Tibia is located in the lower leg and consists of three parts: Proximal end, distal end and a strong shaft. Both ends are also known as Epiphyses and the shaft is known as Diaphysis.
- Proximal end : It is expanded part and comprises of two rounded portions called Condyles (medial and lateral). They join with with the medial and lateral condyles of femur (the bone of thigh) and knee joint is formed as a result. The groove between both condyles is termed as Intercondylar Fossa. Just below the fossa on the anterior surface, there is a prominence called Tibial Tuberosity. This tuberosity provides attachment to the ligaments of the knee .
- Shaft : It is also known as Diaphysis. It is the long, mid part of the bone between both ends. Shaft has three borders and there are three surfaces anatomically. The anterior border is also called Shin where no muscle is attached. So shin is directly covered by the skin and its outer layer, called Periosteum, is susceptible to direct blow or damage. The posterior surface bears a ridge called Soleal line, which is related to a muscle of the leg called Soleus. The lateral border is connected to the other bone called Fibula through a transparent membrane. This membrane is usually known as Interosseous membrane due to which the lateral border of Tibia is also known as Interosseous border.
- Distal end : The distal end of Tibia is also expanded, but less than the proximal end. It forms the ankle joint by joining with the ankle bones called Tarsal bones. On the posterior aspect, there is a groove through which a muscle called Tibialis anterior passes. On its medial aspect, there is a projection, called Medial Malleolus. This projection is prominent and visible outside. On the lateral side, there is a notch present which connects the Tibia with other bone called Fibula. Hence, the notch is termed as Fibular Notch.
Formation of Tibia starts from three centres. One from the middle of the bone and two on its extremities. Tibia is quite massive and is triangular in its cross section.
There are two sources from which Tibia gets its blood supply. A Nutrient Artery is the main supply. This nutrient artery is branch of the Posterior Tibial Artery. The outer layers of Tibia called Periosteal Layers are supplied by Anterior Tibial Artery.
The proximal end of Tibia receives innervation from the nerves supplying the knee joint. The distal end, in the same way, receives innervation from the nerves which supply ankle joint. Periosteum of the Tibia is innervated by the nerves supplying the muscles attached to it.
Tibia has got two major functions to perform:
- Muscle attachment : Tibia provides attachment to muscles of the lower leg and supports knee and ankle. It helps in standing and walking.
- Strength : Tibia is the second largest bone of the leg and it provides strength to a person to stand. It bears all the weight of body. Any deformity in it leads to loss of balance and weakness of legs occur.
- Fractures of the Tibia are common and mostly occur in adults and old age. Among fractures, Bumper fractures are most common and these occur due to road traffic accident when the vehicle hits the pedestrian from front. Proximal end of Tibia is most vulnerable to fractures in this case. However, if Fibula is not fractured, it supports Tibia and prevents it from breaking into fragments. Condyles of the Tibia are also broken in fractures, and knee is affected.Fractures of medial malleolus occur when there is inward twisting of the ankle during a fall or hit by a vehicle from a side. It is known as spiral fracture.
- Deficiency of Vitamin D and Calcium in pregnant women leads to deformities in the formation of Tibia by birth. Malnutrition in children also causes deformities in the children of growing age.
- In old age, deficiency of Calcium and Vitamin D causes Osteoporosis (pores in bones) which is well marked in long bones such as Tibia.