The ankle joint is a complex structure that serves as a bridge between the leg and the foot, managing the body’s weight and facilitating movement. It is a hinge joint, primarily allowing the foot to move up and down, relying on surrounding bony prominences for stability and side-to-side control. The two noticeable, rounded bumps on either side of the ankle are the most prominent structures of this joint. These hard bumps are a normal part of human anatomy, though they are often mistaken for swelling.
The Anatomical Name
The general term for the rounded bony prominence on the ankle is the malleolus. The term is derived from the Latin word for “small hammer,” describing its rounded appearance. Since there are two distinct prominences, one on the inner side and one on the outer side of the ankle, the plural form is malleoli.
These structures are integral parts of the talocrural joint, the primary ankle joint where the leg bones meet the talus foot bone. The malleoli extend downward to cup the talus, providing a secure socket. This bony architecture prevents excessive side-to-side motion and ensures stability for bearing body weight.
Location and Identification
The two bumps on the ankle are formed by the lower ends of the two long bones in the lower leg: the tibia and the fibula. The bump on the inside of the ankle, closer to the body’s midline, is called the medial malleolus. This inner prominence is the downward extension of the tibia, the larger of the two lower leg bones.
The bump on the outside of the ankle, further from the body’s midline, is known as the lateral malleolus. This outer prominence is the lower end of the fibula, the thinner bone of the lower leg. The lateral malleolus descends to a slightly lower level than the medial malleolus, which enhances the stability of the ankle joint.
When Is a Bump NOT Normal?
While the malleoli are permanent, hard, and normal bony features, a reader may be concerned about a bump that feels different. A non-normal bump is typically a soft tissue mass or localized swelling, unlike the rigid, unmoving bone. These abnormal protuberances may be movable, appear suddenly, or be accompanied by pain.
One common cause of a soft, non-bony bump is a ganglion cyst, a fluid-filled sac that develops near joints or tendons. These cysts are usually harmless and non-cancerous, but they can cause discomfort if they press against a nearby nerve. Other non-normal bumps include lipomas (benign tumors of fat cells) or localized edema (swelling caused by fluid accumulation). If a bump is warm, red, painful, or appears after trauma, it may indicate a fracture, sprain, or infection, and warrants professional medical evaluation.