Osgood-Schlatter disease is a condition that affects the upper part of the shin bone (tibia). Overuse of the quadriceps muscle (the muscle on the front of the thigh) can cause repeated strain where this muscle attaches via the patellar ligament to the growing tibia. The tibia hasn't finished growing and isn't quite strong enough to withstand the strain on it. This can cause redness and soreness where the ligament attaches. In some cases, a small flake of bone is pulled off the tibia by the pulling ligament. Healing bone (callus) then forms which may cause a hard bony bump to develop.
This is a companion discussion topic for the original article at https://patient.info/bones-joints-muscles/knee-pain-patellofemoral-pain/osgood-schlatter-disease