A lump on the side of knee – either inside or outside- is most likely a meniscal cyst. A meniscal cyst is a collection of thick fluid arising from a tear of the meniscal cartilage, which is the cushioning of the knee. However, not all lumps in the knee are meniscal cysts. So, how do we diagnose a meniscal cyst, and what do we do about them?
How does a meniscal cyst develop?
Usually, a tear forms in the meniscal cartilage from degeneration or an acute meniscus injury. Fluid from the knee joint then leaks out of the tear, forming a cyst. So, a meniscal cyst is not a true cyst but an outpouching of displaced knee fluid. Also, the cartilage tear can form a one-way valve preventing the fluid from returning to the knee. The liquid then collects as a cyst below the knee cap.
Often, meniscal cysts form in people with a history of a knee injury, cartilage damage, or contact or twisting sports. Also, the presence of arthritis predisposes to the formation of a cyst on the side of the knee.
Clinical findings of a lump on the side of knee
Not all lumps or cysts on the side of the knee are apparent or painful. In cases where the lump is due to a meniscal cyst, the more common symptoms include pain with standing, swelling in the knee joint, and a lump or bump on the side of the knee that can change in size.
When examining the knee, we often find a lump close to the joint line. The lump or cyst in the knee is usually soft and may or may not be painful. Also, twisting or rotating the knee can cause pain.
Generally, we use an MRI to diagnose the meniscal cyst and the corresponding meniscal tear. However, an ultrasound can also confirm a meniscal cyst.
What is the difference between a meniscal cyst and a Baker’s cyst?
A Baker’s cyst is a swelling behind the knee caused by an outpouching of the capsule. Like a meniscal cyst, a Baker’s cyst can form from a meniscal tear. However, they also form from any knee condition that increases knee joint fluid, such as arthritis or ligament damage. Generally, we can tell the difference between a meniscal cyst and a Baker’s cyst based on the lump’s location and size.
Could a lump in the knee be something else?
Yes. Other causes of a lump in the knee include Housemaid’s knee, knee joint swelling, and tumours such as lipoma. If the lump is growing in size or painful, you should consider a referral for further investigations such as an ultrasound or MRI.
Meniscal cyst treatment
Treatment reflects meniscal tear treatment as meniscal cysts arise from a degenerative torn meniscus. Generally, we recommend simple treatments such as anti-inflammatory tablets and exercise to build strength. In cases where the cyst causes pain, a cortisone injection guided by ultrasound into the cyst can help. We suggest surgery if pain continues despite simple treatments or you develop mechanical symptoms such as locking or giving way. The good news is that removing the cyst is not necessary. Simply removing the torn meniscus by arthroscopy is enough to stop it from returning.
More on injections for lump on the side of the knee
In general, injections are helpful for meniscal cysts that are large and painful. Under ultrasound guidance, we pierce the cyst using a needle. First, a numbing solution is injected into the skin and outside the cyst. Second, a needle is placed into the middle of the cyst. The cyst is then decompressed using more numbing fluid. Finally, we inject cortisone into the cyst to reduce inflammation and prevent a recurrence.
Sometimes, PRP injections are helpful for meniscal tears, especially if we want to treat the tear.
Other commonly asked questions about meniscal cysts
Are all meniscal cysts painful?
No. We think about 50% of meniscal cysts are painful.
Are all meniscal cysts associated with a meniscal tear?
No. Studies suggest cysts are associated with a meniscal cyst in 50-75% of cases.
Can a meniscal cyst burst?
Yes. In some cases, the cyst can burst and disappear.
Do all meniscal cysts need treatment?
No. You should seek treatment if the cyst gets bigger and you experience pain in the knee.
Final word on Sportdoctorlondon about a lump on side of knee
A lump on the side of the knee is often due to a meniscal cyst. We treat these cysts with simple treatments followed by an injection. Overall, we should limit surgery to those cases that fail simple therapies.
Very informative
thank you. I’m pleased you found it informative.
Thank you I have a large lump beside my left knee that’s painful and swelling thanks for information
Excellent information i have had this problem for decades but never had any help from my own GPS.they deemed it quite petty.thanks for your wonderful information.
