New Findings In Hip Capsular Anatomy: A Cadaveric Study of the Ligamentous and Muscular Contributions to the Hip Capsule

Abstract

Interest in capsulotomy techniques for access to advanced arthroscopic procedures of the hip continues to grow. Extra-articular capsulotomy has been proposed as an expedient means of obtaining access to the periarticular structures of the hip. The purpose of this study was to establish consistent anatomical landmarks based on observed capsular attachments for safe and reproducible extra articular capsulotomy. Detailed dissections of twelve nonpaired, fresh-frozen cadaveric adult hips were performed. Using a modified hemi-quadrant system, capsular thickness at 40 locations across its length and circumference was recorded. The insertions and attachments of the surrounding pericapsular structures including the minimus, rectus femoris, and iliocapsularis muscles were also recorded according to footprint size and distance from reproducible osseous landmarks. The intra-articular distance of the capsular origin from the bony acetabular rim and the intra-articular distance of the capsular insertion from the femoral head-neck junction was measured. All measurements were made to the nearest 0.1 mm with a digital caliper (Neiko Tools; Ontario, CA) with measurement accuracy of ± 0.02 mm. The intraclass correlation coefficient (ICC) for all measurements taken was > 0.90. Along the acetabular origin, the capsule was thickest along its posterosuperior and superior hemi-quadrants. The midcapsular quadrants were thickest superolaterally. At its femoral insertion, the capsule was thickest anteriorly.Tabled 1QuadrantAcetabular OriginCenter of CapsuleFemoral InsertionPosterior2.1 ± 1.92.4 ± 0.80.5 ± 0.2Postero-Inferior1.9 ± 1.31.5 ± 0.30.8 ± 0.3Inferior1.3 ± 0.31.2 ± 0.41.7 ± 0.8Antero-Inferior1.3 ± 0.71.4 ± 0.53.3 ± 1.5Anterior1.2 ± 0.61.5 ± 0.93.4 ± 1.4Antero-Superior1.6 ± 0.92.3 ± 1.82.0 ± 0.6Superior5.1 ± 3.13.4 ± 2.11.3 ± 0.9Postero-Superior4.2 ± 3.45.3 ± 1.51.0 ± 0.3Capsular Thickness Open table in a new tab The iliocapsularis, indirect head of the rectus and gluteus minimus tendons all demonstrated consistent capsular contributions. Using extra-articular landmarks as a reference, the capsular origin was located approximately 13 mm distal to the AIIS and 11 mm lateral to the pectineal eminence. The mean distance of the capsular insertion along the proximal femur measured from the chondral head-neck junction was 26.2 mm. Safe Zone for Anterior Capsulotomy Our data demonstrates that the hip capsule is thickest along its anterior and superior quadrants. In addition, there are consistent and large muscular contributions from the iliocapsularis, gluteus minimus, and reflected head of the rectus. A precise understanding of the consistent relationships that exist between the pericapsular musculature and capsular thickness may facilitate the identification of a consistent "safe zone" for anterior capsulotomy during hip arthroscopy. Further research is needed to establish whether anterior capsulotomy can be reliably performed in a manner that minimizes damage to this anterior capsular anatomy.