The tibia is the main bone of the leg, forming what is more commonly known as the shin. It expands at the proximal and distal ends, articulating at the knee and ankle joints respectively.
It is the second largest bone in the body, this is due to its function as a weight bearing structure.
In this article, we shall look at the bony landmarks of the tibia, the region anatomy, and look at any clinical correlations.
At the proximal end, the tibia is widened by the medial and lateral condyles, aiding in weight bearing. The condyles form a flat surface, known as the tibial plateau. This structure articulates with the femoral condyles to form the major articulation of the knee joint.
Located between the condyles is a region called the intercondylar eminence – this consists of two tubercles and a roughened area. This area is the main site of attachment for the ligaments and the menisci of the knee joint. The tibial intercondylar tubercles fit into the intercondylar fossa of the femur.
On the anterior surface of the proximal tibia, inferior to the condyles, the tibial tuberosity is situated. This is where the patella ligament attaches
The shaft of the tibia has three borders and three surfaces; anterior, posterior and lateral. For brevity, only the anatomically and clinically important borders/surfaces are mentioned here.
Anterior border – The start of the anterior border is marked by the tibial tuberosity. It is palpable down the anterior surface of the leg as the shin. Here, the periosteal covering of the tibia is susceptible to damage, presenting clinically as bruising.
Posterior surface – This is marked by a ridge of bone called the soleal line. It runs inferomedially, eventually blending with the medial border of the tibia. It is here where part of the soleus muscle originates
Lateral border – Also known as the interosseous border. This gives attachment to the interosseous membrane that binds the tibia and the fibula together.
The distal end of the tibia, like the proximal, widens to help with weight bearing.
There is a bony projection continuing inferiorly on the medial side – this is called the medial malleolus. It articulates with the tarsal bones to form part of the ankle joint. On the posterior surface of the tibia, there is a groove where the tendon of the tibialis posterior muscle passes through.
Laterally, on the distal end, there is a notch, where the fibula is bound to the tibia. It is known as the fibular notch.
Clinical Relevance: Fractures of the Tibia
Fractures of the tibia are relatively common, and occur most frequently in the middle aged and elderly. If the fibula is not fractured, it supports the tibia, and displacement of the fragments is minimal.
The proximal end of the tibia is the site that is most vulnerable to damage, resulting usually from some traumatic accident e.g vehicular. The condyles may be broken up in the fracture and it is not uncommon for there to be injury to the ligaments of the knee.
At the ankle, the medial malleolus can be fractured. This is caused by the ankle being twisted inwards (over-inversion) – the talus of the foot is forced against the medial malleolus, causing a spiral fracture.