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Hard Knee Lump Symptoms, Causes & Common Questions

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Last updated March 29, 2024

Hard knee lump quiz

Take a quiz to find out what's causing your lump.

Are you experiencing a hard bump on the knee? Read more below to learn about six possible causes, questions your doctor may ask about your symptoms, and more.

9 most common cause(s)

Illustration of various health care options.
Illustration of a person thinking with cross bandaids.
Deep Vein Thrombosis
Basal Cell Carcinoma
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Skin cyst
Illustration of a doctor beside a bedridden patient.
Atypical mole
Illustration of a health care worker swabbing an individual.
Benign bony growth (osteochondroma)
Illustration of various health care options.
Synovial chondromatosis

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6 causes of a hard knee lump


Warts, also called common warts or verrucae, are small, rough, rounded growths on the top layer of the skin. They may appear singly or in clusters.

Common warts are caused by the human papilloma virus (HPV) and are contagious through direct contact, especially through a break in the skin. They may spread from one place on the body to another simply through touch.

Anyone can get warts but they are most common in anyone with a weakened immune system, as from illness or chemotherapy. Children and teenagers are also susceptible to warts.

Warts often first appear on the hands and fingers, especially near the nails or after any injury to the skin. This is why biting fingernails is a risk factor for warts.

Warts are benign, meaning they are not cancerous. But they can be unsightly and interfere with normal use of the hands, so treatment is often beneficial.

Diagnosis is made through physical examination. Warts in children sometimes go away without treatment, but otherwise most warts can be easily removed in a doctor's office.

Synovial chondromatosis

Synovial chondromatosis is a disease affecting the synovium, which is a thin flexible membrane around a joint. It can often be confused with tendinitis and/or arthritis.

Rarity: Ultra rare

Top Symptoms: joint swelling, pain in one knee, pain in one hip, swollen knee, spontaneous knee pain

Symptoms that always occur with synovial chondromatosis: joint swelling

Symptoms that never occur with synovial chondromatosis: fever, night sweats, unintentional weight loss, warm red ankle swelling, warm red knee swelling, warm and red elbow swelling

Urgency: Primary care doctor

Skin cyst

A cyst is a small sac or lump, filled with fluid, air, fat, or other material, that begins to grow somewhere in the body for no apparent reason. A skin cyst is one that forms just beneath the skin.

It's believed that skin cysts form around trapped keratin cells – the cells that form the relatively tough outer layer of the skin.

These cysts are not contagious.

Anyone can get a skin cyst, but they are most common in those who are over age 18, have acne, or have injured the skin.

Symptoms include the appearance of a small, rounded lump under the skin. Cysts are normally painless unless infected, when they will be reddened and sore and contain pus.

Diagnosis is made through physical examination. A small cyst can be left alone, though if it is unsightly or large enough to interfere with movement it can be removed in a simple procedure done in a doctor's office. An infected cyst must be treated so that the infection does not spread.

Rarity: Common

Top Symptoms: skin-colored armpit bump, marble sized armpit lump, small armpit lump

Symptoms that always occur with skin cyst: skin-colored armpit bump

Urgency: Wait and watch


Melanoma is the most serious type of skin cancer. Often the first sign of melanoma is a change in the size, shape, color, or feel of a mole. Most s have a black or black-blue area. Melanoma may also appear as a new mole. It may be black, abnormal, or "ugly looking."

You should visit your primary care physician. Surgery is the first treatment of all stages of melanoma. Other treatments include chemotherapy and radiation, biologic, and targeted therapies. Biologic therapy boosts your body's own ability to fight cancer. Targeted therapy uses substances that attack cancer cells without harming normal cells.


A dermatofibroma is a fairly common skin growth that usually appears on the lower legs, but may appear anywhere on the body. These mole-like growths are benign (noncancerous.)

The cause is not known, though a dermatofibroma may appear after a minor injury. The growths are not contagious.

Dermatofibromas are most common in adults and are rarely found in children.

