Lower limb

Femur

Before you say anything

The longest and strongest bone in the body, and the one where a wrong side costs you most, because the examiner will move straight to the blood supply of the head. The linea aspera is the reliable marker: it is posterior, always. Put it at the back, put the head medially, and the side is settled.

Which side? Three checks

Hold it like this first: Hold it vertically with the head directed medially, upwards and slightly forwards, the two condyles resting together at the lower end, and the linea aspera facing backwards.

Check 1 — Find the head
A near-spherical articular surface with a small pit, carried on a long oblique neck
That is the upper end, and the head points medially
Check 2 — Find the linea aspera
A rough vertical ridge running down one surface of the shaft
It is posterior, so that surface must face backwards
Check 3 — Stand the lower end on a flat surface
Both condyles touch the surface together when the bone is held correctly
With the condyles level and the linea aspera behind, the head points to its own side

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Say these first

The longest bone in the body
A spherical head with a fovea on a long oblique neck
A rough linea aspera down the back of the shaft

Do not confuse it with

The humerus
The femoral head is nearly spherical, sits on a long oblique neck and carries a fovea; the humeral head has a short anatomical neck, no fovea, and its shaft carries a spiral groove rather than a linea aspera.

Examiner trap

Using the greater trochanter to call the side. It is lateral, but it is bulky and easily misjudged on a worn bone — the linea aspera is unambiguous and is what a senior uses.

Memory hook

Head medial, linea aspera behind, condyles level.

Why it matters

The head is supplied mainly by retinacular branches of the medial and lateral circumflex femoral arteries running along the neck, so an intracapsular fracture of the neck can produce avascular necrosis of the head.
An intertrochanteric fracture is extracapsular and unites well, because the blood supply to the head is not disturbed.
A fracture of the shaft can bleed more than a litre into the thigh.

Senior’s 30-second takeaway

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

If you see this: The longest bone in the body · A spherical head with a pit, on an oblique neck · A rough ridge down the back of the shaft
If asked to identify it: This is a femur; the head faces medially and the linea aspera backwards, which together give the side.
If asked one more: The lower end is the growing end and its centre is present at birth in a full-term infant.
If asked why it matters: An intracapsular fracture of the neck tears the retinacular vessels and risks avascular necrosis of the head.

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

Before you say anything