Biomedical subjects

J Harlaar

Publications and source records attributed to J Harlaar.

At least 19 recordsLinked to original sources

PubMed2005

Reproducibility of instrumented knee joint laxity measurement in healthy subjects.

OBJECTIVE: To determine the reproducibility of frontal plane knee joint laxity measurement through the assessment of intra- and inter-rater reliability coefficients and intra- and inter-rater agreement coefficients. METHODS: Two raters independently assessed the laxity of the knee joint in the frontal plane by three repeated measurements. Fourteen days later the assessment was repeated. Complete data were obtained from 20 healthy subjects. Laxity was assessed using a device which consisted of a chair with a free-moving arm that supported the subject's lower leg. Medial and lateral loads were applied, resulting in a varus and valgus movement in the knee joint. The intra- and inter-rater reliability coefficients [intraclass correlation coefficients (ICC)] were estimated, as were the intra- and inter-rater agreement parameters [standard error of measurement (SEM) and minimal detectable difference (MDD)]. RESULTS: Adequate intra-rater reliability (ICC>0.80) was calculated for each rater's measurements of laxity. The inter-rater reliability was less adequate (ICC=0.65) when calculated using the first day's measurements. However, inter-rater reliability was adequate (ICC=0.88) when calculated using the day 14 measurements. The intra-rater measurement error calculated across occasions was 1.3 degrees for individual subjects. This resulted in an MDD of 3.7 degrees. The inter-rater measurement error, i.e. the SEM and MDD, was higher (1.5 degrees and 4.3 degrees, respectively). CONCLUSIONS: Intra-rater reliability of knee joint laxity measurement is good. Adequate training of raters establishes the basis for good inter-rater reliability. In clinical trials, it is preferable for one trained rater to perform the laxity measurement. The measurement of knee joint laxity is limited due to its relatively high measurement error in individual subjects; therefore, this measurement should be restricted to group assessment rather than individual patient assessment.

Adult↗

PubMed2004

Influence of hamstring lengthening on muscle activation timing.

The purpose of this study was to describe the changes in muscle activation patterns using surface electromyography (sEMG) during walking in patients with cerebral palsy (CP), before and after hamstring lengthening. In the current clinical use of sEMG during walking in CP for pre-operative planning, various authors have observed that timing of muscle activation patterns hardly changes after surgical intervention. This observation is based on tendon transfer studies and visual interpretation of raw EMG signals. Little is known about the effect of muscle lengthening on muscle activation patterns of the lengthened muscles and their antagonists. Fifteen children with CP comprising a total of 23 hamstring lengthenings were included in this study. Surface EMG of semitendinosus and vastus lateralis was measured before and after surgery. Timing parameters of the sEMG patterns were quantified, using an objective burst detection algorithm and statistically evaluated. Results showed that hamstring lengthening causes statistically significant differences in timing of both the semitendinosus and vastus lateralis. It is concluded that timing parameters of operated muscles and their antagonists after surgery do change. The delayed off-time of the semitendinosus and the decreased burst duration of the antagonist (the vastus lateralis) after surgery were the most important changes.

Adolescent↗

PubMed2004

Validation of the portable VmaxST system for oxygen-uptake measurement.

The aim of this study was to validate the accuracy of a new type of portable gas-analysis system (Sensormedics VmaxST) for the measurement of oxygen-uptake at expenditure levels that are reached during walking in patients with movement disorders. The criterion method was the Douglas Bag (DB) method, which is considered to be the gold standard. Accuracy evaluations were made in two trials, randomly using the VmaxST (ST) and the Douglas Bag method. Ten healthy adult subjects participated in the trials (age: 28.8 (4.3) years; body mass: 75 (13.3)kg; height: 179.3 (8.9)cm). Each trial consisted of two time periods: 5 min of resting in a comfortable chair and 5 min of cycling at an 80 W workload. During the fifth minute of each block, mean minute ventilation (VE), oxygen-uptake (VO2), and carbon dioxide production (VCO2) were measured or calculated for both systems. Energy expenditure (EE) values were calculated and net values calculated by subtracting resting measurements from gross measurements. The results show that no significant differences were found between the VmaxST and the Douglas Bag method for the primary parameters: EEnet and VO2net. Significantly higher values were found for rest and exercise values. However, these differences were very small. Therefore, the validity of the VmaxST is sufficient for use in gait studies to determine the energy cost of walking, especially when net values are calculated.

