The sensitivity of endpoint forces produced by the extrinsic muscles of the thumb to posture

This study utilizes a biomechanical model of the thumb to estimate the force produced at the thumb-tip by each of the four extrinsic muscles. We used the principle of virtual work to relate joint torques produced by a given muscle force to the resulting endpoint force and compared the results to two separate cadaveric studies. When we calculated thumb-tip forces using the muscle forces and thumb postures described in the experimental studies, we observed large errors. When relatively small deviations from experimentally reported thumb joint angles were allowed, errors in force direction decreased substantially. For example, when thumb posture was constrained to fall within ±15° of reported joint angles, simulated force directions fell within experimental variability in the proximal–palmar plane for all four muscles. Increasing the solution space from ±1° to an unbounded space produced a sigmoidal decrease in error in force direction. Changes in thumb posture remained consistent with a lateral pinch posture, and were generally consistent with each muscle’s function. Altering thumb posture alters both the components of the Jacobian and muscle moment arms in a nonlinear fashion, yielding a nonlinear change in thumb-tip force relative to muscle force. These results explain experimental data that suggest endpoint force is a nonlinear function of muscle force for the thumb, support the continued use of methods that implement linear transformations between muscle force and thumb-tip force for a specific posture, and suggest the feasibility of accurate prediction of lateral pinch force in situations where joint angles can be measured accurately.     

Method for measurement of circumduction of the thumb to evaluate results of opponensplasty.

A simple method for measuring circumduction of the thumb, by using a ratio of the range of motion to the length of the first metacarpal, is described. This method can be of value in assessing many aspects of thumb function, especially the improvement in function after opponensplasty. The improved ability to position the thumb in a useful location, both for pinch and grasp, appears to correlate well with the patient's use of the hand for previously impossible tasks.     

Feasibility of using a video-based motion analysis system for measuring thumb kinematics

While several different methods have been used to measure hand kinematics, fluoroscopy is generally considered to be the most accurate. Recently, video-based motion analysis has been developed for the measurement of joint kinematics. This method is versatile, easy to use, and can measure motions dynamically. Surface markers are most commonly used in the video-based motion systems. However, whether the surface markers placed on the thumb accurately represent the true kinematics of the underlying bony segment is questionable.In this study, the feasibility of surface markers to represent thumb kinematics was investigated by fluoroscopy. Both the positions of surface markers and bony landmarks were simultaneous recorded and then digitized. The Ra(2) values comparing the angular changes of the thumb interphalangeal, metacarpal and carpometacarpal joints derived using the surface markers or bony landmarks were 0.9986, 0.9730 and 0.9186 in the flexion/extension plane respectively, 0.8837, 0.9697 and 0.8775 in the abduction/adduction plane; and 0.9884, 0.9643 and 0.9431 in the opposition plane. The ranges, mean and standard deviation of the absolute differences between calculated angles of different marker sets were also compared. These data revealed that the similarities of the two different marker techniques throughout the motion cycle were high. The differences between the two methods were also within clinically allowable range of +/-5 degrees. It is concluded that the application of the video-based motion analysis system with surface markers to thumb kinematics is warranted.     

Quantifying deficits in the 3D force capabilities of a digit caused by selective paralysis: application to the thumb with simulated low ulnar nerve palsy

We present the development of a vision-feedback method to characterize how selective paralysis distorts the three-dimensional (3D) volume representing digit-tip force production capability and its application to healthy individuals producing thumb-tip force with and without simulated low ulnar nerve palsy (LUNP). Subjects produced maximal static voluntary force spanning the transverse, sagittal and frontal planes of the thumb (16, 15 and 10 subjects, respectively). Subjects produced thumb-tip force tasks in guided and self-selected directions. The envelope (convex hull) of extreme forces in each plane approximated that cross-section of the 3D volume of force capability. Some subjects repeated the tasks with a temporary ulnar nerve block applied at the wrist to simulate complete acute LUNP. Three geometric properties of the force convex hull characterized each cross-section's shape: the ratios of its principal moments of inertia (RPMIs), the orientation of its principal axis (OPA), and its centroid location. Our results show that force production in the thumb's sagittal plane may be a reproducible and objective test to grade motor impairment in LUNP: paired t-tests of the larger RPMI in this plane best distinguished the nerve-blocked cases from the control cases in the guided task (p = 0.012), and Discriminant Analysis of the centroid location for the self-selected task in this plane correctly classified 94.7% of subjects into the control and ulnar nerve-blocked groups. We show that our method measures and detects changes in a digit's force production capabilities. Towards a clinical test of motor impairment in LUNP, this biomechanical study dictates which 3D thumb-tip forces to measure (those in the sagittal plane) and how to measure them (using the self-selected task).     

