Quantitative analysis of the linkage between the interphalangeal joints of the index finger. An in vivo study

Finger Kinematics during Human Hand Grip and Release

A bionic robotic hand can perform many movements similar to a human hand. However, there is still a significant gap in manipulation between robot and human hands. It is necessary to understand the finger kinematics and motion patterns of human hands to improve the performance of robotic hands. This study aimed to comprehensively investigate normal hand motion patterns by evaluating the kinematics of hand grip and release in healthy individuals. The data corresponding to rapid grip and release were collected from the dominant hands of 22 healthy people by sensory glove. The kinematics of 14 finger joints were analyzed, including the dynamic range of motion (ROM), peak velocity, joint sequence and finger sequence. The results show that the proximal interphalangeal (PIP) joint had a larger dynamic ROM than metacarpophalangeal (MCP) and distal interphalangeal (DIP) joints. Additionally, the PIP joint had the highest peak velocity, both in flexion and extension. For joint sequence, the PIP joint moved prior to the DIP or MCP joints during flexion, while extension started in DIP or MCP joints, followed by the PIP joint. Regarding the finger sequence, the thumb started to move before the four fingers, and stopped moving after the fingers during both grip and release. This study explored the normal motion patterns in hand grip and release, which provided a kinematic reference for the design of robotic hands and thus contributes to its development.

Studying kinematic linkage of finger joints: estimation of kinematics of distal interphalangeal joints during manipulation

The recording of hand kinematics during product manipulation is challenging, and certain degrees of freedom such as distal interphalangeal (DIP) joints are difficult to record owing to limitations of the motion capture systems used. DIP joint kinematics could be estimated by taking advantage of its kinematic linkage with proximal interphalangeal (PIP) and metacarpophalangeal joints. This work analyses this linkage both in free motion conditions and during the performance of 26 activities of daily living. We have studied the appropriateness of different types of linear regressions (several combinations of independent variables and constant coefficients) and sets of data (free motion and manipulation data) to obtain equations to estimate DIP joints kinematics both in free motion and manipulation conditions. Errors that arise when estimating DIP joint angles assuming linear relationships using the equations obtained both from free motion data and from manipulation data are compared for each activity of daily living performed. Estimation using manipulation condition equations implies a lower mean absolute error per task (from 5.87° to 13.67°) than using the free motion ones (from 9° to 17.87°), but it fails to provide accurate estimations when passive extension of DIP joints occurs while PIP is flexed. This work provides evidence showing that estimating DIP joint angles is only recommended when studying free motion or grasps where both joints are highly flexed and when using linear relationships that consider only PIP joint angles.

[Impact of a simulated DIPJ Arthrodesis on Movement and Force Patterns]

PURPOSE

Distal interphalangeal joint (DIPJ) arthrodesis is a well-proven therapy for osteoarthritis in the DIPJ. Since the upper limb is effectively a linked chain which is moved by interlinked, joint-overlapping muscle-tendon units, impacts on movement and force patterns are expected to occur in response to arthrodesis. In this context, a real-time quantitative analysis has not been performed to date.

MATERIAL AND METHODS

Finger motion and force development during grasping were dynamically measured and quantitatively analyzed in 19 healthy volunteers with a simulated DIPJ arthrodesis using a TUB (Technische Universität Berlin) sensor glove during fist closure and evaluating two types of force grips compared with the physiological grip.

RESULTS

Typical motion patterns were found. During physiological fist closure, the average flexion angle was 71.5° in the metacarpophalangeal joint (MPJ), 76.8° in the proximal interphalangeal joint (PIPJ) and 37.3° in the distal interphalangeal joint (DIPJ). With DIPJ arthrodesis, the flexion angle decreased to 49.6° in the PIPJ, whereas it increased slightly to 77.3° in the MPJ. During force grip I, the average physiological flexion angles were 18.3° in the MPJ, 39.6° in the PIPJ and 42.6° in the DIPJ. With simulated DIPJ arthrodesis, the flexion angle in the MPJ increased to 28.4°, whereas it decreased to 25.2° in the PIPJ. Force grip II yielded physiological flexion angles of 30.9° in the MPJ, 36.6° in the PIPJ and 29.0° in the DIPJ. In response to simulated DIPJ arthrodesis, the angle in the MPJ increased to 34.4° while it decreased to 23.3° in the PIPJ. The forces measured with force grips were almost equally distributed under physiological conditions. In response to simulated DIPJ arthrodesis, the average decrease in the measured force of a finger was no more than 1.4%.

