. However, this mixture may result in the formation of carbon dioxide bubbles. We investigated whether the addition of sodium bicarbonate to rocuronium alters neuromuscular blockade, in 120 patients randomly assigned to receive rocuronium mixed with saline or bicarbonate 8.4%, either in varying doses (for dose-response measurements; 60 patients) or a fixed dose of 600 µg.kg(-1) (for time-course measurements; 60 patients). Sodium bicarbonate resulted in a left-shift of the rocuronium dose-response curve. The effective doses of rocuronium to produce 95% twitch depression were 331.6 (95% CI: 310.4-352.8) and 284.3 (95% CI: 262.0-306.6) µg.kg(-1) mixed with isotonic saline or sodium bicarbonate, respectively (p < 0.001). The mean (SD) onset times of rocuronium 600 µg.kg(-1) were 3.6 (0.6) and 2.7 (0.5) min in the corresponding groups, respectively (p < 0.001). The mean (SD) times to 95% recovery were 35.8 (5.8) and 47.9 (7.1) min, respectively (p < 0.001). We conclude that the mixing of sodium bicarbonate with rocuronium enhances the potency, shortens the onset and prolongs the duration of action.

Analytical model development for the prediction of the frictional resistance of a capsule endoscope inside an intestine.

For the purpose of optimizing the design of the locomotion mechanism as well as the body shape of a self-propelled capsule endoscope, an analytical model for the prediction of frictional resistance of the capsule moving inside the small intestine was first developed. The model was developed by considering the contact geometry and viscoelasticity of the intestine, based on the experimental investigations on the material properties of the intestine and the friction of the capsule inside the small intestine. In order to verify the model and to investigate the distributions of various stress components applied to the capsule, finite element (FE) analyses were carried out. The comparison of the frictional resistance between the predicted and the experimental values suggested that the proposed model could predict the frictional force of the capsule with reasonable accuracy. Also, the FE analysis results of various stress components revealed the stress relaxation of the intestine and explained that such stress relaxation characteristics of the intestine resulted in lower frictional force as the speed of the capsule decreased. These results suggested that the frontal shape of the capsule was critical to the design of the capsule with desired frictional performance. It was shown that the proposed model can provide quantitative estimation of the frictional resistance of the capsule under various moving conditions inside the intestine. The model is expected to be useful in the design optimization of the capsule locomotion inside the intestine.

Minimum effective anaesthetic volume of 0.5% ropivacaine for ultrasound-guided popliteal sciatic nerve block in patients undergoing foot and ankle surgery: determination of ED50 and ED95.

Compared to nerve stimulation or classic paraesthesia techniques, ultrasound (US)-guided popliteal sciatic nerve block requires a smaller volume of local anaesthetic. The up-and-down method was used to determine the minimum effective anaesthetic volume of 0.5% ropivacaine necessary for US-guided popliteal sciatic nerve block to achieve successful surgical anaesthesia for foot and ankle surgery. The study included 32 patients receiving an US-guided popliteal sciatic nerve bock. The starting dose of 0.5% ropivacaine was set at 30 ml, which was decreased by 3 ml if the block succeeded and increased by 3 ml if the block failed. After the injection of local anaesthetic, the degree of sensory and motor blockade of the tibial and common peroneal nerves was assessed every 5 minutes for 30 minutes. The ED50 and ED95 volumes of local anaesthetic were 6 ml and 16 ml, respectively. The success rates of sensory blockade of the tibial nerve and common peroneal nerve were 69% and 88%, respectively. The success rates of motor blockade of these nerves were 75% and 90%, respectively. The ED50 and ED95 of 0.5% ropivacaine for US-guided popliteal sciatic nerve block were 6 ml and 16 ml, respectively.

Frictional resistance characteristics of a capsule inside the intestine for microendoscope design.

