Gross anatomy of the craniolateral antebrachial muscles of the Neotropical river otter (Lontra longicaudis – Olfers, 1818; Carnivora: Mustelidae)

Dorsal forearm approaches are commonly used to repair both partial and complete distal biceps tendon tears. Either the extensor digitorum communis (EDC) or extensor carpi ulnaris (ECU) and the supinator muscles are longitudinally split to expose the radial tuberosity (RT). Despite the known risk of posterior interosseous nerve (PIN) injury, there is little information on the safety of each approach. The purpose of this study was to define the location of the PIN relative to the RT through both EDC and ECU muscle splitting approaches. Additionally, we aimed to find a reliable method to preoperatively locate the PIN, by using a novel line from the olecranon-to-radial styloid (ORS). EDC and ECU muscle splitting approaches were performed on 20 cadaveric specimens, and RT-to-PIN lengths were measured in forearm supination, neutral, and pronation. Additional measurements were made from the olecranon to the point of PIN intersection along the ORS line and to the RT. After RT-to-PIN measurements, the coronal dissection plane for each approach was replicated with strings, and the EDC muscle was reflected to determine if the PIN or its branches crossed either approach lines. The ECU, vs. EDC, approach resulted in longer mean distances between the RT and PIN (≥11 mm; P < .001). In both approaches, the PIN was farthest from the RT in pronation and closest in supination (P < .001). The minimal distance from RT to PIN when using an ECU muscle splitting approach with the forearm in pronation was 21 mm. The PIN crossed the midline of the radial shaft and approach line with an EDC approach, whereas only the ECU motor branch transversed the radial shaft and approach line in an ECU approach. The PIN intersected the ORS line at 35% of its total length. The RT was located 61±5 mm from the tip of the olecranon. The ECU, vs. EDC, muscle splitting approach is less likely to endanger the PIN and/or its branches because the RT-to-PIN length was ≥11 mm longer in all 3 forearm positions (P < .001). Additionally, the PIN crossed the midline of the radial shaft and its approach line using an EDC approach, while only the ECU motor branch transversed the radial shaft and its approach line with an ECU approach. The PIN was located ≥21 mm distal to the RT using an ECU muscle splitting approach in forearm pronation. The ORS line and olecranon are useful landmarks to locate the PIN and RT, respectively.

Extrinsic tEndons n Innervated by the radial nerve n Cross the wrist under extensor retinaculum, which is divided into six compartments (Fig. 70-1)• First compartment  Abductor pollicis longus (APL) Inserts into base of thumb metacarpal  Almost always multiple slips Extensor pollicis brevis (EPB)  Inserts into base of thumb proximalphalanx  Rarely multiple slips• Second compartment  Extensor carpi radialis longus(ECRL)  Inserts into base of index fingermetacarpal  Extensor carpi radialis brevis (ECRB) Inserts into base of middle finger metacarpal• Third compartment  Extensor pollicis longus (EPL) Inserts into base of thumb distal phalanx Relative independence of action across all three joints because of multiple attachments to dorsal apparatusABFig. 70-1 Extensor compartments. (APL, Abductor pollicis longus; ECRB, extensor carpi radialis brevis; ECRL, extensor carpi radialis longus; EDC, extensor digitorum communis; ECU, extensor carpi ulnaris; EDM, extensor digiti minimi; EIP, extensor indicis proprius; EPB, extensor pollicis brevis; EPL, extensor pollicis longus.)• Fourth compartment  Extensor digitorum communis (EDC) Often has two slips to ring finger  Slip to small finger absent in up to 56% of population Extensor indicis proprius (EIP)  Ulnar to EDC of index finger  Most distal myotendinous junction• Fifth compartment  Extensor digiti minimi (EDM); also called extensor digiti quinti (EDQ) Two slips in 80% of population • Sixth compartment  Extensor carpi ulnaris (ECU) Only extensor tendon with a true sheath  Tear of sheath: Leads to ulnar-sided wrist pain and popping sensation withsubluxation of ECUINTRINSICS n Dorsal interossei: Fourmuscles, bipennate (Fig. 70-2) • Innervated by ulnarnerve • Act to abductfingers, flex metacarpophalangeal (MP) joints, and extend interphalangeal (IP) joints (only with MP joints flexed)n Palmar (volar) interossei: Three muscles, unipennate (see Fig. 70-2) • Innervated by ulnar nerve • Act to adduct fingers, flex MPs, extend IPs (only with MP joints flexed)TIP: The function of the interossei can be remembered by the mnemonics DAB (dorsal abduct) and PAD (palmar adduct).

