11 reasons for knee pain when bending your leg

Home » 11 reasons for knee pain when bending your leg

Do you experience pain when bending your knee, or when kneeling? This can be a sign of several different conditions, some of which can be of medical concern.

I will explain the eleven main causes of knee pain when bending or kneeling, as well as the gold-standard treatment options involved. Here we go!

Why can’t I bend my knee without pain?

If you are experiencing pain when bending your knee, the first step is to determine the root cause of this discomfort. Some of the most common causes of knee pain when bending or kneeling include:

Broken cartilage (loose body) in the knee joint space

This occurs when there is damage to the cartilage within the joint, which can lead to inflammation and pain. The pieces of cartilage may break off the end of the thigh bone or shin bone, from degeneration or traumatic injuries.

Often, a sign of this will be your knee joint locking. Loose bodies can cause real issues for your knee joint and may need to be surgically addressed.

Patella subluxation

This is a condition where the patella (kneecap) becomes dislodged from its normal position. It causes pain and usually a lot of swelling, limiting knee movement.

The soft tissues around your knee play a role in keeping the patella in its groove along the thigh bone, but they can become unbalanced, warranting a visit to a physical therapist to get your connective tissues and muscle strength on the right track.

Knee sprain (ACL, PCL, MCL)

A knee sprain occurs when one or more of the ligaments surrounding the knee joint are stretched or torn. This can cause pain, swelling, and instability around the affected joint, stopping your knee from bending properly.

If stretched forcefully, it can be an anterior cruciate ligament tear which may need surgery. But these days, if your muscle strength can keep the knee joint stable it can be avoided. Some people, in rare cases, may tear their ACL without knowing.

A medial collateral ligament sprain is the most common knee sprain and will have you feeling pain in the outer knee, and you’ll have difficulty kneeling or flexing the knee.

[Knee sprains should be treated properly, so read our full post about knee sprains here.]

Baker’s cyst

A Baker’s cyst is a fluid-filled sac that forms behind the knee joint. It can cause discomfort when the knee bends, because of the pressure from the synovial fluid which shouldn’t be there.

[It’s one of the common causes of leg pain behind the knee, which I wrote a full post on here]

Bakers cysts are quite common, however, and usually don’t cause a lot of grief. If big enough, they may need to be addressed with a procedure to extract synovial (joint) fluid.

Patellofemoral pain syndrome (PFPS)

This condition is characterized by anterior knee pain, around the patella (kneecap) and difficulty bending the knee – especially if attempting exercise and sport. A common knee injury, it’s usually caused by repetitive stress on the kneecap and surrounding tissues.

You may have heard of runner’s knee or Hiker’s knee, which are variants of PFPS. Treatment options are pretty straightforward in the beginning:

  • rest, and avoid the aggravating movements for a while
  • attend physical therapy for the best rehab type for you

Check out our video about re-building after hiker’s knee here.


Sciatica is a condition that occurs when the sciatic nerve, which runs from the lower back down the leg, becomes compressed or irritated. It’s generally from a herniated disc in the lumbar spine or bony degenerative changes there.

This can cause pain, numbness, or tingling in not just the buttock and posterior thigh, but also your knee! Generally, with sciatica knee pain, it’s worse when your knee is straightened from a bent position, but kneeling can be a real issue. This is because your pelvis flexes under, putting tension on the sciatic nerve in your low back.

You’ll want to get to the chiro for this one – and potentially seek acupuncture or dry needling, too. [Find out the difference here, and how to help sciatica].

Meniscus tear

The meniscus is a C-shaped piece of cartilage – shock absorbers that sit between the thighbone and shinbone, in the knee joint. A tear in this tissue causes a lot of pain, sometimes swelling, and stiffness that makes it hard to bend the knee.

If bad enough, such as a bucket-handle meniscus tear or complete tear with locking and/or giving way of your knee, you may need surgery from an orthopedic surgeon. This usually involves small incisions to clean up the meniscus (arthroscopic surgery).

You’ll need a knee brace for a while afterward, during recovery. Meniscus tears do change the mechanics of your knee joint, so seek physical therapy to help avoid osteoarthritis down the track.

A proper treatment plan from your healthcare provider can get you bending your knee again.

