I fell on my bent knee playing football and now it feels wobbly going downstairs. Why?

Why stairs show up a PCL problem

Going downstairs, walking downhill and decelerating all ask the knee to control the shin bone as it tends to slide backwards. That is the PCL's main job. When the ligament is stretched or torn, the quadriceps has to work harder to hold the knee, so it tires sooner and the knee can feel shaky or vague.

An ACL tear typically causes giving way with twisting and pivoting. A PCL injury more often shows up as this deceleration-type unsteadiness and aching at the back or front of the knee.

Other possible causes

• A bone bruise from the fall, which can be sore for several weeks
• A meniscus tear, especially if there is catching or locking
• Kneecap pain from the direct blow
• Quadriceps weakness after a period of limping
• An injury to the outer corner of the knee, which often accompanies a PCL tear

What you can do now

Use the handrail on stairs and lead with the uninjured leg going down. Avoid deep squats and kneeling for now. Gentle quadriceps exercises, such as straight-leg raises and tightening the thigh with the knee straight, help support the knee. Ice and elevation settle swelling after activity.

Avoid returning to football or other sport until the knee has been examined, because playing on an unrecognised ligament injury can lead to further damage.

When to see a knee surgeon

Book an assessment if the unsteadiness lasts more than a couple of weeks, the knee keeps swelling, or you cannot trust it on stairs. Dr. Gelber compares both knees with the posterior drawer and sag tests and checks the outer corner of the knee. An MRI usually confirms the grade of injury and guides treatment.