Internal fixation of fracture dislocation of the navicular
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The navicular is the keystone of the medial longitudinal arch and forms part of a “ball and socket” arrangement with the head of the talus, termed by some as the coxa pedis. Together with the talus, three cuneiforms and the medial three rays, the navicular is a key component of the medial column of the foot with the lateral column comprising of the calcaneum, cuboid and the lateral two rays. Owing to its intimate relationships with its surrounding architecture, the navicular is rarely injured in isolation, especially in higher energy injuries.
The talonavicular joint, together with the calcaneo-cuboid joint, forms the transverse tarsal joint, crucial for effective gait – absorbing energy in heel strike and stiffening to aid in propulsion. The combination of these two joints is commonly referred to the Chopart joint. Acute, traumatic fractures of the navicular are relatively uncommon with an incidence of 1.7/100,000/year. In addition, the severity of injuries to the navicular lie on a spectrum dependent upon the amount and nature of the energy imparted across the bone. Injuries range from simple ligamentous avulsions associated with ankle sprains through to crush injuries not only involving the navicular but also the cuboid and have been comprehensively classified into five groups in a recent paper from the Sheffield Foot and Ankle Unit. These latter, high-energy injuries have been shown to correlate with significant long-term morbidity and adverse function especially in the multiply injured patient. Failure to restore the anatomic relationships of the bony components within both columns, together with their relative column length, can result in significant morbidity. Navicular fractures can be subtle and diagnosis is frequently delayed, either through inadequate imaging or the presence of other significant, distracting injuries in the multiply injured patient.
One final crucial element to navicular fractures lies in common with fractures of the talus, namely that the navicular has a poor vascular supply. The bone receives blood via radial vessels leaving the central area prone to avascular change. These radial vessels emirate from both the dorsalis pedis and posterior tibial arteries with an indirect supply through the tendon insertion of the posterior tibial tendon. This means that, with injury, the navicular is prone to avascular necrosis and collapse.
Author: Mark Davies FRCS (Tr & Orth)
Institution: The Northern General Hospital, Sheffield ,UK.