Watching your foot move--an fMRI study of visuomotor interactions during foot movement

The objective of this study was to investigate brain areas involved in distinguishing sensory events caused by self-generated movements from similar sensory events caused by externally generated movements using functional magnetic resonance imaging. Subjects performed 4 types of movements: 1) self-generated voluntary movement with visual feedback, 2) externally generated movement with visual feedback, 3) self-generated voluntary movement without visual feedback, and 4) externally generated movement without visual feedback, this design. This factorial design makes it possible to study which brain areas are activated during self-generated ankle movements guided by visual feedback as compared with externally generated movements under similar visual and proprioceptive conditions. We found a distinct network, comprising the posterior parietal cortex and lateral cerebellar hemispheres, which showed increased activation during visually guided self-generated ankle movements. Furthermore, we found differential activation in the cerebellum depending on the different main effects, that is, whether movements were self- or externally generated regardless of visual feedback, presence or absence of visual feedback, and activation related to proprioceptive input.     

Precision grip function after free toe transfer in children with hypoplastic digits.

Although toe-to-hand transfer has a defined role in the management of congenital hand deformities, it remains unclear how well children integrate the transferred digits into physiological grasping. We analysed fingertip forces in the precision grip of 13 patients when lifting a test object more than three years after free toe transfer for absent or hypoplastic digits. Clinically, most patients showed normal sensibility of transferred digits, but active motion and pinch strength were limited as compared to the normal hand. For the control of fingertip forces, two key features of the normal two-digit opposition grip were seen in all operated hands: adaptation of grip force to object weight and parallel coordination of lift and grip forces. These physiological grasping strategies developed independently of the patients' age at the time of operation, which ranged from one to 13 years. In four patients, we observed increased tangential load forces with the operated hand due to misalignments in the application of fingertips on the grasp surfaces. Such forces lead to increased grip force requirements on both fingers that may overload transferred digits with limited motor function. The need for optimal alignment of the grip axis during toe-transfer surgery is emphasised.     

Activation of brachioradialis muscles transferred to restore lateral pinch in tetraplegia

PURPOSE: Surgical transfers of muscles are used to restore lateral pinch in tetraplegia; however, outcomes are variable. The purpose of this study was to compare activation of the brachioradialis (Br) after transfer to the flexor pollicis longus during maximum effort in its primary function (elbow flexion) with maximum effort in its postoperative function (lateral pinch) and to record Br activation during functional tasks. METHODS: Fine-wire electrodes recorded activation of the Br in 11 arms with tetraplegia. Subjects produced maximum lateral pinch force with and without elbow stabilization and were classified according to elbow strength. The elbow was stabilized by supporting the arm and limiting elbow motion. A force sensor mounted on a custom grip recorded the pinch force. Electromyographic (EMG) signals recorded during lateral pinch were expressed as a percentage of the maximum voluntary contraction recorded during maximum-effort elbow flexion. RESULTS: The EMG activation was significantly lower during lateral pinch compared with resisted elbow flexion. The mean EMG during lateral pinch in the self-supported elbow condition was 34% of the maximum voluntary contraction; with the elbow stabilized the EMG increased to 55% of the maximum voluntary contraction. Postoperative pinch-force magnitude was 14 N with self-support and 20 N with the elbow stabilized. Subjects with weak elbow extension strength produced significantly lower pinch forces compared with subjects with strong elbow extension but had similar ability to activate the Br. The Br activation was higher when the pinch tasks were performed successfully. CONCLUSIONS: These findings suggest a reduced ability to activate the transferred muscle fully in lateral pinch function after surgery, even with the addition of elbow support. The Br activation is linked to successful performance of lateral pinch tasks. The subjects' inability to activate the transferred muscle fully may be affected by postoperative muscle re-education and contribute to postoperative weakness.     

Open versus percutaneous release of the A1-pulley for stenosing tendovaginitis: a prospective randomized trial

A prospective randomized trial for release of the first annular pulley (A-1 pulley) in trigger fingers with a percutaneous technique versus the open surgical technique is presented. Thirty-six patients were randomized to either open (n = 16) or percutaneous (#15 blade; n = 20) release of the A-1 pulley. All patients were evaluated for grip strength, active range of motion of the proximal interphalangeal joint, and residual pain at 1 and 12 weeks after release. Furthermore, the operation time was assessed, and the costs were calculated. Overall, 100% success in terms of grip strength, active range of motion of the proximal interphalangeal joint, and residual pain was obtained in both groups. Mean operation time was significantly longer with the open technique. Because of lower costs and quicker procedure with equal functional outcome when compared with open surgery, we recommend the percutaneous technique using a #15 blade for trigger finger release.     

