Design of a tribological ball joint tester

The automotive industry uses ball joints in the suspension systems of cars. These ball joints are subject to various forces and relative displacements which inevitably invoke wear. The same happens in other applications that use ball joints, for example human hip joints. Nowadays there are only a few test rigs that can correctly simulate wear in these joints or test the joints according to a realistic loading cycle. This paper focuses on the design of a test rig that allows parametric research on these ball joints in order to increase the performance.</jats:p

Mechanical Demands of the Hang Power Clean and Jump Shrug: A Joint-level Perspective

The purpose of this study was to investigate the joint- and load-dependent changes in the mechanical demands of the lower extremity joints during the hang power clean (HPC) and the jump shrug (JS). Fifteen male lacrosse players were recruited from an NCAA DI team, and completed three sets of the HPC and JS at 30%, 50%, and 70% of their HPC 1-Repetition Maximum (1-RM HPC) in a counterbalanced and randomized order. Motion analysis and force plate technology were used to calculate the positive work, propulsive phase duration, and peak concentric power at the hip, knee, and ankle joints. Separate three-way analysis of variances were used to determine the interaction and main effects of joint, load, and lift type on the three dependent variables. The results indicated that the mechanics during the HPC and JS exhibit joint-, load-, and lift-dependent behavior. When averaged across joints, the positive work during both lifts increased progressively with external load, but was greater during the JS at 30% and 50% of 1-RM HPC than during the HPC. The JS was also characterized by greater hip and knee work when averaged across loads. The joint-averaged propulsive phase duration was lower at 30% than at 50% and 70% of 1-RM HPC for both lifts. Furthermore, the load-averaged propulsive phase duration was greater for the hip than the knee and ankle joint. The jointaveraged peak concentric power was the greatest at 70% of 1-RM for the HPC and at 30% to 50% of 1-RM for the JS. In addition, the joint-averaged peak concentric power of the JS was greater than that of the HPC. Furthermore, the load-averaged peak knee and ankle concentric joint powers were greater during the execution of the JS than the HPC. However, the loadaveraged power of all joints differed only during the HPC, but was similar between the hip and knee joints for the JS. Collectively, these results indicate that compared to the HPC the JS is characterized by greater hip and knee positive joint work, and greater knee and ankle peak concentric joint power, especially if performed at 30 and 50% of 1-RM HPC. This study provides important novel information about the mechanical demands of two commonly used exercises and should be considered in the design of resistance training programs that aim to improve the explosiveness of the lower extremity joints

Soleus H-reflex Excitability Changes in Response to Sinusoidal Hip Stretches in the Injured Human Spinal Cord

Imposed static hip stretches substantially modulate the soleus H-reflex in people with an intact or injured spinal cord while stretch of the hip flexors affect the walking pattern in lower vertebrates and humans. The aim of this study was to assess the effects of dynamic hip stretches on the soleus H-reflex in supine spinal cord injured (SCI) subjects. Sinusoidal movements were imposed on the right hip joint at 0.2 Hz by a Biodex system. H-reflexes from the soleus muscle were recorded as the leg moved in flexion or extension. Stimuli were sent only once in every hip movement cycle that each lasted 5 s. Torque responses were recorded at the hip, knee, and ankle joints. A hip phase-dependent soleus H-reflex modulation was present in all subjects. The reflex was facilitated during hip extension and suppressed during hip flexion. There were no significant differences in pre- or post-stimulus soleus background activity between the two conditions. Oscillatory responses were present as the hip was maximally flexed. Sinusoidal hip stretches modulated the soleus H-reflex in a manner similar to that previously observed following static hip stretches. The amount of reflex facilitation depended on the angle of hip extension. Further research is needed on the afferent control of spinal reflex pathways in health and disease in order to better understand the neural control of movement in humans. This will aid in the development of rehabilitation strategies to restore motor function in these patients

Robot Swinging Using van der Pol Nonlinear Oscillators

In this study, we investigated the use of van der Pol oscillators in a 2-dof embodied robotic platform for a swinging task. The oscillator controlled the hip and knee joints of the robot and was capable of generating waveforms with the correct frequency and phase so as to entrain with the mechanical system

Muscle-Specific Effective Mechanical Advantage and Joint Impulse in Weightlifting

