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Biomedical subjects

F C T van der Helm

Publications and source records attributed to F C T van der Helm.

At least 19 recordsLinked to original sources
PubMed2007

Shoulder function: the perfect compromise between mobility and stability.

Shoulder function is a compromise between mobility and stability. Its large mobility is based on the structure of the glenohumeral joint and simultaneous motion of all segments of the shoulder girdle. This requires fine-tuned muscle coordination. Given the joint's mobility, stability is mainly based on active muscle control with only a minor role for the glenohumeral capsule, labrum and ligaments. In this review factors influencing stability and mobility and their consequences for strength are discussed, with special attention to the effects of morphology, muscle function and sensory information.

Acromioclavicular Joint↗
PubMed2006

Morphological muscle and joint parameters for musculoskeletal modelling of the lower extremity.

BACKGROUND: To assist in the treatment of gait disorders, an inverse and forward 3D musculoskeletal model of the lower extremity will be useful that allows to evaluate if-then scenarios. Currently available anatomical datasets do not comprise sufficiently accurate and complete information to construct such a model. The aim of this paper is to present a complete and consistent anatomical dataset, containing the orientations of joints (hip, knee, ankle and subtalar joints), muscle parameters (optimum length, physiological cross sectional area), and geometrical parameters (attachment sites, 'via' points). METHODS: One lower extremity, taken from a male embalmed specimen, was studied. Position and geometry were measured with a 3D-digitizer. Optotrak was used for measurement of rotation axes of joints. Sarcomere length was measured by laser diffraction. FINDINGS: A total of 38 muscles were measured. Each muscle was divided in different muscle lines of action based on muscle morphology. 14 Ligaments of the hip, knee and ankle were included. INTERPRETATION: The presented anatomical dataset embraces all necessary data for state of the art musculoskeletal modelling of the lower extremity. Implementation of these data into an (existing) model is likely to significantly improve the estimation of muscle forces and will thus make the use of the model as a clinical tool more feasible.

Aged↗
PubMed2006

Inverse dynamics calculations during gait with restricted ground reaction force information from pressure insoles.

The number of consecutive strides that can be recorded in measurements of gait have been limited due to the number of force plates and dimensions of the measurement field. In addition, the feet are constrained to land on the force plates. A method to calculate the inverse dynamics from the motion and incomplete information from the ground reaction forces (GRF), vertical component and its application point, is presented and compared to the calculations based on force plate measurements. This method is based on the estimation of the three-dimensional GRF during walking with pressure insoles. RMS errors were lower than 20 W for knee joint power compared to those derived from force plate measurements. The errors were larger during double stance phase due to errors in the application point measured with the insoles. This method, with some technical improvement, could be implemented in new gait analysis protocols measuring several consecutive steps either on a treadmill or over ground, depending on the motion-measurement system, without constraining foot placement.

Adult↗
PubMed2006

The relationship between two different mechanical cost functions and muscle oxygen consumption.

Inverse-dynamic models often use cost functions to solve the load-sharing problem. Although it is often assumed that energy is minimised, most cost functions are based on mechanically related measures like muscle force or stress. The aim of this study was to analyse the relationships of two cost functions with experimentally determined data on muscle energy consumption. Four subjects performed isometric contractions generating combinations of elbow flexion/extension and pro/supination moments. Muscle oxygen consumption (VO2) of the m. biceps breve, m. biceps longum, m. brachioradialis and m. triceps laterale was measured with near infrared spectroscopy. Both cost functions were implemented into an existing inverse-dynamic shoulder and elbow model and the individual cost values per muscle were calculated, normalised and subsequently compared to experimental VO2 values. The minimum stress cost function led to a good correspondence between VO2 and cost for the m. triceps laterale but for the flexor muscles cost was significantly lower. A newly proposed energy-related cost function showed, however, a far better correspondence. The inclusion of a linear term and muscle mass in the new criterion led model results to correspond better to experimental results. The energy-related cost function appeared to be a better measure for muscle energy consumption than the stress cost function and led to more realistic predictions of muscle activation.

Adult↗
PubMed2006

Describing gait as a sequence of states.

