Ann Mil Health Sci Res. 2017 June; 15(2):e62310.
Published online 2017 June 30.
Incidence of Palmaris Longus Agenesis in the Young Iranian
Manouchehr Safari,1Laya Ghahari,2, * and Kamran Hamzei3
1Department of Anatomy, Semnan University of Medical Sciences, Semnan, Iran
2Department of Anatomy, AJA University of Medical Sciences, Tehran, Iran
3Department of Anatomy, Iran University of Medical Sciences, Tehran, Iran
*Corresponding author: Laya Ghahari, Department of Anatomy, AJA University of Medical Sciences, Tehran, Iran. E-mail: firstname.lastname@example.org
Received 2017 April 02; Revised 2017 May 16; Accepted 2017 June 03.
Background: Palmaris longus (PL) is the most variable muscle in the body. The variation includes unilateral or bilateral agenesis,
duplication or Y-shaped tendon.
Methods: A total of 480 students within the age range of 18 to 23 years from Tehran medical institutions were randomly selected for
the current study. The Thompson test was used to support the Schaeﬀer test.
Results: PL muscle was absent bilaterally in 23% and unilaterally in 28.5% of the subjects with the distribution of 16.9% on the left
and 11.6% on the right hands. In females, the bilateral absence was observed in 34.16%, while 18.7% had unilateral absence with the
distribution of 5.8% on the left and 12.9% on the right.
Conclusions: It is believed that palmaris longus muscle is progressively disappearing in Iranian young people and could prove a
degenerative trend in the Iranian population.
Keywords: Palmaris Longus, Agenesis, Incidence
Palmaris longus (PL), phylogenetically degenerated
weak accessory ﬂexor of the wrist joint, have the short,
muscular belly and long tendon, which crosses the ﬂexor
retinaculum and continues as palmar aponeurosis (1). It
is the most variable muscle in the body. The variation in-
cludes unilateral or bilateral agenesis, duplication, or in
the site of insertion. Although the function is very less, PL
receives the attraction of the surgeons for its use in recon-
structive plastic and hand surgery (2). It is also used to re-
pair ptosis, urinary incontinence, and the restoration of fa-
cial paralysis (1).
In males, PL muscle acts as a weak ﬂexor of the wrist,
and aids in cupping of the palm (1). This characteristic
marks the probable evidence of retrogression of this mus-
cle. It also opposes strong shearing forces on the skin of the
palm during gripping, and aiding in cupping of the hand.
Hypothetically, the comparison of the relative length
of tendons and body could show the pathway of the de-
generation of PL; that is, the degeneration could be asso-
ciated with increased tendon length and decreased belly
from more primitive primates to those most derivate, that
is, great apes to modern humans (3).
According to Kapoor SK et al. (4), the agenesis of PL
muscle was observed in 15% of the general population, but
it is not applicable to all populations and varies among eth-
nic groups (5).
The current study aimed at determining the incidence
of unilateral and bilateral agenesis of PL in the young Ira-
A total of 480 ﬁrst- and second-year medical, dental,
and paramedical students from Tehran medical institu-
tions within the age range of 18 to 23 years were enrolled in
the study. Demographic data included age, gender, dom-
inant hand, race, and shape and the presence or absence
of PL muscle in the forearm. Presence or absence of PL
muscle was determined by the Schaeﬀer and the Thomp-
son ﬁst tests. In the Schaeﬀer test, the standard test to de-
termine PL muscle, the examiner asked them to turn back
their thumb to little ﬁnger with semi-ﬂexion at the wrist
(Figure 1). Subjects with any deformities or injur y in the up-
per extremity were excluded from the study. The Thomp-
son test was used to support the Schaeﬀer test and the ex-
aminer asked the subjects to turn back their thumb over
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Safari M et al.
clenched ﬁst with ﬂexion at the wrist (Figure 2). With these
tests, PL tendon was palpated and visualized at distal of the
Figure 1. The Schaeﬀer Test
Figure 2. The Thompson Test
The prevalence of the PL muscle was observed in 480
students. Among the males, PL muscle was absent bilat-
erally in 23% and unilaterally in 28.5% of the subjects with
the distribution of 16.9% on the left and 11.6% on the right
hands. In females, the bilateral absence was observed in
34.16%, while 18.7% had unilateral absence with the distri-
bution of 5.8% on the left and 12.9% on the right hands.
Another variation of the palmaris longus muscle is the
bifurcation of its tendon observed in wrist hand. In fe-
males, V-shaped tendon or bifurcation in tendon was 5.1%.
In males, this anomaly was 0.9% (Table 1).
Finally, of the 480 investigated subjects, PL muscle was
absent in 26.6%, while 47.9% had PL muscle on both hands.
However, there was a signiﬁcant diﬀerence between male
and female subjects in the absence of PL. On the other
hand, many of the V-shaped anomalies were observed in
the female groups.
