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The Law of Transformation of Bone

WOLFF’S LAW
By Renata Trister DO

INTRODUCTION AND HISTORY

Julius Wolff (1836-1902) was a German surgeon and anatomist.

He postulated Wolff’s law (original title 1892: The law of transformation of

the bone), describing the relationship between bone geometry and

mechanical influences on bone. This work established the mechanism and

thus physical factors in evolutionary biology. He saw his work as an

extension of the theory of evolution by Charles Darwin (1809–1882).

Julius Wolff was born 1836 in the eastern part of Prussia/Germany. He was

a German surgeon and anatomist. His research in surgery focused on growth

and inner structure of bone. After decades of work Dr. Wolff published his

research titled “The Law of Transformation of Bone” in 1892. A lengthy

and thorough work – the main discovery of this work can be summarized in

the following passage:

“As a consequence of primary shape variations and continuous loading, or

even due to loading alone, bone changes its inner architecture according to

mathematical rules and, as a secondary effect and governed by the same

mathematical rules, also changes its shape.”

Simplified this “Wolff’s Law” says that structure and shape of bone

permanently adapt to the loading conditions. This law describes the

relationship between bone geometry and mechanical influences on bone.

Dr. Wolff saw his theory as an extension of the theory of evolution by

Charles Darwin (1809–1882). This classic work also established

orthopaedics as an independent discipline.

DISCUSSION

Human bone grows and strengthens under pressure, and weakens when

barely put to use.

This concept — that bone senses and adapts to its mechanical environment –

such as pressure or a lack of it — is an old observation. It’s the reason

astronauts return with reduced bone density after floating in microgravity.

And conversely, it explains why tennis players and fencers develop greater

bone mass in their dominant arms and legs. Although Dr. Wolff gets the

credit for discovering this principle other scientists and writers, such as

Galileo also made similar observations.

Today “Wolff’s law” has evolved and incorporates several concepts, some

of which Dr. wolf never discussed.

1. Optimization of strength with respect to weight. The architecture of

bone is influenced by mechanical forces. Strength is optimized with

respect to weight. Furthermore bone – similarly to structures made by

people – does not remain where it need not be.

2. Alignment of trabeculae with principle stress directions. This

discovery was made when an engineer visiting the lab of an anatomist

noticed the similarity between trabecular arrangement in neck of

femur and a street lamp bracket.

3. The final core principle of Wolff’s law states that self-regulation of

bone structure by cells responding to a mechanical stimulus. This is a

self-regulating biologic mechanism. Bone has the ability to adapt to

changes in its external environment.