Why Are My Knees or Joints Hot? Causes and Treatments

When your joints or knees are hot and swollen, it is generally a sign of inflammation. Inflammation is the immune system's response to injury or infection, used to aid with healing and neutralize disease-causing organisms.

One or multiple joints may be affected, and other symptoms may accompany them (including fever, bruising, and joint stiffness). Together, these signs and symptoms can provide clues as to the underlying cause.

This article explores some of the more common causes of warm joints, including how they are diagnosed and treated. It also explains when it is time to see a healthcare provider.

Arthritis

There are different forms of arthritis, some of which are inflammatory (like rheumatoid arthritis) and others that are non-inflammatory (like osteoarthritis).

But even non-inflammatory arthritis can become inflammatory if enough joint damage occurs, causing bone to rub against bone. This is especially true of knee or finger joints that you constantly use.

Both forms of arthritis are characterized by joint pain and stiffness that can get progressively worse and cause deformity and the loss of joint mobility over time.

Arthritic causes of swollen joints include:

• Osteoarthritis: Also known as "wear-and-tear arthritis," this non-inflammatory form of arthritis causes joint stiffness and pain (especially in the morning). Treatment includes weight loss, exercise, over-the-counter (OTC) painkillers, surgery, and joint replacement in severe cases.
• Gout: This is a very painful form of arthritis caused by uric acid crystals that form in a joint, most commonly the big toe. Treatment may involve an anti-inflammatory drug called Colcrys (colchicine) and the avoidance of high-purine foods that can trigger gout attacks.
• Polymyalgia rheumatica: This is an inflammatory disorder that typically affects people over the age of 50, causing joint pain and stiffness. Intra-articular steroid injections (delivered into a joint space) are usually effective in managing the condition.
• Psoriatic arthritis: This form of arthritis frequently develops alongside the autoimmune skin condition psoriasis. Treatment may involve steroid injections, immunosuppressant drugs, biologic immunotherapy, and joint replacement.
• Rheumatoid arthritis: This autoimmune form of arthritis tends to affect the same joints on both sides of the body at once in episodic flares. Treatment may involve oral or injected steroid injections, immunosuppressants, biologic drugs, and joint replacement.
• Juvenile idiopathic arthritis: This is a form of arthritis of unknown origin that affects kids 16 years and younger. Treatment may include OTC painkillers, oral steroids, immunosuppressants, and biologics.

Trauma and Injury

Joint trauma can affect different structures within a joint, including bones, muscles, tendons, ligaments, and cartilage.

Common injuries that can cause warm joints include:

• Dislocation: This is the partial or full separation of the bones in a joint, resulting in intense pain and an immovable, deformed joint. The joints must be put back into their proper position so they can heal. Casts and splints may be needed along with pain relievers and surgery.
• Fracture: Also known as a broken bone, this injury requires immobilization with a plaster cast or surgically inserting metal rods or plates to hold bone fragments together. Some complex fractures may need surgery and traction to aid with the repair.
• Sprains: This is when ligaments that hold the bones together are damaged or partially torn, causing joint pain, bruising, and swelling. Treatment involves RICE (rest, ice, compression, and elevation). Severe sprains may require surgery to repair torn connective tissues.
• Strains: This is when a muscle and/or tendon is damaged or partially torn due to the overstretching or twisting of a joint. The treatment is the same as that used for a sprain.
  

Infections

Joint infections are often caused by an injury that introduces bacteria or a virus into the body. In other cases, a systemic (whole-body) infection will manifest with symptoms in a joint.

Common signs of a joint infection include:

• Joint warmth, swelling, and redness
• Fever with or without chills
• Feeling uneasy or tired
• Joint pain and stiffness
• General achiness
• A pus-like discharge
  

Infections that can cause a warm joint include:

• Septic arthritis: This is a joint infection caused by a bacteria or fungus, or from a bloodstream infection that has moved to a joint. Symptoms include fever, chills, and the inability to move the joint. Treatment may involve joint aspiration (fluid drainage) and antibiotics.
• Lyme disease: This is a tick-borne bacterial infection that leads to joint pain, a "bulls-eye" rash, and flu-like symptoms. Treatment involves oral antibiotics like doxycycline, amoxicillin, and azithromycin or intravenous (IV) antibiotics in severe cases.
• Cellulitis: This is a potentially life-threatening bacterial skin infection that can cause blisters, severe pain, and swelling. Treatment may involve oral, injected, or IV antibiotics along with limb elevation and rest.
• Osteomyelitis: This is a bacterial infection of the bone more commonly seen with diabetes and sickle cell disease. Symptoms include bone pain, fever, chills, and swelling. Treatment may involve surgery to remove dead or infected bone, followed by a course of IV antibiotics.
• Reactive arthritis: This is a form of arthritis that develops in response to a bacterial infection elsewhere in the body. The treatment varies based on the un cause and may include OTC painkillers, steroids, antibiotics, immunosuppressants, and biologic drugs.
• Rheumatic fever: This uncommon illness, associated with strep throat or scarlet fever, causes inflammation in multiple joints. Symptoms include fever and knee, elbow, ankle, or wrist stiffness. Treatment includes antibiotics like penicillin, OTC painkillers, and bed rest.

Bursitis

Bursitis is inflammation of the fluid-filled sacs in joints called bursa. When the bursa becomes inflamed, it can cause localized warmth, redness, and swelling along with stinging joint pain and stiffness. The pain is usually worse during and after physical activity, leading to increased stiffness and pain the next morning.

Bursitis can be caused by many things, including:

• Repetitive use injury (such as sports or working on an assembly line)
• Traumatic joint injury
• Autoimmune diseases like rheumatoid arthritis
• Joint infections

The treatment of bursitis typically involves RICE therapy along with OTC painkillers and physiotherapy. Chronic bursitis may require joint aspiration and a surgery called bursectomy to remove damaged bursa from the joint space.

When Should I See a Healthcare Provider for Warm Joints?

You should seek medical attention if your warm joint doesn't begin to improve within a day, or if you don't know the cause. Your healthcare provider might refer you to a rheumatologist, a doctor who specializes in autoimmune and inflammatory conditions, for further investigation.

How Are Joint Conditions Diagnosed?

In addition to your joint warmth, your healthcare provider will consider your other symptoms and review your medical history, family history, and medications.

They may also do a physical examination to look for joint pain, tenderness, a rash, swelling, or restricted movement.

Based on your history and physical examination, you might need one or more of the following:

• Blood tests: Various blood tests are done to check for inflammation, antibody levels, uric acid, and genetic markers.
• Imaging tests: Ultrasound, X-ray, computed tomography (CT), and magnetic resonance imaging (MRI) can help visualize bone or soft tissue damage.
• Joint aspiration: Arthrocentesis is the removal of fluid from the joint using a needle. It is generally done if the symptoms are severe and an infection is suspected.
• Blood and tissue cultures: The bacterial or fungal organisms causing an infection can be grown and identified in a lab.
• Antinuclear antibody (ANA) tests: Autoantibodies, which are specific proteins associated with an autoimmune process, can be detected in the blood with this test.

Summary

Warm or hot joints are signs of inflammation caused by arthritis, trauma, infections, and bursitis. These conditions can be diagnosed with a physical exam, medical imaging, and various blood, tissue, and joint fluid tests. The treatment varies by the cause but may involve rest, OTC painkillers, antibiotics, steroids, immunosuppressants, surgery, and other specialist procedures.