SEPTIC ARTHRITIS

Septic arthritis is usually monoarticular and involves knee or hip in ~75% cases. In children, it is more common than osteomyelitis, with higher risk of residual sequelae. Etiology: Staph.

Pathogenesis: Joint Infection is usually acquired via hematogenous route from a distant focus or adjoining infected metaphysis (osteomyelitis), though direct inoculation may occur after penetrating injuries or surgical interventions, e.g. arthroscopy/aspiration.

Pathological sequence in septic arthritis includes:

(i) synovitis and exudation, (ii) pus collection in joint space, (iii) destruction of articular cartilage, and (iv) spread to adjoining bones or extra-articular tissues. Clinically, septic arthritis begins with acute joint pain and restricted movements (pseudoparalysis), followed by local swelling, heat and constitutional signs, e.g. fever. Diagnosis: Early diagnosis requires USG of suspected joint, followed by joint aspiration for pus culture.

Routine X-rays are normal in first week, while later abnormalities may include: (i) widening of joint space,

(ii) synovial capsular swelling/ thickening, (iii) erosion/ destruction of cartilage and (iv) edema or displacement of surrounding tissues.

TABLE 23.8: Causes of acute arthritis

• Infections: Septic arthritis, tubercular arthritis

• Reactive arthritis

• Post-traumatic

• Malignancy e.g. leukemia

• Hemarthrosis: Hemophilia, scurvy

• Vasculitis syndromes: Henoch-Schonlein purpura

• Rheumatoid disorders: JRA, SLE

Radio nucleotide bone scan may be used to exclude associated osteomyelitis.

D/D of septic arthritis includes other causes of acute monoarticular arthritis (Table 23.8), osteomyelitis and soft tissue injuries/infections.

Treatment of septic arthritis includes:

• Empirical antibacterial therapy, as for osteomyelitis, followed by specific therapy after pus culture reports.

• Joint aspiration under USG guidance, in cases with large effusions. Surgical intervention, i.e. arthrotomy and joint-toilet with normal saline is indicated in: (a) severe hip joint arthritis or arthritis after penetrating injuries, (b) rapid refilling of joint space despite repeated aspirations, (c) presence of pus in subperiosteal/metaphyseal space, and (d) poor response to antibiotics.

• Symptomatic treatment to reduce pain, e.g. analgesics and limb immobilization. However, physiotherapy should being as soon as the pain subsides.

Outcome depends on severity, duration and type of joint involvement, with potential risk of long-term disability in all cases. Hip arthritis carries worst functional prognosis, due to frequently impaired blood supply for the head of femur.

Some other important causes of acute arthritis, not discussed elsewhere, are as follows:

Reactive arthritis (Post-infectious arthritis) is a common, transient and self-limiting arthritis, following or asso­ciated with many extra-articular infections, e.g. (a) exanthematous viral illnesses, e.g. measles,varicella, (b) respiratory viral or mycoplasmal infections, (c) enteric infections, e.g. shigellosis, and (d) chlamydial urinary tract infections.

Pathogenesis is exactly not known, probably relates to autoimmune response involving cross-reactive T-lymphocytes or deposition of immune-complexes in joints. A genetic predisposition with presence of HLAB27 is known in chronic reactive arthritis.

Clinically, these cases present during or within 2-4 weeks of causative infection, with arthralgia/ arthritis of one or more large joints. Most cases recover spontaneously within few days and persistent arthritis beyond 6 weeks is rare, except in HLA-B27 positive children.

Diagnosis rests on exclusion of other causes, with transient course and normal X-rays. Acute phase reactants, e.g. ESR, are usually normal.

Treatment is non-specific, except symptomatic pain relief with anti-inflammatory agents till spontaneous recovery. However, cases with prolonged symptoms should be followed up to detect late-abnormalities, e.g. inflammatory bowel disease or uveitis.

Transient synovitis of hip is a common cause of acute painful limping in children. Although exact pathogenesis is uncertain, preceding viral infection is present in ~70% cases. Most cases occur in 3-8 years age group with male preponderance.

Diagnosis is based on exclusion of other causes of hip pain, e.g. trauma or arthritis on the basis of: (a) absence of fever and leukocytosis, (b) minimal restriction of movements, and (c) normal X-rays except mild joint effusion. Bone scan and joint aspirates are normal while synovial biopsy may reveal non-specific inflammation. Management: Bed rest, avoidance of weight bearing and NSAIDs are usually enough for symptomatic relief in this self-limiting condition, while persistent symptoms demand evaluation for more serious disorders.

23.5.3