Extrinsic Flexor Research Articles

Activation of intrinsic and extrinsic finger muscles in relation to the fingertip force vector.

Surface EMG was recorded from two intrinsic and two extrinsic muscles of the index finger during a two-dimensional isometric force task in the plane of flexion and extension. Subjects applied force isometrically at the fingertip in eight equally spaced directions, encompassing 360 degrees. Target forces spanned the range from 20% to 50% of maximum for each direction. The effect of varying the metacarpophalangeal (MCP) and interphalangeal (IP) joint angles was investigated. We found that when applying isometric force with the fingertip, the intrinsic muscles of the index finger behaved as a single unit whose region of activation overlapped that of the extrinsic flexor and extensor muscles. The activation region of the intrinsic muscles also spanned a range of force directions for which the extrinsic muscles were virtually inactive. The activation of all muscles, with the exception of the extrinsic extensor, was modified by changing the MCP and IP joint angles. Both IP flexion and MCP extension produced rotation of the resultant activity vector in the direction of MCP flexion. However, the relative rotation was much greater with IP flexion than MCP extension. The effect of IP flexion is linked to rotation of the force direction where joint torque switches from extension to flexion, while the effect of MCP extension is more likely related to changes in muscle length and MCP moment arm. Our results suggest that the primary role of intrinsic finger muscles is to precisely control the direction of fingertip force, while extrinsic muscles provide stability of the joints.

The effect of finger extensor mechanism on the flexor force during isometric tasks

The role of the intrinsic finger flexor muscles was investigated during finger flexion tasks. A suspension system was used to measure isometric finger forces when the point of force application varied along fingers in a distal-proximal direction. Two biomechanical models, with consideration of extensor mechanism Extensor Mechanism Model (EMM) and without consideration of extensor mechanism Flexor Model (FM), were used to calculate forces of extrinsic and intrinsic finger flexors. When the point of force application was at the distal phalanx, the extrinsic flexor muscles flexor digitorum profundus, FDP, and flexor digitorum superficialis, FDS, accounted for over 80% of the summed force of all flexors, and therefore were the major contributors to the joint flexion at the distal interphalangeal (DIP), proximal interphalangeal (PIP), and metacarpophalangeal (MCP) joints. When the point of force application was at the DIP joint, the FDS accounted for more than 70% of the total force of all flexors, and was the major contributor to the PIP and MCP joint flexion. When the force of application was at the PIP joint, the intrinsic muscle group was the major contributor for MCP flexion, accounting for more than 70% of the combined force of all flexors. The results suggest that the effects of the extensor mechanism on the flexors are relatively small when the location of force application is distal to the PIP joint. When the external force is applied proximally to the PIP joint, the extensor mechanism has large influence on force production of all flexors. The current study provides an experimental protocol and biomechanical models that allow estimation of the effects of extensor mechanism on both the extrinsic and intrinsic flexors in various loading conditions, as well as differentiating the contribution of the intrinsic and extrinsic finger flexors during isometric flexion.

Effects of reconstructed radial collateral ligament on index finger mechanics.

Twenty fresh frozen hand specimens from cadavers were studied. Physiologic levels of extrinsic muscle loads were applied to the extrinsic flexor tendons of the index finger to simulate tip pinch of the finger on a fixed plate. The acute effects of transection of the radial collateral ligament and accessory radial collateral ligament (radial collateral ligament complex) with and without transection of the dorsal capsule and volar plate on the position of the proximal phalanx with respect to the metacarpal bone of the index finger were investigated. The acute effects of reconstruction of the radial collateral ligament, for each of two different surgical techniques, on the position of the proximal phalanx also were investigated. The spatial positions of the metacarpal bone and proximal phalanx were measured with a six-degree-of-freedom digitizing system for flexion angles from 0 degrees to 90 degrees in increments of 15 degrees. Transection of the radial collateral ligament complex resulted in significant increases in ulnar deviation (adduction) of the proximal phalanx and in volar translation. Additional transection of the dorsal capsule and volar plate caused significant increases in ulnar deviation, pronation, volar translation, and ulnar shift. The first surgical technique, one traditionally used to reconstruct the metacarpophalangeal joint of the thumb, failed to return the three-dimensional position of the proximal phalanx on the metacarpal head of the index finger to normal. The second surgical technique, based on anatomy, returned the position of the proximal phalanx to levels not statistically different from normal for most flexion angles.

