OK sign

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Figure 1
Figure 2
The OK (pinch, straight thumb) sign refers to an inability to form the “OK” sign. Patients with weakness of the flexor pollicis longus and the flexor digitorum profundus to the index finger are unable to oppose the tips of the thumb and index finger to form a proper circle, but make a triangle instead, touching the finger pads.(1,2) These muscles are innervated by the anterior interosseous nerve, and the OK sign may be seen in either anterior interosseous or high median neuropathy.

The median nerve may rarely be entrapped proximally where it passes between the two heads of the pronator teres or by the ligament of Struthers, an anomalous fibrous band running from a distal humeral supracondylar spur to the medial epicondyle. Anterior interosseous neuropathy palsy often occurs as an isolated manifestation of neuralgic amyotrophy.(3) Recent MRI evidence indicates the process in many cases of AIN palsy predominantly involves AIN fascicles in the main trunk of the median nerve in the upper arm.(4)

In this video https://www.youtube.com/watch?v=HVHegl-42PE Dr. Nabil Ebraheim discusses AIN and the OK sign.

Figure 1. Patient demonstrating OK sign on the right due to AIN palsy.

Figure 2. On the right, patient with proximal median neuropathy, which developed as a complication following a retrograde brachial angiogram. Normal hand on the left.


1. Campbell WW. Barohn RJ. DeJong's the neurologic examination, 8th ed. Philadelphia: Wolters Kluwer, 2020.

2. Campbell WW. Clinical signs in neurology: a compendium. Philadelphia: Wolters Kluwer Health, 2016.

3. Akane M, Iwatsuki K, Tatebe M, et al. Anterior interosseous nerve and posterior interosseous nerve involvement in neuralgic amyotrophy. Clin Neurol Neurosurg. 2016;151:108-112.

4. Pham M, Bäumer P, Meinck HM, Schiefer J, et al. Anterior interosseous nerve syndrome: fascicular motor lesions of median nerve trunk. Neurology. 2014;82:598-606.