Calf Bone
Fibula
location_on Lateral leg, running parallel to the tibia from knee to ankle
The fibula is the slender bone on the lateral side of the leg that bears almost no body weight (less than 10%) but serves critical roles in muscle attachment, ankle stability, and as a source of vascularized bone graft. The distal end forms the lateral malleolus, which extends further distally than the medial malleolus, providing the primary bony restraint against ankle eversion. The common peroneal nerve wraps around the fibular neck and is vulnerable to injury.
Key Anatomical Features
- Head is the proximal expansion that articulates with the lateral tibial condyle
- Neck is the narrowest part just below the head where the common peroneal nerve wraps around
- Lateral malleolus extends further distally than the medial malleolus, forming the lateral ankle
- Interosseous border faces medially for the interosseous membrane
- The fibula bears less than 10% of body weight and primarily serves for muscle attachment
Muscle Attachments
| Muscle | Attachment | Action |
|---|---|---|
| Biceps femoris | Head of fibula | Flexes the knee and laterally rotates the leg |
| Peroneus (fibularis) longus | Head and upper two-thirds of lateral shaft | Everts the foot and plantarflexes the ankle |
| Peroneus (fibularis) brevis | Lower two-thirds of lateral shaft | Everts the foot and plantarflexes the ankle |
| Extensor digitorum longus | Anterior shaft and interosseous membrane | Extends the lateral four toes and dorsiflexes the ankle |
| Soleus | Posterior head and proximal shaft | Plantarflexes the ankle |
| Flexor hallucis longus | Lower posterior shaft | Flexes the great toe |
Joints and Articulations
| Joint | Type | Connects to |
|---|---|---|
| Proximal tibiofibular joint | Synovial plane | Lateral tibial condyle |
| Distal tibiofibular joint (syndesmosis) | Fibrous syndesmosis | Distal tibia |
| Ankle (talocrural) joint | Synovial hinge | Talus (lateral malleolus contribution) |
Common Pathologies
Lateral malleolus fracture
The most common ankle fracture, classified by the Weber system (A: below syndesmosis, B: at syndesmosis, C: above syndesmosis). Weber C fractures indicate syndesmosis disruption and are most unstable.
Common peroneal nerve palsy
Compression or injury of the nerve as it wraps around the fibular neck, causing foot drop (inability to dorsiflex the foot) and sensory loss over the dorsum of the foot.
Maisonneuve fracture
Spiral fracture of the proximal fibula associated with disruption of the interosseous membrane and deltoid ligament, indicating an unstable ankle injury. The ankle injury is often missed if the proximal fibula is not examined.
Fibular stress fracture
Overuse fracture typically in the distal fibula, common in runners and military recruits.
Clinical Relevance
Always examine the proximal fibula in ankle injuries; tenderness here may indicate a Maisonneuve fracture with a high fibular fracture and complete disruption of the interosseous membrane and ankle mortise. The common peroneal nerve is the most commonly injured nerve in the lower limb; it should be assessed (dorsiflexion and eversion) after any fibular neck fracture or cast/splint application. The fibula is the most commonly used bone for vascularized free bone grafts because it can be harvested with its blood supply while maintaining lower limb function.
Development and Ossification
The fibula ossifies from three centers: one for the shaft (8th fetal week), one for the distal end (around age 2, the first long bone distal epiphysis to appear), and one for the proximal end (around age 4). The distal epiphysis fuses around age 15-17 and the proximal around age 17-19.
Did You Know?
- Fibula means clasp or brooch in Latin, as the bone resembles the pin of an ancient brooch (with the tibia being the bar)
- The fibula can be surgically removed and used as a bone graft elsewhere in the body without significant loss of leg function
- Despite bearing almost no weight, the fibula is essential for ankle stability through the lateral malleolus
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