The northern tamandua (Tamandua mexicana) is a xenarthran mammal with a distribution from Mexico to Peru. This species arrives to wildlife care centres due to illegal trafficking and attacks by domestic dogs, both of which are situations where the northern tamandua's thoracic limbs (forelimbs) can be affected. As such, it is necessary to have anatomical studies that allow us to perform better medical and surgical procedures. Among these, studies about the musculoskeletal system also aid in the muscular reconstructions of extinct species. The aim of this study was to characterize the craniolateral muscles of the forearm in Tamandua mexicana and compare them with other Xenarthrans to determine their gross adaptations. Six dead specimens were used, and none were sacrificed for the purpose of this investigation. In five specimens, arterial repletion was done. Four were fixed with 10% formaldehyde and 5% glycerin, and two were dissected in fresh. All were dissected in the Veterinary Anatomy Laboratory of the Universidad del Tolima. The weights of the muscles from seven forearms were taken and divided in three functional groups for comparison with non-parametric statistics. Two muscular groups were found: one superficial formed by the brachioradialis, brachioradialis accesorius, extensor carpi radialis, extensor digitorum communis, extensor digitorum lateralis and extensor carpi ulnaris; and one deep muscular group formed by the supinator, extensor digiti III et IV, abductor digiti I longus, and extensor digiti I et II. They were supplied by different branches of the cranial interosseous, transverse cubital and superficial brachial arteries, which had the shape of rete mirabile; and all muscles were innervated by the deep branch of the radial nerve. The presence of the brachioradialis accesorius muscle in this species allows its hand to remain in semi-supination when it is mobilized in a quadrupedal manner. It must also support elbow flexion together with the action of the brachioradialis and the extensor carpi radialis muscles. All the antebrachial digital muscles sent tendons for the digit III making it the most functional for different grip activities such as climbing trees and searching for its food, however, the most strength was directed to supination and carpal extension, and therefore also to the flexion of the elbow.

Short-latency excitatory Ia reflex connections were determined between pairs of human wrist flexor and extensor muscles. Spindle Ia afferents were stimulated by either tendon tap or electrical stimulation. The activity of voluntarily activated single motor units was recorded intramuscularly from pairs of wrist flexor or extensor muscles. Cross-correlation between stimuli and the discharge of the motor units provided a measure of the homonymous or heteronymous excitatory input to a motoneurone. Homonymous motoneurone facilitation was generally stronger than that of the heteronymous motoneurones. The principal wrist flexors, flexor carpi radialis (FCR) and flexor carpi ulnaris (FCU), were tightly connected through a bidirectional short-latency reflex pathway. In contrast, the extensor carpi ulnaris (ECU) and the extensor carpi radialis (ECR) did not have similar connections. ECU motoneurones received no short-latency excitatory Ia input from the ECR. ECR motoneurones did receive excitatory Ia input from ECU Ia afferents; however, its latency was delayed by several milliseconds compared with other heteronymous Ia excitatory effects observed. The wrist and finger extensors were linked through heteronymous Ia excitatory reflexes. The reflex connections observed in humans are largely similar to those observed in the cat, with the exception of heteronymous effects from the ECU to the ECR and from the extensor digitorum communis (EDC) to the ECU, which are present only in humans. The differences in the reflex organization of the wrist flexors versus the extensors probably reflects the importance of grasping.

