Book : Human Anatomy
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Tibia Fibula

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The fibula or calf bone is a leg bone located on the lateral side of the tibia, with which it is connected above and below. It is the smaller of the two bones, and, in proportion to its length, the slenderest of all the long bones. Its upper extremity is small, placed toward the back of the head of the tibia, below the level of the knee joint, and excluded from the formation of this joint. Its lower extremity inclines a little forward, so as to be on a plane anterior to that of the upper end; it projects below the tibia, and forms the lateral part of the ankle-joint.

The bone has the following components:

  • Lateral malleolus
  • Interosseous membrane connecting the fibula to the tibia, forming a syndesmosis joint.
  • The superior tibiofibular articulation is an arthrodial joint between the lateral condyle of the tibia and the head of the fibula.
  • The inferior tibiofibular articulation (tibiofibular syndesmosis) is formed by the rough, convex surface of the medial side of the lower end of the fibula, and a rough concave surface on the lateral side of the tibia.

The tibia, also known as the shinbone or shankbone, is the larger and stronger of the two bones in the leg below the knee in vertebrates (the other being the fibula), and it connects the knee with the ankle bones. The tibia is found on the medial side of the leg next to the fibula, and closer to the median plane or centre-line. The tibia is connected to the fibula by the interosseous membrane of the leg, forming a type of fibrous joint called a syndesmosis with very little movement. The tibia is named for the flute tibia. It is the second largest bone in the human body next to the femur. The leg bones are the strongest long bones as they support the rest of the body.

Lower leg fractures include fractures of the tibia and fibula. Of these two bones, the tibia is the only weightbearing bone. Fractures of the tibia generally are associated with fibula fracture, because the force is transmitted along the interosseous membrane to the fibula.

The skin and subcutaneous tissue are very thin over the anterior and medial tibia and as a result of this, a significant number of fractures to the lower leg are open. Even in closed fractures, the thin, soft tissue can become compromised. In contrast, the fibula is well covered by soft tissue over most of its course with the exception of the lateral malleolus.

In a study of compartment syndrome associated with tibial fracture, the odds of compartment syndrome increased by 1.67 per 10% increase in the ratio of fracture length to tibial length when considering all fractures.

The Tibia

The tibia, or shin bone, spans the lower leg, articulating proximally with the femur and patella at the knee joint, and distally with the tarsal bones, to form the ankle joint. It is the major weight-bearing bone of the lower leg.

Proximally, there are five key features of the tibia: 

  • It widens and forms two condyles—the lateral and medial—that articulate with the condyles of the femur. 
  • Between the two condyles is the intercondylar fossa, a small grove, into which two intercondylar tubercles sit. Numerous internal ligaments of the knee joint attach to these tubercles and strengthen it significantly. 
  • On the anterior surface of the proximal region and inferiorly to the condyles is the tibial tuberosity to which the patella ligament attaches.
  • The shaft of the tibia is triangular and the soleus muscle, which gives the calf its characteristic shape, originates on the posterior surface.
  • Distally, the tibia also widens to aid with weight bearing and it displays two key features. The medial malleolus is a bony projection that articulates with the tarsal bones to form the ankle joint. Laterally, there is the fibular notch that articulates with the fibula.

The Fibula

The fibula also spans the lower leg, although proximally it does not articulate with the femur or patella. It serves more as an attachment point for muscles rather than a weight-bearing bone.

Proximally, the fibula head articulates with the lateral condyle of the tibia, and the biceps femoris attaches to the fibula head. As with the tibia, the shaft of the fibula is triangular and numerus muscles are involved in the extension and flexion of the foot. These muscles originate from the fibula's surface and include the extensor digitorum longus, soleus, and flexor hallucis longus, among others. 

Distally, the fibula forms the lateral malleolus, which is more prominent than the medial malleolus of the tibia. It also articulates with the tarsal bones to form the ankle joint.

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