Side Determination of the Femur and Humerus: A Step-by-Step Method

“Which side does this bone belong to?” is usually the second question in an osteology viva, straight after “identify this bone”. You do not need a separate rule for every bone. For any long bone, answer three questions in order.

The three questions

1. Which end is the upper end?
2. Which surface faces forwards?
3. Which side is medial?

Once you know up, front and medial, hold the bone against your own limb in that position. The limb it matches is its side.

Femur

• Upper end: the end with the rounded head, the neck and the two trochanters. The lower end is broad, with two condyles.
• Front: the shaft is convex forwards. The rough ridge, the linea aspera, runs down the back of the shaft.
• Medial: the head faces medially, upwards and slightly forwards. The greater trochanter is lateral.

Putting it together: hold the femur with the head at the top and the linea aspera facing backwards. If the head points to your left, towards the midline of a body facing the same way as you, it is a right femur. If it points to your right, it is a left femur.

Anatomical position: the femur is not vertical in the body. Rest both condyles on a flat surface and the shaft slopes upwards and laterally. That is how to hold it for the examiner.

Humerus

• Upper end: the end with the rounded head. The lower end is flattened from front to back and carries the trochlea and the capitulum.
• Front: the intertubercular sulcus (bicipital groove) is on the front of the upper end. At the lower end, the deep olecranon fossa is on the back.
• Medial: the head faces medially, upwards and backwards. At the lower end the medial epicondyle is the more prominent one.

Putting it together: hold the humerus with the head at the top and the olecranon fossa facing backwards. The side to which the head and the prominent medial epicondyle point is the medial side. If they point to your left, it is a right humerus.

Common mistakes

• Deciding the side before fixing front and back. Always settle upper end, then front, then medial.
• Holding the femur vertically. Remember the slope of the shaft.
• Using only one feature. Confirm the side with a second landmark before you answer.

Practise it

Side determination becomes quick only with a bone in your hand. A bilateral bone set gives you a left and a right to compare; a unilateral set is enough to practise the method. The XBONZ Anatomy Lab also has a side-determination drill on the 3D skeleton, with full access.

This is a revision aid. Check it against your course textbook and what your department teaches.