Objective To analyze the electrophysiological characteristics of Hirayama disease and explore their significance for its diagnosis. Methods Electrophysiological tests were performed on 18 patients who fulfilled the clinical criteria for Hirayama disease. Sixteen were males and 2 were females. The mean age was 24.9years old ( 19-58 years), and the mean case history was 5.2 years ( 1-40 years). The Hirayama disease was clearly unilateral in 10 patients and bilateral in 3, with 5 cases suspected of being bilateral. Motor neuron conduction velocity (MCV) and sensory neuron conduction velocity (SCV) were measured in the median and ulnar nerves.Electromyograms (EMGs) of the abductor digiti minimi, abductor pollicis brevis, extensor digitorum communis,brachioradialis muscle, biceps brachii and sternocleidomastoid were recorded in all cases. The MCV and SCV of the common peroneal nerve and an EMG of the tibialis anterior muscle were examined in one leg. The MCV and SCV of the ulnar nerve and EMGs of the abductor digiti minimi, extensor digitorum communis and brachioradialis muscles were inspected on the contralateral sides of 8 cases, including the patients suspected of suffering bilateral Hirayama disease. The MCVs of the median and ulnar nerves were examined segmentally by stimulating the nerves distally as well as proximally, and recording the amplitude, duration and area of compound muscle action potentials (CMAP) and changes in wave form, then determining whether there was a nerve conduction block. Results (1) No conduction block was detected in any median nerve or ulnar nerve among the 18 cases. (2) All the SCVs and sensory nerve action potentials of the median and ulnar nerves were normal. ( 3 ) All the MCVs and SCVs of the common peroneal nerve and the EMGs of the anterior tibialis muscles were normal. (4) MCV slowing in the upper limbs accounted for 41.3％ (19/44) of the examined nerves. The rates of MCV decrease were 72.2％ (13/18)in the ulnar nerve on the affected sides, 33.3％ (6/18) in the median nerve on the affected sides and 0％ (0/8)in the ulnar nerve on the contralateral sides. (5) Amplitude reduction in the CMAP in the upper limbs accounted for 81.8％ (36/44) of the examined nerves. The rates of amplitude decrease were 100％ (18/18) in the ulnar nerves of the affected sides, 77.8％ (14/18) of median nerves on the affected side and 50％ (4/8) of ulnar nerves on the contralateral side. ( 6 ) Upper limb EMGs revealed a rate of neurogenic damage of 47.0％ ( 62/132). The EMGs decreased in 100％ (18/18) of the abductor digiti minimi and abductor pollicis brevis on the affected side, 88.9％ (16/18) of extensor digitorum communis on the affected side, 62.5％ (5/8) of the abductor digiti minimi on the contralateral side, 37.5％ (3/8) of the extensor digitorum communis on the contralateral side,5.6％ ( 1/18 ) of the brachioradialis and biceps brachii muscles on the affected sides. There was no neurogenic damage of the contralateral brachioradialis muscle or the sternocleidomastoid on the affected side. Conclusions The electrophysiological features of Hirayama disease include unilateral or bilateral neurogenic damage in the upper limbs. According to the abnormal EMGs, spinal anterior horn cells on the affected sides were injured at C7-T1. C6and above C6 were rarely involved. The electrophysiological characteristics of Hirayama disease could provide a clear basis for localization and differentiation in Hirayama disease diagnosis. Key words: Hirayama disease; Electrophysiology

Proprioceptive information about movement is transmitted to the central nervous system by a variety of receptor types, which are widely distributed among the muscles, joints, and skin. Muscle spindles are known to be an important and reliable source of information for the perception of movement kinematics. Previous studies that focused on the characteristics of single muscle spindle firing patterns have left the impression that each receptor fires in relation to a number of kinematic variables, leaving the following question unanswered: what role is played by the ensemble of muscle spindles within the same muscle or within synergistic muscles? The study described in this paper addressed whether the perception of joint position and velocity is based on the net input of muscle spindles residing in all synergistic muscles crossing a joint. Normal human adults performed a motor coordination task that required perception of joint velocity and dynamic position at the wrist. The task was to open the left hand briskly as the right wrist was passively rotated in the flexion direction through a prescribed target angle. In randomly occurring trials, the tendons to three muscles [extensor carpi radialis (ECR), extensor carpi ulnaris (ECU), and extensor digitorum (ED)] were vibrated either individually or in different combinations during the performance of the motor task. Tendon vibration is known to distort muscle spindle firing patterns, and consequently, kinesthesia. By comparing performance errors with and without tendon vibration, the relative influences of muscle spindles residing in ECR, ECU, and ED were quantified. Vibration of the individual ECR, ECU, or ED tendons produced systematic undershoot errors in performance, consistent with the misperception of wrist velocity and dynamic position. Performance errors were larger when combinations of, rather than individual, muscle tendons were vibrated. The error resulting from simultaneous vibration of ECR and ECU was roughly equal to the sum of the errors produced by vibration of the individual tendons. These effects of vibrating synergistic tendons at the wrist suggest that kinesthesia is derived from the integrated input of muscle spindles from all synergistic muscles.

