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Understanding normal anatomy is important for diagnosing pathology of the hip.
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MR arthrography is more sensitive for the detection of intra-articular pathology than noncontrast MR imaging.
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Important components of hip anatomy include the osseous structures, cartilage, muscles and tendons, capsular ligaments, labrum, nerves, and vessels.
MR Imaging of Normal Hip Anatomy
Section snippets
Key Points
Imaging the hip
Hip pain is a common complaint, especially in athletes, and it has a broad differential diagnosis. MR imaging has improved the radiologist's ability to diagnose causes of hip pain, especially soft tissue pathology.1
The hip joint is difficult to image because it is not oriented in the standard axial, coronal, and sagittal planes of the body, and there is significant variation in hip joint orientation from person to person. Acetabular version, for example, can range from −10.8 to +22.1 degrees.2,
Osseous structures
The hip joint is a ball-and-socket joint composed of the femoral head articulating with the acetabulum. The acetabulum is the junction of the three bones of the pelvis: (1) the ilium, (2) the ischium, and (3) the pubis. It is important to evaluate all of these bones and the sacrum in routine hip MR imaging because fractures of any of these bones can present as “hip pain.”11, 12 The acetabulum approximates the surface of two-thirds of a sphere, which is incomplete at the inferior aspect; the
Cartilage
A horseshoe-shaped articular cartilage called the “lunate” lines the acetabulum. A central depression within the acetabulum known as the acetabular fossa lacks this cartilage lining and is instead lined by synovium and filled with fibrofatty tissue.9
In the weight-bearing portion of the superior acetabulum, at approximately the 12-o'clock position, there can be a normal variant called the supra-acetabular fossa. This is an indentation in the acetabular roof that may be filled with cartilage or
Muscles, tendons, and bursae
There are many muscles and tendons that surround the hip and allow it to perform a wide range of motions, including flexion, extension, abduction, adduction, and internal and external rotation. The muscles of the hip and proximal thigh are generally well-delineated from one another by well-defined fascial and fatty planes (Fig. 8). Normal skeletal muscle is intermediate in signal intensity on all pulse sequences.27 T1-weighted MR images are best for evaluating muscle bulk and signal intensity.
Ligaments and synovium/capsule
The iliofemoral, ischiofemoral, and pubofemoral ligaments represent thickenings of the joint capsule that reinforce and stabilize the hip joint. They are named for the bones that they connect. The Y-shaped iliofemoral ligament is one of the strongest ligaments in the body. It reinforces the anterior capsule by limiting anterior translation during extension and external rotation. It originates between the anterior inferior iliac spine and the superior acetabulum and spirals toward the femur,
Labrum
The labrum is a low signal intensity fibrocartilaginous structure that is attached to the acetabular rim. The sensitivity of MR arthrography for the detection of labral tears is at least 90%,24, 42, 47 and its accuracy is 91%,6 compared with conventional noncontrast MR imaging, where the sensitivity and accuracy are 30% and 36%, respectively.6 Byrd and Jones42 found a lower sensitivity (66%) of MR arthrography caused by overinterpretation of labral abnormalities. The specificity of MR
Nerves
On MR imaging, nerves appear round or oval in cross section with a stippled or honeycombed appearance. The stippling represents individual nerve fascicles separated by variable amounts of fat; this appearance is also called a “fascicular pattern.” The fascicles are of similar or slightly higher signal intensity compared with skeletal muscle on T2-weighted MR images, are uniform in size, and give larger nerves, such as the sciatic nerve, a striated appearance when imaged longitudinally.27
The
Vessels
The external iliac artery and vein exit the pelvis with the femoral nerve and become the femoral artery and vein at the level of the inguinal ligament; at the level of the femoral heads, the neurovascular structures from lateral to medial are the femoral nerve, the femoral artery, the femoral vein, and the lymphatics. The femoral artery divides into the superficial femoral artery and the profunda femoris artery as it exits the femoral triangle, approximately 2 to 5 cm below the inguinal
Summary
Imaging evaluation of the hip presents many challenges because of its intrinsically complex biomechanics and multiple anatomic structures, which constitute and surround the hip joint. In addition, there are developmental variations and anatomic variants that can be mistaken for pathology. Awareness of these entities helps the radiologist to make the appropriate diagnosis.
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Cited by (29)
Particularities on Anatomy and Normal Postsurgical Appearances of the Hip
2023, Radiologic Clinics of North AmericaCitation Excerpt :The supraacetabular fossa has smooth margins and does not display bone marrow edema or surrounding cartilage irregularity, characteristics that differentiate it from an osteochondral lesion (Fig. 4). The stellate crease is another focal area that is not covered with hyaline cartilage, located in the inner margin of the acetabular cartilage, close to the superior aspect of the acetabular fossa11 (Fig. 5). The labrum is a fibrocartilaginous ring in continuity with the edge of the acetabulum, which blends inferiorly with the transverse acetabular ligament, that bridges through the acetabular notch, turning it into a foramen.
The Everted Acetabular Labrum: Patho-anatomy, Magnetic Resonance Imaging and Arthroscopic Findings of a Native Variant
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2021, Clinics in Sports MedicineCitation Excerpt :Surgical treatment involves arthroscopy with debridement of the tear, which has been shown to result in both immediate symptom improvement and a decreased risk of future osteoarthritis.18 With the exception of the fovea capitus, a central depression which serves as the origin for the ligamentum teres, the entirety of the femoral head is covered with articular cartilage (Fig. 4).19 Likewise, the acetabulum is covered with articular cartilage in a horseshoe configuration known as the “lunate”.19
Top Ten Adult Manifestations of Childhood Hip Disorders: An Up-To-Date Review for General Radiologists
2020, Radiologic Clinics of North AmericaCitation Excerpt :To accurately assess the hip, the practicing radiologist should have familiarity with its anatomic components and the standard imaging techniques used to visualize them.1–5
Conservative management of femoroacetabular impingement (FAI) in professional basketball
2020, Apunts Sports MedicineLongitudinal assessment of MRI in hip osteoarthritis using SHOMRI and correlation with clinical progression
2016, Seminars in Arthritis and Rheumatism
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Conflict of Interest: None.