**Question:** Thumb printing sign is seen in:

A. Congenital absence of palmar crease
B. Hypoplastic thumb
C. Polydactyly
D. Syndactyly

**Correct Answer:** A. Congenital absence of palmar crease

**Core Concept:** Thumb printing sign is a clinical feature associated with certain congenital anomalies of the hand. It refers to the presence of multiple palmar creases (print-like lines) on the palm due to the absence of the normal single palmar crease.

**Why the Correct Answer is Right:** The correct answer, A. Congenital absence of palmar crease, is related to a specific condition where the normal single palmar crease is replaced by multiple lines on the palm. This sign is indicative of a congenital absence of the palmar digital crease, which is a normal structural element present in healthy individuals.

**Why Each Wrong Option is Incorrect:**

B. Hypoplastic thumb: Hypoplastic thumb refers to a thinner or smaller thumb, but it does not result in the thumb printing sign. The correct answer is not related to the absence of a single palmar crease.

C. Polydactyly: Polydactyly is characterized by an extra digit(s) on the hand or foot. It does not cause the thumb printing sign as it involves the presence of extra digits, not the absence of a single palmar crease.

D. Syndactyly: Syndactyly is a condition where the fingers or toes are fused together. It does not lead to the thumb printing sign because it involves fusion of adjacent digits, not the absence of a single palmar crease.

**Clinical Pearl:** Thumb printing sign helps in identifying specific congenital hand anomalies and helps in distinguishing between various hand deformities. It is essential for clinicians to recognize these signs for accurate diagnosis and appropriate management of patients with hand abnormalities.