Forearm compartment syndrome: anatomical analysis of surgical approaches to the deep space

Forearm compartment syndrome is a surgical emergency that usually requires release of the superficial muscle compartments. In some clinical situations it is imperative to also explore the deep muscle compartments. There are no anatomical guides for surgical exploration of the deep compartments that would minimize collateral damage to surrounding vessels, nerves, and muscles. Surgical injury in the setting of ischemia, especially vascular injury, compounds the tissue damage that has already occurred. The authors evaluated four surgical approaches (three volar and one dorsal) to the deep forearm by performing detailed anatomical dissections on 10 embalmed and plastinated cadavers. They used a scoring system to rate the approaches for their ability to visualize the deep space without causing iatrogenic injury to superficial muscles, arteries, and nerves. In the volar forearm, an ulnar approach to the deep space is simple, causes the least iatrogenic surgical injury, and provides access to the deep volar forearm structures. The plane of dissection is between the flexor carpi ulnaris and the flexor digitorum superficialis. Dividing one or two distal segmental branches of the ulnar artery to the distal flexor digitorum superficialis exposes the pronator quadratus. Lifting the ulnar neurovascular bundle with the flexor digitorum superficialis in the middle third of the forearm exposes the flexor digitorum profundus and the flexor pollicis longus. This approach to the deep space requires no sharp dissection. In the dorsal forearm, a midline approach between the extensor digitorum communis and the extensor carpi radialis brevis is simple and safe.     

Identifying tasks to elicit maximum voluntary contraction in the muscles of the forearm

Maximum voluntary contractions (MVCs) are often used for the normalisation of electromyography data to enable comparison of signal patterns within and between study participants. Recommendations regarding the types of tasks that are needed to collect MVCs for the muscles of the forearm have been made, specifically advocating the use of resisted moment tasks to get better estimates of forearm MVCs. However, a protocol detailing which specific tasks to employ has yet to be published. Furthermore, the effects of limb dominance on the collection of MVCs have not been considered previously. Muscle activity was monitored while 23 participants performed nine isometric, resisted tasks. The tasks that are likely to elicit MVC in the flexor carpi ulnaris, flexor carpi radialis, flexor digitorum superficialis, extensor carpi ulnaris, extensor carpi radialis, extensor digitorum communis, and pronator teres were identified. Thus, targeted protocols can be designed to mitigate against fatigue. Hand dominance had limited effect, with differences being found only in the finger flexors and extensors (p< 0.03). Thus, use of the contralateral flexor digitorum superficialis and extensor digitorum communis muscles to obtain baselines for activation levels and patterns may not be appropriate.     

Muscle activity during maximal isometric forearm rotation using a power grip

This study aimed to provide quantitative activation data for muscles of the forearm during pronation and supination while using a power grip. Electromyographic data was collected from 15 forearm muscles in 11 subjects while they performed maximal isometric pronating and supinating efforts in nine positions of forearm rotation. Biceps brachii was the only muscle with substantial activation in only one effort direction. It was significantly more active when supinating (µ = 52.1%, SD = 17.5%) than pronating (µ = 5.1%, SD = 4.8%, p < .001). All other muscles showed considerable muscle activity during both pronation and supination. Brachioradialis, flexor carpi radialis, palmaris longus, pronator quadratus and pronator teres were significantly more active when pronating the forearm. Abductor pollicis longus and biceps brachii were significantly more active when supinating. This data highlights the importance of including muscles additional to the primary forearm rotators in a biomechanical analysis of forearm rotation. Doing so will further our understanding of forearm function and lead to the improved treatment of forearm fractures, trauma-induced muscle dysfunction and joint replacements.     

