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

A. Septic arthritis typically involves monoarticular infection.
B. Septic arthritis can present with fever and chills.
C. Septic arthritis rarely presents with joint effusion.
D. Septic arthritis is a rare cause of arthritis.

**Core Concept:**
Septic arthritis is an inflammatory joint infection caused by bacterial, viral, or fungal pathogens. It is a clinical emergency requiring prompt diagnosis and treatment to prevent joint damage and systemic complications. Septic arthritis can involve monoarticular (single joint) or polyarticular (multiple joints) infection, and it can present with common clinical signs and symptoms like fever, chills, joint pain, and swelling.

**Why the Correct Answer is Right:**
The correct answer (D) is right because septic arthritis is not always rare. It can be caused by various pathogens and can affect any joint. Septic arthritis is an emergency condition that requires urgent medical attention and treatment.

**Why Each Wrong Option is Incorrect:**
A) Septic arthritis can involve monoarticular, oligoarticular (few joints), or polyarticular (many joints) infection, making the statement "rarely presents with monoarticular infection" incorrect.
B) Septic arthritis can present with fever, joint pain, and swelling, making the statement "rarely presents with fever and chills" incorrect.
C) Septic arthritis can cause joint effusion, making the statement "rarely presents with joint effusion" incorrect.

**Why Option D is Incorrect:**
Option D is incorrect because septic arthritis is not rare. It is a serious medical condition that can affect any joint and should be recognized as a potential diagnosis to avoid delayed treatment and potential joint damage or systemic complications.

**Core Concept:**
Septic arthritis is a type of arthritis caused by microbial invasion of the joint, leading to inflammation and joint damage. It is a serious medical condition that requires prompt diagnosis and treatment to prevent long-term joint damage and systemic complications. Septic arthritis can be caused by bacteria, viruses, fungi, or parasites and can affect any joint, making it essential to consider septic arthritis in the differential diagnosis process.

**Why Each Wrong Option is Incorrect:**
A) Septic arthritis can affect any joint and should be considered in the differential diagnosis process. Thus, stating that it "rarely presents with monoarticular infection" is incorrect.
B) Septic arthritis can present with fever and joint pain, making the statement "rarely presents with fever and chills" incorrect.
C) Septic arthritis can cause joint effusion, making the statement "rarely presents with joint effusion" incorrect.

**Why Option D is Incorrect:**
Option D ("rare") is incorrect because septic arthritis is not rare and should be considered in the differential diagnosis process. It can affect any joint and present with fever, joint pain, and joint effusion. Delayed recognition and treatment can lead to significant joint damage and systemic complications.