Adult↗

PubMed2001

The effect of cooling on muscle co-ordination in spasticity: assessment with the repetitive movement test.

PURPOSE: Cooling muscles might produce a temporary reduction of spasticity. This study investigated muscle co-ordination in spasticity under the influence of cooling. METHODS: A repetitive movement (RM-) test of the ankle was used, while measuring the angle and surface-electromyography (EMG) of the m. tibialis anterior and m. triceps surae. Ensemble averaging provided quantified measures of muscle activation. Sixteen patients with spasticity in their lower extremity due to stroke or spinal cord injury participated in the study. Physical examination and the RM-test was done before and after cooling the m. triceps surae for 20 minutes by coldpacks. RESULTS: The results show that Achilles hyperreflexia and clonus were abolished in all, and all but one patient, respectively. The EMG of the m. triceps surae, acting as a prime mover, was increased (p = 0.028). However, this improved muscle co-ordination resulted in just a slightly increased active range of motion (less than 2 degrees at p = 0.049). CONCLUSION: Apparently, the increase in excitability of the alpha motoneuron pool in voluntary movements of patients with spasticity is not followed by an improvement in the ability to move.

Ankle Joint↗

PubMed2001

Determination of functional rotation axes during elevation of the shoulder complex.

STUDY DESIGN: A cross-sectional, descriptive study of shoulder movements conducted on nonimpaired subjects. OBJECTIVE: To investigate whether a single functional rotation axis about the shoulder complex can be determined during elevation in the coronal or sagittal planes, and to identify their location. BACKGROUND: Accurate measurement of isokinetic torques about a joint requires alignment of the dynamometer axis with an assumed rotation axis of the joint. To assess shoulder function on a dynamometer, the location of a single rotation axis is not evident because the shoulder joint motion is based on several anatomical joints. Therefore, the rotation axis where humerothoracic movements occur should be judged as a functional rotation axis. METHODS AND MEASURES: During slow elevation movements in the sagittal and coronal plane, the position of the epicondyle and acromion were recorded with a motion analysis system. The motion trajectory of the elbow coordinates was fitted to a circle and considered an estimate of the functional shoulder joint rotation axis in the specified plane. RESULTS: The fitted trajectory appeared to be very accurate (root-mean-square error < 2%; N = 7). In the sagittal plane, the estimated functional rotation axis was found at the humeral head; in the coronal plane, it was located about 13 centimeters medial relative to the acromion. CONCLUSION: The shoulder complex of nonimpaired subjects can act as a hinge joint of the upper arm relative to the thorax during elevation in each measured plane.

Adult↗

PubMed2000

Passive stiffness characteristics of ankle plantar flexors in hemiplegia.

OBJECTIVE: To assess the feasibility and reliability of ankle plantar flexor stiffness measurements in hemiplegia. DESIGN: Repeated measurements in five consecutive weeks. BACKGROUND: In hemiplegia, an equinovarus positioning of the foot might be caused by an increased stiffness of the m. triceps surae. METHODS: In eight hemiplegic patients the net joint torque of passive muscle stretch was measured as a function of ankle-angle by a dynamometer, at both sides. Ankle-stiffness was characterised and also a biomechanical model of the passive muscle was fitted. RESULTS: In the vast majority of measurements it was possible to obtain measurements that were not distorted by involuntary muscle contraction. These measurements showed for the angle at which a passive plantar moment of 10 N m was reached a standard error of measurement of less than 2.7 degrees. The muscle model showed the increased stiffness as a shortening of the muscle-fibre-length. CONCLUSION: The feasibility of this method to measure muscle stiffness was fair to good in hemiplegic patients. Provided the abandoning of involuntary muscle activity, the reproducibility warrants application in clinical practice at an individual level. The use of the model relates this changes to a shortened m. soleus and/or m. gastrocnemius. RelevanceEffective clinical decisions for treatment of equinovarus positioning of the foot in the hemiplegic individual, should consider excessive involuntary contractions of the m. triceps surae complex (i.e., spasticity), as well as shortened muscle tissue resulting in high stiffness. Despite the importance of increased stiffness there have been no validated methods of measurement.

Adult↗

PubMed2000

Predictions of mechanical output of the human M. triceps surae on the basis of electromyographic signals: the role of stimulation dynamics.

