Magnetic resonance (MR) imaging is currently the modality of choice for detecting meniscal injuries and planning subsequent treatment. A thorough understanding of the imaging protocols, normal meniscal anatomy, surrounding anatomic structures, and anatomic variants and pitfalls is critical to ensure diagnostic accuracy and prevent unnecessary surgery. High-spatial-resolution imaging of the meniscus can be performed using fast spin-echo and three-dimensional MR imaging sequences. Normal anatomic structures that can mimic a tear include the meniscal ligament, meniscofemoral ligaments, popliteomeniscal fascicles, and meniscomeniscal ligament. Anatomic variants and pitfalls that can mimic a tear include discoid meniscus, meniscal flounce, a meniscal ossicle, and chondrocalcinosis. When a meniscal tear is identified, accurate description and classification of the tear pattern can guide the referring clinician in patient education and surgical planning. For example, longitudinal tears are often amenable to repair, whereas horizontal and radial tears may require partial meniscectomy. Tear patterns include horizontal, longitudinal, radial, root, complex, displaced, and bucket-handle tears. Occasionally, meniscal tears can be difficult to detect at imaging; however, secondary indirect signs, such as a parameniscal cyst, meniscal extrusion, or linear subchondral bone marrow edema, should increase the radiologist's suspicion for an underlying tear. Awareness of common diagnostic errors can ensure accurate diagnosis of meniscal tears. Online supplemental material is available for this article.

The bone marrow is one of the largest organs in the body and is visible in every magnetic resonance (MR) imaging study. It is composed of a combination of hematopoietic red marrow and fatty yellow marrow, and its composition changes throughout life in response to normal maturation (red to yellow conversion) and stress (yellow to red reconversion). MR imaging is highly sensitive for detection of altered marrow signal intensity, and the T1-weighted spin-echo sequence provides the most robust contrast between yellow marrow and disease. Heterogeneous red marrow and red marrow hyperplasia can mimic marrow disease, but should be distinguished from neoplastic replacement (leukemia, lymphoma, primary bone sarcomas, hematogenous metastases) and expected posttreatment changes (radiation therapy, chemotherapy, colony-stimulating factor, bone marrow transplant). Nonneoplastic edema-like processes can also alter marrow signal intensity, including trauma, infection, inflammation (chronic recurrent multifocal osteomyelitis, juvenile inflammatory arthritis), altered biomechanics, and chronic regional pain syndrome. Unfortunately, MR imaging findings are often nonspecific and overlap among many of these vastly different causes. Therefore, a definitive diagnosis is reliant on a combination of imaging findings, clinical evaluation, laboratory assessment, and occasionally tissue analysis. RSNA, 2016.

The growth plates, or physes, are visible on virtually all images obtained in skeletally immature children. The proper function of these growth plates depends on an intricate balance between chondrocyte proliferation, which requires nourishment from the epiphyseal vessels, and chondrocyte death, which requires the integrity of the metaphyseal vessels. Therefore, injury to the growth plate (ie, direct insult) or vascular compromise on either side of the growth plate (ie, indirect insult) can cause growth plate dysfunction. Direct growth plate insults occur most commonly with Salter-Harris fractures, and injuries that allow the transphyseal communication of vessels are at a higher risk for subsequent transphyseal bone bridge formation. Indirect insults lead to different sequelae that are based on whether the epiphyseal blood supply or metaphyseal blood supply is compromised. Epiphyseal osteonecrosis can result in slowed longitudinal bone growth, with possible growth plate closure, and is often accompanied by an abnormal secondary ossification center. In contrast, the disruption of metaphyseal blood supply alters endochondral ossification and allows the persistence of chondrocytes within the metaphysis, which appear as focal or diffuse growth plate widening. Imaging remains critical for detecting acute injuries and identifying subsequent growth disturbances. Depending on the imaging findings and patient factors, these growth disturbances may be amenable to conservative or surgical treatment. Therefore, an understanding of the anatomy and physiologic features of the normal growth plate and the associated pathophysiologic conditions can increase diagnostic accuracy, enable radiologists to anticipate future growth disturbances, and ensure optimal imaging, with the ultimate goal of timely and appropriate intervention. RSNA, 2017.

