## Core Concept
The spring ligament, also known as the plantar calcaneonavicular ligament, plays a crucial role in supporting the medial longitudinal arch of the foot. It is a fibrocartilaginous ligament that connects the calcaneus to the navicular bone.

## Why the Correct Answer is Right
The spring ligament is composed of three bands: the medial, intermediate (or central), and lateral bands. These bands work together to provide support to the head of the talus and maintain the medial longitudinal arch of the foot. The correct answer, which is not a part of the spring ligament, needs to be identified based on the accurate composition and attachments of the spring ligament.

## Why Each Wrong Option is Incorrect
- **Option A:** The medial band is indeed a part of the spring ligament, providing medial support.
- **Option B:** The lateral band is also a component, contributing to the lateral support of the arch.
- **Option C:** The plantar calcaneocuboid ligament, also known as the short plantar ligament, is not considered a part of the spring ligament; it is a separate ligament that supports the lateral arch of the foot.
- **Option D:** The intermediate or central band is a component of the spring ligament.

## Clinical Pearl / High-Yield Fact
A key clinical correlation to remember is that the spring ligament is crucial in conditions like flat foot (pes planus), where its integrity is often compromised, leading to the collapse of the medial longitudinal arch.

## Correct Answer: C. Plantar calcaneocuboid ligament.