Analysis of "Teno-uchi" maneuver in releasing Japanese-style bows based on muscle activities and forces acting on the bow

Since a Japanese-style bow has a very complicated shape and structure, an archer has to apply the "Teno-uchi" maneuver including horizontally twisting torque, or "Nejiri", and sagittally down-pushing torque, or "Uwa-oshi", to the restoring bow in order to hit the target. The purpose of this study was to investigate the biomechanical relationship between the muscular activities of the left forearm and the operation of "Teno-uchi" maneuver. Surface EMG of left forearm muscles and the two kinds of torque acting on the bow around the time of release were recorded in 10 experienced subjects during arrow shooting. The "Biku", an involuntary resignation from release happening in the shooting, was also examined. Close analyses of the results revealed that activation of the extensor carpi ulnaris and extensor digitorum muscles together with inhibition of the flexor carpi ulnaris muscle brought about "Nejiri", while activation of the extensor carpi ulnaris as well as flexor carpi ulnaris muscles and inhibition of the extensor carpi redialis longus and extensor digitorum muscles gave rise to "Uwa-oshi", thus causing activities of trade-off nature in the extensor digitorum and flexor carpi ulnaris muscles for the "Nejiri" and "Uwa-oshi. The trade-off activities were presumably actualized through time-sharing coordination between the muscles.     

Functional implications of radial diaphyseal curvature

A recent study (Galtés et al.: Am J Phys Anthropol 135 (2008) 293-300) demonstrated that during pronation, pronator teres exerts a favorable force for radial lateral bending. On the basis of this finding, we hypothesized that the pattern of muscular loading exerted on the radius by this muscle might play a role as a mechanical stimulus involved in radial bowing. The current work relates the hypertrophy of the forearm muscles to the degree of lateral curvature of the radial diaphysis. The analysis is based on an original osteometrical index to estimate radial curvature, and it applies a visual reference method to grade the osteological appearance of 10 entheses of 104 radii from archaeological and contemporary samples. Using these morphological data as an indirect method to measure the association between muscular hypertrophy and bone curvature, this study reveals that the pattern of muscular loading exerted on the apex of the radial shaft by the pronator teres muscle may play an important role as a mechanical stimulus involved in diaphyseal bowing.     

The neuromuscular compartments of the flexor carpi ulnaris

Learning Objectives: After studying this article, the participant should be able to: 1. Report on the vascular supply and innervation pattern of the flexor carpi ulnaris. 2. Describe the muscle architecture of the flexor carpi ulnaris, including the physiological cross-sectional area and fiber length. 3. State the uses of the flexor carpi ulnaris both for resurfacing defects in the vicinity of the elbow and in local functional tendon transfers. 4. Understand the principles of splitting skeletal muscles based on neurovascular supply to enhance its utilization in reconstructive procedures. The aim of this study was to describe the intramuscular innervation and vascular supply of the human flexor carpi ulnaris, with confirmation of findings by a similar study in the primate. Two distinct intramuscular nerve branches running parallel to each other, on either side of a central tendon, from the proximal quarter of the muscle belly to its insertion were found. The muscle could then be split into a humeral and an ulnar compartment, each with its own primary nerve branch. Perfusion studies confirmed the adequacy of circulation to the two compartments. In the primate flexor carpi ulnaris, electrical stimulation of the respective branches revealed independent contraction of each compartment. This study provides useful information for enabling the local transfer of the muscle as a whole, both for resurfacing in the vicinity of the elbow and for functional tendon transfers. It will also enable the transfer of the muscle as one or two separate compartments (for resurfacing, in tendon transfers for muscle paralysis, congenital defects, and muscle defects resulting from trauma, and after resections for neoplasm and infection).     

The pronator quadratus muscle flap: coverage of the osteotomized radius following elevation of the radial forearm flap.

Skin-graft take following elevation of the osteocutaneous radial forearm flap has been shown to be difficult. The pronator quadratus muscle flap can be elevated to cover the exposed osteotomized radius and flexor carpi radialis and brachioradialis tendons. This technique is technically easy to perform and may significantly reduce donor-site wound-healing problems.     

The importance of abductor pollicis longus in wrist motions: A physiological wrist simulator study

The abductor pollicis longus (APL) is one of the primary radial deviators of the wrist, owing to its insertion at the base of the first metacarpal and its large moment arm about the radioulnar deviation axis. Although it plays a vital role in surgical reconstructions of the wrist and hand, it is often neglected while simulating wrist motions in vitro. The aim of this study was to observe the effects of the absence of APL on the distribution of muscle forces during wrist motions. A validated physiological wrist simulator was used to replicate cyclic planar and complex wrist motions in cadaveric specimens by applying tensile loads to six wrist muscles – flexor carpi radialis (FCR), flexor carpi ulnaris, extensor carpi radialis longus (ECRL), extensor carpi radialis brevis, extensor carpi ulnaris (ECU) and APL. Resultant muscle forces for active wrist motions with and without actuating the APL were compared. The absence of APL resulted in higher forces in FCR and ECRL – the synergists of APL – and lower forces in ECU – the antagonist of APL. The altered distribution of wrist muscle forces observed in the absence of active APL control could significantly alter the efficacy of in vitro experiments conducted on wrist simulators, in particular when investigating those surgical reconstructions or rehabilitation of the wrist heavily reliant on the APL, such as treatments for basal thumb osteoarthritis.     

