Middle Finger Test | Hand Surgery Resource

Exams and Signs

Description

In examination of the hand, wrist and elbow, it is important to differentiate between lateral epicondylitis, elbow synovitis and posterior interosseous nerve (PIN) entrapment. The middle finger tests aids in this differential diagnosis but its accuracy remains controversial.¹
In lateral epicondylitis (tennis elbow), may co-exist with an entrapment neuropathy of the radial nerve and its branches.²

Pathophysiology

Inability to extend the middle and ring fingers against resistance may arise from PIN syndrone.¹
Extending the middle and ring fingers against resistance can cause the pain associated with PIN syndrome as the proximal supinator and extensor muscles tighten and compress the poster interosseous branch of the radial nerve in the area of the supinator and the arcade of Frohse.⁴
Reportedly resisted middle finger extension aggravates posterior interosseous nerve (PIN) compression by pulling on part of the ECRB muscle tendon unit. However, tears of the ECRB origin can cause tennis elbow so pulling on the ECRB may elicit pain and tenderness secondary to tennis elbow and not because of additional posterior interosseous nerve (PIN) compression.³

Instructions

Ask the patient to extend the elbow, pronate the forearm and flex the wrist
Provide resistance as the patient tries to extend his/her middle and ring finger¹

Related Signs and Tests

Diagnoses

Presentation Photos and Related Diagrams

Definition of Positive Result

A positive result occurs when the examiner reproduces the patient’s pain or ache in the affected areas.¹

Definition of Negative Result

A negative result occurs when the examiner does not reproduce the patient’s pain or ache in the affected areas.

Comments and Pearls

To diagnose PIN syndrome, MRI may be useful to delineate a soft tissue mass responsible for compression. Lipomas should be considered, because they are the most commonly reported tumor to cause PIN syndrome.³
A more accurate sign of posterior interosseous nerve (PIN) compression is tenderness at the point distal to the lateral epicondyle where the PIN exits the supinator muscle.⁴
Another sign of posterior interosseous nerve (PIN) compression is PIN tenderness elicited by resisted supination with the elbow extended. During this maneuver the arcade of Frohse thought to compress the posterior interosseous nerve (PIN). ^2,4,5
Weakness of the muscles innervated by the posterior interosseous nerve (PIN) is cause by direct damage to the muscles or by abnormal posterior interosseous nerve (PIN) function. However, abnormal posterior interosseous nerve (PIN) function can be caused by a compression neuropathy (entrapment) or by other causes such as Parsonage-Turner Syndrome.

Diagnoses Associated with Exams and Signs

References

Culp R, Jacoby S. Musculoskeletal Examination of the Elbow, Wrist and Hand: Making the Complex Simple. New Jersey: SLACK Incorporated, 2012
Roles NC, Maudsley RH. Radial Tunnel Syndrome: Resistant Tennis Elbow as a Nerve Entrapment. J Bone and Joint Surgery 1972;54(3):499-508.
Dang A, Rodner C. Unusual Compression Neuropathies of the Forearm, Part I: Radial Nerve. J Hand Surg Am 2009;34(10):1906-10. PMID: 19969199
Lister GD, Belsole RB, Kleinert HE: The radial tunnel syndrome. . J Hand Surg Am 1979; 4:52
Capener N: Tennis elbow and posterior interosseous nerve. Br Med J 1960; 2:120