The zona orbicularis is a circular band of hip capsular fibres that encircle the femoral neck like a collar, formed by the deep circular fibres of the three hip ligaments. It provides a secondary containment mechanism for the femoral head within the acetabulum, supplementing the bony containment and labral seal. Its tightening in hip flexion contributes to the ischiofemoral impingement mechanism.
| Origin | Circular fibres arising from the iliofemoral, ischiofemoral, and pubofemoral ligament fibres that encircle the femoral neck |
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| Insertion | Encircles the femoral neck — not a separate bony attachment but a circularly arranged thickening of the capsule |
| Actions | Maintains femoral head containment; prevents excessive distraction of the femoral head from the acetabulum |
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The zona orbicularis is visualised on hip MRI arthrography as the circular low-signal band around the femoral neck. Its surgical division during hip arthroscopy peripheral compartment access allows complete assessment of the femoral head and neck. Insufficient zona orbicularis release prevents adequate access to the peripheral compartment for cam osteoplasty.
Zona orbicularis division during hip arthroscopy required for access to the femoral head-neck junction for cam FAI osteoplasty.
