Stiff Knee

Written By: Chloe Wilson, BSc(Hons) Physiotherapy
Reviewed by: KPE Medical Review Board

Find out all about the most common causes of knee stiffness

A stiff knee can develop for a number of reasons.  There may be a problem in the joint restricting movement, or weakness in the surrounding muscles.

Knee stiffness is often accompanied by pain and swelling.  Sometimes there may also be redness, warmth, pins and needles and numbness. 

There are a number of different causes of knee stiffness but they generally fall into two categories, those caused by an injury and those caused by a medical condition.

Here we will look at the ten most common causes of a stiff knee and how to improve knee flexibility.

Why Do I Get Knee Stiffness?

Knee stiffness often develops after an injury or due to an underlying knee condition. A stiff knee is usually linked with:

Excess Fluid

When the knee is damaged, there is often a build-up of excess fluid inside the joint. The amount of swelling will depend on the severity of the injury.  

Swelling is a common cause of knee stiffness

With a minor knee injury, irritation inside the joint leads to increased production of synovial fluid. Any excess fluid in the joint can result in a stiff knee as the fluid limits movement by taking up space in the joint.

Knee swelling isn’t always visible, you can't always see it - there can be a considerable amount of excess fluid in the joint before there are any outward signs. So it is possible to have a stiff knee without any other symptoms.

With a more serious knee injury, such as an ACL rupture, there may be bleeding directly into the joint, known as a haemarthrosis which can result in considerable swelling.  

Altered Knee Biomechanics

If one of the structures of the knee is damaged, it can change how the knee moves. There is a sophisticated system of gliding, rolling and spinning movements in the joint to achieve full range of movement.

Knee injuries and swelling often affect these movements, limiting the mobility at the joint, leading to a stiff knee.

Knee Pain Inhibition

Knee pain itself often leads to knee stiffness. It’s a normal reaction – when we move, it hurts, so we stop the movement. In the early stages following a knee injury, this response is helpful in preventing further damage. But if allowed to continue, the muscles and joint can become tight which can lead to long-term knee stiffness. 

In more severe injuries, the pain may be so bad that it actually restricts movement altogether.

Common Causes of A Stiff Knee 

The most common causes of a stiff knee are:

1.  Meniscus Injury

A meniscus tear is a common cause of a stiff knee

A meniscus injury is where there is damage to the special cartilage that lines the knee joint. This can cause knee stiffness by preventing the smooth motion of the knee.

Sometimes a fragment of damaged cartilage can even get stuck in the joint, restricting movement, known as locking.

You can find out more about the symptoms, causes, diagnosis and treatment in the meniscus tear section.

2. Knee Sprain

A mild knee sprain, where one of the knee ligaments has been overstretched and may have torn, can also cause a stiff knee. This may be in part due to some swelling in the knee joint but also due to reduced stability in the joint affecting how the knee moves. LEARN MORE > 

3. Knee Ligament Injuries

An ACL tear or rupture will limit knee movement

Damage to the knee ligaments such as the anterior or posterior cruciate ligament often causes severe bleeding in the knee joint causing it to swell.

Knee swelling from a ligament tear usually comes on immediately and is profuse, limiting movement. LEARN MORE >

4. Bone Fractures

A break or fracture in any of the knee bones can also cause knee stiffness due to pain, instability and misalignment.

It is really important to work hard at your rehab programme if you have broken your knee to help reduce the swelling, prevent muscle tightening and to reduce the risk of long-term knee stiffness.

5. Arthrofibrosis

This is a rare condition that can develop following a knee injury or surgery. It is when the body develops excessive scar tissue adhesions which cause painful restriction to knee movement.

Carefully following your rehab programme helps to reduce the risk of developing arthrofibrosis. In chronic cases, knee surgery may be required to remove the adhesions.

6. Knee Tendonitis 

Tendonitis, inflammation of the tendon, can cause knee stiffness

Irritation or degeneration of the tendons can affect the pull on the knee joint, due to weakness and ineffectiveness, limiting its normal motion. The tendon may become inflamed or tight thus restricting knee motion range.

