Septic Arthritis

CHAPTER 8

Septic Arthritis

Introduction/Etiology/Epidemiology

• Septic arthritis (SA) is also called suppurative arthritis, infectious arthritis, or bacterial arthritis and results from bacterial invasion of a joint with subsequent inflammation (Figure 8-1).

• It usually develops as a result of direct inoculation (eg, penetrating injury) or transient bacteremia, but spread into the joint may also come from a skin lesion, or an extension from an adjacent soft tissue infection.

• SA that complicates osteomyelitis is discussed in Chapter 7, Osteomyelitis, and requires different surgical management than primary SA.

• Rapid and progressive joint destruction may occur if urgent surgical drainage and irrigation are not undertaken.

• Common pathogens are age associated (see Table 8-1).

— Staphylococcus aureus and group A streptococcal disease occur at all ages.

— Children younger than 5 years additionally develop Kingella kingae and Streptococcus pneumoniae (pneumococcal) SA.

— Neisseria gonorrhoeae can be a common cause of polyarticular SA in adolescents.

— Since the introduction of Haemophilus influenzae type b (Hib) conjugate vaccine in 1988, K kingae has supplanted Hib as the predominant gram-negative cause of SA in children 2 months to 5 years of age (Hib infections are rare in immunized children). Obtaining a vaccination history is important.

— Invasive pneumococcal disease has decreased since the introduction of the pneumococcal conjugate vaccine in 2001.

— Reactive arthritis is distinguished from SA by sterile joint fluid and may occur as a complication of Salmonella, Shigella, Campylobacter, Yersinia, Chlamydia trachomatis, Neisseria meningitidis, and many other infections. During reactive arthritis, an immunologic response to infection at another site results in acute inflammation of the joint.

• Mycobacterial and fungal invasions occur rarely, but they can be more common in immunocompromised patients.

• Epidemiology and demographics

— Children younger than 3 years are most commonly affected, with 50% of cases occurring in patients younger than age 2 years.

— Boys are affected twice as often as girls.

— Infection of the hip, knee, and ankle comprises 80% of cases.

— Children with sickle cell disease, diabetes mellitus, immunodeficiencies, preexisting joint damage, or compromised skin integrity from dermatologic conditions (eg, eczema, psoriasis) tend to be particularly susceptible.

Figure 8-1. Arrow indicates hip effusion on T2-weighted magnetic resonance image in a child 2 years of age with fever and inability to bear weight, consistent with a diagnosis of a septic hip.

Table 8-1. Microorganisms Causing Septic Arthritis and Commonly Affected Populations

Microorganism(s)	Commonly Affected Populations
Staphylococcus aureus	Most common (70%–90%) at all ages (hospital-acquired MRSA and CA-MRSA— rising incidence)
Streptococcus (group A β-hemolytic streptococci, Streptococcus pneumoniae), Kingella kingae	Children 2 mo to 4 y of age
Group B streptococcal disease (Streptococcus agalactiae) and gram-negative bacteria	Neonates
Neisseria gonorrhoeae	Sexually active adolescents
Salmonella	Children with sickle cell disease
Borrelia burgdorferi	Children exposed to deer ticks in B burgdorferi–endemic areas