Development and Application of Stereo Camera-Based Upper Extremity Workspace Evaluation in Patients with Neuromuscular Diseases

Background

The concept of reachable workspace is closely tied to upper limb joint range of motion and functional capability. Currently, no practical and cost-effective methods are available in clinical and research settings to provide arm-function evaluation using an individual’s three-dimensional (3D) reachable workspace. A method to intuitively display and effectively analyze reachable workspace would not only complement traditional upper limb functional assessments, but also provide an innovative approach to quantify and monitor upper limb function.

Methodology/Principal Findings

A simple stereo camera-based reachable workspace acquisition system combined with customized 3D workspace analysis algorithm was developed and compared against a sub-millimeter motion capture system. The stereo camera-based system was robust, with minimal loss of data points, and with the average hand trajectory error of about 40 mm, which resulted to ∼5% error of the total arm distance. As a proof-of-concept, a pilot study was undertaken with healthy individuals (n = 20) and a select group of patients with various neuromuscular diseases and varying degrees of shoulder girdle weakness (n = 9). The workspace envelope surface areas generated from the 3D hand trajectory captured by the stereo camera were compared. Normalization of acquired reachable workspace surface areas to the surface area of the unit hemi-sphere allowed comparison between subjects. The healthy group’s relative surface areas were 0.618±0.09 and 0.552±0.092 (right and left), while the surface areas for the individuals with neuromuscular diseases ranged from 0.03 and 0.09 (the most severely affected individual) to 0.62 and 0.50 (very mildly affected individual). Neuromuscular patients with severe arm weakness demonstrated movement largely limited to the ipsilateral lower quadrant of their reachable workspace.

Conclusions/Significance

The findings indicate that the proposed stereo camera-based reachable workspace analysis system is capable of distinguishing individuals with varying degrees of proximal upper limb functional impairments.     

Modeling of the muscle/tendon excursions and moment arms in the thumb using the commercial software anybody

A biomechanical model of a thumb would be useful for exploring the mechanical loadings in the musculoskeletal system, which cannot be measured in vivo. The purpose of the current study is to develop a practical kinematic thumb model using the commercial software Anybody (Anybody Technology, Aalborg, Denmark), which includes real CT-scans of the bony sections and realistic tendon/muscle attachments on the bones. The thumb model consists of a trapezium, a metacarpal bone, a proximal and a distal phalanx. These four bony sections are linked via three joints, i.e., IP (interphalangeal), MP (metacarpophalangeal) and CMC (carpometacarpal) joints. Nine muscles were included in the proposed model. The theoretically calculated moment arms of the tendons are compared with the corresponding experimental data by Smutz et al. [1998. Mechanical advantage of the thumb muscles. J. Biomech. 31(6), 565–570]. The predicted muscle moment arms of the majority of the muscle/tendon units agree well with the experimental data in the entire range of motion. Close to the end of the motion range, the predicted moment arms of several muscles (i.e., ADPt and ADPo (transverse and oblique heads of the adductor pollicis, respectively) muscles for CMC abduction/adduction and ADPt and FPB (flexor pollicis brevis) muscle for MP extension/flexion) deviate from the experimental data. The predicted moment potentials for all muscles are consistent with the experimental data. The findings thus suggest that, in a biomechanical model of the thumb, the mechanical functions of muscle–tendon units with small physiological cross-sectional areas (PCSAs) can be well represented using single strings, while those with large PCSAs (flat-wide attachments, e.g., ADPt and ADPo) can be represented by the averaged excursions of two strings. Our results show that the tendons with large PCSAs can be well represented biomechanically using the proposed approach in the major range of motion.     

Chimpanzee thumb muscle cross sections, moment arms and potential torques, and comparisons with humans.