CONCLUSION

This study was the first to introduce a quantitative analysis of grasping with simulated DIPJ arthrodesis. Based on this analysis, the study demonstrates the dynamic interaction of the finger joints as well as force patterns on the individual finger rays of the hand in real-time.

A Novel Clinical-Driven Design for Robotic Hand Rehabilitation: Combining Sensory Training, Effortless Setup, and Large Range of Motion in a Palmar Device

Neurorehabilitation research suggests that not only high training intensity, but also somatosensory information plays a fundamental role in the recovery of stroke patients. Yet, there is currently a lack of easy-to-use robotic solutions for sensorimotor hand rehabilitation. We addressed this shortcoming by developing a novel clinical-driven robotic hand rehabilitation device, which is capable of fine haptic rendering, and that supports physiological full flexion/extension of the fingers while offering an effortless setup. Our palmar design, based on a parallelogram coupled to a principal revolute joint, introduces the following novelties: (1) While allowing for an effortless installation of the user's hand, it offers large range of motion of the fingers (full extension to 180° flexion). (2) The kinematic design ensures that all fingers are supported through the full range of motion and that the little finger does not lose contact with the finger support in extension. (3) We took into consideration that a handle is usually comfortably grasped such that its longitudinal axis runs obliquely from the metacarpophalangeal joint of the index finger to the base of the hypothenar eminence. (4) The fingertip path was optimized to guarantee physiologically correct finger movements for a large variety of hand sizes. Moreover, the device possesses a high mechanical transparency, which was achieved using a backdrivable cable transmission. The transparency was further improved with the implementation of friction and gravity compensation. In a test with six healthy participants, the root mean square of the human-robot interaction force was found to remain as low as 1.37 N in a dynamic task. With its clinical-driven design and easy-to-use setup, our robotic device for hand sensorimotor rehabilitation has the potential for high clinical acceptance, applicability and effectiveness.

Predictive value of metacarpophalangeal stabilization tests for simulated ulnar nerve lesion measured by a sensor glove

STUDY DESIGN

A within-subject research design was used in this study. The difference of the range of motion (ROM) with and without ulnar nerve block was analyzed.

INTRODUCTION

For the clinical evaluation of the functional effects of ulnar nerve palsy at the hand the relevance of clinical tests is in discussion.

PURPOSE OF THE STUDY

The aim of the study was to evaluate the predictive value of 2 clinical tests for a simulated ulnar nerve lesion by motion analysis with a sensor glove.

METHODS

In 28 healthy subjects, dynamic measurements of the finger joints were performed by a sensor glove with and without ulnar nerve block at the wrist. In the 0° metacarpophalangeal (MCP) stabilization test, the subjects were asked to stabilize the MCP joints actively in 0° while moving the interphalangeal joints, whereas at the 90° MCP stabilization test, the subjects stabilized the MCP joints actively in the 90° position.

RESULTS

In the 0° MCP stabilization test, no remarkable changes of the ROM were found at the MCP joints; at the proximal interphalangeal joints 2-5, the ROM decreased with ulnar nerve block, significantly at the index, middle, and ring fingers (P < .05). In the 90° MCP stabilization test, the average ROM of the MCP joints 2-5 significantly increased with ulnar nerve block (P < .05), whereas at the PIP joints, the average ROM decreased (P < .05).

DISCUSSION

The 90° MCP stabilization test had a high predictive value for the discrimination between healthy subjects and subjects with a simulated peripheral ulnar nerve lesion.

CONCLUSIONS

The results could be relevant for the determination of the functional effect of ulnar nerve palsy and the quantification of clawing in hand rehabilitation.

LEVEL OF EVIDENCE

II.

