Thenar Muscle Atrophy

Test, Exam and Sign Description

The motor branch of the median nerve innervates the thenar muscles which are radial and dorsal to the Flexor Pollicis Longus (FPL). During severe carpal tunnel syndrome, the motor branch component of the median nerve can be compressed in the carpal tunnel.

The motor branch innervates the superficial head of the FPB, the AbPB and the Opponens Pollicis. Its compression can lead to denervation atrophy of these muscles.

DESCRIPTION

With the patient's hand supinated, observe the contours of the hand. Have patient oppose thumb to all fingers in a pinch-like mechanism and palpate the thenar muscle simultaneously.

Presentation Photos and Related Diagrams

Marked Thenar Atrophy
Thenar Atrophy With Retained Opposition
Thenar Atrophy but note: Good opposition

Definition of Positive Result

A positive result is yielded with observation of a flattened thenar eminence as well as a decrease muscle strength with pinch/grip mechanism.

Definition of Negative Result

A negative result is yielded with observation of a round thenar eminence with a slight bulge as well as normal 5/5 muscle strength with no limitations with pinch/grip strength.

Comments and Pearls

Diagnoses Associated with Tests, Exams and Signs

CARPAL TUNNEL SYNDROME

References

Fernandes, C. H., Meirelles, L. M., Raduan Neto, J., Nakachima, L. R., dos Santos, J. B. G., & Faloppa, F. (2013). Carpal tunnel syndrome with thenar atrophy: evaluation of the pinch and grip strength in patients undergoing surgical treatment. Hand (New York, N.Y.), 8(1), 60–63. doi:10.1007/s11552-012-9471-8
Hoppenfeld, S., & Hutton, R. (1976). Physical Examination of the Wrist and Hand. In Physical examination of the spine and extremities (p. 62). New York, New York: Appleton-Century-Crofts.
Toy, E., & Rosenbaum, A., Roberts, T., Dines, J. (2013). Case files. New York, New York: McGraw-Hill Education/Medical.