Final answer:
The correct option is 1. The tibia and fibula are stabilized by a syndesmosis involving an interosseous membrane and ligaments, which also shield the ankle; thus, the ligament is the correct answer.
Step-by-step explanation:
The tibia and fibula are connected and stabilized primarily by the strong syndesmosis formed by the interosseous membrane and specific ligaments at the distal tibiofibular joint.
This physiological architecture not only serves to unite the two bones but also acts as a protective structure for the ankle by preventing separation between the tibia and fibula and maintaining the talus in its proper position. Therefore, the process that the tibia and fibula have in common that acts as a shield for the ankle is option 1. Ligament.