Measurement of plantar pressure distribution during gait for diagnosis of functional lateral ankle instability

Abstract

INTRODUCTION:: Chronic functional instability of the lateral ankle may be difficult to distinguish from mechanical instability when radiological stress tests reveal only small ligamentous defects. For decision making whether to surgically reconstruct the ligaments or not, it can be helpful to use additional information on joint and foot function. Therefore, the aim of a prospective study of patients with longstanding chronic ankle instability was to demonstrate that the dynamic measurement of plantar pressure distribution can identify patients with functional ankle instability. [Table: see text] MATERIALS AND METHODS:: Sixty five patients (mean age 24 (4.6 years)) were included. After clinical examination and radiological stress views, plantar pressure patterns were measured during gait using a capacitive platform, the EMED-SF 2-system. Five trials of each foot were documented and the maximum impulses in eight points of the foot (central heel, lateral and medial heel, midfoot, 1st, 2nd, 5th metatarsal head and hallux) were calculated intraindividually and compared with a group of 100 healthy subjects. The medio-lateral loading factor (MLF) as the quotient of the medial and lateral relative impulses indicated the tendency to walk on the lateral edge of the foot. RESULTS:: Based on clinical criteria alone, two comparable groups of patients were separated, 35 with functional instability and 30 with mechanical instability. After collective analyses of the results, the patients with functional instability showed a significantly increased lateral loading of the unstable foot (p=0 0 1), whereas the mechanically unstable group tended to walk more on the medial side of the unstable foot (Table 1). DISCUSSION:: Dynamic measurement of plantar pressure can identify a group of patients walking on the lateral side of the unstable foot when compared with the stable foot. This finding is explained by a deficit of peroneal strength during stance phase based on a proprioceptive defect after trauma. The new application of the EMED-system provides additional information which helps to make decisions about the individual patient with chronic instability.