In order to assess the significance of the dynamics of neural control signals for the rise time of muscle moment, simulations of isometric and dynamic plantar flexion contractions were performed using electromyographic signals (EMG signals) of m. triceps surae as input. When excitation dynamics of the muscle model was optimized for an M-wave of the medial head of m. gastrocnemius (GM), the model was able to make reasonable predictions of the rise time of muscle moment during voluntary isometric plantar flexion contractions on the basis of voluntary GM EMG signals. The rise time of muscle moment in the model was for the greater part determined by the amplitude of the first EMG burst. For dynamic jumplike movements of the ankle joint, however, no relationship between rise time of muscle moment in the experiment and muscle moment predicted by the model on the basis of GM EMG signals was found. Since rise time of muscle moment varied over a small range for this movement, it cannot be completely excluded that stimulation dynamics plays a role in control of these simple single-joint movements.

Adult↗

PubMed2000

The SYBAR system: integrated recording and display of video, EMG, and force plate data.

A new system--called SYBAR--is introduced, that employs digital video for registration of the movements of a patient while simultaneously recording electromyogram signals of relevant muscles and ground reaction forces (for the lower extremities in gait studies). All information is stored in a multimedia record, which can be viewed by the clinician with a simple user interface. This setup allows an integrated and more detailed view of the movement of the patient and related information (i.e., muscle physiology). It is used by clinicians to assess the causes of movement disorders in their patients. This paper describes the SYBAR system and focuses on the employed methods of data synchronization for both the time and the spatial domains. It is concluded that, although SYBAR was developed for clinical gait studies, the technology can be applied in all situations in which the relation between physiological signals and human or animal behavior is studied.

Electromyography↗

PubMed1998

Electromyography in the biomechanical analysis of human movement and its clinical application.

This article introduces the area of scientific study of human movement. It is primarily intended for readers who wish to form a judgement on the usefulness of scientific movement analysis techniques in the treatment process of patients with abnormal movement patterns. With a focus on the analysis of human locomotion, the paper outlines the historical development of a biomechanical approach towards the understanding of human movement patterns. This approach alone proves to be inadequate in supplying reliable information on neuromuscular control of movement. It follows that electromyographic techniques are essential for this purpose. Scientific literature reveals relevant practical usability of such information. This is the rationale for a review of the historical, physiological, technical and methodological background of electromyographic analysis of movement. The field of management and rehabilitation of motor disability is identified as one important application area. On the basis of relevant literature, the present paper asserts that scientific analysis of human movement patterns can materially affect patient treatment. It provides evidence that patient management and rehabilitation processes in central neurological disorders can be improved through electromyographic techniques. In particular, this evidence supports the use of electromyography for surgical planning in children with cerebral palsy. The paper concludes with a view on future directions in research, development and applications of scientific analysis of human movement. Copyright 1998 Elsevier Science B.V.

Journal Article↗

PubMed1998

[Clinical analysis of motion using multimedia technology].

In disabling orthopaedic and neurological disorders, in addition to clinical and imaging examination, observation of the motion is an important method of examination. It serves as a starting point for the motion analysis using digital video. In this way, muscle functions can be measured with the aid of a kinesiological EMG. Load on the joints of the lower extremities can be deduced from a projection of the foot reaction vector on the body. Combination of a video film of the motion (the gait) with measurement of the kinesiological EMG provides a motion analysis based on multimedia techniques. With modern personal computers, interactive examination of these digital data is simple. Three examples of this functionality can be viewed at the Internet site of this journal (http:@appendix.niwi.knaw.nl): the normal walking cycle, the active stabilization of the knee after an injury of the anterior cruciate ligament and the gait of a woman with cerebral palsy before and after orthopaedic surgery. Motion analysis using multimedia techniques makes it possible to analyse relationships between muscular and articular functions on the one hand and impaired motion on the other in a way that is meaningful to the clinician.

Anterior Cruciate Ligament Injuries↗

PubMed1998

From twitch to tetanus for human muscle: experimental data and model predictions for m. triceps surae.

In models describing the excitation of muscle by the central nervous system, it is often assumed that excitation during a tetanic contraction can be obtained by the linear summation of responses to individual stimuli, from which the active state of the muscle is calculated. We investigate here the extent to which such a model describes the excitation of human muscle in vivo. For this purpose, experiments were performed on the calf muscles of four healthy subjects. Values of parameters in the model describing the behaviour of the contractile element (CE) and the series elastic element (SEE) of this muscle group were derived on the basis of a set of isokinetic release contractions performed on a special-purpose dynamometer as well as on the basis of morphological data. Parameter values describing the excitation of the calf muscles were optimized such that the model correctly predicted plantar flexion moment histories in an isometric twitch, elicited by stimulation of the tibial nerve. For all subjects, the model using these muscle parameters was able to make reasonable predictions of isometric moment histories at higher stimulation frequencies. These results suggest that the linear summation of responses to individual stimuli can indeed give an adequate description of the process of human muscle excitation in vivo.

