Arterial Topographic Anatomy Near the Femoral Head-Neck Perforation with Surgical Relevance Paulo Rego, MD, Vasco Mascarenhas, MD, Diego Collado, MD, Ana Coelho, MD, Luis Barbosa, MD, and Reinhold Ganz, MD Investigation performed at the Department of Orthopaedic Surgery, Hospital da Luz, Lisbon, Portugal Background: Knowledge of the vascular supply of the femoral head is crucial for hip-preserving surgical procedures. The critical area for reshaping cam deformity is at the retinacular vessel penetration, an area with ill-defined topographic anatomy. We performed a cadaver study of the extension of the lateral retinaculum near the head-neck junction, distri- bution of the arterial vascular foramina, and initial intracapital course of these vessels. Methods: In 16 fresh proximal parts of the femur without head-neck deformities, the deep branch of the medial femoral circumflex artery was injected with gadolinium for magnetic resonance imaging (MRI) sequences to identify arterial structures. Results: We found a mean number of 4.5 arterial foramina, showing a predominance from 10 to 12 o’clock. The retinaculum extended 20 mm from 1 to 10 o’clock. The surface distance from the cartilage border to the vascular foramina under the synovial fold was 6.5 mm, and the depth from the same cartilage border to the initial intraosseous vessel pathways was 5.3 mm. Conclusions: The data add further precision to the arterial topography at the retinacular foramina, an area that is crucial for the perfusion of the femoral head. It may overlap with the area of anterolateral cam deformity and plays a role in choosing the cuts for subcapital and intracapital osteotomies. Clinical Relevance: The information is taken from normal hips and may not be directly applicable to the deformed hip. Nevertheless, it is a prerequisite for a surgeon to understand the normal anatomy and use those boundaries to prevent mistakes during intra-articular joint-preserving hip surgical procedures. K nowledge of the femoral-head vascular supply is cru- cial for hip-preserving surgical procedures 1,2 . In many cases of femoroacetabular impingement, the head-neck deformity extends over the area where retinac- ular vessels penetrate into bone (Fig. 1). Excessive bone trimming in this area can jeopardize vessels either where they penetrate into bone (Fig. 2) or along their intraosseous course 3,4 , placing femoral-head perfusion at risk 5 . To our knowledge, the literature has been lacking studies about a safe surface distance from the lateral border of the cartilage to the vascular foramina under the retinacular synovial fold and also about the depth of the intraosseous vessels near the cartilage border. In subcapital and true neck osteotomies, the entire femoral-neck circumference is approached sub- periosteally, creating a soft-tissue tube that includes the lateral and medial retinacular vessels 6,7 . In femoral-head reduction osteotomies 6 , the topography and points of pen- etration of the medial and lateral retinacular vessels have to be identi fied to determine the possible size and orientation of the head segment to be resected 6 . This is relatively easy at the medial retinaculum, which runs on top of the easily visualized Weitbrecht ligament 8 . Identification of the ante- rior border of the lateral retinaculum is equally straight- forward. However, definition of the posterior border of Disclosure: There was no source of external funding for this study. The Hospital da Luz Radiology Department provided the MRI scan facilities for cadaver specimen imaging and all of the processing software necessary for the geometrical analysis. The Portuguese National Institute of Legal Medicine and Forensic Science, Pathology Department, supplied the cadaveric material and facilities for dissections. On the Disclosure of Potential Conflicts of Interest forms, which are provided with the online version of the article, one or more of the authors checked “yes” to indicate that the author had a relevant financial relationship in the biomedical arena outside the submitted work ( http://links.lww.com/JBJS/D438). Peer Review: This article was reviewed by the Editor-in-Chief and one Deputy Editor, and it underwent blinded review by two or more outside experts. The Deputy Editor reviewed each revision of the article, and it underwent a final review by the Editor-in-Chief prior to publication. Final corrections and clarifications occurred during one or more exchanges between the author(s) and copyeditors. 1213 COPYRIGHT Ó 2017 BY THE J OURNAL OF BONE AND J OINT SURGERY,I NCORPORATED J Bone Joint Surg Am. 2017;99:1213-21 d http://dx.doi.org/10.2106/JBJS.16.01386