Having pain behind the knee while bending the leg can be fairly common and harmless most of the time.
It usually resolves on its own, but in some circumstances, it could be a sign that you need to seek medical attention immediately.
The difference between innocuous knee pain and those that might have you need to visit the ER lies largely in the symptoms you’re feeling, your history, age, and other factors that contribute to a diagnosis.
We’re talking about all those today (among other things). So, to start, here are…
9 causes of pain in the back of your knees while bending your leg back
1. Leg cramps
These are very common. It’s estimated that two-thirds of people over 50 years old have experienced these cramps.(1)
They can happen in any muscle but calves are most likely to cramp.(1)
Cramps cause sudden and sharp pain that tends to ease with movement. It can last from a few seconds to minutes, leaving the area sore afterward.
The causes are unclear, but there are several risk factors:
- Too much exercise
- Electrolyte imbalances
- Disorders affecting peripheral nerves or blood vessels
- Renal dialysis
- Some drugs
2. Baker’s cyst
A Baker’s cyst is a sac filled with synovial fluid, located behind the knee. It’s usually a sign of knee arthritis.
Some cysts are asymptomatic, but others cause dull pain when the knee is bent. You could also feel tightness and swelling on the knee joint.
The symptoms usually worsen with activity, like playing sports or walking long distances.
If the cyst ruptures, the fluid will affect the surrounding tissues. This causes sharp pain and swelling, with a sensation of “water running down the calves”.
Treatment is not usually necessary for this type of cyst unless you have any symptoms.
If that’s the case, treatment includes modification of activity, physical therapy, steroid injections, or aspiration of the cyst.
“It’s important to treat the underlying joint disorder, if one exists, in all patients with symptomatic Baker’s cysts. This will help reduce the accumulation of synovial fluid and enlargement of the cyst.” –Leib et al, 2020
3. Hamstring tendonitis
The semimembranosus, semitendinosus, and biceps femoris form the hamstrings. They go from your buttocks to your knees.
Hamstring tendonitis happens when one of its tendons becomes irritated or inflamed. This usually happens after stretching the muscles too far, causing knee pain.
This tendonitis is fairly common in running sports with sudden changes of direction, like soccer, basketball, or tennis.
This knee pain is typically sudden and sharp. There could be swelling and redness on the knee area as well.
4. Gastrocnemius tendonitis
The gastrocnemius muscle is the biggest muscle of your calves and helps you point your foot or stand at the tip of your toes.
It also connects to the backside of the knee joint, along with the hamstrings.
The gastrocnemius may cause pain if it’s fatigued, strained, cramped, or if the tendons are irritated. The pain is usually sudden.
To differentiate from a hamstring injury, try standing on your tiptoe with the injured leg. If you have trouble with it and feel pain in your calves, you likely have a gastrocnemius injury.
In both cases, it’s best to consult with a physical therapist for pain management.
5. Knee osteoarthritis
Knee osteoarthritis (OA) is a term to define the process of degeneration of the knee joint. It’s known as “wear and tear” and it’s very common in people over 70 years old.(6)
Some people have knee pain associated with OA while others don’t. For those with knee pain, the common symptoms include:
- Gradual pain that worsens with activity and improves with rest
- Pain is felt more inside the joint but can refer to the kneecap and the back of the knee as well
- Morning pain and swelling, also knee stiffness
- Pain after sitting or resting for a long time
Some people develop a “flexion contracture”, where the muscles that bend the knees get tight and make it difficult to straighten the joint.
The treatment focuses on physical therapy and strengthening to prevent arthritis from progressing.
At the most severe stage of knee arthritis, the bones (femur, tibia, and kneecap) rub into each other. Here, surgery is required to restore the normal movement of the knee.
6. Pes anserine bursitis
A bursa is a sac filled with fluid that cushions the tendons and assists with movement. An inflammation of a bursa is called “bursitis”.
Pes anserine bursitis happens specifically when the swollen bursa happens, well… in your pes anserine – or where your hamstrings and other muscles connect to the back of your knees.
This usually causes pain on the back and inner side of the knee alongside swelling and tenderness in the area.
