What is the structure, function, and common pathologies of the knee, including crystal arthropathy, haemarthrosis (bleeding into the joint), and septic arthritis?

From the Guidelines

The knee is a complex hinge joint that requires prompt and accurate diagnosis and treatment of common pathologies, including crystal arthropathy, haemarthrosis, and septic arthritis, to prevent permanent joint damage and morbidity. The knee joint is formed by the articulation of the femur, tibia, and patella, stabilized by four main ligaments (ACL, PCL, MCL, LCL) and supported by menisci that absorb shock. It functions to provide mobility while bearing weight, allowing for walking, running, and squatting. Common knee pathologies include:

• Crystal arthropathies like gout and pseudogout, which occur when urate or calcium pyrophosphate crystals deposit in the joint, causing acute inflammation, pain, and swelling. Treatment involves NSAIDs, colchicine for gout, and lifestyle modifications 1.
• Haemarthrosis, bleeding into the knee joint, typically results from trauma, anticoagulant use, or bleeding disorders, presenting with rapid swelling, pain, and limited movement. Management includes RICE (rest, ice, compression, elevation), aspiration if severe, and addressing the underlying cause.
• Septic arthritis, a medical emergency, occurs when bacteria infect the joint space, commonly from hematogenous spread or direct inoculation. Patients present with acute onset of severe pain, swelling, warmth, and limited range of motion, often with fever. Immediate treatment requires joint aspiration for diagnosis, followed by intravenous antibiotics (typically vancomycin or ceftriaxone empirically, then targeted based on culture results) for 2-4 weeks, possible surgical drainage, and joint immobilization 1. Early diagnosis and treatment are crucial to prevent permanent joint damage, particularly in septic arthritis where delayed intervention can lead to cartilage destruction within days. According to the most recent guidelines, drainage or debridement of the joint space should always be performed in cases of septic arthritis 1.

From the Research

Structure of the Knee

• The knee joint comprises two articulations: the patellofemoral and tibiofemoral joints 2
• The stability of the joint is governed by a combination of static ligaments, dynamic muscular forces, meniscocapsular aponeurosis, bony topography, and joint load 2
• The movement of the knee joint consists of a coupled motion between the tibiofemoral and patellofemoral articulations 3

Function of the Knee

• The knee joint plays a crucial role in weightbearing and movement, with the femur and patella working together to facilitate flexion and extension 3
• The kinematic coupling between the tibia, femur, and patella is essential for normal knee joint function 3

Common Pathologies of the Knee

• Crystal Arthropathy: characterized by the deposition of crystals, such as monosodium urate or calcium pyrophosphate dihydrate, within the joint 4, 5, 6
• Haemarthrosis: bleeding into the joint, which can occur due to trauma or underlying conditions such as hemophilia 4
• Septic Arthritis: a bacterial infection of the joint, which can occur due to direct inoculation or hematogenous spread 4, 5
• Gouty arthritis and septic arthritis can coexist, making diagnosis and treatment challenging 5

Clinical Features and Management

• Acute gouty arthritis is characterized by intense pain and inflammation, and can be treated with non-steroidal anti-inflammatory agents, colchicine, or corticosteroids 6
• Septic arthritis requires prompt diagnosis and treatment with antibiotics, and may require surgical debridement or drainage 4, 5
• Management of gout and hyperuricemia involves lowering serum urate levels, avoiding triggers such as alcohol and certain foods, and using medications such as uricosuric agents or xanthine oxidase inhibitors 6