Muscle geometry affects accuracy of forearm volume determination by magnetic resonance imaging (MRI)

Upper extremity musculoskeletal modeling is becoming increasingly sophisticated, creating a growing need for subject-specific muscle size parameters. One method for determining subject-specific muscle volume is magnetic resonance imaging (MRI). The purpose of this study was to determine the validity of MRI-derived muscle volumes in the human forearm across a variety of muscle sizes and shapes. Seventeen cadaveric forearms were scanned using a fast-spoiled gradient echo pulse sequence with high isotropic spatial resolution (1mm(3) voxels) on a 3T MR system. Pronator teres (PT), extensor carpi radialis brevis (ECRB), extensor pollicis longus (EPL), flexor carpi ulnaris (FCU), and brachioradialis (BR) muscles were manually segmented allowing volume to be calculated. Forearms were then dissected, muscles isolated, and muscle masses obtained, which allowed computation of muscle volume. Intraclass correlation coefficients (ICC(2,1)) and absolute volume differences were used to compare measurement methods. There was excellent agreement between the anatomical and MRI-derived muscle volumes (ICC = 0.97, relative error = 12.8%) when all 43 muscles were considered together. When individual muscles were considered, there was excellent agreement between measurement methods for PT (ICC = 0.97, relative error = 8.4%), ECRB (ICC = 0.93, relative error = 7.7%), and FCU (ICC = 0.91, relative error = 9.8%), and fair agreement for EPL (ICC = 0.68, relative error = 21.6%) and BR (ICC = 0.93, relative error = 17.2%). Thus, while MRI-based measurements of muscle volume produce relatively small errors in some muscles, muscles with high surface area-to-volume ratios may predispose them to segmentation error, and, therefore, the accuracy of these measurements may be unacceptable.     

Impact of the contraction of medial forearm muscles during grip tasks in different forearm positions on medial support at the elbow joint

We measured the medial joint distance (MJD), activity of muscles involved in medial elbow-joint support, and grip strength, aiming to examine the supportfunction of muscles.MJD was measured in supinated and pronated positions of the forearm of 10 participants under three conditions: at rest (R), under valgus load on the elbow joint (L), and under valgus load on the elbow joint during the grip task (L-grip). Under the L-grip condition, electromyography was performed on flexor digitorum superficialis (FDS), pronator teres (PT), flexor carpi radialis (FCR), and flexor carpi ulnaris (FCU); subsequently, normalized integrated electromyograms (NIEMG) were calculated. Under the L-grip condition, MJD was shorter in the pronated position than in the supinated position (p < 0.001); however, grip strength was lower in the pronated position. NIEMG of FDS was 90% in both positions, and those of FCR and FCU were low at 10%. However, that of PT was 3.6% in the supinated position and 40.9% in the pronated position, showing higher NIEMG in the pronated position (p < 0.001). Medial support during grip tasks was higher in the pronated position probably because PT activity compensates for the decreased FDS activity.     

Four forearm flexor muscles of the horse, Equus caballus: anatomy and histochemistry.

