Radiographic indicators of ankle instability: changes with plantarflexion

The effect of plantarflexion on radiographic indicators of instability was investigated in matched pairs of stable ankles and unstable ankle fractures with complete deltoid ligament tears to test the hypothesis that differences exist in indicators as a function of either stability or position. The purpose of this study was to determine whether plantarflexion increases radiographic indicators of ankle fracture instability.

Measurements from 34 patients scheduled for operative treatment of unstable ankle fractures were collected prospectively from normal, stable ankles and the injured, unstable ankles. Instability was defined as a positive fluoroscopic stress examination under anesthesia. Stability and instability and neutral position and plantarflexion were associated with eight radiographic indicators of which five were distances in millimeters and three were binomial (either stable or unstable).

Measurements were larger in the unstable ankles than in the normal stable ankles. Plantarflexion was associated with increased distances in stable ankles, and a trend was seen in unstable ankles. Plantarflexion was associated with increased binomial indicators in unstable ankles but not in stable ankles.

Joint positioning affected measurement of ankle stability: plantarflexion increased the sensitivity of radiographic indicators.