Causes / typical injury mechanism: Intrinsic minus hand is characterized by an imbalance between strong extrinsic and deficient intrinsic musculature. This leads to proximal interphalangeal (PIP) and distal interphalangeal (DIP) joint flexion with metacarpophalangeal (MCP) joint hyperextension. Intrinsic minus hand is most commonly caused by a peripheral nerve palsy (ulnar or median) leading to loss of intrinsic function. It can be a chronic condition or the result of acute trauma. If acute trauma is the cause, repair should occur within 72 hours.

Classic history and presentation: The classic patient presents with progressive MCP joint hyperextension and IP joint flexion. This corrects when the MCP joint is brought out of hyperextension. The contracture is more pronounced in the ring and small fingers, and the patient reports numbness and tingling in this distribution.

Risk factors:

• Ulnar nerve palsy – cubital tunnel syndrome, ulnar tunnel syndrome (compression at Guyon's canal)
• Median nerve palsy – trauma (eg, Volkmann ischemic contracture, failure to splint in an intrinsic-plus posture following crush injury), leprosy, hereditary motor-sensory neuropathy (Charcot-Marie-Tooth disease), brachial plexus neuritis

Pathophysiology: Loss of intrinsics leads to loss of baseline MCP flexion and IP extension. Strong unopposed extension of the MCP joints by the extrinsic extensor digitorum communis. Unopposed flexion of the PIP and DIP from unopposed flexor digitorum superficialis and flexor digitorum profundus, respectively.