Traditionally, gait analysis has been based on normalizing the stride time to a percentage and then averaging several strides measured under the same conditions. This procedure relies on the questionable assumptions that gait is a cyclic movement with superimposed noise and that there is no variability in the timing of activation or in the angles within the stride so no rescaling occurs during the percentage conversion. However, there is a fluctuation in the timings at which the peak values occur. A typical hallmark of this time-rescaling is the increase of the joint angle standard deviation when the angular velocity increases. The goal of this paper is to present a description of gait to avoid averaging without distorting the original curves. In addition, it allows the analysis of the fluctuation between consecutive strides. In this method, it is assumed that gait is quasi-periodic. The key point is the representation of gait by a state vector that evolves in time. This state vector can be used to calculate the instantaneous period and provides a measure of the time fluctuations between strides. The sequence of states method describes a quasi-periodic movement like gait with a continuous estimate of cycle time and provides measure of the deviations between cycles.

Ankle Joint↗
PubMed2005

A kinematical analysis of the shoulder after arthroplasty during a hair combing task.

BACKGROUND: After shoulder arthroplasty, post-operative Range of Motion is usually compromised. It is, however, unclear to what extent limitations in Range of Motion are related to functional outcome in terms of Activities of Daily Living. METHODS: The upper extremity motions of 13 patients (16 shoulders) and a control group (N = 24) during four Range of Motion tasks and Activities of Daily Living were measured using a six degree-of-freedom electromagnetic tracking device. Based on the results for the Activities of Daily Living task 'hair combing', the patient groups was divided into a group that could perform this task ('Able', N = 8, 10 shoulders) and a group that could not perform the task ('Unable', N = 6, six shoulders). RESULTS: Both patient groups showed considerable limitation in glenohumeral Range of Motion, when compared to controls, but between patient groups only axial rotation Range of Motion was different: the 'Able' group has a larger external rotational Range of Motion, but less internal rotation. During 'combing hair' the Able group appeared to successfully perform the task through a larger clavicular retraction. INTERPRETATION: The ability to perform, or not perform a task appeared to be related to a compensatory movement implementation by means of clavicular retraction. It is concluded that the functional outcome after arthroplasty is limited due to a lack of glenohumeral Range of Motion but that it is possible to compensate for this restriction.

Activities of Daily Living↗
PubMed2005

Requirements for upper extremity motions during activities of daily living.

BACKGROUND: Functioning of the upper extremity after implantation of an endoprosthesis remains limited despite the achieved pain relief. Upper extremity kinematics can give insight into function after shoulder arthroplasty. Data on ranges of motion related to the performance of a selection of activities of daily living can aid the clinician in evaluating the outcome of the shoulder and elbow arthroplasties. METHODS: Cross-sectional descriptive study of range of motion and activities of daily living kinematics, conducted on non-impaired subjects. The shoulder and elbow motions of 24 healthy female subjects are measured with an electromagnetic tracking device while performing 8 range of motion tasks and five activities of daily living. The angles of shoulder and elbow are calculated during these tasks. RESULTS: A data set with upper extremity joint angles has been obtained. Large glenohumeral rotations are found for the tasks that require high elevation angles. Large axial rotations of the humerus are found for two of the activities of daily living tasks: the perineal care task and the hair-combing task. Large elbow flexions were seen in the following tasks: combing hair, washing the axilla and eating with a spoon. INTERPRETATION: This study shows a suitable method to describe range of motion and activities of daily living and can serve as a starting point for developing a database on how activities of daily living are performed in a larger population and which joint angles are required to perform these tasks. Results can be used to identify restrictions in upper extremity functioning in patients with shoulder impairments.

Activities of Daily Living↗
PubMed2005

Energy analysis of human stumbling: the limitations of recovery.

This study has analyzed the segmental energy changes in the recovery from a stumble induced during walking on a treadmill. Three strategies emerged according to the behavior of the perturbed limb, elevating, lowering, and delayed lowering. These three strategies showed different changes in the segmental energy with respect to normal gait. In the elevating strategy, the energy loss induced by the stumble was restored during the perturbed step and reached normal levels during the recovery step. The largest energy changes occurred in the lowering and delayed lowering strategies during the double stance (DS) phase. Moreover, in some of these trials there was energy absorption during the double stance phase for several strides after the perturbation. The most challenging perturbations had longer duration or occurred at mid-swing, triggering delayed lowering or lowering strategies, because more strides and larger energy changes were needed to recover, suggesting a trade-off between stability and energy efficiency.

Adult↗
PubMed2005

Mechanical properties and functional importance of pulley bands or 'faisseaux tendineux'.