Assessment of hand function during activities of daily living using motion tracking cameras: A systematic review

The human hand is the most frequently used body part in activities of daily living. With its complex anatomical structure and the small size compared to the body, assessing the functional capability is highly challenging. The aim of this review was to provide a systematic overview on currently available 3D motion analysis based on skin markers for the assessment of hand function during activities of daily living. It is focused on methodology rather than results. A systematic review according to the PRISMA guidelines was performed. The systematic search yielded 1349 discrete articles. Of 147 articles included on basis of title, 123 were excluded after abstract review, and 24 were included in the full-text analysis with 13 key articles. There is still limited knowledge about hand and finger kinematics during activities of daily living. A standardization of the task is required in order to overcome the nonrepetitive nature and high variability of upper limb motion and ensure repeatability of task performance. To yield a progress in the analysis of human hand movements, an assessment of human kinematics including fingers, wrist, and thumb and an identification of relevant parameters that characterize a healthy motion pattern during functional tasks are needed.

Digital artery deformation on movement of the proximal interphalangeal joint

This study aimed to characterize in vivo human digital arteries in three-dimensions using photoacoustic tomography in order to understand the specific mechanism underlying arterial deformation associated with movement of the proximal interphalangeal joint. Three-dimensional morphological data were obtained on the radialis indicis artery (radial artery of the index finger) at different angles of the joint. The association between increased curvature of the deformation and the anatomical region was assessed. Characteristic morphological deformations in areas of major deformation were determined. The deformation of the artery was characterized by three consecutive curves in juxta-articular regions, which were particularly noticeable when the joint was flexed at an angle of ≥ 60°. The change in the curvature of the deformation during 30°-90° of flexion was lower in middle-aged individuals than in young individuals. Better understanding of the mechanism underlying deformation of the digital arteries may contribute to advancements in flap procedures and rehabilitation strategies after digital artery repair.

Configuration Synthesis and Performance Analysis of Finger Soft Actuator

Compared with the traditional rigid finger actuator, the soft actuator has the advantages of light weight and good compliance. This type of finger actuator can be used for data acquisition or finger rehabilitation training, and it has broad application prospects. The motion differences between the soft actuator and finger may cause extrusion deformation at the binding point, and the binding forces along nonfunctional direction may reduce drive efficiency. In order to reduce the negative deformation of soft structure and improve comfort, the configuration synthesis and performance analysis of the finger soft actuator were conducted for the present work. The configuration synthesis method for soft actuator was proposed based on the analysis of the physiological structure of the finger, and the soft actuator can make the human-machine closed-loop structure including n joints (n = 1, 2, 3) meet the requirement of DOF (degrees of freedom). Then the typical feasible configurations were enumerated. The different typical configurations were analyzed and compared based on the establishment of mathematical models and simulation analysis. Results show that the configuration design method is feasible. This study offers a theoretical basis for designing the configuration of finger soft actuator.

Change in the temporal coordination of the finger joints with ulnar nerve block during different power grips analyzed with a sensor glove

Ulnar nerve injuries can cause deficient hand movement patterns. Their assessment is important for diagnosis and rehabilitation in hand surgery cases. The purpose of this study was to quantify the changes in temporal coordination of the finger joints during different power grips with an ulnar nerve block by means of a sensor glove. In 21 healthy subjects, the onset and end of the active flexion of the 14 finger joints when gripping objects of different diameters was recorded by a sensor glove. The measurement was repeated after an ulnar nerve block was applied in a standardized setting. The change in the temporal coordination of the metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints with and without the nerve block was calculated within the same subject. In healthy subjects, the MCP joints started their movement prior to the PIP joints in the middle and ring finger, whereas this occurred in the reverse order at the index and little finger. The DIP joint onset was significantly delayed (P<0.01). With the ulnar nerve block, this coordination shifted towards simultaneous onset of all joints, independent of the grip diameter. The thumb and index finger were affected the least. With an ulnar nerve block, the PIP joints completed their movement prior to the MCP joints when gripping small objects (G1 and G2), whereas the order was reversed with larger objects (G3 and G4). The alterations with ulnar nerve block affected mainly the little finger when gripping small objects. With larger diameter objects, all fingers had a significant delay at the end of the PIP joint movement relative to the MCP and DIP joints, and the PIP and DIP joint sequence was reversed (P<0.01). Based on the significant changes in temporal coordination of finger flexion during different power grips, there are biomechanical effects of loss of function of the intrinsic muscles caused by an ulnar nerve block on the fine motor skills of the hand. This can be important for the diagnosis and rehabilitation of ulnar nerve lesions of the hand.

