The paradox of Wolff’s theories

A. Hammer

The upper femur has long held a fascination for both clinicians and bioengineers as it contains two trabecular columns obviously related to its function. In this respect two theories as to the formation of these columns have developed, both associated with Wolff: the Trajectorial Theory, which relates mainly to the passage of forces through the cancellous bone of the upper femur, and Wolff's Law of bone formation, which describes the bone's reaction to these forces and relates to bone in general. The two concepts nevertheless are often used synonymously. The Trajectorial Theory propounds that these cancellous structures in the femoral neck are due to both tension and compression forces, while modern day concepts of Wolff's Law only acknowledge the action of compression forces: and herein lies the paradox. The Trajectorial Theory and Wolff's Law, when applied to the upper femur, are mutually exclusive. The evidence, anatomical and physiological, indicates that bone forms within the femoral neck solely under the influence of compression forces. This would indicate that the Trajectorial Theory is not appropriate for this region. An alternative conceptual way of looking at this region is presented which eliminates this theory and resolves the paradox.