Septic arthritis is also called infectious arthritis. "Arthritis" simply means inflammation of a joint. In septic arthritis, the inflammation is caused by a bacterial, viral, or fungal infection. The most common agent is Staphylococcus aureus, or staph.

These agents reach the joints either from another infection in the body, or from a traumatic injury that contaminates the wounded joint.

Risk factors include existing joint disease or injury; a weakened immune system; and damaged skin. All of these things allow infectious agents to get a foothold.

Symptoms include severe pain in the affected joints, along with redness and swelling. The knees are most often affected but septic arthritis can occur in any joint.

The infection can damage cartilage and bone very quickly, so anyone with these symptoms should see a medical provider as soon as possible.

Diagnosis is made through a sample of the joint fluid; blood tests; and x-ray or CT scan of the joint.

Treatment involves draining the infected fluid from the joint, either with a needle or with surgery, followed by antibiotics.

Septic arthritis is also called infectious arthritis. "Arthritis" simply means inflammation of a joint. In septic arthritis, the inflammation is caused by a bacterial, viral, or fungal infection. The most common agent is Staphylococcus aureus, or staph.

These agents reach the joints either from another infection in the body, or from a traumatic injury that contaminates the wounded joint.

Risk factors include existing joint disease or injury; a weakened immune system; and damaged skin. All of these things allow infectious agents to get a foothold.

Symptoms include severe pain in the affected joints, along with redness and swelling. The knees are most often affected but septic arthritis can occur in any joint.

The infection can damage cartilage and bone very quickly, so anyone with these symptoms should see a medical provider as soon as possible.

Diagnosis is made through a sample of the joint fluid; blood tests; and x-ray or CT scan of the joint.

Treatment involves draining the infected fluid from the joint, either with a needle or with surgery, followed by antibiotics.

Non-specific knee rash

A rash is an area of irritated or swollen skin. Often, rashes are unidentifiable and some variation of normal. For example, scratching one's arm causes it to turn red (which is caused by mast cells releasing chemicals into the local area), but that's completely normal.

At this time, you do not need treatment for this rash. If it worsens, you may need to consult a physician.

Rarity: Common

Top Symptoms: knee redness

Symptoms that always occur with non-specific knee rash: knee redness

Urgency: Wait and watch

Necrotizing fasciitis of the leg

Necrotizing fasciitis is a potentially life threatening skin condition stemming from the infection of a wound or injury. If left untreated, it can spread to body parts surrounding the infection changing the color of the skin and degrading the tissue underneath. This can result in muscle, tissue or limb loss and a severe body-wide response to the infection.

You should visit your local emergency room where blood tests can be run and a consultation can be made by a skin specialist. If caught early, antibiotics, cleaning, and a stay in the hospital can help control the infection. If serious, additionally procedures may be required. It is important to get treatment due to the possibility of this becoming a serious, life-threatening condition.

Rarity: Ultra rare

Top Symptoms: nausea, diarrhea, vomiting, fever, chills

Symptoms that always occur with necrotizing fasciitis of the leg: leg skin changes

Urgency: Hospital emergency room

Lyme disease

Lyme disease is a bacterial illness transmitted through the bite of the deer tick (black-legged tick) after it has been attached for at least 36-48 hours. These may be tiny, immature ticks that are difficult to see, often attaching in a place on the body where hair grows.

The disease does not spread through casual contact, either between humans or between humans and pets.

Early symptoms include fever, chills, headache, and body aches. There may be a rash around the tick bite, which sometimes enlarges to form a clear circle around the bite.

Later symptoms are severe with headaches, neck stiffness, further rashes, facial drooping (palsy,) and joint pain and swelling. This is a medical emergency. Take the patient to the emergency room or call 9-1-1.

Untreated Lyme disease in a pregnant woman can lead to stillbirth, but antibiotics will usually prevent this.

Diagnosis is made through symptoms as well as a blood test.

Treatment consists of oral antibiotics in most cases, though severe cases may require IV antibiotics.

Rarity: Ultra rare

Top Symptoms: fatigue, headache, irritability, muscle aches, loss of appetite

Urgency: Primary care doctor

Insect bite from a chigger

Chiggers are mites that feed on humans and animals only while they are larvae, or their infant form. People can contract chiggers when they contact infected grass. feed for three to four days on a piece of skin, and secrete a fluid that causes intense itching.

