HLTH1008 Chap.4 Hip Joint Anatomy and Biomechanics
Hip Joint Anatomy and Biomechanics
The hip carries the weight of the head, arms and trunk on the femoral head. This chapter starts with a fall that fractures the femoral neck and uses it to explain the blood supply of the head and why distal fractures have a better prognosis.
It then covers the capsule, the three capsular ligaments and the labrum, the angles of inclination and torsion with coxa valga, coxa vara, anteversion and retroversion, the moment balance of the abductors in single-leg stance, and Trendelenburg and lurching gaits. Every angle in the chapter is given with the values the course uses, including the ranges where two sources differ.
The free-body example uses the lecture's own numbers so that each step can be checked.
What this chapter covers
- 01
Retinacular blood supply of the femoral head
- 02
Femoral neck fracture sites and avascular necrosis
- 03
Iliofemoral, pubofemoral and ischiofemoral ligaments
- 04
Acetabular labrum and congruent positions
- 05
Angle of inclination and coxa valga or vara
- 06
Angle of torsion, anteversion and retroversion
- 07
Abductor moments and walking aids
- 08
Trendelenburg and gluteus medius gaits
Worked example · free
Why an intertrochanteric fracture has the better prognosis
- +1The main supply to the femoral head comes from retinacular arteries of the medial and lateral circumflex femoral arteries.
- +1These run along the femoral neck inside the capsule.
- +1A subcapital fracture crosses the neck and can tear them, risking avascular necrosis of the head.
- +1An intertrochanteric fracture lies distal to them, so the supply to the head is usually spared.
Key terms
- Coxa valga
- An angle of inclination above about 125°, which shortens the abductor lever arm.
- Coxa vara
- An angle of inclination below about 125°, loading the medial acetabulum.
- Anteversion
- Increased femoral torsion that turns the femur medially and causes in-toeing.
- Iliofemoral ligament
- The strong inverted-Y ligament in front of the hip that tightens in extension.
- Acetabular labrum
- A fibrocartilage ring that deepens the hip socket.
- Avascular necrosis
- Death of bone after its blood supply is lost, as in the femoral head.
- Trendelenburg sign
- An excessive pelvic drop on the unsupported side in single-leg stance.
- Close-packed position
- The joint position in which ligaments are tightest, extension at the hip.
- Retroversion
- Reduced femoral torsion that turns the femur laterally and the feet outward.
- Gluteus medius lurch
- A lean of the trunk over the stance leg that reduces the load on weak abductors.
- Angle of torsion
- The transverse-plane angle between the femoral neck and the condylar axis.
Hip Joint Anatomy and Biomechanics FAQ
Why does a fractured neck of femur leave the leg short and turned out?
The Week 3 answers explain that muscle spasm pulls the distal fragment upward, shortening the limb, while the lateral rotators turn it outward. Older women are most at risk because osteoporosis lowers bone density, and atherosclerosis may already have reduced blood flow to the head.
What does a positive Trendelenburg sign mean?
Normally the pelvis drops only about 5° on the side of the lifted leg. A much larger drop shows that the abductors of the stance hip are weak or that the superior gluteal nerve supplying gluteus medius and minimus is injured, so the nerve to name belongs to the stance side.
Why should a walking stick be held in the hand opposite a painful hip?
In single-leg stance the abductors must balance the weight of the head, arms and trunk. A stick on the opposite side carries part of that load, so the lecture's numbers fall from 120 to 80 units of abductor force, sparing the painful joint.
What are the angles of inclination at birth, in adults and in old age?
The biomechanics lecture gives about 150° at birth, about 125° in adults, plus or minus 5°, and about 120° in the elderly, with smaller values in females because of the wider pelvis. An angle above 125° is coxa valga and one below it is coxa vara.
In which position is the hip most likely to dislocate?
The Week 3 answers name flexion with adduction and medial rotation as the position that uncovers the femoral head posteriorly, the position avoided after a total hip replacement. The most congruent position, by contrast, is flexion with abduction and lateral rotation.
Exam move
Draw the proximal femur three times: once with the retinacular arteries and the four fracture sites, once with the angle of inclination at 150, 125 and 120 degrees, and once from above showing torsion. Learn the three capsular ligaments with the movements that tighten them.
Then rework the abductor moment example with new numbers until the method is automatic, and finish by describing Trendelenburg gait and the gluteus medius lurch in one sentence each. When two sources give different values, as they do for the centre-edge angle and for torsion, write both with a note of which lecture uses which, and check which your lecturer emphasises.
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