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The Palmaris longus muscle exhibits significant anatomical variance compared with other muscles of the upper extremity. The most frequent variation is the complete absence of the muscle, but a number of other variations exist, these variations include reversed duplicated bifid or hypertrophied Palmaris longus muscles, many authors have reported the variations in case reports and described them using their own terms.
In this case reports and review of literature, we aim to consolidate the current knowledge regarding the anatomic variation of the Palmaris longus muscle and its clinical relevance (Moriya, 1956).
Bilateral Reversed Palmaris Longus Muscle
A rare anatomic variation a case of bilateral reversed Palmaris longus in its upper portion in both arms, was discovered this rare variation has been mentioned only once in the literature as a surgical finding, according to the literature a reversed Palmaris longus muscle may cause a compartment syndrome in the wrist area, carpal tunnel and Guyon's syndrome, the described variation is also useful to the hand surgeon as a tendon for transfer or as an anatomical landmark for operations at this area (Jodhar et al., 2008). Palmaris longus is one of the most variable muscle in the body, it is absent in 11.2% of bodies (all sources).
In a study of 800 living subjects it, was absent on both sides in 7.7% of cases absent on the right in 4.5% and absent on the left in 5.2%, Palmaris longus is absent, more often in females and on the left side in both seven in another study of 276 cadavers (George, 2010) Palmaris longus was present on both sides in 216 (7 females) 78.3% present on the right side only 17 or 6.1% present on the left only in 19 (2 females) or 6.9% absent on both sides in 24 (3 females or 8,7%). Hence, Palmaris longus was absent in (15.2%) of the 552 limbs slightly more frequently in the rights limb (15.6%). Than in the left (14.9%). It was shown that there was no correlation between the presence or absence of Palmaris longus and plantaris muscle. If it is desirable to estimate the probability of the presence or absence of the Palmaris longus knowledge of the presence or absence of the plantaris is of no help the two muscles vary independently. This may be unfortunate for those needing tendons repairs, Palmaris longus may be digastric or fleshly through out its entire length it may have a proximal tendon as well as a distal one. It may be fleshy distally and tendinous proximally (Palmaris inversus) or may be reduced to a mere tendinous band (Roberts. 1972).
Occasionally, there are two Palmaris muscles, one having the usual form and the other one of the forms referred to above or one of the following additional modes of origin, the muscle may arise from the medial intramuscular Septum the biceps or brachialis, the fascia of the forearm proximal or one of the tendons (Valeria, 2007).
Prevalence of the Absence of the Plamaris Longus Muscle
Absence of the Palmaris longus muscle has been well documented in several populations at a prevalence rate ranging between 2.2 and 63.9% which varies according to race, sex and side of the body, there is little documentation of the prevalence of absence of this muscle from the populations in the adult south east Nigerians we examined 40 subjects 3-25 years old for the presence or absence of the Palmaris longus muscle using the conventional test for the presence of this muscle.
Statistical analysis investigates the association of muscle absence with sex, hand dominance and laterality, the Palmaris longus muscle was absent in 7.6% of subjects, bilateral absence (3%) was more common than unilateral absence (7.6%) with the preponderance in female subjects the muscle was absent more often on the left side than the right (P = 0.003) in the right upper limbs, this muscle was in female subjects more than male subjects (P = 0.031).
This study reaffirms that there is population variation in the frequency of the absence of the Palmaris longus muscle tendon of the Palmaris longus bifurcated at the wrist in 7:1% Subjects with male showing this feature more frequently than female subjects in the right hand C = 0,037 and the left hand (P = 0.030) this has not been reported before (Eric et al., 2011).
Force of Gripping of the Palmaris Longus Muscle
The Palmaris longus muscle is described as a weak flexor of the wrist and a tensor of the palmar aponeurosis but not a thumb abductor. The Palmaris longus muscle is believed to aid thumb abduction through its insertion onto the thenar eminence, two groups both right hand dominance were selected from 1200 sampled participants, the first group comprised of 38 subjects with unilateral presence of the Palmaris longus muscle and was used to determine the strength of the thumb abduction, the second group comprised of 30 subjects with bilateral presence of the Palmaris and it was used to calculate the effects of hand dominance, a significant number of subjects with bilateral absence of the Palmaris longus muscle were observed and undocumented using dynamometer in subjects with unilateral presence of the Palmaris longus, the force of thumb abduction was significantly greater on the hand with a Palmaris longus than the one without it (P = 0.014) irrespective of hand dominance in the second sample with bilateral Palmaris longus thumb abduction on the dominant hand was 10% stronger than on the non dominant hand thus 10% was deducted from all the dominant hands and remained greater on the hand with Palmaris longus muscle than the hand without it P = (0.049). The results of this demonstrated the Palmaris longus muscle to be involved in thumb abduction (Sebastin, 2005).
Biomechanical Importance
The clinical significance of the Palmaris longus tendon in the pathophysiology of carpal tunnel syndrome:
- Carpal tunnel syndrome is associated with increased intracarpal canal pressure. The effect of tendon loading on intro carpal canal pressure is documented in Biomechanical studies. Palmaris longus loading in wrist extension induces the greater absolute increase in intracarpel canal pressure. Despite this fact the Palmaris longus is not yet proven independent risk factor for the development of carpal tunnel syndrome the purpose of this prospective clinical study was to assess and quantify the association between the presence of a Palmaris longus tension and carpal tunnel syndrome, thirty six carpal tunnel subjects with bilateral disease were compared with 36 controls. Each subject was clinically examined for the presence of the prevalence of the Palmaris longus, agenesis was significantly lower on the carpal tunnel group, and the Palmaris longus tendon is a strong independent risk factor for carpal tunnel syndrome (King et al., 1950).
- Acrornioclavicular joint dislocation a comparative biomechanical study of the Palmaris longus tendon graft reconstruction with other augmentative methods in cadaveric models: Acromioclavicular injuries arc common in sports medicine, surgical intervention is severally advocated tor chronic instability of rock wood grade III and more severe injuries, various methods of coracoclavicular ligament reconstruction and Augmentation have been described. (Wehbe et al., 1992).
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