Background: Gluteus medius tears are a common hip disorder. Despite this, the etiology of these tears and the anatomical background of the gluteus medius tendon remain unclear. This study aimed to clarify the characteristics of the gluteus medius tendon. We hypothesized that the tendinous portions of the gluteus medius have a nonuniform structure contributing to the tear etiology. Methods: Twenty-five hips from 15 Japanese cadavers were analyzed. Twenty-one of the hips were analyzed macroscopically, and the other 4 were analyzed histologically. In all of the specimens, the 3-dimensional (3D) morphology of the greater trochanter was examined using microcomputed tomography (micro-CT). In 10 of the 21 hips analyzed macroscopically, the local thickness of the gluteus medius tendon, detached from the greater trochanter, was measured. Results: The posterior and anterolateral parts of the gluteus medius tendons were roughly distinguished on the basis of the aspects of the iliac origins. The posterior part of the gluteus medius tendon ran in a fan-like shape and converged onto the superoposterior facet of the greater trochanter. The anterolateral part ran posteroinferiorly toward the lateral facet of the greater trochanter. The thickness was greater in the posterior part than in the anterolateral part, and the border between these 2 parts was relatively thin compared with the other parts. The histological study showed that both the posterior and anterolateral parts inserted onto the greater trochanter via fibrocartilage. Conclusions: The gluteus medius tendon consists of thick posterior and thin anterolateral parts, which were identified by the facet or aspect of the bone structures and thinness of their border region. Clinical Relevance: Our findings indicate that, given the nonuniform structure of the gluteus medius tendon, the thin anterolateral part may be more prone to tears than the thick posterior part is and tears may generally be limited to the anterolateral part.

The iliofemoral ligament, which plays an important role in hip joint stability, is formed on the anterosuperior region of the hip joint capsule. Although the tendon and deep aponeurosis of the gluteus minimus and iliopsoas are partly connected to the same region of the capsule, the precise location of the connections between the joint capsule and the tendons and deep aponeuroses remains unclear. The locations of the tendinous and aponeurotic connections with the joint capsule may clarify whether the iliofemoral ligament can be regarded as the dynamic stabilizer. This study investigated the relationships between the anterosuperior region of the joint capsule and the tendon and deep aponeurosis of the gluteus minimus and iliopsoas. Fourteen hips from nine cadavers (five males; four females; mean age at death 76.7 years) were analyzed. Ten hips were macroscopically analyzed, and four were histologically analyzed. During macroscopic analysis, the joint capsule was detached from the acetabular margin and the femur, and its local thickness was measured using microcomputed tomography (micro‐CT). The gluteus minimus tendon was connected to the joint capsule, and the lateral end of this connection was adjoined with the tubercle of the femur at the superolateral end of the intertrochanteric line. The deep aponeurosis of the iliopsoas was also connected to the joint capsule, and the inferomedial end of its anterior border corresponded with the inferomedial end of the intertrochanteric line. In the micro‐CT analysis, capsular thickening was observed at the base of the connection to the gluteus minimus tendon and at the anterior border of the deep aponeurosis of the iliopsoas. A histological study showed that the gluteus minimus tendon and the deep aponeurosis of the iliopsoas were continuous with the hip joint capsule. Based on the morphology of the tendinous and aponeurotic connections, local capsular thickening and histological continuity, the transverse and descending parts of the iliofemoral ligament were the joint capsules, with fibers arranged according to the connection with the gluteus minimus tendon and the deep aponeurosis of the iliopsoas, respectively. Therefore, the so‐called iliofemoral ligament could be regarded as the dynamic stabilizer, with the ability to transmit the muscular power to the joint via the capsular complex. This anatomical knowledge provides a better understanding of the hip stabilization mechanism.

Background: Despite the fact that many surgeons perform partial capsular detachment from the anterosuperior aspect of the acetabulum to correct acetabular deformities during hip arthroscopy, few studies have focused on whether these detachments influence hip joint stability. The aim of this study was to investigate the capsular attachment on the anterosuperior aspect of the acetabulum. We hypothesized that the attachment on the inferior aspect of the anterior inferior iliac spine (AIIS) is wide and fibrocartilaginous and might have a substantial role in hip joint stability. Methods: Fifteen hips from 9 cadavers of Japanese donors were analyzed. Eleven hips were analyzed macroscopically, and the other 4 were analyzed histologically. In all specimens, the 3-dimensional morphology of the acetabulum and AIIS was examined using micro-computed tomography (micro-CT). Results: Macroscopic analysis showed that the widths of the capsular attachments varied according to the location, and the attachment width on the inferior edge of the AIIS was significantly larger than that on the anterosuperior aspect of the acetabulum. Moreover, the capsular attachment on the inferior edge of the AIIS corresponded with the impression, which was identified by micro-CT. Histological analysis revealed that the hip joint capsule on the inferior edge of the AIIS attached to the acetabulum adjacent to the proximal margin of the labrum. In addition, the hip joint capsule attached to the inferior edge of the AIIS via the fibrocartilage. Conclusions: The capsular attachment on the inferior edge of the AIIS was characterized by an osseous impression, large attachment width, and distributed fibrocartilage. Clinical Relevance: It appeared that the capsular attachment on the inferior edge of the AIIS was highly adaptive to mechanical stress, on the basis of its osseous impression, attachment width, and histological features. Anatomical knowledge of the capsular attachment on the inferior edge of the AIIS provides a better understanding of the pathological condition of hip joint instability.

Although the hip joint is regarded as inherently stable, hip pain and injuries caused by traumatic/non-traumatic hip instability are relatively common in active individuals. A comprehensive understanding of hip anatomy may provide better insight into the relationships between hip stability and clinical problems. In this review, we present our recent findings on the hip morphological characteristics, especially focusing on the intramuscular tendon of the gluteus medius tendon and its insertion sites, hip capsular attachment on the anterosuperior region of the acetabular margin, and composition of the iliofemoral ligament. We further discussed the hip stabilization mechanism based on these findings. The characteristics of the gluteus medius tendon suggest that even a single muscle has multiple functional subunits within the muscle. In addition, the characteristics of the hip capsular attachment suggest that the width of the capsular attachment is wider than previously reported, and its wide area shows adaptive morphology to mechanical stress, such as bony impression and distribution of the fibrocartilage. The composition of the iliofemoral ligament and its relation to periarticular structures suggest that some ligaments should be defined based on the pericapsular structures, such as the joint capsule, tendon, and aponeurosis, and also have the ability to dynamically coordinate joint stability. These anatomical perspectives provide a better understanding of the hip stabilization mechanism, and a biomechanical study or an in vivo imaging study, considering these perspectives, is expected in the future.