Figure. Patient making the “OK sign.”
A 35-year-old mechanic presents to the emergency department having sustained a crush injury of his left arm. Earlier that day, the patient was working underneath a car at his garage when the front tire rolled over his left forearm. The patient complains of pain and numbness in the left hand. On examination, the patient is able to make the “OK sign” (Figure).
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Motor function tests should be performed in all patients with cervical spine and upper extremity injuries. A quick gross motor function assessment includes asking the patient to make the OK sign, give a “thumbs up,” and spread his or her fingers apart.
When assessing the OK sign, the patient is instructed to touch the tip of the index finger to the tip of the thumb. The OK sign specifically tests the anterior interosseous nerve that arises from the median nerve approximately 4 cm distal to the elbow.1 Injury to the anterior interosseous nerve will cause weakness of the flexor pollicis longus muscle, which allows flexion of the thumb, and the flexor digitorum profundus muscle, which allows bending of the fingers.1,2
Motor function of the ulnar nerve can be assessed by instructing the patient to spread his or her fingers apart. The ulnar nerve controls abduction of the little finger. Function of the ulnar nerve can also be assessed by crossing the index and middle fingers. Inability to cross the fingers indicates weakness of the interosseous muscles of the hand that are supplied by the ulnar nerve.1,2
Making a “thumbs up” sign tests motor function of the posterior interosseous nerve, which is a branch of the radial nerve. Motor function of the axillary nerve is assessed with resistance against arm abduction (deltoid muscle).1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants.
1. Moore D. Neck & upper extremity spine exam. OrthoBullets website. https://www.orthobullets.com/spine/2001/neck-and-upper-extremity-spine-exam. Updated October 19, 2018 . Accessed January 17, 2020.
2. Hoppenfield S. Physical Examination of the Spine and Extremities. 1st ed. New York, NY: Appleton-Century-Crofts; 1976:124-125.