Structure of the Articular Capsule
The articular capsule consists of two main layers:
- Fibrous membrane (membrana fibrosa / stratum fibrosum) — the outer layer. In certain joints (such as the glenohumeral joint), this layer is uneven, presenting weak areas alongside thickenings formed by ligaments.
- Synovial membrane (membrana synovialis / stratum synoviale) — the inner layer. It forms synovial folds (plicae synoviales) and villi (villi synoviales).
Derivatives of the capsule include ligaments (ligamenta), which are classified into:
- Intracapsular ligaments (ligg. intracapsularia) — e.g., the ligament of the head of the femur.
- Capsular ligaments (ligg. capsularia) — e.g., the zona orbicularis of the hip joint.
- Extracapsular ligaments (ligg. extracapsularia).
Attachment Features in the Upper Limb
Glenohumeral (Shoulder) Joint: The capsule is loose and relatively thin.
- On the scapula: attaches to the bony margin of the glenoid cavity.
- On the humerus: superiorly encloses the head and terminates at the anatomical neck (collum anatomicum). The greater and lesser tubercles remain outside the joint cavity. Inferiorly and medially, the capsule attaches significantly lower — at the level of the surgical neck (collum chirurgicum), forming the axillary recess (recessus axillaris).
Elbow Joint:
- On the humerus: anteriorly attaches above the coronoid fossa (fossa coronoidea) and radial fossa, posteriorly above the olecranon fossa (fossa olecrani). Laterally, the attachment line runs along the base of the epicondyles, leaving both epicondyles (epicondyli) outside the joint cavity.
- On the forearm bones: along the margins of the articular cartilages. On the radius, it attaches to its neck (collum radii).
Attachment Features in the Lower Limb
Knee Joint:
- On the femur: superiorly ascends around the patellar surface, laterally passes between the condyles and epicondyles, and posteriorly descends to the margins of the articular surfaces of the condyles.
- On the tibia: along the margin of the articular surfaces of the condyles.
- Relationship with accessory elements: the outer circumference of the menisci is fused with the capsule, dividing the cavity into a larger (femoromeniscal) compartment and a smaller (tibiomeniscal) compartment. Anteriorly, the capsule blends with the margins of the articular surface of the patella, incorporating it into the capsule wall.
Ankle (Talocrural) Joint: Attaches along the cartilaginous margin of the articular surfaces. Anteriorly, it extends onto a portion of the neck of the talus. The capsule is thin anteriorly and posteriorly, while being reinforced laterally by collateral ligaments.
Articular Capsule of the Temporomandibular Joint (TMJ)
In the TMJ, the capsule is a cone-shaped connective tissue sheath. It is elastic yet quite strong.
The articular disc is fused with the joint capsule along its entire circumference. This divides the joint cavity into two isolated (non-communicating) compartments containing synovial fluid:
- Upper compartment: volume in adults is 1.0–1.5 mL.
- Lower compartment: volume in adults is 0.5–0.8 mL.
This separation provides high compensatory capabilities. If one compartment is damaged, movement in the other can be preserved.