Anatomical variations of the tibialis anterior tendon.

INTRODUCTION: The tibialis anterior muscle originates from the medial part of the anterior compartment, from the upper two-thirds of the lateral surface of the tibia and the adjacent part of the interosseous membrane, and typically inserts to the medial cuneiform and first metatarsal bone. The goal of the study was to examine the insertion of the tibialis anterior tendon and create a classification in human fetuses. MATERIALS AND METHODS: Fifty spontaneously-aborted human fetuses (26 male, 24 female, 100 lower limbs), aged 18-38 weeks of gestation at death were examined. RESULTS: The classification comprised five types of tibialis anterior tendon insertion. The most common was Type V (60%), which was characterized by a single tendon inserting onto the medial cuneiform bone. The second most frequent was Type I (19%), which was characterized by a tendon which split into two equal-sized parts that insert to the medial cuneiform bone and the base of the first metatarsal. The third was Type II (12%), which was characterized by a tendon splitting into two different-sized parts that inserted onto the medial cuneiform bone (larger component) and the base of the first metatarsal (smaller component). The fourth type was Type III (5%), which was also characterized by a tendon splitting into two different-sized parts that inserted onto the medial cuneiform bone (smaller component) and the base of the first metatarsal (larger component). Finally, Type VI (4%), the least frequent type, was characterized by a tendon splitting into three different-sized parts, inserting onto the medial cuneiform bone (the smallest component) and the base of the first metatarsal (the middle and larger component). CONCLUSION: The tibialis anterior muscle is characterized by high variability in the approach of its tendon to the foot, at least in fetuses. This is classified in the present study for the first time.