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Muscle Test and Tendon Exam: Flexor Digitorum Sublimis (FDS)

Exams and Signs
Origin:Humeral-ulnar head:
Humerus (medial epicondyle via the common flexor tendon)
Ulnar collateral ligament (UCL) of the elbow joint
Ulna (coronoid process, medial side)
Intermuscular septa
Radial Head:
Radius (oblique line on anterior surface)
Insertion:Four tendons arranged in two pairs:
Superficial pair: Long and ring fingers
Deep Pair: Index and little fingers
Innervation:Cervical root(s): C8–T1
Nerve: median nerve

 

Grading of muscle strength:

Grade

Strength

Description

  5*

Normal

Completes range of motion and holds against maximal finger resistance

  4*

Good

Completes range against moderate resistance

3

Fair

Completes range of motion with no resistance

2

Poor

Completes range of motion

1

Trace

Palpable or visible contractile activity, which may or may not be accompanied by a flicker of motion

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 in supination, wrist in neutral position, finger to be tested is in slight flexion at the metacarpophalangeal (MP) joint.  Some suggest that for Grade 0−2, the patient’s forearm is in a neutral position to eliminate the influence of gravity on finger flexion.

Examiner’s Actions

  • Hold all fingers except the one being tested in extension at all joints. Use the other hand to resist the head (distal end) of the middle phalanx of the test finger in the direction of extension. For Grades 0–2, palpate the FDS on the palmar surface of the wrist between the flexor palmaris longus and the flexor carpi ulnaris.

Instructions for the patient

  • “Bend the tip of your finger. Hold it. Don’t let me straighten it. Keep your other fingers relaxed.”
Presentation Photos and Related Diagrams
  • Testing FDS of long finger. The index, ring and little fingers are kept in extension so FDP of all 4 fingers can not function. This allows the FDS of the long finger to be demonstrated.
    Testing FDS of long finger. The index, ring and little fingers are kept in extension so FDP of all 4 fingers can not function. This allows the FDS of the long finger to be demonstrated.
  • Testing the strength of long finger FDS. The FDP II-V can not act independently.
    Testing the strength of long finger FDS. The FDP II-V can not act independently.
  • The FDS of the little finger can be difficult to test because of connections to the ring finger.
    The FDS of the little finger can be difficult to test because of connections to the ring finger.
  • The FDS of the little finger can be demonstrated when the ring and little are allowed to flex together.
    The FDS of the little finger can be demonstrated when the ring and little are allowed to flex together.
  • FDS and FDP not functioning in fifth finger. FDP cut in ring and long with both tendons intact in index finger.
    FDS and FDP not functioning in fifth finger. FDP cut in ring and long with both tendons intact in index finger.
  • FDS Intact with FDP not functioning. FDP cut distal to PIP joint with DIP stiff in slight flexion from scar.
    FDS Intact with FDP not functioning. FDP cut distal to PIP joint with DIP stiff in slight flexion from scar.
  • Anatomy of the Flexor Digitorum Superficial (Sublimus)
    Anatomy of the Flexor Digitorum Superficial (Sublimus)
  • 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 zero.

Comments and Pearls
  • Many patients cannot isolate the little finger. In this case, test the little and ring fingers together.
  • If the wrist is allowed to extend, tension increases in the long finger flexors, and may result in passive flexion of the interphalangeal (IP) joints. This is referred to as a “tenodesis” action.
  • Relaxation of IP extension will result in passive IP extension.
  • The flexor digitorum profundus may substitute for this motion, and this will occur if the distal interphalangeal (DIP) joint is allowed to flex.
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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