Ape thumb deformity is seen in involvement of :
**Core Concept**
Ape thumb deformity, also known as "ape hand," is a rare congenital anomaly characterized by a thumb that is either absent or severely underdeveloped, leading to a claw-like appearance of the hand. This deformity is often associated with other limb abnormalities and can be caused by various genetic and environmental factors.
**Why the Correct Answer is Right**
The correct answer is related to the involvement of the ulnar nerve, which plays a crucial role in the development and function of the hand. The ulnar nerve innervates the intrinsic muscles of the hand, including the interossei and the lumbricals, which are responsible for thumb opposition and finger flexion. Damage to the ulnar nerve during fetal development can lead to the characteristic deformity seen in ape thumb, characterized by a lack of thumb development and a claw-like appearance of the hand.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the radial nerve, while also involved in hand function, is not directly related to the development of the thumb.
* **Option B:** This option is incorrect because the median nerve, although responsible for thumb opposition, is not typically associated with ape thumb deformity.
* **Option C:** This option is incorrect because the musculocutaneous nerve, which innervates the biceps and brachialis muscles, is not directly related to hand development or function.
**Clinical Pearl / High-Yield Fact**
Ape thumb deformity is a rare congenital anomaly that can be associated with other limb abnormalities and is often seen in patients with ulnar nerve damage during fetal development.
**Correct Answer: C.**