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Exams and Signs
Origin:Humerus (lateral epicondyle via common extensor tendon)
Ulna (posterior border by an aponeurosis)
Insertion:5th metacarpal bone (tubercle on medial side of base)
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 for Grade 2, the forearm is supported on a table in neutral position, and for Grades 0 and 1, the forearm is supported on a table with the hand fully pronated.

Examiner’s Actions

  • Sitting or standing at a diagonal in front of patient, support the patient’s forearm and place the hand used for resistance over the dorsal (extensor) surface of metacarpals. Some suggest that for Grade 2, the examiner supports the patient’s wrists for testing, and for Grades 0 and 1, the examiner supports the patient’s wrist in extension. For these Grades, the examiner palpates the tendon on the dorsal surface proximal to the fifth metacarpal and just distal to the ulnar styloid process.

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
  • ECU Muscle Testing
    ECU Muscle Testing
  • ECU anatomy illustration
    ECU 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.
    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 
Comments and Pearls
  • The ECU is considerably weaker than the extensor carpi longus or extensor carpi brevis.
  • 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
  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.
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