Talonavicular ligament: prevalence of injury in ankle sprains, histological analysis and hypothesis of its biomechanical function.

OBJECTIVE: To assess the prevalence of injury of the talonavicular ligament (TNL) in ankle sprains, its anatomy and the stability of the talonavicular joint (TNJ) before and after dividing the TNL in a cadaver.

METHODS: During a prospective study of 100 patients to assess the outcome of ankle injuries, we noted high incidence of TNL injuries; we will discuss here the TNL findings. Each patient had undergone ultrasound and cone beam CT examination of the ankle. Six TNLs were dissected off fresh-frozen cadaveric feet for histological analysis. In further six cadaveric feet, the stability of the TNJ was assessed by mechanical stress before and after division of the TNL; movement at the joint was assessed by measuring the distance between the talus and navicular bone [talonavicular distance (TD)] using ultrasound. The TD was measured on ten randomly selected ultrasound images by three independent observers and repeated twice by a single observer to determine the inter- and intraobserver reliability.

RESULTS: 21% of the patients had an injury to the TNL. Histological examination demonstrated a dense connective tissue composed of bundles of collagen in parallel arrangement along the ligament length. The interobserver and intraobserver reliability of the TD showed almost perfect agreement. Displacement at the TNJ after stress with the TNL intact measured 0.18 ± 0.08 cm and 0.29 ± 0.07 cm (p < 0.005) when divided.

CONCLUSION: The TNL is surprisingly commonly injured in ankle sprains. Its anatomy and histology suggest a role in tensile force transmission during the windlass mechanism in gait. Advances in knowledge: Injury to the TNL is common and has not been described. Its anatomy suggests resistance to tensile forces and its injury allows excessive movement at the TNJ.