The tibia (shin bone) is a long bone of the leg, found medial to the fibula. It is also the the weight bearing bone of the leg, which is why it is the second largest bone in the body after the femur. Fun fact here is that ‘tibia' is the Latin word for tubular musical instruments like the flute. They were sometimes made from tibial bones of animals, so the length of the tibia was useful in many ways other than just for bearing body weight while walking.
Like other long bones, there are three parts of the tibia: proximal, shaft, and distal. The proximal part participates in the knee joint, whereas the distal part contributes to the ankle joint. The tibial shaft on the other hand offers many sites for leg muscle attachment.
|Proximal part landmarks||Lateral and medial condyles (articulation with femur–knee joint)
Anterior and posterior intercondylar areas
Tubercle of iliotibial tract
|Shaft landmarks||Posterior, medial, and lateral surfaces
Soleal line (posterior surface)
Anterior, interosseous, and medial borders
|Distal part landmarks||Medial malleolus (articulation with talus–ankle joint)
Fibular notch (articulation with distal end of fibula)
Superior/proximal tibiofibular joint
Middle tibiofibular joint
Inferior/distal tibiofibular joint
|Muscle Attachments||Muscles that insert onto tibia: sartorius, gracilis, quadriceps femoris, semimembranosus, semitendinosus, popliteus
Muscles that originate from tibia: tibialis anterior, extensor digitorum longus, soleus, tibialis posterior, flexor digitorum longus
This article will focus on the gross anatomy of the tibia and its important anatomical relationships.
The proximal end of the tibia features several important landmarks which function as sites of muscle attachment and articular surfaces: two tibial condyles (medial and lateral) separated by intercondylar areas (anterior and posterior).
The superior surface of the medial condyle is round in shape and somewhat concave, so it fits perfectly into a joint with the medial condyle of the femur. The medial meniscus is sandwiched between the tibia and femur in this joint with attachments to all margins except for the lateral margin. Instead, the lateral margin extends to the medial intercondylar tubercle.
On the other hand, the superior surface of the lateral condyle is pretty much a mirror image of the medial condyle. It is round in shape, somewhat convex, and articulates with the lateral condyle of the femur. The lateral meniscus attaches to all of its margins except for the medial margin. The medial margin extends to the lateral intercondylar tubercle. Note that the lateral and medial menisci are the pads of fibrocartilage inserted to ease the pressure that is transmitted from the femur to the condyles.
The superior surfaces of the condyles are flattened and together they form the superior articular surface called the tibial plateau. Here, the tibial condyles articulate with the femoral condyles within the knee joint. The articular surfaces are separated by two small prominences, the medial and lateral intercondylar tubercles. These tubercles form the intercondylar eminence, which is bordered by the anterior and posterior intercondylar areas.
- The anterior intercondylar area features attachment sites for many structures. Anterior to posterior they are: the anterior horn of the medial meniscus, the anterior cruciate ligament, and the anterior horn of the lateral meniscus.
- The posterior intercondylar area also has facets for structures to attach. Anterior to posterior these are: the posterior horn of the lateral meniscus, the posterior horn of the medial meniscus, and the posterior cruciate ligament.
On the lateral surface of the proximal end of the tibia just inferior to the lateral condyle is the bony prominence called the tubercle of iliotibial tract or Gerdy’s tubercle. Inferior and lateral to it is the articular facet for the head of the fibula where the tibia and fibula articulate via the superior/proximal tibiofibular joint.
At the anterior surface of the proximal end is the tibial tuberosity. It is an attachment site for the patellar ligament and you can easily spot and palpate this prominence just below your knee. Inferiorly, the tibial tuberosity is continuous with the anterior border of the tibia.
The tibial shaft is triangular in cross-section and so it has three surfaces (posterior, medial, and lateral) and three borders (anterior, interosseous, and medial).
The medial surface, commonly called the shin, is bound by the anterior and medial borders. It is subcutaneous, meaning that there is only a little fat between the bone and the skin and it has no muscles attachments along most of it. Because of this, the medial surface is palpable along the entire length of the anteromedial aspect of the leg. The lateral surface is bound by the anterior and medial margins and is covered by the muscles of the anterior leg compartment. The posterior surface is bound by the interosseous and medial margins and features the soleal line crossing this surface diagonally.
Of the three borders, the anterior border is the most prominent. It can be seen as a distinct margin that begins at the tibial tuberosity and descends all the way to the distal part of the bone. The interosseous border begins inferior to the tubercle of the iliotibial tract and descends down the lateral surface of the tibia. This border connects to the interosseous border of the fibula by the interosseous membrane. At the inferior end of the tibia, the interosseous border is replaced with the fibular notch in which the distal end of the fibula fits. The medial border is most prominent on the medial aspect of the middle third of the of tibia.
