A COTA is working with a client who has decreased nerve function. The client has lost precision pinch, thenar opposition, and the ability to bend the index and long fingers at the proximal and distal interphalangeal joints. What deformity does the client most likely have?

• A. Ulnar claw
• B. Boutonniere deformity
• C. Swan neck deformity
• D. Ape hand deformity

Answer: (D)

Ape hand deformity arises from median nerve injury, leading to loss of thenar muscle function and thumb opposition. When the median nerve is impaired, the thenar eminence atrophies, so the thumb cannot oppose and is pulled toward adduction by the adductor pollicis. This loss of opposition, combined with weakness of the median-innervated flexors of the index and middle fingers (flexor digitorum superficialis for PIP joints and part of flexor digitorum profundus for the DIP joints), results in an inability to flex those digits at both joints and a reduced precision pinch between the thumb and index finger. The pattern described—decreased precision pinch, loss of thumb opposition, and inability to bend the index and middle fingers at the PIP and DIP joints—fits median nerve palsy presenting as ape hand.

Other patterns reflect different nerve or mechanism injuries: clawing of the ring and little fingers points to ulnar nerve involvement; boutonniere deformity involves a central slip injury of the extensor mechanism with PIP flexion and DIP hyperextension; and swan neck deformity involves hyperextension of the PIP with DIP flexion due to imbalance in the extensor mechanism.