The tibia (also known as shinbone, Latin: (os) tibia) is the larger and stronger of the two lower leg bones and lies medially next to the fibula. The tibia extends between the knee and the ankle.
As a long bone, the tibia is composed of three parts: a diaphysis or shaft, and two epiphyses or extremities - proximal and distal.
Proximal extremity of tibia
The proximal extremity (or epiphysis, or end) is the upper end of the tibia, and it features the following landmarks:
- medial condyle,
- lateral condyle,
- intercondylar area,
- intercondylar eminence,
- anterior intercondylar area,
- posterior intercondylar area,
- superior articular surface,
- fibular articular surface.
The medial condyle of the tibia is the medial expansion, while the lateral condyle is the lateral expansion at the proximal end of the bone. The medial and lateral condyles are separated by the intercondylar area, which is partitioned into anterior and posterior intercondylar areas by the intercondylar eminence. The intercondylar eminence is a bony elevation between the articular surfaces of the tibia. It serves for the attachment of the cruciate ligaments and menisci.
The anterior intercondylar area is the area between the knee joint surfaces of the tibia and in front of the intercondylar eminence. The posterior intercondylar area is located between the articular surfaces behind the intercondylar eminence.
There are two articular surfaces on the proximal end of the tibia - the superior articular surface and the fibular articular surface. The superior articular surface articulates with the femur at the knee joint. The fibular articular surface is the articular facet for the head of the fibula on the posterolateral aspect of the lateral condyle of the tibia.
Shaft of tibia
The shaft (or body, or diaphysis) of the tibia is the middle part of the bone between the two extremities. It is triangular in cross-sections and has three borders or margins:
- anterior margin, featuring the tibial tuberosity,
- interosseous margin,
- medial margin.
The anterior margin of the tibia is directed anteriorly, while the medial margin or the inner margin is facing medially. The interosseous margin of the tibia is facing the fibula and provides the attachment to the interosseous membrane along most of its length.
The tibial tuberosity is a roughened area on the upper portion of the anterior margin of the tibia. The tibial tuberosity serves as the attachment site for the patellar ligament.
The shaft of the tibia presents three surfaces:
- medial surface,
- lateral surface, and
- posterior surface, which features the soleal line.
The medial surface of the tibia is directed anteromedially, the lateral surface - anterolaterally, and the posterior surface is facing posteriorly.
The soleal line is a line extending obliquely from the upper, lateral part of the shaft of the tibia, downward and across to the medial side. It serves for the attachment of the soleus muscle.
Distal extremity of tibia
The distal extremity (or end, also epiphysis) is the lower extremity of the tibia, and is marked by:
- medial malleolus, with
- malleolar articular surface,
- malleolar groove,
- fibular notch,
- inferior articular surface.
A malleolus refers to a bony prominence on each side of the ankle. The medial malleolus is the prominence on the inner side of the ankle, specifically, on the distal extremity of the tibia. The malleolar articular surface is the lateral articular surface of the medial malleolus, which articulates with the talus. The malleolar groove is a small narrow on the posterior aspect of the medial malleolus for the attachment of the tendon of the tibialis posterior muscle.
The fibular notch is a depression on the lateral surface of the distal tibia, which articulates with the fibula.
The inferior articular surface is the inferior joint surface of the tibia facing the talus.