Introduction

Palmaris longus has long been described as the most variable muscle in the human body ₁ . This small fusiform muscle is absent on one or both sides (usually the left) in approximately 14% of people ₂ , its incidence varies amongst different people ₃

The palmaris longus tendon is a useful guide to the median nerve at the wrist. The tendon lies deep and slightly medial to this nerve before it passes deep to the flexor retinaculum ₂ . To test the muscle, the wrist is flexed and the pads of the little finger and thumb are pinched together. If present, the tendon can be easily seen and palpated ₂₄₅ .

Previous studies showed differences in incidence of the muscle among different races [[[3.]]] Amongst Ugandans, the incidence of agenesis of palmaris longus has been reported to be 1.02% ₆ , amongst Zimbabweans and Congolese, the incidences are 1.5% and 3.0% respectively ₇ . In Turks it has been reported to be 26.6% ₈ .Amongst Indians the incidence is 17.2% ₉ . In a similar study carried out on Americans, percentage of agenesis was found to be 12.8% ₁₀ . A high value of 20.4% was also reported for Germans ₁₁ . For the Japanese and Chinese, the incidences were reported as 3.4% ₁₂ and 2.2% respectively ₁₃ .

In Nigeria, a group of researchers ₁₄ reported the incidence of agenesis of palmaris longus in the Edo tribe of Nigeria, based on sex and side of the body. They worked on a sample of 400 students which comprised 180 females and 220 males and found the incidence to be 1.25% for the limb, 1.0% for the right, 0.5% for females, 1.59% for males and 1.13% for the overall population. Conversely, previous works indicate a higher incidence value for whites than blacks and males than females. The Yorubas were said to have incidence of 6.7% ₁₅ .

The objective of the present investigation was to present a useful data on the frequency of agenesis (absence) of palmaris longus on Nigerian population as a whole.

Materials And Methods

The study was carried out on an open populace who were Nigerians by both parents and grand parents (children were excluded). They were randomly selected across the geopolitical zones of Nigeria. A total of 3000 Nigerians (6000 extremities) were inspected. One thousand nine hundred and thirty-two (1,932) were males (i.e. 3864 extremities), one thousand and sixty – eight (1,068) were females (i.e. 2136 extremities). The palmaris longus tendon was made visible by opposing the thumb on the little finger and slightly flexing the wrist (in vivo examination) ₂₄₅ . ( figure 1).

Figure 1

Figure 1: Palmaris longus made visible by opposing the thumb and little finger and slightly flexing the wrist.

Results

The data obtained in this investigation are presented in table1–3. Incidence (frequency) of agenesis of palmaris longus is recorded in table 1. The values for both sexes and both sides of the hands are shown in the table. The value for the right side in males was 3 while it was 2 for the right side in females. On the left side, incidence of agenesis was 4 in males and 1 in females. The total incidence in males and females were 7 and 3 respectively. In the overall population (male and female), the value was 10. Females did not show bilateral agenesis while there was a case of bilateral agenesis in male.

Table 2 represents the calculated percentages of agenesis of palmaris longus in both sexes in right and left hands. The percentages in the right hands of the males and females were 0.16% and 0.19% respectively. The percentages in the left hands of males and females were 0.21% and 0.09% respectively. The overall percentage in Nigerians was 0.17%.

Table 3 represents the comparison of the overall percentages in total population of males and females in both hands in different populations. From the table, Germans had the highest percentage of agenesis (19.4%) followed by Americans (12.8%), Japanese (3.4%), Chinese (2.2%) Edo Tribe of Nigeria (1.13%), Ugandans (1.02%). Nigerians (present study) had the lowest percentage of 0.17%.

Figure 2

Table 1: Incidence of Agenesis of the palmaris longus muscle in Nigerians.

Figure 3

Table 2: Percentage of Agenesis of the palmaris Longus Muscle in Nigerians.

Figure 4

Table 3: Comparison of percentages of palmaris Longus agenesis in different populations.

Discussion

The frequency of agenesis of palmaris longus recorded in this present study is lower than those recorded for other populations of the world previously reported _{6789101112131415} . The present study supports the findings of Igbigbi and Ssekitoleto ₆ and Remann et al ₁₀ who reported that agenesis was more in males than in females. This is, however, at variant with the findings of Thompson et al ₁₆ who reported higher percentage of agenesis of palmaris longus, in female Caucasians than in males. Unlike Oyinbo et al ₁₄ and Mbaka and Ejiwumi ₁₅ who reported 1.13% and 6.7% for agenesis of palmaris longus in Edo tribe and Yorubas respectively, our findings have shown that in Nigerian population, as a whole, palmaris longus is absent in 0.17% of the population . The larger percentage reported by the previous authors ₁₄₁₅ on Edo and Yoruba tribes might be due to a smaller sample size which does not seem to perfectly represent the Nigerian population.

Conclusion

Amongst Nigerians, palmaris longus is absent in 0.17% of the population and unilateral agenesis is more frequent. Since most Nigerians have palmaris longus muscle, it can be very useful in determining the exact location of the median nerve. The result is also reliable for anthropological studies involving Nigerians .It could be a useful guide to clinicians who may want to localize the median nerve amongst Nigerians.

The tendon can still be counted on by surgeons treating Nigerian patients for use as a donor tendon, which will be present in a vast majority of Nigerian patients.