Functional instability of the ankle: differences in patterns of ankle and knee movement prior to and post landing in a single leg jump.

The aim of this study was to investigate motor control in subjects with functional instability of the ankle joint. This was achieved by analysing patterns of lower extremity motion prior to and immediately following landing during single leg jumping in subjects with functional instability of the ankle. Fourteen subjects with unilateral functional instability and 10 healthy control subjects performed single leg jumps from a 40 cm height whilst angular displacement of their ankle and knee joints were recorded. Subjects with functional instability demonstrated significantly greater ankle dorsiflexion over the period encompassing 10 ms pre landing to 20 ms post landing (p < 0.05). They also exhibited a significantly greater level of knee flexion than controls over the period from 20 ms pre landing to 60 ms post landing (p < 0.05). The timing of these significant differences leads us to conclude that they do not arise as a result of reflexively mediated peripheral events following landing.