Extensor Digitorum Communis Digit Long & Ring(EDC) Exam
EDC & Muscle Testing (Long and Ring Extensor Tendons):
When assessing an injury involving the long or ring finger extensor tendons, the Extensor Digitorum Communis (EDC), the aim is to determine whether the EDC tendon is fully severed, partially transected, or intact. Initially, ask the patient to actively and gently extend the injured finger(s). 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 long and/or ring finger proximal phalanges just distal to the MP joints. Exert resistance in the direction of flexion while instructing the patient to “bend your knuckles back,” which means to straighten or extend the fingers. If the EDC is completely lacerated, the patient will be unable to extend the MP joint of the injured long and/or finger, even against zero resistance.
Definition of Positive Result in EDC 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 EDC 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 EDC to the long and/or ring finger, the MP joints may not actively extend due to a complete transection (cut) of the EDC tendon(s). This results in an abnormal or negative muscle testing with no active MP joint extension. However, these observations also indicate complete EDC laceration requiring surgical repair. Thus, this negative muscle testing exam will be positive for a complete EDC laceration(s).
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EDC muscle testing. Note the EDC tendon slips (arrows). Note the examiner is palpating the EDC muscle belly to evaluate the muscle bulk and contraction.
- MP extension of the fingers is not a strong motion and only slight resistance is required to “break” the end position.
- It is usual for the active range of motion to be considerably less than the available passive range of motion. In this test, therefore, the “full available range” is not used and the active range is accepted.
- Be aware that the juncturae tendinum can sometimes extend a finger at the MP joint even if the EDC is lacerated completely.
- Another way to check whether there is functional extensor strength in the fingers is to “flick” the proximal phalanx of each finger downward; if the finger rebounds, it is functional.