Why your knee hurts going down stairs but not up

It is the complaint that brings most people to the clinic, and it is remarkably specific. Climbing up is fine. Coming down, the knee objects. Patients often assume it means something is torn. Usually it means something much more ordinary.

What descending actually asks of the knee

Walking on level ground puts roughly one and a half times your body weight through the knee. Climbing stairs raises that to about two and a half. Descending raises it further, to around three and a half, and it does so in a way that matters more than the number alone.

Going up, the quadriceps shortens as it contracts. That is concentric work, and it is what muscle is best at. Going down, the same muscle has to lengthen while still under tension, paying out slowly like a rope to stop you dropping onto the next step. That is eccentric work. It generates higher force through the joint, and it demands better control.

So descending is the harder test. When the cartilage surface has roughened or the thigh muscle has weakened, descending is where it shows first.

What the pattern tells a doctor

Where exactly it hurts narrows it further.

• Pain at the front, under or around the kneecap, often with a grating feeling: the patellofemoral joint, the compartment behind the kneecap.
• Pain on the inner side of the knee: the medial compartment, which carries most of the load and wears first in the majority of people.
• Pain with catching, locking or the knee giving way suddenly: worth checking for a meniscal problem alongside the osteoarthritis.
• Pain that is severe, came on suddenly, and is accompanied by heat and swelling: that is not a mechanical pattern and needs assessment rather than reassurance.

What helps, in order of how much it helps

Build the quadriceps

This is first because it is the thing most people skip. The thigh muscle absorbs load before it reaches the joint surface. It weakens fast when a knee hurts, which increases the load, which increases the pain. Breaking that loop is the highest-value thing you can do, and it does not cost anything.

Sit-to-stand repetitions from a dining chair, straight leg raises, and static quadriceps holds are the unglamorous staples. Ten minutes daily beats an hour once a week.

Change how you descend, for now

• Take stairs one at a time, leading with the better leg going up and the painful leg going down.
• Use the handrail properly. Taking even ten per cent of your weight through an arm removes a meaningful load from the knee.
• Shorten your stride on slopes. Long steps downhill increase the eccentric demand sharply.

Deal with the weight, if there is weight to deal with

Each kilogram lost removes roughly three to four kilograms of load from the knee at every step. A five per cent reduction produces a measurable fall in pain scores in trials. It is slow, and it works.

When an injection enters the conversation

An injection is second-line. It is for the person who is already doing the strength work but is still limited, or for the person whose pain is too severe to start the strength work at all. Used that way, it buys the window in which everything else becomes possible.

If your knee is hot and swollen today, a corticosteroid settles it fastest. If it is not swollen but aches on stairs and stiffens after sitting, that is the mechanical pattern hyaluronic acid is designed for, and you should expect improvement over two to six weeks rather than overnight.