A new dimension in the study of human functional joint instability

Functional joint instability is common after joint soft tissue injuries. We present in this report our pilot finding in a study of functional ankle instability. Although past studies have suggested multiple pathological factors for functional ankle instability, none of those factors has been confirmed in the past studies. More importantly, no known factor can provide an explanation for an ankle giving way phenomenon which is a key element in defining a functional ankle instability. In this pilot study, we tested five subjects with functional ankle instability using a dynamic ankle stretching device combined with nociceptive electrical stimulation. Three out of five subjects showed a drastic reaction in which they totally gave up their control of upright standing after their affected ankles were under the combined ankle stretch and nociceptive stimuli. Such drastic reaction was not observed in the same ankles under only the ankle stretch. There was no such drastic reaction in the unaffected ankle under either testing condition. This pilot finding indicates a possibility of a hyper-reactivity to unloading reaction in the ankles with functional ankle instability.