Fractures of the proximal fibula rarely occur in isolation and their significance lies more with this fracture's association with injuries to the ligamentous and neurovascular structures than with the boney injury.
The proximal fibula lies in close association with multiple significant ligamentous and neurovascular structures. The proximal fibula is the insertion point for the biceps femoris posterolaterally, the soleus posteriorly, and the peroneus longus and extensor digitorum longus anteiorly. Additionally, lateral collateral ligament of the knee originates from the lateral epicondlye of the femur to insert on the superior portion of the fibular head and is the major restraint to varus forces on the knee at zero and thirty degrees of flexion. The interosseous membrane between the tibia and fibula runs the length of these bones and originates in the proximal tibia and fibula. This membrane is important in its relationship in transmitting rotational forces from the ankle to the proximal fibula in certain types of ankle injuries.
Classification of these fractures is descriptive and includes description of the location and dominant fracture pattern.
Presentation of these injuries is quite variable and will depend on the amount of energy imparted to the leg and the extent of associated fracture, ligamentous injury or neurovascular injury. There will generally be edema and tenderness to palpation directly over the proximal fibula, however, if there may not be obvious deformity of the leg if the tibia is intact. There may be effusion or hemarthrosis if intra-articular structures of the knee are injured. Often there will be an antalgic gait or inability to bear weight.
Diagnosis of these injuries requires thorough history and physical exam. History should attempt to ascertain the mechanism of injury. This information may give clues to associated injury. Regardless of the mechanism, a detailed ligamentous knee exam and neurovascular exam of the lower extremity should be performed. In blunt trauma, thorough examination of the entire extremity is necessary as these injuries rarely occur in isolation. Instability of the knee may be a sign of avulsion of the LCL, posterolateral corner injury or occult knee dislocation. Deformity or tenderness to palpation at the isilateral ankle should be sought as this may indicate a Maisonneuve injury. These injuries result from an external rotation force applied to the ankle in which the force of the injury propagates along the intraosseous membrane to exit the proximal fibula resulting in proximal fibula fracture. These fractures oft indicate syndesmotic injury and may be the only boney deformity present. Associated pain along the medial malleolus in this setting is a sign of medial malleolus fracuture or deltoid ligament injury.
Radiographic assessment should include AP, lateral and oblique views of the knee and AP, lateral and mortise views of the ankle. AP and lateral views of the tibia and fibula shaft are also needed to asses the entire length of the leg. MRI is appropriate if knee instability is detected or suspected. There should be a low threshold for ateriography or CT angiography if soft findings of vascular injury are noted or occult knee dislocation is suspected.
Treatment of these fractures is dictated by the associated ligamentous or neurovascular injury. Most injuries may be treated symptomatically in a hinged knee brace and appropriate pain control. Early knee motion should be encouraged.
The proximal fibula fracture in a Maisonneuve injury does not require stabilization. However, the intraossesous and/or syndesmotic injury may require fixation near the ankle if the distal tibiofilular joint is unstable. Closed reduction and casting is an additional treatment option.
Open reduction and internal fixation may be indicated acutely for boney avulsions of the LCL. Repair of associated posterolateral corner injuires to the knee can be stabilized at the same time.
Peroneal nerve injury - Often the result of direct contusion and has a variable prognosis.
Vascular injury - Popliteal artery injury can result from occult knee dislocation in which a proximal fibula fracture is present on radiographs.
Nonunion/malunion - may lead to varus knee instability if the LCL insertion is involved.
Compartment syndrome - compartment syndrome monitoring should accompany high energy injuries.
Red Flags and controversies
Excellent outcomes have been reported for Maisonneuve injuries for both open reduction an internal fixation for injuries with unstable syndesmosis and intraosseous ligment injuries and for casting of stable injuries. The proximal fibula fracture was not treated in these cases.