Hip Joint

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Hip Joint
Primary Type	Ball and socket"Ball and socket" is not in the list (Synovial Joint, Cartilaginous Joint, Fibrous Joint, Compound Joint) of allowed values for the "Has joint type" property.
Secondary Type
Bones	Ilium, femur
Ligaments	Iliofemoral, ischiofemoral, ligamentum teres
Muscles
Innervation
Vasculature
ROM
Volume
Conditions

Bones and Articulations

The hip is a ball and socket joint. The ball is the spherical head of the femur, while the socket is the concave acetabulum. The acetabulum is angled obliquely, directed anterior, lateral, and inferior. The acetabular cartilage is thicker in the periphery where it merges with the labrum.

The femur is the largest and strongest bone in the body. The femoral neck is the narrowest part and internally it is primarily composed of trabecular bone, and so it is the weakest component of the femur. The femur angles medially downward to aid in single-leg support during walking and running.

Stability

The labrum is a ring of fibrocartilage that contributes to joint stability. Compared to the glenoid fossa of the shoulder, the acetabular fossa is much deeper and so is more stable.

There are several strong ligaments that contribute to stability.

• Anterior ligaments: Iliofemoral or Y ligament plus the pubofemoral ligament

Posterior ligaments: ischiofemoral ligament

These major ligaments act to twist the head of the femur into the acetabulum during hip extension.

Within the joint capsule is the ligamentum teres which attaches directly from the rim of the acetabulum to the head of the femur.

Bursae

The iliopsoas bursa and deep trochanteric bursa are the most prominent bursae. The iliopsoas is located between the iliopsoas and articular capsule and reduces friction between these two structures. The deep trochanteric bursa reduces friction between the greater trochanter of the femur and the gluteus maximus.

Movements

The pelvic girdle is analogous to the shoulder girdle in that it positions the hip for effective movement. The shoulder girdle is made up of multiple different joints, while the pelvis is non-jointed. Nevertheless, the pelvis is able to rotate in all three planes. With pelvic rotation, the acetabular position is changed so that it is directed towards the impending femoral movement. Posterior pelvic tilt enables increases hip flexion by placing the head of the femur in front of the pelvis. Anterior pelvic tilt increases hip extension, and lateral pelvic tilt increases lateral movements. The pelvis also moves in coordination with the spine.

There are a variety of two-joint muscles. Two-joint muscles function most effectively at one joint when the position of the other joint stretches the muscle slightly.

• Flexion: iliacus, psoas major, pectineus, rectus femoris, sartorius, and tensor fascia lata.
  • Iliopsoas (iliacus and psoas major) is the major hip flexor.
  • Rectus femoris is a two-joint muscle and is active during both hip flexion and knee extension; it works better as a hip flexor with the knee is flexion.
  • Sartorius is also a two-joint muscle.
• Extension: Gluteus maximus, biceps femoris, semitendinosus, and semimembranosus (latter three are the hamstrings).
  • Gluteus maximus is active only with hip flexion
  • Hamstrings are two-joint muscles, and aid in hip extension and knee flexion.
• Abduction: Gluteus medius and minimus
  • Gluteus medius: major abductor
  • Gluteus minimus: assists.
  • Both muscles stabilise the pelvis during the support phase of walking and running and with standing on one leg.
• Adduction:Adductor longus, adductor brevis, adductor magnus, gracilis
  • Active during swing phase of gait to bring the foot below the body's centre of gravity before the support phase. Also active during stair and hill climbing.
  • Gracilis: strap muscle contributes to knee flexion.
  • Adductor longus, adductor brevis, adductor magnus: also contributes to flexion and lateral hip rotation especially with a medially rotated femur.
• Lateral rotators: piriformis, gemellus superior, gemellus inferior, obturator internus, obturator externus, quadratus femoris
  • Stronger than medial rotators.
• Medial rotators: gluteus minimus, tensor fascia lata, semitendinosus, semimembranosus, gluteus medius
• Horizontal abduction
• Horizontal abduction