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Painless Lump in the Knee

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Last updated March 9, 2022

Painless knee lump quiz

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

The usual cause for a painless bump on the knee derives from skin conditions like cysts, warts, or abscesses. Other causes for a lump on the knee with no pain include non cancerous skin growths. Read now for more information on causes and how to get rid of painless lumps on the knee.

6 most common causes

Wart
Illustration of a doctor beside a bedridden patient.
Skin cyst
Dermatofibroma
Basal Cell Carcinoma
Illustration of various health care options.
Synovial chondromatosis
Illustration of a health care worker swabbing an individual.
Baker's cyst (popliteal cyst)

6 causes of painless lump in the knee

This list does not constitute medical advice and may not accurately represent what you have.

Wart

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

Dermatofibroma

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.

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.

Rarity: Uncommon

Top Symptoms: facial skin changes, pink or red facial bump, small facial lump, painless facial bump, growing facial lump

Urgency: Primary care doctor

Baker's cyst (popliteal cyst)

A Baker's cyst, also called as Popliteal cyst, is a fluid-filled mass that causes a bulge and a feeling of tightness behind the knee. The pain can get worse when the knee is fully flexed or extended.

Although a Baker's cyst may cause swelling and make you uncomfortable, treating the probable underlying problem (i.e. knee arthritis) usually provides relief. Your doctor will be able to determine whether surgery, though unlikely, is needed.

Rarity: Uncommon

Top Symptoms: calf pain, swollen knee, knee pain that gets worse when squatting, knee instability, dull, achy knee pain

Symptoms that always occur with baker's cyst (popliteal cyst): lump on the back of the knee, constant knee lump

Urgency: Primary care doctor

Questions your doctor may ask about painless lump in the knee

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

  • What color is the bump?
  • Is your bump getting bigger?
  • Is there anything on the surface of the bump?
  • Any fever today or during the last week?

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

Painless lump in the knee symptom checker statistics

People who have experienced painless lump in the knee have also experienced:

  • 18% Knee Bump
  • 7% Pain In The Outside Of The Knee
  • 7% Soft, Knee Lump

People who have experienced painless lump in the knee were most often matched with:

  • 100% Wart

People who have experienced painless lump in the knee 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.

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