Osgood-Schlatter disease (traction apophysitis)

Osgood-Schlatter disease is an inflammation of the patellar tendon, right at the point where it inserts on the tibial tuberosity, resulting in painful swelling just below the knee. It’s named after two orthopedic surgeons; the American Robert Osgood, and the Swiss Carl Schlatter. Now, just to be clear what we’re talking about, the patellar tendon is sometimes also called the patellar ligament, but tendon is more common.

So, focusing in on the knee, the proximal epiphysis of the tibia, which is the upper end of the tibia that contributes to the knee joint, has a bony prominence called the tibial tuberosity. This is considered an apophysis, meaning that it’s a bony prominence that serves as a site for tendon attachment. The tibial tuberosity specifically serves as the attachment site for the patellar tendon, which is an extension of the quadriceps muscle tendon. When the quadriceps muscle contracts, the patellar tendon tightens, extending the knee. At birth, the proximal epiphysis consists of cartilage, but it contains an ossification center inside. This ossification center begins to ossify or turn to bone between the age of nine and fifteen and becomes a bony tuberosity around the age of eighteen.

Osgood-Schlatter disease typically develops between the age of ten and fifteen when the tuberosity hasn’t ossified yet and therefore isn’t hard enough to resist traction of the patellar tendon. So, this is why the disease is very common in young adolescents who play sports requiring the quadriceps muscles to contract repetitively, causing the patellar tendon to excessively strain on the not-yet-ossified tibial tuberosity. This results in inflammation of the tendon at the point it inserts to the tuberosity, what is known as traction apophysitis. When the traction is too excessive, it can cause the ossification center inside the tuberosity to crack into tiny bone fragments. Eventually, that results in a more prominent tuberosity or a callus during the healing process. Fortunately, Osgood-Schlatter disease resolves itself as the ossification of the tuberosity continues as a child grows.

Symptoms of Osgood-Schlatter disease are anterior knee pain, usually accompanied by a palpable lump just below the knee, which gets worse with physical activities like running, jumping, squatting, and especially when going up or down stairs, or when the knee gets hit by something over that spot.