Optimal control of human‐like musculoskeletal arm: Prediction of trajectory and muscle forces

Optimal trajectory and muscle forces of a human‐like musculoskeletal arm are predicted for planar point‐to‐point movements using optimal control theory. The central nervous system (CNS) is modeled as an optimal controller that performs a reaching motion to final states via minimization of an objective function. For the CNS strategy, a cubic function of muscles stresses is considered as an appropriate objective function that minimizes muscles fatigue. A two‐DOF nonlinear musculoskeletal planar arm model with four states and six muscle actuators is used for the evaluation of the proposed optimal strategy. The nonlinear variational formulation of the corresponding optimal control problem is developed and solved using the method of variation of extremals. The initial and (desired) final states (position and velocity) are used as input kinematic information, while the problem constraints include the motion range of each joint, maximum allowable muscle tension, and stability requirements. The resulting optimal trajectories are compared with experimental data as well as those corresponding to recent researches on model predictions of human arm movements. It is demonstrated that the proposed optimal control strategy using minimum fatigue criterion is more realistic in prediction of motion trajectories in comparison with previous work that has utilized minimum joints' torque criterion. Accordingly, minimization of muscles fatigue is an effective biomechanical criterion for the CNS in prediction of point‐to‐point human arm motions. Copyright © 2016 John Wiley & Sons, Ltd.     

Grip Force Control in Individuals with Hand Osteoarthritis

Individuals with hand osteoarthritis (OA) experience pain and stiffness that could result in significant limitations in the performance of everyday activities involving upper extremities. The purpose of the study was to evaluate grip force control in individuals with hand OA during the lifting of an object. The study design used was a case-control study. Ten females with hand OA and a group of age-matched females performed two functional tasks: lifting an instrumented object vertically while the load was suddenly changed and lifting and placing the object on a shelf. Load Force Peak, Grip force at liftoff, Grip Force Peak, Time Lag, and Latency were measured and analyzed. Individuals with hand OA were able to modulate the magnitude and temporal parameters of grip force; however, they applied higher grip forces (at liftoff [p = 0.002]; Grip Force Peak [p = 0.039]) and demonstrated a longer Latency (p = 0.015) to manipulate the instrumented object when compared with the control subjects. The Load Force Peak and Time Lag were not significantly different between the two groups. Detailed information about how individuals with hand OA perform prehension activities of daily living will help to better understand the limitations of grip force control in these individuals.     

Precision grip function after hand replantation and digital nerve injury.

Understanding how the loss of digital sensibility affects manual dexterity could have important implications for rehabilitation after hand injury. We investigated precision grip function during lifting tasks in seven patients after hand replantation, in five after single digital nerve injury and in four volunteers subjected to digital anaesthesia. Using their affected hand, all participants could successfully lift test objects with parallel and vertical grip surfaces and they all reliably increased the grip force with increasing object weight (0.11-0.55 kg). However, the grip forces used were frequently significantly higher than those applied by the unaffected hand. This was partly due to participants compensating for loss of sensibility with high grip force safety margins against slips, and partly related to misalignments of the fingertips on the grasp surfaces. The latter was most prominent after hand replantation. In a second series of lifting experiments we changed the shape of the grip surfaces in order to investigate the participants' ability to adapt grip forces based on tactile recognition of object shape. An important finding from this series was that in patients with poor clinical outcomes, the contralateral unaffected hand tended to mirror the abnormal grasp patterns of the injured hand. This suggests that control strategies developed for the impaired hand can influence the control of the contralateral uninjured hand.     

The effect of finger joint hypomobility on precision grip force

Study designRepeated measures experiment.IntroductionTraumatic injuries and certain other diseases of the hand typically affect mobility of the finger joints. Decreased mobility may alter grip force control while one is grasping and lifting objects. However, the effect of finger joint hypomobility on grip force control has not yet been systematically investigated.Purpose of the studyThe aim of this study was to investigate the effects of limited finger joint mobility, without other associated symptoms like pain, or sensory/proprioceptive deficits, on precision grip force control.MethodsFifteen healthy subjects performed a pinching and lifting task of an object equipped with a force sensor and an accelerometer, via opposition of the thumb and index finger, in the following experimental conditions: unrestricted finger joint movement (UJM), restricted finger flexion (RFF), restricted finger extension (RFE), mock restricted flexion (MRF), mock restricted extension (MRE). The following pinch force variables were measured and analyzed: grip force at lift off, grip force peak, load force peak, latency, and static force.ResultsA significant increase in latency (F = 4.41, p < 0.01) was noted during RFE relative to UJM and MRF conditions. There were no statistically-significant differences between the conditions among the other variables of precision grip force control.ConclusionsLimited joint mobility of the thumb and index finger may cause temporal changes in precision grip force control, which can lead to reduced manual dexterity. Restoring range of motion might be an important priority to improve thumb-index pinch force control during manipulative tasks.     

