Muscle Test and Tendon Exam: Extensor Carpi Radialis Brevis (ECRB)

Exams and Signs

Origin:	Humerus (lateral epicondyle via common forearm extensor tendon Radial collateral ligament of elbow joint Aponeurosis of muscle
Insertion:	3rd metacarpal bone (base of dorsal surface on radial side) 2nd metacarpal (occasionally)
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

Sitting with elbow flexed, the forearm is fully pronated, and both are supported on a table. Some suggest that the forearm be supported on a table in neutral position for Grade 2, and that for Grades 0 and 1, the forearm supported on a table with hand fully pronated.

Examiner’s Actions

Sitting or standing at a diagonal in front of patient, support the patient’s forearm. Place the hand used for resistance over the dorsal (extensor) surface of metacarpals. Some suggest that for Grade 2, the examiner support the patient’s wrists for testing and for Grades 0 and 1, the examiner support both the patient’s wrist in extension. For these Grades, the examiner palpates the tendon on the dorsal surface of the wrist in line with the third metacarpal bone.

Instructions for the patient

“Bring your wrist up. Hold it. Don’t let me push it down.” Some suggest “bend your wrist back” for Grade 2, and “Try to bring your wrist back” for Grades 0 and 1.

Presentation Photos and Related Diagrams

ECRB Muscle Test. Tendon palpated at RC join level while patient extends wrist against resistance.
ECRB anatomy illustration
ECRB anatomy illustration

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

The ECRB is considerably stronger than the extensor carpi ulnaris (ECU)
A patient with complete quadriplegia at C5–C6 will have only radial wrist extensors remaining; radial deviation during extension is therefore the prevailing extensor motion at the wrist.

Diagnoses Associated with Exams and Signs

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.