Two of the forearm flexors of the horse, the superficial and deep digital flexor muscles, are critical to support the digital and fetlock joints, exhibit differing insertions, and are passively supported by the proximal and distal check ligaments, respectively. These two muscles differ in histochemical composition and architecture. The differences are correlated with the different stress levels transmitted through their tendons, and the different frequencies of clinical breakdown that have been reported. Both muscles contain type I and type IIa fibers. A few type IIb fibers occurred in the deep digital flexor. The superficial digital flexor contained approximately 56% type I fibers, extremely short muscle fibers, and extensive connective tissue investment. In contrast, the deep digital flexor had three muscle heads: ulnar, radial, and "long" and "short" regions of the humeral head. The "long" and "short" regions of the humeral head contained 33% and 44% type I fibers, respectively, fiber lengths three to four times as long as those in the superficial digital flexor, and relatively less connective tissue investment. Flexor carpi radialis and flexor carpi ulnaris compared most closely with the humeral head of the deep digital flexor. These data suggest a correlation of the unique architecture of superficial digital flexor with its proposed elastic storage properties during locomotion in horses, and an explanation for the frequent breakdown of the superficial digital flexor in athletic horses.     

Co-contraction of the pronator teres and extensor carpi radialis during wrist extension movements in humans.

In order to elucidate the functional significance of excitatory spinal reflex arcs (facilitation) between musculus (M.) pronator teres (PT) and M. extensor carpi radialis (ECR, longus: ECRL, brevis: ECRB) in humans, activities of the muscles were studied with electromyography (EMG) and electrical neuromuscular stimulation (ENS). In EMG study, activities of PT, ECRL, ECRB, and M. flexor carpi radialis during repetitive static (isometric) wrist extension and a series of a dynamic motion of wrist flexion/extension in the prone, semiprone, and supine positions of the forearm were recorded in 12 healthy human subjects. In the prone, semiprone, and supine positions, PT and ECR showed parallel activities during the static extension in all, eight, and eight subjects, respectively, and at the extension phase during the dynamic motion in all, eight and five subjects, respectively. These findings suggest that co-contraction of PT and ECR occurs during wrist extension movements at least with the prone forearm. The facilitation must be active during the co-contraction. In ENS study, ENS to PT was examined in 11 out of the 12 and that to ECRL was in the 12 subjects. Before ENS, the forearm was in the prone, semiprone, and supine positions. In all the subjects, ENS to PT induced a motion of forearm pronation to the maximum pronation. ENS to ECRL induced motions of wrist extension to the maximum extension and abduction (radial flexion) to 5-20 degrees of abduction regardless of the positions of the forearm. Moreover, it induced 30-80 degrees supination of the forearm from the prone position. Consequently, combined ENS to PT and ECRL resulted in motions of the extension and abduction while keeping the maximum pronation. These findings suggest that the co-contraction of PT and ECR during wrist extension movements occurs to prevent supinating the forearm. Forearm supination from the prone position should be added to one of the actions of ECRL.     

Upper-limb surface electro-myography at maximum supination and pronation torques: the effect of elbow and forearm angle.

Forearm pronation and supination, and increased muscular activity in the wrist extensors have been both linked separately to work-related injuries of the upper limb, especially humeral epicondylitis. However, there is a lack of information on forearm torque strength at ranges of elbow and forearm angles typical of industrial tasks. There is a need for strength data on forearm torques at different upper limb angles to be investigated. Such a study should also include the measurement of muscular activity for the prime torque muscles and also other muscles at possible risk of injury due to high exertion levels during tasks requiring forearm torques.Twenty-four male subjects participated in the study that involved maximum forearm torque exertions for the right arm, in the pronation and supination directions, and at four elbow and three forearm rotation angles. Surface EMG (SEMG) was used to evaluate the muscular activity of the pronator teres (PT), pronator quadratus (PQ), biceps brachi (BB), brachioradialis (BR), mid deltoid (DT) and the extensor carpi radialis brevis (ECRB) during maximum torque exertions. Repeated measures ANOVA indicated that both direction and forearm angle had a significant effect on the maximum torques (p<0.05) while elbow angle and the interactions were highly significant (p<0.001). The results revealed that supination torques were stronger overall with a mean maximum value of 16.2 Nm recorded for the forearm 75% prone. Mean maximum pronation torque was recorded as 13.1 Nm for a neutral forearm with the elbow flexed at 45 degrees. The data also indicated that forearm angle had a greater effect on supination torque than pronation torque. Supination torques were stronger for the mid-range of elbow flexion, but pronation torques increased with increasing elbow extension. The strength profiles for the maximum torque exertions were reflected in the EMG changes in the prime supinators and pronators. In addition, the EMG data expressed as the percentage of Maximum Voluntary Electrical activity (MVE), revealed high muscular activity in the ECRB for both supination (26-43% MVE) and pronation torques (17-55% MVE). The results suggest that the ECRB acts as a stabiliser to the forearm flexors for gripping during pronation torques depending on forearm angle, but acts as a prime mover in wrist extension for supination torques with little effect of elbow and forearm angle. This indicates a direct link between forearm rotations against resistance and high muscular activity in the wrist extensors, thereby increasing stress on the forearm musculo-skeletal system, especially the lateral epicondyle.     

