Structure of the articular capsule
The articular capsule consists of two main layers:
- Fibrous membrane (membrana fibrosa / stratum fibrosum) is the outer layer. In some joints (e.g., the shoulder joint), this layer is uneven, with weak areas and thickenings formed by ligaments.
- Synovial membrane (membrana synovialis / stratum synoviale) is the inner layer. It forms synovial folds (plicae synoviales) and villi (villi synoviales).
Derivatives of the capsule include ligaments (ligamenta), which are divided into:
- Intracapsular (ligg. intracapsularia) — for example, the ligament of the head of the femur.
- Capsular (ligg. capsularia) — for example, the circular zone (zona orbicularis) of the hip joint.
- Extracapsular (ligg. extracapsularia).
Attachment features in the upper limb
Shoulder joint: The capsule is loose and relatively thin.
- On the scapula: it attaches to the bony margin of the glenoid cavity.
- On the humerus: superiorly, it encompasses 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, it attaches above the coronoid (fossa coronoidea) and radial fossae; posteriorly, above the olecranon fossa (fossa olecrani). On the sides, the line runs at the base of the epicondyles, leaving both epicondyles (epicondyli) outside the joint cavity.
- On the bones of the forearm: 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: anteriorly, it ascends past the patellar surface; laterally, it passes between the condyles and epicondyles; posteriorly, it descends to the margins of the articular surfaces of the condyles.
- On the tibia: along the margin of the articular surfaces of the condyles.
- Relation to accessory elements: the outer circumference of the menisci is fused with the capsule, which divides the cavity into larger (femoromeniscal) and smaller (tibiomeniscal) compartments. Anteriorly, the capsule attaches to the margins of the cartilaginous surface of the patella (patella), which is "inserted" into it like a frame.
Ankle joint: Attaches along the cartilaginous margin of the articular surfaces. Anteriorly, it encompasses part of the neck of the talus. Anteriorly and posteriorly, the capsule is thin, whereas laterally and medially it is reinforced by accessory ligaments.
Joint capsule of the temporomandibular joint (TMJ)
In the TMJ, the capsule is a cone-shaped connective tissue sheath. It is elastic yet quite durable.
The articular disc is fused with the joint capsule throughout its entire extent. 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 is preserved.
Class and exam questions
Do the epicondyles of the humerus enter the elbow joint cavity?
No, the line of attachment of the articular capsule runs at the base of both epicondyles, leaving them outside the joint cavity.
How does the knee joint capsule interact with the menisci?
The outer circumference of the menisci is fused with the articular capsule. This anatomically divides the knee joint cavity into two compartments: a larger (femoromeniscal) and a smaller (tibiomeniscal) one.
What is the axillary recess (recessus axillaris)?
This is a pouch in the inferior part of the shoulder joint capsule. It is formed because inferiorly and medially the capsule attaches to the humerus significantly lower — at the level of the surgical neck.
Do the upper and lower compartments of the TMJ communicate with each other?
No, they are isolated from each other because the articular disc is fused with the joint capsule throughout its entire extent.
What else to study on this topic
- Synovial fluid (Synovia)
- Articular disc and menisci
- Temporomandibular joint (Articulatio temporomandibularis)
- Shoulder joint (Articulatio humeri)
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