Thursday 7 July 2016

Gross Anatomy of the Palmaris Longus


Gross Anatomy of the Palmaris Longus

Palmaris longus is seen as a small tendon between the flexor carpi radialis and the flexor carpi ulnaris, although it is not always present. The muscle is absent in about 14% of the population, however this number varies greatly in Africa, Asia and Native American.
Absence of this muscle does not have an effect on the grip strength. However, lack of Palmaris longus muscles is disadvantageous in that its tendon cannot be harvested as a graft if necessary the Palmaris, longus muscle can be palpated by touching the pads of the fifth finger and thumb while flexing the wrist, the tendon it present. Will be visible in the midline of the anterior wrist.

It is a slender, fursiform muscle lying on the medial side of the flexor carpi radialis. It arises from the medial epicondyle of the humerus by the common flexor tendon from the intramuscular septa between it and the adjacent muscles and from the antebrachial fascia, it ends in a slender flattered tendon which passes over the upper part of the flexor retinaculum and is inserted into the central part of the flexor retinaculum and lower part of the palmar aponeurosis frequently sending a tendinous ship of the short muscles of the thumb (Roberts, 1972). 

Identification and Side Determination of Palmaris Longus Tendon

The Palmaris longus is believed to be functionally redundant, it is frequently used as a tendon for transfer to the thumb to achieve opposition and abduction, the muscle normally arises from the common origin of the tendons with its tendons inserted across the front of the flexor retinaculum into the palmar aponeurosis is Reiman et al, (1944) studied 1600 cadaver extremities the incidence of Agenesis was 12.9% the overall incidence of anomalies was 9.0 % (46 in 530 consecutive arms) excluding agenesis, the authors found that the variations in position and form consisted one half of these cases, (23 in 46) where as accessory slips and substituted structures accounted for 32.6% (15 in 46) of the cases. 

They observed that the muscle belly may be central, distal or digastric proximal and distal muscle belly connected by a central tendon in position, they may also be completely muscular from origin to insertion or only a fibrous strand, Zeiss and Guilliam (1996) used MR1 to demonstrate various muscular anomalies around the volar aspect of the wrist and forearm ultrasonography with a 7.5 MHZ interosseous probe may be an option for identification of the Palmaris longus muscle in pre-operative work up cases where the tendon is clinically not palpable. Depuytl et al (1998) reported two (2) cases of effort related median nerve compression, in the dominant forearm caused by a reversed Palmaris longus. Rubino et al (1995) and Lorenzo et al (1996) also reported an accessory ship of the Palmaris longus causing median nerve compression. Our patient however did not have any median nerve compression he had a posterior interosseous nerve palsy, since he presented late with no objective evidence of nerve recovery, Vic was considered lor a tendon transfer, a slip from the flexor carpi ulnaris had to be used due to the presence of an anomalous reversed Palmaris longus muscle. With possible known anomalies, it may be worth considering routine ultrasonography or MR1 to study Palmaris longus in patient where it is clinically not demonstrable (Rubino et al., 1995).

Since the Palmaris longus tendon is subject to a wide range of anatomical variation in 10% of the cases aplasia is observed in the identification and determination -of its length and thickness is of importance for the pre-operative planning of ligament reconstructive surgery, thirty healthy volunteers aged between 6 and 50 years were examined using high resolution 10-12 MHZ us probes we determined the thickness of the tendon and its relationship to the median nerve in the distal region of the forearm, the examination appeared totally dynamic and the typical tendinous echo-structure, the Palmaris longus tendon was accurately identified in both children and adults ultrasoriography is highly suitable for the identification of the Palmaris longus tendon and aids the pre-operative planning of ligament reconstructions (Suzuki, 1957). 

Formation of Palmar Aponeurosis 

Palmar aponeurosis: is a fibrotendinous complex that functions as the tendinous extension of the Palmaris longus. The palmar aponeurosis (palmar fascia) invests the muscles of the palm and consists of the central, lateral and medial portions (Richard, 2008).

Structure

The central portion occupies the middle of the palm, it is triangular in shape and of great strength and thickness, its apex is continuous with the lower margin of the transverse carpal ligament and receives the expanded tendon of the Palmaris longus (Data, 2004).
Its base divides below into four slips. One for each finger each slip gives off superficial fibers to the skin of the palm and finger. Those to the palm joining the skin at the furrow corresponding to the metacarpophalangcal articulations and those to the fingers passing into the skin at the transverse fold at the bases of the fingers.
The deeper part of each slip subdivides into two (2) processes which are inserted into the fibrous sheaths of the flexor tendons from the sides, these processes offset are attached to the transverse metacarpal ligament.
By this arrangement short channels arc formed on the front of the heads of the metacarpal bones through those of the flexor tendon pass the intervals between the four slips transmit the digital vessels and nerves and the tendons of the lumbricals. At the points of division into the slips mentioned, numerous strong transverse fasciculi bind the separate processes together. The central part of the palmar aponeurosis is intimately bound to the integument by dense fibroareolar tissue forming the superficial volar arch, the tendons of the flexor muscles and the branches of the median and ulnar nerves and either side it gives off a septum which is continuous with the interosseous aponeurosis and separates the intermediate from the collateral groups of muscles (Drake, 2005). 

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