Tibia | Shinbone
Tibia is medial bone of the leg, also known as shinbone or shankbone. It is larger and stronger of the two bones of leg, i.e. it is stronger and longer than fibula.It connects the knee with ankle and is the major weight bearing force of body.Like all other typical long bones, it has two ends and an intervening shaft. The cross-section of tibia is triangular in shape.
Proximal end of tibia:
The proximal end of tibia is expanded and is a bearing surface for weight of the body, which is transmitted through femur. There are massive medial and lateral condyles and an intercondylar area intervening between the condyles. There is also a prominent tibial tuberosity.
There are two condyles of tibia: medial and lateral. The condyles overhang the proximal surface of shaft posteriorly. Both condyles have an articular surface proximally, which articulates with corresponding condyles of femur. There is an intercondylar area between the two condyles, which marks the separation between the two. Both condyles are visible and palpable in living subjects.
Lateral condyle has a fibular facet for attachment of fibula.
Tibial tuberosity is a little projection in the area where the anterior condylar surface merge with each other. It is divided into a proximal smooth and a distal rough region. In living subjects, the distal rough region is palpable. It is separated from the skin by subcutaneous infrapatellar bursa. To the smooth part of tibial tuberosity attaches the patellar tendon.
Shaft of tibia:
As stated above, shaft of tibia is triangular in cross section. Consequently, it consists of three borders and three surfaces.
The borders of tibia are named as: anterior border, medial border and lateral (interosseous border).
- Anterior border: It descends from the tibial tuberosity to the medial malleolus. It is subcutaneous throughout the bone, except in its distal 1/4 where it is indistinct.
- Medial border: It descends from anterior end of medial condyle to posterior margin of medial malleolus.
- Lateral (interosseous) border: It begins anterior to the fibular facet and descends to the fibular notch (explained below). The interosseous membrane is attached to most of its length.
The surfaces of tibial shaft are named as: anteromedial surface, posterior surface and lateral surface.
- Anteromedial surface: It lies between the anterior and medial borders, and is almost entirely subcutaneous.
- Lateral Surface: It lies between the anterior and lateral borders.
- Posterior Surface: It lies between the medial and lateral borders. The posterior surface of the tibia presents, at its upper part, a prominent ridge, the soleal line ( also known as popliteal line), which extends obliquely downward from the back part of the articular facet for the fibula to the medial border
Distal end of Tibia:
Distal end is slightly expanded and has 5 surfaces namely anterior, medial, posterior, lateral and distal. In comparison to the proximal end, the distal end of tibia is rotated laterally, an effect known as tibial torsion. The lateral surface of distal end contains the triangular fibular nothch for attachemnt of fibula.
It is a strong pyramidal process prolonged from the distal end of the tibia medially.It ends proximal to the lateral malleolus, which is also more posterior. Its main role is to deepen the articular surface for ankle joint.
Blood supply of tibia:
Proximal end receives its blood supply form metaphyseal vessels, which arise from genicular arterial anastomosis.
Nutrient foramen of tibia usually lies near the soleal line. The nutrient artery which is transmitted through this foramen comes from posterior tibial artery.
The periosteal blood supply to the shaft arises from anterior tibial artery.
Distal metaphysis receives its blood from anastomosis around the ankle joint.
Nerve supply to tibia:
Proximal end of tibia is innervated by branches of nerves supplying knee joint. Similarly, distal end is innervated by branches of nerves supplying ankle joint. The periosteum of shaft is supplied by branches from nerves innervating the muscles attached to tibia.
Ossification of tibia:
Tibia ossifies from three centers: one in the shaft and one in each epiphysis. The process starts in the middle of shaft at about 7th week of intrauterine life. The proximal epiphysis center is normally present at birth. The fusion occurs in the sixteenth year in females and eighteenth year in males.
Ossification center for distal epiphysis appears early in the first year and joins the shaft in about the fifteenth year in females and seventeenth in males.
Medial malleolus is an extension from the distal epiphysis and starts to ossify in the 7th year.