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At the end of this article, the reader should be able to (1) recognise normal anatomy and anatomical variants of the extensor mechanism of the knee on various imaging modalities, including plain film, ultrasound and MRI; (2) diagnose a broad spectrum of EM injuries in adult and paediatric patients including patellar and quadriceps tendinopathy, Osgood-Schlatter disease, Sindig-Larsen-Johansson syndrome, chondromalacia patellae and patellar fractures on various imaging modalities; and (3) appreciate the important role of imaging in the diagnosis of musculoskeletal injuries. INTRODUCTIONThe extensor mechanism (EM) of the knee comprises the quadriceps muscles and tendon, the patella, patellar tendon and supporting retinaculum ( fi gure 1 ). Injuries of the EM are common and may be due to acute trauma, overuse injuries or chronic degenerative disease, and imaging plays an important role in diagnosis. In addition to clinical evaluation, abnormalities of bone and soft tissues can be visualised with plain fi lms and CT, and tendons can be assessed with ultrasound (US). MRI provides excellent evaluation of the knee and is often the imaging modality of choice in the characterisation of EM injuries. ANATOMY OF THE EM OF THE KNEEThe EM of the knee comprises the quadriceps muscles and tendon, the patella, the patellar tendon and supporting retinacula. The quadriceps muscles include the rectus femoris and the vastus lateralis, vastus intermedius and vastus medialis. The origin of the rectus femoris is the anterior inferior iliac spine, and the vastus muscles originate from the femoral shaft. The quadriceps tendon inserts on the superior pole of the patella and usually has a trilaminar appearance on MR. 1 The superfi cial lamina is composed of the rectus femoris, the intermediate lamina is composed of the vastus lateralis and medialis, and lastly the deep lamina is formed by the vastus intermedius.The patella is the largest sesamoid bone in the body and articulates with the trochlear groove of the femur. It usually possesses a median ridge that divides the proximal patella into medial and lateral facets, and the medial facet is generally smaller. The patellar tendon is mainly composed of rectus femoris fi bres that course over the patella and originates at the superior pole of the patella and inserts on the tibial tuberosity.The medial retinaculum has three components: the superior component is composed of the vastus medialis and patellofemoral ligament, the midportion is composed of the medial collateral ligament fi bres, and lastly the inferior component includes the patellotibial ligament and the medial patellomeniscal ligament. Similarly, the lateral retinaculum is composed of three parts: the superfi cial component includes the iliotibial tract and biceps femoris, the midportion is composed of the vastus lateralis, and the deep component is composed by the joint capsule.Additional soft tissue structures includes fat pads, namely the anterior suprapatellar (quadriceps) fat pad, the posterior suprapatellar (prefemo...

This case study examines the antecedents present in the transformation of the Canada School from its founding to its present state characterized by structural ambidexterity. It provides insights into how an organization's history affects the development of a shared value and belief system focused on continuously searching for new innovations, seizing upon them, and reconfiguring organizational assets to capitalize upon them. Through the use of a single case, the history of the Canada School is traced through five stages of growth.