Lifting greater loads during weightlifting exercises may theoretically be achieved through increasing the magnitudes of net joint impulses or manipulating the joints’ effective mechanical advantage (EMA). The purpose of this study was to investigate muscle-specific EMA and joint impulse as well as impulse-momentum characteristics of the lifter-barbell system across a range of external loads during the execution of the clean. Collegiate-level weightlifters performed submaximal cleans at 65, 75, and 85% of their 1-repetition maximum (1-RM) while data from a motion analysis system and a force plate were used to calculate lifter-barbell system impulse and velocity, as well as net extensor impulse generated at the hip, knee, and ankle joints and the EMA of the gluteus maximus, hamstrings, quadriceps, and triceps surae muscles. The results indicated that the lifter-barbell system impulse did not change as load increased, whereas the velocity of the lifter-barbell system decreased with greater load. In addition, the net extensor impulse at all joints increased as load increased. The EMA of all muscles did not, however, change as load increased. The load-dependent effects on the impulse-velocity characteristics of the lifter-barbell system may reflect musculoskeletal force-velocity behaviors, and may further indicate that the weightlifting performance is limited by the magnitude of ground reaction force impulse. In turn, the load-dependent effects observed at the joint-level indicated that lifting greater loads were due to greater net extensor impulses generated at the joints of the lower extremity and not greater EMAs of the respective extensor muscles. In combination, these results suggest that lifting greater external loads during the clean is due to the ability to generate large extensor joint impulses, rather than manipulate EMA

Spacesuit mobility knee joints

Pressure suit mobility joints are for use in interconnecting adjacent segments of an hermetically sealed spacesuit in which low torques, low leakage and a high degree of reliability are required. Each of the joints is a special purpose joint characterized by substantially constant volume and low torque characteristics and includes linkages which restrain the joint from longitudinal distension and includes a flexible, substantially impermeable diaphragm of tubular configuration spanning the distance between pivotally supported annuli. The diaphragms of selected joints include rolling convolutions for balancing the joints, while various joints include wedge-shaped sections which enhance the range of motion for the joints

Femoroacetabular Impingement (FAI) Syndrome : the medical imaging perspective

Introduction: Sports persons, physicians, orthopods and radiologists have become increasingly aware of the extra stress that is imposed on the hip joints with excessive activity particularly when superadded weight bearing and asymmetrical variations from the normal hip joint anatomy are present leading to Femoroacetabular Impingement. Subject: Presentation of the abnormalities within the ball and socket areas of the hip joint and the resultant types of impingements, the predominant cam, the predominant pincer or mixed types femoroacetabular impingement (FAI) are discussed and illustrated. The different kind of sportspersons that are prone to FAI and the risk factors involved are discussed. Method: The main methods of investigation: The radiological techniques and radiological signs of the disease entity utilizing plain radiography and computerised transverse scanning techniques are elaborated and graphically depicted. Within the ball part of the hip joint, measurements for femoral head asphericity, that is, the Alpha (?) angle and the offset distance between the femoral head and neck are presented. With regard to pincer type FAI affecting the socket part of the hip joint, the acetabular version angle and the depth (or shallowness) of the acetabulum with their methods of quantification are discussed. Conclusion: Femoroacetabular Impingement is a syndrome which is currently more appreciated within the sports medicine field and various approaches to assessment have been devised regarding how to diagnose and quantify congenital anomalies and developmental abnormalities within both the ball and the socket regions of the hip joint.peer-reviewe

The use of intra-articular aneshesia as a diagnostic tool in canine lameness

Lameness in dogs may be difficult to localize because of mild pathologic changes or inconclusive clinical findings. Intra-articular anesthesia is proposed as a diagnostic method to localize the source of lameness. After a description of the preparation, technique and puncture sites, an overview is given of a series of patients admitted for different joint problems. Intra-articular anesthesia proved to be applicable in any joint, provided that the clinician was experienced and the dog was under sedation. In 87% of the cases, intra-articular anesthesia was positive. Medial coronoid disease of the elbow joint was the most frequent indication for intra-articular anesthesia

Prosthetic joint infections

Objectives: To review the available literature on prosthetic joint infections and provide recommendations on management particularly the importance of identifying the causative organism and starting the most appropriate antimicrobial therapy. Methods: The medical literature was searched using PubMed, employing the key words prosthetic joint infections. There appears to be no UK consensus guidelines on the management of prosthetic joint infections or the use of prophylactic antibiotics to prevent them. There is however a number of key documents and trust policies which deal with the subject extensively. We also made use of ‘The Sanford Guide to Antimicrobial therapy 2012’ for the latest recommendations on the correct antimicrobial therapy. Conclusion: Although diagnosis is often difficult, there are a number of investigations which can help us identify the organism. We recommend that the local prevalence of such infections is studied together with identification of the commonest organisms. Work is already underway between the infectious disease team and orthopaedic surgeons to devise locally adapted protocols for the identification and management of such infections. They should work in close liaison to implement the correct treatment which often involves a combination of both surgical and antimicrobial therapy.peer-reviewe