Pain at the back of the knee is known as posterior knee pain. Here we explain the common injuries which cause both sudden onset (acute) and gradual onset (chronic) knee pain.
Did your knee pain occur suddenly or develop gradually over time?
Acute pain behind the knee
The following are common acute injuries which cause pain at the back of the knee:
Hamstring tendon strain
A hamstring tendon strain is a tear of one of the hamstring tendons. This is usually the biceps femoris hamstring muscle, at the point of insertion at the back of your knee. It is more common in sprinters or sports involving kicking. Symptoms include:
- A sudden sharp pain in the back of your knee.
- You may have swelling, tenderness or heat at the site of injury.
- It is important to get an accurate diagnosis and rule out a complete rupture or an avulsion strain.
More on biceps femoris tendon rupture
Biceps femoris tendon avulsion
An avulsion strain occurs when a tendon tears pulling a small piece of bone with it. Like a Biceps femoris tendon strain, this occurs through sprinting or kicking activities. If you suspect you have an avulsion injury, seek professional advice. An X-ray is needed to confirm the diagnosis. Symptoms of an avulsion strain:
- A sudden severe pain at the back of your knee (similar to that of a hamstring tendon strain).
- Sudden swelling and tenderness at a point on the back of your knee.
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Posterolateral corner injury
The Posterolateral corner of the knee consists of a number of structures. It is a less common cause of pain at the back and outside of the knee. Symptoms can include any of the following:
- Pain and swelling at the back, and outside of your knee.
- Tenderness on the outside of your knee when pressing in.
- Knee joint instability.
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Chronic pain behind the knee
Pain at the back of the knee may occur gradually. You are unlikely to be able to pinpoint the exact time your injury occurred. These injuries often start out as a ‘niggle’ which you will attempt to ignore. Eventually they become progressively worse.
Chronic knee injuries can be more difficult to treat so do not ignore the early signs!
A Baker’s Cyst or Popliteal cyst is a swelling that protrudes out the back of the knee. It is often about the size of a golf ball but can vary over time. Symptoms consist of:
- You will feel sensation of pressure in the back of your knee.
- You will have difficulty bending the knee.
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Gastrocnemius tendinopathy (or tendinitis) is inflammation (or more likely degeneration) of the calf muscle tendon at the back of the knee. This is an overuse injury which is more common in runners and sprinters. Symptoms include:
- Gradual onset pain behind the knee, often localized to a specific point.
- Your knee will feel tender when pressing it at the back of your knee.
- Going up on tip toes with your legs straight may be painful.
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Biceps femoris tendinopathy
Biceps femoris tendinopathy or biceps femoris tendonitis is inflammation (or more likely degeneration) of the hamstring tendon where it inserts at the back of your knee. Symptoms include:
- Tenderness and swelling at a specific point at the back of your knee.
- Pain is likely to have developed over time.
- You may have stiffness in the morning, or after sitting for long periods.
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The Popliteus is a small muscle located at the back of the knee. The muscle, or tendon can be torn, especially from twisting activities, or injuried through overuse. Symptoms may include:
- Acute (sudden onset), or gradual onset pain behind the knee.
- The back of your knee will feel tender when pressing in.
- Trying to bend your knee against resistance, whilst your tibia (shin) bone is turned outwards is a specific test used to help diagnose a Popliteus injury.
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Referred knee pain
Posterior knee pain can be caused by injuries or dysfunction in the lower back and hips. Symptoms may include:
- Sciatic pain which radiates down into the back of your leg, knee and/or lower leg.
- The slump test is to identity sciatic type referred pain referred pain.
Knee joint swelling
Swelling within the knee joint is a symptom rather than a specific injury. Swelling alone can be enough to cause pain and tightness behind the knee. A full knee assessment should be done to identify the root cause of any effusion (swelling). Previous injuries can often be the cause of chronic knee swelling and development of a Baker’s Cyst.
Immediate first aid for knee injuries
All acute knee injuries should be treated using the P.R.I.C.E. principles (protection, rest, ice, compression & elevation). You should apply the PRICE principles for at least the first 2 – 3 days.
- Protect knee from further damage. Rest to allow healing to take place
- Apply ice or cold therapy to reduce pain, swelling, and inflammation.
- If you have swelling then then apply compression and elevate your knee to allow tissue fluids to drain away.
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When should I see a doctor?
The majority of knee injuries, especially minor ones, can be treated at home. However, if you have any of the following symptoms you should seek medical assistance.
- Severe pain in or around the knee, especially during walking.
- Severe swelling (oedema) in the knee.
- An audible “pop” or “crack” in the knee joint that is painful.
- A “giving way” feeling in the knee during walking or going up/downstairs.
- A feeling when the knee “locks” whilst bending or straightening it.
- Altered sensation in the foot – such as a feeling of “pins and needles” (paresthesia) or a “loss of feeling” (anesthesia) in the lower leg.
- Inability to complete your normal daily activities after the initial 72 hours.
More on when to see a doctor
References & further reading
- Fritschy D, Fasel J, Imbert J-C et al. The popliteal cyst. Knee Surg Sports Traumatol Arthrosc 2006;14:623–8.