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GENERAL ANALYSIS OF STUDIES OF PALMARIS LONGUS MUSCLE AGENESIS IN DIFFERENT POPULATIONS IN RECENT PAST
Borkach (Barkats) Norbert
Ferenc Rakoczi II Transcarpathian Hungarian Institute
Agenesis of Palmaris longus muscle is widely studied all over the world, and in recent years the frequency of researches and studies related to Palmaris longus muscle agenesis rapidly increased. But there wasn’t made any work yet, which would attempt to summarize the results of studies that were made so far. The main aim of this paper is to attempt to make a summary, and systematization of works related to study of prevalence of absence of Palmaris longus muscle and the results published in them.
Keywords: Palmaris longus muscle, tendon, agenesis, general analysis, absence
Introduction: First report of absence of Palmaris longus muscle (PLM) was made in 1559 by Colombos in De Re Anatomica Libri. The prevalence of absence of the muscle was extensively studied by author at that time.
Nowadays studies of PLM often attempt not only to show the percentage of its absence, but also to find correlation between the prevalence of PLM absence and other anatomical or physiological anomalies .
Palmaris longus muscle is one of the superficial slender muscles of the forearm that acts on the skin and distal digital webs. It is a phylogenetically degenerate muscle, and it functions as a metacarpophalangeal joint flexor . During its phylogenetic degeneration the PLM lost its importance, and its functioning became unnecessary for the proper function of human hand. Probably this is one of the main causes of its great variability and frequent absence because even without it the human palm can function perfectly.
According to the studies done up to date it is believed that agencies of this muscle is phylogenetically retrogressive and will gradually lose its function totally .
It can be stated that the PLM is one of the most variable muscles in the human body, and its agenesis is apparently considered the most frequent anatomical variation .
Many authors suggest that there is a relation between the prevalence of frequency of the PLM agenesis in the subjects and the affiliation of the subjects to different ethnic groups .
The Palmaris longus muscle is a key importance muscle in reconstructive surgery since its tendon is considered to be a dispensable tendon and its absence dos not significantly affect the function of the wrist. It fulfills the necessary requirements of length, diameter and availability, and can be used without producing any functional deformity in reconstruction surgery . It is therefore very useful in orthopaedics, hand and reconstructive surgery. It is commonly used by hand surgeons for tendon transfers , second stage tendon reconstruction, pulley reconstruction as well as tendon grafting.  Plastic surgeons also utilize the Palmaris longus muscle in restoration of lip and chin defects , lip and commissure reconstruction , ptosis correction  , and in the management of facial paralysis .
In the recent years PLM became an extensively and intensively studied muscle all over the world. The main reason of this is the importance of PLM, which was recognized with development of plastic and reconstructive surgery. The possibilities of use of PLM are each day bigger and bigger. Here are some examples of uses of PLM:
1. The Palmaris longus muscle is a key importance muscle in reconstructive surgery since its tendon is considered to be a dispensable tendon and its absence dos not significantly affects the function of the wrist. It fulfills the necessary requirements of length, diameter and availability, and can be used without producing any functional deformity in reconstruction surgery .
2. It is very useful in orthopaedics, hand and reconstructive surgery. It is commonly used by hand surgeons for tendon transfers ,
3. Second stage tendon reconstructions, pulley reconstructions as well as tendon grafting can be done by using PLM tendon. 
4. Plastic surgeons also utilizes the palmaris longus muscle in restoration of lip and chin defects , lip and commissure reconstruction , ptosis correction  , and in the management of facial paralysis. 
Materials and methods: As main source of materials were used: online libraries, publisher archives, and medical journals.
Results: We can see differences in prevalence of PLM absence in different populations if we look through the literature dealing in this topic:
Troha F. in 1990 made a study with North American Caucasians, examined 200 subjects, and got the following results: overall absence of PLM was 5.5%, unilateral absence was detected in 3%, bilateral in 2.5%. 
O. Ceyhan and A. Mavt in 1997 in their study of Turkish population examined 7000 people and got the following results: 63,8% of total PLM agenesis, bilateral agenesis was detected in 43,2%% and unilateral agenesis was detected in 20,6%. 
