Comparing Septic Osteomyelitis and Septic Arthritis

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Septic osteomyelitis and septic arthritis are infections of a bone and a synovial joint. They are sometimes discussed together because they have many similarities and can occur at the same time. There are also several differences between the two conditions.

Keep reading to learn about septic osteomyelitis and septic arthritis, their symptoms, causes, how they are diagnosed and treated, and more.

Bone imaging

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Septic Osteomyelitis vs. Septic Arthritis
  Septic Osteomyelitis Septic Arthritis 
Types Can be acute or chronic Types categorized by their source—viruses, bacteria including Staphylococcus, Streptococcus, Gonococcus, and gram-negative bacilli
 
Symptoms Impacts the use of the affected bone, causing a limp or struggle to bear weight  Severe joint swelling, tenderness, and redness are common
Causes Commonly caused by Staphylococcus bacteria Commonly caused by  Staphylococcus, Streptococcus, and Gonococcus bacteria
Diagnosis Diagnosis based on bone examination; can include bone scans and bone biopsy Diagnosis based on joint examination; includes joint aspiration
Treatment IV antibiotic therapy and surgery to move infected bone or tissue Oral antibiotics, pus drainage, physical therapy, joint splinting, and fever/pain-reducing medicines

Symptoms

Both osteomyelitis and septic arthritis are rare, and they can be life-threatening. Early diagnosis and treatment are vital to reducing the potential for complications. Both conditions are suspected—either alone or together—when someone reports fever along with joint symptoms.

Septic Osteomyelitis

Septic osteomyelitis can be acute or chronic. Acute osteomyelitis results from trauma and will resolve with treatment, usually within a couple of weeks. Chronic osteomyelitis occurs after an acute episode doesn’t fully resolve.

The first symptom of septic osteomyelitis is usually pain in the affected bone. Other symptoms might include:

  • Fever
  • Chills
  • Nausea
  • Redness and swelling at the affected area
  • A general unwell feeling
  • Stiffness at the affected bone, or inability to move the bone and nearby joint
  • Drainage of pus in the affected area

Additional symptoms that might be associated with septic osteomyelitis include:

  • Excess sweating
  • Low back pain if there is spine involvement
  • Swelling in the legs, ankles, and feet
  • Loss of motion in the affected joint
  • Changes in gait (walking might be painful or cause a limp; children may struggle to bear weight on an affected leg)

Chronic osteomyelitis can cause severe bone pain, swelling, redness, and tenderness. A person with the condition may also experience pus drainage from an open area of the affected bone.

Chronic osteomyelitis might lead to the destruction of the bone where pieces of bone will separate from the healthy bone. In these cases, surgery is required to remove bone fragments.

Septic Arthritis

Septic arthritis, also called infectious arthritis, means there is an infection in a joint. Infection can be caused by bacteria or a virus that has spread to a joint or the synovial fluid surrounding the joint. The infection often starts in another area of the body and will spread through the bloodstream to joint tissue. 

Often, only one joint is affected by septic arthritis. The knee is involved more than 50% of the time, but septic arthritis can affect any joint, including the hips, wrists, and ankles. Symptoms of septic arthritis will vary depending on the underlying cause (bacteria, fungal, etc).

Symptoms of septic arthritis might include:

  • Severe joint pain that gets worse when you move
  • Joint swelling
  • Joint redness and warmth
  • Fever
  • Chills
  • Fatigue
  • Weakness in the affected area
  • A rapid heart rate

Joints vs. Bones

Joints are the places where two or more bones meet. Most of your joints are mobile and allow your bones to move.

Causes

Both osteomyelitis and septic arthritis are caused by bacterial, viral, or fungal infections. Staphylococcus aureus (staph) is the most common cause of infections that cause these conditions.

Any type of bacterial, fungal, or viral organism that invades an injury or deep cut can cause an infection to a nearby bone or joint. Bacteria can enter a surgical site, such as during a hip replacement or bone fracture repair, and cause a bone or joint infection.

