Comparison of the Efficacy, Tolerability and Safety of actiTENS to Those of Level 2 Analgesic Treatments.

Inclusion Criteria: * Adult \> or = 55 years. * Being monitored by a rheumatologist in private practice or in a hospital. * Presenting nociceptive pain: * chronic (for at least 3 months), * secondary to knee osteoarthritis confirmed by x-ray: stage 2 and over according to Kellgren and Lawrence. * Of moderate to severe intensity equal to or above 4 on a numerical scale of 0-10. * In a situation of analgesic therapy failure for level 1 analgesics: * paracetamol and NSAIDS, * Prescribed at therapeutic dose : 4 g/d of paracetamol and 1200 mg/d of ibuprofen or equivalent (analgesic dose), * For at least 2 weeks, * Requiring a level 2 prescription. * Affiliated to social security insurance. * Informed of the concept and agreeing to use the TENS as a non-medicinal analgesic treatment. * Capable of understanding how to use the TENS and the level 2 analgesic treatments. * Intellectually and physically able to participate in the study in the opinion of the investigator. * Owns a Smartphone to be able to download the actiTENS application. Exclusion Criteria: * Current or previous allergy to the actiTENS electrodes. * On-going or planned pregnancy and absence of effective contraception (except for menopausal women). * Neuropathic pain with a DN4 result \> 4/10 or with a positive response to one or more questions in the DN4 clinical examination. * Osteoarthritis flare. * Surgery planned in the following 6 months. * History of multiple operations on the knee concerned. * Medicinal or non-medicinal treatments which could influence the pathology being studied. * Modification of medicinal or non-medicinal treatments planned in the following 6 months. * Current participation in another study. * Presence of another painful condition which could perturb the evaluation. * Patient with an absolute contraindication to TENS or level 2 systemic analgesic treatments recommended for the treatment of chronic pain of moderate or severe intensity. * Patient unable to express his/her consent or deprived of liberty. * Patient with cognitive disorder or behaviour rendering him/her unsuitable to follow the instructions for this study. * Patient not affiliated to a social security system.