Pain Behind The Knee? 6 Common Causes + Effective Treatments

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Knee injuries are prevalent but, in most cases, largely preventable. So prevalent, in fact, that research shows that knee injuries make up a whopping 50% of all running injuries.

You may have heard of runner’s knee, IT band syndrome, and patellar tendonitis, but what about posterior knee pain?

Pain in the back of the knee can be caused by a number of issues.

Experiencing an injury can be disheartening, as it can halt your running routine and leave you sidelined for an unknown amount of time. Consistent knee pain can also diminish your confidence.

However, it’s important to keep in mind that injuries can heal with proper treatment protocols. With the right care and attention, knee pain can be managed and prevented so that you can continue to enjoy running for years to come.

In this article, we’ll look to address the six most common injuries that cause pain behind the knee, examining each one individually so that you can equip yourself with the tools to tackle them.

Let’s jump, slowly, into it!

The bones of the the knees, showing pain behind the knee.

6 common Causes of pain behind the knee

#1: Popliteal Tendonitis

What it is:

The popliteus muscle is a small triangular muscle that extends over the posterior aspect of the knee joint.

It is responsible for several important movement functions, namely internal rotation of the knee, forward stabilization, and knee flexion while the knee is extended.

Popliteal tendonitis is characterized by acute pain that occurs at the back of the knee joint.

Symptoms of popliteal tendonitis may include:

  • Sharp pain behind knee
  • Inflammation and localized swelling
  • Redness
  • Tenderness over the lateral side of the knee
  • Crepitus when the tendon is moved
A runner in pain holding his knee.

What causes it:

The most common cause of popliteal tendonitis is overuse.

Overuse injuries occur when a muscle is continually subjected to a physical load that is deemed excessive relative to the muscle’s load capacity.

Without adequate rest or repair, a muscle will accumulate an excessive amount of micro-tears, eventually becoming acute and inflamed.

How to treat it:

In most cases, a program of initial rest, followed by a progressive strengthening regime, is needed in order to treat tendonitis effectively.

Unless symptoms are mild and do not worsen with activity, the first step of managing tendinopathy is resting the affected tendon. Avoid activities that aggravate the tendon. If symptoms are mild, then look to reduce the frequency or intensity of the activity.

During a period of rest, you can still be active. Participating in crosstraining activities that don’t aggravate your tendonitis is essential for maintaining a degree of muscle strength and metabolic conditioning.

A person smiling on an elliptical machine.

After an initial period of rest, and once the pain and inflammation in the tendon have reduced, you can move on to gradually increasing load through the tendon.

A small degree of soreness while performing a rehabilitation exercise is to be expected. However, this pain should remain very mild and stable throughout the course of the exercise.

When treating tendinopathy, a focus on the eccentric phase of exercises has been shown to be effective in promoting the healing of the tendon because the collagen fibers will be set in the functional direction.

Over time, you can begin to make the targetted exercises harder; this may be done by increasing volume, time under tension, or resistance.

As you build strength through the tendon and the pain continues to decrease, you can move on to the final phase of tendinopathy rehab. This involves running specific drills and a gradual return to running.

Specific exercises aimed at strengthening the popliteus include:

  • Squat into a chair: Hold the eccentric (muscle lengthening) portion of this exercise for 10 seconds. This will help strengthen the quads and reduce strain on the popliteus.
  • Leg curl with a resistance band: Lie on the floor with your legs straight and a resistance band wrapped around the affected leg. Slowly bend your knee, pulling your heel towards your buttocks, and then lower it back down.
  • Single-legged Romanian deadlift: Stand on one leg and hinge forward at the hips, reaching towards the ground with your opposite hand. Keep your back straight and your core engaged. Return to standing and repeat for several reps, and then switch to the other leg.
A person doing a single leg deadlift.

#2: Baker’s Cyst

What it is:

A Baker’s cyst, more accurately described as a popliteal cyst, is a fluid-filled swelling that develops at the back of the knee.

The severity of a Baker’s cyst can vary from a small lump to a large swelling that extends down the calf muscle.

Symptoms of a Baker’s cyst may include:

  • Posterior knee pain that is difficult to pinpoint
  • Swelling or mass in the popliteal fossa
  • Limited range of motion
  • Stiffness in the back of the knee that may be exacerbated by activity
  • Tightness behind the knee

What causes it:

Baker’s cysts are usually a result of an underlying knee problem, such as osteoarthritis, rheumatoid arthritis, or a meniscus tear.

These conditions can cause excess synovial fluid to accumulate in the knee joint, which can then push outwards and form a cyst.

A person stretching their leg.

How to treat it:

An asymptomatic Baker’s cyst may resolve itself own over time.

However, if symptoms are present, short-term treatment options include rest and non-steroidal anti-inflammatory drugs (NSAIDs) to manage discomfort and inflammation. Always check with a medical professional before taking NSAIDs.

You can also practice applying ice to the affected area as needed.

After a period of rest, an exercise program can be utilized to reduce symptoms and risk of re-occurrence. This should be done with a physiotherapist and will likely target stretching and strengthening exercises.

