Extensor Digiti Minimi (EDM) Exam

EDM Muscle Testing (Little Extensor Tendon):

When assessing an injury involving the little finger proprius extensor tendon, which include the Extensor Digiti Minimi (EDM), the aim is to determine whether these tendons are fully severed, partially transected, or intact. Initially, ask the patient to actively and gently extend the injured little finger. For a more detailed examination, position the patient’s hand and upper extremity in pronation, with the wrist in a neutral position, and the metacarpophalangeal (MP) and interphalangeal (IP) joints in a relaxed, slightly flexed posture.

Next, stabilize the patient’s wrist in a neutral position. Place your index finger across the dorsum of all the patient’s little finger proximal phalanx just distal to the MP joints. Exert resistance in the direction of flexion while instructing the patient to “bend your knuckle back,” which means to straighten or extend the fingers. If the EDC tendons are all held in passively in a flexed position and the EDM tendons are completely lacerated, the patient will be unable to extend the MP joint of the injured little finger, even against zero resistance. 

Definition of Positive Result in EDM Muscle Testing: In muscle testing, a normal result is a positive one. During a normal muscle test, the examiner should observe a normal muscle contraction that can move the joint or tendon against full resistance.

Definition of Negative Result in EDM Muscle Testing: In muscle testing, an abnormal result is a negative one. During an abnormal muscle test, the examiner should observe an abnormal muscle contraction that cannot move the joint or tendon normally. In a complete denervation injury, such as a complete radial nerve palsy, there will be no evidence of any muscle contraction (function), and the muscle testing grade will be 0. In a patient with a laceration of the EDM, the little MP joint may not actively extend independently due to a complete transection (cut) of the EDMtendons. This results in an abnormal or negative muscle testing with no active index MP joint extension while the index, long, and ring fingers are passively held in flexion. However, these observations also indicate complete EDMlaceration requiring surgical repair. Thus, this negative muscle testing exam will bepositive for a complete EDMlaceration.