N W Thompson et al in 2001 in Northern Ireland examined 300 subjects and found 25% of total PLM agenesis from this bilateral was 9%, unilateral 16%. 
Sandeep J Sebastin et al in 2006 in the work with the Chinese population examined 329 subjects and got the result of the overall prevalence of absence of the PLM was 4.6%. Bilateral agenesis was detected in 1,2% and unilateral agenesis was detected in 3,4%. 
SA Roohi et al in 2007 in Malaysia examined total 450 subjects from 3 different ethnic groups. His study shows that Palmaris longus absence in Malays had a prevalence of 11.3% of total PLM agenesis from this bilateral was 3.3%, and unilateral 8%. This was followed closely by the Indians with 10.7% of total PLM agenesis from this bilateral was 4%, and unilateral 6,7%, whilst the Chinese had the lowest absence rate of PLM 6% of total PLM agenesis from this bilateral was 1.3%, and unilateral 4.7%.
Ozkan Kose in 2009 studied the prevalence of absence of PLM in Turkish population, examined 1350 patients. The overall absence of PLM was 26,6 %, the unilateral 11.56%, the bilateral 15,04%. 
Oluyemi Kayode A. et al in 2008 in their study with Nigerian population examined 600 subjects. They got the following results: 31.25% of total PLM agenesis, bilateral agenesis was detected in 18,75% and unilateral agenesis was detected in 12,5%. 
Sudhir K. Kapoor et al in 2008 examined 500 subjects of Indian population he found 17.2% of total PLM agenesis, 8% bilateral and 9.2% unilateral. 
S. Oladipo et al in 2009 studied the Nigerian Edo tribes population and examined 3000 people from this overall agenesis of muscle was detected only in 0,17%. From 3000 subjects only 1 had bilateral agenesis. 
Gangata H. in 2009 examined 890 black Zimbabwean subjects the results showed that the tendon of the PLM was absent with an overall rate of 1.5% unilaterally in 0.9% of the population, and bilaterally absent in 0.6%. 
Godwin O Mbaka and Adedayo B Ejiwunmi in 2009 in their study of Yoruba population examined 600 subjects, they found 6.7% of total PLM agenesis from this bilateral 1%, unilateral 5.7%. 
Mirela Eri? et al in 2010 it their study examined 800 subjects of Serbian population. The overall absence of Palmaris longus muscle was 37.5%, the bilateral absence was 21,6%, the unilateral 15,9%. 
Pawan Agarwal in 2010 in his study of Indian population examined 385 subjects. He got the following results: 20.2% of total PLM agenesis, bilateral agenesis was detected in 16.9% and unilateral agenesis was detected in 3.3%. 
L. A. Enye et al in 2010 in his work with Nigerian population, examined 500 students from 2 Lagos-Based medical schools and got the following results: 63 cases (12.6%) of total PLM agenesis, bilateral agenesis was detected in 23 cases (4.6%) and unilateral agenesis was detected in 40 cases (8%). 
?zcan Hiz et al in 2011 in study with Turkish population examined 1000 subjects and registered 15.1% of total PLM agenesis. Bilateral agenesis was detected in 13.8% and unilateral agenesis was detected in 1.3%. 
Nilton Alves et al in 2011 in Chinese population examined 200 subjects and observed 20% of total PLM agenesis from this bilateral was 9%, unilateral 11%. 
K Devi Sankar et al in 2011 examined 942 subjects of Andhra population from which overall agenesis of muscle was 28.0%, bilateral agenesis was detected in 8.3% unilateral agenesis was in 19,7%. 
Conclusion: In the past decades the agenesis of PLM was intensively and extensively studied in many countries. The results of these studies tell us about great differences in the prevalence of agenesis of Palmaris longus muscle in different regions in the world, or even within the same region but in different ethnic groups. However these studies always had, sporadic, spot-like character, and this applies even now. Even the modern studies missing the encompassing nature that would be needed to create a comprehensive picture of prevalence of agenesis of PLM in the whole population of the world. Although the amount of acquired data is incredibly small in the comparison with what is needed to make conclusions regarding the population of the planet, generalization of available data can be used as a basic knowledge for the following studies, and for comparative analyses of PLM agenesis in different ethnic groups from the population of different countries, all over the world.
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