Dynamic pedography for assessing functional ankle joint instability

Abstract

Chronic functional instability of the lateral ankle may be difficult to distinguish from mechanical instability when radiological stress test reveal only small ligamentous defects. When a decision for or against surgical reconstruction of the ligaments has to be made it can be helpful to use additional information on joint function. Therefore, a prospective study of 65 patients (mean age 24.1 +/- 4.6 years) with long-standing chronic ankle instability was conducted to demonstrate that the dynamic measurement of plantar pressure distribution can identify patients with functional ankle instability. Plantar pressure patterns were measured during gait by means of a capacitive platform, the EMED-SF system. The impulses at eight points of the foot were calculated intraindividually and compared with those in a group of 100 healthy subjects. On the basis of clinical criteria alone, the two groups of patients were distinguished, 35 with functional instability and 30 with mechanical instability. The patients with functional instability showed significantly increased lateral loading of the unstable foot (P = 0.01), whereas the group with mechanical instability tended to walk more on the medial side of the unstable foot. This finding is explained by a deficit or peroneal strength during the stance phase, based on a proprioceptive deficit after trauma. The new technique provides additional information, which is relevant and sufficiently important to help in making decisions about the individual patient with chronic instability.