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Menisci play an essential role in maintaining normal pain-free function of the knee. While there are decades of MRI literature on the tears involving the meniscus body and horns, there is now a surge in knowledge regarding injuries at the meniscus roots and periphery. The authors briefly highlight new insights into meniscus anatomy and then summarize recent developments in the understanding of meniscus injuries that matter, emphasizing meniscus injuries at the root and peripheral (eg, ramp) regions that may be missed easily at MRI and arthroscopy. Root and ramp tears are important to diagnose because they may be amenable to repair. However, if these tears are left untreated, ongoing pain and accelerated cartilage degeneration may ensue. The posterior roots of the medial and lateral menisci are most commonly affected by injury, and each of these injuries is associated with distinctive clinical profiles, MRI findings, and tear patterns. Specific diagnostic pitfalls can make the roots challenging to evaluate, including MRI artifacts and anatomic variations. As with root tears, MRI interpretation and orthopedic treatment have important differences for injuries at the medial versus lateral meniscus (LM) periphery (located at or near the meniscocapsular junction). Medially, ramp lesions typically occur in the setting of an anterior cruciate ligament rupture and are generally classified into five patterns. Laterally, the meniscocapsular junction may be injured in association with tibial plateau fractures, but disruption of the popliteomeniscal fascicles may also result in a hypermobile LM. Updated knowledge of the meniscus root and ramp tears is crucial in optimizing diagnostic imaging before repair and understanding the clinical repercussions. © RSNA, 2023 Online supplemental material is available for this article. Quiz questions for this article are available in the Online Learning Center.

Patellofemoral pain and instability are common indications for imaging that are encountered in everyday practice. The authors comprehensively review key aspects of patellofemoral instability pertinent to radiologists that can be seen before the onset of osteoarthritis, highlighting the anatomy, clinical evaluation, diagnostic imaging, and treatment. Regarding the anatomy, the medial patellofemoral ligament (MPFL) is the primary static soft-tissue restraint to lateral patellar displacement and is commonly reconstructed surgically in patients with MPFL dysfunction and patellar instability. Osteoarticular abnormalities that predispose individuals to patellar instability include patellar malalignment, trochlear dysplasia, and tibial tubercle lateralization. Clinically, patients with patellar instability may be divided into two broad groups with imaging findings that sometimes overlap: patients with a history of overt patellar instability after a traumatic event (eg, dislocation, subluxation) and patients without such a history. In terms of imaging, radiography is generally the initial examination of choice, and MRI is the most common cross-sectional examination performed preoperatively. For all imaging techniques, there has been a proliferation of published radiologic measurement methods. The authors summarize the most common validated measurements for patellar malalignment, trochlear dysplasia, and tibial tubercle lateralization. Given that static imaging is inherently limited in the evaluation of patellar motion, dynamic imaging with US, CT, or MRI may be requested by some surgeons. The primary treatment strategy for patellofemoral pain is conservative. Surgical treatment options include MPFL reconstruction with or without osseous corrections such as trochleoplasty and tibial tubercle osteotomy. Postoperative complications evaluated at imaging include patellar fracture, graft failure, graft malposition, and medial patellar subluxation. © RSNA, 2023 Quiz questions for this article are available in the supplemental material.

The goal of this study was to establish a normal value for, and evaluate the reliability of, a new measurement of glenoid morphologic features using magnetic resonance imaging: the anterior glenoid angle. A total of 90 magnetic resonance imaging scans of patients without shoulder arthritis were reviewed. The anterior glenoid angle of each glenoid was measured by 4 blinded physicians. The images were randomized and measured again. Finally, the Friedman angle was measured on the same images for reference. Descriptive statistics and inter- and intraclass correlation coefficients were calculated. The mean anterior glenoid angle was 60.4°±3.6°. Of the measured values, 77% were between 56° and 64°. Intraobserver reliability was very good to excellent in single measure (range, 0.763-0.901) and mean measure (range, 0.865-0.948) comparisons. Interobserver reliability was very good to excellent in both single measure (0.769) and mean measure (0.964) comparisons. The mean Friedman angle was 10.2°. Correlation between the anterior glenoid angle and Friedman angle ranged from a moderate negative (-0.496) to a strong negative correlation (-0.711) among the observers. The mean anterior glenoid angle measured via magnetic resonance imaging scan was 60.4° in normal shoulders, and more than 75% of the values were within 4° of the mean. The anterior glenoid angle has excellent inter- and intrarater reliability without using computed tomography scan or including the entire scapula in the field of view. The anterior glenoid angle has a good to very good negative correlation with the Friedman angle because decreasing anterior glenoid angles indicate increasing retroversion. [ Orthopedics . 2022;45(6):361-366.].