INTRODUCTION: Connective tissue bands connect the horizontal rectus muscles at the level of the posterior pole to the orbital wall. These bands, referred to as pulley bands or faisseaux tendineux, purportedly act like springs to keep the rectus muscle bellies in place during eye movement out of the plane of the muscle. We examined the mechanical properties of these bands in human specimens obtained during surgery. In addition, we examined eye motility and stability of rectus muscles in a patient who had no functional pulley bands. METHODS: Exenterations were carried out on two patients with sebaceous gland carcinoma. Pulley bands were identified and force-elongation behavior was examined with a forceps and a force gauge. Stability of rectus muscles was examined in a patient with severe Crouzon's syndrome by orbital CT scans and during surgery under local, eye drop, anesthesia. RESULTS: The pulley bands showed leash-like mechanical behavior: they were slack over approximately 10mm and became taut when stretched further. In the patient with Crouzon's syndrome, both CT and observation of the muscle during surgery showed little sideways displacement of the muscle bellies in eye movement out of the plane of the muscle, despite the lack of functional pulley bands. DISCUSSION: The leash-like mechanical behavior of the pulley bands seems unsuited for stabilization of the muscle bellies. The patient with Crouzon's syndrome had relatively good eye motility and stable rectus muscle paths despite the lack of functional pulley bands.

Aged↗
PubMed2004

Mechanical model of the recovery from stumbling.

Several strategies have been described as a reaction to a stumble during gait. The elevating strategy, which tries to proceed with the perturbed step, was executed as a response to a perturbation during early swing. The lowering strategy, bringing the perturbed leg to the ground and overtaking the obstacle with the contralateral limb, was executed more frequently when the perturbation appeared at mid or late swing. The goal of this paper is to analyze which mechanical factors determine the most advantageous strategy. In order to determine these factors, a mechanical model of the recovery was developed and used to analyze a series of perturbation experiments. It was assumed that the goal of the recovery reaction was to control the trunk as an inverted pendulum during the double-stance phase. In order to be able to control the trunk angle, one foot should be up front and one foot should be behind the hips; otherwise it would be impossible to generate the required trunk torques. The trunk dynamics were expressed in terms of the ground reaction forces and their application point. A larger step (elevation strategy) gives the opportunity to dissolve the perturbation in one step. A small step (lowering strategy) necessarily results in a second quick step, after which the perturbation energy can be dissipated in the second double-stance phase. If a recovery step is too slow, it becomes impossible to counteract the forward flexion of the trunk. It is suggested that a measure of the ability to recover from a stumble could be based on the ability to perform quick steps.

Adult↗
PubMed2004

Bifurcation and stability analysis in musculoskeletal systems: a study in human stance.

Reflexes are important in the control of such daily activities as standing and walking. The goal of this study is to establish how reflexive feedback of muscle length, velocity, and force can lead to stable equilibria (i.e., posture) and limit cycles (e.g., ankle clonus and gait). The influence of stretch reflexes on the behavior and stability of musculoskeletal systems was examined using a model of human stance. We computed branches of fold and Hopf bifurcations by numerical bifurcation analysis of the model. These fold and Hopf branches divide the parameter space, constructed by the reflexive feedback gains, into regions of different behavior: unstable posture, stable posture, and stable limit cycles. These limit cycles correspond to a neural deficiency, termed ankle clonus. We also linked bifurcation analysis to known biomechanical concepts by linearizing the model: the fold branch corresponds to zero ankle stiffness and defines the minimal muscle length feedback necessary for stable posture; the Hopf branch is related to unstable reflex loops. Crossing the Hopf branch can lead to the above-mentioned stable limit cycles. The Hopf branch reduces with increasing time delays, making the subject's posture more susceptible to unstable reflex loops. This might be one of the reasons why elderly people, or those with injuries to the central nervous system, often have trouble with standing and other posture tasks. The influence of cocontraction and force feedback on the behavior of the posture model was also investigated. An increase in cocontraction leads to an increase in ankle stiffness (i.e., intrinsic muscle stiffness) and a decrease in the effective reflex loop gain. On the one hand, positive force feedback increases the ankle stiffness (i.e., intrinsic and reflexive muscle stiffness); on the other hand it makes the posture more susceptible to unstable reflex loops. For negative force feedback, the opposite is true. Finally, we calculated areas of reflex gains for perturbed stance and quiet stance in healthy subjects by fitting the model to data from the literature. The overlap of these areas of reflex gains could indicate that stretch reflexes are the major control mechanisms in both quiet and perturbed stance. In conclusion, this study has successfully combined bifurcation analysis with the more common biomechanical concepts and tools to determine the influence of reflexes on the stability and quality of stance. In the future, we will develop this line of research to look at rhythmic tasks, such as walking.

