Froment Sign and Jeanne Sign: Diagnosing Adductor Pollicis Ulnar Neuropathy

Assessment of motor function in peripheral neuropathies demands rigorous clinical tests capable of exposing subtle muscular imbalances before gross deformities appear. In ulnar neuropathy, whether originating at the cubital tunnel in the elbow or Guyon canal in the wrist, denervation of the intrinsic hand muscles produces characteristic compensatory movement patterns during key pinch. The Froment sign and Jeanne sign represent two classic clinical indicators of severe motor compromise involving the adductor pollicis and deep head of the flexor pollicis brevis muscles. Recognizing these pathognomonic physical signs enables clinicians to identify deep motor branch dysfunction, gauge axonal involvement, and refer patients for urgent structural intervention when conservative management is no longer indicated.

Functional Impairment in Everyday Indian Household and Professional Tasks

In daily life across Indian households, loss of adductor pollicis strength severely disrupts fundamental hand tasks. Patients report dropping stainless steel plates, struggling to hold heavy flat kitchen keys, or failing to pinch a sheet of paper securely. In domestic cooking, holding kitchen tongs (chimta) to turn hot rotis over an open gas flame or tearing dough requires a firm key pinch between the thumb pad and the lateral border of the index finger. When ulnar motor innervation fails, individuals unknowingly compensate by bending their thumb joint awkwardly, dropping utensils and experiencing rapid hand exhaustion during simple manual activities.

Anatomy, Biomechanical Compensation, and Joint Kinematics

The adductor pollicis is the largest intrinsic muscle of the thumb, innervated exclusively by the deep terminal motor branch of the ulnar nerve (C8-T1). During normal lateral key pinch, the adductor pollicis powerfully adducts the thumb metacarpal toward the palm, keeping the interphalangeal (IP) joint stable in extension or mild flexion while the first dorsal interosseous muscle stabilizes the index finger. When the adductor pollicis undergoes denervation and weakness, the patient cannot generate sufficient clamping force. To compensate, the central nervous system recruits the flexor pollicis longus (FPL), an extrinsic muscle innervated by the anterior interosseous branch of the median nerve. This hyper-activation of the FPL produces marked acute flexion of the thumb IP joint, recognized clinically as a positive Froment sign. If the thumb metacarpophalangeal (MCP) joint simultaneously hyperextends due to laxity of the volar plate and absent intrinsic balance, it is designated as a positive Jeanne sign.

Conservative Management, Splinting, and Adaptive Re-Education

A positive Froment or Jeanne sign signifies established motor neuropathy and axonal denervation. Conservative physiotherapy focuses on maintaining joint mobility, preserving remaining motor endplates, and preventing joint contractures. Custom thumb spica splints or lateral pinch stabilization orthoses are fabricated to prevent thumb MCP hyperextension during functional grip tasks. Targeted exercise therapy includes neuromuscular re-education of the first dorsal interosseous and surviving thenar stabilizers, gentle neurodynamic mobilizations of the ulnar nerve, and occupational adaptations such as built-up handles for cooking utensils and writing instruments.

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