Frenula capsulae

At a glance

English

Frenula capsulae

Latin (TA2)

Frenula capsulae

System

Joint

Region

Lower limb

Side

Paired, left and right

About the frenula capsulae

At the hip, the fibrous capsule attaches in front to the intertrochanteric line and behind about halfway along the neck of the femur. From these lines many of its deeper fibres turn back, or are reflected, along the neck towards the head of the femur, covered by synovial membrane. Along the neck these reflected fibres gather into a few raised longitudinal folds. These folds are the frenula, or retinacula, of the capsule.

The folds stand out from the surface of the femoral neck, mostly on its upper and lower aspects, and run up to the edge of the articular cartilage of the head. They carry the retinacular arteries, branches mainly of the medial circumflex femoral artery and to a lesser degree of the lateral circumflex femoral artery, which climb beneath the synovium to enter the bone just below the head. In the adult these vessels bring most of the blood that reaches the femoral head.

Their clinical importance comes from these vessels. A displaced fracture of the femoral neck inside the capsule tears the folds and the arteries within them, so the femoral head may lose its blood supply and collapse later through avascular necrosis. This is why such fractures in older people are often treated by replacing the head rather than fixing it. Surgeons operating on the hip through a dislocation approach take care to protect the folds on the upper back of the neck.

Attachments and function

Formed by

Reflected deep fibres of the hip joint capsule at its attachment to the femoral neck.

Joins

Edge of the articular cartilage of the head of the femur.

Movements

Carry the retinacular arteries along the femoral neck to the head of the femur and bind the reflected capsule to the neck.

Blood supply

They carry, rather than receive, the retinacular branches of the medial and lateral circumflex femoral arteries.