Muscle Test and Tendon Exam: Flexor Digitorum Profundus (FDP)

Exams and Signs

Origin:	Ulna (proximal 3/4 of anterior and medial shaft; medial coronoid process) Interosseous membrane (ulnar)
Insertion:	Four tendons to digits 2–5 (distal phalanges, at base of palmar surface) Index finger tendon is distinct in its course
Innervation:	Cervical root(s): C8–T1; C8–T1 Nerve: median nerve, digits 2–3; ulnar nerve, digits 4–5

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 supination, wrist in neutral position, and proximal interphalangeal (PIP) joint is in extension. Some suggest that for Grade 0–2, the patient’s forearm should be in a neutral position to eliminate gravity.

Examiner’s Actions

Stabilize the middle phalanx in extension by grasping it on either side. Resistance is provided on the distal phalanx in the direction of extension.

Instructions for the patient

Presentation Photos and Related Diagrams

FDP Laceration right ring finger
FDP examination right index finger
FDP examination right long finger
FDP 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

The wrist must be kept in neutral position and must not be allowed to extend to rule out the tenodesis effect of the wrist extensors.
Patients may extend the distal interphalangeal (DIP) joint and then relax, which can give the false impression of finger flexion.
To identify weakness of high ulnar innervated muscles compare FDP II & III (median nerve innervated) to FDP IV & V (ulnar nerve innervated) during simultaneous muscle testing of the two pairs.

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.