Rendos, NK, Heredia Vargas, HM, Alipio, TC, Regis, RC, Romero, MA, and Signorile, JF. Differences in muscle activity during cable resistance training are influenced by variations in handle types. J Strength Cond Res 30(7): 2001-2009, 2016-There has been a recent resurgence in the use of cable machines for resistance training allowing movements that more effectively simulate daily activities and sports-specific movements. By necessity, these devices require a machine/human interface through some type of handle. Considerable data from material handling, industrial engineering, and exercise training studies indicate that handle qualities, especially size and shape, can significantly influence force production and muscular activity, particularly of the forearm muscles, which affect the critical link in activities that require object manipulation. The purpose for this study was to examine the influence of three different handle conditions: standard handle (StandH), ball handle with the cable between the index and middle fingers (BallIM), and ball handle with the cable between the middle and ring fingers (BallMR), on activity levels (rmsEMG) of the triceps brachii lateral and long heads (TriHLat, TriHLong), brachioradialis (BR), flexor carpi radialis (FCR), extensor carpi ulnaris, and extensor digitorum (ED) during eight repetitions of standing triceps pushdown performed from 90° to 0° elbow flexion at 1.5 s per contractile stage. Handle order was randomized. No significant differences were seen for triceps or BR rmsEMG across handle conditions; however, relative patterns of activation did vary for the forearm muscles by handle condition, with more coordinated activation levels for the FCR and ED during the ball handle conditions. In addition, the rmsEMG for the ED was significantly higher during the BallIM than any other condition and during the BallMR than the StandH. These results indicate that the use of ball handles with the cable passing between different fingers can vary the utilization patterns of selected forearm muscles and may therefore be advantageous for coaches, personal trainers, therapists, or bodybuilders for targeted training or rehabilitation of these muscles.

The contractile properties of motor units (MUs) in two multi-tendoned forelimb muscles were investigated. In anesthetized cats single MUs of the extensor carpi ulnaris (ECU) and extensor digitorum communis (EDC) muscles were selectively activated by stimulation of cervical ventral root filaments. MUs were characterized by various tests including single twitches, series of tetanic contractions providing a tension-frequency relation and a fatigue test. They were classified by the parameters contraction time (CT, time-to-peak within unpotentiated single twitches) and fatigue-index (RB, according to Burke). The ECU muscle is composed of 38% type FR MUs (fast, fatigue-sensitive; CT less than 38 ms; RB less than 0.5), 35% type FR MUs (CT less than 38 ms, RB greater than 0.5) and 27% type S MUs (slow; CT greater than 38 ms, RB greater than 0.5). 46% of the EDC MUs were classified as FF (RB less than or equal to 0.25), 29% as FI (fast, intermediately fatiguable; 0.25 less than RB less than 0.75) and 25% as FR/S (fatigue-resistant, fast or slow; RB greater than or equal to 0.75). The latter group was devised since most MUs appeared as fast and the unequivocal presence of slow MUs could neither be demonstrated nor excluded. Normalized tension-frequency relations of fast ECU and EDC MUs were nearly identical and similar to those reported for fast MUs of other muscles. In contrast to this, the tension-frequency relation of slow ECU MUs has a different shape supporting the use of this function to distinguish fast from slow MUs. The distribution of different types of MUs is discussed with regard to the structure and function of the parent muscles and in relation to hindlimb muscles of comparable architecture. As revealed by comparison to EMG data gained in behaving animals (Fritz et al. 1985; Hoffmann et al. 1986, Botterman et al. 1985), the three muscles of the cat distal forelimb investigated so far seem to be adapted to different tasks: the EDC to rapid movements with a high proportion of type FF MUs, flexor carpi radialis to sustained contractions during the body support with a high proportion of fatigue-resistant MUs; the ECU which changes synergism between both muscles has an intermediate composition.

The objective of the article is to evaluate the impact of the friction force mouse-pad in the contraction level of the forearm muscles M. extensor carpi ulnaris, M. extensor digitorum and M. extensor carpi radialis longus. A standard protocol of mouse movements was performed involving horizontal, vertical and diagonal mouse displacements drag-anddrop type. The operators were instructed to execute the protocol with their normal working speed. The movements protocol were performed by each subject (n=17) with three selected pairs mouse-pad, classified as low, medium and high friction force pairs. The mean time to execute the protocol with each mouse was ~138 s. Mean values of ~13%MVE (Maximum Voluntary Electromyography signal), ~17%MVE and ~10%MVE were found in the M. extensor digitorum, M. extensor carpi ulnaris and in the M. extensor carpi radialis longus respectively when performing the movements’ protocol. A 8.1% increase in %MVE was observed in the M. extensor digitorum and a 9.4% increase in %MVE was observed in the M. extensor carpi ulnaris when the high friction force pair was operated, relatively to the low friction force pair (p<0.05). The main conclusions of this study is that operating a high friction force mouse-pad (with 79 g of static longitudinal friction force measured with a compression force of 100 g on the mouse) may increase the risk to symptoms or disorders in the wrist, particularly during work with drawing applications, due to an increase in the forearm muscles contraction levels.