A Study of the Use of a Wrist Splint to Prevent WMSDs at a Sprout Grower

Awkward postures and repetitive forceful motions have been implicated as risk factors for the development of work related musculoskeletal disorders (WMSDs). The use of wrist splints in the work environment has been adapted by some employers in an effort to control at least one of these risk factors. The hypothesis follows that if workers wear wrist splints they can avoid awkward wrist postures, which may reduce their risk for the development of WMSDs. The affect of the wrist splint on the amount of force exerted by the workers is unknown. This study was undertaken at a sprout grower to analyze the relative force exerted by workers with and without a splinted dominant wrist during two hand intensive jobs. It was found that the ability to exert peak grip force was significantly impaired with the use of the wrist splint. In addition, extrinsic flexor electromyography (EMG) and anterior deltoid EMG were relatively higher while subjects worked with splinted wrists as compared to working without a wrist splint. This preliminary data suggests that a wrist splint may limit awkward wrist postures at the expense of increasing the force required to perform hand intensive tasks. The opinions expressed in this paper are those of the authors and do not necessarily represent the opinions of the Occupational Safety and Health Administration.

Contribution of the extrinsic and intrinsic hand muscles to the moments in finger joints

Objective. The purpose of this current work is to develop a method of estimating force produced by the extrinsic and intrinsic hand muscles, and to estimate the contribution of these muscles to the finger joint moments. Design. Experimental methods and a biomechanical model were developed for the estimation of (a) moments produced at finger joints, and (b) contribution of the intrinsic and extrinsic muscles to the moments, (c) forces of the extrinsic and intrinsic muscles within individual fingers. Background. Because of the differential insertions of the extrinsic flexors, it is possible to isolate their mechanical effect at finger joints. Methods. During the experiment, the location of force application was varied in parallel along individual fingers. The points of force application were on the distal phalanx, at the distal interphalangeal joint, or at the proximal interphalangeal joint. Results. When the point of force application was varied in the proximal direction from the distal phalanx to the proximal interphalangeal joint the moment at a given joint decreased. The intrinsic and extrinsic muscle forces were dependent on the experimental conditions. The extrinsic muscles were the major contributors in counterbalancing finger joint moments when the point of force application was distal beyond the proximal interphalangeal joint. Conclusion. This current work provides both an experimental protocol and a biomechanical model that allows estimation of the contribution of the intrinsic and extrinsic muscles to finger joint moments. Relevance This study suggests ways of identifying the source of functional deficiency in the hand.

EXTENSOR TENDON DISLOCATION IN CEREBRAL PALSY

An 18-year-old man with cerebral palsy presented with a flexion deformity of the middle finger particularly at the metacarpophalangeal joint and ulnar dislocation of the extensor tendon. Releasing the tight ulnar sagittal band and imbricating the attenuated radial sagittal band allowed centralization of the extensor tendon. For complete correction of other deformities intrinsic release and extrinsic flexor muscle lengthening were done. Extensor tendon instability in this case was due to the combined forces of the extrinsic and intrinsic muscles on the retinacular system of the extensor mechanism.

A Study of the Effect of a Wrist Splint on Extrinsic Flexor and Anterior Deltoid Electromyography during a Pick and Place Task

A Study of the Effect of a Wrist Splint on Extrinsic Flexor and Anterior Deltoid Electromyography during a Pick and Place Task

Activity of Index Finger Muscles during Typing

An electromyographic investigation was conducted of finger and wrist muscle activity during typing. Examination of the data revealed substantial activity of the extrinsic extensor, a muscle which is ignored in many existing biomechanical finger models. This paper describes activity of the extensor muscle during typing, in absolute terms and relative to activity of the extrinsic flexors. Amplitude probability distribution analyses demonstrated that static extensor activity exceeded 5% MVC for all subjects. Two subjects exhibited pronounced patterns of coactivity in the extrinsic extensor and flexor muscles. Biomechanical modeling efforts demonstrated similar force contributions from the extrinsic extensors and flexors. Based on these results, neglect of finger extensor activity would result in underestimation of finger joint loading.

Volkmann's ischemic contracture of the foot and ankle: evaluation and treatment of established deformity.