Thank you, a friend is suffering from pain in the back of her knee. Now I know where to get the information to help guide and support her through treatment.She is hoping to get cortisone injections,, ffluid removed. Her biggest fear is having a knee replacement
Behind my left knee have a painful lump
You could have a Baker’s cyst. See my blog on Baker’s cyst:
https://sportdoctorlondon.com/bakers-cyst-drainage/
Lorenzo
I got more help with this article than I did with a specialist.
I find this very informative, my mom has a lump at the side of her knee and is due for operation soon because it’s painful. Thank you for the information
I have two pea size bumps inside side of knee dr said there is not test to see what it is?
ultrasound may help clarify the cause if you can feel it. LM
wow thank you for the information … I cannot get an appointment with my GP at the moment but have a telephone consultation on 8th June … so hopefully I will get some help then … what would we do without Doctor Google tho and you of course … thank you again
Thanks, Sandy for your positive feedback.
Thank you for info, I have a lump on my right knee and now my ankle is very swollen and when I elevate my knee it’s very painful. I saw er dr they gave me a brace said it will take a longtime to go away! It hurts to walk and they didn’t do anything to see what’s wrong with my knee,
Thank you for this information. I have had a large lump on the side of my right knee since a car accident in September. I just had surgery almost two weeks ago on this knee and the lump is back. It will go away, then return.
Hi ,I have a lump on inner left knee, that hardens when flexed, I recently upped my exercise. Ultrasound diagnosis is Baker cyst usually sited at rear of knee. Symptoms are pain when kneeling siting cross legged niggling pain to side of leg. Fit 12.5 stone 57 year old fully mobile.
Would welcome general rehab tips
Paul
Please see my blog on Baker’s cyst:
https://sportdoctorlondon.com/bakers-cyst-drainage/
This cyst is secondary to excessive knee joint swelling. Treatment should be directed at reducing swelling. In the case of arthritis, we recommend the following treatment:
https://sportdoctorlondon.com/best-treatment-for-arthritis/
Thank you for your information and discussion comments. after a fall, there was no pain in knee and was not checked by emt’s called. After stepping down from a high step leaving the ambulance, after walking to car, I could not lift or bend knee to get in and knee had swelled up a lot. At emergency room, all x-rays were o.k. Went home with leg wrapped in Ace bandages. …removed after three days…two days later, skin was black from knee to lower calf. I have had a diagonsis of veinous insufficiency years ago. A fine surgeon has considered surgery, prior to covid pandemic, and we postponed. by the time I got in to see my M D as follow up on fall, the skin was normal color. The lump on right knee started after that. it is now nine weeks since fall.
Hi, you could have developed a meniscal cyst. I suggest investigations as outlined in my blog. All the best LM
But can they be on the sides of both knees? Could that be something more serious?
yes both sides are possible. I’d speak to your doctor about investigations. Lorenzo
Thank you so much for a very informative article. I have a decent sized lump on the ĺeft side of my left knee. Quite painful, though not all the time, but sometimes it gives way. I did have a new half knee 12 yrs ago on the inner side, I was worried that it might be something to do with that. Thanks again for your help.
Hi Patricia, Chances are it’s a meniscal cyst. I’d see your doctor to confirm. And thank you for the compliment. I try to write simple and unbiased articles.
LM
Hi i have a very tender and painful area on the left side of my right knee more towards the bottom of the knee. It has slight swelling but now has hardened and feels like a lump area has developed. I got this previously about 3months ago then it subsided and went away.
This time it came the next day after we had done a lot of walking around London and when i woke up the pain came down the side of the knee just as it goes to the back of the knee came again then over the cause of the next few days it hardened up and now the hardened lump area is about 50mm-75mm and still tender to touch.
What do you think i have?
You could have a Baker’s cyst
or a meniscal cyst
Hi.
A few hours after a 16km run my right knee felt a bit restricted when crouching down onto my honkers. I then noticed some swelling in it but it has not had any pain.