Osteomyelitis

According to the Cleveland Clinic, osteomyelitis affects 2 out of every 10,000 people. Osteomyelitis can affect both adults and children. With children, it usually affects the long bones of the arms or legs. For adults, it commonly affects the spine bones or the hip bones

Most cases of osteomyelitis are related to staph bacteria. Bacteria can enter the bone in different ways, including from:

  • Injuries: A puncture wound can bring bacteria to the inside of the body. If that injury becomes infected, the bacteria can spread to a nearby bone. This can also occur if you break a bone and it sticks out through the skin.
  • Bloodstream: Bacteria from another part of the body—such as from a bladder infection or pneumonia (in the lungs) can travel through the body and infect an area of weak bone.
  • Surgery: Direct contact with bacteria during a joint or bone surgery can contaminate the area and lead to osteomyelitis.

Risk factors that may increase someone’s risk for osteomyelitis include:

  • Long-term skin infections
  • Uncontrolled diabetes
  • Being on dialysis
  • Poor blood circulation
  • Risk factors related to poor blood circulation: high blood pressure, smoking, high cholesterol, and diabetes
  • Having a prosthetic joint
  • Having had a recent injury or joint or bone surgery
  • A weakened immune system
  • Use of injected illicit drugs

Septic Arthritis

Septic arthritis affects 2 to 10 per 100,000 people in the United States and Western Europe, according to a 2020 report in the journal BMC Infectious Diseases. It can affect anyone regardless of age or sex.

It occurs when bacteria, mycobacteria, or other organisms get into the synovial fluid of the joints and start to multiply and cause inflammation (swelling, tenderness, stiffness, etc.).

Types of septic arthritis are categorized by their source, including:

  • Staphylococci: Bacteria that can cause skin infections
  • Gram-negative bacilli: Bacteria commonly found in the gut and feces, including E. coli
  • Streptococci (strep): Bacteria that cause a variety of diseases, including strep throat
  • Gonococci: Bacteria that cause the sexually-transmitted infection, gonorrhea
  • Mycobacteria: A rare cause of septic arthritis acquired during a medical procedure such as a joint injection

The three main types of bacteria that cause septic arthritis are staph, strep, and gonococci. The bacteria related to septic arthritis usually travels through the bloodstream.

People who have an increased risk for septic arthritis might include those who have these risk factors:

  • Autoimmune arthritis conditions, like rheumatoid arthritis (RA) or psoriatic arthritis
  • Open wound
  • Use intravenous drugs
  • Diabetes
  • Weakened immune system
  • Contact with nonsterilized needles
  • Another infection elsewhere in the body

Diagnosis

To distinguish between osteomyelitis and septic arthritis, a doctor will rely on a variety of testing methods. This might include a physical exam, a medical history, blood tests, other lab work, imaging, and bone biopsies.

Distinguishing between the two conditions is usually not difficult as the location of the pain is different, as are imaging findings.

Osteomyelitis

Your doctor will ask about your medical history, review your symptoms, and complete a physical examination. With the physical exam, they will look for signs of tenderness, redness, and swelling in soft tissue and bones. Your doctor may also request bloodwork, imaging, a needle aspiration, and/or a bone biopsy:

  • Imaging: X-rays can show bacterial damage to bones and areas of bone infection. Magnetic resonance imaging (MRI) can look at fluid in the bones and see how far the infection has spread. Bone scans can check how healthy bone tissue is and find bone abnormalities earlier than they would be seen on X-rays.
  • Bloodwork: Bloodwork is done to look for signs of infection. This might include a complete blood count (CBC) to check for increased white blood cells, test for erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) to look for and measure inflammation. 
  • Blood culture: Your doctor might request a blood culture test to detect bacteria that may have gotten into the bloodstream. With this test, blood is drawn into bottles of culture media and incubated. If bacteria grow, they are identified and tested to see which antibiotics are best to treat the infection.
  • Needle aspiration test: A needle is used to remove a sample of fluid and cells from a bony area. The sample is then sent to a lab to be examined for signs of infection.
  • Bone biopsy: A tissue sample from the affected bone is taken and tested for signs of infection and an infectious source.

Septic Arthritis

To diagnose septic arthritis, your doctor will do a physical examination and ask you about your medical and symptom history. If they suspect septic arthritis, they may request further testing, including bloodwork, taking a sample of fluid from the affected joint, as well as imaging.