You might feel the pain while rising from a chair, going upstairs, or sitting with your legs crossed.
Runners, basketball, and tennis players may be prone to suffering from this, as well as people with knee arthritis.
7. PCL injury
The posterior cruciate ligament (PCL) is one of the main ligaments of the knee.
It stabilizes the knee with other three ligaments, such as:
- The ACL (anterior cruciate ligament), and
- The medial and lateral collateral ligaments
The PCL is almost twice as strong as the ACL, making it less prone to injuries.
The most common cause for PCL injury in non-athletes is during a car accident when the knee is forced into the dashboard.
In sports, this type of injury is common in football, skiing, soccer, and baseball.
You might feel knee pain on the back of the joint that worsens when kneeling. Swelling is also a likely symptom as well as a sensation of “giving out” while walking or standing.
That being said, the symptoms of ACL and PCL injuries are very similar. They differ in the severity of symptoms and usually the mechanism of injury.
It’s best to see a doctor if you suspect of having a PCL injury.
8. Meniscal tears
A meniscus is a piece of cartilage that works as a shock absorber and also helps keep the knees stable. We have two menisci in each knee.
These injuries are very common in tennis, soccer, or any other sport with sudden changes of direction.. But, they can also happen to people with knee arthritis.
Symptoms of a meniscal tear include:
- A “pop” in the knee at the moment of injury
- Knee pain and swelling, usually worse after 24 hours of the injury
- Stiffening while straightening the knee
- Locking of the knee
- Clicking or catching of the joint
- Intermittent inability to fully extend the knee
- Feeling of the knee giving way
Males over 40 years old have an increased risk of having a meniscus tear.(9)
The treatment will depend on the cause and size of the tear, but it usually includes(9):
- MRI to determine the size of the tear
- Knee sleeves to reduce the swelling
- 4-6 weeks of physical therapy to help with pain swelling, recover range of movement, and determine if there’s spontaneous healing
Ice or NSAIDS also help reduce pain and swelling. However, it might be best to use them only if there’s severe pain, as some studies suggest that they hinder the healing process.(10)
“Patients with persistent pain, swelling, and mechanical symptoms despite conservative management should be assessed for potential surgical intervention.” – Raj et al, 2020
9. Deep vein thrombosis (DVT)
DVT happens when a blood clot forms within the deep veins, usually on one leg.
This is considered an emergency, and you should see a doctor immediately if you have any of the following symptoms:
- Throbbing or cramping pain in one leg, usually around the calf, knee, and/or thigh
- Knee pain increases when standing up
- Swelling in just one leg
- Warm, red, and/or darkened skin around the painful area
- Visibly swollen veins that are hard or sore when you touch them
If not treated, the clot could travel to your lungs and cause a pulmonary embolism which can be fatal.
A DVT is more likely to happen if you are(12):
- Over 60
- A smoker
- Staying or recently left the hospital, especially if you can’t move much (like after surgery)
- Confined to bed
- Pregnant, or have had a baby in the last 6 weeks
- Spending more than 3 hours on a plane, car or train
The best way to prevent DVT is to stay at a healthy weight, staying active, keep hydrated, and quit smoking.(12)
What does it mean when the back of your leg hurts behind the knee?
Pain at the back of your knee when bending depends on several factors. These include how the pain started, your age, medical history, and so on.
If you are an athlete and/or play contact sports often, you could have:
- A hamstring or gastrocnemius tendinitis
- Pes anserine bursitis
- PCL – or any other knee ligament- injury
- A meniscal tea
If you’re over 60 years old, you could have:
- A leg cramp
- Baker’s cyst
- Knee arthritis
- DVT. (Remember that this is a medical emergency. If this is the case, go to the doctor immediately.)
If you’re not sure or if you’ve had pain for more than 6 weeks, go to the doctor to find out what’s going on.
What can I do at home?
There are a bunch of things you can do at home, including:
- Modifying your activities. Temporarily changing certain movements that hurt your knee will help it heal.
- Practicing low-impact activities that aren’t painful. Examples would be walking, swimming, or biking.
- Wearing a knee sleeve. It provides compression and warmth that can help reduce the pain.
