Muscle Test and Tendon Exam: Extensor Digitorum Minimi (EDM)

Test, Exam and Sign Description

Origin: Humerus (lateral epicondyle via common extensor tendon)

Intermuscular septum

Insertion: 5th digit (extensor hood)

Innervation: Cervical root(s): C7 and C8

Nerve: radial nerve (posterior interosseous branch)

Grading of muscle strength:

Grade	Strength	Description
5*	Normal	Completes full range of motion against maximal finger resistance
4*	Good	Tolerates moderate resistance
3	Fair	Completes full range of motion with no resistance
2	Poor	Completes partial range of motion
1	Trace	Slight contractile activity
0	Zero	No contractile activity
*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 is in pronation; wrist is in neutral position. The metacarpophalangeal (MP) and interphalangeal (IP) joints are in a relaxed, flexion posture.

Examiner’s Actions

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

Instructions for the patient

“Bend your knuckles back as far as they will go.”

Presentation Photos and Related Diagrams

EDM Muscle (Hover over right edge to see more images)
EDM 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 Tests, Exams and Signs

DORSAL TENOSYNOVITIS

EXTENSOR TENDON RUPTURE (VAUGHAN-JACKSON SYNDROME)

CERVICAL RADICULOPATHY

RHEUMATOID ARTHRITIS

Video

Muscle Testing of Extensor Digitorum Minimi (EDM)

References

1. 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.

2. Kendall FP, McCreary EK, Provance PG. Muscles Testing and Function. 4th ed. Baltimore, MD: Williams & Wilkins, 1993, pp. 235–298.