  • Joint aspiration: Your doctor will request that a sample of fluid be taken from an affected joint and tested for signs of infection. This is the only way to diagnose septic arthritis.
  • Blood tests: Bloodwork for septic arthritis, similarly to osteomyelitis, includes checking for high white blood cell counts and inflammatory proteins.
  • Blood culture: A blood culture can be done to determine the type of infection and to see how far the infection has spread.
  • Imaging: X-rays and MRI scans can assess the damage caused by the joint infection.

Early diagnosis of septic arthritis is important to prevent damage to affected joints.

Treatment

Treatment for both osteomyelitis and septic arthritis usually involves antibiotics and surgical drainage of pus from an affected bone or joint. Early diagnosis and treatment can give people with the condition the best chance for a full recovery.

Delayed treatment, on the other hand, could lead to chronic osteomyelitis or permanent joint damage from septic arthritis.

Osteomyelitis

Treatment for osteomyelitis focuses on treating the infection and preserving as much bone as possible. This includes treatment with antibiotics, surgery, or both.

Antibiotics will bring the infection under control and reduce the need for surgery. Initially, antibiotic therapy starts with an IV (through a vein) and then switches over to oral antibiotics. Antibiotic therapy needs to target the pathogen that has caused the infection.

Chronic osteomyelitis might require surgery to remove infected bone or tissue. This prevents the infection from spreading and getting to the point where amputation is the only treatment option. Surgery to remove affected tissue is usually bone debridement (removing diseased bone) or reconstructive surgery.

Septic Arthritis

Septic arthritis needs treatment with antibiotics as soon as possible. Antibiotic therapy can improve symptoms within 48 hours. If septic arthritis was caused by a fungal infection, it will need to be treated with antifungal medicine.

Treatment for septic arthritis might also include draining pus from the affected joint. Pus buildup can damage the joints if left untreated.

Drainage can be done with a needle, tube, or surgery (a procedure called arthroscopic drainage). Pus may need to be drained two or more times to completely treat the affected joint and to remove bacteria.

Other treatment for osteomyelitis might include:

  • Fever and pain-reducing medicines
  • Physical therapy
  • A splint on the affected joint to relieve pain

Prevention

Both osteomyelitis and septic arthritis are preventable conditions.

Osteomyelitis

The best way to prevent osteomyelitis is to keep the skin clean. If you or a child have a cut, especially a deep cut, wash the area completely.

If you have conditions like autoimmune arthritis or diabetes that might increase your risk for infection, it is important to manage the symptoms of those conditions effectively. Contact your doctor at the first signs of infection, including fever or chills and swelling in the affected area.

Early treatment of acute osteomyelitis can prevent it from becoming a chronic problem.

Septic Arthritis

Like osteomyelitis, it is possible to prevent septic arthritis by avoiding and treating infections, wounds, or other damage to your skin. You should also manage any conditions that could increase your risk for septic arthritis, including RA, diabetes, or skin infections.

Concurrent Osteomyelitis and Septic Arthritis

Osteomyelitis and septic arthritis can occur independently, or they can appear together. When these conditions coexist, one condition might be treated without knowledge of the second condition, leading to delayed treatment of the second condition.

A study reported in 2013 in the Journal of Pediatric Orthopaedics reported on a chart review of 200 children with septic arthritis. Using CT, MRI, and bone scans, researchers found evidence that 72% of shoulder infections and 50% of elbow, hip, knee, or ankle infections were concurrent to osteomyelitis infections.

The researchers concluded that having confirmation of a second, concurrent infection could improve treatment outcomes. It could also mean reduced hospital stays, decreased need for surgical procedures, and the ability to limit additional or chronic infections or permanent damage.

A Word From Verywell

The outlook for both osteomyelitis and septic arthritis can be good if these conditions are treated early and aggressively. Most people will start to feel better and notice symptom improvement within 48 hours of starting treatment. But untreated osteomyelitis or septic arthritis can cause permanent bone or joint damage and could put your life at risk.

Ensure you see your doctor if you experience bone or joint pain or swelling that has no known cause or if you experience other signs of these conditions, including fever and chills. 

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