Pain behind the knee is one of the more challenging musculoskeletal problems. The causes are many — muscle tears, tendon injuries, nerve damage, and even blood clots. As with most problems, the key is an early, accurate diagnosis. So what causes pain behind the knee, and how do you find the cause?

This is the hub for pain at the back of the knee. For pain on the inside of the knee, see inner knee pain.

What’s behind the knee?

The back of the knee has complex anatomy. The knee joint sits in the middle, with the thigh and calf muscles passing through. The large hamstring muscles run from the pelvis across the knee to the lower leg bones, and the calf muscles begin at the bottom of the thigh and cross the knee to form the Achilles tendon. Vital nerves and blood vessels also pass behind the knee to supply the lower leg and foot.

How do we find the cause of pain behind the knee?

We use a methodical process. First, a thorough assessment of the joints, ligaments, and tendons that cross the back of the knee. We then use imaging to confirm our reasoning — X-rays pick up significant arthritis, and MRI detects soft-tissue problems such as tendonitis or muscle tears. Occasionally we add blood tests, ultrasound, or nerve studies, depending on the presentation.

Back-of-knee pain location chart

Use the chart below to find possible causes by location, and follow the links to learn more about each.

back knee pain location chart
Inside back of knee Top of the calf Outside back of the knee Central back of the knee

Central back of the knee

Baker's cyst 

PCL tear

Osteoarthritis 

Common causes of pain behind the knee

Knee arthritis

Osteoarthritis causes bone spurs and inflammation at the back of the knee, often with tightness and restricted movement. Exercise and load management are the best treatments, and a knee sleeve can help. Occasionally we use cortisone or PRP injections.

Meniscal tears

Meniscal tears cause pain behind the knee, usually more to the inside or outside. Most are degenerative. Sometimes the meniscus ‘root’ tears, where it attaches to the middle of the knee — then the meniscus stops working as a shock absorber, increasing stress on the joint. Treatment of degenerative tears is mostly conservative, except in younger patients after trauma, root tears, and knees that lock or give way.

Baker’s cyst

A Baker’s cyst is a fluid collection at the back of the knee, arising from the joint — so joint swelling makes the cyst bigger. Bigger cysts press on the joint, muscles, and nerves, causing pain. Ultrasound confirms it, and painful cysts can be drained under ultrasound.

Tendon and muscle injuries

Tendon injuries are common in runners. The tendons most affected are the hamstring on the inside (semimembranosus) or outside (biceps femoris). Rarely, the small popliteus tendon swells. Hamstring muscle tears occur about 5 cm above the knee — locating the tear matters, as it sets the return-to-sport time. A pulled calf or soleus tear near the knee can also cause pain here.

Nerve damage

Pinched nerves in the lower back (sciatica) or buttock (piriformis syndrome) can radiate down the leg into the back of the knee. But pain isolated to the back of the knee isn’t usually from nerve damage.

DVT (deep venous thrombosis)

DVT rarely causes pain only at the back of the knee — usually it extends to the calf and inner thigh, often with a swollen ankle and calf. The risk is higher with obesity, cancer, recent surgery, or long-haul travel. A hot, swollen, painful calf needs urgent medical assessment.

Frequently asked questions about pain behind the knee

Why is the back of my knee swollen?

Most often a Baker’s cyst, though these aren’t usually painful. See your doctor for severe pain and swelling — other causes include DVT or, rarely, a popliteal aneurysm.

What causes pain behind the knee and in the calf?

Pain spanning the knee and calf often points away from the knee joint — possible causes include nerve pain from the lumbar spine, piriformis syndrome, a calf or soleus tear, or a DVT. A hot, swollen calf needs urgent review.

What causes pain at the back of the leg behind the calf?

Pain behind the calf is often muscular — a calf strain or soleus tear — but can also be the Achilles higher up, or referred pain from the spine. If it comes with calf swelling and warmth, a DVT must be excluded first.

My knee MRI was normal — what does that mean?

A normal MRI doesn’t rule out every problem. We’d then consider causes outside the joint, such as DVT or referred pain from the spine.

When should I worry about pain behind the knee?

Seek urgent help if the calf is hot, swollen, and tender (possible DVT), or if you have severe pain after trauma, a locked knee, or the knee giving way. Persistent pain beyond a few weeks should be assessed.

Final word from Sport Doctor London about pain behind the knee

Pain behind the knee isn’t straightforward. Some causes, such as a DVT, can be serious; others need further investigation and treatment. See a sports medicine specialist for an accurate diagnosis and management plan.

To book a knee assessment with Dr Masci in London, contact the team here or call +44 (0) 203 488 0350.

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