Fibrotic contracture of skeletal muscle can follow weeks or months after the severe ischemic insult of compartment syndrome. Commonly known as Volkmann's ischemic contracture, the affected limb often becomes dysfunctional and painful, and may lose sensibility. The pathogenesis of the muscle contracture includes prolonged ischemia, myonecrosis, fibroblastic proliferation, contraction of the cicatrix, and myotendinous adhesion formation. Resultant shortening or overpull of involved muscles leads to stiffness and deformity. Simultaneously, nerve injury from initial ischemia or subsequent soft tissue fibrotic compression leads to muscle paresis or paralysis of the involved compartment and of those muscles more distally innervated. The resultant deformity is thus a combination of varying degrees of contracture and weakness depending on which muscles and nerves are affected. Deformity and functional impairment in the foot and ankle secondary to ischemia are determined by many factors, including: (1) which leg compartment, if any, has been affected and to what degree extrinsic flexor or extensor overpull is exhibited, (2) degree of nerve injury sustained causing weakness or paralysis of extrinsic or intrinsic foot and ankle muscles (3) which foot compartment, if any, has been affected and to what degree intrinsic overpull is exhibited, and (4) degree of sensory nerve injury leading to anesthesia, hypoesthesia, or hyperesthesia of the foot. Therefore, a variety of clinical presentations can be encountered following compartment syndrome of the leg and foot. Treatment is based on an appreciation of the pathoanatomy of the deformity. Nonoperative therapy is aimed at obtaining or preserving joint mobility, increasing strength, and providing corrective bracing and accommodative footwear. Operative management is usually reserved for treatment of residual nerve compression or severe and problematic deformities. Established surgical protocols are performed in a stepwise fashion, to include: (1) release of residual or secondary nerve compression, (2) release of fixed contractures, using infarct excision, myotendinous lengthening, muscle recession, or tenotomy, (3) tendon transfers or arthrodesis to increase function, and (4) ostectomy or amputation for severe, refractory deformities.

Coordination of index finger movements

The purpose of this investigation was to describe the patterns of coordination among the joint motions of the index finger, and among the EMGs of index finger muscles. Index finger movements involving all three joints were varied in speed and direction. Joint motions were recorded along with finewire EMG from all the muscles that insert into the index finger. We observed nearly linear relationships for angular position between the two interphalangeal (IP) joints, and between the metacarpophalangeal (MP) and proximal IP (PIP) joints regardless of movement, speed and direction. The activities of the extrinsic flexors were of similar magnitude and were highly correlated when they acted as agonists but were poorly correlated when they acted as antagonists to the movement. Extrinsic extensor muscles behaved in this way also. The activation patterns of the intrinsic musculature correlated weakly except for extension movements voluntarily limited to the IP joints. We conclude that the highly coordinated action of the extrinsic flexors during flexion contribute importantly to the linked motions of the IP joints in part because these muscles span two or all the three index finger joints. Hence, interjoint movement patterns appear not to arise solely from restraints imposed by passive tissues, especially for fast flexion movements. The weakly correlated intrinsic mucle activity does not uncouple the flexion motions at the PIP and DIP joints because these muscles exert extensor torques at both IP joints. However, the actions of the intrinsic muscles are necessary for stabilizing the MP joint in flexion postures during IP motion and in producing motions voluntarily limited to the MP joint.

RECONSTRUCTION OF TRAUMATIC ABSENCE OF THE THUMB IN THE ADULT BY POLLICIZATION

Amputation of the thumb is a severe handicap. In an emergency situation, thumb amputation must be treated by means of reimplantation when possible. If reimplantation cannot be performed or fails, several methods of thumb reconstruction can be used according to various factors. These include the number of surviving fingers and the level of the thumb amputation. Pollicization is the first choice for amputations proximal to the metacarpophalangeal joint when four and even three fingers are present. It is the easiest and safest operation that supplies the best results both from the motor and sensory points of view. Pollicization can be done even in an emergency situation in selected patients. The index finger is preferred because it can be pollicized without palmar scar or tendons, vessels, or nerves crossing over. If a damaged finger is present, it is preferred to the index finger to leave one more sound finger; a damaged finger can frequently be used, because the thumb is shorter than the other fingers, and although its mobility is very important at the trapeziometacarpal joint, it is less important at the metacarpophalangeal and interphalangeal joint levels. It is preferable to take as much second metacarpal bone as necessary to place the transferred second metacarpophalangeal joint at the position of the thumb metacarpophalangeal joint so that the tendons of the index interosseous muscles can be sutured to the intrinsic muscles of the thumb. According to this concept, the distal phalanx of the transferred finger should be amputated. In this manner, the new thumb will have a normal size, only two phalanges, only one extrinsic flexor, and normal insertion of the muscles of the thumb.

