Lower limb

Hip bone

Before you say anything

A large irregular bone that intimidates students because there is so much on it. Ignore the detail until you have done three things: point the acetabulum laterally, turn the ischial tuberosity down and back, and put the pubis in front. Everything else can then be described in order, and the examiner will usually move to sex determination.

Which side? Three checks

Hold it like this first: Hold it so that the acetabulum faces laterally, downwards and slightly forwards; the ischial tuberosity points downwards and backwards; and the anterior superior iliac spine and the pubic tubercle lie in the same vertical plane.

Check 1 — Find the acetabulum
A deep cup-shaped socket notched below
It faces laterally, so it points to the side the bone belongs to
Check 2 — Find the ischial tuberosity
The thick roughened mass below and behind the acetabulum
It points downwards and backwards, which fixes front from back
Check 3 — Locate the obturator foramen
A large gap below and in front of the acetabulum, bounded in front by the pubis and behind by the ischium
The pubic part lies anteriorly and medially, confirming the orientation

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Say these first

A deep cup-shaped acetabulum notched inferiorly
A large obturator foramen
Three fused parts meeting at the acetabulum

Do not confuse it with

The scapula
Both are flat bones with a socket, but the acetabulum is deep, cup-shaped and notched, while the glenoid cavity is shallow and unbroken; only the hip bone has an obturator foramen.

Examiner trap

Calling the side from the iliac crest alone. The crest is symmetrical enough to fool you on a worn bone; the acetabulum and ischial tuberosity together are decisive.

Memory hook

Socket out, tuberosity down and back, pubis to the front.

Why it matters

The iliac crest is the usual site for bone marrow aspiration and for harvesting cancellous bone graft.
In sex determination the female pelvis has a wider greater sciatic notch, a subpubic angle greater than a right angle and a more circular pelvic inlet.
A sudden sprint can avulse the anterior superior iliac spine with sartorius, or the ischial tuberosity with the hamstrings, in an adolescent whose secondary centres have not yet fused.

Senior’s 30-second takeaway

Hip bone — the whole bench in four lines. Read this on the way in.

If you see this: A deep notched socket · A large obturator foramen · A thick roughened tuberosity below and behind
If asked to identify it: This is a hip bone; the acetabulum faces laterally and the ischial tuberosity downwards and backwards, which gives the side.
If asked one more: The ilium, ischium and pubis meet at the triradiate cartilage, which fuses at about 15 to 16 years.
If asked why it matters: The iliac crest is the standard site for marrow aspiration, and the bone is central to determining sex from a skeleton.

Then stop. Let the examiner ask the next question.

🩺 Before you say anything

Which side? Three checks

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Senior’s 30-second takeaway

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Before you say anything