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Pain Behind Knee

To understand what causes pain behind the knee it is first important to understand the anatomy of the joint. The knee joint is a crucial joint due to its anatomical position and the role it plays. A number of hard tissue and soft tissue structures converge here to load the weight of the body and allow movement.

Injury or abnormality of cartilage, tendons, ligaments, muscles or bones (kneecap, thigh bones, etc.) can manifest itself as knee pain. The overall prevalence of knee pain was found to be a whopping 46.2% in a study.

The location of the knee pain sufficiently describes the differential diagnosis of the underlying issue.

Posterior knee pain is a common complaint at healthcare facilities. Pain in the back of the knee when straightening the leg can be caused by various knee issues.

Understanding The Anatomy Of Pain Behind Knee

Before we go on to explain the causes of posterior knee pain, it is crucial that we have a hint of what composes the back part of the knee.

A complex network of soft tissue structures i.e. muscles, ligaments and tendons are present at the back of the knee that extend support to the knee. These stabilizers may be active or passive.

The important knee ligaments (passive stabilizers) are:

  • Medial collateral ligament (MCL)
  • Lateral collateral ligament (LCL)
  • Anterior cruciate ligament (ACL)
  • Posterior cruciate ligament (PCL)

The ligaments connect the knee to the leg bones (tibia).

Active stabilizers of the joint are:

  • Hamstring muscles
  • Popliteus muscle
  • Extensor muscles

Causes Of Pain Behind Knee

The list of knee infirmities leading to pain in the back of the knee is as follows:

Hamstring Injury

As per a study published in 2016, hamstring injuries are on the rise in athletes/players since 2001. This particular injury is a major culprit in keeping players off the field.

Hamstring refers to the trica of muscles that run through the back of your thigh. The muscles involved are the semitendinosus muscle, semimembranosus muscle, and biceps femoris muscle.

Overstretching or sports injury to any of the muscles is termed a hamstring injury. When the biceps femoris tendon is affected the condition is more specifically known as biceps femoris tendonitis/biceps femoris tendinopathy.

This type of soft tissue injury is linked to posterolateral knee pain. If the muscles tear, healing can be a tiring and loathsome process.

Calf Strain

The back of your lower leg i.e. calf is made up of two muscles:

  • Soleus muscle
  • Gastrocnemius muscle

Strenuous sports activities standing and running in quick successions (such as in long tennis) can injure these muscles and lead to tearing of the gastrocnemius muscle.

Older athletes or those having suffered leg injury must be cautious when training as they are at a greater risk of developing calf strain.

Gastrocnemius tendonitis/tendinopathy causes pain in the posterior region while soleus injuries are felt on the lateral side of the knee.

Arthritis as a cause of pain behind knee

Chronic degenerative diseases of the bones and joints can have musculoskeletal manifestations. Osteoarthritis of the knee is a highly prevalent malady in older adults that is characterized by knee pain, stiffness and compromised quality of life.

It is a common cause of the ache you get when straightening the leg. And it is not just osteoarthritis that causes posterior knee pain.

As per a study, rheumatoid arthritis patients are also known to suffer from posterior knee pain. Lupus and psoriatic arthritis can have the same symptoms too.


Knee sprains are common in the active, young lot of the society. Twisting a leg or a forceful kick in a football match can cause inflammation and pain in the back of the knee.

Sprains are common in daily life and pain arising from a sprain usually goes away by doing rest.

Patellar Tendonitis

Generally known as the jumper’s knee, patellar tendonitis is a condition of tendon injury. This should not be confused with the runner’s knee which causes pain on the front side of the knee.

The patellar tendon is an important structure that connects the kneecap (patella) to the shinbone.

Sports injuries (mostly) or hectic movements can induce microtears in the tendon which swells up as a result. A whopping 40-50% of volleyball players suffer from jumper’s knees. Thus, it can be classified as an overuse injury.

It starts off as mild pain but transforms into debilitating pain as the tendon gets further damaged. The pain is most appreciable when straightening the leg.


Another condition that affects the knees is chondromalacia (cartilage breakdown). This very condition is mostly associated with anterior knee pain, however, extensive damage as in prolonged arthritis may lead to the development of pain while straightening the leg.

Anterior Cruciate Ligament Injury/Tear

Detailed analysis of posterolateral knee pain cases has revealed ligament injury and tear to be a major underlying cause.

Anterior cruciate ligament injury is yet another prevalent sports activity consequence that can cause pain in the extension of the leg.