AI improves radiologist's bone age assessment by increasing accuracy and decreasing variability and RMSE. The utilization of AI by radiologists improves performance compared to AI alone, a radiologist alone, or a pooled cohort of experts. This suggests that AI may optimally be utilized as an adjunct to radiologist interpretation of imaging studies to improve performance.

Juvenile idiopathic arthritis (JIA) and osteoarticular infection can cause nonspecific articular and periarticular complaints in children. Although contrast material-enhanced magnetic resonance imaging is the reference standard imaging modality, musculoskeletal ultrasonography (US) is emerging as an important adjunct imaging modality that can provide valuable information relatively quickly without use of radiation or the need for sedation. However, diagnostic accuracy requires a systemic approach, familiarity with various US techniques, and an understanding of maturation-related changes. Specifically, the use of dynamic, Doppler, and/or multifocal US assessments can help confirm sites of disease, monitor therapy response, and guide interventions. In patients with JIA, ongoing synovial inflammation can lead to articular and periarticular changes, including synovitis, tenosynovitis, cartilage damage, bone changes, and enthesopathy. Although these findings can manifest in adult patients with rheumatoid arthritis, important differences and pitfalls exist because of the unique changes associated with an immature and maturing skeleton. In patients who are clinically suspected of having osteoarticular infection, the inability of US to evaluate the bone marrow decreases its sensitivity. Therefore, the US findings should be interpreted with caution because juxtacortical inflammation is suggestive, but neither sensitive nor specific, for underlying osteomyelitis. Similarly, the absence of a joint effusion makes septic arthritis extremely unlikely but not impossible. US findings of JIA and osteoarticular infection often overlap. Although certain clinical scenarios, laboratory findings, and imaging appearances can favor one diagnosis over the other, fluid analysis may still be required for definitive diagnosis and optimal treatment. US is the preferred modality for fluid aspiration and administering intra-articular corticosteroid therapy. RSNA, 2017.

Background: Vascularized fibula epiphyseal flap was first described in 1998 for proximal humeral reconstruction in children/infants. The authors aim to review their international, multi-institutional, long-term outcomes. Methods: An international, multi-institutional review (2004 to 2020) was conducted of patients younger than 18 years undergoing free vascularized fibula epiphyseal transfer for proximal humeral reconstruction. Donor- and recipient-site complications, pain, and final ambulatory status were reviewed. Growth of the transferred bone was assessed under the guidance of a pediatric musculoskeletal radiologist. Results: Twenty-seven patients were included with a median age of 7 years (range, 2 to 13 years). Average follow-up was 120 ± 87.4 months. There were two flap failures (7.4%). Recipient-site complications included fracture [n = 11 (40.7%)], avascular necrosis of the fibula head [n = 1 (3.7%)], fibular head avulsion [n = 1 (3.7%)], infection [n = 1 (3.7%)], and hardware failure [n = 1 (3.7%)]. Operative fixation was necessary in one patient with a fracture. The case of infection necessitated fibula explantation 2 years postoperatively, and ultimately, prosthetic reconstruction. Sixteen patients developed peroneal nerve palsy (59.3%): 13 of these cases resolved within 1 year (81% recovery), and three were permanent (11.1%). One patient (3.7%) complained of upper extremity pain. Longitudinal growth was confirmed in all but three cases [n = 24 (88.9%)] at an average rate of 0.83 ± 0.25 cm/year. Conclusions: The vascularized fibula epiphysis for proximal humerus reconstruction in children preserves the potential for future growth and an articular surface for motion. Peroneal nerve palsy is common following harvest, although this is often transient. Future efforts should be geared toward reducing postoperative morbidity. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, IV.