48 hours on there is still swelling to the knee, above knee cap towards the outside of the leg and below the knee cap towards the outside. When I tense my quads you can see a small finger length, squashy lump on the lower part.
I run regular and 16km was not a far run for me generally. I damaged the meniscus twice (4 and 10 years ago).
I have been icing this the last two days. I am training for a half marathon and reluctantly decided to rest a few days in hope this settles.
Any advice as to what this may be or if I should seek advice from a physio etc would be very much appreciated!
I suspect the ‘lump’ is, in fact, swelling from the knee joint. Swelling is indicative of your joint reacting to the load – so I’d suggest a few more days rest and reducing your volume by about 20-30%. If you continue to struggle, you should see a physio.LM
Thank you for this helpful information.
I have a swelling on the outside of my left knee and have no pain, just a stiffness when climbing stairs. This only appeared a couple of days ago.
I had an ultra sound done yesterday and read the Radiologist report on my Patient Portal. He says Bakers cyst and I am no doctor but I feel certain from all I have read here and elsewhere that this is a meniscal cyst.
I have a referral to see an Orthopedic surgeon who is a knee specialist. I would however like to hear your opinion.
if the lump is outside of the knee, then it’s more likely a meniscal cyst.
LM
Hello,
Yesterday a 3″ round lump has developed on the left side of my left leg, just above the kneecap area. It is very painful if I try to kneel on that knee or bend it too far. I can walk on the leg without a lot of pain but I do feel pressure in that area. I have done nothing to cause it. As a matter of fact I walked for 45 minutes yesterday am and did not notice the lump until later in the morning yesterday. As the lump developed the pain got worse. I do have Lupus (with no flare in about 9 years) and I take Plaquenil for that, I also have slow developing Parkinson’s (only tremor on the right side right now) which is why I try to walk 45 minutes a day, 5 days a week. What do you think this is? Do you think it will go away on its own if I take it easy? If not, what type of Dr. would you recommend I see?
Hi Loretta, The lump might be knee joint swelling. I’d suggest you see a musculoskeletal doctor to assess your knee.
LM
Hello, Thank you for this information, I have a large lump on the inside of my left knee, I’ve had it for several years now, all my GP has said is that it’s probably a sebaceous cyst, but in my opinion it looks nothing like a sebaceous cyst its skin coloured, occasionally looks like its bruised and once a clear watery fluid leaked out, it is now very painful especially walking and bending knee, I have made another appointment with my GP and I will ask about meniscal cyst, it’s about the size of a ping pong ball now what is your opinion about it, once again thank you.
Agree – you could have a meniscal cyst arising from the knee joint or a ganglion – which is a cyst-like structure arising from the tendons on the outside of the knee. https://sportdoctorlondon.com/bakers-cyst-on-ultrasound/ Ultrasound or MRI will clarify.
LM
Hi I have a solid fluid semi sphere ~2″ diameter mass (confirmed via MRI) on medial side of knee starting at bottom of knee cap and extending downward. My knee doesn’t really bother me, but this mass is bothering me and causing tightness.
MRI showed no obvious meniscus tears
Thoughts?
You could have a cyst without a meniscal cyst – although this is less common. Treatment is similar to a meniscal cyst: consider drainage if increases in size or causes pain.
My husband has swelling on the out side of his rught knee. It causes severe pain if he kneels on it and his leg aches if he is up on it for a long time , carries anything or when he is laying down at night. What could this be?
it could be a meniscal cyst – you should see a doctor to get a diagnosis
LM
Thank you your helpful information. For 10 years I went to orthopedic he said it is not your knee it is your back.long story short, it took 5doctors and one finally MRI severe pain.I now have a meniscus tear and cyst, arthritis and bone on bone. Getting a total joint in march
Thank you for this informative article! I’m wondering, does this meniscal cyst can causing weight loss?
Weight loss doesn’t usually affect the size of the cyst.
Thanks very much,I have had this problem for a long time since 2015 and i was about to panic,when i saw this post i know right it could be treated… sometimes/somedays i get pain on this lump which only lasts 3 minutes,then am okay again