At the distal end of the tibia, the bone has changed shaped from triangular in cross section to rectangular in cross section.
- The medial surface of the distal end features a bony extension called the medial malleolus. It articulates with the talus within the ankle joint.
- The posterior surface shows a vertical groove which is a passage for the tendon of the tibialis posterior muscle.
- The lateral surface and interosseous border of the distal end provides a facet for the distal end of fibula, called the fibular notch. The tibia and fibula are bound together at this spot by a thickening of interosseous membrane in the inferior/distal tibiofibular joint.
- The anterior surface is smooth and covered by the tendons of the extensor leg muscles. Its lower margin features a rough depression for the attachment of the articular capsule of the ankle joint.
Two major joint in which the tibia takes part are the knee joint and the ankle joint. The tibia also has additional articulations with the fibula where it is anchored to the fibula by the superior, middle, and inferior tibiofibular joints.
The knee joint is certainly something that deserves special attention. Its articular surfaces are the superior surfaces of lateral and medial condyles of the tibia, and the inferior surfaces of the lateral and medial condyles of the femur. At the distal end of the tibia is another major joint: the ankle joint. Here, the talus of the foot articulates with the distal ends of the tibia and fibula.
The tibia also has three articulations with the fibula. The superior/proximal tibiofibular joint is where the proximal end of tibia articulates with the head of the fibula. The articulation site on the tibia is found on the lateral side of its proximal part, while the fibula participates with the medial surface of its head. This joint is reinforced by the anterior and posterior ligaments of fibular head.
The middle tibiofibular joint is the interosseous membrane which spans between the shafts of the tibia and fibula, attaching to the interosseous margins of each bone. It is a sheet of fibrous tissue that joins the tibia and fibula in the tibiofibular syndesmosis.
The inferior/distal tibiofibular joint is formed by the fibular notch of the distal end of the tibia and triangular area of the distal end of the fibula. These articulation surfaces are anchored by extensions of the superior interosseous membrane, while the entire joint is supported by the anterior and posterior tibiofibular ligaments. All three of the tibiofibular joints join the two leg bones together.
The tibia is the site of attachment for many leg muscles. Roughly speaking, the lateral surface of the tibia provides attachment sites for the muscles of the anterior compartment of the leg, while the posterior surface provides attachment sites for the muscles of the posterior leg compartment. The muscles of the lateral leg compartment attach to the fibula.
Muscles that insert onto the tibia are the: sartorius, gracilis, quadriceps femoris, semimembranosus, semitendinosus, and popliteus muscles.
|Sartorius and gracilis||Medial surface of proximal tibia (via pes anserinus)|
|Quadriceps femoris||Tibial tuberosity (via patellar ligament)|
|Semimembranosus||Medial condyle of tibia|
|Semitendinosus||Proximal end of tibia below medial condyle of tibia (via pes anserinus)|
|Popliteus||Posterior surface of proximal tibia|
Muscles that originate from the tibia are the: tibialis anterior, extensor digitorum longus, soleus, tibialis posterior, and flexor digitorum longus muscles.
|Tibialis anterior||Lateral surface of tibia, Interosseous membrane|
|Extensor digitorum longus||Proximal half of medial surface of fibula, Lateral tibial condyle|
|Soleus||Soleal line, Head of fibula, Posterior border of fibula|
|Tibialis posterior||Posterior surface of tibia, Posterior surface of fibula, Interosseous membrane|
|Flexor digitorum longus||Posterior surface of tibia|
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The tibia is the most fractured long bone in humans. Its most vulnerable part is the tibial shaft and it generally takes a strong force to break this bone. This usually happens in car crashes and when falling from heights–since these are the most common traumatic injuries the tibia is the most fractured long bone. Various factors determine what kind of fracture will occur, but the most common types are:
- Transverse fracture - the fracture line is horizontal through the shaft
- Oblique fracture - the fracture line is angled through the shaft
- Spiral fracture - the fracture line is spiral resulting from twisting of the bone
- Comminuted fracture - the bone is broken into three or more pieces
- Open fracture - the broken parts of bone penetrate the surrounding skin and communicate with the environment (high risk of infections)
The symptoms that follow a tibial fracture include sharp and disabling pain when the bone is fractured followed with an inability to walk or move the limb because the tibia can no longer carry out its role of bearing body weight. Depending on the type of fracture, the lower limb can seem deformed or bone fragments can penetrate the skin.
Fractures are easily seen on an X-ray of the affected leg. Usual recovery procedures include immobilization of the limb by a casket or brace. Severe cases can undergo surgical treatment in which intramedullary titanium nails (a metal nail that is put into the medullary cavity of the bone) are used for putting the parts of the broken bone back in position. Tibial fractures will typically heal within four to six months after treatment, whether it is by immobilization of the affected limb or by surgery.