Purpose Lack of data on the in vivo morphology and morphometry of the normal adult coccyx hampers understanding of radiological abnormalities in idiopathic coccydynia. The aim of this study was to investigate normal adult sacrococcygeal morphometry. Methods Retrospective analysis of 112 adult CT scans (mean age 63 ± 14.6 years, 50 males) evaluated the following: number of coccygeal segments; joint fusion; coccygeal spicules, subluxation, sacralization, and scoliosis; sacrococcygeal straight and curved lengths and curvature indices; sacrococcygeal and intercoccygeal angles; and lateral deviation of the coccyx tip. Results Four coccygeal segments were present in 76 % of scans. Sacrococcygeal fusion was present in 57 % and intercoccygeal fusion was increasingly common more caudally; there was no significant association with age or gender. A bony spicule was present in 23 %. Subluxation was rare. Nine of 12 coccyges with a retroverted tip were female. Mean coccygeal curved length was 4.4 ± 0.8 cm in men and 4.0 ± 0.8 cm in women (P \ 0.01). Mean angle between first and last coccygeal segments was 138°± 25°in men and 147°± 25°in women (P = 0.08). There was no significant correlation between coccygeal length or curvature and stature, age or BMI. Conclusions In this first detailed study of the CT morphology and morphometry of the adult coccyx, sacrococcygeal and intercoccygeal joint fusion was common. Female coccyges were shorter, straighter, and may be more prone to retroversion, factors that may be relevant to the markedly higher prevalence of idiopathic coccydynia in women.

This is the most detailed comparison of coccygeal morphology and morphometry in adults with and without coccydynia investigated using cross-sectional imaging. Anatomical differences in joint fusion and coccygeal curvature may either predispose to the development of coccydynia or arise as a result of this condition.

The functional significance of the ligament of the head of femur (LHF), or ligamentum teres has often been debated. Having gained recent attention in clinical practice, it is suggested to partly provide some mechanical stability to the hip joint. However, the anatomy of this ligament is not well studied. This paper systematically reviews the anatomy of the LHF with the aim of exploring our current understanding of this structure and identifying any gaps in knowledge regarding its morphology and function. A systematic search of Medline, Embase, ProQuest, Web of Science, and Scopus databases was undertaken and relevant data extracted, analyzed. A total of 69 references were obtained, that included 53 full text articles, three published abstracts, and 13 textbooks. Many publications related to clinical studies (n = 11) rather than gross anatomy (n = 7), with one report on variation of the LHF. Considerable inconsistency in the naming and description of the LHF morphology was observed. Variable attachment sites were reported except for the acetabular notch, transverse acetabular ligament, and the femoral fovea. Presence and patency of the ligamental arteries supplying the head of the femur and their exact location were variably described and were often incomplete. The LHF is believed to be taught in extreme hip adduction, but there is little evidence to support this. In conclusions, further investigation of the anatomy of the LHF is recommended, particularly to clarify its mechanical role, innervation, and vascular contribution to the developing and adult femur, so to better inform clinical practice.

This study shows that the fovea consistently lies posteroinferior to the true centre of the femoral head and is usually oval in shape. Patent vascular foramina clustered within the LHF attachment site suggest that the ligament conveys some blood supply to the femoral head in adults.

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