Functional Anatomy of the Hip-Bones and Ligaments
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Description[edit | edit source]
The hip joint is considered one of the largest joints of the human body. It connects the pelvis to the lower extremities. The primary roles of the hip joint are to allow lower extremities weight bearing and to provide stability in standing and during mobility such as walking or running.
Structure[edit | edit source]
The hip joint is a ball-and-socket joint which provides stability for the body and sustains forces that can exceed the total body weight multiple times. This ability to accept such significant load is due to a combined work of the static and dynamic elements of the joint paired with a proper body alignment. The static stabilisers include bones, ligaments, capsule and bursae. Muscles, nerves and vascular supply are all dynamic elements of the hip joint
Bones[edit | edit source]
The hip joint is made out of two structures: the acetabulum and the femoral head.
Acetabulum[edit | edit source]
The acetabulum is a lateral part of the pelvis and its concave shape allows for the fitting of the femoral head. The femoral head is a proximal aspect of the femoral bone which distally connects to the tibia and the fibula.
What is referred to as a normal pelvis and acetabulum is in fact difficult to define.[1]A better understanding of the topographic map of the acetabulum is important for creating a good anatomic implant design when replacement or reconstruction of the acetabulum is needed. [1] The superior and posterior walls of the acetabulum are in anteversion and abduction. The face of the acetabulum has an average of 20.7 degrees of anteversion and 39.8 degrees of abduction. The anterior portion of the acetabulum is flat while the posterior portion is angled with its highest point at the sciatic notch. [1]
The margin of the acetabulum is 75% circle, except for its anteroinferior aspect called the acetabular notch. The transverse ligament of the hip closes the circle at this notch. This is a place where the acetabular labrum attaches allowing for an increase of the articular area of the acetabulum. Because of this anatomical structure, 50% of the femoral head can fit into the acetabulum. [2]
The acetabulum is divided into anterior and posterior columns. The anterior column includes anterior ilium, anterior wall, anterior dome of the acetabulum, and superior pubic ramus. The posterior column consists of greater and lesser sciatic notches, posterior wall, posterior dome of the acetabulum, and ischial tuberosity.[2]
Femoral Head[edit | edit source]
Ligaments[edit | edit source]
The hip joint itself is reinforced by 3 primary fibrous capsular ligaments (iliofemoral, ischiofemoral, and pubofemoral), and each serves distinct functional roles to stabilize the joint5,8. The iliofemoral ligament is composed of lateral (superior) and medial (inferior) fibrous branches, which insert together into the anterior inferior iliac spine of the pelvis, each extending out to attach along the femoral intertrochanteric line, forming the inverted Y-shaped ligament of Bigelow (Fig. (Fig.1),1), to reinforce the capsule during external rotation and extension. The ischiofemoral ligament inserts in the ischium, posteroinferior to the acetabular rim, and attaches to the posterior intertrochanteric line to reinforce the capsule during internal rotation in neutral positions as well as in combined flexion-adduction positions (i.e., FADIR [flexion, adduction, and internal rotation]). The pubofemoral ligament inserts in the superior pubic ramus and converges with the medial iliofemoral and inferior ischiofemoral ligaments to insert into the femur7, reinforcing the inferior capsule to restrict excessive abduction and external rotation during hip extension. Another important structure is the triangular-shaped ligamentum teres, which reinforces between the peripheral inferior acetabular notch and the fovea of the femoral head (Fig. (Fig.2).2). As a small auxiliary ligament overlying the fat pad, the ligamentum teres provides a conduit for small vessels and innervations to the femoral head and plays a critical role in proprioception and structural stability27-32, which may decrease in function with progressive age33. In addition to the longitudinal fibers of the primary capsular ligaments, the circular fibers of the zona orbicularis form a stability-inducing collar, which closes around the femoral neck much like an aperture mechanism. During hip extension, the posteroinferior aspect of the zona orbicularis overlaps to medialize and secure the head anteriorly, while during deep flexion, the anteroinferior aspect of the zona orbicularis medializes and secures the head posteriorly (Fig. (Fig.2).2). It has also been proposed that the zona orbicularis has a role in circulating synovial fluid between the central and peripheral compartments within the capsule2.[3]
Joint Capsule[edit | edit source]
Joint capsule is a supporting structure of the hip joint. It is fibrous
The capsule plays a significant role in the hip joint stability[4]The hip joint capsule contributes to the stability of the hip joint and lower extremity,
There is general agreement that Pacinian, Ruffini and Golgi corpuscles are present in the hip capsule of individuals with no known pathology and patients with OA
A greater density of Pacinian and Ruffini corpuscles appear to be present in the hip capsules of both healthy individuals [28] and patients with OA [28, 49] compared to other mechanoreceptors. These mechanoreceptors act to monitor vibration and tensile loading, respectively. However, it is unclear if individuals have more Pacinian or Ruffini corpuscles in their hip capsular complex. When comparing the changes in density of specific mechanoreceptors in the hip capsules of those with and without OA Pacinian corpuscles are more greatly reduced in the OA group compared to the healthy group than the reduction in Ruffini corpuscles [28]. This may have an effect on biomechanical functioning of the joint, but more research is required to confirm this.[5]
Bursae[edit | edit source]
Function[edit | edit source]
Clinical relevance[edit | edit source]
- Coxa profunda is a pathology related to an increase depth of the acetabular socket. This is a problem more commonly present in females.
- Acetabular retroversion refers to an abnormal posterior angulation of the superolateral acetabular rim. This pathology is causing the femoral head to be excessively covered and predisposes to femoroacetabular impingement. It is also considered a risk factor for the osteoarthritis of the hip.
- Development of larger cross-sectional areas and tighter capsular ligaments can be the result of progressive arthritis. [3]
- Surgical procedure involving capsular closure restores the biomechanics of the hip, study has found. [4]
Resources[edit | edit source]
References[edit | edit source]
- ↑ 1.0 1.1 1.2 Krebs V, Incavo SJ, Shields WH. The anatomy of the acetabulum: what is normal? Clin Orthop Relat Res. 2009 Apr;467(4):868-75. doi: 10.1007/s11999-008-0317-1. Epub 2008 Jul 22.
- ↑ 2.0 2.1 Bannai M, Rock P. Acetabulum. Reference article. Radiopaedia.org. Available at https://radiopaedia.org/articles/acetabulum (last access 20.02.2022).
- ↑ 3.0 3.1 Ng KCG, Jeffers JRT, Beaulé PE. Hip Joint Capsular Anatomy, Mechanics, and Surgical Management. J Bone Joint Surg Am. 2019 Dec 4;101(23):2141-2151.
- ↑ 4.0 4.1 Freeman KL, Nho SJ, Suppauksorn S, Chahla J, Larson CM. Capsular Management Techniques and Hip Arthroscopy. Sports Med Arthrosc Rev. 2021 Mar 1;29(1):22-27.
- ↑ Tomlinson J, Zwirner J, Ondruschka B, Prietzel T, Hammer N. Innervation of the hip joint capsular complex: A systematic review of histological and immunohistochemical studies and their clinical implications for contemporary treatment strategies in total hip arthroplasty. PLoS One. 2020 Feb 26;15(2):e0229128.
