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Biomedical subjects

C W Spoor

Publications and source records attributed to C W Spoor.

At least 19 recordsLinked to original sources
PubMed2006

The active straight leg raising test (ASLR) in pregnant women: differences in muscle activity and force between patients and healthy subjects.

Pregnancy-related low back and pelvic pain (PLBP) is a frequent complication of pregnancy. Although pathological mechanisms underlying PLBP are obscure, dysfunction of the sacroiliac joints (SI-joints) seems to play an important role. A cross-sectional study was performed on 24 pregnant women with and without PLBP. The objective was to determine muscle activation patterns of trunk and leg muscles during the active straight leg raising test (ASLR) and static hip flexion, and to determine maximal hip flexion force at 0 and 20 cm leg raise height. Moreover, the effort to raise the leg was scored. The measurements resulted in several significant differences between the patients and healthy controls; among others (a) patients scored subjectively more effort during ASLR, (b) at both 0 and 20 cm leg raise height patients had less hip flexion force, and (c) patients developed more muscle activity during ASLR. Since pregnant women with PLBP developed a higher muscle activity during ASLR with a significantly lower output at 0 and 20 cm than healthy pregnant women, it could be proposed that the ASLR demonstrates a disturbed load transfer across the SI-joints in this population.

Abdominal Muscles↗
PubMed2006

Stability of sitting postures: the influence of degrees of freedom.

Observational studies of sitting have shown that, during spontaneous sitting, people adopt a variety of postures. Various researchers have formulated theories to explain why people adopt their sitting postures. Branton (1969) hypothesized that there is continual need for postural stability while sitting. Dempster (1955) stated that additional stability could be obtained through temporarily closing chains of body segments, or, in other words, through decreasing the number of degrees of freedom of the body. The present study elaborates on Dempster's theory. The aim of this study was to determine the influence of the degrees of freedom of the body on postural stability in sitting postures. For 21 different sitting postures, the total number of degrees of freedom was determined. Postural sway, a measure for postural stability, was determined using a 3D motion and position measurement system with ten healthy subjects. This study shows that the mean path length at the level of the second thoracic vertebra (PL0.05), a measure derived from postural sway, increases significantly (p < 0.0001) with an increase of the number of degrees of freedom of the body (DoFB). Closer examination of the data showed that a model taking into account only the degrees of freedom of the lumbar and thoracic spine and pelvis seems to be a better predictor of postural sway than the total number of degrees of freedom of the body.

Biomechanical Phenomena↗
PubMed2004

The minimum number of muscles to control a chain of joints with and without tenodeses, arthrodeses, or braces--application to the human finger.

While the underlying principles of controlling a single joint have been well described, the principles of simultaneously controlling multiple joints have not been comprehensively addressed in the literature of reconstructive hand surgery. This article analyzes (1) how many muscles are minimally required to fully control a chain of joints with in total N Degrees of Freedom (DoF), and (2) to what degree tenodeses, arthrodeses or braces can reduce the required number of muscles. It is demonstrated by mathematical analysis and illustrated by examples that the minimal number of muscles to control a chain of N DoF is N + 1. The number of muscles required for control can be reduced by mechanisms that reduce the number of DoF in the chain. (i) An arthrodesis is a permanent surgical fixation of a joint. An arthrodesis eliminates as many DoF in the chain as the arthrodized joints contributed. (ii) Tenodeses are coordinative tendon constructions. Each independent tenodesis eliminates one DoF from the chain. (iii) Braces are removable external supports. They eliminate as many DoF for muscle control as they immobilize. These principles are applied to illustrate the fundamental importance of tendinous structures in control in the human finger. Being able to determine the minimum number of muscles needed for multiarticular control gives additional knowledge in the design of functional reconstruction.

Arthrodesis↗
PubMed1999

Measuring muscle and joint geometry parameters of a shoulder for modeling purposes.