A hybrid system for upper limb movement restoration in quadriplegics

Generally, quadriplegic individuals have difficulties performing object manipulation. Toward satisfactory manipulation, reach and grasp movements must be performed with voluntary control, and for that, grasp force feedback is essential. A hybrid system aiming at partial upper limb sensory-motor restoration for quadriplegics was built. Such device is composed of an elbow dynamic orthosis that provides elbow flexion/extension (range was approximately from 20 degrees to 120 degrees , and average angular speed was approximately 15 degrees /s) with forearm support, a wrist static orthosis and neuromuscular electrical stimulation for grasping generation, and a glove with force sensors that allows grasping force feedback. The glove presents two user interface modes: visual by light emitting diodes or audio emitted by buzzer. Voice control of the entire system (elbow dynamic orthosis and electrical stimulator) is performed by the patient. The movements provided by the hybrid system, combined with the scapular and shoulder movements performed by the patient, can aid quadriplegic individuals in tasks that involve reach and grasp movements.     

Suspensionplasty for basal joint arthritis: why and how

Abductor pollicis longus suspensionplasty is a simple, effective treatment alternative forbasal joint arthritis. Use of a suspensionplasty technique acknowledges our current understanding of forces involved during pinch and grip, as well as the role of normal ligamentous anatomy. The primary rationale for performing suspensionplasty revolves around resisting the sagittal plane collapse that will occur when the thumb is loaded during pinch. In the absence of a volar-based suspension of the metacarpal, cantilever bending forces and axial force transmission will result in the dissipation of force along the thumb lever arm, and ultimately longitudinal collapse. Maximal grip and pinch strength require suspensionplasty, which can be performed using a variety of techniques. The author's current technique for suspensionplasty is described.     

Method for the measurement of friction between tendon and pulley

An experimental system was developed that allows direct measurement of friction at the tendon-pulley interface, and the results were interpreted by use of a theoretical model for friction of a cable around a fixed pulley. Validation experiments were conducted with a nylon cable around a nylon rod. One end of the cable was connected to an actuator via a load cell, and the other end was connected to a 4.9 N load via a similar load cell. The cable was passed around the nylon rod and then pulled toward the actuator. Tests were performed at five different arcs of contact. The friction forces, as measured by the difference between two load transducers, were compared with those determined for a theoretical model and were used for calculation of the friction coefficient. The measurement system then was used to study the friction force between the flexor digitorum profundus tendon and the A2 pulley on nine fresh frozen index digits. The method allows us to measure the direct interaction between the tendon and pulley and could be used to evaluate and compare procedures for tendon-pulley and pulley repair and reconstruction, as well as for the study of tendon-pulley friction in various pathological conditions.     

The influence of wrist position on individual finger forces during forceful grip

Nine healthy subjects sustained maximum grip of an instrumented handle while voluntarily moving the wrist joint within their available range of motion of the wrist in a continuous and random manner. Individual finger forces and wrist angular positions in flexion/extension and radial/ulnar deviation were recorded simultaneously. Wrist position had a significant effect on individual finger force and total force production. Peak finger forces were produced at 20 degrees of wrist extension and 5 degrees of ulnar deviation. At this position, a mean total grip force of 114.9 (+/-12.8) N was produced with force-sharing percentages of 32.2% (+/-3.8%), 32.6% (+/-4.3%), 23.5% (+/-4.5%), and 11.7% (+/-4.9%) among the index, middle, ring, and small finger, respectively. As the wrist was moved farther away from this position, the forces produced by individual fingers decreased incrementally; however, the decreases in individual finger forces were not proportional, leading to a dependence of finger force-sharing patterns on wrist position.     

Effects of Different Extents of Pulley Release on Tendon Excursion Efficiency and Tendon Moment Arms

To compare the excursion efficiency and moment arms of flexor digitorum superficialis (FDS) and profundus (FDP) among different conditions of pulley integrity related to trigger finger treatment, cadaveric fingers were first tested with an intact pulley system, and then the first (A1) and second (A2) annular pulleys were released gradually from the proximal to distal part. Linear position sensors and a motion capture system were used to measure the tendon excursion and joint rotation simultaneously. The tendon excursion efficiency was defined as the range of motion of the involved joints per unit of tendon excursion, and the tendon moment arm was determined by the slope of the linear fitting result of tendon excursion versus metacarpophalangeal (MCP) joint rotation. No significant differences were found between the release of the A1 pulley and the release extending to half the proximal part of the A2 pulley in the FDP excursion efficiency and the moment arms of FDS and FDP with respect to the MCP joint. These results imply that the release could extend to half the proximal A2 pulley, if necessary, without significantly decreasing the FDP excursion efficiency and increasing the moment arms of FDS and FDP with respect to the MCP joint. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:224–228, 2015.

