Septic Arthritis

Septic Arthritis is an abrupt onset of swelling and pain involving one joint is the classic presentation. Many patients have serious underlying illnesses and are febrile. Shaking chills may occur in bacteremia patients. Septic arthritis can be divided into two classes; gonococcal (caused by gonorrhea's) and non-gonococcal. Adults who are young and healthy are more likely to have a gonococcal septic arthritis, while small children, the elderly and the immunocompromised are more likely to have nongonococcal.

Etiology

The way that organisms are able to reach the synovium to cause septic arthritis differ between patients. The most common mechanisms are:

1. Hematogenous from a remote infection

2. Dissemination from adjacent osteomyelitis (especially in children)

3. Lymphatic spread from infection near the joint

4. Iatrogenic infections from arthrocentesis or arthroscopy

5. Penetrating trauma from plant thorns or other contaminated objects

The risk factors for septic arthritis are:

• Impaired host defence

  • Neoplastic disease

  • Elderly

  • Chronic severe illness (diabetes, cirrhosis, chronic renal disease)

  • Immunosuppressive agents (glucocorticoids, chemotherapy)

• Direct penetration

  • IVDU

  • Puncture wounds

  • Invasive procedures

• Joint damage

  • Prosthetic joints

  • Chronic arthritis (RA, hemarthrosis, osteoarthritis)

• Host phagocytic defects

  • Complement deficiencies; impaired chemotaxis

In nongonococcal septic arthritis, Staphylococcus Aurea is the most common organism responsible (61%). Beta-hemolytic streptococci (15%), gram-negative bacilli (17%), Streptococcus pneumoniae (3%) and polymicrobial (4%) are also common causes. In neonates, Staph A is the most common organism due to hospital-acquired infections, but streptococci and gram-negative bacilli can also be found. In children aged less than 2 years old, Haemophilus Influenza is the most common followed by Staph A. In children aged 2-15, Staph A is the most common followed by Strep pyogenes.

History and presentation

In children, septic arthritis is often secondary to adjacent osteomyelitis. Furthermore, children have a higher incidence of hip involvement.

Diagnosis and Investigations

Arthrocentesis with demonstration of the bacteria on Gram Stain or culture establishes the diagnosis of septic arthritis. Of the test that can be run on the synovial fluid, culture; gram stain; and WBC count are the most helpful. Only 40-50% of all patients with septic arthritis have synovial fluid WBC counts >100,000 cells/mm³ so even if synovial fluid is not classic for septic arthritis, there is still a chance of infection.

Blood cultures are useful in septic arthritis - 50% of patients with nongonococcal septic arthritis have positive cultures. On FBCs, leukocytosis and a raised ESR are seen in most individuals but are not usually helpful diagnostically.

Initially, a plain film radiograph (XRAY) should be obtained to rule out adjacent osteomyelitis and establish a baseline, however, definitive changes of septic arthritis may take several days to 2 weeks to develop. The radiological changes in septic arthritis can be remembered as ABCDES

_{Pannus = Growth over the joint}

A: Bony ankylosis

B: Osteoporosis - Increased blood flow

C: Joint space loss - Pannus with cartilage destruction

D: Joint deformity - Endstage of arthritic destruction

E: Erosions - Pannus with bony destruction

S: Soft-tissue swelling

Other radiographic tests are indicated when joints that are deep or difficult to palpate (hip, sacroiliac, and sternoclavicular joints) are involved. They are also helpful early on in a septic process; when plain films do not yet demonstrate any abnormalities.

Treatment and Management

If there is systemic involvement, with signs of bacteremia, local sepsis guidelines and the sepsis six must be started. If a patient has a NEWS score of 7 or more, they must be reviewed within 30 minutes by a senior clinician. If they are NEWS 5 or 6, they should be reviewed within 1 hour.

Antibiotic therapy in accordance with local guidelines should be started after blood cultures and joint aspiration is completed. According to NICE/BNF guidelines, antibiotic therapy is as follows:

• Flucloxacillin

  • 4-6 weeks

• Penicillin-allergic: Clindamycin

  • 4-6 weeks

• MRSA Staph A suspected: Vancomycin or teicoplanin

  • 4-6 weeks

  • Recent inpatients, Nursing home residents or those with leg ulcers/urinary catheters may be at higher risk for MRSA

• Gonococcal arthritis/Gram-negative infection: Cefotaxime/Ceftriaxone

  • 4-6 weeks

  • Treat gonococcal infection for 2 weeks

Unusual organisms may occur in patients who are IVDU or known to have a colonization of other organs such as cystic fibrosis. Exposure to ticks in endemic areas may cause septic arthritis; if the patient has a history of erythema migrans, migratory joint pain, and later oligoarthritis, lyme may be suspected.

Surgical drainage is absolutely indicated for a septic joint if:

1. Infected hip joints and probably shoulder joints

2. Vertebral osteomyelitis with cord compression

3. Anatomically difficult-to-drain joints (sternoclavicular)

4. Inability to remove purulent fluid by needle drainage because fluid is too thick

5. Joints failing to respond to needle drainage

6. Prosthetic joints

7. Associated osteomyelitis requiring surgical drainage

8. Arthritis associated with a foreign body

9. Delayed onset of therapy (>7 days)

Prognosis

Despite improving surgical techniques and antibiotics, there is a 7%-15% mortality rate for in-hospital septic arthritis. Most of these patients have a chronic debilitating underlying disease that contributes to the mortality. Of the surviving patients, 30% have residual abnormality - pain or limited movement. Risk factors for poor outcome in nongonococcal septic arthritis:

1. Rheumatoid arthritis

2. Polyarticular seepsis

3. Positive blood cultures

4. Elderly age

5. Delayed diagnosis

6. Immunosuppressive therapy

7. Gram-negative organisms