Is there a relationship between the occurrence of frenular ligaments and the type of fibularis longus tendon insertion?

Purpose: The fibularis longus muscle (FLM) is located in the lateral compartment of the leg. Although the FLM presents high morphological variability, particularly the tendon, little is known of its insertion. Similarly, little information exists regarding the great diversity of the Frenular ligament. The main aim of the study was hence to characterize the morphology of the fibularis longus tendon (FLT) and its accessory bands, to classify it and to determine the incidence of frenular ligaments. I hypothesize that the presence of anterior/posterior frenular ligament can be closely correlated with a given type of fibularis longus tendon insertion.

Methods: Classical anatomical dissection was performed on 100 lower limbs (50 female, 50 male) fixed in 10% formalin solution. The morphology of the insertion of the FLT and of the frenular ligaments was evaluated.

Results: The FLM was present in all specimens. Three types of insertion were observed, the most common being Type I (49%): a single distal attachment in which the tendon inserts into the lateral tubercle of the base of the I metatarsal bone. The second most common type was Type II (40%): bifurcated distal attachment, the main tendon inserts into the lateral tubercle of the base of the I metatarsal bone. This group was divided into three subtypes (A-C), subtype (A) - the accessory band inserts into the medial cuneiform bone; subtype (B) - a strong, accessory band inserts into both the base of the I metatarsal bone and the medial cuneiform bone, including the first metatarsal-cuneiform joint; subtype (C) - the accessory band inserts into the first interosseus dorsalis muscle. The rarest type was Type III (9%), characterized by a single distal tendon, which fuses with other adjacent muscle tendons before insertion. The main tendon inserts into the lateral tubercle of the base of the I metatarsal bone; this group was divided into two subtypes (IIIA - fusion with the tibialis posterior tendon and IIIB - fusion with the adductor hallucis longus). The anterior frenular ligament was present in 49% of specimens, whereas the posterior frenular ligament joined the FLT to the long calcaneo-cuboid ligament and was present in 9%.

Conclusion: Both the fibularis longus tendon and frenular ligament present high morphological variability. The anterior frenular ligament is closely correlated with Type I of the proposed classification, while the posterior frenular ligament is associated with Type II b. Knowledge of particular types of insertion is essential for both clinicians and anatomists.

Level Of Evidence: - II basic science research.