The zona orbicularis is a band of circular capsular fibres encircling the femoral neck within the hip joint capsule, forming an intraarticular ring at the mid-femoral neck level. It functions as a ligamentous collar around the femoral neck, tightening the capsule around the neck and reinforcing the capsule between the iliofemoral, ischiofemoral, and pubofemoral ligament complexes. It is not a distinct ligament but a circular thickening of the deep capsular layer.
Creates a transverse constriction of the hip capsule around the femoral neck that resists distraction of the femoral head from the acetabulum; provides circumferential stability between the major ligamentous condensations of the hip capsule.
The zona orbicularis is relevant in hip arthroscopy, where the interportal capsulotomy must be planned to preserve the orbicular fibres on the femoral neck to maintain capsular integrity and prevent post-operative hip instability. Iatrogenic hip instability after hip arthroscopy has been attributed in part to excessive capsulotomy disrupting the zona orbicularis. In hip arthroplasty, capsular closure incorporating the zona orbicularis remnants is recommended in posterior approaches to reduce dislocation risk.
Extensive interportal capsulotomy that divides the zona orbicularis circular fibres along with the iliofemoral ligament produces post-operative hip hyperlaxity and instability; contemporary hip arthroscopy technique aims for anatomic capsular repair or plication of the zona orbicularis at procedure completion to preserve circumferential femoral neck support.
