In the young and healthy shoulder, cranially directed forces during abduction are counteracted by co-contraction of the rotator cuff muscles. In this way, it is prevented that the humerus moves... Show moreIn the young and healthy shoulder, cranially directed forces during abduction are counteracted by co-contraction of the rotator cuff muscles. In this way, it is prevented that the humerus moves cranially towards the acromion, thus entrapping subacromial tissues. During ageing however, shoulder tissues are subject to marked degeneration, which particularly concerns the rotator cuff muscles. This may have two consequences. First, due to reduced contribution of the upper parts of the rotator cuff to the abduction movement, the deltoid has to compensate, which results in a more cranially, instead of mediocranially directed force. Second, reduced stabilising force by the rotator cuff may jeopardise counteraction of cranial deltoid forces. These changes could lead to cranialisation of the humerus with painful compression of subacromial tissues, as observed in patients with Subacromial Pain Syndrome (SAPS). Previous studies have shown that by co-contraction of arm adductors, humeral-head depression may be accomplished, for the purpose of unloading subacromial tissues. In this thesis, we investigated the role of adductor co-contraction in the ageing asymptomatic population and in patients with SAPS. This has resulted in eight scientific publications with which the fundaments for evidence-based therapy in SAPS have been built, with as cornerstone training of adductor co-contraction. Show less
The aim of this thesis was to explore the neuromechanics of recovery of arm-hand function after stroke. A literature review revealed six articles that measured biomechanical and electromyographical... Show moreThe aim of this thesis was to explore the neuromechanics of recovery of arm-hand function after stroke. A literature review revealed six articles that measured biomechanical and electromyographical outcome measures simultaneously, while applying active and passive tasks and multiple movement velocities to separate neural and non-neural contributors to movement disorders after stroke. Therefore, a neuromechanic assessment protocol was developed. Parameters were responsive to clinical status and had good to excellent test-retest reliability. Selective muscle activation was assessed with high measurement reliability and was significantly lower in chronic stroke patients compared to healthy participants. Longitudinally, neuromechanical parameters were combined with data on arm-hand function at six months after stroke. Paresis and diminished modulation of reflexes were associated with poor functional outcome. Changes in tissue properties were represented by a shift in wrist rest angle towards flexion and decline in passive range of motion. Increase in active range of motion and steady rest angle contributed most to prediction of functional outcome. The precision diagnostics provided by a neuromechanical assessment protocol could support clinical decision making and should be used in prediction models and as biomarkers in recovery of arm-hand function after stroke, for example by improving the selection of time-window and patients. Show less
In the chronic stage of Complex Regional Pain Syndrome (CRPS), motor disturbances are common and cause significant disability. The motor dysfunction of CRPS is a poorly understood phenomenon that... Show moreIn the chronic stage of Complex Regional Pain Syndrome (CRPS), motor disturbances are common and cause significant disability. The motor dysfunction of CRPS is a poorly understood phenomenon that is characterized predominantly by a decrease or loss of voluntary muscle control. This thesis aims to obtain a better understanding of the pathophysiology underpinning the motor dysfunction of CRPS by examining the potential roles of decreased inhibition of the motor system, changes in sensory processing and problems in sensory-motor integration. In specific, characteristics of muscle activity recordings are scrutinized in order to determine whether the loss of voluntary motor control and abnormal postures in CRPS exhibit characteristics of dystonia that are associated with reduced inhibition of the motor system (i.e., excessive muscle activation and enhanced mirror activity). The potential role of impaired processing of proprioceptive information related to wrist orientation and force production is examined, as well as the involuntary and voluntary (sensory-)motor interactions between the affected and unaffected arm. Furthermore, a systematic review of the literature on the motor consequences of experimental pain in healthy humans is presented in order to gain insight into the potential role of pain-related processes in the motor and sensory and motor disturbances of CRPS. Show less
The studies reported in this thesis aimed to survey the prevalence of inclusion body myositis (IBM), to describe its clinical features and course, to investigate whether the major... Show moreThe studies reported in this thesis aimed to survey the prevalence of inclusion body myositis (IBM), to describe its clinical features and course, to investigate whether the major histocompatibility complex predisposed subjects to IBM and autoimmune disorders (AID), to investigate the possible affliction of the neuromuscular junction (NMJ) and finally, to study whether the progression of IBM could be slowed down. On July 1st, 1999, the prevalence was estimated on at least 4.9.10-6 inhabitants in the Netherlands. The incidence rate increased since the 1980s. Time of onset was generally after the age of forty. Symptons at onset could be linked to weakness of the quadriceps muscles , the finger flexors or pharynbgeal muscles. Weakness showed a variable progression rate. Progression of weakness was faster when onset was over the age of 56. Ankylosis was common, but could be helpful in performing skilful movements. Ventral muscles were more frequently and severely affected than dorsal muscles, and girdle muscles were relatively spared, a specific pattern. Repetitive nerve stimulation studies showed normal compound muscle action potential patterns suggestive of normal NMJ transmission. In IBM patients a high frequency of AID was observed. Compared to controls, patients had a high frequency of HLA-antigens of the HLA-A1-B8-DR3-DR52-DQ2 complex. This high frequency could be related to IBM alone and not to the presence of AID. Lastly, in a randomized placebo controlled trial with methotrexate no important effect on weakness progression could be demonstrated. Show less