This study investigates the morphological basis of differences between humans and chimpanzees in the kinematical and dynamical parameters of the musculature of the thumb. It is partly intended to test an hypothesis that human thumb muscles can exert significantly greater torques, due to larger muscle cross-sectional areas or to longer tendon moment arms or to both. We focus on the estimation of the potentials of thumb muscles to exert torques about joint axes in a sample of eight chimpanzee cadaver hands. The potential torque of a muscle is estimated by taking the product of a muscle's physiological cross-sectional area (an estimator of force) with its dynamical moment arm (derived from the slope of tendon excursion versus joint angular displacement, obtained during passive movements of cadaver thumb joints). Comparison of our results with similar data obtained for humans at the same Mayo Clinic laboratory shows significant differences between humans and chimpanzees in potential torque of most thumb muscles, those of humans generally exhibiting larger values. The primary reason for the larger torques in humans is that their average moment arms are significantly longer, permitting greater torque for a given muscle size. An additional finding is that chimpanzees and humans differ in the direction of secondary thumb metacarpal movements elicited by contraction of some muscles, as shown by differences in moment arm signs for a given movement in the same muscle. The differences appear to be related to differences in the musculo-skeletal structures of the trapeziometacarpal joint.     

Simple method for reconstruction of the cleft hand with an adducted thumb.

We describe a new, simple method for reconstruction of a cleft hand. Ulnar transposition of the index ray followed by creation of a thumb web space is an effective way to get sufficient abduction of the thumb. This procedure is simpler than the traditional "translocation of the flap," and also it produces no circulatory troubles to worry about.     

Reconstruction of the thumb with a trimmed-toe transfer technique

The trimmed-toe transfer is a new modification of the existing great-toe transfer technique for thumb reconstruction. This procedure was devised to circumvent patient concerns regarding overly large reconstructed digits following total great-toe-to-hand transfer. This technique involves reduction of both the bony and soft-tissue elements along the medial aspect of the transferred great toe in order to produce a more normal sized thumb. Follow-up of the initial 20 patients from 1983 to 1986 demonstrates good stability, grip strength, and pinch strength. Although compared with total great-toe transfer a modest reduction in joint motion of trimmed toes has been observed, the overall appearance and usefulness of the reconstructed thumbs have been excellent.     

Coordination of thumb joints during opposition

Thumb opposition plays a vital role in hand function. Kinematically, thumb opposition results from composite movements from multiple joints moving in multiple directions. The purpose of this study was to examine the coordination of thumb joints during opposition tasks. A total of 15 female subjects with asymptomatic hands were studied. Three-dimensional angular kinematics of the carpometacarpal (CMC), metacarpophalangeal (MCP) and interphalangeal (IP) joints were obtained by a marker-based motion analysis system. Thumb opposition revealed coordination among joints in a specific direction (inter-joint coordination) and among different directions within a joint (intra-joint coordination). In particular, linear couplings existed between the flexion and pronation at the CMC joint, and between the flexion of the CMC joint and flexion of the MCP joint. Principal component analysis showed that only two principal components adequately represented the thumb opposition data of seven movement directions. A term functional degrees of freedom by virtue of principal component analysis was proposed to uncover the extent of movement coordination in functional tasks.     

A new assay for endocytosis in erythrocyte ghosts based on loss of acetylcholinesterase activity

A new method for assaying endocytosis in erythrocyte ghosts is presented. The method involves measuring the percentage loss of acetylcholinesterase activity which occurs when vacuoles form, making the acetylcholinesterase on the vacuole surface inaccessible. This method is compared to other methods of measuring endocytosis in this system, including phase contrast microscope estimation of vesiculation, stereological analysis of electron micrographs to determine vesiculation and loss of sialic acid accessible to neuraminidase due to endocytosis. Comparison of the percentage loss of acetylcholinesterase activity with the electron micrographic and sialic acid methods showed that all three methods gave a quantitative measure of the percentage of total membrane area taken in as vesicles. Since the acetylcholinesterase method was fast, easy, inexpensive, and quantitative, it was the preferred method for assay of endocytosis. The inhibition of endocytosis by Ca²⁺ was observed with this method; the success of this experiment demonstrated the applicability of the method to the study of inhibitors of endocytosis.     

