If you’re a regular runner, you’ve probably experienced the occasional run-in with knee pain. Running is generally good for our knee joints, but it’s easy to pick up niggles from time to time.
Pes anserinus bursitis (sometimes referred to as pes anserine bursitis) is an injury that often affects runners, or otherwise fit and active people, and can sometimes be hard to shake off.
The pain usually happens on the inside of the knee just below the shinbone, during or after exercise. One reader on an online running forum describes the problem like this: “Currently I don’t notice it in everyday life, and at the start of runs everything seems fine, but invariably after 30-40mins it resurfaces very rapidly and I have to bail out of finishing whatever run I planned to do.”
A fellow sufferer writes: “I did a 20-mile trail run… Didn’t feel anything until I woke up next morning and both knees were hurting with very slight swelling. Tried to resume running for a month but had to stop.”
Obviously, this type of persistent injury can be pretty frustrating if you love running. So what’s going on – and what can you do about it?
Where is the “pes anserinus” – and what is it for?
“Pes anserinus” is a bit of a mouthful in English. The Latin version is better! It means goose foot, because it’s comprised of three tendons that are arranged in a triangular shape, rather like the toes on a water-going fowl. Those three tendons are the sartorius, gracilis and semitendinosus: guy-rope-like structures that enable your knee to flex, rotate and adduct (move in an inward direction).
What is bursitis?
A bursa is a thin ‘sac’ that sits between many different tissues, bones and joints in our bodies. Its purpose is to help these structures slide smoothly against each other. It does this chiefly through something called synovial fluid, a thick liquid that fills the sac, providing cushioning and reducing friction. Bursitis is what happens when one of those sacs becomes irritated. In response, more fluid flows into the bursa and it becomes swollen and inflamed. You can read about this in more detail here: What on earth is knee bursitis? (and how to get rid of it)
What does pes anserinus bursitis pain feel like?
It’s usually an ache, a tenderness or a burning feeling on the inner (medial) side of the knee, at the top of the shinbone (tibia). As the runners above mention, it usually comes on with exercise, and gradually rather than immediately. People often describe discomfort when walking up or down stairs. And there may be some swelling too (though, unlike a Baker’s cyst, the swelling rarely gets very large).
What causes pes anserinus bursitis?
Bursitis is usually provoked by a new activity that involves repetitive impact. In the case of a Baker’s cyst ( also known as popliteal bursitis) that’s often something like kneeling on a hard surface while gardening or laying a carpet. Pes anserinus bursitis tends to be triggered more by mechanical repetition: things like running, playing tennis, or overtraining. It’s also more common if you have tight hamstrings, flat feet (which are caused by abnormal knee alignment) or if you’ve injured your MCL in the past.
How do you treat pes anserinus bursitis?
As with many new knee injuries, the first line of treatment is usually time and rest. In short, the RICE protocol:
- Rest – don’t try to ignore the pain or run through it
- Ice – try applying an ice pack to reduce the swelling
- Compression – consider lightly wrapping a bandage around your knee for support
- Elevation – periodically raise your knee on a pillow, to reduce swelling
Most pes anserinus bursitis cases tend to settle down naturally in time. A rule of thumb is about six to eight weeks. Part of your recovery, though, should be to think carefully about what might have provoked it in the first place. While the cause isn’t always obvious, there’s often a discernible trigger, from changing your regular activity or overdoing it (that half-marathon programme you started last month…) to changing the type of ground you run on. You’ll find some more examples in this blog about Runner’s Knee (see No 2, ‘Analyse your setup’).
What if it won’t go away?
If RICE doesn’t fix the problem, there are other solutions. Physiotherapy, with targeted exercises to improve strength in the hamstrings for example, is very effective for many patients. Another potential approach is an ultrasound-guided injection; this is usually with a steroid, to reduce the inflammation. In the most severe cases, it’s possible to have surgery to remove the bursa (or, if tendonitis is involved, to “release” the tendons), but this is really quite rare. Perhaps the main piece of advice is to get a reliable diagnosis. Pes anserinus bursitis is easily confused with other inside-knee pain problems. It can also be tricky to detect – pes anserinus swelling doesn’t always show up clearly in X-rays or even MRI scans. Getting proper diagnosis from a knee specialist can help you establish exactly what’s going on under the surface, so you know what you’re dealing with and can take the right next steps.
