Morphological features of the bifurcated ligament.

Damage to the bifurcate ligament is one of the most difficult injuries to diagnose from imaging techniques. A probable reason for this is that the morphological characteristics of this structure have yet to be sufficiently elucidated. We, therefore, endeavored to elucidate the morphological characteristics of the bifurcate ligament through a large-scale study involving numerous specimens. This study included 100 feet from 52 formalin-fixed cadavers. The bifurcate ligament was classified into three types: presence of both calcaneonavicular ligament and calcaneocuboid ligament (Type I); absence of calcaneocuboid ligament (Type II); and absence of calcaneonavicular ligament (Type III). Morphological characteristics of the bifurcate ligament were determined by measuring fiber bundle length, width, and thickness at the center of each ligament. This classification resulted in 68 Type I feet (68%), 32 Type II feet (32%), and 0 Type III feet (0%). The calcaneonavicular ligament was 20.8 ± 2.9 mm long, 4.9 ± 1.2 mm wide, and 3.8 ± 1.1 mm thick. The calcaneocuboid ligament was approximately 10.5 ± 2.7 mm long, 4.7 ± 2.4 mm wide, and 1.5 ± 0.6 mm thick. The bifurcate ligament was located deep under the extensor hallucis brevis and extensor digitorum brevis muscles in all specimens. The calcaneal origin of the calcaneonavicular ligament was situated deep under the interosseous talocalcaneal ligament in all specimens. Two sides were identified in which the calcaneocuboid ligament was located deep under the dorsal calcaneocuboid ligament. Such variations and positional relationships were suggested to be factors complicating the diagnostic imaging of bifurcate ligament injuries. The present study results will likely form useful basic data for diagnostic imaging.