A unique bilateral accessory forearm flexor muscle.

Muscular and neurovascular variations in the upper extremity are of utmost clinical significance. Here we report a unique bilateral accessory muscle in the forearm and palm of an 89-year-old male cadaver. The accessory muscle presented two bellies on the right side, one in the forearm, innervated by the anterior interosseous nerve, and the other in the palm, innervated by a branch of the median nerve. A long tendon interconnected the two bellies. On the left side, the muscle had a single belly in the palm, which began at the end of a long tendon that extended from the forearm. However, on both sides, the muscle originated from the posterior surface of the flexor digitorum superficialis belly and inserted along with the first lumbrical muscle into the dorsal digital expansion of the index finger. The proximal parts of the variant muscles were sandwiched between the flexor digitorum muscles. The palmar bellies coursed distally through the carpal canal and lay deep to the superficial palmar arch, and superficial to the first lumbrical, between the thenar muscles and the lateral-most tendon of the flexor digitorum superficialis. Arguably, the accessory muscle might be a variant of a lumbrical muscle, as reported before, but innervation of the proximal belly by the anterior interosseous nerve suggests that the muscle may well be a deep accessory muscle at the forearm, probably appeared as a diverted part of the flexor digitorum profundus. Its space-occupying course through the forearm and palm, especially through the carpal canal, might be clinically significant as it might contribute to nerve compression pathologies in the upper extremity. This accessory muscle also indicates the complex nature of individual muscle formation and evolution of the upper extremity with constant changes in the morphology of muscles based on their changing functions.

Mapping of finger fascicles within the flexor digitorum superficialis and profundus muscles.

INTRODUCTION: In this study we aimed to systematically investigate and map localization of the individual finger fascicles within the flexor digitorum superficialis (FDS) and the flexor digitorum profundus (FDP) muscles. METHODS: Using B-mode ultrasonographic assessments, the right forearms of ten healthy participants (five males and five females) were examined during active and passive finger movements. RESULTS: A topographical map indicating clear core areas of fascicle activation within the FDS and FDP muscles was created. Borders that could, to some degree, define individual differences were also indicated. DISCUSSION: Our findings offer a detailed image of fascicle distributions within the FDS and FDP muscles. Various challenges, such as managing individual muscular profiles or the existence of the palmaris longus muscle, are discussed and should always be taken into consideration. The current map can serve as a general orientation for future measurements or injection therapies.

Inervación del músculo flexor superficial de los dedos / Innervation of the superficial flexor digitorum muscle

La inervación del músculo flexor superficial de los dedos (FSD) es controversial. Diversos autores describen que los ramos de este músculo surgen independiente o desde un tronco común que proviene desde el nervio mediano, dentro de la región cubital. Otras descripciones señalan la presencia de ramos adicionales en los tercios medio y distal del antebrazo. Estas diferencias también se reflejan al describir los puntos motores. El objetivo fue determinar el número, ubicación y patrones de distribución de los ramos para el FSD. Se utilizaron 30 antebrazos de cadáveres adultos brasileños formolizados. En relación al número de ramos, el 26 % presentó un solo ramo (R1). El 57 % presentó dos ramos (R1 y R2) y el 17 % presentó 3 ramos (R1, R2 y R3). Respecto al formato de origen, el 87 % de los R1 surgieron independiente, mientras que el 13 % surgió desde un tronco común. En el caso de los R2 y R3, el 100 % surgió independiente. En relación a los puntos de origen, el 90 % de los R1 se originó en el tercio proximal del antebrazo, en tanto, el 60 % de los R2 surgieron en el tercio medio, y de los 5 R3, el 60 % se originó en el tercio medio y los dos restantes surgieron en el tercio distal. Esta misma variabilidad se presentó en la distribución de los puntos motores. Respecto a los patrones de distribución de estos ramos motores se identificaron de dos tipos. El patrón I se presentó en el 85 % y se caracterizó por que todos sus ramos surgieron en un punto distal al origen del nervio interóseo anterior (NIA), en cambio, en el patrón tipo II (15 % de la muestra), el primer ramo se originó proximal al origen del NIA.