Identiﬁcation of the PL is very important to clin-
icians since its tendon is used as a graft in various
surgical procedures and during the administration of
medicine/corticosteroids in the carpal tunnel to relieve
pain due to carpal tunnel syndrome/arthritis.
According to the literature, there are various methods
to ﬁnd the tendon of PL, each with its own identifying
techniques. The most common and traditionally followed
method is the Schaﬀer test as a standard test or model to
identify PL muscle (1,2,6-20).
The techniques of the Schaeﬀer and the Thompson’s
ﬁst tests were used in the current study to prove the pres-
ence or absence of PL muscle.
Some authors suggested that the PL muscle absence
is more common in females (2,7,10,14), consistent with
the ﬁndings of the current study regarding the bilateral
absence. Unilateral absence occurred more often on the
left hand in males (6,12,21) and unilateral absence on the
right hand in the females (7,14,17). The current study re-
ported a similar prevalence in females and males in bilat-
eral absence, but recorded higher absence than the valid
reference (5) and other populations (4,9,10,12,14,17,19-21).
The authors agreed with the current study (2) and reported
higher ﬁgures than that of the current study records (7).
Another variation of the PL muscle is the bifurcation of
its tendon or the belly (23-25) and V shape anomaly in ten-
don (26). The current study recorded 2.3% variation in ten-
don 5% in females and 1% in males. Since the authors (24,
26) reported an abnormal case for tendon shape, the varia-
tion was not clear and it was not reported statistically.
Knowledge of the PL muscle variations and its normal
anatomy is useful. The tendon of PL muscle is a signiﬁcant
anatomical landmark for surgical approaches in this area
and may cause compression of the median nerve (23).
According to Sebastin SJ (27) lack of any diﬀerence in
favor of the normal population may indicate the gradual
phylogenetic degenerative trend for this muscle; authors
believe that PL muscle is progressively disappearing in Ira-
nian young people and could prove a degenerative trend
in the Iranian population.
Conﬂict of Interest: The authors declared no conﬂict of
2Ann Mil Health Sci Res. 2017; 15(2):e62310.
Safari M et al.
Table1. The Shape of the Palmaris Longus Muscle in the Study Subjects
TotalSample (N = 480) Males (N = 325) Females (N = 155)
Presence (normal) 71.11% 77.2% 60.71%
Presence (Y-shaped) 2.29% 0.9% 5.1%
Absence 26.6% 21.8% 34.19%
Table2. Prevalence of the Palmaris Longus Muscle in the Literature Review
Study Population (Author,
Caucasian population (20)
Thompson Mockford et al.,
300 150/150 18 - 40 %8.6 %6.6 %9.6 %75.2
A Chinese population study
(19) Sebastin and Lim 2006
329 120/209 7 - 85 %1.2 %2.4 %0.9 %95.5
Indian population (4)
Kapoor Tiwari et al., 2008
500 236/264 6 - 65 %8 %6.2 %3 %82.8
Kose Adanir et al., 2009
1350 675/675 18 - 85 %15.04 %7.04 %4.51 %73.41
Yoruba population (17)
Mbaka and Ejiwunmi 2009
600 335/265 8 - 60 %6.7 %3.2 %2.5 %87.6
Indian population (21)
385 195/190 20 - 24 %3.37 %11.16 %5.7 %79/74
The Northern, Serbia (15)
Eric, Krivokuca et al., 2010
800 400/400 18 - 75 %15.9 %13 %8.6 %62.5
Chilean Subjects (14) Alves
Ramírez et al., 2011
200 86/114 17 - 32 %9 %6 %5 %80
Pakistani population (10)
610 378/228 18 - 74 %12.95 %4.91 %3.60 %78.54
East African population (12)
Kigera and Mukwaya 2011
800 391/409 12 - 70 %1.1 %2.3 %1 %95.6
Indian population (2)
Sankar Bhanu et al., 2011
942 450/492 18 - 23 %8.28 %10.19 %9.55 %71.98
A population of Saudi
Arabia (10) HUSSAIN 2012
400 200/200 21 - 25 %7.75 %9 %7.75 %75.5
Korean population (9)
Kyung Lee et al., 2012
269 149/120 18 - 30 %2.23 % 1.11 %0.74 %95.9
An orthopedic surgery
center in Iran (22)
Abdolahzadeh Lahiji et al.,
1000 682/318 - %6.7 %5.9 %10.2 %77.2
Egyptian population (7)
Raouf, Kader et al., 2013
386 112/274 19 - 70 %31.1 %7.8 %11.9 %49.2
South African population
(6) Venter VanSchoor et al.,
706 363/343 5 - 99 %11.9 %7.7 %6.9 %73.5
Young Iranian population
The current study,2017
480 325/155 18 - 23 %26.6 %13.3 %12.08 %47.91
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