Joint capsule

Capsula articularis

Also known as: articular capsule, fibrous capsule, capsular ligament

The sleeve-like envelope that encloses a synovial joint, consisting of an outer fibrous layer of dense connective tissue and an inner synovial membrane.

Synovial Joint — Structure

Overview

The fibrous layer of the capsule attaches to the bones at or near the margins of their articular surfaces and is continuous with the periosteum. It is composed of dense irregular collagenous tissue, locally thickened into intrinsic (capsular) ligaments — for example the glenohumeral ligaments of the shoulder and the iliofemoral ligament of the hip. Its laxity varies with the mobility of the joint: the shoulder capsule is loose (with a redundant inferior fold, the axillary recess), the hip capsule tight and strong.

The capsule is richly innervated with mechanoreceptors (Ruffini endings, Pacinian corpuscles) that provide proprioception and with nociceptors; tension in it signals joint position and stretch. The synovial membrane lines its inner surface.

Location: Surrounds every synovial joint, attached around the articular margins.

Parts & subdivisions

Fibrous layer
Dense irregular connective tissue continuous with periosteum.
Intrinsic (capsular) ligaments
Local thickenings — e.g. glenohumeral, iliofemoral, collateral ligaments.
Synovial layer
Inner lining that produces synovial fluid.

Anatomy

Innervation: Articular branches of nerves crossing the joint (Hilton’s law).

Function

Encloses the joint cavity and contains synovial fluid
Provides passive stability and limits excessive movement
Proprioception (joint position sense)

Clinical significance

Adhesive capsulitis (frozen shoulder)

Inflammation and fibrous contracture of the glenohumeral capsule (especially the rotator interval and axillary recess) causes painful, then stiff, loss of both active and passive movement — especially external rotation; associated with diabetes.

Test yourself

Why is the medial meniscus injured more often than the lateral meniscus?

It is attached to the tibial collateral ligament and joint capsule, making it less mobile
It is avascular throughout
It is attached to the popliteus tendon, which tears it during flexion
It is thinner and O-shaped

Answer: It is attached to the tibial collateral ligament and joint capsule, making it less mobile

The C-shaped medial meniscus is firmly attached to the capsule and the deep fibres of the tibial collateral ligament, so it cannot move out of the way of the femoral condyle during twisting. The lateral meniscus is more mobile, being separated from the fibular collateral ligament by the popliteus tendon.