Flexor Digitorum Superficialis (Sublimis)

Some variations in this muscle have been termed retrogressive in that they represent remnants of the connections between two sheets of muscle. Thus, a slip very frequently connects superficialis with the long flexor of the thumb (flexor pollicis longus) or flexor digitorum profundus as muscular slips occasionally pass between superficialis and deep flexors of the fingers. Sometimes a muscular slip derived, but separated from superficialis, or on a tendon that joins one of the tendons of the deep flexor (accessorius profundus digitorum [Gantzer] is found.) Wood reported this muscle present in five of 36 subjects. Tendinous slips frequently connect the tendons of the two muscles. On the other hand, the occasional separation (up to their origins) of individual muscle bellies has been considered a progressive variation.

The extensive origin of the muscle from the radius is a human feature. The radial head shows much variability; complete absence has been recorded. Mori reported the radial head absent in 7.5% and poorly developed in 12.5% of his subjects. One or more of the muscle's distal divisions, e.g., the radial head to the index finger, may be deficient or absent. The belly to the middle finger may be absent or reinforced by a slip from the radial tuberosity. The most common example of this is the absence of the belly for the little finger. Normally this is the smallest division of the muscle, and it arises from the side of the intermediate tendon. The tendon arising from the muscle for the fifth digit may pass superficial to the transverse carpal ligament to terminate on the fifth digit. In the absence of the fourth belly of the muscle, its place may be taken by a muscle arising from the medial collateral ligament of the ulna, the deep flexor, the transverse carpal ligament and palmar aponeurosis or the ligament alone, or the fourth lumbrical. A slip has been seen passing from the superficial aspect of the muscle to palmaris longus; or replace it if absent, ending in the fascia of the forearm or palmar aponeurosis.

A palmaris longus may replace the superficialis slip to the fourth digit and end, as usual, by splitting and inserting on the volar surface of the middle phalanx. Mori reported the following deviant developments in flexor digitorum superficialis: a) a small fasciculus arising from the distal portion of the radial head fused with the tendon for the fifth finger about 1.5 cm. from the radio-carpal joint. Seen in 2.5% of Mori's subjects. b) In 0.8% of Mori subjects, the terminal tendon of the middle (long) finger of superficialis and flexor digitorum profundus were fused, a small muscle fascicle may be present at the point of fusion, c)The terminal tendon for the second finger is divided longitudinally into a large and small tendon. The small part has a muscle and its terminal tendon is fused with the first lumbrical muscle. This was found in 1:205 arms. d) The terminal tendon for the fifth finger is inserted on the radial side of the middle phalanx of the little finger in 1:205 arms. Mori also found flexor digitorum superficialis joined with pronator teres 2.5% of subjects, flexor pollicis longus in 45%, and with flexor digitorum profundus in 8% of subjects (205 arms).

Macalister reported the variations in flexor digitorum sublimis (superficialis) as follows:

  1. Absence of the tendon for the little finger by Wood and Macalister;
  2. Suppression of the radial origin (Wood);
  3. A deep slip to the annular ligament, coexisting with palmaris longus;
  4. A doubled coronoid origin-the upper slip fleshy, the lower one tendinous;
  5. Otto has seen a slip from the insertion of the pronator teres to the radial origin;
  6. From the outside of the coronoid origin a slip arose, which, becoming tendinous, became the sole origin of the first lumbrical (Wood). Wood also described a case in which the lumbrical had a second usual origin, and a third instance in which a muscular slip joined this tendon to the indicial tendon of profundus;
  7. A connecting muscular band sometimes exists between the origins of the flexor sublimis and flexor pollicis longus (Wood and Macalister);
  8. Turner has noticed the variation in the length of the radial origin of this muscle- it may vary from half an inch to four inches in length (1 inch = 2.54 cm);
  9. In a case in which this muscle sent no tendon to the little finger, Kelly found its representative to arise from the front of the synovial sheath of the fourth perforating tendon;
  10. Macalister found the index perforated flexor as a separate muscle arising from the coronoid process (also by Wood);
  11. Macalister and Wood have both found cases, in which the separate muscle was digastric;
  12. A similar digastric muscle, supplying both the index and middle fingers has been described;
  13. The entire muscle was found to be digastric by Dursy;
  14. A separate coronoid tendon joining the radial origin was seen by Wood;
  15. Wood also found a separate fusiform muscle for the little finger arising from the medial condyle of the humerus;
  16. Macalister found the tendons for the index and little finger arising from a separate digastric muscle, with a condyloid and coronoid origin;
  17. Wood found all the tendons connected to separate bellies-the first being digastric and condyloid, the second radial and coronoid, the third and fourth condyloid;
  18. Macalister (1868) described a case where the radial head and part of the condyloid went to the middle finger, a tendon from the muscle, a few inches below the condyle, becoming fleshy, supplied the ring finger, and the remainder supplied the index and little fingers;
  19. A slip from this muscle to the palmar fascia coexisting with a feeble palmaris longus, has been found by Rosenmüller, Wood, and by Macalister;
  20. Wood has seen a doubled tendon for the middle digit;
  21. In case of absence of the little finger tendon, Wood found the perforated flexor for this finger supplied by the fourth lumbrical;
  22. Macalister found the little finger slip of the flexor sublimis (superficialis) coalescing with, and not split by, the corresponding tendon of flexor profundus;
  23. Cross slips joining the muscle bundles for separate digits were found by Turner;
  24. The same author reported a slip from flexor sublimis to the medial side of palmaris longus, crossing under that muscle, and joining the tendon of supinator longus (brachioradialis at the lower end of the forearm.)