The design of the capsule body for a self-propelled endoscope is important from the frictional resistance point of view. The motivation of this work was to gain a better understanding of the effect of capsule shape on the frictional resistance of the capsule inside a small intestine. Special experimental set-ups were built to investigate the frictional resistance of the capsule and the viscoelastic deformation characteristics of the small intestine specimen of a pig. Tests were performed with capsules of various shapes and dimensions. Experimental data showed that a smooth cylindrical capsule geometry resulted in the least frictional resistance due to the shape and relatively small surface area. Also, it was found that the variation of frictional resistance of the capsule was closely related to the local change in the viscoelastic property of the intestine due to the heterogeneity of the internal structure of the intestine.

The medial crosssover toe: a cadaveric dissection.

UNLABELLED: The development of a medial crossover second toe (second toe crossing over the first toe) is not a rare clinical condition. It often occurs in the setting of hallux valgus, although not exclusively so. The resulting displacement of the second toe can cause pain in shoes, with surgical correction being problematic. The pathologic anatomy of this condition has not been fully described. In an effort to better understand it, dissection of a cadaveric specimen with a full crossover toe is presented. The dissection revealed findings not previously documented. They include medial displacement of the flexor tendons and plantar plate along with deformity of the plate itself. These changes are in addition to contracture of the medial collateral ligaments and the previously described rupture of the lateral collateral ligaments. Both the plantar plate and the collateral ligaments, the two major static soft tissue stabilizers of the lesser MP joint, were found to be significantly involved. Pull on the flexor tendons only accentuated the malalignment of the toe. CLINICAL SIGNIFICANCE: The extensive soft tissue changes explain the difficulty in achieving a successful long term correction of a full medial crossover toe with a soft tissue procedure. With attenuation of the plantar plate and medial displacement of the flexor tendons, there is an imbalance of muscle forces across the MP joint. This muscle imbalance would not be corrected by release of the medial collateral ligament, dorsal capsular release or extensor tendon lengthening. Reconstruction of the collateral ligament is at risk for incomplete correction since it is unlikely to resolve deformity in the plate if already present.

Deltoid ligament strain after correction of acquired flatfoot deformity by triple arthrodesis.

Deltoid insufficiency represents a difficult surgical challenge. We have witnessed patients who have developed a valgus tibiotalar deformity following a properly positioned triple arthrodesis. To investigate whether the triple arthrodesis itself, by creating a rigid triple joint complex below the ankle, leads to increased strain of the deltoid complex, a flatfoot model was created in 8 fresh-frozen below-knee amputation specimens. Each specimen was loaded in three gait cycle (GC) positions: Heel strike (0% GC), midstance (10% GC), and heel rise (40% GC). The three components of the ground reaction force (GRF) and the tendon forces consistent with those respective positions were applied. To simulate a posterior tibial tendon insufficient state the posterior tibial tendon was not loaded. Strain at the tibiocalcaneal fibers of the superficial deltoid ligament complex was determined at each of the three foot positions. A triple arthrodesis was performed and the deltoid strains were again recorded for each position. A significant increase in the strain of the deltoid ligament was observed for only the heel rise position (p=0.007) in our cadaver model following triple arthrodesis. The results favor medializing the calcaneus following arthrodesis to protect the deltoid complex.

Biomechanics of the ankle joint. A perspective on total ankle replacement.

The biomechanics of the ankle present a unique set of challenges for arthroplasty surgery. Its biomechanics are not simple. Although the ankle joint may seem like a hinge, it is not in a line perpendicular to the tibia. The axis of rotation does not stay constant during range of motion, despite a relative congruency of this joint. Allowing for rotational forces must be accomplished, while maintaining the stability of the joint and its components. Success of the arthroplasty depends on how successful designs can dissipate these rotational forces, while maintaining the stability of the joint. It is not yet clear from the biomechanical analysis of the normal ankle joint that this dissipation of forces has been accomplished successfully in modern implants, although early results in the semiconstrained designs are encouraging. Careful assessment of long-term follow-up will determine how close the present designs are to mimicking the unique requirements of the arthritic foot and ankle. Further work on the biomechanics of these replacements would be beneficial.