Minimally invasive procedures play a crucial role in the diagnosis and treatment of many pediatric musculoskeletal conditions. Although computed tomography and fluoroscopy are commonly used for image guidance, the associated exposure to ionizing radiation is especially concerning in pediatric patients. Ultrasonography may be used successfully in a subset of interventions, but it is often not useful for complex, deep, and osseous targets. Interventional magnetic resonance imaging (iMRI) facilitates targeting and treatment of musculoskeletal lesions at many locations with high accuracy due to its excellent tissue contrast. Furthermore, MRI provides imaging guidance without the use of ionizing radiation and as such complies with the ALARA practice mandate in a formidable fashion. MRI guidance is our method of choice for lesion that are not visible by other modalities or when other techniques and modalities failed. MRI guidance is especially useful for selective targeting of complex lesions, intra-articular lesions, cyst aspirations in difficult locations of the body, and lesions that are located adjacent to surgical hardware. Tumor-related diagnostic sampling is more frequently performed under MRI; however, MRI guidance is also exquisitely well suited for a variety of therapeutic percutaneous osseous or articular conditions, such as osteoid osteoma, epiphyseal bone bridging, osteochondritis dissecans lesions, and aneurysmal bone cysts. In this article, we will describe the technical aspects and clinical indications of a variety of MRI-guided pediatric procedures in the musculoskeletal system.

IntroductionThe forearm is the most common fracture location in children, with an increasing incidence. Displaced forearm shaft fractures have traditionally been treated with closed reduction and cast immobilisation. Diaphyseal fractures in children have poor remodelling capacity. Malunion can cause permanent cosmetic and functional disability. Internal fixation with flexible intramedullary nails has gained increasing popularity, without evidence of a better outcome compared with closed reduction and cast immobilisation.Method and analysisThis is a multicentre, randomised superiority trial comparing closed reduction and cast immobilisation to flexible intramedullary nails in children aged 7–12 years with >10° of angulation and/or >10 mm of shortening in displaced both bone forearm shaft fractures (AO-paediatric classification: 22D/2.1–5.2). A total of 78 patients with minimum 2 years of expected growth left are randomised in 1:1 ratio to either treatment group. The study has a parallel non-randomised patient preference arm. Both treatments are performed under general anaesthesia. In the cast group a long arm cast is applied for 6 weeks. The flexible intramedullary nail group is immobilised in a collar and cuff sling for 4 weeks. Data are collected at baseline and at each follow-up until 1 year.Primary outcome is (1) PROMIS paediatric upper extremity and (2) forearm pronation-supination range of motion at 1-year follow-up. Secondary outcomes are Quick DASH, Paediatric Pain Questionnaire, Cosmetic Visual Analogue Scale, wrist and elbow range of motion as well as any complications and costs of treatment.We hypothesise that flexible intramedullary nailing results in a superior outcome.Ethics and disseminationWe have received ethical board approval (number: 78/1801/2020) and permissions to conduct the study from all five participating university hospitals. Informed consent is obtained from the parent(s). Results will be disseminated in peer-reviewed publications.Trial registration numberNCT04664517.