Adult↗

PubMed1998

Accuracy of the sagittal vertical axis in a standing lateral radiograph as a measurement of balance in spinal deformities.

Sagittal balance of the spine is becoming an important issue in the assessment of the degree of spinal deformity. On a standing lateral full-length radiograph of the spine, the plumb line, or sagittal vertical axis (SVA), can be used to determine the spinal sagittal balance. In this procedure patients have to adopt a habitual standing position with the knees extended during radiographic examination, though it is not known whether small changes in the position of the lower extremities affects the location of the SVA. The purpose of the present study was to investigate the effect of postural change on shifts of the SVA, and to evaluate whether the SVA as measured on a standing full-length lateral radiograph can be used as an accurate measurement of spinal balance in clinical practice. Sagittal balance was analyzed using a patient with ankylosis of the entire spine due to ankylosing spondylitis, to eliminate segmental movement of the spine. A virtual SVA was constructed for seven different standing postures by cross-referring the coordinate systems from a standing full-length lateral radiograph of the spine with video analysis. The horizontal distance between the SVA and the anterior superior corner of the sacrum was measured for each posture. Small changes in the joint angles of the lower extremities affected the SVA significantly, and resulted in the horizontal distance between the SVA and the anterior superior corner of the sacrum varying from -4.5 to +14.9 cm. High correlations were found between this distance and the joint angle of the hip (r = -0.959), knee (r = -0.936), and ankle (r = 0.755) (P < 0.01). The results of the study showed that SVA translations during standing radiographic analysis in a patient with a fixed spine depend on small changes in the hip, knee, and ankle joints. Thus, sagittal spinal (im)balance in ankylosing spondylitis can not be measured from the SVA on a standing lateral full-length radiograph of the spine unless strict procedures are developed to control for the angle of the hip, knee, and ankle joints. The accuracy of the SVA as a measurement of sagittal spinal balance in other spinal deformities, with possible additional segmental movements, therefore remains questionable.

Adult↗

PubMed1998

Reliability assessment of isometric knee extension measurements with a computer-assisted hand-held dynamometer.

OBJECTIVE: To assess clinically relevant indexes of measurement error of hand-held dynamometer measurements using a computer-assisted hand-held dynamometer (CAHN-DY). DESIGN: In separate sessions, different physical therapists performed repeated measurements of maximal isometric knee extension. SETTING: Four physical therapy practices and outpatient departments. PATIENTS: Consecutive samples of 30 male and 28 female patients aged 13 to 77 years, with isolated orthopedic knee disorders participated in this study. MAIN OUTCOME MEASURES: For intrarater and interrater applications, the standard error of measurement (SEM) and related 95% confidence intervals and minimal detectable changes were assessed. RESULTS: Sixty percent of the patients performed within the therapist's upper force limit. Variance between sessions performed by the same or different therapists accounted for a large percentage of the measurement error (70% to 81%). For single measurements, the standard error of measurement was assessed not to exceed 10N x m. Minimal detectable changes for different designs varied from 13.8 to 28.2N x m. CONCLUSIONS: The CAHN-DY facilitated standardization of test performance in a satisfactory manner, resulting in less measurement error compared with simple hand-held dynamometry.

Adolescent↗

PubMed1998

Impairment assessment in rehabilitation medicine: the potential role of technology to assist clinical decision making.

Assessment in rehabilitation medicine needs to be conceptualized using the ICIDH. Generally, an un-impaired function is conditional for good performance at the disability level. So, treatment at the level of impairment might be necessary to eventually minimize the amount of disability. At this point it is compulsory to assess the impairment firstly for an indication of the therapy, and also during and/or after the impairment therapy for evaluation. Finally, the tentative idea that the impairment was responsible for the disability is subjected to evaluation using the D-level assessment again. In this concept, specific assessment of impairment is nested within the assessment at the level of disability. It is concluded that this framework of clinical decision making in rehabilitation medicine can be used to judge whether instruments for impairment assessment will potentially be useful in clinical decision making.

