Froment's Sign (Bunnell's "O" or Newspaper Sign)

Exams and Signs

Motor function is necessary to assess for ulnar neuropathy. Pinch and grip strength are recorded. Grip can be weaked with diminished small and ring finger strength but is usually close to normal with ulnar neuropathy at the wrist level.

With weakness of the ulnar nerve-innervated adductor pollicis muscle, a positive Froment sign may be observed - compensatory IP flexion of the thumb using the FPL during pinch mechanism. The thumb interphalangeal joint flexes in an attempt to substitute flex pollicis longus activity for inadequate adductor pollicis strength.

Description

A piece of paper is held in between the thumb and index finger. Finger position while pinching is to be observed. The examiner can attempt to pull the piece of paper to add resistance.

Presentation Photos and Related Diagrams

Froment's sign only slightly positive. Noted marked thumb IP flexion caused by weak ulnar intrinsics. Patient otherwise making almost normal "O" sign.
Positive Froment's sign. Patient is supporting index with the other fingers, hyperflexing the thumb IP joint and the space between the thumb and index is a rectangular space not a perfect "O".
Positive Froment's Test - When the examiner pulls on the envelop the patient's right thumb will easily slip loose because of the weak ulnar intrinsics while the normal left side will be held firmly with the normal ulnar intrinsics which support a strong pinch.

Definition of Positive Result

A positive Froment's sign occurs when the patient flexes the thumb interphalangeal joint in order to maintain an adequate pinch against resistance.

Definition of Negative Result

A negative Froment's sign occurs when the patient's thumb interphalangeal joint remains neutral and demonstrates adequate pinch against resistance.

Comments and Pearls

If the test is positive, it indicates recruitment of median innervated musculature to compensate for the weakened ulnar innervated pinch muscles (adductor pollicis and first dorsal interosseous).
Although a positive Froment's sign is indicative of ulnar neuropathy, it does not localize the site of compression.

Diagnoses Associated with Exams and Signs

References

Peimer, C. (1996). Compression Neuropathies: Ulnar. In Surgery of the hand and upper extremity (Vol. 2, pp. 1345-1346). New York, NY: McGraw-Hill, Health Professions Division.
Skinner, H., McMahon, P. (2014). Hand Surgery. In Current diagnosis & treatment in orthopedics (5th ed., p. 484). New York, NY: McGraw-Hill Medical

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