A proposal for a new classification of the fibular (lateral) collateral ligament based on morphological variations

The fibular collateral ligament (FCL) is subject to varus forces at all knee flexion angles and is also resistant to external rotation near extension. It originates on the lateral epicondyle of the femur and inserts on the lateral surface of the head of the fibula. However, its anatomical characteristics are inconsistent. Recent publications have focused on morphological variations concerning mainly femoral and fibular attachments, as well as morphometric measurements. Less attention has been paid to the morphology of the FCL and its relationship to the antero-lateral ligament (ALL).

The aim of this paper is therefore to introduce the first complete classification of the FCL that includes all important aspects of morphological variability.

Classical anatomical dissection was performed on 111 lower limbs (25 isolated and 86 paired) fixed in 10% formalin solution. The lateral compartment of the knee was investigated in detail.

The fibular collateral ligament was present in all specimens. The FCL originated most commonly (72.1% of cases) from the lateral femoral epicondyle, and the inserted on the lateral surface of the head of the fibula (Type I). In addition, bifurcated (Type IIa - 12.6%) and trifurcated (Type IIb - 0.9%) ligaments were also found with two and three distal bands, respectively. A double FCL was also found (Type III - 6.3%), as was fusion of the FCL and ALL (Type IV - 8.1%).

The FCL is characterized by high morphological variability. Knowledge of these variants is essential for surgeries performed in this region concerning the FCL and the ALL.

Distinguishing FCL from the FCL-ALL Complex is necessary when planning surgical procedures.