An extensive set of muscle and joint geometry parameters was measured of the right shoulder of an embalmed male. For all muscles the optimal muscle fiber length was determined by laser diffraction measurements of sarcomere length. In addition, tendon length and physiological cross-sectional area were determined. The parameter set was needed to enhance the reliability of a computer model of the shoulder (Van der Helm, 1994a,b Journal of Biomechanics 27, 527-550, 551-569). With the model, an abduction of the arm was simulated in seven positions, at 30 degrees intervals. In each of the simulated arm positions, actual sarcomere lengths were calculated from the lengths of 104 muscle elements, distributed over 16 shoulder muscles. For most muscle elements, the simulated abduction appeared to take place within the sarcomere length range in which the muscle elements can exert force. The muscle elements can then act on the ascending limb as well as on the plateau and on the descending limb of the relative force-length curves of sarcomeres. The produced data set is not only important for the refinement of shoulder modeling, but also for functional analyses of shoulder movements in general.

Cadaver↗
PubMed1997

Roentgen stereophotogrammetric analysis of metal-backed hemispherical cups without attached markers.

A method for the detection of micromotion of a metal-backed hemispherical acetabular cup is presented and tested. Unlike in conventional roentgen stereophotogrammetric analysis, the cup does not have to be marked with tantalum markers; the micromotion is calculated from the contours of the hemispherical part and the base circle of the cup. In this way, two rotations (tilt and anteversion) and the translations along the three cardinal axes are obtained. In a phantom study, the maximum error in the position of the cup's centre was 0.04 mm. The mean error in the orientation of the cup was 0.41 degree, with a 95% confidence interval of 0.28-0.54 degree. The in vivo accuracy was tested by repeated measurement of 21 radiographs from seven patients. The upper bound of the 95% tolerance interval for the translations along the transversal, longitudinal, and sagittal axes was 0.09, 0.07, and 0.34 mm, respectively: for the rotation, this upper bound was 0.39 degree. These results show that the new method, in which the position and orientation of metal-backed hemispherical cup is calculated from its projected contours, is a simple and accurate alternative to attaching markers to the cup.

Acetabulum↗
PubMed1996

A two dimensional model for the prediction of muscle shape and intramuscular pressure.

Traditional pennate skeletal muscle models with straight fibres and straight tendinous sheets cannot assume realistic muscle shapes and are unsuitable for predicting intramuscular pressure. The two dimensional models proposed here have flexible fibres and tendinous sheets of which the curvatures are in mechanical equilibrium with the intramuscular pressure distribution. Analytical relationships between fibre stress, pressure, curvatures and lengths of fibres and tendinous sheets have been derived based on physical laws and functional demands. These relationships were used to generate unipennate muscle shapes and to calculate pressure distributions. The results compare well with the shapes of the medial gastrocnemius muscles of man and cat and with maximum intramuscular pressures as reported in the literature.

Animals↗
PubMed1993

Modelling the pressure and force equilibrium in unipennate muscles with in-line tendons.

Several of the models proposed in the literature of unipennate muscles, which have two tendinous sheets and in-line tendons, cannot meet the criterion of mechanical stability. Based on the theory of Van Leeuwen & Spoor (Phil. Trans. R. Soc. Lond. B 336, 275-292 (1992)), we discuss how mechanically stable solutions for (planar) unipennate architectures could be obtained. A mathematical model is proposed in which the muscle architecture is generated numerically using the principles of mechanical stability and assuming that all muscle fibres shorten by the same relative amount. The tendinous sheets are attached tangentially to their respective tendons, as predicted from their low bending stiffness. The curvature, however, is discontinuous at the junction because of the sudden absence of muscle fibres from aponeurosis to tendon. In two of the muscle shapes generated, the sheets adjacent to the tendon show a region of negative curvature connected to a region of positive curvature. A sheet with a concave outer side is defined to have a negative curvature. In another example, two negative curvature regions are present with a positive region in-between. We show also a generated shape with a negative curvature of the sheets over their whole length. A good resemblance was found between the unipennate medial gastrocnemius muscle of the cat and a simulated architecture. The pressure distribution has also been calculated. With all muscle fibres exerting the same tensile stress of 200 kPa, a high pressure region is present in the centre of the muscle belly, half-way along its length. The highest pressures are predicted for muscles with long tendinous sheets, large attachment angles, and strongly curved fibres. Maximum pressures (2.40, 9.54, 10.47, and 7.57 kPa for the four discussed examples, and 15.05 kPa for the simulated gastrocnemius muscle) were at the lower side of the range as predicted previously for bipennate muscles and the unipennate medial gastrocnemius muscle of man (Van Leeuwen & Spoor 1992).