A soft stretchable bending sensor and data glove applications

Soft sensors are required to accommodate the flexible and deformable natures of the human body in wearable device applications. They are also suitable for integration with soft robotic devices to monitor the performance status and provide references for feedback control. However, the choices for bending sensors are still highly limited. In this paper, a soft bending sensor is presented. By careful design with a blend of sensitive and insensitive regions, the sensor could be stretchable while being insensitive to stretching. An analytical study was presented on how to design the sensor with the named bending/stretching feature. This feature enables the sensor to be implemented in measuring human motions where a large amount of skin stretch is involved. Two sensor gloves were designed and fabricated based on the proposed soft bending sensor, aiming for different application scenarios. Both the sensor and the gloves were evaluated using a dedicated evaluation platform with experimental results compared against each other.

Assessment of Workspace Attributes Under Simulated Index Finger Proximal Interphalangeal Arthrodesis

This article presented an assessment of quantitative measures of workspace (WS) attributes under simulated proximal interphalangeal (PIP) joint arthrodesis of the index finger. Seven healthy subjects were tested with the PIP joint unconstrained (UC) and constrained to selected angles using a motion analysis system. A model of the constrained finger was developed in order to address the impact of the inclusion of prescribed joint arthrodesis angles on WS attributes. Model parameters were obtained from system identification experiments involving flexion-extension (FE) movements of the UC and constrained finger. The data of experimental FE movements of the constrained finger were used to generate the two-dimensional (2D) WS boundaries and to validate the model. A weighted criterion was formulated to define an optimal constraint angle among several system parameters. Results indicated that a PIP joint immobilization angle of 40-50 deg of flexion maximized the 2D WS. The analysis of the aspect ratio of the 2D WS indicated that the WS was more evenly distributed as the imposed PIP joint constraint angle increased. With the imposed PIP joint constraint angles of 30 deg, 40 deg, 50 deg, and 60 deg of flexion, the normalized maximum distance of fingertip reach was reduced by approximately 3%, 4%, 7%, and 9%, respectively.

Effective Length Design of Humanoid Robot Fingers Using Biomimetic Optimization

In this study, we propose an effective design method for the phalangeal parameters and the total size of humanoid robot fingers based on a biomimetic optimization. For the optimization, an interphalangeal joint coordination parameter and the length constraints inherent in human fingers are considered from a biomimetic perspective. A reasonable grasp formulation is also taken into account from the viewpoint of power grasping, where the grasp space of a humanoid robot finger is importantly considered to determine the phalangeal length parameters. The usefulness of the devised biomimetic optimization method is shown through the design examples of various humanoid robot fingers. In fact, the optimization-based finger design method enables us to determine effectively the proper phalangeal size of humanoid robot fingers for human-like object handling tasks. In addition, we discuss its contribution to the structural configuration and coordinated motion of a humanoid robot finger, and address its practical availability in terms of effective finger design.

Analysis of Coordinated Motions of Humanoid Robot Fingers Using Interphalangeal Joint Coordination

In this study, we analyse the coordinated motions of humanoid robot fingers using an interphalangeal joint coordination. For this purpose, four humanoid robot fingers with different sizes have been considered. A biomimetic interphalangeal joint coordination (IJC) formulation based on the grasp configuration of human fingers has been presented for humanoid robot fingers. The usefulness of the specified IJC formulation for human-like finger motion has been verified through comparative demonstrations. As a result, a proper coordination of humanoid robot fingertips can be achieved by applying our IJC formulation. Also the IJC formulation can be used to design of humanoid robot fingers.

