My Knee Hurts When I Straighten It and Put Pressure On It | 9 Reasons Why

Written By on May 30, 2021 — Medically Reviewed By Kristopher Ceniza

Written by on May 30, 2021 — Medically Reviewed By: Kristopher Cenzia

If you’re here, you’re probably asking: “My knee hurts when I straighten it and put pressure on it. Why?” Well, we come across this question fairly often and there are at least 9 possible reasons for this.

Some of them are harmless and could resolve on their own with some rest, like patellar tendinitis.

Others need physical therapy and maybe surgery to get better, like a ligament tear.

Whatever the case, this list has you covered with 9 common conditions so you know what to do next.

9 common conditions that cause knee pain while straightening it and putting pressure on it

1) Patellofemoral pain syndrome (PFPS)

This is the most common cause of knee pain with studies suggesting 25-40% of active people suffering from it.(2,3)

PFPS is also known as “runner’s knee”, but it can affect anyone – not just runners.

It also tends to be used interchangeably with the term “chondromalacia patella“, but they’re not the same injuries.

PFPS could happen alongside chondromalacia but it could also materialize without it.

Generally, we use the diagnosis of “patellofemoral pain syndrome” for describing pain around the kneecap when every other knee problem has been ruled out.

The pain is usually around the kneecap and tends to get worse when you:

Knee Force Knee Sleeve
  • Walk or run – hence “runner’s knee”.
  • Stand up or sit on a chair.
  • Climb or go downstairs.
  • Do squats, lunges, and similar knee movements.

“It has been reported that 74% of individuals experiencing PFP will limit or stop sport participation due to their painful symptoms.”Glaviano et al, 2015

Generally, the best treatment for patellofemoral pain syndrome includes rest, physical therapy, and wearing appropriate knee braces. These are usually effective at reducing time spent away from sports.

2) Chondromalacia patellae

Chondromalacia patellae is another common knee injury that’s present in approximately 20% of people with PFPS. It’s also more common in women than men.(3)

It happens when the cartilage behind the kneecap gets damaged due to wear and tear. The cartilage helps keep your patella in its place while it glides on top of your thigh bone.

This condition may or may not produce symptoms. But, if it did, they’re similar to those in PFPS, including:

  • Knee pain and/or swelling.
  • Worse with activities that put pressure on the kneecap, like climbing stairs, squatting, etc.

Even though they’re similar, it’s important to check whether the PFPS includes chondromalacia or not as the knee pain treatment will be different in each case.(5)

Recommended: The most effective knee supports for chondromalacia patella

3) Muscle weakness

You’ll be more susceptible to knee injuries if your leg muscles are weak because they won’t be able to:

  • Stabilize your knee when you’re walking, exercising, or doing your daily activities.
  • Control the kneecap and keep it in its place.
  • Protect your ligaments, tendons, and other tissues.
  • Absorb external forces which increase the impact within the joint.

You can prevent injuries by increasing your daily movement, like walking instead of taking the bus or moving more often in general.

4) Knee bursitis

A bursa is a sac filled with fluid that reduces friction between tendons and bones, helping them move better. Bursitis happens when this sac gets swollen or inflamed.

And, since there are multiple bursae in your knee, there are also several types of bursitis.

For example, a prepatellar bursitis (or carpenter’s knee) is a type where the bursa on top of your kneecap gets irritated. This happens mostly in people who kneel more often.

The pain and swelling of prepatellar bursitis happens right on top of the kneecap and could get worse when kneeling or standing up.

Other causes of bursitis include gout, rheumatoid arthritis, diabetes, steroid use, or infections. People with a weak immune system are also prone to have this condition on their knees.(6)

If you have any of those medical conditions, check with your doctor before undergoing any treatment for knee pain.

Related: Will Knee Bursitis Go Away?

5) Knee osteoarthritis

Knee osteoarthritis (OA) happens when the cartilage of the knee joint degenerates over time. Elderly people are the most common patients.

