Presence or Absence of Palmaris Longus and Fifth Superficial Flexor Digitorum; Is There Any Effect on Median Nerve Surface Area in Wrist Sonography

BACKGROUND: Carpal tunnel syndrome (CTS) describes a set of symptoms caused by compression of the median nerve in the wrist, which is the most common site of nerve compression in the upper limb. This syndrome is a primary source of pain and reduced function in these patients, and the cause is compression of the median nerve where it passes beneath the flexor retinaculum in the wrist. OBJECTIVES: The aim of the present cross sectional study is to assess the absence of palmaris longus and fifth superficial flexor digitorum tendon as normal anatomic variations on the sonographic measurement of median nerve surface area in healthy individuals’ wrists. PATIENTS AND METHODS: Ninety-three healthy volunteers underwent clinical evaluation for determining the presence of tendons in both wrists and sonographic measurement of median nerve surface area. RESULTS: In 41 of 186 (22%) hands, the palmaris longus tendon was absent and absence of the fifth flexor digitorum tendon was noted in eight (4.30 %). The median surface area in the hands without palmaris longus was meaningfully lower than the hands with it (P = 0.025), while the difference in the median surface area was not statistically significant with regard to presence of the fifth flexor digitorum tendon (P = 0.324). CONCLUSIONS: Based upon the findings of the present study, it seems that the median surface area as a sonographic finding is probably related to presence or absence of the palmaris longus tendon, so that hands with the tendon present have larger surface areas. In addition, it seems that this sonographic finding does not depend on the function of the fifth superficial flexor digitorum tendon. Therefore, no correlation between CTS and the presence of palmaris longus tendon should be observed.