Structure
The proximal tibia is a broad block of cancellous bone formed by the medial and lateral condyles. Their upper surfaces, the tibial plateaus, carry the menisci and the femoral condyles. The medial plateau is larger, oval and slightly concave; the lateral is smaller, rounder and slightly convex.
Between the plateaus lies the intercondylar area, raised in the middle into the intercondylar eminence with its medial and lateral intercondylar tubercles, the 'tibial spines'. From front to back the area takes the anterior horn of the medial meniscus, the ACL, the anterior horn of the lateral meniscus, the posterior horns of the lateral then medial meniscus, and finally the PCL.
- Tibial tuberosity: the raised oblong on the front of the upper shaft for the patellar ligament.
- Gerdy's tubercle: a smooth facet on the front of the lateral condyle for the iliotibial tract.
- Medial surface: broad, flat and subcutaneous along the whole shaft.
- Posterior surface: crossed obliquely by the soleal line; above it lies a triangular area for popliteus.
- Fibular facet: on the underside of the lateral condyle, for the proximal tibiofibular joint.
The fibular head is the knob at the top of the fibula, with a pointed apex (styloid process). Below it the narrow fibular neck is wrapped by the common fibular nerve.
Attachments
The upper tibia and fibula anchor the tendons that stabilise the knee from each side.
| Structure | Attachment |
|---|---|
| Sartorius, gracilis, semitendinosus (pes anserinus) | Upper medial surface of the tibia, front to back in that order |
| Medial collateral ligament | Medial condyle and upper medial surface, deep to and behind the pes anserinus |
| Semimembranosus | Horizontal groove on the back of the medial condyle |
| Iliotibial tract | Gerdy's tubercle on the lateral condyle |
| Biceps femoris | Fibular head, its tendon split around the lateral collateral ligament |
| Lateral collateral ligament | Fibular head, in front of the apex |
| Popliteus | Posterior tibia above the soleal line |
| Soleus | Soleal line and medial border of the tibia; back of the fibular head and upper fibula |
| Patellar ligament | Tibial tuberosity |
Relations: compartments of the leg
Below the knee, the tibia, fibula, interosseous membrane and fascial septa divide the leg into four compartments, each with its own nerve.
| Compartment | Muscles | Nerve | Artery |
|---|---|---|---|
| Anterior | Tibialis anterior, extensor hallucis longus, extensor digitorum longus, fibularis tertius | Deep fibular | Anterior tibial |
| Lateral | Fibularis (peroneus) longus and brevis | Superficial fibular | Branches of the fibular and anterior tibial arteries |
| Superficial posterior | Gastrocnemius, soleus, plantaris | Tibial | Sural branches of the popliteal; posterior tibial |
| Deep posterior | Popliteus, flexor digitorum longus, flexor hallucis longus, tibialis posterior | Tibial | Posterior tibial and fibular |
The popliteal artery divides into anterior and posterior tibial arteries at the lower border of popliteus, just behind the upper tibia. The anterior tibial passes forwards above the interosseous membrane to reach the anterior compartment.
Clinical relevance
The subcutaneous position of the tibia and the exposed course of the common fibular nerve make this area a frequent site of injury.
- Fibular neck fracture: can injure the common fibular nerve, causing foot drop and numbness of the dorsum of the foot.
- Tibial plateau fracture: usually lateral, from a valgus force; the joint surface must be restored to prevent early arthritis.
- Compartment syndrome: most often in the anterior compartment after a tibial fracture. Pain out of proportion and pain on passive stretch are early signs; urgent fasciotomy decompresses all four compartments.
- Open tibial fracture: the medial surface lies directly under the skin, so shaft fractures are often open.
- Intraosseous access: the flat medial surface about a finger's breadth below and medial to the tibial tuberosity is a standard site.
- Pes anserine bursitis: pain over the upper medial tibia below the joint line, where the bursa separates the three tendons from the MCL.
- Osgood–Schlatter disease: traction apophysitis at the tibial tuberosity in adolescents.
On the specimen
The station combines the bones of the upper leg with the tendons that attach to them. Side the tibia by the tuberosity (front), the fibular facet (posterolateral, under the lateral condyle) and the soleal line (back). The tibial spines are the two points on the eminence between the plateaus.
On the medial side, the three pes anserinus tendons fan onto the upper tibia; sartorius is the most anterior and broadest, gracilis is in the middle and thin, and semitendinosus is the lowest and most posterior. On the lateral side, the thin cord of the LCL and the thick biceps tendon both reach the fibular head, and the iliotibial tract ends further forward on the tibia. The label 'popliteal surface' refers to the flat area on the back of the bone above the soleal line, beneath popliteus.