Summary Lateral epicondylitis of the elbow, commonly known as “tennis elbow,” is a painful, debilitating condition. It strikes the working-age population in particular and affects both men and women. In some job sectors, one in every five workers suffers from tennis elbow. The condition is associated with overuse of the wrist and forearm. Despite the advances of modern medicine, treatment of epicondylitis still often presents a considerable therapeutic challenge. A number of different treatment options are available. No treatment consensus or standard treatment protocol exists. The direct health care costs of tennis elbow and especially the indirect costs related to disability and workers’ compensation are still very high. The first line of treatment is to rest the elbow in accordance with ergonomic guidelines aimed at avoiding any demand on the epicondyle tendons. Physiotherapy and/or rehabilitation through a program of exercises to be done at home are also recommended. This approach leads to healing in over 80% of patients at 12 months. Nevertheless, some patients do not respond to medical treatment ranging from rest and rehabilitation to wearing a brace, extracorporeal shock wave treatment and injections of cortisone, platelet-rich plasma or other substances. These patients may remain symptomatic and continue to suffer from functional disability at work for many months, if not years. When other medical treatment options fail, surgery involving debridement and repair of the unhealthy tendon can be offered. There are a number of different surgical techniques, but the one most often used is to make a short incision in the skin to give access to the tendon and to resect a few millimetres of it to remove the pathological tissue. The skin is then sewn up and the tissue allowed to heal. With studies reporting therapeutic efficacy in the order of 70% to 80%, surgery is still regarded as the ultimate treatment option for epicondylitis. Ultrasound-guided tendon fenestration is a relatively new, minimally invasive procedure. After local anaesthesia of the skin, and with ultrasound guidance, a fine needle is used to make a number of controlled perforations in the damaged region of the tendon and to abrade the underlying surface of the bone. The purpose of this technique is to debride the unhealthy tissue and trigger an inflammatory reaction that will stimulate the physiological mechanisms of cell proliferation and tendon healing. A few studies assessing the technique’s therapeutic efficacy have reported encouraging results. No study has yet compared the efficacy of ultrasound-guided fenestration with that of surgery.- The main goal of our study was to assess the therapeutic efficacy of ultrasound-guided fenestration and that of open-release surgery on workers suffering from chronic epicondylitis who had not responded to at least six months of medical treatment. A further goal was to examine the impact of these two treatment options on various aspects of occupational activity, including grip strength, and on the morphological characteristics and mechanical properties of the tendon assessed by ultrasound. The hypothesis underlying the study was that ultrasound-guided fenestration is an effective, minimally invasive technique for the treatment of chronic epicondylitis and constitutes a viable therapeutic alternative to open-release surgery. The study was conducted at the Centre hospitalier de l’Université de Montréal from 2016 to 2020. Sixty-four workers suffering from chronic epicondylitis were divided into two equal treatment groups and were followed for 12 months. Periodically, the patients responded to questionnaires, their grip strength was measured using a dynamometer and their elbow was examined by ultrasound. No undesirable effects associated with the procedures occurred during the study. The mean age of the workers who took part was 48, with an equal number of men and women. The patients had been suffering from epicondylitis for 23 months, on average, and all of them had received medical treatment for at least six months before they joined the study. Most of the patients had tried several different types of treatment. Some of the most common treatment options were wearing a brace, physiotherapy, cortisone injections, and a program of exercises to be done at home. Aht the time of joining the study, 20% of the patients were off work, and 5% were assigned to light duties. With regard to their work, most of the patients reported having to perform one or more of the following activities: repetitive movements with the forearm; bending movements of the wrist; bending and extending of the elbow; light or heavy physical work; use of a computer keyboard or mouse. On the basis of various clinical indicators, the rate of therapeutic success among the patients treated by ultrasound-guided fenestration was comparable to that of patients treated surgically. In each treatment group, 80% of the patients said they were “much improved or completely recovered” six months after the procedure. In addition, the clinical improvement of the patients over time was comparable. The study results showed that patients treated by fenestration were able to return to work sooner than those treated by surgery. Open-release surgery requires a certain convalescence period to allow the incision and the tendon, which has been partially resected, to heal. Fenestration promotes healing of the tendon through inflammatory mechanisms. There is no incision in the skin. There is no resection of tissue. As a result, the tendon repair and remodelling seem to take place faster. Moreover, analysis of the imaging parameters suggests that fenestration impairs the structure of the tendon less and promotes faster improvement in the tendon’s mechanical properties than surgery does. In conclusion, ultrasound-guided fenestration is an effective, minimally invasive therapeutic technique for treating chronic epicondylitis of the elbow. In cases of epicondylitis that do not respond to treatment after six months, this option can be proposed. This therapeutic algorithm could lead to a reduction in direct and indirect costs related to tennis elbow. Our study has laid the foundations for future clinical trials that have greater statistical power and take a pragmatic approach to confirm the results and define the place of ultrasound-guided fenestration in the algorithm for treating epicondylitis of the elbow.