Claw deformity results from loss of which muscle group leading to MCP hyperextension and IP flexion?

Study for the NBCOT Hand Injuries and Intervention Test. Prepare with flashcards and multiple choice questions, each question offers hints and explanations. Get ready for success!

Claw deformity happens when the intrinsic hand muscles that are supplied by the ulnar nerve—especially the interossei and the medial two lumbricals—are paralyzed. Those intrinsic muscles normally flex the metacarpophalangeal joints and help extend the interphalangeal joints. When they’re lost, the extensor digitorum at the MCP joints acts unopposed, causing MCP hyperextension, while the flexor digitorum profundus and superficialis continue to pull the IP joints into flexion. The result is the characteristic claw pattern of the fingers. So, the best match is loss of intrinsic ulnar-innervated muscles. The other groups don’t produce this exact balance of MCP hyperextension with IP flexion: the extrinsic radial extensors aren’t the primary cause of this pattern, and the thenar or hypothenar groups alone don’t produce the claw posture.