Neandertal radial tuberosity orientation

Examination of adult and immature Neandertal radii demonstrates that the medial versus anterior orientations of their radial tuberosities fall within recent human ranges of variation, but on the average their radial tuberosities are significantly more medially, as opposed to anteromedially, oriented. This more posterior positioning of their radial tuberosities implies a maintenance of an effective moment arm for M. biceps brachii through the full range of supination, an interpretation which fits with the hypertrophy of and increased moment arms for their forearm pronator muscles. It is an additional indication of the muscular hypertrophy evident elsewhere in Neandertal upper limbs.     

The accessory middle cerebral artery--a variant of the recurrent artery of Heubner (A. centralis longa)?

Three accessory middle cerebral arteries are described in two out of 75 brains dissected under the operating microscope. Each artery originated from the anterior cerebral artery, lateral to its junction with the anterior communicating artery, followed the proximal segment (A1, pars precommunicalis) of the anterior cerebral artery, then the horizontal portion (M1, pars sphenoidalis) of the middle cerebral artery towards the lateral sulcus. Each supplied the lateral orbital gyrus, the gyrus longus of the insula, part of the putamen, the head of the caudate nucleus and the anterior limb of the internal capsule. The presence of the accessory middle cerebral artery is discussed with regard to the recurrent artery of Heubner (A. recurrens, A. centralis longa).     

Salvage of chronically exposed Gore-Tex vascular access grafts in the hemodialysis patient

Exposure and infection of a Gore-Tex vascular access graft often results in removal of the graft. Salvage of the graft is possible, however, with the use of well-vascularized muscle flaps. In 1982, Hodgkinson was the first to use a sublimis muscle flap to cover an exposed vascular access graft. We used the flexor carpi ulnaris and flexor digitorum superficialis to cover exposed Gore-Tex grafts in nine patients. The sublimis was used to cover distal graft exposures, and the longer flexor carpi ulnaris muscle was used to cover more proximal sites. Multiple exposures required both flaps or combinations of muscle flaps and local rotation flaps. Eight of nine chronically exposed grafts were salvaged using these techniques; a graft was removed from one patient because of diffuse unrecognized graft bed infection. Disability is minimized by using only part of the sublimis, and loss of the flexor carpi ulnaris is compensated by local muscles with similar actions. Vascular puncture can be continued during healing.     

Biomechanical model of pronation efficiency: new insight into skeletal adaptation of the hominoid upper limb

Despite considerable literature on the functional anatomy of the hominoid upper limb, there are no quantitative approaches relating to bone design and the resulting muscular-activity enhancement. The purpose of this study is to quantitatively analyze the relationship between the rotational efficiency of the pronator teres muscle and the design of the skeletal structures on which it acts. Using conventional scan images of a human forearm for three rotational positions, this study develops an original biomechanical model that defines rotational efficiency as a mathematical function expressing a geometrical relationship between the origin and insertion muscular sites. The results show that this parameter varies throughout the entire pronation range, being maximal when the forearm lies around its functional position. Moreover, the rotational-efficiency formula allows us to demonstrate, by several simulation conditions, that an improvement in pronation efficiency is derived from a large shaft radius curvature, a large humeral medial epicondyle, and a more proximal pronator teres radial attachment. The fact that forearm pronation efficiency can be inferred, even quantified, throughout the entire rotational range, by applying the biomechanical model developed here allows us to undertake anatomical approaches in the field of Evolutionary Anthropology, to interpret more precisely how skeletal design is related to upper-limb function in extant and fossil primate taxa.     