Ankle↗
PubMed2004

Effectiveness of tendon transfers for massive rotator cuff tears: a simulation study.

UNLABELLED: OBJECTIVE To determine what the most effective tendon transfer is in the case of a dysfunctional rotator cuff. DESIGN: A tendon transfer procedure of latissimus dorsi, teres major or a combination of these two to the insertions of either teres minor, infraspinatus, supraspinatus, or subscapularis is simulated using a biomechanical musculoskeletal model of the upper extremity. BACKGROUND: Massive rotator cuff tears are not easily repaired. To compensate for this loss of rotator cuff function other techniques like muscle transfers are developed. METHODS: Three range of motion tasks and six activities of daily living of 24 subjects were measured. Kinematics from these tasks were used as input to the Delft Shoulder and Elbow Model. The muscle parameters of the Delft Shoulder and Elbow Model were modified to simulate a rotator cuff tear and the ability to perform the measured tasks with and without simulated transfer procedures was checked. RESULTS: The highest improvements (28-30%, P = 0.00 ) in the ability to perform tasks were observed after a simulated tendon transfer of either both muscles or teres major alone attached to the supraspinatus or infraspinatus insertion. Although all transfer procedures produce significant improvements (P = 0.00 ), there is a significant difference between the procedures (Chi square=58.8, P = 0.00 ) dependent on attachment site. CONCLUSIONS: According to the simulation procedure used in the current study, a tendon transfer of teres major and latissimus dorsi or teres major alone to the supraspinatus insertion appears to be the most effective procedure in the case of a dysfunctional rotator cuff. Practical factors, like subacromial space, volume of the muscles and tendons, tensile properties and the ability to split the muscles, will finally determine which is the preferred transfer option.

Analysis of Variance↗
PubMed2004

Biomechanical analysis of tendon transfers for massive rotator cuff tears.

OBJECTIVE: To determine why certain tendon transfers are mechanically more effective than other tendon transfers for the treatment of a massive rotator cuff tear. DESIGN: A tendon transfer procedure of latissimus dorsi, teres major or a combination of these two to the insertions of either teres minor, infraspinatus, supraspinatus, or subscapularis is simulated using a biomechanical musculoskeletal model of the upper extremity. BACKGROUND: Massive rotator cuff tears are not easily repaired. To compensate for the loss of rotator cuff function, techniques such as muscle transfers are developed. METHODS: Three range of motion tasks were used as input to the Delft shoulder and elbow model. The muscle parameters of the Delft shoulder and elbow model were modified to simulate a rotator cuff tear. A biomechanical analysis of the transferred muscles was performed, taking outcome variables such as moment arms, muscle length and muscle force into account. RESULTS: Due to the massive rotator cuff tear, an elevation and external rotation moment is lost. When the tendon was transferred to the insertions of infraspinatus or supraspinatus, the humerus was capable of elevating and externally rotating. CONCLUSIONS: On the basis of mechanical parameters such as moment arms, muscle length and force it can be concluded that a tendon transfer of the teres major to the supraspinatus insertion will produce the best functional outcome in the treatment of massive rotator cuff tears. RELEVANCE: To find biomechanical evidence for an optimal tendon transfer that will lead to improved treatment of patients with a massive rotator cuff tear.

Biomechanical Phenomena↗
PubMed2004

The possibilities of uncemented glenoid component--a finite element study.