You should go to a retail clinic to be treated, as household remedies aimed at killing the mite are unlikely to be effective. The infected area should be kept clean with soap and water. A hydrocortisone cream or local anesthetic may be helpful to reduce the itching. You should avoid scratching the wounds!

Rarity: Rare

Top Symptoms: lower leg itch, lower leg redness, knee itch, ankle itch, ankle redness

Urgency: Phone call or in-person visit

Eczema (atopic dermatitis)

Atopic dermatitis, also called eczema, dermatitis, atopic eczema, or AD, is a chronic skin condition with an itchy rash.

AD is not contagious. It is caused by a genetic condition that affects the skin's ability to protect itself from bacteria and allergens.

AD is most often seen in infants and young children. Most susceptible are those with a family history of AD, asthma, or hay fever.

Infants will have a dry, scaly, itchy rash on the scalp, forehead, and cheeks. Older children will have the rash in the creases of elbows, knees, and buttocks.

Without treatment, a child may have trouble sleeping due to the intense itching. Constant scratching may cause skin infections and the skin may turn thickened and leathery.

Diagnosis is made through physical examination, patient history, and allergen skin tests.

AD cannot be cured, but can be controlled through prescribed medications, skin care, stress management, and treatment of food allergies. Those with AD often have allergies to milk, nuts, and shellfish. Keeping the skin clean and moisturized helps prevent flareups.

Cellulitis

Cellulitis is a bacterial infection of the deep layers of the skin. It can appear anywhere on the body but is most common on the feet, lower legs, and face.

The condition can develop if Staphylococcus bacteria enter broken skin through a cut, scrape, or existing skin infection such as impetigo or eczema.

Most susceptible are those with a weakened immune system, as from corticosteroids or chemotherapy, or with impaired circulation from diabetes or any vascular disease.

Symptoms arise somewhat gradually and include sore, reddened skin.

If not treated, the infection can become severe, form pus, and destroy the tissue around it. In rare cases, the infection can cause blood poisoning or meningitis.

Symptom of severe pain, fever, cold sweats, and fast heartbeat should be seen immediately by a medical provider.

Diagnosis is made through physical examination.

Treatment consists of antibiotics, keeping the wound clean, and sometimes surgery to remove any dead tissue. Cellulitis often recurs, so it is important to treat any underlying conditions and improve the immune system with rest and good nutrition.

Allergic contact dermatitis of the knee

Allergic contact dermatitis means the skin has touched something that provoked an allergic reaction, causing inflammation and irritation.

"Contact" means the allergic reaction came from touching something, not from consuming something. The first exposure to the substance sensitizes the immune system, and then the second exposure actually causes the symptoms.

The most common causes of allergic contact dermatitis are:

Nickel, a metal often used in belt buckles, the buttons on pants, and jewelry, including piercing jewelry.
Poison ivy.
Various types of perfumes, including those founds in soaps, fabric softeners, and detergents.
Of course, there are many more.

Symptoms include red, itching, scaling, flaking skin that may be painful due to the irritation and inflammation.

Diagnosis is made through first avoiding contact with any suspected substance, to see if the dermatitis clears. Patch testing can be done if the results are not certain.

Treatment involves fully avoiding the allergy-provoking substance and using topical steroid cream as prescribed. Cool compresses and calamine lotion can help to ease the discomfort.

Rarity: Common

Top Symptoms: knee redness, knee itch, scabbed area of the knee

Symptoms that always occur with allergic contact dermatitis of the knee: knee redness

Urgency: Self-treatment

Skin infection of the knee

Cellulitis is an infection of the skin and tissues underneath it. It is most commonly caused by Group A strep and typically enters the body through a break in the skin.

Rarity: Uncommon

Top Symptoms: fever, knee pain, knee redness, knee injury, painful knee swelling

Symptoms that always occur with skin infection of the knee: knee redness, area of skin redness

Urgency: Primary care doctor

Questions your doctor may ask about knee redness

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

Do you have a rash?
Is the red area flaky and rough to the touch?
The redness affects one knee or both knees?
Did your symptoms start after you were exposed to nickel (commonly found in jean snaps, metal pens, paper clips, cigarettes, etc.)?

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