Where does the knee joint capsule end?

Knee Joint Capsule Anatomical Boundaries

Direct Answer

The knee joint capsule attaches to the tibia at variable distances from the joint line, with the most extensive proximal attachment occurring on the femoral side anteriorly (up to 6.5 cm above the joint line laterally), while tibial attachments remain much closer to the joint line (typically within 0.09-1.45 cm below it). 1

Femoral Attachments

The capsule extends significantly proximal on the femur, with distinct regional variations:

Anterior Aspect

• Lateral side: approximately 6.5 cm above the femoral joint line 1
• Medial side: approximately 4.57 cm above the femoral joint line 1
• This represents the most extensive capsular reflection in the entire knee joint

Middle Coronal Plane

• Lateral side: approximately 2.74 cm above the joint line 1
• Medial side: approximately 1.74 cm above the joint line 1

Posterior Aspect

• Lateral side: approximately 1.52 cm above the joint line 1
• Medial side: approximately 1.99 cm above the joint line 1

Tibial Attachments

The capsule attaches much closer to the tibial joint line compared to the femoral side:

Anterior Aspect

• Lateral side: approximately 0.09-1.45 cm below the joint line (with cadaveric studies showing up to 1.45 cm) 1
• Medial side: approximately 0.11 cm below the joint line 1

Middle Coronal Plane

• Lateral side: approximately 0.34 cm below the joint line 1
• Medial side: approximately 0.26 cm below the joint line 1

Posterior Aspect

• Lateral side: approximately 0.62 cm below the joint line 1
• Medial side: approximately 0.34 cm below the joint line 1

Special Anatomical Considerations

Lateral Tibial Attachment

At the posterior border of Gerdy's tubercle, the capsular attachment demonstrates unique characteristics:

• Width averages 8.6 mm (SD 3.0) 2
• Contains well-developed uncalcified fibrocartilage at this location 2
• The attachment gradually tapers toward the posterolateral aspect 2
• Becomes linear at the apex of the fibular head, where it adheres to the proximal tibiofibular joint capsule 2

Attachment Structure

The capsule attaches to bone through specialized zones:

• Contains fibrocartilage at attachment sites, derived from embryonic bone rudiment 3
• Rich in type II collagen and glycosaminoglycans at these attachment zones 3
• Thickness varies according to mechanical stresses 3

Clinical Implications

Imaging Considerations

MRI tends to underestimate the distal extent of the knee capsule on the tibial side, particularly outside the lateral posterior plane 1. This is critical when:

• Planning external fixator pin insertion 1
• Evaluating capsular injuries
• Assessing joint effusions 1

Surgical Relevance

The inferior margin of the posterior capsule requires special surgical techniques for reattachment to the tibia 4, reflecting the anatomical complexity of this region where the capsule ends most distally.

The capsule forms a three-layered pattern on the medial side 5, which is important for understanding injury patterns and surgical repair approaches.