OBJECTIVE: (1) Determine the initial stress distributions within an uncemented implanted glenoid during elevation of the arm and to investigate whether failure is caused by stresses generated within this implant-bone structure. (2) Compare stress patterns between the uncemented design and two basic models of cemented prostheses. DESIGN: The uncemented component consists of a polyethylene cup with a metal-backing. All material interfaces were assumed to be fully bonded. BACKGROUND: Cemented glenoid components have been frequently vulnerable to failure within itself and at the cement-bone interface. A 3-D finite element analysis of an uncemented design is required to investigate whether clinical observations on failure can be better explained with a stress analysis. METHODS: A 3-D finite element submodel an uncemented prosthesis was generated using CT-scan data and realistic loading conditions (humeral abduction, 30-180 degrees ). The submodelling approach was based on an overall solution of a complete scapula acted upon by all muscles, ligaments and joint reaction forces. RESULTS: High Von Mises stresses (20-70 MPa) were generated in the metal-backing during abduction. Stresses were reduced in the polyethylene cup by 17-20% as compared to the cemented designs. Stresses in the underlying bone were substantially lower than to the natural glenoid. Stress-shielding can be observed in the trabecular bone underlying the prosthesis. The implant-bone interface is secure against interface failure at moderate loads, although the implant-bone (metal-bone) interface around the superior edge of the prosthesis is subject to high stresses (normal: 11.85 MPa, shear: 6.67 MPa) as compared to the cemented prosthesis. Whereas, the cement-bone interface, appears more likely to fail either at locations adjacent to the keel or at locations around the superior edge of the cemented design. The uncemented design therefore appeared to be a reasonable alternative to fixation with cement. RELEVANCE: Results of this study strongly agree with clinical and radiographic findings. Although indications of stress-shielding and separation of modular parts of the prosthesis were apparent, the implant-bone interface seems less likely to fail as compared to cemented designs. Once initial fixation of the implant is achieved, the uncemented design appears to have better prospects than cemented ones.

Equipment Failure Analysis↗
PubMed2004

Biomechanical analysis of scapular neck malunion--a simulation study.

OBJECTIVE: To explain loss of shoulder function following scapular neck malunion in terms of biomechanical changes around the gleno-humeral joint. DESIGN: Biomechanical modelling study. BACKGROUND: Residual rotation of the scapular neck after fracture can lead to pain and loss of function, and the indications for surgical intervention are contested. METHODS: A 3D, large-scale, musculo-skeletal model of the upper limb was used to compare shoulder biomechanics in the case of scapular neck malunion with normal anatomy. Abduction of the humerus was simulated with three models: normal anatomy, 24 degrees and 40 degrees inferior scapular neck rotation. RESULTS: Predicted muscle activation differed greatly between the control and the fracture cases. The motion required additional muscle effort for the maintenance of gleno-humeral stability in the fracture cases. Higher moments in the plane of abduction were generated by the teres major, pectoralis major and biceps brachii muscles with high humeral elevation angles. The rotator cuff muscles were severely shortened in the post-fracture cases and the forces in these muscles were greatly reduced in a test of loaded abduction with the humerus at 90 degrees. CONCLUSIONS: Given the function of the rotator cuff muscles as stabilisers of the gleno-humeral joint, it is concluded that the loss of force in these muscles, together with other changes in muscle activation, will lead to loss of arm function in patients with scapular neck malunion. RELEVANCE: These findings will contribute to the improved treatment of patients with scapular neck malunion by identifying important factors in the consideration of surgical intervention.

Biomechanical Phenomena↗
PubMed2004

Estimating muscle attachment contours by transforming geometrical bone models.

For individualization of a biomechanical model, it is necessary to estimate the muscle attachments of the person to whom it is to be adapted. One of the methods to estimate muscle attachments is to use model transformations to transform a model with known muscle attachments to the bones of a person. We hypothesize that the location and shape of muscle attachment sites correlate with the shape of the bones they are attached to. If this hypothesis holds, it is possible to predict the location of muscle attachments when the shape of the bones is known. To validate this hypothesis, geometric models of three sets of shoulder bones were built. These models consist of 3-D surface models of the scapula, clavicle, and humerus, with the muscle attachment contours connected to them. By means of geometric transformations, the models were transformed, so the muscle attachments of the different data sets could be compared. Using these techniques, 50 per cent of the muscle attachment contours could be predicted with high accuracy. The muscle attachment contours that could not be predicted were all influenced by measurement errors. For 30 per cent of the muscle attachment contours, it was not possible to distinguish the interindividual differences from the inaccuracies of the method used. From this study, we concluded that most muscle attachment contours can be predicted by means of geometric models of the bones.

Algorithms↗
PubMed2004

Use of pressure insoles to calculate the complete ground reaction forces.

A method to calculate the complete ground reaction force (GRF) components from the vertical GRF measured with pressure insoles is presented and validated. With this approach it is possible to measure several consecutive steps without any constraint on foot placement and compute a standard inverse dynamics analysis with the estimated GRF.

Computer Simulation↗