Alternatives to thumb replantation

LEARNING OBJECTIVES: After studying this article, the participant should: 1. Have a variety of options for thumb reconstruction. 2. Know the advantages and disadvantages of the nonmicrosurgical and microsurgical techniques for thumb reconstruction. 3. Understand the decision making from the variety of thumb reconstruction techniques based on patient needs. 4. Have a basic understanding of the various thumb reconstruction techniques discussed. The traumatic amputation of the thumb is an absolute indication for attempted replantation. The profound disability of the hand resulting from absence of the thumb, with loss of pinch and grasp, obliges the surgeon to make every attempt to replant the amputated thumb and preserve hand function. However, not all attempts at replantation result in survival of the amputated portion, and unreconstructable damage to or complete loss of the amputated part may preclude attempted replantation. In such situations, the surgeon must have alternative methods of dealing with the sequelae of thumb loss. This article will discuss nonmicrosurgical and microsurgical techniques for thumb reconstruction.     

Comparison of tendon tensions estimated from two biomechanical models of the thumb

Despite the paramount function of the thumb in daily life, thumb biomechanical models have been little developed and studied. Moreover, only two studies provided quantitative anthropometric data of tendon moment arms. To investigate thumb tendon tensions, biomechanicians and clinicians have to know the performances and the limits of these two data sets. The aim of this study was thus to compare the results of these two models and evaluate their performances in regard to prior electromyographic measurements (EMG).Thumb posture was recorded during the classical key pinch and pulp pinch grips. Various fingertip forces applied at the distal segment were simulated in a range including extension, adduction, flexion, abduction. Input data of thumb postures and fingertip forces were used to compute tendon tensions with both models. Tendon tensions obtained using these two models were then compared and correlated to EMG measurements provided in the literature.The results showed that both models predicted relevant muscle coordination for five of the nine muscles modelled. Opponent and abductor longus muscle coordinations were badly estimated by both models. Each model was sensible to kinematic errors but not in the same proportion. This study pointed out the advantages/limits of the two models to use them more appropriately for clinical and/or research purposes.     

Measuring vessel length in vascular plants: can we divine the truth? History,theory, methods,and contrasting models

Key message

The Cohen method of measuring vessel-length distributions is much more accurate than the DD algorithm on integer values, which should be abandoned. More research is needed to get the real distribution of vessel length.

Abstract

Scientists have been measuring the vessel length of plants for more than 50 years. The method involves infusing stem or segments with a visible substance that completely fills vessels cut open at the infusion surface. The number of infused vessels is then quantified versus distance from the infusion surface. A theoretical model is then used to convert the counts of infused vessels to a vessel length distribution. Over the years the methods and theory have changed greatly. The purpose of this review is to give the reader an understanding of why vessel length is important and to provide a theoretical basis for selection of the best method and theory to arrive at vessel length data.     

Development of a dynamic index finger and thumb model to study impairment

Modeling of the human hand provides insight for explaining deficits and planning treatment following injury. Creation of a dynamic model, however, is complicated by the actions of multi-articular tendons and their complex interactions with other soft tissues in the hand. This study explores the creation of a musculoskeletal model, including the thumb and index finger, to explore the effects of muscle activation deficits. The OpenSim model utilizes physiological axes of rotation at all joints, passive joint torques, and appropriate moment arms. The model was validated through comparison with kinematic and kinetic experimental data. Simulated fingertip forces resulting from modeled musculotendon loading largely fell within one standard deviation of experimental ranges for most index finger and thumb muscles, although agreement in the sagittal plane was generally better than for the coronal plane. Input of experimentally obtained electromyography data produced the expected simulated finger and thumb motion. Use of the model to predict the effects of activation deficits on pinch force production revealed that the intrinsic muscles, especially first dorsal interosseous (FDI) and adductor pollicis (ADP), had a substantial impact on the resulting fingertip force. Reducing FDI activation, such as might occur following stroke, altered fingertip force direction by up to 83° for production of a dorsal fingertip force; reducing ADP activation reduced force production in the thumb by up to 62%. This validated model can provide a means for evaluating clinical interventions.     