Knee tendonitis most commonly affects the patellar tendon at the front of the knee which joins the kneecap to the shin bone, known as patellar tendonitis of Jumpers Knee. LEARN MORE >

7. Post Exercise Stiffness

Not technically an injury, but overworked muscles quickly become tight and weak making the leg feel stiff. This is a common cause of knee stiffness in runners. Ensure you warm up and cool down effectively to avoid this.

8. Knee Arthritis

Osteoarthritis is more commonly known as wear-and-tear arthritis and causes the breakdown of knee cartilage and bone. 

Arthritis in the knee will often cause knee stiffness

With knee arthritis, the joint loses its smooth surfaces and the space between the bones decreases causing knee stiffness. 

Knee stiffness from arthritis tends to be worse first thing in the morning or after prolonged rest, easing fairly quickly with movement. It typically only affects one or two joints. 

Rheumatoid Arthritis is a chronic, systemic disorder that causes inflammation and fibrosis of multiple joints. It can result in damage to the cartilage and bones causing knee stiffness, usually in both legs, and is often accompanied by redness, warmth and swelling. 

Symptoms of rheumatoid arthritis fluctuate, with good spells and bad spells. It tends to affect multiple joints, such as the hands and feet as well as the knees.

Knee arthritis is the most common cause of knee stiffness in people over 60. LEARN MORE >

9. Knee Bursitis

Bursitis, inflammation of one of the knee bursa, is a frequent cause of a stiff knee and swelling

Bursitis is another common cause of knee stiffness and develops when there is swelling in one of the bursa, small fluid filled sacs that provide cushioning between bones and tendons around the knee  

The bursa get inflamed either from excessive friction or a sudden blow that squashes them. 

Knee bursitis usually presents as a squashy lump, a bit like a small orange, most commonly in front of or behind the knee. LEARN MORE >

10. Gout Knee

Gout is a type of inflammatory arthritis caused by a build-up of uric acid which deposits crystals, most commonly in the knees or feet. 

Symptoms of gout knee come on rapidly over a few hours and as well as knee stiffness, the joint tends to also feel hot, very painful and looks red.  Repeat episodes of gout are common. LEARN MORE >

Rare Causes of Knee Stiffness

There are a few other rare causes of a stiff knee, but they are potentially very serious, and require immediate medical attention.

  1. Tumour: An abnormal growth in the bone
  2. Infection: Such as osteomyelitis (infection in the bone) or septic arthritis (infectious arthritis)

Stiff Knee Pain Treatment

The best course of treatment for a stiff knee will depend on the cause and stage of your knee problem. It might be that an exercise programme is what you need, you might need to think about the position you sit in or how active you are, change your diet or you might even need a course of physical therapy.

Check out our article on How To Improve Knee Flexibility for loads of great ways to reduce knee stiffness and regain knee motion range.

In the early stages of knee stiffness, particularly after a knee injury, following PRICE principles can really help:

Ice can help reduce knee swelling
  • Protect: the joint from further damage, e.g. with a brace. 
  • Rest: from aggravating activities, but keep the leg gently moving so it doesn’t seize up. 
  • Ice: regular ice treatment can help reduce swelling and therefore knee stiffness. 
  • Compression: specially designed bandages such as tubigrip help to support the knee and reduce swelling. 
  • Elevation: keeping the leg elevated helps excess fluid in the joint to drain away. 

You can find out more about each of these in the PRICE treatment section.

Supplements For Knee Stiffness

Supplements such as glucosamine and chondroitin can help to reduce knee stiffness

There are various supplements that claim to reduce the symptoms of a stiff knee, particularly with arthritis.

The most popular ones include omega-3, glucosamine and chondroitin which can help to improve knee joint lubrication. 

You can find out more about how taking supplements can help to reduce knee stiffness and how they work in the supplements section

What Next?

Any new cases of a stiff knee, especially if the cause is unknown, should always be checked out by your doctor for an accurate diagnosis. The same is true if the knee swelling doesn't start to reduce after a couple of days. 

In most causes, the earlier treatment begins, the quicker recovery tends to be, so early intervention is key for reducing knee swelling and to stop you getting a stiff knee.

Don't forget to check out our top tips on How To Improve Knee Flexibility!

Page Last Updated: 18/06/21
Next Review Due: 18/06/23

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