[The metatarsophalangeal articulation and the transverse metatarsal ligament: anatomical observations].

The authors conducted a macroscopic anatomical study of the metatarsophalangeal joints of the middle toes in order to add to our knowledge of the anatomy and physiology of this structure. Anatomical observations reveal the foot's lack of transverse ligamentous formations (as the sagittal bundle in the hand) connecting the extensor tendon to the glenoid plate. Consequently, the containment of the extensor tendon above the metatarsophalangeal joint is considerably less stable in the foot than in the hand, since it is entrusted to the posterior portion of the interossei muscles and the deep and superficial retinacula (all formations which run in a prevalently oblique direction). Hyperextension of the metatarsophalangeal joint causes the posterior portion of the interossei muscles, bound to the extensor tendon, to slide proximally, straightening the fibers and loosening the structures that stabilize the extensor tendon. The tendon can then easily shift in a lateral direction with respect to the rotation axis of the metatarsophalangeal joint, acquiring a valgus action. Even though the metatarsophalangeal joint is equipped with strong collateral ligaments, the valgus action of the extensor tendon eventually overcomes the resistance of both these and the weaker connections to the plantar aponeurosis of the foot and the extensor tendons. In conclusion, the lack of structures to provide passive stabilization of the extensor tendon in the metatarsophalangeal joints of the toes makes the foot particularly susceptible to multiple-toe deformity.