Ankle microinstability: arthroscopic findings reveal four types of lesion to the anterior talofibular ligament's superior fascicle.

PURPOSE: ATFL's superior fascicle injury has been considered to be the underlying cause in cases of ankle microinstability. As its clinical diagnosis can be difficult, arthroscopic examination may be the only objective diagnostic tool. The purpose of this study was to determine what types of injuries to the ATFL's superior fascicle are associated with ankle microinstability, and to provide the reader with an arthroscopic classification of the types of microinstability affecting the ankle.

METHODS

Ankle arthroscopy video records obtained during a four-year period from 232 patients with the diagnosis of ankle microinstability were reviewed. The characteristics of the ATFL's superior fascicle injury were identified, described and recorded along with any concomitant intra-articular pathology.

RESULTS

Four different injury patterns were consistently seen affecting the ATFL's superior fascicle. These ranged from ligament attenuation associated with loss of tension (type I), through to partial detachment (type II) or total detachment (type III) from the fibula. Finally, a total or partial resorption of the ATFL's superior fascicle (type IV) was also observed. There was a statistically significant association between the type of injury identified and the rate of intra-articular pathology observed arthroscopically. Equally, the higher the type in the classification, the higher the rate of loose bodies, lateral talar OCD, deltoid "open book" tears, and anterior soft-tissue formation.

CONCLUSION

Different types of ATFL's superior fascicle injury can be observed in patients with ankle microinstability, ranging from ligament attenuation associated with a loss of tension (8.2%) to different degrees of partial (69.1%) and total (16.8%) ligament detachment from the fibula, or ligament remnant resorption (5.9%). As the type of injury progresses along with the proposed classification, the rate of intra-articular injuries also increases. The clinical relevance of this study is that a morphological ATFL's superior fascicle tear is recognized in patients with the diagnosis of ankle microinstability.

LEVEL OF EVIDENCE: IV.