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The hip joint is a synovial joint between the femoral head and the acetabulum of the pelvis. This article considers the hip joint specifically, however it is worth noting that the word hip is often used to refer more generally to the anatomical region around this joint.
articulation: ball and socket joint between the head of the femur and the acetabulum
movements: thigh flexion and extension, adduction and abduction, internal and external rotation
The hip joint is a ball and socket joint that represents the articulation of the bones of the lower limb and the axial skeleton (spine and pelvis). The rounded femoral head sits within the cup-shaped acetabulum.
The acetabulum is formed by the three bones of the pelvis (the ischium, ilium and pubis). Between them is a Y-shaped cartilaginous growth plate (the triradiate cartilage) which is usually fused by age 14-16. The ball and socket articulation allows for a high degree of mobility. The acetabular labrum increases the depth of the joint 1, thereby increasing the stability of the joint but causes a reduction in the movement at the joint. In comparison to the shoulder joint, it permits less range of movement due to the increased depth and contact area but displays far more stability.
The acetabulum covers nearly half of the femoral head. The actual hyaline articular cartilage-covered area (lunate surface) is C-shaped and forms an incomplete ring due to the acetabular notch. This notch is traversed by the transverse ligament. The central non-articular part of the acetabulum is filled with the Haversian fat pad (also known as the pulvinar).
The femoral head is attached to the body of the femur via the neck, which holds it at an angle. It is covered with hyaline cartilage except at the convexity of the head where the fovea exists. Through the fovea, the head is attached to ligamentum teres.
The joint is surrounded by a fibrous capsule, which is attached to the margins of the labrum and the transverse ligament on the acetabulum. It extends to the femur to attach anteriorly to the intertrochanteric line but as not as extensive posteriorly, attached halfway to the intertrochanteric crest. There are circular (internal) and longitudinal (external) fibers. The zona orbicularis is a set of internal circular fibers forming a collar around the femoral neck and partly blended with pubofemoral and ischiofemoral ligaments
Retinacular fibers are the reflected part of the capsule traveling back to the femoral head from its distal attachment to the neck, binding down the nutrient arteries arising from the trochanteric anastomosis.
The synovial membrane is attached to the articular margins and lines the inner capsule. The ligament of the head of the femur and the surrounding fat are enclosed in a reflecting layer of the synovium.
iliofemoral ligament of Bigelow (strongest): inverted V/Y shaped in appearance, it arises from the lower half of the anterior inferior iliac spine and the acetabular rim with diverging limbs attached to the upper and lower ends of the intertrochanteric line
pubofemoral ligament: from the iliopubic eminence and the obturator crest to the capsule on the inferior part of the femoral neck
ischiofemoral ligament (weakest): arises from the body of ischium behind and below the acetabulum with fibers directed laterally and upwards to attach to the posterosuperior part of the base of the femoral neck, covering the posterior aspect of the hip joint
There are a number of different muscles that permit flexion/extension, adduction/abduction, and internal/external rotation of the hip joint. See: Hip muscles.
reflected head of rectus femoris medially
gluteus minimus laterally
transverse branch of medial circumflex femoral artery
transverse branch of lateral circumflex femoral artery
ascending branch of first perforator artery from profunda femoris artery
descending branch of inferior gluteal artery
descending branch of superior gluteal artery
ascending branch of medial circumflex femoral artery
ascending branch of lateral circumflex femoral artery
often joined by inferior gluteal artery
anterior hip joint drains to deep inguinal nodes
posterior and medial hip joint drain to internal iliac nodes 4
Multiple articular branches are derived from several nerves (Hilton's law):
nerve to rectus femoris from the femoral nerve
obturator nerve from its anterior division
superior gluteal nerve variably
synovial herniation pits (Pitt pits)
communication between the iliopsoas bursa and the hip joint 5
accessory iliacus tendon
congenital absence of the ligamentum teres 5
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- 5. Mike S. Nguyen, Valeriy Kheyfits, Brian D. Giordano, Gregory Dieudonne, Johnny U. V. Monu. Hip Anatomic Variants That May Mimic Pathologic Entities on MRI: Nonlabral Variants. (2013) American Journal of Roentgenology. doi:10.2214/AJR.12.9861