Zona orbicularis
Zona orbicularis
Definition
The zona orbicularis of the hip consists of circular fibers that encircle the femoral neck, forming a ring-like structure. This anatomical feature is crucial for maintaining hip stability, particularly in resisting femoral head distraction.[1-3]
Anatomically, the zona orbicularis is most consistently identified when the hip joint is distended, appearing as a horseshoe-shaped structure in approximately 75% of cases.[2] It is aligned perpendicular to the long axis of the femoral neck superiorly and twists from postero-lateral to antero-medial as it moves inferiorly.[2] Histological studies have shown that the zona orbicularis is not an independent structure but rather a dynamic inward protrusion of the joint capsule that changes morphology depending on the hip position.[1]
Biomechanically, the zona orbicularis acts as a locking ring around the femoral neck, contributing significantly to hip joint stability by resisting distraction forces.[3] This function is supported by cadaveric studies demonstrating a reduction in distraction load when the zona orbicularis is intact.[3]
References
1.Dynamic Changes of the Joint Capsule in Relation to the Zona Orbicularis: An Anatomical Study With Possible Implications for Hip Stability Mechanism.Tsutsumi M, Nimura A, Utsunomiya H, Akita K.Clinical Anatomy (New York, N.Y.). 2021;34(8):1157-1164. doi:10.1002/ca.23767.
2.Anatomy of the Zona Orbicularis of the Hip: A Magnetic Resonance Study.Malagelada F, Tayar R, Barke S, Stafford G, Field RE.Surgical and Radiologic Anatomy : SRA. 2015;37(1):11-8. doi:10.1007/s00276-014-1300-z.
3.The Proximal Hip Joint Capsule and the Zona Orbicularis Contribute to Hip Joint Stability in Distraction.Ito H, Song Y, Lindsey DP, Safran MR, Giori NJ.Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society. 2009;27(8):989-95. doi:10.1002/jor.20852.
