Pain in the back of the knee

The back of the knee is called the 'popliteal' region of the knee, deriving its name from the popliteus muscle and tendon that are situated in this region. Doctors refer to pain at the back of the knee as 'popliteal pain'. Popliteal pain may arise from a number of causes.

• Baker's cyst
• Popliteus tendinitis
• Injury to the posterior horn of the meniscus
• Hamstrings tendinitis (biceps femoris tendinitis)
• Gastrocnemius tendinitis

Baker's cyst

One of the common causes of popliteal pain is a Baker's cyst (or popliteal cyst).

This is a fluid-filled lump at the back of the knee caused by lubricating fluid which has built up under pressure within the knee cavity in response to an inflammatory problem within the knee and not directly related to the lump itself. Here the capsule is weak between the gastrocnemius and semimembranosus tendons. The depression in the middle of the back of the knee is called the 'popliteal fossa'. Any build-up of fluid pressure inside the knee joint may result in the capsule bulging in the area, and forming a Baker's cyst.

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Popliteus tendinitis

If we consider just the bit at the back of the knee - the posterior horn - of the lateral meniscus, there may be a tear of the meniscus itself, or there may be a disruption in the fibres that frequently attach the rim of the posterior horn to the popliteus tendon as it sweeps along the back of the meniscus.

Either of these possibilities may result in pain at the back of the knee.

The pain may be accompanied by feelings of knee instability and giving way.

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Injury to the posterior horn of the meniscus

If we consider just the bit at the back of the knee - the posterior horn - of the lateral meniscus, there may be a tear of the meniscus itself, or there may be a disruption in the fibres that frequently attach the rim of the posterior horn to the popliteus tendon as it sweeps along the back of the meniscus.

Either of these possibilities may result in pain at the back of the knee. The pain may be accompanied by feelings of knee instability and giving way.

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Hamstrings tendinitis

Inflammation of the biceps femoris tendon as it sweeps along the back of the knee may give rise to pain in this area.

The biceps femoris tendon is one of the hamstrings tendons. It may become damaged via overuse during a repetitive activity such as running or cycling, where the tendon abrades over the bone of the femur at the back of the knee. The pain is experienced at the outer side of the knee at the back.

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Gastrocnemius tendinitis

The other tendon inflammation that may cause pain at the back of the knee is gastrocnemius tendinitis. Pain may be experienced on the inner or outer aspects of the back of the knee.

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Less common causes of pain at the back of the knee

There are less common but nonetheless important conditions that can cause pain at the back of the knee -

• Popliteal artery aneurysm

  A popliteal aneurysm is a defect of the popliteal artery where the wall of the artery loses its elasticity and the artery bulges out into a spindle shape. This condition usually occurs in older people and the cause is usually age-related loss of elasticity and hardening of the artery wall.

  The bulging of the aneurysm can cause local compression and pain, but more important symptoms may be the result of clots forming on the walls and shooting down to the lower leg, obstructing the blood supply initally causing claudication (pain in the calf and foot on walking) and later more advanced arterial obstruction and a cold white foot (a medical emergency).

• Posterolateral corner injury

  The posterolateral corner is the region on the outer aspect of the back of the knee where several structures contribute to stability in the knee. There is always a story of a significant injury followed by feelings of knee instability accompanying the pain.