Independent digit control: failure to partition perceived heaviness of weights lifted by digits of the human hand.

1. A weight-matching task was used to investigate the ability to estimate heaviness when weight lifting was isolated to the extrinsic flexor muscles (or portions thereof) that act on the digits of the hand. 2. Subjects matched a reference weight (200 g) lifted by a digit on the right with a variable weight lifted by the left thumb; a concurrent weight was simultaneously lifted by a digit on the right (reference) side. The reference and concurrent weights were lifted either by the same muscle (digital portions of flexor digitorum profundus), or anatomically separate but functionally related muscles (flexor digitorum profundus and flexor pollicis longus). Anaesthesia of the radial nerve and/or posturing of the hand was used to eliminate any small forces generated by co-contraction of the extensor muscles of the digits. 3. When the concurrent weight was equal to or greater than the reference weight, the perceived heaviness of the reference weight increased significantly from control trials (in which no concurrent weight was lifted). Although perceived heaviness of the reference weight increased progressively as the concurrent weight increased, reproducibility (expressed as the coefficient of variation) did not deteriorate when a weight was lifted concurrently. These findings were qualitatively similar when the reference and concurrent weights were lifted by two digital portions of flexor digitorum profundus or when the weights were lifted by flexion of the thumb and index finger. Also, anaesthesia of the digits which lifted the reference and concurrent weights did not alter the changes in perceived heaviness. 4. Perceived heaviness of the reference weight lifted by flexor digitorum profundus did not change when subjects lifted the concurrent weight with a remote muscle group (ankle dorsiflexors). 5. This study shows that signals of heaviness are systematically overestimated whenever more than one portion of the extrinsic muscles which flex the different digits are simultaneously active. Given that estimates of heaviness are biased by the central motor command, one explanation is that when the total motor drive increases, the central nervous system is unable to partition precisely the destination of motor commands to functionally related 'muscles'.

Response of biomechanical correlates of cumulative trauma disorders in the carpal tunnel and extrinsic flexor musculature to simulated working conditions

Response of biomechanical correlates of cumulative trauma disorders in the carpal tunnel and extrinsic flexor musculature to simulated working conditions

A system to predict internal factors related to the development of cumulative trauma disorders of the carpal tunnel and extrinsic flexor musculature

Non-physical balance training has demonstrated to be efficient to improve postural control in young people. However, little is known about the potential to increase corticospinal excitability by mental simulation in lower leg muscles. Mental simulation of isolated, voluntary contractions of limb muscles increase corticospinal excitability but more automated tasks like walking seem to have no or only minor effects on motor-evoked potentials (MEPs) evoked by transcranial magnetic stimulation (TMS). This may be related to the way of performing the mental simulation or the task itself. Therefore, the present study aimed to clarify how corticospinal excitability is modulated during AO + MI, MI and action observation (AO) of balance tasks. For this purpose, MEPs and H-reflexes were elicited during three different mental simulations (a) AO + MI, (b) MI and (c) passive AO. For each condition, two balance tasks were evaluated: (1) quiet upright stance (static) and (2) compensating a medio-lateral perturbation while standing on a free-swinging platform (dynamic).AO + MI resulted in the largest facilitation of MEPs followed by MI and passive AO. MEP facilitation was significantly larger in the dynamic perturbation than in the static standing task. Interestingly, passive observation resulted in hardly any facilitation independent of the task. H-reflex amplitudes were not modulated.The current results demonstrate that corticospinal excitability during mental simulation of balance tasks is influenced by both the type of mental simulation and the task difficulty. As H-reflexes and background EMG were not modulated, it may be argued that changes in excitability of the primary motor cortex were responsible for the MEP modulation. From a functional point of view, our findings suggest best training/rehabilitation effects when combining MI with AO during challenging postural tasks.

