Which ligament is involved in Pes planus of foot ?
**Core Concept**
Pes planus, also known as flat foot, is a condition characterized by partial or complete collapse of the medial longitudinal arch of the foot. This occurs due to a combination of factors, including ligamentous laxity, muscle weakness, and bone deformities.
**Why the Correct Answer is Right**
The ligament primarily involved in Pes planus is the **plantar calcaneonavicular ligament** (PCNL). This ligament plays a crucial role in supporting the medial longitudinal arch of the foot by providing a connection between the calcaneus and the navicular bone. In cases of Pes planus, the PCNL is often found to be lax or incompetent, leading to the collapse of the arch.
**Why Each Wrong Option is Incorrect**
* **Option A:** The **spring ligament** is also involved in the medial longitudinal arch but is more commonly associated with the support of the head of the talus, rather than the primary cause of Pes planus.
* **Option B:** The **deltoid ligament** is a strong ligament that supports the medial aspect of the ankle joint, but it is not directly involved in the pathogenesis of Pes planus.
* **Option C:** The **peroneal tendons** are involved in the lateral ankle and are not directly related to the medial longitudinal arch or Pes planus.
**Clinical Pearl / High-Yield Fact**
In cases of Pes planus, it is essential to assess the function of the plantar calcaneonavicular ligament, as well as the strength and tone of the intrinsic foot muscles, to determine the best course of treatment.
**Correct Answer: C. Plantar calcaneonavicular ligament.**