The Osgood-Schlatter lesion is a common cause of knee pain in active adolescents. Two authors, Robert Bayley Osgood and Carl Schlatter, working independently, were the first to describe the condition, in 1903. Originally, the Osgood-Schlatter lesion was thought to result from an avulsion of bone or cartilage in the tibial tuberosity. However, subsequent findings have indicated that most cases of Osgood-Schlatter disease are caused by microtrauma in the deep fibers of the patellar tendon at its insertion on the tibial tuberosity; even so, avulsion may be present in some cases.
(See the images below.)
In children, the cartilaginous tibial tuberosity is an inferior extension of the proximal tibial physis. The tuberosity usually ossifies as an inferior extension of the main epiphyseal ossification center. Sometimes, one or more secondary ossification centers develop separately in the cartilaginous tuberosity. These eventually unite with the main, proximal tibial epiphyseal ossification center. Hence, the presence of multiple ossific nodules anterior to the tibial metaphysis is, by itself, a normal variant. The patellar tendon extends anterior to the infrapatellar fat pad of Hoffa and inserts into the cartilage of the anterior tibial tuberosity.
The quadriceps femoris muscle, the largest muscle in the human body, inserts on a relatively small area of the tibial tuberosity. As a consequence, naturally high tension exists at the insertion site. In children, additional stress is placed on the cartilaginous site as a result of vigorous physical activity, leading to traumatic changes at the insertion; this is especially true in the case of activities, such as kicking, that involve particularly high stress at the insertion.
The diagnosis of an Osgood-Schlatter lesion is usually made on the basis of characteristic localized pain at the tibial tuberosity, and radiographs are not needed for diagnosis. However, radiographic results confirm the clinical suspicion of the disease and exclude other causes of knee pain.
Lateral radiographs of the knee demonstrate pertinent soft-tissue findings in Osgood-Schlatter disease, as well as bony changes, such as ossicle formation. If the tibial tuberosity must be examined in detail, the knee should be slightly rotated internally to obtain a lateral view, because the tibial tuberosity lies slightly lateral to the midline of the knee. An anteroposterior (AP) image can be obtained to exclude other pathologic bone conditions.
Computed tomography (CT) scanning and magnetic resonance imaging (MRI) are not routinely performed, but they may be helpful in cases in which additional pathologic conditions are being considered or in rare cases in which a complication may not be detectable with plain radiographs. Examples of the latter situation include the presence of a physeal fusion bar, which may lead to the complication of tibia recurvatum, or the existence of a small, painful, unfused ossicle.
Ultrasonography is not routinely performed in most centers. With an experienced imager, the findings can confirm the diagnosis. Ultrasonography can show both bone and soft tissue from a variety of angles and reveal bony irregularities or neovascularization of surrounding tissue.
Radiograph of a patient who is skeletally mature. Note that the tibial tubercle is enlarged and that an ossicle is present, with an overlying bursa. Image courtesy of J Andy Sullivan, MD.
Radiograph of a patient who is skeletally immature. The tubercle is elongated and fragmented, and overlying soft-tissue swelling is present. Image courtesy of J Andy Sullivan, MD.