Osteomyelitis and septic arthritis Flashcards
What is the pathophysiology of septic arthritis?
Bacteria invade the joint space, triggering an inflammatory response with neutrophil infiltration, leading to the release of proteolytic enzymes that degrade cartilage and increase intra-articular pressure, potentially causing permanent joint damage.
What are the primary routes of infection leading to septic arthritis?
The main routes are hematogenous spread (most common), direct inoculation (from trauma, surgery, or injections), and contiguous spread from adjacent osteomyelitis or soft tissue infections.
What factors increase the risk of developing septic arthritis?
Risk factors include advanced age, diabetes, immunosuppression, IV drug use, alcoholism, prior joint surgery, intra-articular corticosteroid injections, trauma, and skin infections.
Why is septic arthritis more common in large joints?
Large joints, such as the knee and hip, have a greater synovial surface area and blood supply, making them more vulnerable to hematogenous bacterial seeding and inflammation.
How do clinical presentations of septic arthritis differ in children versus adults?
In children, it often presents with fever, irritability, and refusal to bear weight. In adults, the presentation includes acute joint pain, warmth, swelling, and restricted motion, commonly in a single large joint.
What are the key diagnostic criteria for septic arthritis?
Diagnosis is based on clinical presentation, elevated inflammatory markers (ESR, CRP, WBC), and synovial fluid analysis showing high WBC (>50,000 cells/µL), positive Gram stain or culture, and low glucose levels.
Why is prompt diagnosis and treatment essential in septic arthritis?
Delays can lead to irreversible joint destruction, osteonecrosis, sepsis, and systemic complications. Articular cartilage damage can occur within 8 hours of infection onset.
What distinguishes transient synovitis from septic arthritis in children?
Transient synovitis is self-limiting, associated with recent viral infection, and has lower inflammatory markers. Septic arthritis involves high fever, severe pain, and elevated WBC, ESR, and CRP levels.
What is the role of arthrocentesis in managing septic arthritis?
Arthrocentesis confirms the diagnosis by allowing synovial fluid analysis (cell count, Gram stain, culture) and relieves intra-articular pressure to prevent further cartilage damage.
What are the stages of osteomyelitis development?
Osteomyelitis progresses through four stages: 1) Initial inflammation and bacterial invasion, 2) Pus formation and vascular thrombosis, 3) Sequestrum (dead bone) formation, 4) Involucrum (new bone) formation around the necrotic tissue.
How does the blood supply to the metaphysis influence osteomyelitis in children?
The metaphysis has slow, turbulent blood flow and lacks phagocytic cells, making it a prime site for bacterial colonization and hematogenous osteomyelitis in children.
Why are transphyseal vessels important in neonatal osteomyelitis?
Neonates have transphyseal vessels that allow bacteria to cross the growth plate, facilitating the spread of infection from the metaphysis to the joint, increasing the risk of concurrent septic arthritis.
What are the distinguishing features of acute, subacute, and chronic osteomyelitis?
Acute osteomyelitis presents with sudden pain and fever, subacute forms have mild symptoms and may present as a Brodie abscess, and chronic osteomyelitis involves persistent infection with sinus tract formation.
What imaging modalities are most useful for diagnosing osteomyelitis?
MRI is the most sensitive for early detection of bone and soft tissue involvement, while X-rays may show late-stage changes like periosteal reaction and bone destruction.
Why is chronic osteomyelitis difficult to eradicate?
It involves the formation of sequestra (avascular, dead bone) that serves as a reservoir for bacteria, making it resistant to antibiotics and requiring surgical debridement.
What are the long-term complications of untreated osteomyelitis?
Potential complications include chronic pain, pathological fractures, growth disturbances in children, amyloidosis, and recurrent infections.
What are the hallmark symptoms of vertebral osteomyelitis?
Symptoms include localized back pain, fever, and neurological deficits due to spinal cord compression if the infection spreads to the epidural space.
Why is hematogenous osteomyelitis more common in children than adults?
Children’s bones are more vascularized and have active growth plates, making them more susceptible to bacterial seeding through the bloodstream.
What is the significance of the involucrum in chronic osteomyelitis?
The involucrum is a layer of new bone that forms around necrotic tissue, encapsulating the infected area and contributing to persistent infection and recurrent abscesses.
How do laboratory tests guide the diagnosis of osteomyelitis?
Elevated inflammatory markers (ESR, CRP, WBC) suggest infection, and blood cultures or bone biopsy confirm the causative organism.
What is the difference between hematogenous and contiguous osteomyelitis?
Hematogenous osteomyelitis results from bloodstream infection, common in children, while contiguous osteomyelitis arises from adjacent soft tissue or trauma, more common in adults.
How is osteomyelitis managed in diabetic patients?
Management includes aggressive surgical debridement, long-term antibiotic therapy, and optimized glycemic control to prevent recurrence and amputation.
What is the relationship between sickle cell disease and osteomyelitis?
Patients with sickle cell disease are more prone to Salmonella osteomyelitis due to compromised blood flow and bone infarction.
Why is early MRI preferred over X-rays for osteomyelitis diagnosis?
MRI detects early marrow changes and soft tissue involvement, while X-rays show abnormalities only after significant bone destruction.
What factors predispose patients to chronic osteomyelitis?
Open fractures, orthopedic implants, compromised immune systems, and inadequate treatment of acute osteomyelitis increase the risk of chronic infection.
What are the clinical features of pediatric septic arthritis of the hip?
Features include fever, limping or refusal to walk, pain with internal rotation, and a characteristic flexion-external rotation posture to relieve pain.
What are the indications for surgical intervention in osteomyelitis?
Indications include failure of medical therapy, presence of sequestra or abscesses, and persistent infection despite antibiotic treatment.
What is the significance of elevated CRP in osteomyelitis and septic arthritis?
CRP is a sensitive marker for acute inflammation and is useful for monitoring treatment response and detecting persistent infection.
How can septic arthritis and osteomyelitis be prevented in high-risk patients?
Prevention involves proper wound care, early treatment of infections, avoiding unnecessary invasive procedures, and prompt management of bacteremia in immunocompromised patients.
