To assess the prognostic value of a characteristic evaluation of gait in persons suffering from hip OA for subsequent indications for THR.

Inclusion Criteria:

• Men or women aged between 45 and 75 years Suffering from primary hip osteoarthritis defined according to ACR criteria who presented pain in the hip for at least one month in the preceding 3 months Radiological stage II, III or IV hip OA according to the Kellgren and Lawrence classification Patients able to understand simple instructions des packaging instructions, to give their written informed consent.

Exclusion Criteria:

• Indication for THR at the time of inclusion. Pregnant or breast-feeding women Alzheimer's disease Chronic respiratory insufficiency with clinical manifestations Parkinson's disease Motor neuron disease Major musculo-skeletal disorder (other than hip OA) Severe non-stabilised diabetes Non-stabilised hypertension Hip OA inflammation flare Rapidly-destructive hip OA Radiography to evaluate structural evolution of the disease done more than 12 months previously Presence of OA in another joint, or another osteoarticular or periarticular disease of the lower limbs with, in the opinion of the patient, disability due to this other disease that is greater than the disability caused by the hip OA.

Spine disease causing gait disturbance (radiculalgia, lumbar canal stenosis,… with, in the opinion of the patient, disability due to this other disease that is greater than the disability caused by the hip OA.)