This article reviews current magnetic resonance imaging (MR imaging) techniques for imaging the lower extremity, focusing on imaging of the knee, ankle, and hip joints. Recent advancements in MR imaging include imaging at 7 T, using multiple receiver channels, T2* imaging, and metal suppression techniques, allowing more detailed visualization of complex anatomy, evaluation of morphologic changes within articular cartilage, and imaging around orthopedic hardware.

Overuse injuries are a common and important cause of morbidity in elite and recreational athletes. They are increasingly recognized in the sedentary population. This article reviews the major classes of overuse injuries of the lower extremity. The underlying pathologic condition is correlated with the imaging appearances, and the often variable relationship between the imaging appearances and patients' symptoms are reviewed. Attempts at imaged-based grading systems and the ability of imaging to predict patients' prognosis are considered. Image-guided injection therapy for tendinopathy is an important and rapidly changing area; the indications, risks, and potential benefits of these interventions are reviewed.

Impingement is a clinical syndrome of end-range joint pain or motion restriction caused by the direct mechanical abutment of bone or soft tissues. Impingement syndromes at the ankle may occur after acute macrotrauma or repetitive microtrauma. Modern imaging modalities can show underlying diseases and anatomic variations and assist with patient management. Implicit in the definition of impingement as a clinical syndrome is that the diagnosis remains clinical, because imaging changes alone do not reliably predict symptoms or clinical relevance. This article reviews the anatomy, pathogenesis, clinical features, differential diagnosis, imaging, and management of various impingement syndromes around the ankle.

Sports ankle injuries are very common worldwide. In the United States, it is estimated that 2 million acute ankle sprains occur each year, averaging to $318 to $914 per sprain. Magnetic resonance imaging is excellent for depicting normal ankle anatomy and can elegantly demonstrate ligamentous injuries of the ankle and associated conditions after ankle sprain. This article encompasses epidemiology, biomechanics, normal anatomy, and pathologic conditions of the ankle and foot ligaments. The specific ligaments discussed include the syndesmotic ligaments, lateral ligament complex of the ankle, deltoid ligament, spring ligament, ligaments of the sinus tarsi, and the Lisfranc ligament.

Cystic lesions are common around the knee and are often encountered as an incidental finding on routine magnetic resonance imaging examinations. The clinical presentation of cysts and other fluid collections is variable, depending on their size, location, and relationship to adjacent anatomic structures. This article reviews the anatomy, etiology, clinical presentation, and imaging features of commonly occurring cystic lesions around the knee and discusses some of the potential pitfalls that may be encountered in clinical practice.

Posterolateral (PLC) and posteromedial (PMC) corners of the knee represent complex anatomic regions because of intricate soft tissue and osseous relationships in small areas. Concise knowledge of these relationships is necessary before approaching their evaluation at imaging. Magnetic resonance imaging offers an accurate imaging diagnostic tool to establish normal anatomy and diagnose and characterize soft tissue and osseous injury. It is important to carefully evaluate the PLC and PMC structures on magnetic resonance imaging before planned surgical intervention to avoid potential complications resulting from occult injury.

Disorders related to the knee extensor mechanism are common and rarely require imaging. Non specific anterior knee pain, fracture, dislocation, overuse tendinopathy and chronic patellofemoral instability are the commonest conditions encountered. Imaging is used in acute trauma, and for the assessment of cases of anterior knee pain resistant to conservative measures. The role of the radiograph is now largely restricted to cases of suspected fracture. Ultrasound is the optimum technique for suspected tendon and bursal pathology and MRI is widely used for the assessment of dysplasia and instability of the patellofemoral joint, including acute dislocation.

Meniscal injuries are common. Magnetic resonance imaging is considered the imaging modality of choice in diagnosing meniscal pathologic conditions in the nonoperative knee. Meniscal-preserving surgery is becoming more frequent, with a resultant increase in postoperative meniscal imaging, which is particularly challenging for the reporting radiologist. This article provides a review of the anatomy, pathologic conditions, and diagnostic pitfalls of meniscal injury, with a synopsis of the issues faced with postoperative meniscal imaging.

Soft tissue abnormalities about the hip represent a common clinical problem. Although the signs and symptoms of some of these abnormalities are clinically evident, other entities are frequently overlooked. This article provides an overview and discusses the role of major imaging modalities, especially MR imaging, the primary modality for evaluation of many soft-tissue abnormalities. An introduction to fundamental imaging anatomy and functional roles of soft tissue structures about the hip is provided, recognizing their importance in making the correct diagnosis. Intra-articular and extra-articular soft tissue abnormalities reviewed systematically according to their mechanism of injury and anatomic or functional compartments.