The intensity of the symptoms varies from person to person, but they tend to get worse over time.

Common symptoms include:

  • Pain that worsens with movement or with rest.
  • Morning stiffening and/or swelling of the joint.
  • Knee joint instability.

Treatment includes physical therapy, weight management, and a strength training regime. The goal of these methods is to delay the progression of arthritis.

On the other hand, severe cases may require knee replacement surgery.

Knee Force Knee Sleeve

Learn more: Our comprehensive guide on knee osteoarthritis.

6) Meniscus tear

A meniscus is a piece of cartilage that works as a shock absorber and also helps keep the knee joints stable. We have two menisci in each knee.

Meniscus tears are very common in sports with sudden changes of direction, like soccer or tennis. They can also happen to people with knee OA.

Males over 40 years old also have an increased risk of having a meniscus tear. (8)

You may have a meniscus tear if you have any of the following:

  • A “pop” in the knee at the moment of injury.
  • Feeling stiff while trying to straighten your knee.
  • Locking of the knee.
  • Pain and swelling, usually worse after 24 hours of the injury.

The treatment will depend on the cause and size of the tear, but it usually includes:

  • MRI to determine the size of the tear.
  • Knee sleeves to reduce the swelling.
  • Physical therapy to help with pain, swelling, and movement.

Check with your doctor if you think you might have a torn meniscus after a knee injury to plan the best course of action.

Related: Common causes of knee stiffness while bending and how to treat them.

7) Jumper’s knees

The patella has two tendons:

  • The quadriceps tendon, which connects the quadriceps muscles to the top of the kneecap.
  • The patellar tendon, the strong and thick band below the kneecap.

A tendinitis happens when one of these tendons accumulates small tears over time without enough time to heal.

This is also known as patellar tendinitis. As the name suggests, it’s common in jumping sports like basketball, volleyball, skiing, and even long-distance running.

This tendinitis can cause knee pain and swelling above or below the kneecap. Jumping or continuing the exercise activity will make it worse.

Related: 5 common reasons for knee pain while exercising and their solutions

8) ACL ligament tear

The anterior cruciate ligament (ACL) is one of the four ligaments of the knee and the most likely to tear.(10)

This tear usually happens after a traumatic knee injury and often during sports with sudden changes of direction or direct collisions.

Common symptoms of an ACL tear include:

  • A sudden pop and a feeling that the knee gave out at the moment of injury.
  • Knee joint instability.
  • Pain and swelling.
  • Loss of range of motion on the leg.
  • Difficulty walking.
  • Locking, clicking, and/or catching of the knee.

Depending on the severity of the tear, it may need surgery.

9) Kneecap dislocation

This happens when the kneecap gets pushed partially or completely out of the groove of the femur, where it slides to allow knee movements.

It usually occurs after a direct injury or in people with a soft tissue condition called hypermobility.

The obvious sign is a deformity in the knee, usually after feeling like the knee gave away with a “pop”. Swelling tends to happen fast afterward.

“The recurrence rate following a first-time dislocation can be 15-60%” Hayat et al, 2020

As the recurrence is so high, it’s important to get it treated properly with physical therapy care.

Related: Common causes of knee pain while lying on your side.


What is wrong if it hurts to straighten your knee?

Causes of pain when you straighten your knee generally include traumatic injury, overuse injuries, previous medical conditions, and other factors.

– If you’re new to training and haven’t had a direct injury, you could have jumper’s knee, runner’s knee, and/or muscle weakness.
– If you kneel often, play sports, or have health issues like diabetes, gout, etc, you could have knee bursitis.
– If you’re over 60 years old, overweight, or obese, you could have knee OA.
– If you play sports, you could have jumper’s knee, runner’s knee, a knee dislocation, or a ligament/meniscus tear.

In any case, it’s best to check with a physical therapist or a doctor to diagnose and treat the cause of knee pain and rule out other conditions.

What’s the treatment for this type of knee pain?

