Definition
A.Infection of a joint, generally caused by bacteria, but can be caused by fungi or mycobacteria.
B.Devastating form of acute-onset arthritis; considered an orthopedic emergency.
C.Although all types of septic arthritis are infectious, not all types of infectious arthritis are classified as septic. Systemic diseases that can trigger an inflammatory response in joints include:
1.Lyme disease.
2.Chikungunya: Mosquito-borne illness (in the family of alphaviruses).
3.Rubella.
4.Parvovirus.
5.Hepatitis B and C.
Incidence
A.Incidence is 2 to 10 per 100,000 in general population.
B.The incidence is increased in patients with rheumatoid arthritis or joint prostheses, 30 to 70 per 100,000.
C.The prevalence has been estimated to range from 8% to 27% in adults presenting with one or more acutely painful joints.
D.Mortality has been at the persistent rate of 5% to 15% over the past 25 years.
Pathogenesis
A.Hematogenous seeding from bacteremia. Bacteria cause acute synovitis after entering the closed joint space within hours. The synovium is very vascular with no membrane barriers, making it susceptible to seeding by bacteria.
1.Synovial reaction: Results in swift entry of acute and chronic inflammatory cells.
2.Release of cytokines and proteases, which causes cartilage degradation.
3.Bone loss: Evident within a few days.
4.Generally monomicrobial.
5.Most cases (75%): Involvement of only one joint (monoarticular).
a.Polyarticular infection is commonly seen in rheumatoid arthritis.
B.Joint surgery, joint aspiration, or local steroid injections: Often polymicrobial infections.
C.Puncture wounds or bites: Also possibly inoculant into the joint.
D.Bacteria most often involved.
1.Staphylococcus aureus: Primary cause.
2.Beta hemolytic streptococci: Next most common.
3.Neisseria gonorrhoeae: Most common pathogen among younger, sexually active adults, causing more than 75% of septic arthritis cases.
E.In intravenous (IV) drug users, gram-negative bacilli implicated most often.
1.Klebsiella pneumoniae.
2.Escherichia coli.
3.Pseudomonas aeruginosa.
Predisposing Factors
A.Age greater than 80 years.
B.Immunocompromised status.
C.Preexisting joint disease (gout, systemic connective tissue disorders).
D.Diabetes mellitus.
E.Rheumatoid arthritis.
F.Disseminated gonococcal infections in young healthy adults. Develops in 1% to 3% of untreated cases of gonorrhea.
G.All substance abuse, particularly IV drug use.
H.Skin infections; cutaneous ulcers.
I.Previous intra-articular corticosteroid injections.
Subjective Data
A.Common complaints/symptoms.
1.Native joints: Acute joint pain, swelling, warmth, erythema, decreased range of motion, fever, or malaise.
2.Prosthetic joints: Possibly minimal symptoms.
B.Common/typical scenario.
1.History of joint swelling, pain, fever, general malaise, or chills of acute onset.
2.Other recent infection (e.g., urinary tract infection [UTI], cellulitis; cutaneous infections from IV drug use; sexually transmitted diseases, particularly gonorrhea; endocarditis).
3.Recent orthopedic surgery or joint replacement: Can be early onset, delayed onset (3–24 months), or late onset (24 months after surgery).
4.History of rheumatoid arthritis; receiving anti-tumor necrosis factor (TNF).
a.Anti-TNF therapy associated with doubling of risk of septic arthritis.
b.Can result in higher mortality because septic arthritis can be mistaken for an acute rheumatoid arthritis flare up and lead to delay in treatment.
5.History of immunosuppressive diseases, including:
a.Liver disease.
b.Diabetes.
c.Solid tumors.
d.Lymphomas.
e.HIV.
C.Family and social history.
1.History of IV drug use.
2.Smoking history.
3.Sexually active with multiple partners (gonococcal bacterial arthritis).
D.Review of systems.
1.Constitutional: Fatigue, malaise, lethargy, decreased appetite, or recent trauma.
2.Gastrointestinal: Unintentional weight loss, or diarrhea.
3.Genitourinary (GU): Frequent infections.
4.Musculoskeletal: Pain in joint(s), joint swelling, decreased range of motion, or arthritis.
5.Skin: Lesions, erythema, cutaneous wounds, needle marks, or bites.
