## **Core Concept**
Sabre tibia refers to a characteristic deformity of the tibia seen in congenital syphilis, where the tibia becomes bowed or curved, resembling a sabre. This condition results from periostitis and osteitis caused by syphilis infection.

## **Why the Correct Answer is Right**
The correct answer, **C. Congenital syphilis**, is right because sabre tibia is a classic manifestation of congenital syphilis. In congenital syphilis, the infection is transmitted from mother to child during pregnancy, leading to various skeletal abnormalities, including sabre tibia. The deformity is due to inflammation of the periosteum and bone (periostitis and osteitis), which causes the tibia to become bowed.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because while trauma can cause fractures or deformities of the tibia, it does not characteristically cause the sabre-like deformity associated with congenital syphilis.
- **Option B:** This option is incorrect because rickets, a disease caused by vitamin D deficiency leading to softening of bones, can cause bowing of the legs but does not typically cause the characteristic sabre tibia deformity.
- **Option D:** This option is incorrect because osteogenesis imperfecta, a genetic disorder characterized by fragile bones, does not specifically cause sabre tibia.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that sabre tibia is one of the Hutchinson's teeth and other stigmata of congenital syphilis. Clinicians should consider congenital syphilis in the differential diagnosis of skeletal abnormalities in children, especially when characteristic signs like sabre tibia are present.

## **Correct Answer:** . Congenital syphilis