Septic Arthritis

What are the musculoskeletal signs and symptoms of reactive arthritis?

The musculoskeletal manifestations of reactive arthritis include three main features: (1) Arthritis: acute onset, ASYMMETRIC OLIGOARTHRITIS; most commonly affects the lower extremities (knees, ankles, feet); can also affect upper extremities and small joints; less commonly, axial arthritis and sacroiliac joint involvement; minority of patients progress to chronic reactive arthritis (arthritis not resolving within 6 months); (2) Enthesitis: inflammation at the enthesis — the site of insertion of ligaments, tendons, joint capsule, or fascia to bone; common sites include the heel (Achilles tendon insertion and plantar fascia); (3) Dactylitis: inflammation of an entire digit producing a "sausage toe" or "sausage finger" appearance — characteristic of spondyloarthropathies; involves both the joints and surrounding soft tissues of the whole digit.

What are all the extraarticular signs and symptoms of reactive arthritis?

Extraarticular manifestations of reactive arthritis include: (1) Ocular: conjunctivitis (most common); less frequently — anterior uveitis (which may require slit-lamp examination), episcleritis, and corneal ulcers; (2) Genitourinary tract: dysuria, pelvic pain, urethritis, cervicitis, prostatitis, salpingo-oophoritis, or cystitis; in Chlamydia-triggered cases, the initial urogenital infection may be ASYMPTOMATIC; (3) Oral: mucosal ulcers; (4) Constitutional symptoms: fever, malaise, headache, and weight loss — occur during the acute phase and generally resolve; (5) Skin: keratoderma blennorrhagica — hyperkeratotic skin lesions on the soles and palms (resembles pustular psoriasis); erythema nodosum; (6) Nail changes: resemble psoriatic nail changes; however, NAIL PITTING — which is often present in psoriasis — is typically ABSENT in reactive arthritis; (7) Genital lesions: circinate balanitis — shallow, painless ulcerations on the glans penis; (8) Cardiac manifestations (uncommon): pericarditis during the acute illness; valve disease (aortic insufficiency) with greater chronicity.

What is the classic triad of reactive arthritis (Reiter's syndrome) and its association with HLA-B27?

The classic Reiter's triad of reactive arthritis consists of: (1) Arthritis; (2) Urethritis; (3) Conjunctivitis. This triad was historically referred to as "Reiter's syndrome." It is associated with enteric or genitourinary infection followed by these three features. HLA-B27 association: Reactive arthritis is classified as a spondyloarthropathy (SpA), and HLA-B27 positivity is strongly associated with the condition

What is septic arthritis — its definition, predisposing factors, and sources of infection?

Septic arthritis refers to bacterial infection in a joint, but the term also includes fungal and mycobacterial infections. Bacterial septic arthritis is often a DANGEROUS and DESTRUCTIVE form of acute arthritis.
Predisposing factors: (1) Age greater than 80 years; (2) Diabetes mellitus; (3) Rheumatoid arthritis (RA); (4) Prosthetic joint; (5) Recent joint surgery; (6) Skin infection or cutaneous ulcers; (7) IV drug abuse; (8) Alcoholism; (9) Previous intra-articular corticosteroid injection.

Source of infection: in MOST cases, bacterial arthritis arises from HEMATOGENOUS SPREAD to the joint (bacteria seed the joint via the bloodstream);
in some cases, bacterial arthritis is the presenting sign of infective endocarditis (IE)

What are the clinical manifestations and common joint involvement in septic arthritis?

Patients with bacterial (septic) arthritis usually present ACUTELY with a SINGLE swollen and painful joint — i.e., monoarticular arthritis.
Features: acute onset; severe joint pain; joint swelling and warmth; restricted range of motion; systemic signs of infection — fever, rigors, leukocytosis. Joint distribution: the KNEE is involved in MORE THAN 50% of cases; other commonly infected joints: wrists, ankles, and hips; in patients with underlying polyarticular disease (e.g., RA), multiple joints may be involved simultaneously — this polyarticular pattern carries an extremely poor prognosis.
Specific populations: Patients with RA are at higher risk and may have more subtle presentations with septic arthritis masking as a flare; Patients with HIV may develop septic arthritis from opportunistic organisms (fungi, mycobacteria) in addition to typical bacteria.

