Knee Anatomy Overview
The knee joint is a complex weight-bearing articulation consisting of two functional compartments: the tibiofemoral joint (medial and lateral compartments) and the patellofemoral joint, stabilized by both passive and active structures that work together to transmit loads and allow controlled motion.
Structural Components
Bony Architecture
The tibiofemoral joint accepts body weight from the femur onto the tibia while permitting a small degree of axial rotation 1. The joint is divided into medial and lateral compartments, with the medial compartment bearing approximately 70-80% of joint load during the mid-stance phase of gait because the center of mass is located medial to the knee joint center 1.
Passive Stabilizers
The knee's passive stability system includes 1:
- Cruciate ligaments (anterior and posterior) - form the central rotational pillar
- Collateral ligaments (medial and lateral) - restrict excessive varus/valgus motion
- Menisci (medial and lateral) - distribute loads across the articular surface
Active Stabilizers
The principal dynamic stabilizers are 1:
- Quadriceps muscles - primary knee extensors and anterior stabilizers
- Hamstrings muscles - posterior stabilizers and flexors
- Gastrocnemius muscle - assists with posterior stability
Additional muscles contribute to overall joint stability and control.
Functional Biomechanics
Load Distribution
During normal gait, the medial compartment experiences the majority of compressive forces. The mechanical axis of the lower limb (the angle formed by joining the hip, knee, and ankle joint centers) determines how loads are distributed across the joint surfaces 1.
Joint Structures Affected by Pathology
All knee structures are interconnected in function 1:
- Hyaline cartilage covering the articular surfaces
- Subchondral bone beneath the cartilage
- Meniscal fibrocartilage
- Ligamentous structures providing passive restraint
- Fat pad tissues
- Neuromuscular control systems
Clinical Relevance
Understanding knee anatomy is essential because injury to passive stabilizers and weakness of active stabilizers are established risk factors for developing symptomatic knee pathology 1. The ligaments restrict joint motion to preserve physiological load distribution, while muscles provide dynamic protection and control during movement.
The knee's anatomical complexity requires that clinicians understand the interaction between osseous components, soft tissue structures, and their division into medial and lateral compartments when evaluating knee disorders 2, 3.