Stress fracture, in its most inclusive description, includes both fatigue and insufficiency fracture. Fatigue fractures, sometimes equated with the term "stress fractures," are most common in runners and other athletes and typically occur in the lower extremities. These fractures are the result of abnormal, cyclical loading on normal bone leading to local cortical resorption and fracture. Insufficiency fractures are common in elderly populations, secondary to osteoporosis, and are typically located in and around the pelvis. They are a result of normal or traumatic loading on abnormal bone. Subchondral insufficiency fractures of the hip or knee may cause acute pain that may present in the emergency setting. Medial tibial stress syndrome is a type of stress injury of the tibia related to activity and is a clinical syndrome encompassing a range of injuries from stress edema to frank-displaced fracture. Atypical subtrochanteric femoral fracture associated with long-term bisphosphonate therapy is also a recently discovered entity that needs early recognition to prevent progression to a complete fracture. Imaging recommendations for evaluation of stress fractures include initial plain radiographs followed, if necessary, by magnetic resonance imaging (MRI), which is preferred over computed tomography (CT) and bone scintigraphy. Radiographs are the first-line modality and may reveal linear sclerosis and periosteal reaction prior to the development of a frank fracture. MRI is highly sensitive with findings ranging from periosteal edema to bone marrow and intracortical signal abnormality. Additionally, a brief description of relevant clinical management of stress fractures is included.

The iliotibial tract, also known as Maissiat's band or the iliotibial band, and its associated muscles function to extend, abduct, and laterally rotate the hip, as well as aid in the stabilization of the knee. A select group of associated injuries and pathologies of the iliotibial tract are seen as sequela of repetitive stress and direct trauma. This article intends to educate the radiologist, orthopedist, and other clinicians about iliotibial tract anatomy and function and the clinical presentation, pathophysiology, and imaging findings of associated pathologies. Specifically, this article will review proximal iliotibial band syndrome, Morel-Lavallée lesions, external snapping hip syndrome, iliotibial band syndrome and bursitis, traumatic tears, iliotibial insertional tendinosis and peritendonitis, avulsion fractures at Gerdy's tubercle, and Segond fractures. The clinical management of these pathologies will also be discussed in brief.

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Hypertrophic osteoarthropathy (HOA) is a medical condition characterized by abnormal proliferation of skin and periosteal tissues involving the extremities and characterized by three clinical features: digital clubbing (also termed Hippocratic fingers), periostosis of tubular bones, and synovial effusions. HOA can be a primary entity, known as pachydermoperiostosis, or can be secondary to extraskeletal conditions, with different prognoses and management implications for each. There is a high association between secondary HOA and malignancy, especially non-small cell lung cancer. In such cases, it can be considered a form of paraneoplastic syndrome. The most prevalent secondary causes of HOA are pulmonary in origin, which is why this condition was formerly referred to as hypertrophic pulmonary osteoarthropathy. HOA can also be associated with pleural, mediastinal, and cardiovascular causes, as well as extrathoracic conditions such as gastrointestinal tumors and infections, cirrhosis, and inflammatory bowel disease. Although the skeletal manifestations of HOA are most commonly detected with radiography, abnormalities can also be identified with other modalities such as computed tomography, magnetic resonance imaging, and bone scintigraphy. The authors summarize the pathogenesis, classification, causes, and symptoms and signs of HOA, including the genetics underlying the primary form (pachydermoperiostosis); describe key findings of HOA found at various imaging modalities, with examples of underlying causative conditions; and discuss features differentiating HOA from other causes of multifocal periostitis, such as thyroid acropachy, hypervitaminosis A, chronic venous insufficiency, voriconazole-induced periostitis, progressive diaphyseal dysplasia, and neoplastic causes such as lymphoma. RSNA, 2016.

The posteromedial corner of the knee (PMC) is an important anatomic structure that is easily seen but often overlooked on magnetic resonance (MR) images. Whereas the posterolateral corner has been referred to as the "dark side of the knee" by some authors owing to widespread lack of knowledge of its complex anatomy, even less is written about the PMC; yet it is as important as the posterolateral corner in multiligament injuries of the knee. The PMC lies between the posterior margin of the longitudinal fibers of the superficial medial collateral ligament (MCL) and the medial border of the posterior cruciate ligament (PCL). The anatomy of the PMC can be complex and the literature describing it can be confusing, at times oversimplifying it and at other times adding unnecessary complexity. Its most important structures, however, can be described more simply as five major components, and can be better shown with illustrations that emphasize the anatomic distinctions. Injuries to the PMC are important to recognize, as disruption of the supporting structures can cause anteromedial rotational instability (AMRI). Isolated PMC injuries are rare; most occur in conjunction with injuries to other important stabilizing knee structures such as the anterior cruciate ligament (ACL) and PCL. Unrecognized and unaddressed injury of the PMC is one of the causes of ACL and PCL graft failures. Recognition of PMC injuries is critical, as the diagnosis will often change or require surgical management.