Pain at the back (posterior) of the knee

The most likely structures to cause pain at the back of the knee are ligaments, muscle tendons, bones, cysts and bursae. Posterior knee pain may be a problem following a total knee dislocation, fracture to any of the bones within the knee joint, cartilage damage or soft tissue injury. Can result from recreational activities and / or obesity, being flexible and is more common in teenagers and young adults, more often girls. Short tight muscles or muscular weakness may also cause or refer pain to the knee plus, spinal conditions e.g. ‘sciatica’ can refer pain to the joint.

Posterior cruciate ligament (PCL)

Like an ACL injury you will be acutely aware when and if you have knackered your PCL. The PCL provides stability between the thigh bone and shin bone and can be susceptible to injury when the knee is bent such as, falling forwards and landing with force or through a road traffic accident where the bent knee forcibly collides with the vehicle dashboard. Can be ruptured through over-extending the knee (hyper extension), beyond straight, most likely with added force applied for example sporting activities such as skiing, rugby and American football.
It is more common to damage the PCL in combination with other ligaments and cartilage of the knee than in isolation. Posterior knee pain may be present when walking downhill, slowing down from running or walking downstairs. Complete rupture may require surgical repair, a stretched PCL is unlikely to require surgery, in either case dedicated prolonged (9-12 months) rehabilitation is required to regain stability, strength and be able to consider a return to sporting hobbies.

Osteoarthritis (OA)

Osteoarthritis commonly affects the knees. A healthy joint is made up of two bones whose ends are covered in a shiny smooth coating of cartilage which in part allows the joint to slide, glide and rotate providing functional movement. The cartilage within each joint is bathed in synovial fluid which nourishes the cartilage, maintaining good health and further providing shock absorption.
Over time our knee joints, essentially our cartilage may become worn like the tread on a tyre following years of bending, straightening and bearing weight. Our bodies attempt to repair the cartilage however are unable to replace cartilage tissue like-for-like with the shiny smooth cartilage slowly being replaced with rough bone. The change in joint structure causes symptoms of stiffness, swelling and pain that is known as osteoarthritis. Most common in the over 50’s.

Popliteal cyst (Bakers cyst)

A cyst is a collection of fluid in the back of the knee which can be tender, painful and may prevent the knee from fully straightening. The size of the collection may vary from day-to-day and is linked to conditions such as osteoarthritis and rheumatoid arthritis plus degeneration of the meniscus (cartilage) within the knee joint.