     

Palmar and digital flexor tendon pulleys

Retinacular structures, called pulleys, maintain the flexor tendons of the hand in constant relationship to the joint axes and promote economy and efficiency in finger flexion. This system is composed of the transverse carpal ligament, the palmar aponeurosis pulley, and the digital flexor pulley system. Of these three components, the digital pulleys are the most critical to finger flexion. In their normal state, these pulley components are ideal in all aspects including configuration and location, which accomodates a 260 degrees arc of motion without impingement and with minimum friction while at the same time using muscle tendon excursion that is well within the natural range of the muscle. An absent pulley results in an increased moment arm and requires increased tendon excursion to produce the same arc of motion. Because muscle excursion is not a limitless factor and is directly proportional to muscle fiber length, the effectiveness of tendon excursion is dependent on maintenance of the critical relationship between pulleys and the adjacent joints. Preservation and reconstruction of this system is based on knowledge of the anatomy and an understanding of the relative functional significance of each component of the system.     

An electromyographic analysis of the shoulder during cones and planes of arm motion.

Shoulder motion has traditionally been described in reference to arbitrarily defined planes of motion (e.g., sagittal/flexion, coronal/abduction). This study examined shoulder muscle recruitment during conical arm movements, which include all planes of motion. Electromyographic (EMG) data was collected with intramuscular wire electrodes from ten muscles in five normal volunteers. Each muscle showed peak EMG activity in association with a direction of action consistent with its anatomic alignment. These findings were similar for movements in both the sagittal and coronal planes, calling into question conventionally held designations of shoulder muscles as flexors and abductors. Muscle recruitment was as follows: Clavicular pectoralis major, to move the arm medially along the horizontal; anterior deltoid, to move the arm obliquely upward inclined toward the midline; middle deltoid, to move the arm obliquely upward inclined away from the midline; posterior deltoid, to move the arm laterally along the horizontal; and teres major and latissimus dorsi, to move the arm obliquely downward away from the midline. Rotator cuff muscles were maximally active during elevation, consistent with the concept of a force couple.     

Comparison of skeletal traction forces in patients treated in conventional and oscillating hospital beds

This study compares the forces in two types of skeletal traction systems: a standard hospital bed with balanced suspension traction and an oscillating hospital bed using a flexion cable system. In line traction, forces were continuously measured, using a specially designed transducer. Changes in the magnitude of traction forces of up to two times the applied force were caused by patient movement, nursing procedures, and changes in bed configuration. The oscillating hospital bed was found additionally to impart a moderate (20-50%) rhythmic, sinusoidal variation in applied traction forces. The traction forces applied with the flexion cable system on the oscillating hospital bed were well tolerated and equivalent to those applied in conventional balanced suspension on a standard hospital bed. Although different in design, standard balanced suspension traction on a conventional hospital bed and traction using the flexion cable system on the oscillating hospital bed appear to be equally effective in stabilizing fracture sites.     

Output control of da Vinci surgical system's surgical graspers

Introduction

The number of robot-assisted surgeries performed with the da Vinci surgical system has increased significantly over the past decade. The articulating movements of the robotic surgical grasper are controlled by grip controls at the master console. The user interface has been implicated as one contributing factor in surgical grasping errors. The goal of our study was to characterize and evaluate the user interface of the da Vinci surgical system in controlling surgical graspers.

Materials and methods

An angular manipulator with force sensors was used to increment the grip control angle as grasper output angles were measured. Input force at the grip control was simultaneously measured throughout the range of motion. Pressure film was used to assess the maximum grasping force achievable with the endoscopic grasping tool.

Results

The da Vinci robot's grip control angular input has a nonproportional relationship with the grasper instrument output. The grip control mechanism presents an intrinsic resistant force to the surgeon's fingertips and provides no haptic feedback. The da Vinci Maryland graspers are capable of applying up to 5.1 MPa of local pressure.

Conclusions

The angular and force input at the grip control of the da Vinci robot's surgical graspers is nonproportional to the grasper instrument's output. Understanding the true relationship of the grip control input to grasper instrument output may help surgeons understand how to better control the surgical graspers and promote fewer grasping errors.     

