What is the appropriate workup and treatment for septic arthritis?

From the Guidelines

Septic arthritis requires prompt diagnosis and treatment to prevent joint destruction, and the workup begins with joint aspiration for synovial fluid analysis, including cell count, Gram stain, culture, and crystal examination, with immediate empiric antibiotic therapy and surgical drainage as the cornerstone of treatment. The diagnosis of septic arthritis is primarily clinical, with a synovial fluid white blood cell count above 50,000 cells/mm³ with predominant neutrophils strongly suggesting septic arthritis 1. Blood cultures should be obtained before starting antibiotics, as they are positive in about 50% of cases. Imaging studies like plain radiographs can show joint effusion, while MRI may detect early osteomyelitis or abscess formation.

Initial Management

Treatment involves immediate empiric antibiotic therapy, with vancomycin 15-20 mg/kg IV every 8-12 hours plus ceftriaxone 2g IV daily being appropriate initial therapy for adults, covering Staphylococcus aureus (including MRSA) and gram-negative organisms 1. For children, cefazolin 100-150 mg/kg/day divided every 8 hours is recommended, with vancomycin added if MRSA is suspected.

Surgical Drainage

Surgical drainage via arthroscopy or open arthrotomy is necessary for most cases, especially for hip, shoulder, and other deep joints, as it helps in removing the infected material and reducing the bacterial load, thus preventing further joint damage 1.

Antibiotic Duration

Antibiotics should be adjusted based on culture results and continued for 2-4 weeks for uncomplicated cases, with longer courses (4-6 weeks) for patients with comorbidities or complex infections 1. Recent studies suggest that shorter courses of antibiotics may be adequate for certain cases, but this should be decided on a case-by-case basis, considering the severity of the infection, the presence of comorbidities, and the response to treatment 1.

Rehabilitation

Joint immobilization initially followed by early passive range of motion exercises helps preserve joint function. Rapid treatment is crucial as delayed therapy beyond 24-48 hours significantly increases the risk of permanent joint damage.

Key Considerations

• Prompt diagnosis and treatment are essential to prevent joint destruction and improve outcomes.
• Empiric antibiotic therapy should be started immediately, with coverage for Staphylococcus aureus and gram-negative organisms.
• Surgical drainage is often necessary, especially for deep joints.
• Antibiotic duration should be tailored to the individual case, but typically ranges from 2-6 weeks.
• Rehabilitation with joint immobilization and passive range of motion exercises is important for preserving joint function.

From the FDA Drug Label

Bone and joint infections including acute hematogenous osteomyelitis caused by Staphylococcus aureus and as adjunctive therapy in the surgical treatment of chronic bone and joint infections due to susceptible organisms The appropriate workup for septic arthritis is not directly addressed in the drug label. However, the treatment for bone and joint infections including septic arthritis can involve the use of clindamycin as an adjunctive therapy in the surgical treatment of chronic bone and joint infections due to susceptible organisms 2. Key points to consider in the treatment of septic arthritis include:

• Identifying the causative organism and its susceptibility to clindamycin
• Using clindamycin as adjunctive therapy in conjunction with surgical procedures
• Considering the use of clindamycin in patients who are allergic to penicillin or for whom penicillin is inappropriate.

From the Research

Diagnosis of Septic Arthritis

• Septic arthritis should be considered in patients presenting with acute atraumatic joint pain, swelling, and fever, especially in those with risk factors such as age older than 80 years, diabetes mellitus, rheumatoid arthritis, recent joint surgery, hip or knee prosthesis, skin infection, and immunosuppressive medication use 3.
• Physical examination findings and serum markers, including erythrocyte sedimentation rate and C-reactive protein, are helpful in the diagnosis but are nonspecific 3.
• Synovial fluid studies are required to confirm the diagnosis, with a synovial fluid white blood cell count usually greater than 50,000 per mm3 in patients with septic arthritis 4.
• However, in the presence of crystalline arthropathy, a synovial cell count greater than 85,000/mm3 may be more appropriate to diagnose concomitant septic arthritis 5.

Treatment of Septic Arthritis

• Empiric antibiotic therapy should be initiated if there is clinical concern for septic arthritis, with oral antibiotics being suitable for most cases 3.
• The choice of antibiotic should be guided by Gram stain results, with vancomycin used for gram-positive cocci, ceftriaxone for gram-negative cocci, and ceftazidime for gram-negative rods 4.
• Evacuation of purulent material with arthrocentesis or surgical methods is necessary, with consideration given to patients with prosthetic joint infection 4.
• The total duration of antibiotic therapy ranges from two to six weeks, with certain infections requiring longer courses 3, 6.

Laboratory Tests

• Gram stain microscopy has a low sensitivity (22%) but high specificity (99.6%) for diagnosing septic arthritis, and a negative result should not overlook clinical findings and biochemical markers 7.
• Synovial fluid culture is essential for confirming the diagnosis and guiding antibiotic therapy 4.
• Biochemical markers, such as erythrocyte sedimentation rate and C-reactive protein, are helpful in the diagnosis but are nonspecific 3.