Innervation of the flexor digitorum superficialis muscle (FDS) is controversial. Several authors describe that the branches of this muscle arise independently or from a common trunk that comes from the median nerve, within the ulnar region. Other descriptions indicate the presence of additional branches in the middle and distal third of the forearm. These differences are also reflected when describing the motor points. The aim was to determine the number, location and distribution patterns of the branches for the FDS. 30 forearms of Brazilian adults were used. About the number of branches, 26 % presented a single branch (R1). 57 % presented two branches (R1 and R2) and 17 % presented 3 branches (R1, R2 and R3). Regarding the format of origin, 87 % of the R1 emerged independently, while 13 % emerged from a common trunk. In the case of R2 and R3, 100 % emerged independently. About the points of origin, 90 % of the R1 were originated in the proximal third of the forearm, while 60 % of the R2 emerged from the middle third, and of the 5 R3, 60 % were originated in the middle third and the remaining two emerged in the distal third. This same variability was present in the motor points distribution. Regarding the distribution patterns of these motor branches, two types were identified. Pattern I was present in 85 % and was characterized by all branches arising at a point distal to the origin of the anterior interosseous nerve (AIN), however, in the type II pattern (15 % of the sample), the first branch was originated proximal to the origin of the AIN.

Development of digastric muscles in human foetuses: a review and findings in the flexor digitorum superficialis muscle.

The digastricus and omohyoideus muscles are digastric muscles with two muscle bellies. An insertion tendon of the posterior belly becomes an intermediate tendon in digastricus muscles, whereas a single band-like muscle in omohyoideus muscles may later be interrupted by an intermediate tendon, possibly due to muscle cell death caused by mechanical stress. In human foetuses, an intermediate tendon provides the temporal origins of the tensor veli palatini and tensor tympani muscles. Some reptiles, including snakes, carry multiple series of digastric-like axial muscles, in which each intersegmental septum is likely to become an intermediate tendon. These findings indicate that many pathways are involved in the development of digastric muscles. A review of these morphologies suggested that the flexor digi-torum superficialis (FDS) muscle was a digastric muscle, although the intermediate tendon may not be visible in the surface view in adults. The present observations support the hypothesis that the proximal anlage at the elbow develops into a deep muscle slip to a limited finger, while the distal anlage at the wrist develops into the other slips. The findings suggest that, in the FDS muscle, the proximal and distal bellies of the embryonic digastric muscle fuse together to form a laminar structure, in which muscle slips accumulate from the palmar to the deep side of the forearm. (Folia Morphol 2018; 77, 2: 362-370).

A combined variation of Palmaris longus and Flexor digitorum superficialis: Case report and review of literature.

The muscles of the anterior compartment of the forearm often exhibit anatomic variations. During dissection of the upper right limb of a preserved cadaver, morphological variations in the Palmaris longus and Flexor digitorum superficialis muscles were found. The Palmaris longus muscular fibers converged to a tendon that passed beneath the Flexor retinaculum, and inserted at the base of the middle phalanx of the fourth digit, replacing the tendon of Flexor digitorum superficialis. The Flexor digitorum superficialis was divided into two muscular heads: a digastric medial head giving tendons to the second and fifth digits, and a lateral head giving one tendon to the third digit. All these tendons were inserted in the respective digits by two bundles between which were located the tendon of the Flexor digitorum profundus muscle. Variations of flexor muscles must be documented because of their clinical significance and their potential use of these muscles in orthopaedic and reconstructive surgery.

Topographic Anatomy of the Median Nerve and the Pronator Teres and the Flexor Digitorum Superficialis Muscles / 대한해부학회지

The pronator teres syndrome can occur when the median nerve is compressed by the adjacent structures in the proximal forearm. The pronator teres and the flexor digitorum superficialis muscles have been suggested to contribute to this syndrome. This study was performed to clarify the topographical relationship among the median nerve, the pronator teres muscle and the flexor digitorum superficialis muscle in 55 Korean adult cadavers (100 sides of arms). The two heads of the pronator teres muscle met at the point of 61.3 mm distal to the biepicondylar line and inserted to the radius at the point of 141.5 mm distal to the line. The ulnar side of its ulnar head was muscular in 8%, tendinous in 70%, and mixed in 20%. The radial side of its humeral head was muscular in 53%, tendinous in 14%, and mixed in 33%. The median nerve was completely covered by the pronator muscle within 26.5 mm from the biepicondylar line and entered between the two heads of the pronator muscle at 54.2 mm from the line and exited it after running 25.5 mm. The most distal part of the musculotendinous arch of the flexor digitorum superficialis muscle was located at the average 80.9 mm from the biepicondylar line. The distalmost radial head of the flexor digitorum superficialis muscle originated from the distal point of the pronator teres insertion in 28.6%, distal to that point in 54.3%, and proximal to that point in 14.3%.