Where does the knee joint capsule start on the femur?

Knee Joint Capsule Attachment on the Femur

Anatomical Origin Points

The knee joint capsule attaches to the femur approximately 1-2 cm proximal to the articular margins of the femoral condyles, with the suprapatellar pouch extending significantly higher on the anterior femur. This attachment pattern creates the boundaries necessary for synovial fluid containment and joint stability.

Specific Attachment Locations

Anterior Femoral Attachments

• The capsule attaches to the anterior femur well above the articular cartilage margins, creating the suprapatellar pouch that extends proximally between the femur and quadriceps muscle 1
• Ultrasound imaging in maximal knee flexion demonstrates the femur and articular cartilage within the suprapatellar region, confirming the capsular attachment extends above the visible cartilage surface 1
• The capsule originates approximately 0.5 cm above the femoral head in the hip (analogous joint), suggesting similar proximal extension patterns in the knee 1

Posterior Femoral Attachments

• The posterior capsule attaches to the posterior femoral condyles proximal to the articular surface, creating the space where popliteal cysts can communicate with the joint 1
• This posterior attachment allows for the comma-shaped extension of Baker's cysts between the medial gastrocnemius and semimembranosus tendon 1

Layered Capsular Structure

Three-Layer Organization

The knee capsule demonstrates a consistent three-layered pattern that must be understood when considering capsular attachments 2, 3:

• Layer 1: Deep crural fascia (superficial layer) 3
• Layer 2: Superficial portion of the medial collateral ligament, which fuses with Layer 1 anteriorly 3
• Layer 3: True joint capsule, deep MCL portions, and meniscal attachments, which fuses with Layer 2 posteriorly 3

Functional Implications

• The capsule functions as a sheet of fibrous tissue rather than a traditional ligament, transmitting forces between adjacent regions rather than along a single longitudinal axis 4
• The fibrous layer of the joint capsule continues into the meniscal lamellar layer and tie fibers, while the synovial layer continues to the superficial meniscal network 5

Clinical Relevance

Imaging Considerations

• Small effusions are best detected in the suprapatellar pouch where the capsule extends furthest from the articular surface 1
• Ultrasound scanning in maximal flexion optimally visualizes the femoral attachment points and any capsular pathology 1

Surgical Implications

• Understanding the proximal extent of capsular attachment is critical for arthroscopic portal placement to avoid inadvertent capsular violation 6
• The capsule's innervation includes six primary nerve branches, with constant distal contact points on the femur that are relevant for pain management procedures 6

Common Pitfalls

• Do not assume the capsule attaches directly at the articular cartilage margin—it extends significantly proximal to this landmark 1
• Avoid confusing the capsular layers with surrounding fascial structures, as they have distinct anatomical and functional properties 3
• Remember that the anterolateral capsule does not function as a traditional ligament and should not be treated as such during surgical repair 4