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Journal of the Anatomical Society of India

Palmaris Longus - Upside Down !!!!!

Author(s): Oommen, A; Rajarajeshwari

Vol. 51, No. 2 (2002-07 - 2002-12)

Department of Anatomy, K.S. Hegde Medical Academy, Deralakatte, Mangalore INDIA

Abstract

Palmaris longus is a muscle, which shows a lot of variations. Frequently the muscle may be absent. The muscle may be digastric, reduplicated or may have a proximal tendon. It may end in antebrachial fascia. In this case, the muscle had a proximal tendinous origin and a distal thick muscular belly, which continued as a membrane to join palmar aponeurosis.

Key words: Palmaris Longus, variations, tendinous origin, distal belly.

Introduction:

Normally palmaris longus is a slender fusiform muscle medial to flexor carpi radialis and it arises from medial epicondyle by common flexor tendon, from adjacent inter muscular septa and antebrachial fascia. It's long slender tendon passes anterior to the flexor retinaculum and is attached to its distal half and centrally to the palmar aponeurosis often sending a tendinous slip to the thenar muscles. A rare variation of tendinous origin and thick muscular belly towards the insertion is reported here.

Materials and Methods:

In routine dissection of an adult male cadaver in the department of Anatomy a variation was noted. The superficial flexors of the forearm were dissected and cleaned and the specimen was photographed.

Results:

In the present case, the Palmaris longus took origin from the medial epicondyle by the common flexor tendon and from the ante-brachial fascia in both limbs. But the origin instead of being by a muscle belly was found to be by a long thin tendon bilaterally. On both sides the tendon was replaced by a muscle belly around the middle of the fore-arm. In the region of the wrist the muscle fibres ended and a tendon continued into the palmar aponeurosis.

On the right side, the upper 1/3rd of Palmaris longus was found to be tendinous while the lower 2/3rd was found to be muscular. On the left side, the tendinous portion occupied the upper half of the Palmaris Longus while the lower half was found to be muscular. The Palmaris Longus muscle was found to be thicker on the right side as compared to the left side.

Discussion:

To the medial epicondyle is attached by a common tendon the superficial forearm flexor muscles namely pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis and flexor carpi ulnaris. They are also attached to overlying antebrachial fascia and to septa from this passing between individual muscles.

Palmaris longus takes origin along with other superficial forearm flexor muscles as a fleshy belly and forms a long slender tendon which passes in front of flexor retinaculam and is continuous with the central part of palmar aponeurosis. It may send a tendinuous slip to the thenar muscles. Proximal to the wrist joint, the median nerve is deep to the tendon, projecting beyond its lateral edge. Often absent on both sides, the muscle may be highly variable. (Machado & Didio, 1967).

Palmaris longus has been suggested to be phylogenetically degenerate metacarpophalangeal flexor. (Williams et al, 1995). It is supposed that the muscle once existed as a flexor of the proximal phalanges, with it's tendons lying in the palm superficial of those of flexor digitorum superficialis and splitting around them to be attached to proximal phalanges. (McMinn 1997).

The muscle may have a proximal tendon or be reduced to a tendinous strand. It may be digastric or reduplicated. It may also end in antebrachial fascia, tendon of flexor carpi ulnaris, pisiform, scaphoid etc., (Williams et al, 1995). Reimann et al (1944) found the muscle absent in 281 out of 2205 specimens. 15 muscles had accessory slips and four were double. In addition about 9% of palmaris longus showed noticeable variations, of which about half were variation in form such as a centrally or distally placed belly instead of a proximal one, and duplication or splitting of the tendon (Hollinshead, 1956).

In the present case, however, the palmaris longus muscle took origin as a long thin tendon and it became a thick muscle around the middle of the forearm and at the region of the wrist, the muscle fibres abruptly stopped and it became membraneous and it was found to be continuous with the palmar aponeurosis.

Palmaris longus is a weak flexor of the wrist and it is also a tensor of palmar fascia. Just proximal to the wrist the median nerve projects laterally deep to the palmaris longus and lies between flexor carpi radialis and palmaris longus. In this case the median nerve is covered by the muscle belly. Flexor digitorum superficialis is also covered by palmaris longus since the muscle is thick towards its insertion. It can even be mistaken for flexor digitorum superficialis.

References:

  1. Grant, J.C.B. : Grant's Methods of Anatomy. Basmajian, J.V. & Slonecker, C.E. Edr. (11th Edn) B.I. Waverly Pvt Ltd. Waverly : p. 402 (1997).
  2. Hollinshead, W.H.: Anatomy for surgeons: Back & limbs. Jocker Harper, New York: p. 403 (1956).
  3. Machado, A.B; DiDio, L.J. (1967): Frequency of the musculus palmaris longus studied in vivo in some Amazon Indians, American Journal of Physical Anthropology. 27: pp 11-20.
  4. McMinn; R.M.H: Last's Anatomy. 9th Edn. Churchill Livingstone London; p 89 (1997).
  5. Reimann, A.F.; Daseler, E.H. Anson, B.J., Beaton, L.E. (1944): The palmaris longus muscle and tendon. Anatomical Record 89: pp 495-505.
  6. Williams, P.L; Bannister, L.H; Dyson, M; Berry, M.M; Collins, P; Dussek, J.E.; Fergusson, M.W.J: Gray's Anatomy In: The muscular system. 38th Edn, Churchill Livingstone, London: p 846 (1995).

Missing Image

Fig 1 shows abnormal Palmaris Longus (both sides) 1 - Pronator teres,
2 - Flexor carpi radialis
3A - Origin of Palmaris longus
3B - Insertion of Palmaris longus
4 - Flexor carpi ulnaris
5 - Palmar aponeurosis

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