Symptoms include a hard, raised growth that is red, pink, or brown and less than half an inch across. They are usually painless but may be tender or itchy, and may appear alone or in groups.

Any new growth on the skin should be seen by a medical provider, especially if the growth is very dark in color or changes its shape or appearance quickly.

Diagnosis is made through physical examination and sometimes biopsy.

A dermatofibroma does not require treatment unless it is interfering with clothing or is unsightly. They can be surgically removed, though this will leave a scar and the growth may eventually return.

Deep vein thrombosis

A deep vein thrombosis (DVT) occurs when a blood clot forms in a vein deep in the body, usually in the lower leg or thigh. DVT can cause swelling, pain, and redness in the affected leg. Some of the risk factors for developing DVT include obesity, pregnancy, cancer, surgery, and previous history of blood clots.

You should consider calling your primary care or urgent care provider. Deep vein thrombosis can be evaluated with a review of your symptoms, a physical exam, and an ultrasound. A blood test may also be performed. Once diagnosed, DVT can be treated with blood-thinning medication, which is usually taken for three months.

Rarity: Uncommon

Top Symptoms: fever, thigh pain, upper leg swelling, calf pain, butt pain

Urgency: Hospital emergency room

Benign bony growth (osteochondroma)

An osteochondroma is a non-cancerous growth that usually develops during childhood or adolescence. It is a benign tumor that forms on the surface of a bone near the growth plate.

You should visit your primary care physician for X-Ray evaluation. In most cases this condition is treated by careful observation over time to make sure the tumor does not grow. Surgery is considered if the osteochondroma causes pain, puts pressure on a nearby nerve or blood vessel, or has a large cap of cartilage.

Rarity: Ultra rare

Top Symptoms: lower leg bump, upper leg bump, numbness in one thigh, painful thigh lump, hip bump

Urgency: Primary care doctor

Basal cell carcinoma

Basal cell carcinoma (BCC) is the most common kind of skin cancer. It can develop almost anywhere on the body. It appears as abnormal spots or bumps on the skin. These bumps are often pink, red, or skin-colored and sometimes have a shiny surface. The main risk factor for developing this condition is prolonged exposure to ultraviolet (UV) radiation. Sun exposure and tanning beds are both sources of UV radiation. People with a history of sunburns, previous skin cancer, and a weakened immune system are at higher risk for this condition.

Most cases of BCC can be easily treated because they grow slowly. Though if not treated, it can spread inside the body. Your provider will do a skin exam and possibly skin sample test, known as a biopsy. Treatment will depend on where the cancer is, its size, and your medical history. Some treatment options include cutting out the bump, freezing it, or using medicated skin cream.

Atypical mole

Moles are growths on the skin. They happen when pigment cells in the skin, called melanocytes, grow in clusters. Certain moles are considered "atypical" because of their size and characteristics, which require careful watching and possibly even biopsy in order to monitor for development into cancer. Atypical moles, also called dysplastic nevi deserve more attention than normal moles.

You should go see your primary care doctor to examine the mole. He or she can determine if next steps are necessary.

Questions your doctor may ask about hard knee lump

To diagnose this condition, your doctor would likely ask the following questions:

  • What color is the bump?
  • Do you feel pain when you touch the bump?
  • Is your bump getting bigger?
  • Is there anything on the surface of the bump?

Self-diagnose with our free Buoy Assistant if you answer yes on any of these questions.

Hard knee lump symptom checker statistics

People who have experienced hard knee lump have also experienced:

  • 29% Knee Pain
  • 5% Swollen Knee
  • 3% Pain In The Outside Of The Knee

People who have experienced hard knee lump were most often matched with:

  • 100% Synovial Chondromatosis

People who have experienced hard knee lump had symptoms persist for:

  • 39% Over a month
  • 25% Less than a week
  • 15% Less than a day

Source: Aggregated and anonymized results from Buoy Assistant.