- Using anti-inflammatories or icing only if necessary. They help make the pain more manageable but they might also impair tissue healing.
If your pain and/or swelling worsens over time, or if it limits you in your daily activities, please go to your doctor or physical therapist.
How long does pain behind the knee takes to resolve?
How long the pain behind your knees will take to resolve depends on the cause of the knee pain, its severity, treatment, and your overall health.
However, 6 to 12 weeks is generally a good timetable for conservative methods (i.e. physical therapy).
Knee surgeries (e.g. PCL or meniscus repair) will take longer to fully recovery and could take anywhere from 8 weeks to 12 months.
When to seek medical help for knee pain?
Seek medical help if you have:
- Pain that hasn’t resolved in 6 weeks
- Can’t straighten or bend your knee fully
- Knee noises that weren’t there before
- Can’t bear weight on the leg
- Swelling and/or redness in the area
- Knee arthritis
- Gait issues
- Pain right after a knee injury
- History of DVT or cardiovascular problems
Conclusion: Pain on the backside of the knee while bending
If the back of your knee hurts while bending, take it easy because all you might need is some rest and temporarily changing your activities to allow the healing process to do its thing.
And, as there are many possibilities (at least 9), it’s best to be thorough.
See a doctor if:
- The knee pain persists for more than 6 weeks
- If it gets worse
- If you think you might have DVT
- Young G. (2015). Leg cramps. BMJ clinical evidence, 2015, 1113. Retrieved on April 21, 2021 from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4429847/
- Leib AD, Roshan A, Foris LA, et al. Baker’s Cyst. [Updated 2020 Jul 17]. StatPearls. Retrieved on April 21, 2021 from: https://www.ncbi.nlm.nih.gov/books/NBK430774/
- Poudel B, Pandey S. Hamstring Injury. [Updated 2020 Sep 10]. StatPearls. Retrieved on April 21, 2021 from: https://www.ncbi.nlm.nih.gov/books/NBK558936/
- Hsu D, Chang KV. Gastrocnemius Strain. [Updated 2020 Aug 29]. StatPearls. Retrieved on April 21, 2021 from: https://www.ncbi.nlm.nih.gov/books/NBK534766/
- Hsu H, Siwiec RM. Knee Osteoarthritis. [Updated 2020 Jun 29]. StatPearls. Retrieved on April 21, 2021 from: https://www.ncbi.nlm.nih.gov/books/NBK507884/
- Cui A, Li H, Wang D, et al. (2020) Global, regional prevalence, incidence and risk factors of knee osteoarthritis in population-based studies. EClinical Medicine by The Lancet, 29, 100587. https://doi.org/10.1016/j.eclinm.2020.100587
- Mohseni M, Graham C. Pes Anserine Bursitis. [Updated 2020 Nov 26]. StatPearls. Retrieved on April 21, 2021 from: https://www.ncbi.nlm.nih.gov/books/NBK532941/
- Raj MA, Mabrouk A, Varacallo M. Posterior Cruciate Ligament Knee Injuries. [Updated 2021 Jan 22]. StatPearls. Retrieved on April 21, 2021 from: https://www.ncbi.nlm.nih.gov/books/NBK430726/
- Raj MA, Bubnis MA. Knee Meniscal Tears. [Updated 2020 Jul 19]. StatPearls. Retrieved on April 21, 2021 from: https://www.ncbi.nlm.nih.gov/books/NBK431067/
- Dubois, B., & Esculier, J. F. (2020). Soft-tissue injuries simply need PEACE and LOVE. British journal of sports medicine, 54(2), 72–73. https://doi.org/10.1136/bjsports-2019-101253
- Waheed SM, Kudaravalli P, Hotwagner DT. Deep Vein Thrombosis. [Updated 2020 Aug 10]. StatPearls. Retrieved on April 21, 2021 from: https://www.ncbi.nlm.nih.gov/books/NBK507708/
- DVT (Deep vein thrombosis) [Updated 2019 October 23]. NHS. Retrieved on April 21, 2021 from: https://www.nhs.uk/conditions/deep-vein-thrombosis-dvt/