Osteomyelitis (inflammation of bone) can be due to autoimmune rheumatoid conditions, age-related osteoarthritis, or infection.
When the cause is infection, the spread to the bone and/or joints will have occurred via any of 3 methods:
- Hematogenous seeding: Spread of infectious organisms into the bone and joints from the blood. This usually involves only one infectious organism (monomicrobial). Gonococcal arthritis (gonorrhea) is one example. This type of infection occurs more often in children.
- Contiguous spread: Infection that spreads from adjacent tissues into the bones and joints. These bone and joint infections usually involve more than one infectious organism (polymicrobial). Contiguous spread occurs primarily in younger persons with trauma or surgery-related infections; in older persons it is typically spread from decubitus ulcers.
- Introduced directly via trauma: Typically this is a polymicrobial infection of the bones and joints.
If inflammation creates an exudate (pus) that ruptures the outer layer of periosteum, the blood supply to the bone is compromised, leading to necrosis. Additionally, vascular compromise to the bone (vascular insufficiency) occurs frequently in diabetics and in sickle cell anemia. This is not an infection, but the hypoxia and necrosis from it can provide an opportunistic bed for infection to seed.
Acute osteomyelitis is bone infection before there is bone death. It is termed a “septic arthritis,” and pus into the joints adds a secondary septic arthritis. Acute osteomyelitis begins as a dull pain and then progresses to involve the signs of infection, the classic dolor, calor, rubor, and tumor–tenderness, warmth, erythema, and swelling, respectively. Systemic fever may also be present.
Chronic osteomyelitis can present with pain, erythema, or swelling. There may be a draining sinus tract, which establishes the diagnosis of chronic osteomyelitis. Decubitus ulcers that do not heal can indicate the likelihood of chronic osteomyelitis, especially over bony prominences. Fractures that do not heal may persist as chronic osteomyelitis.
Septic arthritis is infection in a joint that can ultimately destroy the joint. The joint can be infected by bacteria (most often), fungi, or mycobacteria. Most infections occur through hematogenous spread from the blood, although direct inoculation via trauma or surgery can cause it.
Other causes include infective endocarditis (Staphylococcus aureus, enterococci, or strep), bacterial meningitis, femoral venipuncture, or sexually transmitted infections (gonorrhea). Bacteria and their toxins inflame the synovial membranes and the joint inflammation quickly creates purulence; the pro-inflammatory cytokines that is part of the innate immune system can degrade the cartilage.
- Age, especially persons > 80 years of age
- Rheumatoid or osteoarthritis–not an infection, but pre-existing arthritis makes bacteria more likely to invade
- Artificial joint
- Joint surgery
- Trauma (including animal bites)
When these risk factors accumulate into a multiple risk pool, the risks rise considerably, especially in those with alcoholism or intravenous drug abuse.
How Are Bone and Joint Infections Diagnosed?
The diagnosis of osteomyelitis is with a positive culture of bacteria from a bone biopsy and microscopic findings of inflammation. Alternately, this step may not be necessary in patients with imaging (X-Ray) results that are typical of osteomyelitis when blood cultures are positive.
In diabetics or those with deep ulcers, probing a lesion for underlying bone can help identify associated osteomyelitis.
Treatment of bacterial infections depend on identification of the infecting organism. Bone biopsy is used to culture which organism(s) are responsible and to test sensitivity to an array of antibiotic choices: this drives the therapy.
Other causes of the signs and symptoms of osteomyelitis must be ruled out, These include:
● Tissue infection: Separable from bone infection by the use of a bone probe.
● Avascular bone necrosis (malignancy, sickle cell anemia, diabetes).
● Gout: Detection of uric acid crystals in joint fluid.
● Fracture: Associated with prior trauma and positive findings on radiological imaging.
● Bursitis: Distinguishable from osteomyelitis by bursa aspiration.
● Synovitis: Common in osteo- and rheumatoid arthritis.
Bacteria in synovial fluid confirms the diagnosis for septic arthritis:
● Synovial fluid aspiration: for Gram stain and culture, white blood cell count, and identifying any crystals. Aspiration can be guided by CT, ultrasound, or fluoroscopy.
● Concurrent physical findings of pain: especially with joint mobility.
How Can I Manage Bone and Joint Infections?
A combination of surgery and antibiotic therapy is often necessary:
- Surgical debridement of necrotic material.
- Antibiotic therapy based on cultures and sensitivities to antibiotics; therapy with antibiotics is a lengthy process, until the bone has been re-covered by soft tissue that has a good blood supply.
- Hyperbaric oxygen chamber in patients who do not respond in a timely fashion.
- Antibiotics: Based on Gram stain and culture and sensitivities derived from synovial fluid aspiration. Duration is typically at least a month: 2 weeks of intravenous antibiotics, followed by oral antibiotics for another 2 weeks.
- Joint drainage: This is beneficial in that it is analogous to drainage of any persistent, closed abscess. In some joints, arthroscopy guidance (knee, shoulder, wrist) or open surgical drainage (hip) may be required.
How Can I Prevent Bone and Joint Infections?
Prevention of both bone and joint infections is centered on the underlying causes and their risk factors.
For extrinsic risks:
- Avoiding intravenous drug abuse is self-evident, as is avoidance of high-risk behaviors that invite trauma or sexually transmitted infections
For inherent risks:
- Fractures require thorough irrigation, debridement, and prophylactic antibotics, along with fracture fixation and stabilization
- Diabetes. Strict glycemic control and frequent neurologic assessments for pin-prick sensitivity, pressure ulcers, or vascular compromise. Probing for bone can identify osteomyelitis while it is acute, before becoming chronic
- Sepsis and bacteremia unrelated to bone or joint health call for aggressive treatment, along with scrupulous surveillance for any of the hallmarks of bone and joint involvement developing as a complication–tenderness, redness, warmth, and swelling
- Sickle cell anemia has many problems, with vascular compromise of bone only one of them. Besides a hematologist, an infectious disease and orthopedic specialist should be part of the prevention team
- Rheumatoid disease patients should include heightened surveillance for bone and joint infections by patients’ immunologists/rheumatologists