The zona orbicularis is a circular band of deep hip capsular fibres that encircles the femoral neck like a collar, blending with the iliofemoral, ischiofemoral and pubofemoral ligaments. It is not a separate ligament but a circular thickening of the deep layer of the capsule, most prominent posteriorly and inferiorly. It provides a secondary containment mechanism for the femoral head, supplementing the bony socket and labral seal.
| 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 |
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Encircles the femoral neck like a collar, helping to hold the femoral head in the acetabulum and resist distraction.
The zona orbicularis is visualised on hip MRI arthrography as a circular low-signal band around the femoral neck and at arthroscopy as a ring in the peripheral compartment. Capsulotomy during hip arthroscopy may divide it to access the femoral head-neck junction for cam osteoplasty. Extensive capsulotomy that disrupts the zona orbicularis together with the iliofemoral ligament has been linked to post-operative hip instability, so capsular repair or plication at the end of the procedure is commonly performed.
Zona orbicularis division during hip arthroscopy required for access to the femoral head-neck junction for cam FAI osteoplasty.
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