Decision Support Techniques↗

PubMed1998

Measurement of impaired muscle function of the gastrocnemius, soleus, and tibialis anterior muscles in spastic hemiplegia: a preliminary study.

Based on the results of several electrodiagnostic and biomechanical studies, the following classification of muscle dysfunction in spastic hemiplegia is proposed: changes in muscle activation (excess symptoms, e.g., spasticity, and deficit symptoms, e.g., paresis); changes in muscle stiffness; and changes in muscle length. The clinical significance of this classification is that different types of muscle dysfunction might require specific treatment. The authors have developed techniques to measure quantitatively each type of muscle dysfunction: free frequency repetitive movement (FFRM) and torque angle diagram (TAD). Surface EMGs of tibialis anterior, gastrocnemius, and soleus muscle are recorded during active (FFRM) and passive (TAD) ankle movements. EMG data are converted to parameters for abnormal muscle activation (excess and deficit symptoms). Parameters for muscle stiffness and muscle length are derived from the hysteresis curve of the TAD. This article describes the measurements and the results of a validation study. For the validation study, four hypotheses were formulated: 1) in nonimpaired control subjects, parameters expressing abnormal muscle activation are low; 2) in hemiplegic subjects, differences between the affected and the unaffected sides will be found for all types of parameters; 3) after local anaesthesia of the tibial nerve on the hemiplegic side, excess symptoms will decrease, while muscle stiffness remains unchanged; and 4) despite a uniform gait pattern, between-subject differences can be detected with regard to muscle activation, stiffness, and length. The first hypothesis was tested and confirmed in two controls; the remaining three were tested and confirmed in ten hemiplegic subjects (mean age 47.7 yrs, mean time since onset 10.7 yrs). However, the level of co-contraction of the gastrocnemius muscle was low, probably indicating that the clinical significance of this phenomenon might be limited. The results support the validity of the proposed classification and measurements.

Adult↗

PubMed1997

Neonatal hearing screening with an automated auditory brainstem response screener in the infant's home.

Universal neonatal hearing screening is essential if all infants with congenital or perinatally acquired hearing impairment are to begin treatment before the age of 6 months to facilitate development of speech, language, communication and academic skills. Screening cannot always take place in hospital because of the increase in very short-stay deliveries. Therefore screening in the home may be necessary to achieve a high level of screening. We describe a feasibility study with an automated auditory brainstem response (AABR) screener in the infant's home as part of the service offered by the Well Baby Clinics in the Netherlands. Of the 277 infants who completed the screening 266 had the results "pass", 7 "refer" and 4 had inconclusive results. The mean time needed per screening was 18 min. This study shows that neonatal hearing screening by nurses using an AABR infant screener in the home is feasible.

Electronic Data Processing↗

PubMed1996

Computer-assisted hand-held dynamometer: low-cost instrument for muscle function assessment in rehabilitation medicine.

In rehabilitation medicine, muscle function is assessed during the physical examination of the patient. Although a simple hand-held instrument improves the assessment of static strength, it is rarely used in clinical practice, where dynamic measurements are preferred. A computer-assisted hand-held dynamometer (CAHNDY) has been developed that enables the clinician to measure dynamic muscle function in a standardised manner, using simple (i.e. portable and low-cost) apparatus. The CAHNDY comprises a force transducer and a movement transducer interfaced to a personal computer. In the study dynamic measurement protocols are used, based on a biomechanical analysis of daily activities. In this way, iso-functional profiles can be established, describing the kinematics of muscle function in its functional context. Using the iso-functional profiles as a basis for standardisation, the double feedback algorithm of the CAHNDY assists the tester in meeting this standard, during maximal muscle function testing. In a multi-centre trial, the CAHNDY is evaluated by physical therapists for knee extensor and flexor function. The CAHNDY enables iso-functional dynamic muscle function testing, although application is limited by the maximal strength of the tester. It is concluded that the CAHNDY is suitable for use in rehabilitation medicine.

Ambulatory Care↗

PubMed1995

Stiffness control for lower leg muscles in directing external forces.

The role of lower leg muscles is investigated during contact control tasks, in which the external force, applied by the foot on the surface, has to be controlled. Force, position and muscle activation were recorded. All subjects showed a stereotyped activation pattern to accomplish the tasks. The torques about hip and knee changed by a reciprocal activation pattern of the upper leg muscles, whereas the ankle torque remained remarkably constant as a result of a strong co-activation of the ankle muscles.

Adult↗