Background Overuse injuries are common in sporting children and adolescents. These injuries are a particular concern when they involve the epiphyseal-physeal-metaphyseal (EPM) complex given their potential to disturb skeletal growth. Specifically, the limits of mechanical tolerance of the EPM complex to repetitive stress may be exceeded by the intense and continuous training characteristic of many youth sports today. Objective This article describes the present status of knowledge on the occurrence and outcome of primary periphyseal stress injuries (PPSIs) affecting the EPM complex in the extremities of children and adolescents involved in youth sports. Methods A comprehensive review of the sports medicine literature was conducted to determine the nature and extent of PPSIs affecting the EPM complex of the extremities among youth sports participants and the potential for consequent skeletal growth disturbance and resultant limb deformity associated with these injuries. Results Our initial search uncovered 128 original published scientific articles reporting relevant data on PPSIs. There were 101 case reports/series, 19 cross-sectional, 1 case-control, and 7 cohort studies with relevant data. The case reports/series studies reported 448 patients with PPSIs involving the extremities. Children and adolescents representing a variety of high impact repetitive youth sports activities-including baseball, badminton, climbing, cricket, dance, gymnastics, rugby, soccer, swimming, tennis, and volleyball-may sustain PPSIs involving the shoulder, elbow, hand and wrist, knee, and ankle and foot. Although incidence data from prospective cohort studies are lacking, data arising from cross-sectional studies suggest that PPSIs may be common in select groups of youth athletes-including the shoulder in baseball players (0-36.6%), wrist in gymnasts (10-83%) and platform divers (52.6%), and fingers in rock climbers (5-58%). Notably, not all stress-related skeletal changes detected on imaging were symptomatic in these studies. When diagnosed and treated with an appropriate period of rest and rehabilitation, most patients studied were able to return to their sport activities. However, our data also show that 57/448 PPSIs (12.7%) produced growth disturbance, and that 28/448 patients (6.2%) underwent surgery for their injuries. Absence of treatment, delayed presentation and diagnosis, and non-compliance with a rest regimen were common in cases that produced growth disturbance. Conclusions PPSIs may affect the extremities of children and adolescents engaged in a variety of youth sports, especially at advanced levels of training and competition. Most skeletally immature patients with PPSIs respond well to timely treatment; however, in extreme cases, PPSIs can progress to produce skeletal growth disruption which may necessitate surgical intervention. Clearly, establishing the early diagnosis of PPSIs and providing timely treatment of these injuries are needed to ensure the skeletal health of youth sports participants. Rigorous prospective lo...

Background: Osteochondritis dissecans (OCD) occurs most commonly in the knees of young individuals. This condition is known to cause pain and discomfort in the knee and can lead to disability and early knee osteoarthritis. The cause is not well understood, and treatment plans are not well delineated. The Research in Osteochondritis Dissecans of the Knee (ROCK) group established a multicenter, prospective cohort to better understand this disease. Purpose: To provide a baseline report of the ROCK multicenter prospective cohort and present a descriptive analysis of baseline data for patient characteristics, lesion characteristics, and clinical findings of the first 1000 cases enrolled into the prospective cohort. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Patients were recruited from centers throughout the United States. Baseline data were obtained for patient characteristics, sports participation, patient-reported measures of functional capabilities and limitations, physical examination, diagnostic imaging results, and initial treatment plan. Descriptive statistics were completed for all outcomes of interest. Results: As of November 2020, a total of 27 orthopaedic surgeons from 17 institutions had enrolled 1004 knees with OCD, representing 903 patients (68.9% males; median age, 13.1 years; range, 6.3-25.4 years), into the prospective cohort. Lesions were located on the medial femoral condyle (66.2%), lateral femoral condyle (18.1%), trochlea (9.5%), patella (6.0%), and tibial plateau (0.2%). Most cases involved multisport athletes (68.1%), with the most common primary sport being basketball for males (27.3% of cases) and soccer for females (27.6% of cases). The median Pediatric International Knee Documentation Committee (Pedi-IKCD) score was 59.9 (IQR, 45.6-73.9), and the median Pediatric Functional Activity Brief Scale (Pedi-FABS) score was 21.0 (IQR, 5.0-28.0). Initial treatments were surgical intervention (55.4%) and activity restriction (44.0%). When surgery was performed, surgeons deemed the lesion to be stable at intraoperative assessment in 48.1% of cases. Conclusion: The multicenter ROCK group has been able to enroll the largest knee OCD cohort to date. This information is being used to further understand the pathology of OCD, including its cause, associated comorbidities, and initial presentation and symptoms. The cohort having been established is now being followed longitudinally to better define and elucidate the best treatment algorithms based on these presenting signs and symptoms.