What is patellofemoral pain?
Patellofemoral pain, commonly called runner's knee, is pain around or behind the kneecap, where it glides in a groove on the thigh bone. Every step loads that joint; downhills, stairs and deep bends load it hardest.
- Aching around or under the kneecap during or after running
- Worse on stairs, especially going down, squatting, or sitting with bent knees for a while (the "cinema sign")
- Occasional grinding or a puffy feeling, but rarely true swelling or locking
It's not damage to the kneecap cartilage in most cases. It's an irritated joint being asked to handle more load than it currently tolerates.
What causes it?
The primary mechanism
The kneecap tracks in a groove on the thigh bone, and how well it tracks depends heavily on the muscles above and around it, particularly the hips. Weak glutes let the thigh rotate inward under load, which changes how the kneecap sits in its groove and irritates the joint surface underneath it.
Common contributing factors
- A sudden jump in running volume or intensity
- Weak hip abductors and external rotators
- Quad weakness relative to the demands being placed on the knee
- Tight quads, hip flexors or calves
Patellofemoral pain is not arthritis, and running does not wear healthy knees out. Population studies consistently fail to show recreational running causing knee arthritis, which makes the "my knees are wearing out" fear one of the most common and least accurate things patients tell me.
What the evidence says
The strongest evidence in runner's knee treatment is for combined hip and knee strengthening, not for rest, taping or bracing. A slightly quicker running cadence, around 5–7% more steps per minute at the same speed, reduces per-step knee load and is one of the few running-form changes with decent evidence behind it.
Recovery protocol
Step 1: calm it down (weeks 0–2)
- Reduce, don't stop. Trim running volume and avoid the biggest aggravators, downhill and speedwork, keeping pain during and after runs at 3/10 or less.
- Ice for comfort; simple analgesia if appropriate.
- Keep cycling and swimming going. The knee tolerates movement without spikes well.
Step 2: build the support system (weeks 2–12)
- Hips: side-lying abduction, crab walks, single-leg bridges. The glutes control how the thigh, and therefore the kneecap groove, behaves on landing.
- Quads: squats to a comfortable depth, step-ups, leg press, progressing load weekly.
- Mobility: quad, hip flexor and calf flexibility work alongside the strength programme.
Step 3: rebuild the running (weeks 4–12)
- Return gradually: alternate days, flat routes, conversational pace, volume up roughly 10% weekly.
- Add the cadence increase once strength is progressing well.
Common misconceptions
- "I need a knee brace or special taping." Taping can ease symptoms short-term as a comfort tool while the strength work takes effect. It isn't the treatment itself.
- "Rest will heal it." Rest empties the pain, then running refills it, because nothing about capacity has changed. Strength changes capacity.
When to seek professional help
Most runner's knee responds to the reduce-and-strengthen approach above. A scan is rarely needed since the diagnosis is clinical and imaging findings correlate poorly with symptoms.
- See a physio if: pain hasn't budged after 4–6 weeks of consistent hip-and-quad work, or you're working to a race date and want the loading progressed as fast as safely possible.
- Seek assessment sooner if: there's swelling, locking, or a history of trauma, since these don't fit the typical patellofemoral picture.