Development of a tendon-driven robotic finger for an anthropomorphic robotic hand

Our paper proposes a tendon-driven robotic finger based on an anatomical model of a human finger and a suitable method for its analysis. Our study aims to realize an anthropomorphic robotic hand that has the same characteristics and dexterity as that of a human hand, and it also aims to identify the advantages of the human musculoskeletal structure for application to the design and control of robot manipulators. When designing an anthropomorphic robotic hand, several devices are required to apply the human finger structure to a tendon-driven robotic finger. Reasons for this include that one of the human finger muscles, namely, the lumbrical muscle, is situated between tendons, which is an unfavorable configuration for the tendon-driven mechanism. Second, unlike a standard pulley used in a tendon-driven mechanism, some moment arms of the human finger change nonlinearly according to the joint angle. In our robotic finger design, we address these difficulties by rearranging its tendons and develop a mechanism to change the moment arm. We also propose a method to analyze and control this robotic fingers coordinating joints using non-stretch branching tendons based on the human extensor mechanism with a virtual tendon Jacobian matrix and the advantage is that this constraint virtually reduces the degrees-of-freedom (DOF) of the mechanism. Further, we build a prototype to confirm its motion using this method. In addition, we show that the state with the reduced DOF can be lost by external forces acting on the mechanism, and this condition can be changed manually by adjusting the tendon forces. This makes it possible to control the virtual DOFs to satisfy the requirements of the task. Finally, we discuss the benefits from anthropomorphic structures including the tendon arrangement, which mimic the human lumbrical muscle, and the above mentioned mechanism with non-linear moment arms from the perspective that there are two states of DOFs. These insights may provide new perspectives in the design of robotic hands.

An Adaptive Neural Network Learning-based Solution for the Inverse Kinematics of Humanoid Fingers

This paper presents an adaptive neural network learning-based solution for the inverse kinematics of humanoid fingers. For the purpose, we specify an effective finger model by considering the interphalangeal joint coordination inherent in human fingers. In order to find a proper joint combination for any fingertip trajectory, we propose an adaptive learning scheme by using a multi-layered neural network. It is interesting to use an adaptive learning rate algorithm that leads the neural network to get the inverse kinematic solution quickly. The usefulness of the proposed approach is verified by exemplary simulations for the general motion of humanoid fingers.

Human hand modelling: kinematics, dynamics, applications

An overview of mathematical modelling of the human hand is given. We consider hand models from a specific background: rather than studying hands for surgical or similar goals, we target at providing a set of tools with which human grasping and manipulation capabilities can be studied, and hand functionality can be described. We do this by investigating the human hand at various levels: (1) at the level of kinematics, focussing on the movement of the bones of the hand, not taking corresponding forces into account; (2) at the musculotendon structure, i.e. by looking at the part of the hand generating the forces and thus inducing the motion; and (3) at the combination of the two, resulting in hand dynamics as well as the underlying neurocontrol. Our purpose is to not only provide the reader with an overview of current human hand modelling approaches but also to fill the gaps with recent results and data, thus allowing for an encompassing picture.

Reverse engineering finger extensor apparatus morphology from measured coupled interphalangeal joint angle trajectories - a generic 2D kinematic model

The interphalangeal (IP) finger joints coordinate as a mechanism when the deep flexor is active. This mechanism is created by the complex finger extensor apparatus (EA) - a confluence of end tendons of one or two extensors, radial and ulnar interossei, and lumbrical - which inserts as a single structure into both the middle and distal phalanges. Although the IP-coupling principle was well demonstrated more than half a century ago, the detailed relationship between EA morphology and IP coupling remains not well described. Main reasons are that by dissection the EA's fiber network loses functional consistency, while fibers becoming taut or slack beyond measuring resolutions complicate measuring functional fiber motions. To circumvent these difficulties, we present a two dimensional kinematic multi tendon-string EA model of fiber slackness and tautness through IP motion, including the retinacular and oblique retinacular EA ligaments. The model parameters were the strings' lengths and attachment points. The model's functional redundancies were resolved by individually interactively fitting model IP trajectories to previously measured IP trajectories of 68 fingers. All model trajectories accurately fitted their target IP trajectories for proximal interphalangeal (PIP) joint ranges smaller than 25° to 45°; about half accurately fitted over the entire IP range with the remaining half having maximum approximation errors between 3° to 12°, while all models again converged to target trajectories for full IP flexion. These accuracies suggest the model reflects real functional EA principles, with potential applications in biomechanical modeling, surgical reconstruction, rehabilitation, and prosthetic EA replacements.

