Why does osteochondritis dissecans cause knee locking?

Osteochondritis dissecans affects a small area beneath the joint cartilage, often in the lower end of the thigh bone. Reduced support to that area can allow the bone and its overlying cartilage to soften, crack, or separate. If the area remains in place, symptoms may include activity-related pain, swelling, or catching. If it becomes partly detached or loose, it can interrupt the smooth arc needed to bend or straighten the knee.

Knee locking is a common presentation of Osteochondritis Dissecans, but knee locking can have other causes as well. A true lock means the knee cannot complete movement, whereas a brief catch may feel like a momentary snag or hesitation. The distinction helps a clinician decide whether imaging is needed to assess the cartilage and the stability of the affected area.

Avoid forcing a locked knee straight or repeatedly testing the movement. Pause activities that load the knee, such as running, jumping, deep squats, or kneeling, until you have been assessed. Keep the leg in a comfortable position and use support when walking if the knee feels unstable. A clinician may examine your range of motion and order an X-ray or MRI to check the lesion, loose fragments, and surrounding cartilage. Treatment depends on factors such as age, lesion stability, symptoms, and whether the joint surface is intact.

Arrange a medical assessment if locking keeps returning, the knee will not fully straighten, swelling follows activity, or pain is limiting walking or sleep. Seek urgent care if the knee becomes suddenly locked and you cannot bear weight, if it looks deformed, or if severe swelling and pain follow an injury. Prompt assessment can help identify a displaced fragment and reduce the chance of repeatedly stressing the joint.

You could ask: Is the osteochondritis dissecans area stable? Is the locking caused by a loose fragment or another problem inside the knee? Which activities should I pause, and what movement is safe? Do I need imaging or follow-up to check whether the joint surface is healing?