• Residual ankle instability evaluated using the Cumberland Ankle Instability Tool (CAIT) [ Time Frame: at one year ] [ Designated as safety issue: Yes ]
  

• Lower Extremity Functional Squale (LEFS) Score [ Time Frame: at one year ] [ Designated as safety issue: Yes ]
  
• Lower Extremity Functional Squale (LEFS) Score [ Time Frame: at two years ] [ Designated as safety issue: Yes ]
  
• Baecke Physical Activity Questionnaire Score [ Time Frame: at the clinical examination ] [ Designated as safety issue: No ]
  
• Cumberland Ankle Instability Tool (CAIT) Score [ Time Frame: at two years ] [ Designated as safety issue: Yes ]
  
• Number of lesions in the group echography/stress radiography versus in the group echography. [ Time Frame: at the clinical examination ] [ Designated as safety issue: Yes ]
  

The lateral ankle sprain is the most frequent purpose of consultation in emergency traumatology of the locomotive system.

If the ankle sprain is neglected or badly cared, it can induce a recurrence or several complications particularly functional ones. So a gravity diagnosis is necessary in order to choose the most accurate treatment.

Considering the difficulty of the clinical estimation, additional examinations aim to support the positive diagnosis, to clarify the gravity and to dismiss differential diagnosis.

Thus we suggest to evaluate three strategies in order to get a gravity diagnosis, make a better choice of treatment and so decrease the long-term functional complications : instability and recurrence.

The patients are randomly separated into three groups of 130 people. All the patients have a radiography and then, according to their group, they have either an ultrasonography or an ultrasonography and a stress radiography or only a stress radiography. The patients are followed up during two years by sending two questionnaires (CAIT and LEFS) at one and two years. The functional scores of these questionnaires assess and compare the functional complications for each group. Thus the radiologic examinations can be assessed in term of prognosis.

Inclusion Criteria:

• Lateral ankle sprain.
• Sprain occurred for less than 48 hours.
• Age between 18 and 55.
• Person affiliated at the Social Security.

Exclusion Criteria:

• Recurrent lateral ankle sprain occurred for less than 2 years and diagnosed by a doctor.
• Bilateral sprain, medio-tarsal sprain, syndesmosis sprain, subtalar sprain.
• Tendinous luxation (fibular, posterior tibial).
• Homolateral ankle fracture occurred for less than 2 years.
• Cuboid fracture, external tubercle of astragalus fracture, calcaneum fracture, fracture of the talus extremity, base of the fifth metatarsal bone fracture.
• Tearing of internal malleolus, tearing of astragalus posterior tubercle.
• Osteochondral lesions of the astragalus dome.
• Probable difficulty to follow up the patient.
• Patient taking anticoagulant.
• Accident at work.
• Pregnant woman, parturient, breast-feeding mother.
• Person deprived of freedom after a judicial or an administrative decision, person with legal protection measure.