Animals↗
PubMed1993

The tensile testing machine applied in the study of human nerve rupture: a preliminary study.

A tensile testing machine was used to provoke lesions of fixed and unfixed brachial plexus nerves. The forces and mechanical work were measured before and during rupture. Fixed nerves resist continued tensile forces better than unfixed nerves do. Increasing the speed of the tensile forces results in a decrease of the extension a brachial plexus nerve can withstand. The mechanical work needed to start rupture is equal to the mechanical work used to complete rupture of the nerve.

Biomechanical Phenomena↗
PubMed1992

Modelling mechanically stable muscle architectures.

This paper presents a planar architectural model for an activated skeletal muscle, with mechanical equilibrium throughout the muscle belly. The model can predict the shape of the muscle fibres and tendinous sheets as well as the internal pressure distribution in the central longitudinal plane (perpendicular to the tendinous sheets) of uni- and bipennate muscle bellies. Mechanically stable solutions for muscle architectures were calculated by equating the pressure developed by curved muscle fibres with the pressure under a curved tendinous sheet. The pressure distribution under a tendinous sheet is determined by its tension, its curvature and the tensile stress of the attached muscle fibres. Dissections showed a good resemblance of the architecture of embalmed muscles with those from our simulations. Calculated maximum pressures are in the same order of magnitude as pressure measurements from the literature. Our model predicts that intramuscular blood flow can be blocked during sustained contraction, as several experimental studies have indeed demonstrated. The volume fractions of muscle fibres and interfibre space in the muscle belly were also calculated. The planar models predict a too low volume fraction for the muscle fibres (about 45% for the bipennate models with a straight central aponeurosis, and about 60% for the simulated unipennate muscle). It is discussed how, in a real muscle, this volume problem can be solved by a special three-dimensional arrangement of muscle fibres in combination with varying widths of the tendinous sheets.

Animals↗
PubMed1992

Knee muscle moment arms from MRI and from tendon travel.

We tested magnetic resonance imaging (MRI) as a means to collect geometric data for moment arm estimation. A knee specimen in five successive flexion postures was scanned by MRI, while simultaneously tendon positions of loaded muscles were measured (long head of biceps femoris, lateral and medial gastrocnemius, gracilis, rectus femoris, sartorius, semimembranosus, semitendinosus, and tensor fasciae latae). Discrete rotation centres were derived from MRI pictures. Moment arms were estimated as the distances from these centres to the tendons. The ratio of tendon travel over the increment of joint angulation was the alternative, more reliable estimate of the moment arm. An important principal shortcoming of MRI is the impossibility of accounting for force distribution in taut tissue. As a consequence, for some muscles, considerable inaccuracies in moment arm estimation are found in a relatively small range of joint angulation (up to about 30% for the rectus femoris and semimembranosus). For the tensor fasciae latae, the moment arm cannot be estimated by MRI, while the estimate by tendon travel is unreliable owing to the deformability and attachments of the fascia lata.

Aged↗
PubMed1991

Active force-length relationship of human lower-leg muscles estimated from morphological data: a comparison of geometric muscle models.