The flexor function of the m. pronator teres in man: a quantitative electromyographic study

The muscle pronator teres was studied by surface electromyography during elbow flexion in a horizontal plane. The forearm was in semi-pronation and movement was performed at various velocities. A quantitative comparison was made between pronator teres activity and two main elbow flexors, biceps brachii and brachioradialis. The mean timing of the onset of activity was constant: biceps brachii was activated first followed by pronator teres and brachioradialis, and the lower the velocity of flexion, the earlier was the onset of biceps brachii activity. There was a linear relationship between the integrated EMG from each muscle and the work done. However, this relationship was less exact for pronator teres and brachioradialis at low values of work, a finding which opens questions about the generality of this relationship and about the "muscle equivalent" concept. Pronator teres appears to participate in elbow flexion besides its role in pronation. Despite similar anatomical peculiarities, pronator teres does not behave in the same way as anconaeus or popliteus and, above all, it is not the sole muscle active in slow movement. Thus, all the stocky muscles lying close to an articulation do not behave in the same way.     

猕猴执行痛,热延缓辨别作业时额叶神经元及肌电...

To study the functional implication of neuronal responses in frontal cortex to noxious and innocuous heat stimuli, experiments were carried out on two monkeys (Macaca mulatta) during performing a delayed discrimination GO/NO-GO task. The animals were trained to hold a lever for at least 3 s in the response period when an innocuous heat stimulus had been applied to the forearm in the cue period, or release it within 1 s with a noxious one. After a criterion of 90% of correct responses in 3 successive days was reached, single neuronal activity was recorded from the frontal cortex along with EMGs from six muscles in both arms. Of 142 task-related neurons recorded, 87 (66.4%) were related to heat, 34 to visual, and 21 to both visual and heat stimuli. Among the heat-related neurons, 22 were responsive to noxious heat, 18 to innocuous heat, and 47 to both. Of the neurons responding to both noxious and innocuous heat stimuli, 4 neurons showed changes in discharge rates, depending on the type of stimuli. In most cases, muscular activities just appeared at the moment of lever pressing and/or releasing in m. extensor digitorium communis, m. flexor carpi ulnaris and m. flexor carpi radialis of the performing arm. No regular muscular activities appeared in other muscles and in other periods of the task. The result showed that the neuronal responses in frontal cortex elicited by heat stimuli in the cue period were not related directly to the initiation and modulation of behaviours.(ABSTRACT TRUNCATED AT 250 WORDS)     

Architectural properties of distal forelimb muscles in horses,Equus caballus

Articular injuries in athletic horses are associated with large forces from ground impact and from muscular contraction. To accurately and noninvasively predict muscle and joint contact forces, a detailed model of musculoskeletal geometry and muscle architecture is required. Moreover, muscle architectural data can increase our understanding of the relationship between muscle structure and function in the equine distal forelimb. Muscle architectural data were collected from seven limbs obtained from five thoroughbred and thoroughbred-cross horses. Muscle belly rest length, tendon rest length, muscle volume, muscle fiber length, and pennation angle were measured for nine distal forelimb muscles. Physiological cross-sectional area (PCSA) was determined from muscle volume and muscle fiber length. The superficial and deep digital flexor muscles displayed markedly different muscle volumes (227 and 656 cm3, respectively), but their PCSAs were very similar due to a significant difference in muscle fiber length (i.e., the superficial digital flexor muscle had very short fibers, while those of the deep digital flexor muscle were relatively long). The ulnaris lateralis and flexor carpi ulnaris muscles had short fibers (17.4 and 18.3 mm, respectively). These actuators were strong (peak isometric force, Fmax=5,814 and 4,017 N, respectively) and stiff (tendon rest length to muscle fiber length, LT:LMF=5.3 and 2.1, respectively), and are probably well adapted to stabilizing the carpus during the stance phase of gait. In contrast, the flexor carpi radialis muscle displayed long fibers (89.7 mm), low peak isometric force (Fmax=555 N), and high stiffness (LT:LMF=1.6). Due to its long fibers and low Fmax, flexor carpi radialis appears to be better adapted to flexion and extension of the limb during the swing phase of gait than to stabilization of the carpus during stance. Including muscle architectural parameters in a musculoskeletal model of the equine distal forelimb may lead to more realistic estimates not only of the magnitudes of muscle forces, but also of the distribution of forces among the muscles crossing any given joint.