Fibula

Introduction

Introduction to the Fibula

The fibula is the slender lateral bone of the leg. It does not bear significant body weight but serves primarily for muscle attachment, contributes to the ankle mortise, and provides stability to the leg through the interosseous membrane and tibiofibular syndesmoses. Its proximal end, the head, articulates with the lateral condyle of the tibia. The distal end forms the lateral malleolus, which is the lateral prominence of the ankle and a critical component of ankle stability. The fibula is a common source of bone grafts and is frequently involved in fractures, particularly those associated with ankle injuries.

Study

1. General Features and Orientation

The fibula is a long, thin bone with an expanded proximal head, a triangular shaft, and an expanded distal lateral malleolus. It is oriented vertically and lies lateral to the tibia. It has three borders (anterior, interosseous, posterior) and three surfaces (medial, lateral, posterior). The interosseous membrane attaches along the interosseous border, connecting it to the tibia. The bone is almost entirely covered by muscles, except for the subcutaneous lateral malleolus and the fibular head region.

2. Proximal End

The proximal fibula consists of the head, neck, and styloid process (apex). The head is an irregular expansion with an oval articular facet that articulates with the fibular facet on the posteroinferior aspect of the lateral tibial condyle, forming the superior tibiofibular joint—a plane synovial joint. The styloid process projects upward from the posterolateral part of the head and provides attachment for the fibular collateral ligament of the knee and the biceps femoris tendon. The neck is the constricted part below the head, around which the common peroneal nerve winds from the popliteal fossa to the lateral compartment of the leg.

3. Shaft

The fibular shaft is variably shaped but typically has three borders and three surfaces. The anterior border runs from the head to the anterior margin of the lateral malleolus. The interosseous border lies medially and gives attachment to the interosseous membrane. The posterior border runs down to the lateral malleolar sulcus. The medial surface faces the tibia, the lateral surface is subcutaneous in its distal part, and the posterior surface is related to the flexor muscles. The nutrient foramen, directed distally, is usually found on the posterior surface of the proximal shaft and transmits a branch of the peroneal (fibular) artery.

4. Distal End – Lateral Malleolus

The distal fibula expands to form the lateral malleolus, which is the lateral prominence of the ankle. It extends more distally than the medial malleolus. Its medial surface bears a triangular articular facet covered with hyaline cartilage that articulates with the lateral surface of the talus. Posterior to the articular facet is the malleolar fossa, a rough depression for attachment of the posterior talofibular ligament. The lateral surface is subcutaneous and palpable. The anterior border provides attachment for the anterior talofibular ligament. The posterior aspect has a groove for the peroneus brevis and longus tendons. The tip of the lateral malleolus gives attachment to the calcaneofibular ligament. Above the malleolar fossa is the roughened area for the inferior tibiofibular syndesmosis, forming the fibular notch counterpart.

5. Ossification

The fibula ossifies from one primary centre, appearing in the eighth week of intrauterine life, and two secondary centres. The distal epiphysis appears during the second year; the proximal epiphysis appears around 4 years. The distal epiphysis fuses by 15–17 years, and the proximal epiphysis fuses at 16–18 years. The order of epiphyseal appearance and fusion is opposite to that of the tibia: the fibular distal end is the growing end that contributes more to length. The styloid process may have a separate small ossification centre.

6. Clinical Considerations

Fibular fractures are often associated with ankle injuries. The Weber classification of lateral malleolar fractures relates the fracture line to the syndesmosis: type A (below), type B (at the level), type C (above). Isolated fibular shaft fractures without syndesmosis disruption are often stable. A Maisonneuve fracture involves a proximal fibular fracture with disruption of the interosseous membrane and ankle syndesmosis. The common peroneal nerve is at risk in proximal fibular fractures and during surgical approaches to the fibular neck. The fibula is a common donor site for non‑vascularised bone grafts (proximal or mid‑shaft) without significant functional loss, as the tibia remains the weight‑bearing bone. The distal fibula is critical for ankle stability; malunion or shortening of the lateral malleolus can lead to ankle arthritis.

Summary

Summary of the Fibula

The fibula is a slender lateral leg bone providing muscle attachments and ankle stability. Its proximal head articulates with the tibia; its shaft bears the interosseous membrane; its distal lateral malleolus forms the lateral ankle mortise and is anchored by the lateral ligament complex. Ossification involves primary and secondary centres. Fractures are classified by Weber, and the common peroneal nerve is a critical relation. The bone is expendable for grafting due to tibial weight‑bearing.