A slip, radiopalmaris, may arise directly from the radius beneath sublimis and attach to the palmar aponeurosis or the common sheath of the flexor tendons. Some variation occurs in the origin of the tendons from the flexor digitorum superficialis: a slip from the deep part of the muscle sometimes forms the chief part of the ring finger division or there may be a slip from the deep part to the middle finger tendon to the fourth digit. The tendon for the third digit arises from the extreme radial side of the radial head only and is reinforced by a tendon arising from the epicondyle.

An accessory slip is sometimes present passing from the tuberosity of the ulna to the index and middle finger portions. Another slip may arise from the muscle and attach to the tendon of brachioradalis. Very rarely the whole muscle is digastric. Cases in which the medial and deep tendons are replaced by a sheet of muscle (representing a second superficial flexor) and in which the tendon has failed to divide within the flexor sheath have been reported.

An anomalous muscle (palmar flexor digitorum superficialis accessorius) may arise from the palmar fascia and distal border of the transverse carpal ligament and end in a tendon that joins the flexor tendon of the index finger at the level of the metacarpophalangeal joint. The muscle is innervated by the median nerve.

Syn.: m. Flexor digitorum sublimis, Flexor digitorum perforatus.

Oberflächlicher or durchbohrter Fingerbeuger, Fléchisseur superficiel or sublime (Cruveilhier).

Digastric Flexor Digitorum Superficialis.

In a medical student.

An Unusual Flexor Digitorum Sublimis Muscle.

This case is an example where the index portion of the left flexor digitorum superficialis of an adult male formed two bellies with separate tendons in the distal third of the forearm, and a further smaller belly in the palm of the hand. An explanation for the preceding and following illustrations. from Mainland.

Flexor Digitorum Superficialis Accessorius

Accessory palmar muscle mass associated with the superficialis muscle.
Dissecting room specimen, University of Iowa
See Tountas and Halikman.

References

Badolle, M. (1874) Anomalie du Fléchisseur sublime. Lyon Med. 15:500.

Carrel, M. (1872) Anatomy anormale. 1. Biceps humeral trifide. Lyon Med 10:43-44.

Cassell, M.D., and R.A. Bergman (1990) An unusual palmaris longus muscle substituting for the slip of flexor digtorum superficialis serving the ringfinger. Anat. Anz. 171(3):201-204.

Chowdhary, D.S. (1951) A rare anomaly of m. flexor digitorum sublimis. J. Anat. 85:100-101.

Curnow, J. (1873) Notes of some irregularities in muscles and nerves. J. Anat. Physiol. 7:304-309.

Garel, -. (1873) Anomalie du fléchisseur sublime. Lyon Med. 13:36.

Graper, L. (1917-18) Eine sehr Varietät des M. flexor digitorum sublimis. Anat Anz. 50:80-84.

Gruber, W. (1887) Auftreten des Zeigefingerbauches des flexor digitorum sublimis al Venter bifissus digastricus biceps. Arch. Path. Anat. Physiol. Klin. Med. 110:559-561.

Iwami, S. (1951) Two cases of anomalous flexor digitorum superficialis. Igaku Kenyu. 21:36-37. In Japanese.

Kater, N.W. (1902) Two cases of supernumerary radio-palmar muscle- muscle surnumeraire radio-palmaire of Testut. J. Anat. Physiol. 36:76.

Macalister, A. (1875) Additional observations on muscular anomalies in human anatomy (third series), with a catalogue of the principal muscular variations hitherto published. Trans. Roy. Irish Acad. Sci. 25:1-134.

Mainland, D. (1927) An uncommon abnormality of the flexor digitorum sublimis muscle. J. Anat. 62:86-89.

Mori, M. (1964) Statistics on the musculature of the Japanese. Okajimas Fol. Anat. Jap. 40:195-300.

Nakano, T. (1923) Beiträge zur Anatomie der Chinesen. Die Statistik der Muskelvarietäten. Okajimas Folia Anat. Jpn. 1:273-282.

Tillaux, -.(1861) Anomalie musculaire couche antibrachial superficialis. Bulletins et Mem. de la Société Anatomique de Paris XXXVI(2,3):40.

Tountas, C.P. and L.A. Halikman. (1976) An anomalous flexor digitorum sublimis muscle. A case report. Clin. Orthop. Rel. Res. 121:230-233.

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