Tibia

Tibia

Also known as: shinbone, shin bone, tibial plateau, medial malleolus, tibial tuberosity

The large, medial, weight-bearing bone of the leg (the second longest bone), articulating with the femur at the knee and the talus at the ankle. Its anteromedial surface is subcutaneous along its whole length.

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Overview

Length≈36–40 cm

Share of axial load in the leg≈85–90%

Proximal end: expanded into medial and lateral condyles whose upper surfaces form the tibial plateau (superior articular surfaces) for the femoral condyles and menisci. Between them, the intercondylar eminence with medial and lateral intercondylar tubercles separates the anterior and posterior intercondylar areas (attachments of the ACL anteriorly, PCL posteriorly and the horns of the menisci). The lateral condyle bears a facet for the head of the fibula (proximal tibiofibular joint) and, anteriorly, Gerdy's tubercle (iliotibial tract). The tibial tuberosity below the condyles receives the patellar ligament.

Shaft: triangular in section with a sharp anterior border (the shin) and a subcutaneous medial surface; the interosseous border faces the fibula. Posteriorly, the oblique soleal line marks the origin of soleus; the nutrient foramen below it is one of the largest in the skeleton.

Distal end: the medial malleolus projects downward on the medial side (deltoid ligament); the inferior articular surface with the malleolus forms the medial part of the ankle mortise for the talus. The fibular notch laterally receives the fibula at the distal tibiofibular syndesmosis. Behind the medial malleolus a groove carries the tendon of tibialis posterior ("Tom, Dick And Very Nervous Harry" order of structures).

Location: Medial bone of the leg, from knee to ankle.

Parts & subdivisions

Medial and lateral condyles (tibial plateau)
Articulate with the femoral condyles via the menisci.
Intercondylar eminence
Separates anterior (ACL, meniscal horns) and posterior (PCL) intercondylar areas.
Tibial tuberosity
Insertion of the patellar ligament (quadriceps).
Gerdy’s tubercle
Insertion of the iliotibial tract.
Anterior border and medial surface
Subcutaneous "shin".
Soleal line
Origin of soleus; popliteus inserts above it.
Medial malleolus
Medial ankle prominence; deltoid ligament.
Fibular notch
Distal tibiofibular syndesmosis.

Anatomy

Arterial supply: Nutrient artery from the posterior tibial artery; genicular and malleolar anastomoses at the ends.
Articulations: Femur (knee), fibula (proximal and distal tibiofibular joints), talus (ankle).
Ossification: Primary centre ≈week 7. Proximal epiphysis appears ≈36 weeks’ gestation/birth and is the growing end (fuses ≈16–20 years); distal epiphysis ≈1 year (fuses ≈15–18 years); tibial tuberosity has its own tongue-like apophysis (≈10–13 years).

Function

Transmits body weight from the femur to the talus (≈85–90% of leg load)
Forms the lower surface of the knee joint and the roof and medial side of the ankle mortise
Attachment for quadriceps (via patellar ligament), hamstrings (pes anserinus), soleus, tibialis anterior and posterior

Clinical significance

Open tibial fracture

The commonest long-bone open fracture because the anteromedial surface lies directly under the skin; poor soft-tissue cover in the distal third slows healing; risk of compartment syndrome (pain out of proportion, pain on passive stretch).

Osgood–Schlatter disease

Traction apophysitis of the tibial tuberosity in active adolescents: painful swelling below the knee, worse with kneeling and jumping; self-limiting.

Tibial plateau fracture

Typically the lateral plateau from a valgus force (car bumper — "bumper fracture"); associated MCL and meniscal injuries.

Intraosseous access

The flat anteromedial surface 1–2 cm below the tibial tuberosity is the standard site for emergency intraosseous infusion in children.

Test yourself

A footballer is struck on the lateral side of the knee while his foot is planted. Which combination makes up the classic "unhappy triad"?

PCL, fibular collateral ligament and lateral meniscus
ACL, PCL and patellar ligament
Tibial collateral ligament, patella and lateral meniscus
ACL, tibial collateral ligament and medial meniscus

Answer: ACL, tibial collateral ligament and medial meniscus

A valgus blow with rotation tears the tibial collateral (MCL) ligament, the ACL and the medial meniscus — the medial meniscus being attached to the deep MCL. (MRI studies show the lateral meniscus is often injured in acute ACL tears, but the classic triad remains a high-yield exam answer.)

Why is the medial meniscus injured more often than the lateral meniscus?

It is attached to the tibial collateral ligament and joint capsule, making it less mobile
It is avascular throughout
It is attached to the popliteus tendon, which tears it during flexion
It is thinner and O-shaped

Answer: It is attached to the tibial collateral ligament and joint capsule, making it less mobile

The C-shaped medial meniscus is firmly attached to the capsule and the deep fibres of the tibial collateral ligament, so it cannot move out of the way of the femoral condyle during twisting. The lateral meniscus is more mobile, being separated from the fibular collateral ligament by the popliteus tendon.