What are the investigations used in the diagnosis of septic arthritis?

Investigations for septic arthritis: (1) Synovial fluid aspiration (arthrocentesis) — MOST IMPORTANT diagnostic step and should be performed immediately; Gram stain: identifies organisms in many cases; Culture; Leukocyte count and differential: infected fluid is usually PURULENT with an AVERAGE leukocyte count of 50,000–150,000 cells/mm³ (most of which are neutrophils) — this is markedly higher than in reactive arthritis (2,000–64,000/mm³) or OA;
Synovial fluid glucose: often DEPRESSED (bacteria consume glucose); Lactic acid: ELEVATED in synovial fluid; (2) Blood cultures: essential as septic arthritis often arises from bacteremia; bacteria may be grown even when synovial fluid culture is negative; (3) Imaging: plain radiographs — initial assessment and to exclude fractures; CT scanning — for deep joints (e.g., hip, sacroiliac joint) or when plain X-ray is insufficient; MRI — most sensitive for early bone involvement, soft tissue changes, and extent of infection.

What is the antibiotic treatment protocol for septic arthritis, including choice, duration, and why intraarticular antibiotics are NOT recommended?

Empirical antibiotic choice: systemic antibiotics targeting the most likely organisms; 3rd generation cephalosporins are used as empirical treatment, including: Ceftazidime, Ceftriaxone, Cefotaxime; Choice should ultimately be guided by Gram stain and culture results.
Duration: typically give PARENTERAL antibiotics for AT LEAST 14 DAYS, followed by ORAL therapy (if possible) for an ADDITIONAL 14 DAYS (total minimum: 4 weeks);
Longer courses of parenteral therapy (3–4 weeks) may be necessary for difficult-to-treat pathogens such as Pseudomonas aeruginosa or Enterobacter spp.

Why intraarticular antibiotics are NOT recommended: effective parenteral or oral therapy already produces ADEQUATE levels of antimicrobial agents in joint fluid; direct instillation of antibiotics into a joint may CAUSE an inflammatory response. Serial synovial fluid analyses should be performed after initiating treatment to confirm the fluid has become sterile and the total leukocyte count is decreasing; if not improving, consider more definitive joint drainage and/or alteration in antibiotic regimen.

What is joint drainage in septic arthritis — why is it needed, methods used, monitoring, and complications to prevent?

Joint drainage is RECOMMENDED IN ALL PATIENTS with septic arthritis because the condition represents a CLOSED ABSCESS COLLECTION.
Three drainage procedures: (1) Needle aspiration (closed) — single or multiple; most peripheral joints can be drained with closed needle aspiration; DAILY aspiration may be necessary; infected knees often continue to accumulate fluid and require daily aspiration for 7–10 days; (2) Arthroscopic drainage — used if adequate drainage cannot be obtained by needle aspiration; (3) Arthrotomy (open surgical drainage) — used when needle aspiration and arthroscopy fail or are inadequate. Adequacy of needle aspiration is best assessed using CLINICAL CRITERIA: improvement in temperature, WBC count, joint swelling, and pain.

Monitoring after drainage: serial synovial fluid analyses should show the fluid is becoming sterile and total leukocyte count is decreasing; if not → consider more definitive drainage and/or antibiotic change.

Additional care: attention to JOINT POSITION and RAPID MOBILIZATION to prevent contractures and promote optimal nutrition to articular cartilage. Prognosis: mortality from bacterial arthritis depends on comorbidities (advanced age, renal disease, cardiac disease, immunosuppression); POLYARTICULAR septic arthritis — especially due to S. aureus or in patients with RA — has an EXTREMELY POOR PROGNOSIS with mortality rates as high as 50