Sonographic measurement of instability of the subtalar joint

A sonographic method of measuring instability of the subtalar joint was dev eloped. After defining reference points, we determined a sonographic fibulo -trochlear angle. This angle was measured in a neutral position and under a n inversion stress position. A ratio q representing the relationship betwee n the fibulo-trochlear angle measured in the neutral position and under str ess, was determined. The method was tested on volunteers with clinically an d radiologically stable subtalar joints and a control group with unstable s ubtalar joints. The stress radiograph using the Zwipp method was utilized f or radiologic correlation. A sonographic ratio q> 1.6 correlated with a rad iological unstable subtalar joint. The borderline zone in which there was a n overlap of stable and unstable subtalar joints was characterized by a q v alue of 1.2-1.6.A ratio q< 1.2 correlated with a stable subtalar joint.