Overview
The tibia is the medial long bone of the leg and the one that carries the load; the fibula, lateral and slender, contributes little. It articulates proximally with the femur (femorotibial joint), laterally with the head of the fibula and distally with the talus (tarsocrural joint). Its medial surface is subcutaneous along almost its whole length, which makes it easy to palpate and very prone to open wounds when it fractures.
Proximal end
- Medial and lateral condyles (condylus medialis et lateralis): almost flat articular surfaces that receive the femoral condyles through the menisci. Together they form the tibial plateau, which is not horizontal but slopes caudally.
- Intercondylar eminence (eminentia intercondylaris): central ridge with two tubercles. In front of it, in the cranial intercondylar area, the cranial cruciate ligament inserts; behind it, in the popliteal notch, the caudal cruciate ligament.
- Tibial tuberosity (tuberositas tibiae): cranial projection where the patellar ligament inserts; it continues distally as the tibial crest (margo cranialis).
- Extensor groove (sulcus extensorius): lateral notch through which the tendon of the long digital extensor passes.
- Fibular facet: small caudolateral surface that articulates with the head of the fibula.
Shaft
Triangular in its proximal third and cylindrical distally. On its caudal surface lie the popliteal line (linea poplitea), origin of the popliteus muscle and of the digital flexors, and the nutrient foramen. The interosseous space between tibia and fibula is closed by the interosseous membrane.
Distal end
- Tibial cochlea (cochlea tibiae): two sagittal grooves separated by a ridge that receive the trochlea of the talus and make the tarsocrural joint a hinge.
- Medial malleolus (malleolus medialis): medial projection, origin of the medial collateral ligament of the tarsus. The lateral malleolus belongs to the fibula.
Clinical relevance
- Cranial cruciate ligament rupture: the slope of the tibial plateau (tibial plateau angle) generates cranial tibial thrust; corrective osteotomies (TPLO, TTA) act on this end of the bone.
- Patellar luxation: tibial tuberosity transposition realigns the extensor mechanism.
- Fractures: common, often open because of the thin soft-tissue cover; the distal third is most often involved.
- Osteosarcoma: the proximal tibia is one of its classic sites in the pelvic limb.