6.Hematologic/lymphatic: Swollen lymph nodes or exposure to Lyme disease.
Physical Examination
A.Low grade fever.
1.Chills and spiking fever atypical.
2.Fever less likely in older adults.
B.Possible joint swelling, warmth, erythema, and limited range of motion.
C.Generally monoarticular. Polyarticular disease is present in about 20% of cases, generally in patients with rheumatoid arthritis or other systemic connective tissue disease.
1.Knee most common (50%).
2.Hip (20%).
3.Ankle (7%).
4.Wrists (7%).
5.Sacroiliac joints (1%–4%).
6.Axial joint septic arthritis (sternoclavicular, sternomanubrial joints): Most common in IV drug abuse.
D.Joint effusion.
E.Limited active and passive range of motion.
F.Prosthetic joint infections: Later physical findings often minimal.
1.Slight to no swelling.
2.May have draining sinus.
Diagnostic Tests
A.Synovial fluid aspiration.
1.Synovial fluid leukocyte count and neutrophil percentage: Reliable measure before cultures available. Synovial fluid leukocyte count greater than 50,000/mm³ with polymorphonuclear leukocyte predominance is usually indicative of septic arthritis but can also be seen in gout.
2.Cytology: Used to exclude gout or other crystal arthritis types. Mycobacteria and fungi may also be identified by cytology.
3.Cultures.
a.Complete blood count.
i.Leukocytosis present in most cases but has low sensitivity and specificity.
b.Inflammatory markers.
i.Erythrocyte sedimentation rate (ESR): Useful only in patients with native joint infections without underlying hematological or rheumatological conditions.
ii.C-reactive protein (CRP): Typically elevated, but also lacks specificity.
c.Radiologic studies.
i.Plain films not usually helpful except to rule out an injury that might produce similar symptoms.
ii.CT better than plain films in identifying joint effusion, soft tissue swelling, and abscesses.
iii.MRI sometimes useful in native joint infections. Newer machines may allow for assessment of prosthetics.
4.Bone scintigraphy: Sensitive in identifying joint infections but is not specific enough to distinguish infection from other pathologies.
B.Other diagnostics.
1.CT or ultrasound guided biopsy: Used in axial skeletal joints and sternoclavicular joints.
2.Open biopsy: Highest sensitivity and specificity but is rarely done.
3.Arthroscopy: Useful to evaluate for septic arthritis of the knee.
Differential Diagnosis
A.Traumatic effusion.
B.Hemarthrosis.
C.Bursitis.
D.Cellulitis.
E.Acute synovitis (inflammation of synovial membrane).
F.Gout or pseudo gout.
G.Viral arthritis (rubella, hepatitis B and C, HIV).
H.Lyme disease.
I.Reactive arthritis—seronegative spondyloarthropathies such as Reiter’s syndrome, psoriatic arthritis, ankylosing spondylitis, inflammatory bowel disease-related arthritis.
J.Endocarditis—can present with sterile synovitis or joint pain similar to septic arthritis. Fifteen percent of patients with infective endocarditis have concomitant septic arthritis or osteomyelitis.
Evaluation and Management Plan
A.General plan.
1.Considered a medical emergency.
2.Early treatment (<7 days from onset): Improved outcome.
3.Antibiotics: First-line treatment.
a.Empiric treatment aimed at most common bacteria of staphylococci and streptococci.
b.Concomitant infections such as UTIs: Possible use of antibiotics for gram-negative bacteria.
c.Prosthetic joint infections: Vancomycin if methicillin-resistant coagulase-negative staphylococci.
4.Drainage.
a.Hip, shoulder, and sacroiliac joints: Not easily drained with needle aspiration; may require open arthrotomy.
b.Sternomanubrial and sternoclavicular joints: Generally managed with open irrigation and debridement.
5.Splinting.
a.Knees splinted in extension.
b.Elbows splinted at 90°.
c.Hips in balanced suspension with no rotation.
d.Joint range of motion to begin when infection improved.
6.Removal of prosthetic joint often necessary.
7.Dental prophylaxis: Should be considered in patients who have prosthetic joints and immunosuppression, diabetes, or rheumatoid arthritis.
B.Pharmacotherapy.
1.Antibiotic therapy: Initiated empirically, then tailored based on gram stain/cultures after joint aspiration.