Orthopaedic Surgeon

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Pain behind the knee

Pain at the back of the knee  can be from problems with the bones, muscles, tendons, ligaments, nerves, blood vessels and the bursae. Very few of these require surgical intervention.


Bakers Cyst

All knees produce fluid to aid in lubrication of the joint and to provide nutrition to the joint lining cartilage cells. In some people this fluid is pumped into a sac at the back of the knee through a one way valve. As the fluid accumulates the sac stretches and the patient may notice a rounded swelling about the size of a golf ball at the back of their knee. The size of the lump often changes at different times of the day. There may be a sensation of pressure in the back of the joint which can go down into the calf muscle and if the lump is big enough it may create difficulties in bending the joint.

Generally speaking Bakers cysts are ignored. If they are large enough to cause symptoms then they can be surgically removed but it is important to find out what caused the extra fluid to be produced in the joint in the first place. The most common cause of extra fluid production is osteoarthritis of the joint and unless the underlying cause is addressed when the cyst is removed there is a very high recurrence rate of the Bakers Cyst. Usually this means that arthroscopy is necessary to fix or remove torn menisci or joint lining cartilage. Over time, the cyst usually disappears or reduces in size and does not need drainage or removal.

Ruptured Bakers Cyst

These cysts occasionally rupture or burst and spill synovial fluid into the muscle compartment of the calf. This usually creates quite severe pain and swelling which can take 3 months to settle. If it happens applying a compressive stocking, using ice packs and pain killers and seeing a physiotherapist can help. Once it has ruptured it is rare for the lump to come back again.

It is worthwhile having a doctor examine any lump that develops at the back of the knee to make sure it is not an aneurysm of a blood vessel or something that might be suspicious of a tumour of some kind. In most cases all that is needed is a plain xray of the area and then treatment of the underlying condition. MRI scanning is rarely used to diagnose a Bakers Cyst.

Popliteus injury

Injury to the popliteus tendon is most commonly seen in running athletes.  To treat this condition rest, ice, elevation and compression are used. You need to do gradual stretching exercises in multiple planes and see a physiotherapist who will take you through an exercise programme (closed kinetic-chain eccentric strengthening exercises, multidirectional lunges etc) 

These are some of the causes of posterior knee pain:

  • Baker's cyst
  • Soft-tissue or bone tumor
  • Meniscal tear
  • Hamstring injury
  • Gastrocnemius tendon calcification
  • Popliteus tendon injury
  • Posterolateral corner injury
  • Popliteal artery entrapment syndrome
  • Common peroneal nerve entrapment
  • Tibial nerve entrapment
  • Degenerative joint disease

Other causes of posterior knee pain

Pain can be referred to the back of the knee from a meniscal tear, chondral injury or ligament injury but this is not common.  The pain can also be from a remote structure like a nerve passing by the knee and sometimes a pinched nerve in the lower back or even arthritis of the hip can be felt as pain in the back of the knee.

Symptoms vary widely:

Feeling of fullness in the popliteal fossa, Knee locking, palpable
mass, pain without weight bearing, increasing pain with deep knee flexion, posterior knee pain with sudden acceleration or deceleration, pain with running - especially downhill.

A careful history and physical examination can often provide an accurate diagnosis. Always start with a plain xray but there are times when investigations such as an MRI scan or bone scan are very helpful. CT scanning is rarely helpful in diagnosing causes of posterior knee pain. Arthroscopic knee surgery is not usually performed to treat posterior knee pain.