Muscle contribution to elbow joint valgus stability

Mapping Origins of Tendons on the Lateral Epicondyle.

Givissis, Panagiotis K. MD, PhD; Stavridis, Stavros I. MD; Ditsios, Konstantinos T. MD, PhD; Christodoulou, Anastasios G. MD, PhD Author Information

To examine the effect of concurrent physical and cognitive demands as well as age on indicators of muscle fatigue at the wrist. There are few studies examining risk indicators for musculoskeletal disorders associated with work-related physical and cognitive demands that often occur simultaneously in the workplace. Twenty-four gender-balanced older and 24 gender-balanced younger (mean age 60 and 23years) participants performed four 30min dual tasks. Tasks differed by the muscular load level during force tracking: 5% and 10% of maximum voluntary contraction force (MVC) and concurrent cognitive demands on the working memory: easy and difficult. Muscle fatigue was assessed by MVC decline and changes in surface electromyography (increased root mean square: RMS, decreased median frequency: MF) at the extensor digitorum (ED) and extensor carpi ulnaris (EU). A decline in MVC was found in all participants when tracking was performed at 10% MVC (mean ± SD: 137.9 ± 49.2 - 123.0 ± 45.3N). Irrespective of age, muscular, or cognitive load, RMS increased (ED 12.3 ± 6.5 - 14.1 ± 7.0% MVE, EU 15.4 ± 7.6 - 16.9 ± 8.6% MVE) and MF decreased (ED 85.4 ± 13.6 - 83.2 ± 12.8Hz, EU 107.2 ± 17.1 - 104.3 ± 16.7Hz) in both muscles. However, changes in MF of EU tended to be more pronounced in the older group at higher cognitive and lower muscular load, without reaching statistical significance. Maximum voluntary contraction indicated no interaction between muscle fatigue, cognitive load, or age. However, the tendencies toward altered muscle activity due to an increase in cognitive load and older age suggest muscular adaptations while maintaining tracking performance during the onset of fatigue signs in the sEMG signal. If the tendencies in muscle activity are confirmed by further studies, ergonomic assessments in industrial workplaces should consider cognitive load and age when describing the risk of musculoskeletal disorders.

The anatomical variations of the extensor carpi ulnaris (ECU) muscle can cause a functional impairment of the wrist and the little finger. The aim of this study was to determine the number, thickness and type of accessory tendon arising from the ECU. The presence of an accessory tendinous slip from the ECU muscle was examined in terms of gross appearance, size, shape, thickness, location and distribution in 54 cadaveric forearms. The accessory slips arising from the ECU muscle were observed in three specimens (5.6%) (two left, one right). These slips ran to the ulnar side of the extensor digiti minimi tendon, originated from the head of the ECU, and ended on the extensor apparatus of the fifth finger. The mean width of the tendinous slips was 1.4±0.01 mm. This anatomic variation of the ECU should be considered in diagnostic and surgical procedures involving the dorsum of the hand. Its clinical importance in the treatment of tenosynovitis and subluxation of joints is also stressed.

Individuals with lateral epicondylalgia (LE) have delayed upper limb reaction time (RT); however, it is unknown if the mechanisms of this dysfunction are related to neural processing or the affected forearm muscles. The aim of this study was to examine the timing of processes that occur before and after forearm muscles are activated during the RT task. Eleven LE (42 ± 11 yr) and 11 healthy controls (42 ± 11 yr) performed rapid wrist extension in response to an audio cue. Intramuscular EMG was obtained from extensor carpi radialis brevis (ECRB), extensor digitorum communis (EDC), extensor carpi ulnaris (ECU), and anconeus. Premotor time (PMT) was the duration from an audio cue to the onset of muscle activity, and motor time (MT) was the onset of muscle activity to the onset of wrist extension. Standard clinical assessments of LE were also performed. RT was significantly slower (33; 95% CI, 1-66 ms) in the LE group. There were no group differences in PMT and the order of muscle activation. Instead, the MT of ECRB (18; 95% CI, 6-31 ms), EDC (12; 95% CI, 1-23 ms), ECU (28; 95% CI, 9-46 ms), and anconeus (33; 95% CI, 11-56 ms) showed significant delay in LE group. Regression analyses revealed that the duration of LE could predict RT, ECRB, and anconeus PMT, whereas cold pain threshold predicted ECRB MT. Delayed RT in LE was predominantly caused by deficits in ECRB and EDC MT. This study provides preliminary evidence that in the people with longer LE symptoms, duration appeared to have faster RT, although confirmation of this finding is required before firm conclusions can be drawn.