The knee is a complex joint that facilitates a wide range of movements, from walking and running to bending and squatting. To better understand its functions and address potential issues, the knee is anatomically categorized into distinct “compartments.” This compartmentalization provides a structured approach to comprehending the knee’s mechanics and maintaining overall knee health.
The Knee’s Structural Divisions
The knee’s compartments are distinct functional and anatomical regions within the joint, based on the articulating surfaces of the bones and surrounding structures. The knee is typically divided into three primary compartments: the medial tibiofemoral, the lateral tibiofemoral, and the patellofemoral. This division is significant for understanding how forces are distributed across the joint during movement and for clinical evaluation.
The medial and lateral tibiofemoral compartments involve the main weight-bearing surfaces between the thigh and shin bones. The patellofemoral compartment, located at the front, is where the patella interacts with the thigh bone. This compartmentalization helps in precisely diagnosing and localizing problems within the knee.
Anatomy of Each Compartment
The knee’s complex structure relies on the precise interaction of bones, cartilage, and specialized tissues within each compartment. The medial tibiofemoral compartment, on the inner side of the knee, is formed by the articulation between the medial condyle of the femur (thigh bone) and the medial tibial plateau of the tibia (shin bone). Between these bone surfaces lies the medial meniscus, a C-shaped fibrocartilaginous structure that acts as a shock absorber and helps distribute load across the joint. Both the femoral condyle and tibial plateau in this compartment are covered with smooth articular cartilage, which reduces friction during movement.
The lateral tibiofemoral compartment occupies the outer side of the knee. Similar to the medial compartment, this area contains the lateral meniscus, a C-shaped fibrocartilaginous structure that helps in cushioning and stabilizing the joint. The bone ends within this compartment are also lined with articular cartilage to facilitate smooth gliding motion.
The patellofemoral compartment is located at the front of the knee, involving the patella and the trochlear groove of the femur. The patella slides within this groove as the knee bends and straightens. The undersurface of the patella and the trochlear groove are covered with articular cartilage, allowing for low-friction movement. This compartment is particularly involved in activities that require significant knee flexion, such as climbing stairs or squatting.
Common Conditions and Compartments
Understanding the knee’s compartments is significant for identifying and treating common knee conditions. Osteoarthritis, a degenerative joint disease characterized by the breakdown of articular cartilage, frequently affects specific compartments. Medial compartment osteoarthritis is the most common form, where cartilage wear occurs predominantly on the inner side of the knee, leading to pain and stiffness. Lateral compartment osteoarthritis, though less common, involves similar degeneration on the outer side of the knee.
Patellofemoral osteoarthritis specifically impacts the joint between the patella and thigh bone, causing pain typically felt behind the patella, especially during activities like climbing stairs or prolonged sitting. Meniscal tears are also compartment-specific injuries; a medial meniscus tear affects the inner knee, while a lateral meniscus tear impacts the outer knee. Medial meniscus tears are more frequently observed due to the medial meniscus’s firm attachment to other knee structures.
Patellofemoral pain syndrome, often called “runner’s knee,” is a common condition characterized by pain around or behind the patella, arising from issues within the patellofemoral compartment. This condition is often linked to overuse, muscle imbalances, or improper tracking of the patella within the femoral groove. Recognizing which compartment is affected allows healthcare professionals to accurately diagnose problems and tailor treatment plans, ranging from physical therapy to targeted surgical interventions.