The tibia is the main weight-bearing bone of the lower leg. It is larger than the fibula with which it is paired. The tibia is also the second longest bone in the body and is located right below the skin. The proximal end of the tibia forms the medial and the lateral condyle, which articulates with the condyles of the femur to form the knee joint. Between the articulating surfaces is the irregular elevated area known as the intercondylar eminence that serves as the inferior attachment point for two supporting ligaments of the knee. On its proximal end is an elevated area called the tibial tuberosity, the final site of attachment for the muscle tendon associated with the patella. On the posterior side of the tibia is the roughened ridge called the soleal line to which the posterior leg muscles attach. A large expansion called the medial malleolus is present at the distal tibia forming the large bony bump at the ankle region. On the lateral side of the distal tibia is a wide groove called the fibular notch, which articulates with the distal end of the fibula forming the distal tibiofibular joint.
The fibula is the slender bone located on the lateral side of the leg. It does not bear significant weight but acts as a primary site for muscle attachment. The head of the fibula articulates with the lateral tibial condyle forming the proximal tibiofibular joint. The thin shaft of the fibula has an interosseous border that serves as an attachment site for the interosseous membrane that spans the fibula and tibia. The distal end of the fibula forms the lateral malleolus, which forms the easily palpated bony bump on the lateral side of the ankle. The medial surface of the lateral malleolus articulates with the talus bone of the foot as part of the ankle joint. The distal fibula also articulates with the fibular notch of the tibia.
This text is adapted from Openstax, Anatomy and Physiology 2e, Section 8.4: Bones of the lower limb
