Prevalence of Absence of the Palmaris Longus Muscle among Medical Students of An-Najah National University: A Cross-Sectional Study from Palestine

The Palmaris Longus (PL) is a slender; spindle shaped elongated muscle which is visible as a small tendon between other superficial muscles of the forearm, i.e., pronator teres, flexor carpi radialis and the flexor carpi ulnaris. The PL muscle is a highly variable muscle. However, the most common variation is its absence, which is more commonly seen on the left side. There is a wide scope of variation in the prevalence of absence of this muscle in different racial groups, which varies from 3.1% in some populations up to 63.9% in others. This study aims at finding out the prevalence of absence of the PL muscle among Palestinian population. To determine the prevalence of the absence of PL, a cross-sectional design utilizing the Schaeffer's test in a sample of 300 medical students at An-Najah National University with ages ranging between 18-22 years old was used. The overall prevalence of absence of PL muscle in our sample subjects was found to be 32%. Prevalence of bilateral absence was found to be 15.7 %, while the prevalence of unilateral absence of PL was found to be 16.3%. Unilateral absence of the PL muscle on the left side was 8.7 %, which was found to be a little more than that of the right side 7.7% among our 300 subjects. A significant gender-related difference in the overall prevalence of absence of PL on one or both sides, as well as in the prevalence of bilateral absence of muscle and in the prevalence of left-sided absence of muscle where all three indicators were more common in females. We recommend that our findings as well as the findings of other clinical studies be corroborated by conducting dissection studies. This is especially important in the absence of any accurate measurement of the specificity and sensitivity of these tests, while at the same time producing such a wide range of variation in their results in different populations.