Kinematic evaluation of the finger's interphalangeal joints coupling mechanism--variability, flexion-extension differences, triggers, locking swanneck deformities, anthropometric correlations

The human finger contains tendon/ligament mechanisms essential for proper control. One mechanism couples the movements of the interphalangeal joints when the (unloaded) finger is flexed with active deep flexor. This study's aim was to accurately determine in a large finger sample the kinematics and variability of the coupled interphalangeal joint motions, for potential clinical and finger model validation applications. The data could also be applied to humanoid robotic hands. Sixty-eight fingers were measured in seventeen hands in nine subjects. Fingers exhibited great joint mobility variability, with passive proximal interphalangeal hyperextension ranging from zero to almost fifty degrees. Increased measurement accuracy was obtained by using marker frames to amplify finger segment motions. Gravitational forces on the marker frames were not found to invalidate measurements. The recorded interphalangeal joint trajectories were highly consistent, demonstrating the underlying coupling mechanism. The increased accuracy and large sample size allowed for evaluation of detailed trajectory variability, systematic differences between flexion and extension trajectories, and three trigger types, distinct from flexor tendon triggers, involving initial flexion deficits in either proximal or distal interphalangeal joint. The experimental methods, data and analysis should advance insight into normal and pathological finger biomechanics (e.g., swanneck deformities), and could help improve clinical differential diagnostics of trigger finger causes. The marker frame measuring method may be useful to quantify interphalangeal joints trajectories in surgical/rehabilitative outcome studies. The data as a whole provide the most comprehensive collection of interphalangeal joint trajectories for clinical reference and model validation known to us to date.

Motion coordination patterns during cylinder grip analyzed with a sensor glove

PURPOSE

To determine whether the grip of a healthy subject's hand shows certain universal characteristics. To accomplish this, we examined the complex interactions of the fingers during gripping of different-size cylindrical objects.

METHODS

A total of 48 subjects (11 women, 37 men) performed 5 cylinder grips with different object sizes. The 14 joint angular profiles of the 5 digits were measured dynamically with a Technische Universität Berlin sensor glove.

RESULTS

Frequently, initial movement was detected before the actual grip. This movement consisted of passive flexion of the fingers the moment the hand rose from the table, followed by active extension of the fingers before gripping the object. Along with the type of joint, the size of the object gripped influenced the frequency of these initial movements (p<.001). During actual grip, the proximal interphalangeal joints' flexion was significantly greater than the flexion of the metacarpophalangeal and distal interphalangeal joints (p<.001). The mean flexion of the proximal interphalangeal joints was 43 degrees , that of the metacarpophalangeal joints was 28 degrees , and that of the distal interphalangeal joints was 26 degrees. Apart from these findings, the larger the flexion angle was, the more time tended to be needed to fulfil the motion.

CONCLUSIONS

The results show that there is a universal motion pattern with the cylinder grip in healthy individuals concerning the range of movement of the finger joints. However, to fully understand the cylinder grip in healthy individuals, our next step will be to analyze the dynamics of the cylinder grip as well. For that purpose, we examine the dynamic interactions between the fingers--that is, their chronological sequence during the cylinder grip.

Trajectory of the index finger during grasping

The trajectory of the index finger during grasping movements was compared to the trajectories predicted by three optimization-based models. The three models consisted of minimizing the integral of the weighted squared joint derivatives along the path (inertia-like cost), minimizing torque change, and minimizing angular jerk. Of the three models, it was observed that the path of the fingertip and the joint trajectories, were best described by the minimum angular jerk model. This model, which does not take into account the dynamics of the finger, performed equally well when the inertia of the finger was altered by adding a 20 g weight to the medial phalange. Thus, for the finger, it appears that trajectories are planned based primarily on kinematic considerations at a joint level.

[Aspects of finger mobility]

The movements of the finger, centrally induced and controlled via open or closed loops, need the simultaneous action of several muscles and muscle groups. In this way, rigid differentiation between antagonists and synergists is functionally abolished. Synchronous flexion and extension of a finger needs not only a palmar flexion and a dorsal extension motor system but also a third oblique running motor system. This is given by the interosseous-lumbricalis system. Opposition and repositioning of the thumb require muscle configuration other than that provided by the other fingers.

