The Effect of Presence of Palmaris Longus and Fifth Superficial Flexor Tendons on Median Nerve Surface Area; A Cross-sectional Study with Sonography

Background & Aims: Sonography has enjoyed much attention as a noninvasive diagnostic tool for carpal tunnel syndrome in recent years. The aim of the present study was to assess the effect of anatomic variations of existence or absence of palmaris longus and fifth superficial flexor tendons on the sonographic measurement of median nerve surface area in healthy individuals’ wrists. Methods: 93 volunteers without any symptoms related to carpal tunnel syndrome underwent clinical evaluation for determining presence of tendons in both wrists and also, sonographic measurement of median nerve surface area. Results: In 22 of 186 hands (11.82%), there was absence of the palmaris longus tendon and absence of the fifth flexor was noted in 8 (4.30%). The median nerve surface area in the hands without palmaris longus was meaningfully less than the hands with it (P = 0.025), while the difference in the median nerve surface area was not statistically significant regarding the presence of the fifth flexor (P = 0.324). Conclusion: Based on the findings of the present study, it seems that the median nerve surface, area as a sonographic finding, is probably related to presence or absence of the palmaris Longus tendon. So, those hands with the tendon present have larger surface areas. Also, it seems that this sonographic finding is not dependent on the presence of fifth superficial flexor tendon.