RUNNING IN LOWER LIMB AMPUTEES: ADVANTAGES AND LIMITATIONS OF NEW SPORTS PROSTHETIC COMPONENTS

Until some years ago, running in lower limb amputees was basically restricted by the inadequate dimensions of available prosthetic components that usually did not allow for the adequate dynamics necessary for running at lower speeds. Newly developed prosthetic components for recreational sports have enabled a great number of lower limb amputees to participate in running as an endurance sport. The present paper compares biomechanical parameters representing the functional benefits that result from the use of these components. The results were used to define potential advantages and limitations of lower limb amputee running depending on the level of amputation. Running of TF amputees is characterised by specific constraints based on the absence of knee stabilising muscles and the technical features of prosthetic components

GAIT ANALYSIS OF PATIENTS AFTER DIFFERENT TREATMENTS OF ACL RUPTURED KNEES

INTRODUCTION: The disruption of the anterior cruciate ligament (ACL) is treated by different techniques. Besides augmented repairs or non-surgical treatments, patellar tendon autograft reconstruction is the most important treatment. Different results have been published on the effects of the different treatments on the rehabilitation process (Daniel et al., 1994, Minnich et al., 1997). The purpose of the present study was to evaluate, by means of gait analysis data, the rehabilitation of various groups of patients treated with the different techniques after disruption of the anterior cruciate ligament (ACL). METHODS: One year post-surgically, gait analysis was performed during level walking on 35 patients with a patellar tendon autograft reconstructed knee and on 15 patients with an augmented repair. These groups were compared with a nonsurgically treated group of 18 patients and a group of 30 normal controls. The measurements of the non-surgically treated patients were performed 52 weeks after the occurrence of the rupture. An optoelectronic system for recording the kinematics of gait (Primas, NL) and two force plates concealed under a 12m-walkway for measuring the ground reaction forces (Kistler, CH) were used as technical equipment. For the purpose of evaluation, quantitative parameters were derived from knee joint kinematics, the horizontal ground reaction force and the moment acting on the knee joint (Schmalz et al., 1998). RESULTS: Differences in important gait parameters between the two groups of surgically treated patients and the controls persisted up to 52 weeks after the operation. Deficiencies clearly appeared during knee extension in the midstance phase of the surgically treated patients. Only a minority of these subjects (33%) showed results comparable to the controls. Differences were not found between the groups of patients with patellar tendon autograft reconstructed knees and with augmented repaired knees. However, at the time of investigation, the nonsurgically treated patients showed no deficiencies in gait parameters compared to the controls. CONCLUSIONS: The gait parameters of the non-surgically treated patients are indications that the deficient knee stabilisation function of the ACL is compensated by neuromuscular control. The deficiencies of the surgically treated groups are attributed to biomechanical problems like ligament graft positioning, fixation, or pre-tensioning appearing during the operation. From a therapeutic standpoint, good training with special exercises in midstance are recommended as soon as possible after surgery

IS GAIT ANALYSIS USEFUL IN REHABILITATION ?

INTRODUCTION: In current clinical practice, physical examination, X-rays and subjective impressions are the most frequent methods for evaluation of an individual’s orthopaedic condition. These familiar methods cannot predict the biomechanical function (i.e. forces, structural integrity) of joints, of a complete leg or of the locomotor apparatus. In addition to clinical evaluation more specific functional measurements of the movement apparatus, particularly during gait, seem to be desirable. This presentation illustrates our experiences with instrumented gait analysis and its efficiency as a scientific and clinical tool. The main problem is to look for sensitive parameters (indicators), which characterize the functional state of patient’s locomotor apparatus. METHODS: Our gait analysis is based on measurement of kinematic and kinetic data during level walking on a 12 m walkway, and sometimes EMG data for special cases. Measurement systems are one optoelectronical device (PRIMAS, Delft, NL) and two force plates (KISTLER, Winterthur, CH). Since 1992, 600 individuals (including amputees, orthopaedic patients and normal subjects) were measured in our gait lab. Selected systematic tests were performed with amputees, whereby different prosthetic components and prosthetic alignments were used. Also, single cases without positive clinical or X-ray findings, who complained of functional pain, received gait analysis. RESULTS: Joint moments are the single best indicators of the manner in which amputees adapt their motor activity to changes in the prosthesis. Patients complaining of pain despite negative clinical findings walk with asymmetrical muscle joint moments. Such joint moments often objectively document the patient’s rehabilitation state and his or her progress. CONCLUSIONS: The human gait cycle is a consistant and precise repeatable complex of movements performed one million times annually. Therefore, gait analysis can only be clinically useful if measurement systems can very sensitively and fastly determine external joint moments. For orthopaedic and prosthetic tasks, such measurement equipment is now available. In addition to instrumented gait analysis biomechanical knowledge is absolutly necessary so that orthopaedic patients can benefit from the valuable data of gait and motion analysis

Confidence Cycles

We provide a model that rationalizes variations in confidence of rational agents, both in the time-series and the cross-section. Combining horizon-dependent risk aversion (“anxiety”) and selective memory, we show that over- and underconfidence can arise in the Bayesian equilibrium of an intra-personal game. In the time-series, overconfidence is more prevalent when actual risk levels are high, while underconfidence occurs when risks are low. In the cross-section, more anxious agents are more prone to biased confidence and their beliefs fluctuate more, leading them to buy in booms and sell in crashes. Lastly, fluctuations in confidence can amplify boom-bust cycles

Horizon-Dependent Risk Aversion and the Timing and Pricing of Uncertainty

We address two fundamental critiques of established asset pricing models: that they (1) require a controversial degree of preference for early resolution of uncertainty; and (2) do not match the term structures of risk premia observed in the data. Inspired by experimental evidence, we construct preferences in which risk aversion decreases with the temporal horizon. The resulting model implies term structures of risk premia consistent with the evidence, including timevariations and reversals in the slope, without imposing a particular preference for early or late resolutions of uncertainty or compromising on the ability to match standard moments in the returns distributions

From the Hubbard to the PPP Model

This paper presents an extension of the Hubbard Model to Pariser-Parr-Pople form. Although the Hubbard model contains most of the essentials of chemical bonding, it is unable to describe excited states with separated charges, such as the lowest 1Bu states of linear polyenes. The PPP model adds longrange electron-electron repulsions to the Hubbard model to remedy this defect. If the long range repulsion integrals are assumed to follow a standard form, all parameters in the model can be evaluated exactly from high accuracy ab initio computations on stretched ethlyene. This yields a model based on the Mataga- Nishimoto form for the long-range integrals which gives excellent agreement with both excitation energies and ground-state bond lengths, but with a significantly smaller value of the one center electron repulsion U than is usually assumed. A major conclusion of this work is that the exact form of the long-range integrals is not so important, but that the value of the one center integral U must be chosen smaller than traditional values. The PPP-MN model is recommended for applications because it contains no adjustable parameters, with all parameter values determined directly from ab initio results. (doi: 10.5562/cca2297