Kinematic assessment of manual skill following functional hand surgery in tetraplegia

To determine whether surgical key grip reinforcement actually leads to a better movement ability we developed a procedure for the kinematic analysis of manual skill following hand surgery in tetraplegia. The functional results of surgery in 5 cases were examined by the kinematic analysis of drawing movements using an electronic pen and a digitizer under 3 conditions: with eyes open, with eyes closed, and while performing a concurrent arithmetic task. Movement velocity and dysfluency (ie, the number of velocity changes per centimeter) were measured before and at several moments after surgery during subsequent rehabilitation. Both movement velocity and dysfluency showed good stability across repeated trials and were consistently affected by visual deprivation. Movement velocity showed a 39% increment between the first and last assessment. Although grip strength increased in all patients, it was not associated with the change of movement velocity. These results suggest that other factors (eg, deep sensibility, cognition, muscle coordination) play a critical role in the ability to use improved grip force for controlling drawing movements and emphasize the value of a kinematic assessment besides measuring isolated grip force in the evaluation of functional hand surgery.     

Transfer from table to wheelchair in men and women with spinal cord injury: coordination of body movement and arm forces

STUDY DESIGN: A complex set-up was used to investigate kinematics and ground reaction forces. SETTING: Motor Control and Physical Therapy Research Laboratory, Neurotec Department, Karolinska Institutet, Huddinge, Sweden. OBJECTIVE: To investigate how men and women with spinal cord injury (SCI) perform transfers from table to wheelchair with regard to timing and magnitude of force generation beneath the hands and associated body movements. METHODS: A total of 13 subjects (seven men, six women) with thoracic SCI. Kinematics of body movement were recorded (Elite 2000 system) simultaneously with the signals from three force plates (AMTI) placed beneath the buttocks and hands. Temporal and spatial parameters regarding head, trunk and trailing arm displacement, loading amplitudes and loading torque directions of both hands were analyzed for each trial and subject and compared between genders. RESULTS: Men and women used similar amplitudes of head bending and forward displacement of the trailing shoulder, while female subjects had significantly larger trunk rotation. Both genders applied significantly more weight on the trailing hand. Differences between genders were seen in direction and timing of peak torque beneath the hands. CONCLUSIONS: The forces beneath the trailing hand were larger than those in the leading, if there is weakness or pain in one arm, this arm should be selected as the leading. To avoid excessive load on the arms, technical aids and environmental factors should be very well adapted. SPONSORSHIP: This project was funded by the Swedish Research Council and the Health Care Science Committee of Karolinska Institutet.     

Biomechanics of the knee-extension exercise. Effect of cutting the anterior cruciate ligament

We conducted this study to determine the effective moment arm of the knee extensor mechanism and the conditions under which the anterior cruciate ligament is loaded during knee-extension exercises. The moment arm was calculated from measurement of the quadriceps force required to extend the knee with and without resistive weights placed at the foot, the leg weight, and the location of its center of gravity. Changes in three-dimensional joint motion after the anterior cruciate ligament was removed were considered to be an indication that the ligament was loaded. The quadriceps force rose during the initial phase of knee extension and remained nearly constant at an average value of 177 newtons between 50 and 15 degrees. With extension past 15 degrees it rose rapidly, reaching an average of 350 newtons at zero degrees of extension, and continued to increase with hyperextension. The addition of thirty-one newtons (seven pounds) at the foot approximately doubled the quadriceps force that was required to extend the knee. The effective moment arm of the extensor mechanism increased with knee extension, peaked at approximately 20 degrees, and rapidly decreased with further extension. No change was found in the quadriceps force or its effective moment arm when the anterior cruciate ligament was sectioned except in hyperextension, where the quadriceps force decreased in two of five specimens. There was, however, an increased anterior tibial displacement in the range of 30 degrees to full extension, suggesting that the anterior cruciate ligament is loaded in that flexion arc. Clinical Relevance: This study demonstrates that very large quadriceps forces are required to accomplish the last 15 degrees of extension during leg-raising exercises, typically twice those required to reach 30 degrees of flexion. The large forces that are required to obtain full extension explain why an extensor lag occurs with quadriceps weakness even though a full passive range of motion is possible. Since thirty-one newtons (seven pounds) of resistive weight added at the foot approximately doubles the quadriceps forces required to extend the leg alone, using such weights can produce very large quadriceps forces and concurrent patellofemoral and tibiofemoral contact forces. Because the quadriceps force increases little as the leg is extended from 50 to 15 degrees, in patients with patellofemoral chondroses for whom a full range of joint motion is not desired, quadriceps exercises can be limited to the amount of extension without decreasing quadriceps force.(ABSTRACT TRUNCATED AT 400 WORDS)