Preferred elbow position in confined wheelchair configuration

High mechanical load leads to pain and damage in the upper extremities of wheelchair users. Wheelchair users suffer a limited range of motion of the upper extremities due to the confining wheelchair configuration. This is a key factor affecting the efficiency of wheelchair propulsion and upper extremity loading. With a view toward further understanding the interaction between the user and wheelchair, this study identifies the accessible workspace of the elbow under conventional wheelchair design and identifies the actual location and range of motion of the elbow during wheelchair propulsion. An eight-camera motion analysis system recorded the kinematics of 14 non-experienced wheelchair users. Users under standardized conservative wheelchair-sitting position moved their right elbow as widely as possible at five different wheel angles while elbow positions were recorded, thereby establishing the maximum possible elbow workspace. Actual positions of the right elbow were recorded during wheelchair propulsion. The arc angles of the elbow workspace range from 68.8° to 83.4° and are located at the lateral and posterior quadrant of the circle on which the elbow trajectories located. Reachable workspace is smaller when the hand holds the hand rim at a larger wheel angle. The preferred positions for propulsion are located approximately 2/3's of the way through the total workspace. The obtained data will be useful for improved wheelchair design and biomechanical modeling of the wheelchair/user system.     

6R instrumented spatial linkages for anatomical joint motion measurement--Part 2: Calibration.

The six-revolute-joint instrumented spatial linkage (6R ISL) is often the measurement system of choice for monitoring motion of anatomical joints. However, due to tolerances of the linkage parameters, the system may not be as accurate as desired. A calibration algorithm and associated calibration device have been developed to refine the initial measurements of the ISL's mechanical and electrical parameters so that the measurement of six-degree-of-freedom motion will be most accurate within the workspace of the anatomical joint. The algorithm adjusts the magnitudes of selected linkage parameters to reduce the squared differences between the six known and calculated anatomical position parameters at all the calibration positions. Weighting is permitted so as to obtain a linkage parameter set that is specialized for measuring certain anatomical position parameters. Output of the algorithm includes estimates of the measuring system accuracy. For a particular knee-motion-measuring ISL and calibration device, several interdependent design parameter relationships have been identified. These interdependent relationships are due to the configuration of the ISL and calibration device, the number of calibration positions, and the limited resolution of the devices that monitor the position of the linkage joints. It is shown that if interdependence is not eliminated, then the resulting ISL parameter set will not be accurate in measuring motion outside of the calibration positions, even though these positions are within the ISL workspace.     

A comparison of methods for measuring the colonisation of a root system by fluorescent Pseudomonads

Methods are described for measuring the colonisation of a radish (Raphanus sativus) root system by seedlings with rifampicin resistant fluorescent pseudomonads by dilution plating, and which would take account of differences in root morphology. Differences in the levels of pseudomonad colonisation was highly dependent on the units in which surface areas was expressed. Population levels are expressed using estimates of surface area based on root length, tap-root length and root weight. The best estimate of surface area was root length, but the most practical method was surface area calculated as a function of dry weight. This method could differentiate differences in the levels of root colonisation independent of differences in root morphology and was efficient enough to allow the routine processing of a large number of replicate root samples.     

Development of a high-content screening method for chemicals modulating DNA damage response

The cellular response to DNA damage is emerging as a promising target for cancer therapy. In the present study, the authors exploited the relationship between the level of the phosphorylated form of histone H2AX (γH2AX) and the extent of DNA damage and developed a quantitative, cell-based, high-content screening system for measuring the DNA damage response (DDR). In this system, the authors quantified the level of γH2AX by measuring DNA damage-induced γH2AX nuclear foci using an automated cell imager. They found that the total area of γH2AX foci per cell exhibited a good correlation with the concentration of DNA damage-inducing agents, including etoposide. The effects of 2 well-known inhibitors of DNA damage could be quantified using this system, suggesting the suitability of the γH2AX-foci quantification method for large-scale screening applications. This was confirmed by using this method to screen a chemical library; the resulting "hits" included compounds that inhibited early signaling events in DDR, as well those that inhibited subsequent DNA damage repair processes. Overall, this γH2AX foci-measuring system may be an effective screening method for identifying DNA damage response inhibitors that could eventually be used to develop novel anticancer drugs.