The structure that forms a bony bulge on the distal, lateral surface of the lower leg is the

The lateral malleolus found on the distal lateral surface of the fibula is responsible for the bony bulge on the lower leg. 

The lateral malleolus is the prominence on the outer or lateral side of the ankle. It is pyramidal in form and somewhat flattened. In clinical significance, a bimalleolar fracture is an ankle fracture that involves both the medial and lateral malleolus. This condition is more common in women especially the 60 year old age group. Another clinical condition of the said anatomical structure is the trimalleolar fracture which involves the lateral, medial, and the distal posterior aspect of the tibia or the posterior malleolus. This is primarily caused by ligament damage and dislocation.