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Flexor Digitorum Superficialis (FDS) is the
only muscle of
the intermediate layer of
the forearm muscles. It arises by two heads, a humeroulnar head and a
radial head. They arise from the medial epicondyle of the humerus and
the anterior oblique line of the radius, respectively. FDS has four
tendons that attach to
the palmar aspect of the
index, middle, ring, and little
fingers. FDS is responsible for flexion of multiple joints crossed by its tendons, that is, wrist joints, intercarpal joints,
carpometacarpal joints, metacarpophalangeal joints, and the proximal
interphalangeal joints [1].
The prevalence of functional FDS muscle agenesis for the little
finger in Saudi Arabia is unknown. In contrast, the prevalence of FDS
absence in other studied populations is known, for example, in the
Caucasian population (15–21%), in the Chinese population (6.4%),
and in the Indian population (0.25%) [10, 11].
The PL is an
accessory muscle with a
lesser functional significance. The absence of the PL has a negligible
effect on the strength of the handgrip
[12–14].
Surgically, it has been used as an ideal tendon graft in a wide variety of procedures in
plastic surgeries and in the procedures carried out on
the hand itself
[13, 14].
Similarly, the absence of the tendon of the FDS for the little finger does not affect the functionality
of the little finger
[15].
In addition, when the little
finger is injured, some surgeons tend to examine the
other hand to check for the
absence of FDS assuming the agenesis is bilateral
[16, 17].
Based on the above indicated observations, we studied the prevalence
of the absence of both the Palmaris Longus and the Flexor Digitorum Superficialis muscles in the
Saudi Arabia population.
2. Objectives
The objectives were
as follows:(I)To study the prevalence of congenital absence of
Palmaris Longus muscle and
the Flexor Digitorum
Superficialis tendon in the Riyadh city universities.(II)To
compare the results of the studied prevalence with the national and
international observations.
3. Materials and
Methods
This study was carried
out in the Saudi Arabian population on volunteers, males
164 (49.5%) and females 167 (50.5%), in Riyadh city. This was a random
cross-sectional study conducted from January 2016 after an approval
from the Ethical Review Committee of the King Abdullah International
Medical Research Center (KAIMRC). We carried out our study on the
volunteers from four government based universities in Riyadh city. The
total number of students (i.e., volunteers) present in these
universities was 156,733. These were King Saud bin Abdulaziz
University for Health Sciences (KSAU-HS)
[18],
college of medicine, 850 volunteers, King Saud University (KSU),
66,174 volunteers, Imam Muhammad ibn Saud Islamic University (IMAM),
37,401 volunteers
[19],
and Princess Nourah Bint Abdulrahman University (PNU), 52,308
volunteers
[20].
We calculated the sample size (≈284 volunteers) for this population,
that is, 156,733, with a 95% confidence interval level, ±5% margin of
error, and estimated agenesis of 24.5% by using the Raosoft
Inc. calculator
[9].
We used the Cluster Sampling technique in the indicated universities,
that is, PNU, KSAU-HS, KSU, and IMAM, and took the volunteers at
random from this population. Randomization was done by dividing each
university into colleges, and each college was divided into
specialties and each specialty was divided into batches by academic
year. Three colleges were chosen from each university by simple random
sampling. In each college, we took three specialties by simple random
sampling. In each specialty, we picked three batches randomly, and,
from each batch, we selected three students by systematic random
sampling via a computer generator randomization. So total sample size
was 3 students per batch × 3 batches per specialty × 3 specialties by
college × 3 colleges per university × 4 universities = 324 volunteers,
but we selected 331 volunteers to attain the total number if someone
shows noncompliance. We distributed entire population individuals to
the coinvestigator’s groups. In each of the groups the volunteers were
asked to fill up a questionnaire and they signed an informed
consent.
The volunteers were
given information about the examination and protocols of the project
they were about to participate in. The inclusion and the exclusion
criteria were decided. In this study, we recruited any Saudi subject
who was willing to voluntarily participate while studying at any
academic level. Volunteers from both genders were enrolled. We
excluded the volunteers who had a positive history of trauma on their
hands and forearm, volunteers showing any sign of inflammation of the
hands or forearms, and students with a history of surgical
intervention on their hands and presence of any other known
congenital anomaly of the hands.
During the first
visit of the subject, the investigating medical interns (one female
and one male) were fully educated and trained to carry out the
clinical examination of the hand using tests to assess the PL and FDS
absence. The accuracy of the methods used by the students to diagnose
the agenesis was counterchecked by the PI who is a clinician as well
as the subject expert. The collected data was entered in an Excel
sheet with the subject’s serial number, gender, nationality, date
of birth, age, and the pattern of dominance of hand. The pattern of
hand dominance was determined by history and observation by asking
the patient to write on a paper.
Both hands of the
participant were assessed for PL and FDS absence. The data were
entered with the following mean parameters: (i) presence of anomalies
in both hands, (ii) absence of anomaly in both hands, (iii) presence
of anomaly in the right hand only, and (iv) presence in the left hand
only. In order to test the absence of the PL, Schaeffer’s test was
used, in which the wrist was slightly flexed and the thumb and little
finger were opposite each other. This caused a raised ridge just
proximal to wrist which indicated the presence of the PL muscle and
absence of this ridge was diagnostic of PL muscle absence (Figure 1)
[10].
The FDS absence was tested by using a Modified test in which the
subject was asked to flex the fourth and fifth digit while the
interphalangeal joints of the other digits were held in full
extension by the
examiner’s hand to prevent
any effect generated by the flexor
digitorum profundus tendon. Failure of the subject to flex the
fourth or fifth digit is
diagnostic of FDS absence. This test has a known high accuracy for FDS
absence
(Figure 2)
[21].