Venous Malformations as a Rare Cause of Knee Joint Pain in Children and Young Adults: Clinical and Radiological Manifestations

<b>Background</b>: Venous malformations (VMs) are congenital vascular abnormalities characterized by tortuosity, slow blood flow, and gradual growth. Intra-articular venous malformations (IAVMs) of the knee are rare and often present with symptoms similar to juvenile idiopathic arthritis (JIA) or late sequelae of trauma. VM in children is commonly misdiagnosed as hemangioma. This study aims to analyze the clinical and MRI features of IAVM in the knee joint. <b>Methods</b>: This retrospective study analyzed patients from a reference unit for the treatment of vascular malformations in the Pediatric Surgery Department. The group was collected starting from the year 2014 until the 100th patient was identified in the year 2018, all with MRI-confirmed VM based on a predefined protocol. From this group, 19 patients with lower limb symptoms were identified, and 9 patients with VM involving the knee joint were selected for further analysis. <b>Results</b>: The most common symptoms in IAVM patients were pain and swelling, chronic in five (55%) and intermittent in four (45%). Four (45%) reported worsening pain during or after physical activity. A history of intra-articular bleeding was noted in five (55%), leading to mild knee contracture (10° reduction in extension) and decreased mobility. Limb deformities were observed in eight (89%). Diffuse VMs, affecting both intra- and extra-articular tissues, were present in eight (89%), involving the thigh in seven (78%), crus in five (56%), gluteal muscles in three (33%), and foot tissues in one (11%). The suprapatellar recess and Hoffa's fat pad were involved in all patients (100%). <b>Conclusions</b>: IAVMs are rare causes of knee dysfunction in children and young adults, particularly in cases of unexplained pain, swelling, or instability. They should be considered in the differential diagnosis of hemophilic arthropathy, JIA, or late post-traumatic sequelae. Untreated IAVMs can lead to intra-articular bleeding, cartilage degeneration, and disability. Early diagnosis via MRI and ultrasound is crucial to identifying IAVMs and preventing joint degeneration. Timely treatment helps avoid further damage and long-term disability.