In severe cases, there might be tearing of the ACL. The most evident symptoms of an ACL injury include pain on stretching/straightening the leg which interferes with walking. Swelling due to ligament injury is also evident.

Posterior Cruciate Ligament Injury (PCL injury)

Repetitive hectic sports activities (overstretching the knee) can also injure the posterior cruciate ligament, however, the chances of this are lesser (as compared to ACL).

Injuring the PCL is not that easy. Non-athletic persons usually suffer from PCL injury after a hard blow to the front of the knee.

The ligament might tear under excessive pressure causing severe keen pain on the backside. Posterior knee pain is a clinical sign in cases of PCL injury.

Meniscal Tear as a cause of pain behind knee

Cartilage damage in the knee region might also trigger knee pain in the back. The meniscus is special cartilage that stabilizes the joint while providing a cushioning effect.

Overenthusiastic athletes can injure the meniscus during a squat. As the cartilage becomes weak and prone to damage in old age, increasing age is another risk factor for a meniscus tear.

A torn meniscus can present you with severe pain in different regions of the knee. In a study, 69% of the participants reported medial, lateral and posterior knee pain.

Patients have also reported popping sounds when moving or straightening the leg. The condition is usually unnoticeable in the beginning but gradually becomes painful.

Fractures And Misalignment

A misaligned or dislocated patella can give make leg straightening a painful task for you.

Stress fractures of the knee and leg bones (femur, tibia, etc.) can make the backside of the knee sore and achy. Studies suggest that repairing the avulsed, obliterated and torn tissues alleviate posterolateral knee pain.

Ipsilateral fractures of the femur and tibia are termed floating knee injuries that need proper treatment.

Baker’s cyst (Popliteal Cyst)

Your knee has specialized structures called bursa that reduce friction and provide cushioning to the joint. These areas are prone to the development of a cyst.

A cyst on the backside of the knee can hinder your daily movement and activities. A commonly found fluid-filled cyst bulging on the back of the knee is the popliteal cyst (due to its presence in the popliteal fossa).

If you are a woman (aged over 40) facing knee pain, there is a good chance that it might be due to a baker’s cyst.

It is also known as a baker’s cyst and causes pain in the back of the knee when straightening the leg. The development of this abnormality can be attributed to degeneration of soft tissues (cartilage tear) and arthritis.

The most commonly experienced symptoms of a baker’s cyst include pain on the backside of the knee accompanied by stiffness. Evident swelling is noted by the majority of patients. Most people also complain of being unable to straighten/flex the knee.

Research suggests that these cysts may be associated with trauma or juvenile idiopathic arthritis (JIA) and usually resolve spontaneously.

A popliteal cyst is usually associated with conditions such as:

  • Meniscus tear
  • Rheumatoid arthritis
  • Osteoarthritis

A diagram of pain behind knee

Deep Venous Thrombosis as a cause of pain behind knee

The human body has a dense network of veins running through its entire course. Your legs are supplied with a circuit of deep veins that can develop blood clots (thrombus). This condition of blood clot formation in the deep veins of the legs is known as deep venous thrombosis (DVT).

DVT can cause knee pain, especially in the posterior knee. People who form duties involving long hours of standing (such as guards) are more prone to developing DVT.

The disorder presents itself as swelling and warmth in the region. It must be diagnosed and treated as soon as possible because it can lead to the lodging of clots in critical arteries such as the lungs (pulmonary embolism) or the heart (myocardial infarction).

An infected knee might also cause DVT. A 2010 case study revealed a young 26-year-old man suffering from DVT induced by a septic knee.


Infection of the knee usually involves the contamination of synovial fluid present in the knee joint. Such a joint is then called a septic joint.

Infection in the knee joint is usually the outcome of surgical procedures. The highlighting symptom of post-surgical knee infection is severe pain paired with swelling/redness and stiffness.

Referred Pain

You might experience pain in the back of the knee even when there is nothing wrong with the knee itself. Such pain is known as referred knee pain.

It is a pain that arises (has origin) in another part of the body (lower leg, shins, hip, etc.) but is felt in the knee region.

Diagnosing Pain Behind Knee

Diagnosis is based on multiple tests and imaging results. Generally, the doctor takes a complete medical history of the patient followed by a clinical examination.

Sporty and athletic individuals face soft tissue (cartilage, tendon, meniscus) inflammation and rupture (tear). The older population complains of posterior knee pain as a result of arthritis or cysts.

X-rays, MRIs, and ultrasonography are used to detect underlying abruptions.