Muscle fibre lengths, pennation angles, and sarcomere lengths were measured (the latter by a diffraction technique) for each of the muscles of three embalmed lower-leg specimens. From these data and filament lengths from Walker & Schrodt (1973), the optimum fibre lengths were determined. Relationships between length and active force (at full activation) of the lower-leg muscles were calculated by use of (i) a unipennate muscle model, (ii) a bipennate model, and (iii) bipennate models in which the cosine of the pennation angle is approximated as length independent. It is concluded that the first two models are equally useful and that the use of the last models is discouraged in case of strongly pennated muscles. Non-uniformity of fibre parameters within one muscle appears to have little effect on the force-length relationship.

Aged↗
PubMed1990

Estimation of instantaneous moment arms of lower-leg muscles.

Muscle moment arms at the human knee and ankle were estimated from muscle length changes measured as a function of joint flexion angle in cadaver specimens. Nearly all lower-leg muscles were studied: extensor digitorum longus, extensor hallucis longus, flexor digitorum longus, flexor hallucis longus, gastrocnemius lateralis, gastrocnemius medialis, peroneus brevis, peroneus longus, peroneus tertius, plantaris, soleus, tibialis anterior, and tibialis posterior. Noise in measured muscle length was filtered by means of quintic splines. Moment arms of the mm. gastrocnemii appear to be much more dependent on joint flexion angles than was generally assumed by other investigators. Some consequences for earlier analyses are mentioned.

Achilles Tendon↗
PubMed1989

Elastic strain energy in the low back muscles during human walking.

A simple model of the thorax, pelvis and three columns of the intrinsic lumbar back muscles (= ILBM) was constructed. The model was used to study the length of the ILBM during the different stages of the walking cycle. The length of the right ILBM (especially the lateral column) was largest at right toe off, exactly the stage of the walking cycle in which most force was needed to prevent the torso from falling forwards and laterally.

Back↗
PubMed1989

A model study of muscle forces and joint-force direction in normal and dysplastic neonatal hips.

Orthopaedic treatment of congenital hip dysplasia does not always give the desired result. With the present model, prediction of the effects of various treatments on the force direction in the hip joint could help to improve and select treatment (the force direction is presumed to control the collum growth direction). The model contains three-dimensional mathematical descriptions of all muscles passing the hip joint, for various degrees of femoral dysplasia, and for various hip postures. Muscles run straight or curve round some skeletal parts. Muscle forces (all isometric) are calculated from muscle mass, density, pennation angle, mean fibre length, muscle elongation, and assumed activation levels. The latter serve as parameters for optimization. Resting lengths are taken from an assumed fetal posture, and from the observed neonatal posture. Differences between force directions before and after birth, as calculated with the model, agree with collum direction changes described by von Lanz and Mayet (1953).

Biomechanical Phenomena↗
PubMed1989

An experimental setup for the measurement of forces on a human cadaveric foot during inversion.

An experimental setup was developed for statically measuring seven vertical and three horizontal reaction forces on the foot. In the setup, the leg can be simultaneously loaded (1) by a vertical force, (2) by an externally applied axial moment, and (3) by simulated muscle forces. The foot is free to invert under influence of the external loads. Statical analysis and test experiments were used for evaluation. The setup can be used in combination with Roentgen photogrammetry to measure bone positions simultaneously with forces.

Cadaver↗
PubMed1989

A model of the human knee, derived from kinematic principles and its relevance for endoprosthesis design.

A mainly deductive kinematic model of the human knee is described. The modelling procedure is based upon the application of a four-bar mechanism. Emphasis has been laid upon elucidating the functional anatomical relationship between several morphological characteristics concerning the shape of the articular surfaces and the constellation of the cruciate ligaments. Starting from a simple planar model, which simulates motions in a sagittal plane only, a spatial model was developed, which allowed an additional longitudinal rotation of the tibia also. The conclusions drawn from this modelling procedure have been used to evaluate from an functional anatomical point of view the current designs of presently available endoprostheses for the knee.

Humans↗