**Question:** All are true about septic arthritis except -

A. Septic arthritis is a joint infection caused by bacteria, viruses, or fungi.
B. Septic arthritis can be caused by direct inoculation of pathogens from adjacent skin or bone infections.
C. Septic arthritis typically affects the knee joint.
D. Septic arthritis is always a rare complication of joint injections or arthrocentesis.

**Correct Answer: C. Septic arthritis typically affects the knee joint.**

**Core Concept:** Septic arthritis is a serious joint infection that can lead to severe complications if not diagnosed and treated promptly. It is often caused by hematogenous spread from distant sources, such as bacteremia, and can affect any synovial joint, although the knee is the most commonly affected due to its large size, rich vascular supply, and frequent use.

**Why the Correct Answer is Right:** Septic arthritis can involve any joint, but the knee is mentioned as less common due to its larger size, increased vascularity, and greater frequency of use, which makes it more susceptible to damage from the infectious agent. However, this does not exclude the infection from occurring in other joints.

**Why Each Wrong Option is Incorrect:**

A. This option is correct as septic arthritis can be caused by various microorganisms and is not limited to bacteria.
B. While direct inoculation from adjacent skin or bone infections is a potential route for septic arthritis, it does not exclusively cause the infection. Septic arthritis can occur via hematogenous spread as well.
D. This option is incorrect because septic arthritis can affect any joint, not just the knee.

**Clinical Pearl:** A high index of suspicion is essential in diagnosing septic arthritis, as early recognition and timely treatment are crucial to prevent joint destruction and amputation. If you suspect septic arthritis, consider:

1. Order a complete blood count (CBC) with a differential to look for a leukocytosis (increased white blood cell count) and an elevated neutrophil count.
2. Obtain a joint aspirate (joint fluid sample) for culture and sensitivity testing to identify the causative organism and its susceptibility to antibiotics.
3. Start empirical therapy with broad-spectrum antibiotics until the culture and sensitivity results are available.
4. In severe cases, consider arthrocentesis (joint tap) for diagnostic confirmation and treatment.