Anatomy of the Knee Joint

Overview

• The knee joint is a large hinge-type synovial joint.
• Allows flexion and extension of the lower limb.
• Three main articular areas:
  • Lateral and medial femorotibial articulations (between femur and tibia condyles).
  • Intermediate femoropatellar articulation (between the patella and femur).
• The fibula does not participate in the knee joint.

Articular Surfaces

• Medial and lateral femoral condyles.
• Patellar surface of the femur (trochlear groove).
• Articular surfaces of the medial and lateral condyles of the tibia.
• The patella fits into the patellar surface.

Stability

• Knee joint relies on tibiofemoral ligaments and surrounding muscles (e.g., quadriceps) for stability.

Joint Capsule

• Consists of an external fibrous capsule and an internal synovial membrane.
• Attachments:
  • Superiorly: Femur, proximal to articular margins.
  • Inferiorly: Margin of the tibial plateau.
• The fibrous layer is continuous with quadriceps tendon, patella, and patellar ligament.
• The synovial membrane lines surfaces not covered by cartilage.

Intracapsular Structures

• Cruciate ligaments (ACL and PCL) are located within the fibrous capsule but outside the synovial cavity.

Anterior Cruciate Ligament (ACL)

• Prevents anterior translation of tibia.
• Prevents hyperextension and excessive internal rotation.

Posterior Cruciate Ligament (PCL)

• Prevents posterior translation of tibia.
• Prevents hyperflexion.
• Stronger than ACL.

Menisci

• Medial and lateral menisci are C-shaped fibrocartilage discs within the synovial cavity.
• Function for joint congruency, load distribution, and stability.

Ligaments

• Six extracapsular ligaments:
  • Patellar Ligament
  • Tibial (Medial) Collateral Ligament: Limits valgus movements.
  • Fibular (Lateral) Collateral Ligament: Limits varus movements.
  • Anterolateral Ligament
  • Oblique Popliteal Ligament: Reinforces posterior capsule.
  • Arcuate Popliteal Ligament: Strengthens joint capsule posterolaterally.

Bursae

• Fluid-filled structures to reduce friction.
• Important bursae include:
  • Subcutaneous prepatellar and infrapatellar bursae.
  • Supra patellar, popliteus, anserine, and gastrocnemius bursae communicate with the synovial cavity.

Movements of the Knee Joint

• Flexion: Primarily by hamstrings.
• Extension: Primarily by quadriceps femoris.
• Medial Rotation: By semitendinosus and semimembranosus.
• Lateral Rotation: By biceps femoris.
• Popliteus muscle initiates unlocking of the knee.

Neurovascular Supply

• Arterial supply from periarticular genicular anastomosis:
  • Superior lateral, superior medial, inferior lateral, inferior medial, and middle genicular arteries.
  • Additional supply from femoral and tibial branches.
• Nerve supply includes articular branches from femoral, tibial, and common fibular nerves.

Summary

• The knee joint is a complex structure with multiple articulating surfaces, ligaments, and bursae contributing to its stability and function.
• Understanding the anatomy, movements, and neurovascular supply is crucial for clinicians.