Attritional flexor tendon ruptures by an old lunate dislocation

A 76-year-old man sustained attritional disruption of the extrinsic flexor tendons to the ulnar two fingers over 40 years after an untreated palmar lunate dislocation. Spontaneous flexor tendon rupture is rare without wrist joint pathology, even in the absence of chronic pain or median nerve compression.

In Vivo Estimation of the Coefficient of Friction between Extrinsic Flexor Tendons and Surrounding Structures in the Carpal Tunnel

It has been suggested that the coefficient of friction between the finger flexor tendons and the structures over which they slide is normally quite small, but increases with irritation of the tendon. This paper utilizes a belt and pulley model of the wrist in the in vivo measurement of the frictional coefficient. An estimated value of 0.12 for the frictional coefficient was obtained from a sample of five symptom free subjects.

Surgical Procedure for the Cleft Hand: Especially in Relation to Restoration of Instinsic Muscle Function of the Shifted Index Finger*

ABSTRACT We have thirty‐eight patients of cleft hand, and they were divided into three groups from the surgical point. Four patients (seven hands) has only one digit on the radial side of the cleft. In these patients there was little indication for the surgical improvement. The thumb and index finger are completely webbed in six patients (seven hands), and reconstruction to permint thumb function is essential above all in these. In most patients of cleft hand (thirty‐one out of thirty‐eight) thumb function is preserved, but abduction of the thumb was more or less limited. Surgical procedure for these patients are discussed.There are three important point in surgical reconstruction of the celft hand; First is a skin incision to restore thumb abduction; Second is a realignment of the second metacarpal (index ray); and Third is a restoration of intrinsic function. Regarding the first and second point we reported previously (Miura and Komada, 1979). Now, we would like to emphasis that intrinsic function act as a key to get satisfactory result in surgical procedure for the cleft hand. We could use the extrinsic extensor or flexor muscles of the missing middle finger as a proper force for restoration of intrinsic function. We were pleased to use the extrinsic extensor that is found in same incision for the translocation of the index ray. The extrinsic flexor in extrinsic extensor was used. The extrinsic extensor of the middle finger was abscent in one patient.

A clinical study of forces generated by the intrinsic muscles of the index finger and the extrinsic flexor and extensor muscles of the hand

A study of the forces generated by the intrinsic muscles of the index finger and coordinating muscles of the hand found that the intrinsic muscles of the index finger contributed combined forces equivalent to approximately 80% of those generated by the flexor profundus and superficialis, and to 73% of the moment for the motion of metacarpopalangeal flexion with simultaneous interphalangeal joint extension. No current tendon transfer operation can correct this deficit, though several supply sufficient force at the metacarpophalangeal joint to counterbalance the extrinsic extensors.

Clinical and experimental studies on the effect of extensor carpi radialis longus transfer in the rheumatoid hand

Digital ulnar drift in the rheumatoid hand is a complex problem. The radial deformity of the wrist causes abnormal forces on the extrinsic flexor and extensor tendons which aggravate metacarpophalangeal ulnar drift. Analysis of the results of the transfer of the extensor carpi radialis longus to the extensor carpi ulnaris in 20 wrists showed that 13 of 20 had significant correction of the wrist deformity. The transferred tendon did not contract during active ulnar deviation. Laboratory studies of the transfer on cadaveric rheumatoid wrist models showed correction of the wrist deformity. The dorsal ulnar capsule was determined to be a stabilizer of wrist position, as evidenced by deformity after transection.

A systematic study of the oblique retinacular ligament of the human finger: Its structure and function

A dissection of 14 preserved and two fresh human hands, a total of 64 fingers, all from different individuals, showed the oblique retinacular ligament to vary incompleteness and to be functionally present in only 40 to 50% of the specimens, except for the ulnar side of the ring finger where it was present in over 90%. When present, it was made taut by flexion of the distal phalanx, regardless of the postition of the proximal interphalangeal joint. Excision of the ligament when present or in its absence in these fingers, did not alter the coordinated motion of the interphalangeal joints produced by traction on the extrinsic flexors and the lateral bands. In absence of the ligament, a constant finding was the presence of a proximally located osteocapsular ligament which became taut on extension of the proximal interphalangeal joint.