Active tail flexion in concert with passive hydrodynamic forces improves swimming speed and efficiency

Fish typically swim by periodic bending of their bodies. Bending seems to follow a universal rule; it occurs at about one-third from the posterior end of the fish body with a maximum bending angle of about $30^{\circ }$ . However, the hydrodynamic mechanisms that shaped this convergent design and its potential benefit to fish in terms of swimming speed and efficiency are not well understood. It is also unclear to what extent this bending is active or follows passively from the interaction of a flexible posterior with the fluid environment. Here, we use a self-propelled two-link model, with fluid–structure interactions described in the context of the vortex sheet method, to analyse the effects of both active and passive body bending on the swimming performance. We find that passive bending is more efficient but could reduce swimming speed compared with rigid flapping, but the addition of active bending could enhance both speed and efficiency. Importantly, we find that the phase difference between the posterior and anterior sections of the body is an important kinematic factor that influences performance, and that active antiphase flexion, consistent with the passive flexion phase, can simultaneously enhance speed and efficiency in a region of the design space that overlaps with biological observations. Our results are consistent with the hypothesis that fish that actively bend their bodies in a fashion that exploits passive hydrodynamics can at once improve speed and efficiency.

EFFECT OF HYDROTHERAPY ON CHRONIC PAIN IN THE LUMBAR REGION

Purpose: To develop and study the effectiveness of methods and algorithms using a specialized magnetotherapy with underwater water-jet massage for chronic lumbar pain. Material/Methods: 30 subjects from two experimental groups (EG-1 from 15 athletes and EG-2 from 15 non-athletes) were examined, all with chronic lumbar pain. Testing is performed - before and after one month of physiotherapy. The test battery includes: anthropometry (height, body weight); visual-analogue pain scale; Laseg test - for the neurodynamics of n.ischiadicus. Physiotherapy includes hydrotherapy, with a water temperature of 360 – 370 and magnetotherapy with a duration of 30 - 35 min - treatment of the paravertebral muscle in the lumbar region, gluteus and lower limbs - dorsal and ventral. The procedures are applied 3 times a week for one month. Results: Methods and algorithms using a specialized magnetotherapy with underwater water-jet massage for patients with chronic lumbar pain have been developed. Pain on the Visual-Analog Scale of EG-1 athletes was studied - before physiotherapy (with hydrotherapy) X= 4.93±1.39mm, V% = 28.12%, which is an indicator of severe pain in the lumbar region. After 30 days, physiotherapy was reduced to X= 1.53±0.99mm, at V% = 64.59%. Its decrease is 31.03%, P<0.01. Pain beforehysiotherapy was found in EG-2 X= 6.87±1.64mm, at V% = 23.91%. After physiotherapy, it is reduced to X= 1.93±1.49mm, at V%=76.89%, P<0.01. A study of the neurodynamics of n.ischiadicus, through the Laseg test, found that passive flexion in the hip joint of the healthy leg - before physiotherapy with EG-1 hydrotherapy wasX=76.33±8.76o, at V% = 11.47%. After hydrotherapy increased to X= 86.33±5.51o, at V%=6.37%. Passive flexion in the hip joint of the injured leg before hydrotherapy was detected in EG-1. X= 69.67±10.43o, which indicates its strong limit. Post-hydrotherapy X= 80.33±10.08o, at V%=12.55%. P<0.0. In EG-2, the passive flexion in the hip joint – before hydrotherapy, the healthy leg was X= 71.67±14.1o, V% = 19.67%. After hydrotherapy increased to X= 81.53±8.37o. In V% = 10.26%. In the injured leg, passive flexion - before hydrotherapy wasv X= 71.00±11.37o, after it X= 82.07±7.70o, V% = 9.39%. P<0.01. Conclusion: The proven technique and algorithms of hydrotherapy, with a specialized with underwater water-jet massage, is effective for the recovery of persons with chronic lumbar pain. The technique reduces the neurological and pain symptoms and the restoration of n.ischiadicus.

Adhesions as a component of the trigger finger: a dynamic sonographic study

We performed a detailed dynamic high-resolution ultrasound examination of the flexor tendons in trigger fingers and compared this with normal contralateral digits. There was a loss of defined linear tendon margins and/or traction of the flexor tendons on the surrounding soft tissue during passive flexion of the distal interphalangeal joint in 17 out of 20 trigger fingers, which indicated adherence to the surrounding tissues. The differential motion between the flexor digitorum profundus tendon and the flexor digitorum superficialis tendons was also lost in ten trigger fingers, which suggested adherence between the tendons. No signs of peritendinous or intertendinous adhesions were found in the healthy control fingers. We conclude that tendon adhesions are present in the majority of trigger fingers. We could not determine a relationship between the severity of triggering and the presence of adherence due to limited sample size. Level of evidence: II

Effect of Stifle Flexion Angle on the Repeatability of Real-Time Elastosonography of the Patellar Ligament in Medium- to Large-Breed Dogs

Objective The aims of this study were to describe the elastosonographic findings of the patellar ligament in healthy dogs >15 kg in different positions and determine the most appropriate stifle angle to perform elastosonography of the patellar ligament. Study Design Eighteen clinically healthy dogs, weighing >15 kg, were prospectively recruited. B-mode ultrasound and real-time elastosonography of both patellar ligaments were performed on days 0 and 14. Elastosonography examinations were performed with the stifle in four positions: standing position, lateral recumbency with the stifle positioned at 135 degrees extension and in full passive flexion and extension. Results The percentage hardness of the patellar ligament was significantly lower when the elastosonographic examination was performed with the dog standing, compared with the other positions (p < 0.005). The variability in the elastosonography readings for each stifle position was lowest when the dog was standing (89.32%). Conclusion Elastosonography is a feasible technique for evaluating the elasticity of the normal canine patellar ligament in dogs >15 kg and would be a useful technique for investigating the mechanical changes within the patellar ligament following stifle surgery. Elastosonography of the patellar ligament should be performed with the dog standing to provide the most accurate elastosonograms with lowest variability between readings.

A numerical investigation of the infrapatellar fat pad

The infrapatellar fat pad is an adipose tissue in the knee that facilitates the distribution of synovial fluid and absorbs impulsive actions generated through the joint. The correlation between morphological configuration and mechanical properties is analyzed by a computational approach. The microscopic anatomy of the infrapatellar fat pad is studied aiming to measure the dimension of adipose lobules and the thickness of connective septa. Results from histomorphometric investigations show that the infrapatellar fat pad is an inhomogeneous tissue, constituted by large lobules in the superficial part and smaller lobules in the deepest one. Finite element models of the infrapatellar fat pad are developed. The first model considers the inhomogeneous conformation of the infrapatellar fat pad, composed of micro- and macro-chambers, while the second model considers a homogeneous distribution of adipose lobules with similar dimensions. Computational analyses are performed considering the static standing configuration and the passive flexion–extension movement. The computational results allow us to identify the different stress and strain fields within the tissue and to appreciate the variation of the mechanical performance of the overall system considering the distribution of adipose lobules. Results show that the distribution of adipose lobules in macro- and micro-chambers allows major deformation of the infrapatellar fat pad, decreasing the stress inside the tissues.