**Core Concept**
The deltoid ligament is a strong, fan-shaped ligament that provides medial stability to the ankle joint. It is composed of two layers: superficial and deep. The superficial layer is attached to the medial malleolus, whereas the deep layer is attached to the medial aspect of the talus and calcaneus.

**Why the Correct Answer is Right**
The deltoid ligament is primarily attached to the medial malleolus, talus, and calcaneus. The medial malleolus serves as the primary attachment site for the superficial layer, while the deep layer is attached to the medial aspect of the talus and calcaneus. The medial cuneiform, on the other hand, is a bone in the midfoot that does not have any direct attachment to the deltoid ligament.

**Why Each Wrong Option is Incorrect**
**Option A:** The medial malleolus is indeed a primary attachment site for the deltoid ligament, making this option incorrect.
**Option C:** The spring ligament, also known as the plantar calcaneonavicular ligament, is a separate ligament that supports the head of the talus, but it is not attached to the deltoid ligament.
**Option D:** The sustentaculum tali is a strong, longitudinal ligament that serves as a support for the talus, and it is not directly attached to the deltoid ligament.

**Clinical Pearl / High-Yield Fact**
The deltoid ligament plays a crucial role in providing medial stability to the ankle joint, and its injury can lead to medial ankle instability.

**✓ Correct Answer: B. Medial cuneiform**