Muscle Test: Thenars (ABPB, ABPL, OP, FPB)

Exams and Signs

Testing the thenar muscles in carpal tunnel syndrome is very important. Weak median innervated thenar muscles suggests more severe carpal tunnel syndrome for which surgical treatment should be recommended.

Abductor pollicis brevis (ABPB)
Origin	Flexor retinaculum Scaphoid tubercle Trapezium tubercle ABPB tendon
Insertion	Medial fibers: thumb (base of proximal phalanx, radial side) Lateral fibers: extensor expansion of thumb
Innervation
Cervical root(s)	C8–T1
Nerve	Median
Abductor pollicis longus (ABPL)
Origin	Ulna (posterior surface laterally) Radius (middle 1/3 of posterior aspect of shaft) Interosseous membrane
Insertion	Thumb: 1st metacarpal (radial side of base) Trapezium
Innervation
Cervical root(s)	C7–C8
Nerve	Nerve: radial (posterior interosseous branch)
Opponens pollicis (OP)
Origin	Trapezium tubercle Flexor retinaculum
Insertion	1st metacarpal (length of lateral border, lateral half of palmar surface)
Innervation
Cervical root(s)	C8–T1
Nerve	Median, ulnar (terminal branch)
Flexor pollicis brevis (FPB)
Origin	Superficial head: flexor retinaculum (distal border); trapezoid tubercle Deep head: trapezoid, capitate, palmar ligaments of distal carpals
Insertion	Thumb (base of proximal phalanx, radial side)
Innervation
Cervical root(s)	C8–T1
Nerve	Superficial head: median (lateral branch) Deep head: ulnar (deep 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.

Abductor pollicis brevis (ABPB)
Position of patient’s hand and upper extremity	Forearm in supination, wrist in neutral, thumb relaxed in adduction
Examiner’s actions	Stabilize metacarpals by placing your hand across patient’s palm with the thumb on the dorsal surface of the patient’s hand (somewhat like a handshake but maintaining the patient’s wrist in neutral). Apply resistance to the lateral aspect of the proximal phalanx of the thumb in the direction of adduction. For Grades 0–1, some suggest palpation of the belly of the ABPB in the center of the thenar eminence, medial to the OP
Instructions for the patient	“Lift your thumb vertically until it points to the ceiling.” For Grades 0–2, some suggest “Try to lift your thumb so it points at the ceiling.”
Abductor pollicis longus (ABPL)
Position of patient’s hand and upper extremity	Forearm is supinated, and the wrist is in neutral; the thumb is relaxed in adduction
Examiner’s actions	Stabilize the metacarpals of the four fingers and the wrist. Resistance is given on the distal end of the 1st metacarpal in the direction of adduction
Instructions for the patient	“Lift your thumb straight up.”
Opponens pollicis (OP)
Position of patient’s hand and upper extremity	Forearm in supination, wrist in neutral, thumb in adduction with MP and IP joints in flexion
Examiner’s actions	Stabilize hand by holding th wrist on the dorsal surface. The examiner may prefer the hand to be stabilized on a table. For Grades 0–1, some suggest palpation along the radial shaft of the 1st metacarpal, which lies lateral to the ABPB
Instructions for the patient	“Bring your thumb to your little finger and touch the two pads, forming the letter ‘O’ with your thumb and little finger.”
Flexor pollicis brevis (FPB)
Position of patient’s hand and upper extremity	Forearm in supination, wrist in neutral. The CMC joint is at 0°; the IP joint is at 0°; thumb in adduction, lying relaxed and adjacent to the 2nd metacarpal
Examiner’s actions	Stabilize 1st metacarpal firmly to avoid wrist or CMC motion. The other hand gives 1-finger resistance to MP joint flexion on the proximal phalanx in the direction of extension
Instructions for the patient	“Bring your thumb across the palm of your hand. Keep the thumb in touch with your palm. Don’t bend the end joint. Hold it. Don’t let me pull it back.”

Presentation Photos and Related Diagrams

Thenar Muscle testing

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

When testing the ABPL/ABPB, if the ABPL is stronger than the ABPB, the thumb will deviate toward the radial side of the hand; if the ABPB is stronger than the ABPL, deviation will be toward the ulnar side of the hand.
When testing the FPB, the long thumb flexor can substitute for this motion, but only after flexion of the IP joint begins. To avoid this, do not allow flexion of the distal joint of the thumb
When testing the OP, the flexor pollicis longus and the FPB can draw the thumb across the palm towards the little finger. If this motion occurs in the plane of the palm, it is not in opposition, and contact will be at the tips, not the pads of the digits. Also, the ABPB may substitute, but the rotation component of the motion will not be present.

Diagnoses Associated with Exams and Signs

Videos

Thenar muscle testing is part of the 35 second carpal tunnel syndrome complete exam.

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.

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