This depends on the caus but common knee pain treatments includes:

– Physical therapy according to your needs, lifestyle, priorities, and goals.
– Activity modification to allow the healing of the tissues.
– Nonsteroidal anti-inflammatory drugs (NSAIDS) if the knee pain is unbearable and if it’s not contraindicated by a doctor.
– Surgery as a last resort, or if there’s a complete tear of ligaments/meniscus.

How do I know if my knee pain is serious?

See a doctor if you have:

– So much knee pain you can’t put weight on your leg.
– A recent knee injury.
– Locking, popping, and/or catching of the joints associated with the knee pain.
– Have had previous injuries on your knees.
– Knee pain for more than 6 weeks.
– Can’t straighten your leg fully.
– Fever.
– Swelling and/or redness on the back of your knee.
– History of any cardiovascular conditions.

Conclusion: Knee pain while straightening it and putting pressure on it

If your knee hurts, you’re not alone. Knee pain is fairly common with 25% of adults said to experience it.(1)

The cause of this pain depends on many factors. But, in any case, it’s best to go to a physical therapist or a doctor so you can get back to your daily activities as soon as possible.

Book an appointment with your doctor if the pain started after a knee injury or if you have previous health conditions like diabetes, knee OA, or gout.


  1. Nguyen, U. S., Zhang, Y., Zhu, Y., Niu, J., Zhang, B., & Felson, D. T. (2011). Increasing prevalence of knee pain and symptomatic knee osteoarthritis: survey and cohort data. Annals of internal medicine155(11), 725–732.
  2. Bump JM, Lewis L. Patellofemoral Syndrome. [Updated 2020 May 24]. StatPearls. Retrieved on May 03, 2021 from:
  3. Glaviano, N. R., Kew, M., Hart, J. M., & Saliba, S. (2015). DEMOGRAPHIC AND EPIDEMIOLOGICAL TRENDS IN PATELLOFEMORAL PAIN. International journal of sports physical therapy10(3), 281–290. Retrieved on May 03, 2021 from:
  4. Habusta SF, Coffey R, Ponnarasu S, et al. Chondromalacia Patella. [Updated 2020 Oct 27]. StatPearls. Retrieved on May 03, 2021 from:
  5. McCarthy, M. M., & Strickland, S. M. (2013). Patellofemoral pain: an update on diagnostic and treatment options. Current reviews in musculoskeletal medicine6(2), 188–194. Retrieved on May 03, 2021 from:
  6. Rishor-Olney CR, Pozun A. Prepatellar Bursitis. [Updated 2021 Feb 22]. StatPearls. Retrieved on May 03, 2021 from:
  7. Hsu H, Siwiec RM. Knee Osteoarthritis. [Updated 2020 Jun 29]. StatPearls. Retrieved on May 03, 2021 from:
  8. Raj MA, Bubnis MA. Knee Meniscal Tears. [Updated 2020 Jul 19]. StatPearls. Retrieved on May 03, 2021 from:
  9. Santana JA, Mabrouk A, Sherman Al. Jumpers Knee. [Updated 2021 Mar 17]. StatPearls. Retrieved on May 03, 2021 from:
  10. Evans J, Nielson Jl. Anterior Cruciate Ligament Knee Injuries. [Updated 2021 Feb 19]. StatPearls. Retrieved on May 03, 2021 from:
  11. Hayat Z, El Bitar Y, Case JL. Patella Dislocation. [Updated 2020 Jul 10]. StatPearls. Retrieved on May 03, 2021 from:
  12. Dubois, B., & Esculier, J. F. (2020). Soft-tissue injuries simply need PEACE and LOVE. British journal of sports medicine54(2), 72–73.
Mitch Torres (PT)
Mitch is a physical therapist, personal trainer, and nutrition coach. Fascinated with the knee joint, Mitch poured that passion into writing about knee pain and how to overcome it with movement. His goal is to teach you how to apply this knowledge into your daily life, so you can keep knee pain away for good.