Muscle Test and Tendon Exam: Extensor Digitorum Communis (EDC)

Exams and Signs

Origin:	Humerus (lateral epicondyle via common extensor tendon) Intermuscular septum Antebrachial fascia
Insertion:	Four tendons to digits 2–5 (via the extensor expansion, to dorsum of middle and distal phalanges; one tendon to each finger)
Innervation:	Cervical root(s): C7 and C8 Nerve: radial nerve (posterior interosseous branch)

Grading of muscle strength:

Grade	Strength	Description
5*	Normal	Normal strength
4*	Good	Movement against external resistance but less than normal
3	Fair	Movement against gravity but not against added resistance
2	Poor	Movement at the joint with gravity eliminated
1	Trace	Trace of contraction but no movement at the joint
0	Zero	No contraction or muscle movement
*The distinction between Grades 4 and 5 is based on comparison with the normal hand and, barring that, extensive experience in testing the hand.

Position of patient's hand and upper extremity

Forearm in pronation, wrist in neutral. Metacarpophalangeal (MP) and interphalangeal (IP) joints are in a relaxed, flexion posture. Some suggest that for Grades 0–2, the forearm should be in mid-position.

Examiner’s Actions

Stabilize the wrist in neutral position. Place the index finger of the resistance hand across the dorsum of all proximal phalanges just distal to the MP joints. Exert resistance in the direction of flexion.

Instructions for the patient

Presentation Photos and Related Diagrams

EDC Muscle Testing. Small arrows EDC tendons
EDC anatomy illustration
This illustration represents the anatomy of the muscle and tendon origin and insertion. Should an individual sustain a laceration as depicted, the observer can assume that the underlying tendon may be at risk for complete transection. A proper examination is needed to determine the integrity of the tendon.

Definition of Positive Result

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 muscle testing, an abnormal result is a negative one. During an abnormal muscle test, the examiner should observe an abnormal muscle contraction that can move the joint or tendon. In a complete denervation injury, such as a complete nerve laceration, there will be no evidence of any muscle function and the muscle testing grade will be 0.

Comments and Pearls

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.
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.

Diagnoses Associated with Exams and Signs

Videos

Muscle Testing Extensor Digitorum Communis (EDC)

References

Hislop JH, Avers D, Brown M. Daniels and Worthingham's Muscle Testing, Techniques of Manual Examination and Performance Testing. 9th ed. St. Louis, Missouri: Elsevier Saunders, 2014, pp. 138–202.
Kendall FP, McCreary EK, Provance PG. Muscles Testing and Function. 4th ed. Baltimore, MD: Williams & Wilkins, 1993, pp. 235–298.