Osteoarthritis (OA) of the knee

One of the most common causes of knee pain when bending, OA causes inflammation and damage. It often affects older adults but can occur sooner if people get injured as young adults (e.g anterior cruciate tears, meniscus tears)

This type of arthritis is a degenerative condition. Contrast this with other types such as Rheumatoid arthritis, which is auto-immune, and can cause difficulty bending your knee too.

knee OA flexing pain
knee OA is a common underlying cause of your knee pain and joint stiffness when bending

As a common knee condition, we cover everything you need to know about bone-on-bone knees here.

To address the joint stiffness of knee osteoarthritis, you first need an x-ray to see how bad the degeneration is. However, even advanced sufferers of OA can get gains in knee flexion with a good treatment plan and return to a more active lifestyle.

Chondromalacia patella (CMP)

This condition is characterized by damage to the cartilage on the back of the kneecap. It can cause pain behind or around the kneecap, as well as difficulty bending the knee because of friction and inflammation.

Housemaid’s knee (prepatellar bursitis)

This condition is caused by inflammation of the bursa, a fluid-filled sac that cushions the kneecap. It can cause pain and swelling around the kneecap, as well as difficulty bending the knee.

elastic bandage for bending knee pain

Quadriceps tear

The quadriceps are a group of four muscles that run from the hip to the knee, at the front of the thigh. A tear in one of these muscles can cause pain and weakness in the leg, as well as difficulty bending the knee because your stretch receptor nerves will stop the movement to avoid further damage!

You should get assessed by a sports medicine doctor if you suspect a quad tear, after following the RICE protocol immediately after injury.

With therapeutic exercises and rest, your knee flexion will return as the quadriceps muscles heal, and surrounding soft tissues strengthen.

Torn tendon in your hip? Learn about recovery time here.

How kneeling stresses the knee joint

When you kneel, the pressure of your body weight is placed on your knee, which is a hinge joint, so it’s more susceptible to injury than other types of joints. This stress on the ligaments, tendons, and cartilage causes issues for the front of the knee, like patellofemoral pain syndrome (runner’s knee).

You could also be getting knee bursitis if kneeling on hard surfaces, because of the pressure on your knee cap.

Be careful when kneeling, and avoid it for extended periods of time – unless it’s a part of your stretching exercises from a health care provider.

Learn which doctor to see for knee pain here.

Treatment for kneeling pain, and knee bending

Whilst not an exhaustive list, the following options exist for help with bending and kneeling pain:

  • physical therapy
  • ice packs
  • elastic bandage
  • anti-inflammatory medications (NSAIDs or steroidal)
  • knee braces
  • sports medicine doctor consult
  • modification of everyday activities
  • therapeutic exercises, such as stretching exercises
physical therapy for bending knee pain

What is the treatment for sharp, needle-like pain when kneeling?

Depending on your age group, a torn meniscus is the most common cause of sharp, needle-like pain when kneeling. Physical therapy is the typical first-line treatment, followed by corticosteroid injections if the pain does not improve. Surgery may be necessary for more severe cases.

Serious medical causes of pain when flexing the knee

Some serious medical causes of pain when flexing the knee can include infection, osteochondritis dissecans, and tumor. If you are experiencing any pain when flexing your knee, it is important to seek medical attention in order to receive a proper diagnosis and treatment plan ASAP.

How can I get my knee to bend again?

For many of the above conditions, you can get your knee to bend again by gradually restoring the movement and flexibility of the soft tissues around the joint. This can take a long time, especially if you’re not able to do everyday activities that help keep those tissues healthy and mobile.

It’s important to be patient and take things slowly, because if you try to do too much too soon you could end up re-injuring yourself. A little bit of incremental movement each day is more likely to produce lasting results than a lot of activity all at once.

I’ve seen even elderly people make tremendous improvements in their joint health, even if they initially said: “Doc, why can’t I bend my knee!!?”

Which therapies have got you bending your knee properly again? Let us all know in the comments below.

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Author Bio

Dr Jason Whealing headshot

Dr. Jason Whealing is a Chiropractor with extensive experience across the UK and Australia. He is passionate about family care and injury management. The cases Jason works with daily include back pain, neck pain, jaw pain, sciatica, knee pain, shoulder pain, headaches and migraine.

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Mayo Clinic: Ostochondritis Dissecans [https://www.mayoclinic.org/diseases-conditions/osteochondritis-dissecans/symptoms-causes/syc-20375887]

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