Treatment Options

Most cases of knee pain in the back when straightening the leg go away by just giving rest to the legs. You can follow simple home strategies to get rid of posterior knee pain:

Home Remedies (RICE Principle)

  1. Rest (R)
  2. Ice application for 20 minutes (I)
  3. Compression (via a bandage)
  4. Elevate the knee using pillows

You can use crutches to avoid weight on the knee. Over-the-counter painkillers such as ibuprofen can also help provide relief.

Pharmacological And Surgical Management

Conservative treatment is indicated for cases of injury to the ligaments (ACL, PCL, etc.). Meniscal tear repair is done in cases with severe pain.

Management of gastrocnemius and hamstring muscle involves different procedures including:

  • NSAIDs
  • Immobilization
  • Cryotherapy
  • Electrophysical therapy
  • Surgery (in severe cases)

Most of the time the orthopaedic surgeon prefers dealing with the issue in a conservative method. An aggressive surgical approach is limited to severe, non-refractory cases.

Advanced osteoarthritis is treated with Intra-articular injections of corticosteroids. An effective treatment modality for Baker’s cyst is sclerotherapy.

Physical therapy is an extremely effective treatment modality in alleviating posterior knee pain.


Many of the structures have a poor blood supply, which is why they can struggle to heal on their own. It is the oxygen and nutrients in our blood supply that help to heal these structures.

Prolotherapy involves the injection of a regenerative solution into these structures to provide a direct supply of what is required to heal and repair.

As the treatment is helping to treat the root cause of the problem, it is deemed to be a permanent fix.


Pain in the back of the knee when straightening the leg can be caused by a number of reasons. Young and enthusiastic athletes can injure knee joint soft tissues during exercise, or game. Most common soft tissue injuries that cause posterior knee pain include sprains, ligament injuries (ACL, MCL, PCL, etc.), hamstring injury, patellar tendonitis, calf strain and meniscal tear. Longstanding arthritis (osteoarthritis, rheumatoid arthritis) is also linked to knee pain. Baker’s cyst can also be a source of pain and stiffness in the knee. Infection, stress fractures, and deep vein thrombosis can also cause pain in the backside of the knee. The best treatment is to follow the RICE principle (Rest, Ice, Compression, Elevation). Conservative management is preferred, however, surgery is required to repair torn ligaments, tendons, cysts and severe cases of arthritis.


Frequently Asked Questions

Why Does the Back of My Knee Hurt When I Straighten my Leg?

There are a number of reasons that may cause the back of the knee to hurt as an individual straightens their legs. These include the formation of blood clots, injuries to the muscles, injuries to the tendon, arthritis of the knee, or the presence of cysts. However, in the majority of the cases, these symptoms may be improved by taking adequate rest, icing the affected idea, and using pain medications. 

Should I Be Worried About Pain Behind the Knee?

The pain behind the knee can be caused by several reasons, including the formation of blood clots, formation of cysts, injury of the tendon, injury of the muscles, or arthritis. While some of these causes may be less severe, the others may be more severe and require immediate medical consultation. This is why it is often advised to consult a doctor when an individual experiences sudden and unusual pain behind the knee. 

How Do You Know if You Tore Something Behind Your Knee?

Tearing tissues is usually characterized by sudden and immense pain. This pain may be of the highest intensity when the individual tries to rotate or twist their knee. They may also face difficulty in straightening their knee completely. Hence, when an individual experiences a sudden pain and feel as if their knee is locked in place – they are likely to be experiencing a tissue tear injury. 

How Do You Treat Tendon Pain Behind the Knee?

Individuals who experience tendon pain behind the knee may be advised to take rest. This should include avoiding any strenuous physical activity and using the affected knee as much as possible. The individual may also be asked to ice their knee for 20 minutes at a time. This practice can be repeated numerous times a day. A compression bandage is often recommended to help support the tissues and prevent swelling and inappropriate bending of the structure from making the condition worse. If the patient is experiencing swelling, they may also be asked to keep the leg elevated by using a small stool while sitting on a chair in front of them or using a pillow below their feet when lying down. 

What Is The Back Of the Leg Behind the Knee Called?

The area at the back of the leg, more specifically behind the knee, is known as the popliteal fossa. It is a diamond-shaped space made by the muscles of the posterior leg and thighs. This is an important site through which the structure between thighs and legs pass through. 

What Does It Mean When the Back of your Leg Hurts Behind The Knee?

An individual who frequently complains of pain in the legs and behind the knee may be affected by osteoarthritis. This is because this symptom is often seen in osteoarthritis patients due to increased inflammatory activity in their joints. However, one should always consult a health expert who will evaluate the patient and provide them with an accurate diagnosis. 



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