Finger flexor motor control patterns during active flexion: an in vivo tendon force study

An in vivo tendon force measurement system was used to evaluate index finger flexor motor control patterns during active finger flexion. During open carpal tunnel release surgery (N=12) the flexor digitorum profundus (FDP) and flexor digitorum superficilias (FDS) tendons were instrumented with buckle force transducers and participants performed finger flexion at two different wrist angles (0 degrees or 30 degrees ). During finger flexion, there was concurrent change of metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joint angles, but the FDP and FDS tendon force changes were not concurrent. For the FDS tendon, no consistent changes in force were observed across participants at either wrist angle. For the FDP tendon, there were two force patterns. With the wrist in a neutral posture, the movement was initiated without force from the finger flexors, and further flexion (after the first 0.5s) was carried out with force from the FDP. With the wrist in a flexed posture, the motion was generally both initiated and continued using FDP force. At some wrist postures, finger flexion was initiated by passive forces which were replaced by FDP force to complete the motion.

Experimental protocol for the kinematic analysis of the hand: definition and repeatability

A quantitative and objective method based on the optoelectronic kinematic analysis of hand segments and on the calculation of global and partial parameters, which provide measures of the degree of long finger and thumb extension is proposed for the evaluation of the hand's voluntary range of motion and maximal opening of the fingers and thumb. To test the precision and repeatability of the method, the protocol was applied on 14 healthy subjects (28 hands). The proposed parameters are repeatable and show a precision between 5.5 degrees and 10.4 degrees (mean value: 7.3 degrees), comparable to values obtained with other methods. Advantages of the present approach include simultaneous analysis of all fingers, absence of cumbersome connecting cables and no need for individually customized devices. The method, also applied to the paretic hands of two hemiplegic stroke patients before and after electrical stimulation of the wrist and finger extensor muscles, has shown encouraging results for its clinical feasibility and utility in addition to functional tests.

Three-dimensional rotations of human three-joint fingers: an optoelectronic measurement. Preliminary results

Longitudinal axial rotations of phalanges during flexion motions of digits have scarcely been analyzed with current anatomical or radiological methods. Recent optoelectronic systems were developed for three-dimensional (3D) kinematic analysis of human motion. These systems have the advantages of being non-invasive and non-irradiating. The current study was based on the VICON optoelectronic system. A validation of the protocol was made among a sample of volunteers for further direct clinical applications. An experimental protocol was set up with adaptations to the requirements of finger analyses (multiple infrared markers inside small-sized capture volumes). The set-up and the protocol details are described. Kinematic studies consisted in recording the movements of the right hand of six volunteers (free from any visible pathology). Results were displayed for the joints of each three-joint finger with calculation of 3D rotations. Metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) flexion angles ranged from 78 degrees to 118 degrees, 72 degrees to 119 degrees and 9 degrees to 66 degrees respectively. Lateral angles ranged from 5 degrees to 39 degrees (MCP), 4 degrees to 39 degrees (PIP) and 4 degrees to 30 degrees (DIP). Mean longitudinal axial rotations of MCP, PIP and DIP joints ranged from 11 degrees pronation to 26 degrees supination. The index finger was in a global pronation position (five of the six specimens). The fourth and fifth fingers were in a global supination position in every case. The third finger was in a more variable global rotation (pronation in four of the six specimens). An experimental protocol using an optoelectronic system (VICON) has been developed for a kinematic analysis of three-joint finger. A global measure study should be initiated among a wider sample of adults. A database should be created with direct clinical applications. Patients' kinematic deficits could be graded either for standard movements (flexion/extension and abduction/adduction) or for longitudinal axial rotations.

Objective analysis of finger function

Hand motor tasks, even those commonly required by daily life activities, entail complex muscle activation. This article describes a self-contained experimental set-up for the objective kinetic and kinematic analysis of each finger function under several working conditions. Special attention is given to grasping and pressing under isometric conditions. The analysis of the contribution of the thumb is particular to this system. This system has proved accurate, reliable, easy-to-use, and suitable for applications in research environments, and as a support to clinicians for diagnosis and during rehabilitation.