Hear what 1 other is saying
Once your story receives approval from our editors, it will exist on Buoy as a helpful resource for others who may experience something similar.
The stories shared below are not written by Buoy employees. Buoy does not endorse any of the information in these stories. Whenever you have questions or concerns about a medical condition, you should always contact your doctor or a healthcare provider.
Painless bump below the knee cap.Posted January 9, 2021 by 6.
Hello, I'm 69yrs old and wish to give MY information of a recently discovered a 2" diameter Extruding BUMP right below my left knee cap. I don't know if any of this has anything to do with the appearance of said Bump but I've undergone 3 Major Shoulder Repair Surgeries in 10 months. Anyway, To describe the Medium Size (2" diameter) Bump RIGHT Below my Knee Cap. I only discovered my Bump one day as I kneeled down it felt as if my left knee wasn't sitting FLAT against the flat floor surface like normal. After I stood back up I pulled my pant leg up and found a round 2" diameter round Bump definitely protruding out that seemingly appeared overnight. I used my fingers, testing it, by pushing on it at different angles at different locations. Pressures and then actually pushed it around in all directions TRYING to find out if it were painful. After that initial feeling test I wanted to test the Bump by kneeling Directly down on it. With all my weight ONLY on that one affected knee, I found it was still not Painful but only slightly unsettling. It only felt strange in that the Bump feels like it gives and moves ALL without giving me any discomfort in the slightest...Basically, it just feels weird. There was absolutely no pain what so ever so I put it out of my mind and forgot about it with the mindset that it would eventually go away on its own. It's already been an amazing quick time-lapse of nearly 8 or 9 months since I first noticed it. I have to say that I really did forget it was even there. My bump still exists...Is Still NOT giving me any pain at all and doesn't affect any movement nor has it grown much, that I can tell. It presents no limitations or problems with getting dressed or with ANY other normal daily activities. I've been diagnosed with two different forms of Arthritis, Ostio and Rheumatoid so these may be a contributing factor or not. I mention it only that someone may find that information useful in some way. I mostly feel it's important mentioning that I've always been a very active male, Contact sports, Football, Soccer, Tennis, Cross-Country Running, Hiking, Hunting, Fishing, Snowmobiling, Dirt Bikes, Road Bikes, Bicycling, as well as other machines made for outdoor fun and just about ANY other physical outdoor activity you can imagine. I only point these out to show how active I've always been All my life. Certainly not trying to brag BUT only inserting as much background useful data for those possibly looking for any of MY data only. In Addition; For most of my adult life I've worked at several physically demanding jobs. Due to those demands, year after year, I've injured both knees more than a few times. Never to the point of needing surgical repair but the very typical and normal day or two of resting type. Just rest and good-to-go again, just like those... It never seemed like the bumps and bangs were ever that serious or that they needed attending by a Doctor. I can't say with any certainty but this may have some degree of possibility to do with the Bump that resides below my left knee cap. Once my shoulder Physical Therapy is concluded I will make time for an appointment with my Family Doctor to have him properly diagnose it. Since there is no pain I can only assume this is not life-threatening at this point so I don't feel any urgency to have it assessed right away. I only tell my story here for anyone else with the same symptoms or experience. Sometimes it's just comforting to know your situation isn't all that different. Call it a kind of misery loves company sort of kindred experience. Good luck to all of you and PLEASE don't take my situation or attitude of MY BUMP as Gospel. IF you are in the least at all concerned then you MUST have it checked out by a professional.... Listen to your body and go with what your brain is telling you to do...not what the guys will think. If it turns out to be nothing then at least you know and that's Always a good I right? If you have any pain associated with yours then Be Smart about it and have it diagnosed... Honestly people, Please do not take my experience to be at all similar to yours. Who knows, I may be doing more harm by delaying having mine checked out...I really don't know. I just don't want to be the cause for your, or anyone's Bump to get worse or have more serious consequences. My hope is to bring awareness from a first-person accounting and experience. Mine may not be typical or the correct thing for even me to be delaying, HOWEVER, if my contribution is in some small way may be helpful for you and more importantly may be useful for any actual experienced data for Physicians. Thanks, 69yr Old Guy

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