Progressively stretching the leg muscles will help promote tissue flexibility, while strengthening the area will provide more knee support to reduce the risk of future aggravation.

If the Baker’s cyst is severe and symptomatic, you can have the cyst either drained or removed by surgical methods.

A person holding their hamstring in pain.

#3: Hamstring Strain/Tendonitis

What it is:

The hamstrings are a group of three muscles located at the back of the thigh. The three muscles that make up the hamstrings are the biceps femoris, semitendinosus, and semimembranosus. They are primarily involved in knee flexion.

A hamstring strain can range from minimal pain and a minor muscle tear to severe pain and a full muscle detachment.

Some common symptoms of a hamstring strain include:

  • Pain or tenderness in the back of the thigh
  • Sharp pain behind knee
  • Swelling or bruising in the affected area
  • Stiffness or limited range of motion in the hip or knee
  • Difficulty walking or running, especially when trying to extend the leg
  • Weakness in the affected leg
  • Muscle spasms or cramping
A Nordic hamstring curl exercise.

What causes it:

A hamstring strain can occur after a direct impact on the hamstring or, most commonly when your training demands exceed your body’s training tolerance.

How to treat it:

Hamstring tendonitis treatment should consist of relative rest of the affected area, mobility, icing, and a progressive strength program with an eccentric focus.

Refer to the blueprint used in the Popliteal treatment for a more in-depth look at treating tendinopathy.

Check out these specific exercises aimed at strengthening the hamstring.

For a detailed look at hamstring strains, check out: Can I Run With A Hamstring Strain?

A person holding their knee.

#4: Pinched Nerve In Knee

What it is:

The peroneal nerve is a branch of the sciatic nerve. It runs along the upper lateral side of the popliteal fossa to the posterior part of the head of the fibula.

Having a pinched nerve in the knee may cause an inability to lift your foot toward your leg, which subsequently causes your foot to drag when you walk.

What causes it:

Pain isolated to the back of the knee is not usually associated with peroneal nerve damage. If nerve damage is present, it will likely run down the leg into the foot.

Traumatic injuries, such as a break, can compress the nerve. As a result, it becomes inflamed, which causes the symptoms of a pinched nerve in the knee.

How to treat it:

Physical therapy treatment aimed at reducing pain and improving mobility may be effective.

Long-term compression can cause permanent damage. Therefore, it’s best to consult with a healthcare professional or physical therapist to get an accurate diagnosis and treatment plan.

A patient with a physical therapist.

#5: Torn Meniscus

What it is:

The meniscus acts as a cushion between the bones in the knee joint. It is a horseshoe-shaped bit of cartilage that distributes weight and provides stability in movement.

There are numerous types of meniscus tears. Symptoms will vary depending on the severity of the tear, which may be torn or completely ruptured.

Many meniscal tears are never recognized as they do not present symptoms, and some heal on their own.

Symptoms of a meniscus tear may include:

  • Pain in the knee joint
  • Swelling
  • Stiffness
  • Difficulty moving the knee, particularly when trying to bend or straighten it fully
A therapist holding a patient's knee.

What causes it:

A meniscus tear is a common injury in running that can result from a sudden fall or twisting of the knee. It can also arise from general wear and tear over time.

How to treat it:

Treatment will depend on the severity of the tear.

For incomplete tears, conservative treatment may be possible. This will include a progressive strengthening program that looks to specifically strengthen the quadriceps muscles and, more generally, build strength and confidence around the knee.

If the tear is severe or if the tear is peripheral and longitudinal, then conservative treatment is rarely successful and surgical treatment to repair the lesion is usually required.

A person doing an air squat.

#6: Posterior Cruciate Ligament

What it is:

The posterior cruciate ligament (PCL) is one of the four main ligaments in the knee joint and sits at the back of your knee. Its job is to keep the knee stable by preventing the tibia from moving too far backward in relation to the femur.

If you have injured your PCL, it is likely not an isolated injury. The PCL can be overly stretched, resulting in a strain or completely torn. Over 95% of PCL injuries come hand in hand with damage to either the anterior cruciate ligament or medial cruciate ligament.

What causes it:

The most common cause of a PCL strain or tear is a direct force on the knee.

How to treat it:

If the PCL injury is mild, i.e., a grade I/II strain, then physical therapy is an effective treatment option.

Rehabbing a ligament observes a similar protocol to rehabbing a tendon. With an initial phase of rest, followed by a phase of adding load, followed by a phase of functional rehab, and lastly, a return to running.

Surgical treatment is required in extreme strains or tears.

Pain behind the knee can occur for a number of reasons. If you want to give yourself the best protection against knee injuries, check out: Leg Strengthening Workouts.

If you have pain in the back of the knee, or pain that is more general, be sure to read 6 Common Causes of Knee Pain After Running + How to Fix Them.

A person doing a machine hamstring curl.
Photo of author
Ben is a qualified Personal Trainer and Sports Massage Therapist with a particular interest in running performance and injury. He has spent the last 9 years working with runners at his clinic in Brighton. Ben is a keen runner and avid cyclist. Evenly splitting his time between trail running, road biking, and MTB.

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