Knee Joint Anatomy and Biomechanics

Knee Joint

The knee joint is formed by the articulation of the femur, tibia, fibula, and patella. It is a complex joint responsible for weight-bearing and locomotion.

Bony Structures

1. Femur

The distal femur has two condyles (medial and lateral) separated by an intercondylar fossa. The anterior aspect features the patellar surface (trochlea) for articulation with the patella.

2. Tibia

The proximal tibia has two condyles (medial and lateral) that articulate with the femoral condyles. The tibial tuberosity is a prominent anterior projection for the patellar ligament attachment.

3. Fibula

The fibula is a slender bone lateral to the tibia. Its head articulates with the lateral tibial condyle, and its distal end forms the lateral malleolus of the ankle.

4. Patella

The patella is a sesamoid bone embedded in the quadriceps tendon. It articulates with the patellar surface of the femur, improving leverage during knee extension.

Articulations

1. Femoropatellar Joint

The femoropatellar joint is a gliding joint between the patella and the femur. It facilitates quadriceps function.

2. Femorotibial Joint

The femorotibial joint is a hinge joint between the femur and tibia, allowing primarily flexion and extension. It also permits some internal and external rotation.

3. Proximal Tibiofibular Joint

The proximal tibiofibular joint is a plane joint between the tibia and fibula. It allows slight movement to accommodate ankle motion.

Joint Capsule and Synovial Membrane

The knee joint is enclosed by a fibrous capsule lined with a synovial membrane. The synovial membrane produces synovial fluid, which lubricates the joint and nourishes the articular cartilage.

Menisci

The knee joint contains two C-shaped fibrocartilaginous menisci (medial and lateral) on the tibial condyles. They improve joint congruency, distribute load, and absorb shock.

• Medial Meniscus: Larger and more C-shaped, less mobile.
• Lateral Meniscus: Smaller and more circular, more mobile.

Ligaments

The knee joint is stabilized by several ligaments:

1. Collateral Ligaments

• Medial Collateral Ligament (MCL): Resists valgus stress (lateral to medial force).
• Lateral Collateral Ligament (LCL): Resists varus stress (medial to lateral force).

2. Cruciate Ligaments

• Anterior Cruciate Ligament (ACL): Prevents anterior tibial translation and internal rotation.
• Posterior Cruciate Ligament (PCL): Prevents posterior tibial translation and external rotation.

Knee Movements

The primary movements of the knee are:

• Flexion: Bending the knee.
• Extension: Straightening the knee.
• Internal Rotation: Rotating the tibia medially.
• External Rotation: Rotating the tibia laterally.

Muscles Acting on the Knee

Several muscles contribute to knee movement and stability:

• Knee Extensors: Quadriceps femoris (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius).
• Knee Flexors: Hamstrings (biceps femoris, semitendinosus, semimembranosus), gastrocnemius, sartorius, gracilis, popliteus.