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
- ligaments: ischiofemoral, iliofemoral, pubofemoral and transverse acetabular ligaments, and the ligamentum teres
- movements: thigh flexion and extension, adduction and abduction, internal and external rotation
- blood supply: branches of the medial and lateral circumflex femoral, superior and inferior gluteal arteries and obturator arteries
- innervation: femoral, obturator and superior gluteal nerves, and nerve to quadratus femoris
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 ,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 (lunate surface) covered area 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 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 neck of femur and partly blended with pubofemoral and ischiofemoral ligaments
Retinacular fibers are the reflected part of the capsule traveling back to the head of the femur 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 neck of the femur
- 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.
- pectineus separates the hip joint from the femoral vein
- more laterally, iliopsoas with its underling bursa separates the hip joint from the femoral artery and femoral nerve
- straight head of rectus femoris
- reflected head of rectus femoris medially
- gluteus minimus laterally
- posteroinferiorly: obturator externus spirals obliquely to the posterior aspect of the hip joint accompanied by the ascending branch of medial circumflex femoral artery
- obturator internus and gemelli muscles contact the joint capsule separating it from sciatic nerve
- quadratus femoris
The cruciate and trochanteric anastomoses supply the joint in adults . A branch from the posterior branch of the obturator artery may also be present in the ligamentum teres.
- 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
- obturator 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
- femoral nerve via nerve to rectus femoris
- sciatic nerve via nerve to quadratus femoris
- obturator nerve from its anterior division
- superior gluteal nerve variably
- synovial herniation pits
- os acetabuli
- communication between the iliopsoas bursa and the hip joint
- accessory iliacus tendon
- congenital absence of the ligamentum teres
- hip plicae
- pectinofoveal fold
- supra-acetabular fossa
- accessory superior acetabular notch
- femoro-acetabular impingement
- hip dislocation
- developmental dysplasia of the hip
- femoral head fracture
- acetabular fracture
- neck of femur fracture
- labral tear
- acetabular protrusion
- coxa profunda
- coxa magna
- coxa plana
- coxa vara
- coxa valga
- slipped upper femoral epiphysis
- fovea alta