Popliteus is a relatively small muscle found in the back of the knee. It crosses the knee joint from the lateral Femoral condyle (lowest part of the thigh bone on the outer knee) and head of the Fibula, almost horizontally, down to the inner Tibia. This muscle also has some fibres which attach at the top to the lateral meniscus. Its job is to both help to rotate the Tibia and to unlock the knee joint from a fully extended position.
Popliteus – The Key of the Knee
Due to this unlocking function, the Popliteus is often referred to as the key of the knee joint. However, it is not only this analogy that gives rise to this nickname. The Popliteus is a very important and often overlooked muscle when it comes to injury prevention.
As well as initiating flexion at the knee joint and helping to rotate the Tibia, the Popliteus has a few other functions which help to make the knee joint more stable.
Firstly, it helps the PCL to prevent excessive posterior translation of the Tibia (this is where the shin bone moves backwards underneath the thigh). Without this muscle there would be a higher rate of PCL injuries.
Secondly, it helps to tuck the meniscus out of harms way during knee flexion – reducing the risk of injuring this ring of cartilage.
Thirdly, it helps to reduce the amount of external (lateral) rotation and varus force on the knee joint(the lower leg being forced inwards compared to the knee position) when the knee is flexed.
This muscle is rarely injured as a result of a traumatic force or impact etc. It tends to be an overuse injury which develops gradually with a bit of pain or aching in the back of the knee which increases the more you run. Some people may call it a tendonitis (or any variation of that term), but I personally feel that it’s more likely a ‘tight’ / ‘facilitated’ muscle causing problems.
It is most common in runners and especially those who do a lot of hill running. You may also be more prone to developing this problem if you have a history of knee ligament injuries which has left your knee a little unstable.
Symptoms of Popliteal Injury
- Pain at the back of the knee
- Pain is worse running downhill
- Rotating the lower leg inwards whilst the knee is flexed may cause pain
- Tenderness when pressing really deep into the very upper calf*
*Please don’t push too hard! There are a lot of blood vessels and nerves in the popliteal fossa at the back of the knee! Maybe leave that to a professional!
Causes of Popliteus Injury in Runners
As with most overuse running injuries, biomechanics and muscle imbalances play a vital part.
The hamstrings are a great place to start looking. Weakness or inhibition of the hamstrings means the Popliteus has to work harder to control tibial rotation in stance phase.
As well as weakness in the hamstrings, take a look at Gluteus Maximus. This big hip extensor muscle is commonly inhibited in those who sit for long periods due to short hip flexors. A reduction in Glute Max force requires the hamstrings and so Popliteus to work harder.
Initially, the runner should rest from running and anything else that aggravates the pain. Focus on gentle stretching of the hamstrings and any other tight musculature.
Deep tissue massage can be very effective at reducing tension in a facilitated Popliteus. It does tend to be pretty uncomfortable for the patient though! Don’t try to do this yourself as it is a very complex area which should be left to a professional.
Once pain-free to do so, start correcting any muscle imbalances. Work on hamstring and Gluteus Maximus function with exercises like glute squeezes, bridges and progressing on to deadlifts and eccentric (Nordic) hamstring curls. Make sure you include exercises with a rotational element as these movements are included in the function of Popliteus. Things like Lunges with a medicine ball twist or single leg clock squats.
One pain-free on a daily basis and when testing the muscle with rotation and flexion of the knee, you may be ready to start a return to running program. Start with short runs on a completely flat surface – no hills allowed! And when I say short – I mean short! 10 mins tops!
If this goes ok, without pain at the time or for the following 2 days, you can try again, although- although again – keep it short. Presuming all is still well start to increase your distance very gradually, still avoiding hills as much as possible. If you do start to feel a recurrence of the pain, stop and go back a step!